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UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 14A

Proxy Statement Pursuant to Section 14(a) of
the Securities Exchange Act of 1934 (Amendment No.          )

Filed by the Registrant ý

Filed by a Party other than the Registrant o

Check the appropriate box:

o

 

Preliminary Proxy Statement

o

 

Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2))

ý

 

Definitive Proxy Statement

o

 

Definitive Additional Materials

o

 

Soliciting Material under §240.14a-12

 

IDERA PHARMACEUTICALS, INC.

(Name of Registrant as Specified In Its Charter)

N/A

(Name of Person(s) Filing Proxy Statement, if other than the Registrant)

Payment of Filing Fee (Check the appropriate box):

ý

 

No fee required.

o

 

Fee computed on table below per Exchange Act Rules 14a-6(i)(1) and 0-11.
    (1)   Title of each class of securities to which transaction applies:
        
 
    (2)   Aggregate number of securities to which transaction applies:
        
 
    (3)   Per unit price or other underlying value of transaction computed pursuant to Exchange Act Rule 0-11 (set forth the amount on which the filing fee is calculated and state how it was determined):
        
 
    (4)   Proposed maximum aggregate value of transaction:
        
 
    (5)   Total fee paid:
        
 

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Fee paid previously with preliminary materials.

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Check box if any part of the fee is offset as provided by Exchange Act Rule 0-11(a)(2) and identify the filing for which the offsetting fee was paid previously. Identify the previous filing by registration statement number, or the Form or Schedule and the date of its filing.

 

 

(1)

 

Amount Previously Paid:
        
 
    (2)   Form, Schedule or Registration Statement No.:
        
 
    (3)   Filing Party:
        
 
    (4)   Date Filed:
        
 

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EXPLANATORY NOTE

           This joint proxy statement/prospectus amends and restates the joint proxy statement/prospectus dated March 29, 2018, which was previously mailed to the stockholders of BioCryst Pharmaceuticals, Inc. and the stockholders of Idera Pharmaceuticals, Inc. on or about April 2, 2018 in connection with the proposed strategic business combination of BioCryst and Idera in order to (1) revise the record date for the special meeting of Idera stockholders and the special meeting of BioCryst stockholders to May 29, 2018 and (2) revise the date of the special meeting of Idera stockholders and the special meeting of BioCryst stockholders to July 10, 2018.


LOGO

 

LOGO

MERGERS PROPOSED—YOUR VOTE IS VERY IMPORTANT

Dear Stockholders:

           As previously disclosed, the BioCryst Pharmaceuticals, Inc. ("BioCryst") board of directors (the "BioCryst board") and the Idera Pharmaceuticals, Inc. ("Idera") board of directors (the "Idera board") have unanimously approved and BioCryst and Idera have entered into an Agreement and Plan of Merger, dated as of January 21, 2018 (the "merger agreement") with respect to a strategic business combination. Pursuant to the terms of the merger agreement, (i) Island Merger Sub, Inc. ("Merger Sub A"), a wholly owned subsidiary of Nautilus Holdco, Inc. ("Holdco"), which is in turn a wholly owned subsidiary of BioCryst and a party to the merger agreement, will merge with and into Idera, with Idera surviving as a wholly owned subsidiary of Holdco (the "Idera merger"), and (ii) Boat Merger Sub, Inc. ("Merger Sub B"), a wholly owned subsidiary of Holdco and a party to the merger agreement, will merge with and into BioCryst, with BioCryst surviving as a wholly owned subsidiary of Holdco (the "BioCryst merger" and together with the Idera merger, the "mergers"). Upon completion of the mergers, BioCryst and Idera, and their respective subsidiaries, will become wholly owned subsidiaries of Holdco and will operate as a combined company under the name Valenscion Incorporated.

           Upon completion of the mergers, each issued and outstanding share of Idera common stock will be converted into the right to receive 0.20 shares of Holdco common stock (the "Idera exchange ratio"), and each issued and outstanding share of BioCryst common stock will be converted into the right to receive 0.50 shares of Holdco common stock (the "BioCryst exchange ratio" and together with the Idera exchange ratio, the "exchange ratios"). The exchange ratios will not be adjusted for changes in the market price of either BioCryst common stock or Idera common stock between the date of signing of the merger agreement and completion of the mergers. Upon completion of the mergers, each issued and outstanding share of Idera preferred stock (with certain exceptions described in the accompanying joint proxy statement/prospectus) will be converted into the right to receive an amount of Holdco common stock based on its liquidation preference.

           Upon closing of the mergers, BioCryst stockholders (including holders of securities convertible, exchangeable or exercisable for shares of BioCryst common stock) immediately prior to the closing of the mergers will beneficially own approximately 51.6% of Holdco, and Idera stockholders (including holders of securities convertible, exchangeable or exercisable for shares of Idera common stock) immediately prior to the effective time of the mergers will beneficially own approximately 48.4% of Holdco, each calculated on a fully diluted basis using the treasury stock method. BioCryst and Idera will each hold a special meeting of its respective stockholders to consider the mergers. At the special meeting of BioCryst stockholders (the "BioCryst special meeting"), BioCryst stockholders will be asked to vote on a proposal to adopt the merger agreement, a proposal to approve, on a non-binding advisory basis, the compensation that may become payable to BioCryst's named executive officers that is based on or otherwise relates to the mergers, and a proposal to adjourn the BioCryst special meeting, if necessary or appropriate, to solicit additional proxies if there are not sufficient votes to adopt the merger agreement. At the special meeting of Idera stockholders (the "Idera special meeting"), Idera stockholders will be asked to vote on a proposal to adopt the merger agreement and a proposal to approve, on a non-binding advisory basis, the compensation that may become payable to Idera's named executive officers that is based on or otherwise relates to the mergers.

           Affiliates of Baker Bros. Advisors, LP ("Baker Brothers"), the beneficial owner of approximately 14% of issued and outstanding BioCryst common stock and approximately 18% of issued and outstanding Idera common stock, have agreed, among other things, to vote their shares of BioCryst common stock and Idera common stock in favor of the proposal to adopt the merger agreement at each of the BioCryst special meeting and Idera special meeting.

           On or about April 2, 2018, Idera stockholders and BioCryst stockholders were mailed a joint proxy statement/prospectus related to the special meetings that were originally scheduled for May 9, 2018. On April 10, 2018, BioCryst and Idera announced the postponement of their respective special meetings, following investor feedback, to provide stockholders adequate time to consider new clinical data from Idera regarding its IMO-2125 program, which will be presented at the American Society of Clinical Oncology meeting being held June 1-5, 2018 in Chicago, Illinois. Each of the BioCryst special meeting and the Idera special meeting will now be held on July 10, 2018. In connection with the postponed meeting dates, the revised record date for each of Idera and BioCryst is May 29, 2018.

           We cannot complete the mergers unless the BioCryst stockholders and Idera stockholders approve the respective proposals of each company with respect to the mergers as described above. Your vote is very important, regardless of the number of shares you own. Whether or not you expect to attend either special meeting in person, please submit a proxy to vote your shares as promptly as possible so that your shares may be represented and voted at the BioCryst special meeting or the Idera special meeting, as applicable. However, if you previously submitted a proxy for either the Idera special meeting or the BioCryst special meeting originally scheduled for May 9, 2018, which proxy has not subsequently been revoked, and are a holder of record on May 29, 2018 and you do not want to change or revoke your proxy, you do not need to take any action. Accordingly, Idera or BioCryst, as applicable, intend to vote such proxy at the respective special meeting on July 10, 2018, as directed by your previously submitted proxy.

           The BioCryst board has unanimously approved the merger agreement and determined that the merger agreement and the transactions contemplated thereby, including the mergers, are advisable, fair to and in the best interests of BioCryst and its stockholders. The BioCryst board unanimously recommends that BioCryst stockholders vote "FOR" the proposal to adopt the merger agreement, "FOR" the proposal to approve, on a non-binding advisory basis, the compensation that may become payable to BioCryst's named executive officers that is based on or otherwise relates to the mergers and "FOR" the proposal to adjourn the BioCryst special meeting, if necessary or appropriate, to solicit additional proxies if there are not sufficient votes to adopt the merger agreement.

           The Idera board has unanimously approved the merger agreement and determined that the merger agreement and the transactions contemplated thereby, including the mergers, are advisable, fair to and in the best interests of Idera and its stockholders. The Idera board unanimously recommends that Idera stockholders vote "FOR" the proposal to adopt the merger agreement and "FOR" the proposal to approve, on a non-binding advisory basis, the compensation that may become payable to Idera's named executive officers that is based on or otherwise relates to the mergers.

           The obligations of BioCryst and Idera to complete the mergers are subject to the satisfaction or waiver of several conditions set forth in the merger agreement. The accompanying joint proxy statement/prospectus contains detailed information about BioCryst, Idera, the special meetings, the merger agreement and the mergers. BioCryst and Idera encourage you to read the joint proxy statement/prospectus carefully and in its entirety, including the section entitled "Risk Factors" beginning on page 22 of this joint proxy statement/prospectus.

           We look forward to the successful combination of BioCryst and Idera.

Sincerely,       Sincerely,    
    GRAPHIC


      GRAPHIC


    Vincent J. Milano       Jon P. Stonehouse
    President and Chief Executive Officer       President and Chief Executive Officer
    Idera Pharmaceuticals, Inc.       BioCryst Pharmaceuticals, Inc.

           Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved the mergers and other transactions described in the joint proxy statement/prospectus, nor have they approved or disapproved of the securities to be issued under this joint proxy statement/prospectus or determined if this joint proxy statement/prospectus is accurate or complete. Any representation to the contrary is a criminal offense.

           This joint proxy statement/prospectus is dated May 30, 2018 and is first being mailed to Idera stockholders and BioCryst stockholders on or about June 4, 2018.


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LOGO

Idera Pharmaceuticals, Inc.
167 Sidney Street
Cambridge, Massachusetts 02139
(617) 679-5500

NOTICE OF SPECIAL MEETING OF STOCKHOLDERS

To Be Held On July 10, 2018

To the Stockholders of Idera Pharmaceuticals, Inc.:

        We are pleased to invite you to attend the special meeting of stockholders (the "Idera special meeting") of Idera Pharmaceuticals, Inc. ("Idera"), a Delaware corporation, which will be held at Idera's offices located at 505 Eagleview Boulevard, Suite 212, Exton, Pennsylvania 19341, on July 10, 2018, at 10:00 a.m., Eastern Time, for the following purposes:

        The Idera special meeting was originally scheduled for May 9, 2018 but has been postponed and rescheduled for July 10, 2018, following investor feedback, to provide stockholders adequate time to consider new clinical data from Idera regarding its IMO-2125 program, which will be presented at the American Society of Clinical Oncology meeting being held June 1-5, 2018 in Chicago, Illinois.

        Idera will transact no other business at the Idera special meeting except such business as stated in the notice of the Idera special meeting. Please refer to the joint proxy statement/prospectus of which this notice forms a part for further information with respect to the business to be transacted at the Idera special meeting.


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        Completion of the mergers is conditioned on, among other things, approval by the Idera stockholders of the proposal to adopt the merger agreement.

        The Idera board of directors (the "Idera board") has unanimously approved the merger agreement and determined that the merger agreement and the transactions contemplated thereby, including the mergers, are advisable, fair to and in the best interests of Idera and its stockholders. The Idera board unanimously recommends that Idera stockholders vote "FOR" the proposal to adopt the merger agreement and "FOR" the proposal to approve, on a non-binding advisory basis, the compensation that may become payable to Idera's named executive officers that is based on or otherwise relates to the mergers.

        The Idera board has fixed the close of business on May 29, 2018 as the Idera record date for determination of Idera stockholders entitled to receive notice of, and to vote at, the Idera special meeting or any adjournments or postponements thereof. Only holders of record of Idera common stock at the close of business on the Idera record date are entitled to receive notice of, and to vote at, the Idera special meeting or any adjournments or postponements thereof.

        A list of the names of Idera stockholders of record will be available for 10 days prior to the Idera special meeting for any purpose germane to the special meeting during regular business hours, at the office of Idera's Assistant Secretary, 505 Eagleview Boulevard, Suite 212, Exton, Pennsylvania 19341. The Idera stockholder list will also be available at the Idera special meeting for examination by any stockholder present at such meeting.

        YOUR VOTE IS VERY IMPORTANT REGARDLESS OF THE NUMBER OF SHARES THAT YOU OWN.    The mergers cannot be completed without the adoption of the merger agreement by the affirmative vote of the holders of a majority of the issued and outstanding shares of Idera common stock entitled to vote on the merger agreement proposal as of the record date for the Idera special meeting.

        Whether or not you expect to attend the Idera special meeting in person, we urge you to submit a proxy to vote your shares as promptly as possible by either (1) logging on to www.investorvote.com/IDRA and following the instructions on your proxy card; (2) dialing 1-800-652-VOTE (8683) and listening for further directions; or (3) signing and returning the enclosed proxy card in the postage-paid envelope provided, so that your shares may be represented and voted at the Idera special meeting. If your shares are held in the name of a bank, broker or other nominee, including an employee benefit plan trustee, please follow the instructions on the voting instruction card furnished by the record holder, as appropriate. However, if you previously submitted a proxy for the Idera special meeting originally scheduled for May 9, 2018, which proxy has not subsequently been revoked, and are a holder of record on May 29, 2018 and you do not want to change or revoke your proxy, you do not need to take any action. Accordingly, Idera intends to vote such proxy at the Idera special meeting on July 10, 2018, as directed by your previously submitted proxy.

        The enclosed joint proxy statement/prospectus provides a detailed description of the mergers and the merger agreement as well as a description of the compensation that may become payable to Idera's named executive officers that is based on or otherwise relates to the mergers. We urge you to read this joint proxy statement/prospectus, including any documents incorporated by reference, and the Annexes carefully and in their entirety. If you have any questions concerning the mergers or this joint proxy statement/prospectus, would like additional copies or need help voting your shares of Idera common stock, please contact Idera's proxy solicitor:

LOGO

1407 Broadway, 27th Floor
New York, New York 10018
Stockholders May Call Toll-Free: 800-322-2885
Banks and Brokers May Call Collect: 212-929-5500
Email: proxy@mackenziepartners.com


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    By Order of the
Idera Pharmaceuticals, Inc. Board of
Directors,

 

 

GRAPHIC


Louis J. Arcudi, III
Senior Vice President of Operations, Chief Financial Officer, Treasurer and Assistant Secretary

 

 

Cambridge, Massachusetts
May 30, 2018

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LOGO

BIOCRYST PHARMACEUTICALS, INC.
4505 Emperor Blvd., Suite 200
Durham, North Carolina 27703

NOTICE OF 2018 SPECIAL MEETING OF STOCKHOLDERS

To Be Held On July 10, 2018

To the Stockholders of BioCryst Pharmaceuticals, Inc.:

        This is a notice that a special meeting of stockholders (the "BioCryst special meeting") of BioCryst Pharmaceuticals, Inc., a Delaware corporation ("BioCryst"), will be held at BioCryst's corporate offices at 4505 Emperor Blvd., Suite 200, Durham, North Carolina 27703 on July 10, 2018 at 10:00 a.m., Eastern Time, for the following purposes:

        The BioCryst special meeting was originally scheduled for May 9, 2018 but has been postponed and rescheduled for July 10, 2018, following investor feedback, to provide stockholders adequate time to consider new clinical data from Idera regarding its IMO-2125 program, which will be presented at the American Society of Clinical Oncology meeting being held June 1-5, 2018 in Chicago, Illinois.

        BioCryst's board of directors (the "BioCryst board") unanimously (i) determined that the merger agreement and the transactions contemplated thereby, including the mergers, are fair, advisable and in the best interests of BioCryst and its stockholders, (ii) approved the execution, delivery and performance by BioCryst of the merger agreement and the consummation of the transactions contemplated thereby, including the mergers, and (iii) resolved to recommend that the stockholders of BioCryst approve the adoption of the merger agreement and the transactions contemplated thereby. Accordingly, the BioCryst board recommends that BioCryst stockholders vote "FOR" the adoption of the merger agreement, "FOR" the approval on a non-binding advisory basis, the compensation that may become payable to BioCryst's named executive officers that is based on or otherwise relates to the mergers and "FOR" the adjournment of


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the BioCryst special meeting, if necessary or appropriate, to solicit additional proxies if there are not sufficient votes to adopt the merger agreement.

        May 29, 2018 has been fixed as the BioCryst record date for determination of BioCryst stockholders entitled to receive notice of, and to vote at, the BioCryst special meeting or any adjournments or postponements thereof. Only holders of record of BioCryst common stock at the close of business on the BioCryst record date are entitled to receive notice of, and to vote at, the BioCryst special meeting.

        A list of the stockholders entitled to vote at the BioCryst special meeting will be open to examination by any stockholder, for any purpose germane to the BioCryst special meeting, during ordinary business hours, for a period of at least 10 days prior to the BioCryst special meeting at the principal executive offices of BioCryst in Durham, North Carolina.

        YOUR VOTE IS VERY IMPORTANT REGARDLESS OF THE NUMBER OF SHARES THAT YOU OWN.    The mergers cannot be completed without the adoption of the merger agreement by the affirmative vote of the holders of a majority of the issued and outstanding shares of BioCryst common stock entitled to vote on the merger agreement proposal as of the record date for the BioCryst special meeting.

        Whether or not you expect to attend the BioCryst special meeting in person, we urge you to submit a proxy to have your shares voted as promptly as possible by either: (1) logging on to the website shown on your proxy card and following the instructions to vote online; (2) dialing the toll-free number shown on your proxy card and following the instructions to vote by phone; or (3) signing and returning the enclosed proxy card in the postage-paid envelope provided, so that your shares may be represented and voted at the BioCryst special meeting. If your shares are held in a BioCryst plan or in the name of a broker, bank or other nominee, please follow the instructions on the voting instruction form furnished by the plan trustee or administrator, or such broker, bank or other nominee, as appropriate. However, if you previously submitted a proxy for the BioCryst special meeting originally scheduled for May 9, 2018, which proxy has not subsequently been revoked, and are a holder of record on May 29, 2018 and you do not want to change or revoke your proxy, you do not need to take any action. Accordingly, BioCryst intends to vote such proxy at the BioCryst special meeting on July 10, 2018, as directed by your previously submitted proxy.

        The enclosed joint proxy statement/prospectus provides a detailed description of the mergers and the merger agreement as well as a description of the compensation that may become payable to BioCryst's named executive officers that is based on or otherwise relates to the mergers. We urge you to read this joint proxy statement/prospectus, including any documents incorporated by reference, and the Annexes carefully and in their entirety. If you have any questions concerning the mergers or this joint proxy statement/prospectus, would like additional copies or need help voting your shares of BioCryst common stock, please contact BioCryst's proxy solicitor:

LOGO

Innisfree M&A Incorporated
501 Madison Avenue, 20th floor
New York, New York 10022
Stockholders May Call Toll Free: 888-750-5834
Banks & Brokers May Call Collect: 212-750-5833

    By Order of the
BioCryst Pharmaceuticals, Inc. Board of
Directors,

 

 

GRAPHIC


Alane P. Barnes
Corporate Secretary

 

 

Durham, North Carolina
May 30, 2018

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ADDITIONAL INFORMATION

        This joint proxy statement/prospectus incorporates important business and financial information about Idera Pharmaceuticals, Inc. ("Idera") and BioCryst Pharmaceuticals, Inc. ("BioCryst") from other documents that are not included in or delivered with this joint proxy statement/prospectus. This information is available to you without charge upon your request. You can obtain the documents incorporated by reference into this joint proxy statement/prospectus free of charge by requesting them in writing or by telephone from the appropriate company's proxy solicitor at the following addresses and telephone numbers:

If you are an Idera Stockholder:   If you are a BioCryst Stockholder:

LOGO

 

LOGO

1407 Broadway, 27th Floor

 

501 Madison Avenue, 20th floor
New York, New York 10018   New York, New York 10022
Stockholders May Call Toll-Free: 800-322-2885   Stockholders May Call Toll Free: 888-750-5834
Banks & Brokers May Call Collect: 212-929-5500   Banks & Brokers May Call Collect: 212-750-5833
Email: proxy@mackenziepartners.com    

        You may also obtain any of the documents incorporated by reference into this joint proxy statement/prospectus without charge through the U.S. Securities and Exchange Commission (the "SEC") website at www.sec.gov. In addition, you may obtain copies of documents filed by Idera with the SEC by accessing Idera's website at www.iderapharma.com under the tab "Investors" and then under the heading "SEC Filings." You may also obtain copies of documents filed by BioCryst with the SEC by accessing BioCryst's website at www.biocryst.com under the tab "Investors" and then under the heading "SEC Documents."

        We are not incorporating the contents of the websites of the SEC, Idera, BioCryst or any other entity into this joint proxy statement/prospectus. We are providing the information about how you can obtain certain documents that are incorporated by reference into this joint proxy statement/prospectus at these websites only for your convenience.

        If you would like to request any documents, please do so by July 3, 2018 in order to receive them before the special meetings.

        For a more detailed description of the information incorporated by reference in this joint proxy statement/prospectus and how you may obtain it, see "Where You Can Find More Information" beginning on page 172 of this joint proxy statement/prospectus.


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ABOUT THIS JOINT PROXY STATEMENT/PROSPECTUS

        This joint proxy statement/prospectus, which forms part of a registration statement on Form S-4 filed with the SEC by Holdco, constitutes a prospectus of Holdco under Section 5 of the Securities Act of 1933, as amended (the "Securities Act"), with respect to the shares of Holdco common stock to be issued to Idera stockholders and BioCryst stockholders pursuant to the mergers. This joint proxy statement/prospectus also constitutes a joint proxy statement for both Idera and BioCryst under Section 14(a) of the Securities Exchange Act of 1934, as amended (the "Exchange Act"). It also constitutes a notice of meeting with respect to the special meeting of Idera stockholders (the "Idera special meeting") and a notice of meeting with respect to the special meeting of BioCryst stockholders (the "BioCryst special meeting").

        You should rely only on the information contained in or incorporated by reference into this joint proxy statement/prospectus. No one has been authorized to provide you with information that is different from that contained in, or incorporated by reference into, this joint proxy statement/prospectus. This joint proxy statement/prospectus is dated May 30, 2018. You should not assume that the information contained in this joint proxy statement/prospectus is accurate as of any date other than that date. You should not assume that the information incorporated by reference into this joint proxy statement/prospectus is accurate as of any date other than the date of the incorporated document. Neither our mailing of this joint proxy statement/prospectus to Idera stockholders or BioCryst stockholders nor the issuance by Holdco of shares of common stock pursuant to the merger agreement will create any implication to the contrary.

        This joint proxy statement/prospectus does not constitute an offer to sell, or a solicitation of an offer to buy, any securities, or the solicitation of a proxy in any jurisdiction to or from any person to whom it is unlawful to make any such offer or solicitation. Information contained in this joint proxy statement/prospectus regarding Idera has been provided by Idera and information contained in this joint proxy statement/prospectus regarding BioCryst has been provided by BioCryst.

        All references in this joint proxy statement/prospectus to "Idera" refer to Idera Pharmaceuticals, Inc., a Delaware corporation; all references in this joint proxy statement/prospectus to "BioCryst" refer to BioCryst Pharmaceuticals, Inc., a Delaware corporation; all references to "Holdco" refer to Nautilus Holdco, Inc., a Delaware corporation and wholly owned subsidiary of BioCryst formed for the sole purpose of becoming the parent entity of each of Idera and BioCryst following the mergers; all references to "Merger Sub A" refer to Island Merger Sub, Inc., a Delaware corporation and wholly owned subsidiary of Holdco formed for the sole purpose of effecting the Idera merger; all references to the "Idera merger" refer to the merger of Merger Sub A with and into Idera, with Idera as the surviving entity, continuing as a wholly owned subsidiary of Holdco; all references to "Merger Sub B" refer to Boat Merger Sub, Inc., a Delaware corporation and wholly owned subsidiary of Holdco formed for the sole purpose of effecting the BioCryst merger; all references to the "BioCryst merger" refer to the merger of Merger Sub B with and into BioCryst, with BioCryst as the surviving entity, continuing as a wholly owned subsidiary of Holdco; and all references to "mergers" refers, collectively, to the Idera merger and BioCryst merger. Unless otherwise indicated or as the context requires, all references in this joint proxy statement/prospectus to "we," "our" and "us" refer to Idera and BioCryst collectively; and, unless otherwise indicated or as the context requires, all references to the "merger agreement" refer to the Agreement and Plan of Merger, dated as of January 21, 2018, by and among BioCryst, Idera, Holdco, Merger Sub A and Merger Sub B, a copy of which is attached as Annex A to this joint proxy statement/prospectus. Holdco, following completion of the mergers, is sometimes referred to in this joint proxy statement/prospectus as the "combined company," "Valenscion Incorporated" or "Valenscion."


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  Page  

QUESTIONS AND ANSWERS

    v  

SUMMARY

   
1
 

The Companies

    1  

The Mergers

    2  

U.S. Federal Income Tax Consequences of the Mergers

    4  

Recommendation of the Idera Board

    4  

Recommendation of the BioCryst Board

    5  

Opinion of Idera's Financial Advisor—Goldman Sachs

    5  

Opinion of BioCryst's Financial Advisor—J.P. Morgan

    5  

Interests of Idera Directors, Executive Officers and Certain of their Affiliates in the Mergers

    6  

Interests of BioCryst Directors and Executive Officers in the Mergers

    6  

Holdco Board, Management and Certain Governance Matters Following the Mergers

    7  

Regulatory Clearances Required for the Mergers

    7  

Amended and Restated Certificate of Incorporation of Holdco

    7  

Completion of the Mergers

    7  

The Merger Agreement

    8  

Voting and Support Agreements

    11  

Accounting Treatment

    12  

No Appraisal Rights

    12  

Litigation Related to the Mergers

    12  

Risk Factors

    12  

Comparison of Rights of Idera Stockholders, BioCryst Stockholders and Holdco Stockholders

    12  

Listing of Holdco Common Stock; De-Listing and Deregistration of Idera Stock and BioCryst Stock

    13  

The Idera Special Meeting

    13  

The BioCryst Special Meeting

    13  

SUMMARY HISTORICAL FINANCIAL DATA

   
15
 

Summary Historical Financial Data of Idera

    15  

Summary Historical Consolidated Financial Data of BioCryst

    17  

UNAUDITED EQUIVALENT AND COMPARATIVE PER SHARE DATA

   
19
 

CAUTIONARY STATEMENT REGARDING FORWARD-LOOKING STATEMENTS

   
20
 

RISK FACTORS

   
22
 

Risk Factors Relating to the Mergers

    22  

Risk Factors Relating to the Combined Company Following the Mergers

    29  

Other Risk Factors of Idera and BioCryst

    32  

THE COMPANIES

   
33
 

THE BIOCRYST SPECIAL MEETING

   
35
 

Date, Time and Place

    35  

Purpose of the BioCryst Special Meeting

    35  

Recommendation of the BioCryst Board

    35  

Attendance at the BioCryst Special Meeting

    36  

BioCryst Record Date; Stockholders Entitled to Vote

    36  

BioCryst Voting and Support Agreement

    37  

Voting by BioCryst's Directors and Executive Officers

    37  

i


 
  Page  

Quorum

    37  

Required Vote

    37  

How to Vote

    38  

Shares Held in Street Name

    39  

Proxies and Revocation

    40  

Tabulation of Votes

    40  

Solicitation of Proxies

    40  

Adjournments

    40  

Householding of Special Meeting Materials

    41  

Questions and Additional Information

    41  

BIOCRYST PROPOSALS

   
42
 

BioCryst Proposal 1: The BioCryst Merger Proposal

    42  

BioCryst Proposal 2: The BioCryst Merger-Related Compensation Proposal

    42  

BioCryst Proposal 3: The BioCryst Adjournment Proposal

    43  

THE IDERA SPECIAL MEETING

   
44
 

Date, Time and Place

    44  

Purpose of the Idera Special Meeting

    44  

Recommendation of the Idera Board

    44  

Idera Record Date; Stockholders Entitled to Vote

    44  

Idera Voting and Support Agreement

    45  

Voting by Idera's Directors and Executive Officers

    45  

Quorum

    45  

Required Vote

    45  

Failure to Vote, Broker Non-Votes and Abstentions

    46  

How to Vote

    46  

Voting of Idera Common Stock Held in Street Name

    47  

How Proxies are Counted

    48  

Revocation of Proxies

    48  

Tabulation of Votes

    49  

Solicitation of Proxies

    49  

Adjournments

    49  

Householding of Special Meeting Materials

    49  

Questions and Additional Information

    50  

IDERA PROPOSALS

   
51
 

Idera Proposal 1: The Idera Merger Proposal

    51  

Idera Proposal 2: The Idera Merger-Related Compensation Proposal

    51  

THE MERGERS

   
53
 

Effects of the Mergers

    53  

Background of the Mergers

    54  

Idera's Reasons for the Mergers; Recommendation of the Idera Board

    67  

BioCryst's Reasons for the Mergers; Recommendation of the BioCryst Board

    71  

Certain Financial Forecasts Utilized by the Idera Board and Idera's Financial Advisor in Connection with the Mergers

    76  

Certain Financial Forecasts Utilized by the BioCryst Board and BioCryst's Financial Advisor in Connection with the Mergers

    80  

Important Information about the Financial Forecasts

    83  

Opinion of Idera's Financial Advisor—Goldman Sachs

    84  

Opinion of BioCryst's Financial Advisor—J.P. Morgan

    94  

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  Page  

Amended and Restated Certificate of Incorporation of Holdco

    99  

Interests of Idera Directors, Executive Officers and Certain of their Affiliates in the Mergers

    99  

Idera Stockholder Advisory Vote on Merger-Related Compensation for Idera's Named Executive Officers Proposal

    103  

Interests of Biocryst Directors and Executive Officers in the Mergers

    106  

Employee Benefits

    112  

BioCryst Stockholder Advisory Vote on Merger-Related Compensation for BioCryst's Named Executive Officers Proposal

    112  

Holdco Board, Management and Certain Governance Matters Following the Mergers

    114  

Regulatory Clearances Required for the Mergers

    114  

Listing of Holdco Common Stock

    115  

De-Listing and Deregistration of Idera Stock

    115  

De-Listing and Deregistration of BioCryst Stock

    115  

No Appraisal Rights

    115  

Litigation Related to the Mergers

    115  

THE MERGER AGREEMENT

   
116
 

Terms of the Mergers; Merger Consideration

    116  

Completion of the Mergers

    117  

Exchange of Shares in the Mergers

    117  

Representations and Warranties

    118  

Conduct of Business Pending the Effective Time

    120  

No Solicitation of Competing Proposals

    123  

Changes in Board Recommendations

    124  

Efforts to Obtain Required Stockholder Votes

    125  

Efforts to Complete the Mergers

    126  

Governance Matters After the Mergers

    127  

Employee Benefits Matters

    127  

Treatment of Idera Stock Options and Warrants

    128  

Treatment of BioCryst Stock Options and RSUs

    129  

Treatment of Equity Plans and Employee Stock Purchase Plans

    129  

Compensation Actions between Signing of Merger Agreement and Completion of Mergers

    130  

Other Covenants and Agreements

    130  

Conditions to Completion of the Mergers

    131  

Termination of the Merger Agreement

    133  

Expenses and Termination Fees; Liability for Breach

    134  

Amendments, Extensions and Waivers

    136  

Parties in Interest

    136  

Specific Performance

    136  

U.S. FEDERAL INCOME TAX CONSEQUENCES OF THE MERGERS

   
137
 

General

    138  

U.S. Federal Income Tax Consequences of the Mergers to U.S. Holders of BioCryst Common Stock and Idera Common Stock

    138  

Information Reporting and Backup Withholding

    139  

ACCOUNTING TREATMENT

   
140
 

SELECTED UNAUDITED PRO FORMA CONDENSED COMBINED FINANCIAL INFORMATION OF IDERA AND BIOCRYST

   
141
 

Summary Unaudited Pro Forma Condensed Combined Financial Information

    141  

Unaudited Pro Forma Condensed Combined Financial Statements

    142  

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  Page  

Unaudited Pro Forma Condensed Combined Balance Sheet as of March 31, 2018

    143  

Unaudited Pro Forma Condensed Combined Statement of Operations for the Three Months Ended March 31, 2018

    144  

Unaudited Pro Forma Condensed Combined Statement of Operations for the Year Ended December 31, 2017

    145  

Notes to the Unaudited Pro Forma Condensed Combined Financial Statements

    146  

COMPARATIVE STOCK PRICE DATA AND DIVIDENDS

   
154
 

Stock Prices

    154  

Dividends

    154  

SECURITY OWNERSHIP OF CERTAIN BENEFICIAL OWNERS OF BIOCRYST

   
155
 

SECURITY OWNERSHIP OF CERTAIN BENEFICIAL OWNERS OF IDERA

   
158
 

DESCRIPTION OF HOLDCO CAPITAL STOCK

   
161
 

Description of Holdco Common Stock

    161  

Description of Holdco Blank Check Preferred Stock

    162  

Anti-Takeover Provisions

    162  

COMPARISON OF RIGHTS OF IDERA STOCKHOLDERS, BIOCRYST STOCKHOLDERS AND HOLDCO STOCKHOLDERS

   
164
 

NO APPRAISAL RIGHTS

   
169
 

LEGAL MATTERS

   
169
 

EXPERTS

   
169
 

Idera

    169  

BioCryst

    169  

FUTURE STOCKHOLDER PROPOSALS

   
169
 

Idera

    169  

BioCryst

    170  

OTHER MATTERS

   
171
 

Other Matters Presented at the Special Meetings

    171  

WHERE YOU CAN FIND MORE INFORMATION

   
172
 

Annex A—Agreement and Plan of Merger, dated January 21, 2018

    A-1  

Annex B—Opinion of Goldman, Sachs & Co. LLC

    B-1  

Annex C—Opinion of J.P. Morgan Securities LLC

    C-1  

Annex D—Form of Amended and Restated Certificate of Incorporation of Holdco

    D-1  

Annex E—Form of Amended and Restated Bylaws of Holdco

    E-1  

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QUESTIONS AND ANSWERS

        The following are some questions that you, as a stockholder of Idera or a stockholder of BioCryst, may have regarding the mergers and the other matters being considered at the special meetings and the answers to those questions. Idera and BioCryst urge you to carefully read the remainder of this joint proxy statement/prospectus because the information in this section does not provide all the information that might be important to you with respect to the mergers and the other matters being considered at the special meetings. Additional important information is also contained in the Annexes to, and the documents incorporated by reference into, this joint proxy statement/prospectus.

Q:    Why am I receiving this joint proxy statement/prospectus and a new proxy card?

A:
As previously disclosed, BioCryst and Idera have agreed to a strategic business combination pursuant to the terms of the merger agreement that is described in this joint proxy statement/prospectus. A copy of the merger agreement is included as Annex A to this joint proxy statement/prospectus.

Q:    What should I do if I already voted using the proxy card sent in the joint proxy statement/prospectus that was mailed on or around April 2, 2018?

A:
If you previously submitted a proxy for either the Idera special meeting or the BioCryst special meeting originally scheduled for May 9, 2018, which proxy has not subsequently been revoked, and are a holder of record on May 29, 2018, BioCryst and Idera, as applicable, intend to vote such proxy at the respective special meeting on July 10, 2018, as directed by the previously submitted proxy by you. Accordingly, if you have already submitted a proxy, you do not need to take any action unless you want to change or revoke your proxy.

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Q:    What will stockholders receive in the mergers?

A:
Idera Stockholders:    If the mergers are completed, (i) holders of Idera common stock will receive 0.20 shares of Holdco common stock for each share of Idera common stock they hold at the effective time of the mergers (the "Idera exchange ratio") and (ii) holders of Idera preferred stock will receive for each share of Idera preferred stock they hold at the effective time of the mergers, that number of shares of Holdco common stock equal to (a) $1.00 divided by the 20-trading-day average trading price of Idera common stock, ending with the trading day prior to the third day prior to the closing date, multiplied by (b) 0.20. Holders of Idera common stock and Idera preferred stock will not receive any fractional shares of Holdco common stock in the mergers. Instead, Idera stockholders will receive cash in lieu of any fractional shares of Holdco common stock that the holders of Idera common stock and Idera preferred stock would otherwise have been entitled to receive.

Q:    What is the value of the merger consideration?

A:
BioCryst stockholders and Idera stockholders will receive a fixed number of shares of Holdco common stock in the BioCryst merger and the Idera merger, respectively, rather than a number of shares of Holdco common stock with a particular fixed market value. Because the exchange ratios are fixed and will not be adjusted to reflect any changes in the market prices of BioCryst common stock or Idera common stock, the market value of the Holdco common stock issued in the BioCryst merger or the Idera merger, as applicable, and the BioCryst common stock and Idera common stock surrendered in the BioCryst merger and the Idera merger, respectively, may be higher or lower than the values of these shares on dates earlier to the effective time of the

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Q:    What percentage of Holdco will Idera stockholders and BioCryst stockholders, respectively, own following the mergers?

A:
Upon completion of the mergers, BioCryst stockholders (including holders of securities convertible, exchangeable or exercisable for shares of BioCryst common stock) immediately prior to the effective time of the mergers are expected to beneficially own approximately 51.6% of Holdco and Idera stockholders (including holders of securities convertible, exchangeable or exercisable for shares of Idera common stock) immediately prior to the effective time of the mergers are expected to beneficially own approximately 48.4% of Holdco, in each case, calculated on a fully diluted basis (using the treasury method).

Q:    When and where will the special meetings be held?

A:
Idera Stockholders:    The Idera special meeting will be held at Idera's offices located at 505 Eagleview Boulevard, Suite 212, Exton, Pennsylvania 19341, on July 10, 2018, at 10:00 a.m., Eastern Time.

Q:    Who is entitled to vote at the special meetings?

A:
Idera Stockholders:    The Idera record date for the Idera special meeting is May 29, 2018. Only holders of record of issued and outstanding shares of Idera common stock as of the close of business on the Idera record date are entitled to notice of, and to vote at, the Idera special meeting or any adjournments or postponements of the Idera special meeting.

Q:    What am I being asked to vote on and why is this approval necessary?

A:
Idera stockholders are being asked to vote on the following proposals:

(1)
to adopt the merger agreement, a copy of which is attached as Annex A to this joint proxy statement/prospectus; and

(2)
to approve, on a non-binding advisory basis, the compensation that may become payable to Idera's named executive officers that is based on or otherwise relates to the mergers.

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Q:    What vote is required to approve each proposal at the Idera special meeting?

A:
Adoption of the merger agreement requires the affirmative vote of holders of a majority of the issued and outstanding shares of Idera common stock entitled to vote on the proposal. Failures to vote, abstentions and "broker non-votes" (as defined in "Questions and Answers" beginning on page v of this joint proxy statement/prospectus) will have the effect of a vote against the proposal.

Q:    What vote is required to approve each proposal at the BioCryst special meeting?

A:
Adoption of the merger agreement requires the affirmative vote of holders of a majority of the issued and outstanding shares of BioCryst common stock entitled to vote on the proposal. Failures to vote, abstentions and broker non-votes will have the effect of a vote against the proposal.

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Q:    What constitutes a quorum at the special meetings?

A:
Idera Stockholders:    Stockholders who hold shares representing at least a majority of the issued and outstanding shares of common stock entitled to vote at the Idera special meeting must be present in person or represented by proxy to constitute a quorum for the transaction of business at the Idera special meeting. If a quorum is not present, the Idera special meeting may be adjourned by the chairman of the Idera special meeting, to reconvene at the same or another place, and notice need not be given of any such adjourned meeting if the time and place thereof are announced at the meeting at which the adjournment is taken.

Q:    How does the Idera board of directors recommend that Idera stockholders vote?

A:
The Idera board of directors (the "Idera board") has unanimously approved the merger agreement and determined that the merger agreement and the transactions contemplated thereby, including the mergers, are fair, advisable and in the best interests of Idera and its stockholders. The Idera board unanimously recommends that the Idera stockholders vote "FOR" the proposal to adopt the merger agreement and "FOR" the proposal to approve, on a non-binding advisory basis, the compensation that may become payable to Idera's named executive officers that is based on or otherwise relates to the mergers.

Q:    How does the BioCryst board of directors recommend that BioCryst stockholders vote?

A:
The BioCryst board of directors (the "BioCryst board") has unanimously determined that the merger agreement and the transactions contemplated thereby, including the mergers, are fair, advisable and in the best interests of BioCryst and its stockholders. The BioCryst board recommends that BioCryst stockholders vote "FOR" the proposal to adopt the merger agreement, "FOR" the proposal to approve, on a non-binding advisory basis, the compensation that may become payable to BioCryst's named executive officers that is based on or otherwise relates to the mergers and "FOR" the proposal to adjourn the BioCryst special meeting, if necessary or appropriate, to solicit additional proxies if there are not sufficient votes to adopt the merger agreement.

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Q:    How do I vote if I am a stockholder of record?

A:
If you are a stockholder of record of Idera as of May 29, 2018, which is referred to as the Idera record date, or a stockholder of record of BioCryst as of May 29, 2018, which is referred to as the BioCryst record date, you may submit your proxy before your respective company's special meeting in one of the following ways:

use the toll-free number shown on your proxy card;

visit the website shown on your proxy card to vote via the Internet; or

complete, sign, date and return the enclosed proxy card in the enclosed postage-paid envelope.

Q:    How many votes do I have?

A:
Idera Stockholders:    Holders of Idera common stock are entitled to one vote for each share owned as of the close of business on the Idera record date. As of the close of business on the Idera record date, there were 217,310,991 shares of Idera common stock issued and outstanding and entitled to vote at the Idera special meeting.

Q:    My shares are held in "street name" by my broker, bank or other nominee. Will my broker, bank or other nominee automatically vote my shares for me?

A:
No. If your shares are held in the name of a broker, bank or other nominee, you are considered the "beneficial holder" of the shares held for you in what is known as "street name." You are not the "record holder" (as defined in "The Idera Special Meeting—How to Vote" beginning on page 46 of this joint proxy statement/prospectus) of such shares. If this is the case, this joint proxy statement/prospectus has been forwarded to you by your broker, bank or other nominee. As the beneficial holder, unless your broker, bank, or other nominee has discretionary authority over your shares, you generally have the right to direct your broker, bank or other nominee as to how to vote your shares. If you do not provide voting instructions, your shares will not be voted on any proposal, as your broker, bank or other nominee will not have discretionary voting authority with respect to any of the proposals described in this joint proxy statement/prospectus. This is often called a "broker non-vote."

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Q:    What will happen if I fail to vote or I abstain from voting?

A:
For purposes of each of the Idera special meeting and the BioCryst special meeting, an abstention occurs when a respective stockholder attends the applicable special meeting in person and does not vote or returns a proxy with an "abstain" vote.

Q:    What will happen if I return my proxy card without indicating how to vote?

A:
Idera Stockholders:    If you properly complete and sign your proxy card but do not indicate how your shares of Idera common stock should be voted on a matter, the shares of Idera common stock represented by your proxy will be voted as the Idera board recommends and, therefore, "FOR" the proposal to adopt the merger agreement and "FOR" the proposal to approve, on a

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Q:    Can I change my vote or revoke my proxy after I have returned a proxy or voting instruction card?

A:
Yes.

Q:    What are the U.S. federal income tax consequences of the mergers to U.S. holders of Idera common stock and BioCryst common stock?

A:
Consequences to holders of Idera common stock and BioCryst common stock:    It is a condition to BioCryst's obligation to complete the BioCryst merger that BioCryst receive an opinion from Skadden, Arps, Slate, Meagher & Flom LLP ("Skadden"), dated as of the closing date of the mergers (the "closing date"), to the effect that the BioCryst merger will qualify as a "reorganization" within the meaning of Section 368(a) of the U.S. Internal Revenue Code of 1986, as amended (the "Code") or, alternatively, the mergers together will be treated as an "exchange" described in Section 351 of the Code. It is a condition to Idera's obligation to complete the Idera merger that Idera receive an opinion from Latham & Watkins LLP ("Latham"), dated as of the closing date, to the effect that the mergers together will be treated as an "exchange" described in Section 351 of the Code. Assuming the mergers are treated for U.S. federal income tax purposes

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Q:    When do you expect the mergers to be completed?

A:
Idera and BioCryst are working to complete the mergers as soon as practicable and expect the closing of the mergers to occur in the third quarter of 2018. However, the mergers are subject to the satisfaction or waiver of certain conditions, and it is possible that factors outside the control of Idera and BioCryst could result in the mergers being completed at a later time or not at all.

Q:    Do I need to do anything with my shares of Idera common stock or BioCryst common stock other than voting for the proposals at the Idera special meeting or BioCryst special meeting, respectively?

A:
Idera Stockholders:    If you are an Idera stockholder, at the effective time of the mergers, (i) each share of Idera common stock you hold will be converted automatically into the right to receive 0.20 shares of Holdco common stock and (ii) each share of Idera preferred stock will be converted automatically into the right to receive a number of shares of Holdco common stock equal to (a) $1.00 divided by the 20-trading-day average trading price of Idera common stock, ending with the trading day prior to the third day prior to the closing date, multiplied by (b) 0.20, in each case, together with cash in lieu of any fractional shares. You will receive instructions at that time regarding exchanging your shares of Idera common stock and Idera preferred stock for shares of Holdco common stock. You do not need to take any action at this time. Please do not send your Idera stock certificates with your proxy card.

Q:    Are stockholders entitled to appraisal rights?

A:
No. Under the General Corporation Law of the State of Delaware, as amended (the "DGCL"), neither the Idera stockholders nor the BioCryst stockholders will be entitled to exercise any appraisal rights in connection with the mergers or the other transactions contemplated by the merger agreement.

Q:    What happens if I sell my shares of Idera common stock before the Idera special meeting?

A:
The record date for the Idera special meeting is earlier than the date of the Idera special meeting and the date that the mergers are expected to be completed. If you transfer your Idera shares after the Idera record date but before the Idera special meeting, you will retain your right to vote at the

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Q:    What happens if I sell my shares of BioCryst common stock before the BioCryst special meeting?

A:
The record date for the BioCryst special meeting is earlier than the date of the BioCryst special meeting and the date that the mergers are expected to be completed. If you transfer your BioCryst shares after the BioCryst record date but before the BioCryst special meeting, you will retain your right to vote at the BioCryst special meeting, but will have transferred the right to receive the merger consideration in the mergers. In order to receive the merger consideration, you must hold your shares through the effective date of the mergers.

Q:    What if I hold shares in both Idera and BioCryst?

A:
If you are a stockholder of both Idera and BioCryst, you will receive two separate packages of proxy materials. A vote cast as an Idera stockholder will not count as a vote cast as a BioCryst stockholder, and a vote cast as a BioCryst stockholder will not count as a vote cast as an Idera stockholder. Therefore, please submit separate proxies for your Idera shares and your BioCryst shares.

Q:    Who can help answer my questions?

A:
Idera stockholders or BioCryst stockholders who have questions about the mergers, the other matters to be voted on at the special meetings, or how to submit a proxy or desire additional copies of this joint proxy statement/prospectus or additional proxy cards should contact:
If you are an Idera stockholder:   If you are a BioCryst stockholder:

LOGO

 

LOGO

1407 Broadway, 27th Floor

 

501 Madison Avenue, 20th floor
New York, New York 10018   New York, New York 10022
Stockholders May Call Toll-Free: 800-322-2885   Stockholders May Call Toll Free: 888-750-5834
Banks & Brokers May Call Collect: 212-929-5500   Banks & Brokers May Call Collect: 212-750-5833
Email: proxy@mackenziepartners.com    

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SUMMARY

        This summary highlights selected information contained in this joint proxy statement/prospectus and does not contain all the information that may be important to you with respect to the mergers and the other matters being considered at the Idera special meeting and BioCryst special meeting. Idera and BioCryst urge you to read carefully this joint proxy statement/prospectus in its entirety, including the attached Annexes, and the other documents to which we have referred you. See also the section entitled "Where You Can Find More Information" beginning on page 172 of this joint proxy statement/prospectus. We have included page references in this summary to direct you to a more complete description of the topics presented below.

The Companies

Nautilus Holdco, Inc. (see page 33)

        Nautilus Holdco, Inc. is a Delaware corporation and wholly owned subsidiary of BioCryst formed for the sole purpose of becoming the parent entity of each of Idera and BioCryst following the mergers. At the effective time of the mergers, Nautilus Holdco, Inc. will be renamed "Valenscion Incorporated."

Idera Pharmaceuticals, Inc. (see page 33)

        Idera is a clinical-stage biopharmaceutical company focused on the discovery, development and commercialization of novel oligonucleotide therapeutics for oncology and rare diseases. Idera uses two distinct proprietary drug discovery technology platforms to design and develop drug candidates: its Toll-like receptor, or TLR, targeting technology and its nucleic acid chemistry technology (formerly referred to as Idera's third generation antisenses, or 3GA technology). Idera developed these platforms based on its scientific expertise and pioneering work with synthetic oligonucleotides as therapeutic agents. Using its TLR targeting technology, Idera designs synthetic oligonucleotide-based drug candidates to modulate the activity of specific TLRs. Using its nucleic acid chemistry technology, Idera is developing drug candidates to turn off the messenger RNA, or mRNA, associated with disease causing genes. Idera believes that its nucleic acid chemistry technology may potentially reduce the immunotoxicity and increase the potency of earlier generation antisense and RNA interference, or RNAi, technologies.

        Idera's business strategy is focused on the clinical development of drug candidates for oncology and rare diseases characterized by small, well-defined patient populations with serious unmet medical needs. Idera believes it can develop and commercialize these targeted therapies on its own. To the extent Idera seeks to develop drug candidates for broader disease indications, it has entered into and may explore additional collaborative alliances to support development and commercialization.

        Idera's common stock is traded on the Nasdaq Global Select Market (the "Nasdaq") under the symbol "IDRA."

        The principal executive offices of Idera are located at 167 Sidney Street, Cambridge, Massachusetts 02139, and its telephone number is (617) 679-5500. Idera maintains another office at 505 Eagleview Boulevard, Suite 212, Exton, Pennsylvania 19341.

BioCryst Pharmaceuticals, Inc. (see page 33)

        BioCryst is a biotechnology company that designs, optimizes and develops novel small molecule drugs that block key enzymes involved in the pathogenesis of diseases. BioCryst focuses on the treatment of rare diseases in which significant unmet medical needs exist and align with BioCryst's capabilities and expertise. BioCryst integrates the disciplines of biology, crystallography, medicinal chemistry and computer modeling to discover and develop small molecule pharmaceuticals through the process known as structure-guided drug design. Structure-guided drug design is a drug discovery

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approach by which BioCryst designs synthetic compounds from detailed structural knowledge of the active sites of enzyme targets associated with particular diseases. BioCryst uses X-ray crystallography, computer modeling of molecular structures and advanced chemistry techniques to focus on the three-dimensional molecular structure and active site characteristics of the enzymes that control cellular biology. Enzymes are proteins that act as catalysts for many vital biological reactions. BioCryst's goal generally is to design a compound that will fit in the active site of an enzyme and thereby prevent its catalytic activity.

        BioCryst's common stock is traded on the Nasdaq under the symbol "BCRX."

        The principal executive offices of BioCryst are located at 4505 Emperor Blvd., Suite 200, Durham, North Carolina 27703, and its telephone number is (919) 859-1302.

Island Merger Sub, Inc. (see page 34)

        Island Merger Sub, Inc. is a Delaware corporation and wholly owned subsidiary of Holdco formed for the sole purpose of effecting the Idera merger.

Boat Merger Sub, Inc. (see page 34)

        Boat Merger Sub, Inc. is a Delaware corporation and wholly owned subsidiary of Holdco formed for the sole purpose of effecting the BioCryst merger.

The Mergers

        A copy of the merger agreement is attached as Annex A to this joint proxy statement/prospectus. Idera and BioCryst encourage you to read the entire merger agreement carefully because it is the principal document governing the mergers. For more information on the merger agreement, see the section entitled "The Merger Agreement" beginning on page 116 of this joint proxy statement/prospectus.

Effects of the Mergers (see page 53)

        Subject to the terms and conditions of the merger agreement, at the effective time of the mergers:

    Merger Sub A, a Delaware corporation that was formed on January 16, 2018 as a wholly owned subsidiary of Holdco for the sole purpose of effecting the mergers, will be merged with and into Idera, with Idera surviving the Idera merger as a wholly owned subsidiary of Holdco; and

    Merger Sub B, a Delaware corporation that was formed on January 16, 2018 as a wholly owned subsidiary of Holdco for the sole purpose of effecting the mergers, will be merged with and into BioCryst, with BioCryst surviving the BioCryst merger as a wholly owned subsidiary of Holdco.

        As a result, among other things, (1) Holdco will become the ultimate parent of Idera, BioCryst and their respective subsidiaries, (2) existing holders of Idera common stock and Idera preferred stock will receive shares of Holdco common stock and (3) existing holders of BioCryst common stock will receive shares of Holdco common stock, in accordance with the terms of the merger agreement. Upon completion of the mergers, BioCryst and Idera, and their respective subsidiaries, will operate as a combined company under the name Valenscion Incorporated.

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        The organization of BioCryst, Idera and Holdco before and after the mergers is illustrated below:


Prior to the Mergers

GRAPHIC


The Mergers

GRAPHIC

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After the Mergers

GRAPHIC

U.S. Federal Income Tax Consequences of the Mergers (see page 137)

        It is a condition to BioCryst's obligation to complete the BioCryst merger that BioCryst receive an opinion from Skadden, dated as of the closing date, to the effect that the BioCryst merger will qualify as a "reorganization" within the meaning of Section 368(a) of the Code or, alternatively, the mergers together will be treated as an "exchange" described in Section 351 of the Code. It is a condition to Idera's obligation to complete the Idera merger that Idera receive an opinion from Latham, dated as of the closing date, to the effect that the mergers together will be treated as an "exchange" described in Section 351 of the Code. Assuming the mergers are treated for U.S. federal income tax purposes as described above, a U.S. holder of BioCryst common stock or Idera common stock will not recognize any gain or loss for U.S. federal income tax purposes upon the exchange of shares of BioCryst common stock or Idera common stock for shares of Holdco common stock in the BioCryst merger or the Idera merger, respectively, except with respect to cash received by BioCryst and Idera stockholders in lieu of fractional shares of Holdco common stock.

        Please carefully review the information set forth in the section entitled "U.S. Federal Income Tax Consequences of the Mergers" beginning on page 137 of this joint proxy statement/prospectus for a discussion of the U.S. federal income tax consequences of the mergers. Please consult your own tax advisors as to the specific tax consequences to you of the mergers.

Recommendation of the Idera Board (see page 44)

        After careful consideration, the Idera board unanimously approved the merger agreement and determined that the merger agreement and the transactions contemplated thereby, including the mergers, are fair, advisable, and in the best interests of Idera and its stockholders. For more information regarding the factors considered by the Idera board in reaching its decision to approve the merger agreement, see the section entitled "The Mergers—Idera's Reasons for the Mergers; Recommendation of the Idera Board" beginning on page 67 of this joint proxy statement/prospectus.

        The Idera board unanimously recommends that Idera stockholders vote "FOR" the proposal to approve the merger agreement and the transactions contemplated thereby, including the mergers, and "FOR" the proposal to approve, on a non-binding advisory basis, the compensation that may become payable to Idera's named executive officers that is based on or otherwise relates to the mergers.

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Recommendation of the BioCryst Board (see page 71)

        After careful consideration, BioCryst's board unanimously approved the merger agreement and determined that the merger agreement and the transactions contemplated thereby, including the mergers, are fair, advisable and in the best interests of BioCryst and its stockholders. For more information regarding the factors considered by the BioCryst board in reaching its decision to approve the merger agreement, see the section entitled "The Mergers—BioCryst's Reasons for the Mergers; Recommendation of the BioCryst Board" beginning on page 71 of this joint proxy statement/prospectus.

        The BioCryst board unanimously recommends that BioCryst stockholders vote "FOR" the proposal to adopt the merger agreement and the transactions contemplated thereby, including the mergers, "FOR" the proposal to approve, on a non-binding advisory basis, the compensation that may become payable to BioCryst's named executive officers that is based on or otherwise relates to the mergers and "FOR" the proposal to adjourn the BioCryst special meeting, if necessary or appropriate, to solicit additional proxies if there are not sufficient votes to adopt the merger agreement.

Opinion of Idera's Financial Advisor—Goldman Sachs (see page 84)

        At a meeting of the Idera board held on January 21, 2018, Goldman, Sachs & Co. LLC ("Goldman Sachs") delivered to the Idera board its oral opinion, subsequently confirmed in writing, to the effect that, as of January 21, 2018 and based upon and subject to the factors and assumptions set forth in Goldman Sachs' written opinion, the Idera exchange ratio of 0.20 shares of Holdco common stock for each share of Idera common stock pursuant to the merger agreement was fair from a financial point of view to the holders (other than BioCryst and its affiliates) of shares of Idera common stock.

        The full text of the written opinion of Goldman Sachs, dated January 21, 2018, which sets forth the assumptions made, procedures followed, matters considered, qualifications and limitations on the review undertaken in connection with the opinion, is attached as Annex B to this joint proxy statement/prospectus. The summary of Goldman Sachs' opinion contained in this joint proxy statement/prospectus is qualified in its entirety by reference to the full text of Goldman Sachs' written opinion. Goldman Sachs' advisory services and opinion were provided for the information and assistance of the Idera board in connection with its consideration of the transactions contemplated by the merger agreement and the opinion does not constitute a recommendation as to how any holder of shares of Idera common stock should vote with respect to the transactions contemplated by the merger agreement or any other matter.

        Pursuant to an engagement letter between Idera and Goldman Sachs, Idera has agreed to pay Goldman Sachs for its services in connection with the transactions contemplated by the merger agreement an aggregate fee of $7.0 million, $0.7 million of which became payable at announcement, and the remainder of which is contingent upon consummation of the transactions contemplated by the merger agreement.

        For further information, see the section entitled "The Mergers—Opinion of Idera's Financial Advisor—Goldman Sachs" beginning on page 84 of and Annex B to this joint proxy statement/prospectus.

Opinion of BioCryst's Financial Advisor—J.P. Morgan (see page 94)

        BioCryst retained J.P. Morgan Securities LLC ("J.P. Morgan") to act as financial advisor to BioCryst in connection with the mergers. At the meeting of the BioCryst board on January 21, 2018, J.P. Morgan rendered its oral opinion to the BioCryst board that, as of such date and based upon and subject to the assumptions made, procedures followed, matters considered and limitations on the review

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undertaken by J.P. Morgan in preparing the opinion, the BioCryst exchange ratio of 0.50 shares of Holdco common stock for each share of BioCryst common stock pursuant to the merger agreement was fair, from a financial point of view, to the holders of shares of BioCryst common stock. J.P. Morgan confirmed this oral opinion by delivering its written opinion to the BioCryst board, dated January 21, 2018.

        The full text of the written opinion of J.P. Morgan, dated January 21, 2018, which sets forth the assumptions made, procedures followed, matters considered and limitations on the review undertaken by J.P. Morgan in preparing the opinion, is attached as Annex C to this joint proxy statement/prospectus and is incorporated herein by reference. BioCryst stockholders are urged to read the opinion in its entirety. J.P. Morgan's written opinion was addressed to the BioCryst board (in its capacity as such) in connection with and for the purposes of its evaluation of the mergers, was directed only to the BioCryst exchange ratio in the proposed BioCryst merger and did not address any other aspect of the mergers. The opinion does not constitute a recommendation to any stockholder of BioCryst as to how such stockholder should vote with respect to the mergers or any other matter.

        For a description of the opinion that the BioCryst board received from J.P. Morgan, see the section entitled "The Mergers—Opinion of BioCryst's Financial Advisor—J.P. Morgan" beginning on page 94 of this joint proxy statement/prospectus.

        Pursuant to an engagement letter between BioCryst and J.P. Morgan, BioCryst has agreed to pay J.P. Morgan for its services in connection with the transactions contemplated by the merger agreement an aggregate fee of $7.0 million, $2.0 million of which became payable to J.P. Morgan for advisory services rendered up until the time J.P. Morgan delivered its opinion, and the remainder of which is contingent upon the consummation of the mergers.

Interests of Idera Directors, Executive Officers and Certain of their Affiliates in the Mergers (see page 99)

        In considering the recommendation of the Idera board, Idera stockholders should be aware that certain of Idera's executive officers, directors and certain of their affiliates have interests in the mergers that may be different from, or in addition to, those of the Idera stockholders generally. These interests may present such executive officers, directors and certain of their affiliates with actual or potential conflicts of interest. The Idera board was aware of these interests during its deliberations on the merits of the mergers and in deciding to recommend that Idera stockholders vote for the Idera proposals. For additional information on the interests of Idera's directors, officers and certain of their affiliates in the mergers, see "The Mergers—Interests of Idera Directors, Executive Officers and Certain of their Affiliates in the Mergers" beginning on page 99 of this joint proxy statement/prospectus.

Interests of BioCryst Directors and Executive Officers in the Mergers (see page 106)

        In considering the recommendation of the BioCryst board, BioCryst stockholders should be aware that certain of BioCryst's executive officers and directors have interests in the mergers that may be different from, or in addition to, those of the BioCryst stockholders generally. These interests may present such executive officers and directors with actual or potential conflicts of interest. The BioCryst board was aware of these interests during its deliberations on the merits of the mergers and in deciding to recommend that BioCryst stockholders vote for the BioCryst proposals. For additional information on the interests of BioCryst's directors and officers in the mergers, see "The Mergers—Interests of BioCryst Directors and Executive Officers in the Mergers" beginning on page 106 of this joint proxy statement/prospectus.

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Holdco Board, Management and Certain Governance Matters Following the Mergers (see page 114)

        Immediately following the effective time of the mergers, the board of the combined company will consist of nine members, including: Vincent J. Milano, a director and the current chief executive officer of Idera, James A. Geraghty, the current chairman of the Idera board, Maxine Gowen, Ph.D., a director of Idera, Mark Goldberg, M.D., a director of Idera, Jon P. Stonehouse, a director and the current chief executive officer of BioCryst, Robert A. Ingram, the current chairman of the BioCryst board, Nancy Hutson, Ph.D., a director of BioCryst, Kenneth B. Lee, Jr., a director of BioCryst, and one person to be mutually agreed to by the Idera board and the BioCryst board who shall not be a director, officer or affiliate of either Idera or BioCryst. All directors, other than Messrs. Milano and Stonehouse, will qualify as "independent directors" under the Nasdaq rules.

        Upon completion of the mergers, Mr. Ingram will serve as the chairman of the board of the combined company, and Mr. Milano will serve as the chief executive officer of the combined company.

        The corporate headquarters for the combined company and its subsidiaries will be located in Exton, Pennsylvania, and the primary location for research and development for the combined company and its subsidiaries will be located in Birmingham, Alabama.

Regulatory Clearances Required for the Mergers (see page 114)

        BioCryst and Idera have each agreed to take certain actions in order to obtain the regulatory clearances required to complete the mergers. Required regulatory clearances include expiration or termination of the required waiting period under the Hart-Scott Rodino Antitrust Improvement Act of 1976, as amended, and the rules and regulations promulgated thereunder (the "HSR Act"), following required notifications and review by either the Federal Trade Commission (the "FTC") or the Antitrust Division of the U.S. Department of Justice (the "Antitrust Division"). On February 2, 2018, each of BioCryst and Idera filed its notification under the HSR Act. On February 15, 2018, the FTC notified Idera and BioCryst that their request for early termination of the applicable waiting period was granted, thereby satisfying the condition under the merger agreement relating to the expiration or termination of the applicable waiting period under the HSR Act.

        The antitrust and competition laws of certain foreign countries often apply to transactions such as the mergers, and notifications may be required when such laws are applicable. However, BioCryst and Idera do not believe that any such foreign antitrust filings are required in connection with the mergers, and accordingly, the obligations of BioCryst and Idera to consummate the mergers are not subject to conditions precedent related to any such foreign antitrust filings.

Amended and Restated Certificate of Incorporation of Holdco (see page 99)

        The amended and restated certificate of incorporation of Holdco (the "Holdco charter") will be in substantially the same form attached as Annex D to this joint proxy statement/prospectus. Please see the section entitled "Comparison of Rights of Idera Stockholders, BioCryst Stockholders and Holdco Stockholders" beginning on page 164 of this joint proxy statement/prospectus for a discussion of the Holdco charter.

Completion of the Mergers (see page 117)

        BioCryst and Idera are working to complete the mergers as soon as practicable and expect the closing of the mergers to occur in the third quarter of 2018. However, the mergers are subject to the satisfaction or waiver of various conditions, and it is possible that factors outside the control of BioCryst and Idera could result in the mergers being completed at a later time or not at all. There may be a substantial amount of time between the BioCryst and Idera special meetings and the completion of the mergers.

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The Merger Agreement

Merger Consideration (see page 116)

        At the effective time of the mergers, each issued and outstanding share of Idera common stock (other than shares held by Idera, BioCryst, Holdco, Merger Sub A or Merger Sub B, or any subsidiary of each of the aforementioned entities, or by Idera as treasury shares, which will cease to remain outstanding and will be canceled and retired and cease to exist) will be converted into the right to receive 0.20 fully paid and nonassessable shares of Holdco common stock, with cash paid in lieu of fractional shares.

        At the effective time of the mergers, each issued and outstanding share of Idera preferred stock (other than shares held by Idera, BioCryst, Holdco, Merger Sub A or Merger Sub B, or any subsidiary of each of the aforementioned entities, or by Idera as treasury shares, which will cease to remain outstanding and will be canceled and retired and cease to exist) will be converted into the right to receive an amount of fully paid and nonassessable shares of Holdco common stock equal to (i) $1.00 divided by the 20-trading-day average trading price of Idera common stock, ending with the trading day prior to the third day prior to the closing date, multiplied by (ii) 0.20, with cash paid in lieu of fractional shares.

        At the effective time of the mergers, each issued outstanding share of BioCryst common stock (other than shares held by Idera, BioCryst, Holdco, Merger Sub A or Merger Sub B, or any subsidiary of each of the aforementioned entities, or by BioCryst as treasury shares, which will cease to remain outstanding and will be canceled and retired and cease to exist) will be converted into the right to receive 0.50 fully paid and nonassessable shares of Holdco common stock, with cash paid in lieu of fractional shares.

No Solicitation of Competing Proposals (see page 123)

        The merger agreement prohibits BioCryst and Idera from soliciting or engaging in discussions or negotiations with a third party with respect to a proposal for a competing transaction, including the acquisition of a significant interest in BioCryst common stock or assets or Idera common stock or assets. However, if, prior to obtaining approval from its stockholders, BioCryst or Idera, as the case may be, receives an unsolicited written proposal from a third party for a competing transaction that the BioCryst board or the Idera board, as applicable, among other things, determines in good faith (i) after consultation with its outside legal and financial advisors, is reasonably likely to lead to a proposal that is superior to the mergers and (ii) after consultation with its outside legal advisors, the failure to enter discussions regarding such proposal would constitute a breach of its fiduciary obligations under applicable law, BioCryst or Idera, as applicable, may furnish non-public information to and enter into discussions with, and only with, that third party regarding such competing transaction.

Treatment of Idera Stock Options and Warrants (see page 128)

        Idera Stock Options.    As of the effective time of the mergers, each Idera stock option that is outstanding and unexercised immediately prior to the effective time of the mergers, whether or not then vested or exercisable, will be assumed by Holdco and converted into a Holdco stock option. In addition, each such stock option will vest in full, other than Idera stock options held by an individual who is a party to a Severance and Change of Control Agreement (each, a "Severance and Change of Control Agreement"). Each converted Holdco stock option will be subject to the same terms and conditions (other than, in the case described above, vesting) as applied to the original Idera stock option immediately prior to the effective time of the mergers, except that it will be exercisable for that number of whole shares of Holdco common stock (rounded down to the nearest whole share) equal to the number of shares subject to the Idera stock option multiplied by the Idera exchange ratio (0.20), at an exercise price per share (rounded up to the nearest whole cent) equal to the exercise price per

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share applicable to the Idera stock option divided by the Idera exchange ratio. This treatment will be subject to certain provisions of the Code, as described in the merger agreement.

        Idera Warrants.    At the effective time of the mergers, each outstanding Idera warrant and Idera pre-funded warrant to purchase shares of Idera common stock ("Idera warrants") will be assumed by Holdco and converted into a warrant to acquire Holdco common stock on the same terms and conditions as applied to the Idera warrants immediately prior to the completion of the mergers, except that each Idera warrant and Idera pre-funded warrant (i) will cover a number of whole shares of Holdco common stock (rounded down to the nearest whole share) equal to the number of shares of Idera common stock subject to the Idera warrant or Idera pre-funded warrant, as applicable, multiplied by 0.20, and (ii) will have an exercise price per share of Holdco common stock (rounded up to the nearest whole cent) equal to the per share exercise price of the Idera warrant or Idera pre-funded warrant, as applicable, divided by 0.20.

Treatment of BioCryst Stock Options and RSUs (see page 129)

        BioCryst Stock Options.    As of the effective time of the mergers, each BioCryst stock option that is outstanding and unexercised immediately prior to the effective time of the mergers, whether or not then vested or exercisable, will vest in full and be assumed by Holdco and converted into a Holdco stock option. Each converted option will be subject to the same terms and conditions (other than vesting) as applied to the original BioCryst stock option immediately prior to the effective time of the mergers, except that it will be exercisable for that number of whole shares of Holdco common stock (rounded down to the nearest whole share) equal to the number of shares subject to the BioCryst stock option multiplied by the BioCryst exchange ratio (0.50), at an exercise price per share (rounded up to the nearest whole cent) equal to the exercise price per share applicable to the BioCryst stock option divided by BioCryst exchange ratio. This treatment will be subject to certain provisions of the Code, as described in the merger agreement.

        BioCryst RSUs.    As of the effective time of the mergers, each restricted stock unit covering BioCryst common stock (a "BioCryst RSU") that is outstanding immediately prior to the effective time of the mergers will be assumed by Holdco and will vest in full and be converted into a restricted stock unit covering Holdco common stock (a "Holdco RSU"). Each converted Holdco RSU will be subject to the same terms and conditions (other than vesting) as applied to the original BioCryst RSU immediately prior to the effective time of the mergers, except that it will be a restricted stock unit to acquire that number of whole shares of Holdco common stock (rounded down to the nearest whole share) equal to the number of shares subject to the BioCryst RSU multiplied the BioCryst exchange ratio.

Conditions to Completion of the Mergers (see page 131)

        Each party's obligation to consummate the mergers is conditioned upon the satisfaction (or, to the extent permitted by applicable law, waiver by such party) at or prior to the closing of the mergers of each of the following:

    adoption of the merger agreement by holders of a majority of the issued outstanding shares of each of Idera common stock and BioCryst common stock entitled to vote thereon;

    authorization of the listing on the Nasdaq of the shares of Holdco common stock to be issued to Idera stockholders and BioCryst stockholders pursuant to the mergers, subject to official notice of issuance;

    effectiveness of the registration statement of which this joint proxy statement/prospectus forms a part and the absence of a stop order in respect thereof;

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    absence of any law, order, injunction, decree, statute, rule or regulation by a governmental entity that prohibits, restrains or makes illegal the consummation of the mergers; and

    the waiting period (and any extension thereof) applicable to the mergers under the HSR Act having expired or been earlier terminated, and any other antitrust, competition, investment, trade regulation or similar approval required under law having been obtained prior to the closing.

        In addition, the obligations of each of BioCryst and Holdco, on the one hand, and Idera, on the other hand, to effect the mergers is subject to the satisfaction or waiver of the following additional conditions:

    the representations and warranties of the other party, other than the representations related to corporate organization, capitalization, the authority with respect to the execution, delivery, and performance of the merger agreement and the due and valid authorization and enforceability of the merger agreement, the fees payable to a financial advisor, broker or finder in connection with the transactions under the merger agreement, the delivery of an opinion from such party's financial advisor, and with respect to BioCryst only, the representation that none of Holdco, Merger Sub A or Merger Sub B has engaged in any business activity other than in connection with the merger agreement, and the non-occurrence of any event or development having a "material adverse effect" (as defined in "The Merger Agreement—Representations and Warranties" beginning on page 118 of this joint proxy statement/prospectus) on the other party since October 1, 2017, will be true and correct in all respects (without giving effect to any "materiality" (as defined in "The Merger Agreement—Representations and Warranties" beginning on page 118 of this joint proxy statement/prospectus) or material adverse effect qualifications contained in such representations and warranties) as of the closing date (other than those representations and warranties that address matters only as of a particular date, which need only be true and correct as of such date), except to the extent that any failures of such representations and warranties to be so true and correct, individually or in the aggregate, have not had and would not reasonably be expected to have a material adverse effect;

    the representations and warranties of the other party relating to corporate organization, the authority with respect to the execution, delivery, and performance of the merger agreement and the due and valid authorization and enforceability of the merger agreement, the fees payable to a financial advisor, broker or finder in connection with the transactions under the merger agreement, the delivery of an opinion from such party's financial advisor, and with respect to BioCryst only, the representation that none of Holdco, Merger Sub A or Merger Sub B has engaged in any business activity other than in connection with the merger agreement, will be true and correct in all material respects (without giving effect to any materiality or material adverse effect qualifications contained in such representations and warranties) as of the closing date (except to the extent such representations or warranties address matters only as of a particular date, which need only be true and correct as of such date);

    the representation and warranties of the other party relating to capitalization are true and correct in all respects as of the closing date (except to the extent such representations or warranties address matters only as of a particular date, which need only be true and correct as of such date), except for de minimis inaccuracies;

    the representation and warranty of the other party relating to the non-occurrence of any event or development having a material adverse effect on the other party since October 1, 2017, will be true and correct in all respects as of the date of the merger agreement and as of the closing date;

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    receipt of a certificate executed by an executive officer of the other party certifying as to the satisfaction of the conditions described in the preceding four bullet points;

    the other party (and, in the case of BioCryst, Holdco) having performed or complied with, in all material respects, all of its obligations under the merger agreement at or prior to the closing of the mergers and the other party shall have delivered a certificate executed by an executive officer of the other party certifying as to the satisfaction of this condition;

    no change, event, development, condition, circumstance or effect will have occurred since the date of the merger agreement that has had, or would reasonably be expected to have, individually or in the aggregate, a material adverse effect on the other party;

    with respect to BioCryst's and Holdco's obligations, BioCryst's receipt of an opinion from Skadden to the effect that the BioCryst merger will qualify as a "reorganization" within the meaning of Section 368(a) of the Code or, alternatively, the mergers together will be treated as an "exchange" described in Section 351 of the Code; and

    with respect to Idera's obligation, Idera's receipt of an opinion from Latham to the effect that the mergers together will be treated as an "exchange" described in Section 351 of the Code.

Termination of the Merger Agreement (see page 133)

        BioCryst and Idera may mutually agree to terminate the merger agreement at any time. Either company may also terminate the merger agreement if the mergers are not completed by July 21, 2018 (regardless of whether such date is before or after the stockholders of the party approve the transactions). See the section entitled "The Merger Agreement—Termination of the Merger Agreement" beginning on page 133 of this joint proxy statement/prospectus for a discussion of these and other rights of each of BioCryst and Idera to terminate the merger agreement.

Expenses and Termination Fees (see page 134)

        Generally, all fees and expenses incurred in connection with the merger agreement and the transactions contemplated by the merger agreement will be paid by the party incurring those expenses, subject to the specific exceptions discussed in this joint proxy statement/prospectus where (i) BioCryst may be required to pay a termination fee of $25 million to Idera and Idera may be required to pay a termination fee of $25 million to BioCryst and (ii) either company may be required to pay the other company a fixed expense reimbursement amount of $6 million. See the section entitled "The Merger Agreement—Expenses and Termination Fees; Liability for Breach" beginning on page 134 of this joint proxy statement/prospectus for a discussion of the circumstances under which such termination fee will be required to be paid.

Voting and Support Agreements (see pages 37 and 45)

        Simultaneously with the execution of the merger agreement, each of BioCryst and Idera entered into a voting and support agreement with affiliates of Baker Brothers. Baker Brothers and its affiliates own approximately 14% of issued and outstanding BioCryst common stock and approximately 18% of issued and outstanding Idera common stock. Pursuant to the voting and support agreements, Baker Brothers has agreed, among other things, to vote its shares of BioCryst common stock and Idera common stock in favor of the adoption of the merger agreement at each of the BioCryst special meeting and the Idera special meeting respectively. In addition, Baker Brothers has agreed to be present at each of the BioCryst special meeting and the Idera special meeting for purposes of establishing a quorum.

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Accounting Treatment (see page 140)

        Holdco prepares its financial statements in accordance with accounting principles generally accepted in the United States ("GAAP"). The mergers will be accounted for using the acquisition method of accounting. Although the business combination of Idera and BioCryst is a "merger of equals," GAAP requires that one of the two companies in the merger be designated as the acquirer for accounting purposes based on the evidence available. Accordingly, Idera will be treated as the acquirer for accounting purposes. In identifying Idera as the acquiring entity, the companies took into account the structure of the transaction, the composition of the governing body of the combined company and the designation of certain senior management positions of the combined company. As a result, the historical financial statements of Idera will become the historical financial statements of the combined company.

No Appraisal Rights (see page 169)

        Under the DGCL, none of the holders of shares of Idera common stock, Idera preferred stock or BioCryst common stock are entitled to exercise any appraisal rights in connection with the mergers or the other transactions contemplated by the merger agreement.

Litigation Related to the Mergers (see page 115)

        Since the announcement on January 22, 2018 of the execution of the merger agreement, three putative class action complaints have been filed in connection with the mergers. On March 6, 2018 plaintiff Melvin Klein filed a lawsuit captioned Klein v. BioCryst Pharmaceuticals, Inc., et al., No. 1:18-cv-00358, in United States District Court for the District of Delaware, naming BioCryst, members of the BioCryst board, Idera, Holdco, Merger Sub A and Merger Sub B as defendants. On March 14, 2018, plaintiff Lisa Raatz filed a lawsuit captioned Raatz v. Idera Pharmaceuticals, Inc., et al., No. 1:18-cv-10485, in United States District Court for the District of Massachusetts, naming Idera, members of the Idera board, BioCryst, Holdco, Merger Sub A and Merger Sub B as defendants. On March 22, 2018, plaintiff Ricky Cohen filed a lawsuit captioned Cohen v. Idera Pharmaceuticals, Inc., et al., No. 1:18-cv-00428, in United States District Court for the District of Delaware, naming Idera and members of the Idera board as defendants.

Risk Factors (see page 22)

        In deciding how to vote your shares of Idera common stock or BioCryst common stock, you should read carefully this entire joint proxy statement/prospectus, including the documents incorporated by reference herein and the annexes and exhibits hereto, and in particular, you should read the "Risk Factors" section beginning on page 22 of this joint proxy statement/prospectus. See also "Where You Can Find More Information" beginning on page 172 of this joint proxy statement/prospectus.

Comparison of Rights of Idera Stockholders, BioCryst Stockholders and Holdco Stockholders (see page 164)

        Idera stockholders and BioCryst stockholders receiving merger consideration will have rights different from their rights prior to the effective time of the mergers once they become stockholders of the combined company due to differences between the governing corporate documents of Idera and BioCryst, respectively, and the proposed governing corporate documents of Holdco. Please see the section entitled "Comparison of Rights of Idera Stockholders, BioCryst Stockholders and Holdco Stockholders" beginning on page 164 of this joint proxy statement/prospectus for a discussion of these differences.

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Listing of Holdco Common Stock; De-Listing and Deregistration of Idera Stock and BioCryst Stock (see page 115)

        It is a condition to the completion of the mergers that the shares of Holdco common stock to be issued to Idera stockholders and BioCryst stockholders pursuant to the mergers be authorized for listing, and Idera and BioCryst have agreed to use their reasonable best efforts to cause such shares to be listed, on the Nasdaq subject to official notice of issuance. Upon completion of the mergers, shares of Idera common stock and shares of BioCryst common stock currently listed on the Nasdaq will cease to be listed on the Nasdaq and will be subsequently deregistered under the Exchange Act.

The Idera Special Meeting (see page 44)

        The Idera special meeting is scheduled to be held at Idera'a offices located at 505 Eagleview Boulevard, Suite 212, Exton, Pennsylvania 19341 on July 10, 2018 at 10:00 a.m., Eastern Time, subject to any adjournments or postponements thereof. The Idera special meeting is being held in order to consider and vote on:

    the proposal to adopt the merger agreement, which is further described in the sections titled "The Mergers" and "The Merger Agreement," beginning on pages 53 and 116, respectively, of this joint proxy statement/prospectus; and

    the proposal to approve, on a non-binding advisory basis, the compensation that may become payable to Idera's named executive officers that is based on or otherwise relates to the mergers.

        Only holders of record of Idera common stock at the close of business on May 29, 2018, the record date for the Idera special meeting, are entitled to notice of, and to vote at, the Idera special meeting or any adjournments or postponements thereof. At the close of business on the Idera record date, 217,310,991 shares of Idera common stock were issued and outstanding, approximately 18% of which were held by Idera's directors and executive officers and their affiliates. We currently expect that Idera's directors and executive officers will vote their shares in favor of each proposal being submitted to a vote of the Idera stockholders at the Idera special meeting, although no director or executive officer has entered into any agreement obligating him or her to do so.

        You may cast one vote for each share of Idera common stock you own. The proposal to adopt the merger agreement requires the affirmative vote of the holders of a majority of the issued and outstanding shares of Idera common stock entitled to vote on the proposal. Assuming a quorum is present, approval of, on a non-binding advisory basis, the compensation that may become payable to Idera's named executive officers that is based on or otherwise relates to the mergers requires the affirmative vote of the holders of a majority of the shares of Idera common stock present represented in person or by proxy at the Idera special meeting and voting on the proposal, although such vote will not be binding on Idera, the Idera board or any of its committees, or, following completion of the mergers, the combined company.

        If a quorum is not present, the Idera special meeting may be adjourned by the chairman of the Idera special meeting, to reconvene at the same or another place, and notice need not be given of any such adjourned meeting if the time and place thereof are announced at the meeting at which the adjournment is taken.

The BioCryst Special Meeting (see page 35)

        The BioCryst special meeting is scheduled to be held at BioCryst's corporate offices at 4505 Emperor Blvd., Suite 200, Durham, North Carolina 27703 on July 10, 2018 at 10:00 a.m.,

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Eastern Time, subject to any adjournments or postponements thereof. The BioCryst special meeting is being held in order to consider and vote on:

    the proposal to adopt the merger agreement, which is further described in the sections titled "The Mergers" and "The Merger Agreement," beginning on pages 53 and 116, respectively, of this joint proxy statement/prospectus;

    the proposal to approve, on a non-binding advisory basis, the compensation that may become payable to BioCryst's named executive officers that is based on or otherwise relates to the mergers; and

    the proposal to adjourn the BioCryst special meeting, if necessary or appropriate, to solicit additional proxies if there are not sufficient votes to adopt the merger agreement.

        Only holders of record of BioCryst common stock at the close of business on May 29, 2018, the record date for the BioCryst special meeting, are entitled to notice of, and to vote at, the BioCryst special meeting or any adjournments or postponements thereof. At the close of business on the BioCryst record date, 98,821,091 shares of BioCryst common stock were issued and outstanding, approximately 1% of which were held by BioCryst's directors and executive officers and their affiliates. We currently expect that BioCryst's directors and executive officers will vote their shares in favor of each proposal being submitted to a vote of the BioCryst stockholders at the BioCryst special meeting, although no director or executive officer has entered into any agreement obligating him or her to do so.

        You may cast one vote for each share of BioCryst common stock you own. The proposal to adopt the merger agreement requires the affirmative vote of the holders of a majority of the issued and outstanding shares of BioCryst common stock entitled to vote on the proposal. Assuming a quorum is present, approval of, on a non-binding advisory basis, the compensation that may become payable to BioCryst's named executive officers that is based on or otherwise relates to the mergers requires the affirmative vote of the holders of a majority of the shares of BioCryst common stock present in person or represented by proxy, at the BioCryst special meeting and voting on the proposal, although such vote will not be binding on BioCryst, the BioCryst board or any of its committees, or, following completion of the mergers, the combined company. Approval of the proposal to adjourn the BioCryst special meeting, if necessary or appropriate, to solicit additional proxies if there are not sufficient votes to adopt the merger agreement requires the affirmative vote of holders of a majority of the issued and outstanding shares of BioCryst common stock present in person or represented by proxy at the BioCryst special meeting and voting on the proposal, assuming a quorum is present.

        If a quorum is not present, the BioCryst special meeting may be adjourned by the vote of the holders of a majority of the shares of BioCryst common stock present or represented by proxy and entitled to vote, to reconvene at the same or another place. If a quorum is present at the BioCryst special meeting but there are not sufficient votes at the time of the BioCryst special meeting to adopt the merger agreement, then BioCryst stockholders may be asked to vote on the BioCryst adjournment proposal. Notice need not be given of any such adjourned meeting if the time and place thereof are announced at the meeting at which the adjournment is taken.

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SUMMARY HISTORICAL FINANCIAL DATA

Summary Historical Financial Data of Idera

        The following statement of operations and comprehensive loss data for the years ended December 31, 2017, 2016 and 2015 and the balance sheet data as of December 31, 2017 and 2016 have been derived from the audited financial statements of Idera contained in its Annual Report on Form 10-K for the fiscal year ended December 31, 2017, which is incorporated into this joint proxy statement/prospectus by reference. The statement of operations data and comprehensive loss data for the years ended December 31, 2014 and 2013 and the balance sheet data as of December 31, 2015, 2014 and 2013 have been derived from the audited financial statements of Idera not incorporated into this joint proxy statement/prospectus by reference.

        The statement of operations and comprehensive loss data for the three months ended March 31, 2018 and 2017 and the balance sheet data as of March 31, 2018 have been derived from Idera's unaudited interim financial statements contained in its Quarterly Report on Form 10-Q for the quarterly period ended March 31, 2018, which is incorporated into this joint proxy statement/prospectus by reference. The financial data as of March 31, 2017 are derived from Idera's unaudited financial statements from Idera's Quarterly Report on Form 10-Q for the quarterly period ended March 31, 2017, which is not incorporated by reference into this joint proxy statement/prospectus. These interim financial statements are unaudited, but, in the opinion of Idera's management, contain all adjustments necessary to present fairly Idera's financial position, results of operations and cash flows for the periods indicated.

        The information set forth below is only a summary and it is not necessarily indicative of the results of future operations of Idera, nor does it include the effects of the mergers. Interim results for the three months ended as of March 31, 2018 are not necessarily indicative of, and are not projections for, the results to be expected for the fiscal year ended December 31, 2018.

        You should read this summary historical financial data together with the financial statements that are incorporated by reference into this joint proxy statement/prospectus and their accompanying notes and management's discussion and analysis of financial condition and results of operations of Idera contained in such reports.

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  Year Ended December 31,   Three Months Ended
March 31,
 
 
  2017   2016   2015   2014   2013   2018   2017  
 
  (In thousands, except share and per share data)
 

Statement of Operations and Comprehensive Loss Data:

                                           

Alliance revenue

  $ 902   $ 16,199   $ 249   $ 73   $ 47   $ 255   $ 378  

Operating expenses:

                                           

Research and development

    50,653     39,824     33,699     27,493     10,475     13,556     11,485  

General and administrative

    16,716     15,132     15,396     11,332     7,741     6,979     4,081  

Total operating expenses

    67,369     54,956     49,095     38,825     18,216     20,535     15,566  

Loss from operations

    (66,467 )   (38,757 )   (48,846 )   (38,752 )   (18,169 )   (20,280 )   (15,188 )

Other income (expense):

                                           

Interest income

    574     415     357     66     11     211     153  

Interest expense

    (50 )   (80 )   (105 )   (27 )       (7 )   (16 )

Foreign currency exchange gain (loss)

    (41 )   33     39     71     (68 )   (19 )   (6 )

Net loss before extinguishment of convertible preferred stock, and preferred stock accretion and dividends

  $ (65,984 ) $ (38,389 ) $ (48,555 ) $ (38,642 ) $ (18,226 ) $ (20,095 ) $ (15,057 )

Loss on extinguishment of convertible preferred stock, and preferred stock accretion and dividends

                519     2,866          

Net loss applicable to common stockholders

  $ (65,984 ) $ (38,389 ) $ (48,555 ) $ (39,161 ) $ (21,092 ) $ (20,095 ) $ (15,057 )

Basic and diluted net loss per share applicable to common stockholders

  $ (0.42 ) $ (0.30 ) $ (0.42 ) $ (0.47 ) $ (0.48 ) $ (0.10 ) $ (0.10 )

Shares used in computing basic and diluted net loss per common share applicable to common stockholders

    157,398     127,597     115,092     82,827     43,906     199,037     149,100  

Net loss

    (65,984 )   (38,389 )   (48,555 )   (38,642 )   (18,226 )   (20,095 )   (15,057 )

Other comprehensive gain (loss):

                                           

Unrealized gain (loss) on available-for-sale securities

    17     117     (117 )   (10 )   (7 )       16  

Other comprehensive gain (loss):

    17     117     (117 )   (10 )   (7 )       16  

Comprehensive loss

  $ (65,967 ) $ (38,272 ) $ (48,672 ) $ (38,652 ) $ (18,233 ) $ (20,095 ) $ (15,041 )

 

 
  As of December 31,   As of March 31,  
 
  2017   2016   2015   2014   2013   2018   2017  
 
  (In thousands, except share and per share data)
 

Balance Sheet Data:

                                           

Cash, cash equivalents and investments

  $ 112,629   $ 109,014   $ 87,157   $ 48,571   $ 35,592   $ 107,459   $ 91,262  

Working capital

    106,512     101,691     56,427     35,384     25,867     97,711     88,490  

Total assets

    118,417     113,231     92,276     51,426     36,867     111,751     97,573  

Capital lease obligations

    15     15     22     21     9     12     22  

Note payable

    209     501     762     870         131     431  

Accumulated deficit

    (604,494 )   (538,470 )   (500,081 )   (451,526 )   (412,884 )   (624,589 )   (553,568 )

Total stockholders' equity

    107,695     103,349     83,582     43,402     32,452     98,884     90,191  

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Summary Historical Consolidated Financial Data of BioCryst

        The following statement of operations data for the years ended December 31, 2017, 2016 and 2015 and the balance sheet data as of December 31, 2017 and 2016 have been derived from the audited consolidated financial statements of BioCryst contained in its Annual Report on Form 10-K for the fiscal year ended December 31, 2017, and any amendments thereto, which is incorporated into this joint proxy statement/prospectus by reference. The statement of operations data for the years ended December 31, 2014 and 2013 and the balance sheet data as of December 31, 2015, 2014 and 2013 have been derived from the audited financial statements of BioCryst not incorporated into this joint proxy statement/prospectus by reference.

        The statement of operations and comprehensive loss data for the three months ended March 31, 2018 and 2017 and the balance sheet data as of March 31, 2018 have been derived from BioCryst's unaudited interim financial statements contained in its Quarterly Report on Form 10-Q for the quarterly period ended March 31, 2018, which is incorporated into this joint proxy statement/prospectus by reference. The financial data as of March 31, 2017 are derived from BioCryst's unaudited financial statements from BioCryst's Quarterly Report on Form 10-Q for the quarterly period ended March 31, 2017, which is not incorporated by reference into this joint proxy statement/prospectus. These interim financial statements are unaudited, but, in the opinion of BioCryst's management, contain all adjustments necessary to present fairly BioCryst's financial position, results of operations and cash flows for the periods indicated.

        The information set forth below is only a summary and is not necessarily indicative of the results of future operations of BioCryst nor does it include the effects of the mergers. Interim results for the three months ended as of March 31, 2018 are not necessarily indicative of, and are not projections for, the results to be expected for the fiscal year ended December 31, 2018.

        You should read this summary historical financial data together with the financial statements that are incorporated by reference into this joint proxy statement/prospectus and their accompanying notes and management's discussion and analysis of the financial condition and results of operations of BioCryst contained in such reports. For more information, see "Where You Can Find More Information" beginning on page 172 of this joint proxy statement/prospectus.

 
  December 31,   March 31,  
 
  2017   2016   2015   2014   2013   2018   2017  
 
  (In thousands, except per share amounts)
 

Statement of Operations Data:

                                           

Total revenues

  $ 25,186   $ 26,353   $ 48,257   $ 13,608   $ 17,331   $ 3,976   $ 9,437  

Cost of product sold

    1,142     2,297     1,368     1              

Research and development expenses

    66,962     61,008     72,758     51,796     41,943     18,441     16,770  

General and administrative expenses

    13,933     11,253     13,047     7,461     6,007     7,609     3,058  

Royalty expense

    560     402     528     121     98     140     294  

Loss from operations

    (57,411 )   (48,607 )   (39,444 )   (45,771 )   (30,717 )   (22,214 )   (10,685 )

Net loss

    (65,782 )   (55,144 )   (43,019 )   (45,189 )   (30,108 )   (25,777 )   (14,219 )

Basic and diluted net loss per share

  $ (0.78 ) $ (0.75 ) $ (0.59 ) $ (0.68 ) $ (0.55 ) $ (0.26 ) $ (0.19 )

Weighted average shares outstanding

    84,451     73,699     72,901     66,773     55,216     98,592     75,167  

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  December 31,   March 31,  
 
  2017   2016   2015   2014   2013   2018   2017  
 
  (In thousands)
 

Balance Sheet Data:

                                           

Cash, cash equivalents and investments

  $ 158,978   $ 65,122   $ 100,858   $ 114,038   $ 40,788   $ 137,505   $ 105,283  

Receivables

    6,117     8,768     6,243     9,490     2,115     5,694     9,564  

Inventory

        500     1,612     683         7     655  

Total assets

    178,259     89,847     122,359     134,238     45,791     155,372     129,513  

Long-term deferred revenue

        8,184     9,674     3,552     4,736         7,888  

Non-recourse notes payable

    28,682     28,243     27,804     27,364     26,925     28,792     28,353  

Senior credit facility

    23,214     22,777                 21,611     22,887  

Accumulated deficit

    (631,843 )   (566,061 )   (510,917 )   (467,898 )   (422,709 )   (656,494 )   (580,280 )

Total stockholders' equity (deficit)

    83,767     1,578     47,724     75,635     (1,126 )   62,054     38,530  

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UNAUDITED EQUIVALENT AND COMPARATIVE PER SHARE DATA

        Presented below are BioCryst's and Idera's historical per share data for the three months ended March 31, 2018 and the year ended December 31, 2017 and unaudited pro forma combined per share data for the three months ended March 31, 2018 and the year ended December 31, 2017. This information should be read together with the consolidated financial statements, in the case of BioCryst, the financial statements, in the case of Idera, and related notes of BioCryst and Idera that are incorporated by reference in this joint proxy statement/prospectus and with the unaudited pro forma combined financial data included under "Selected Unaudited Pro Forma Condensed Combined Financial Information of Idera and BioCryst" beginning on page 141 of this joint proxy statement/prospectus. The pro forma information is presented for illustrative purposes only and is not necessarily indicative of the operating results or financial position that would have occurred if the mergers had been completed as of the beginning of the periods presented, nor is it necessarily indicative of the future operating results or financial position of the combined company. The historical book value per share is computed by dividing total stockholders' equity (deficit) by the number of shares of common stock issued and outstanding at the end of the period. The pro forma income (loss) per share of the combined company is computed by dividing the pro forma income (loss) by the pro forma weighted average number of shares issued and outstanding. The pro forma book value per share of the combined company is computed by dividing total pro forma stockholders' equity (deficit) by the pro forma number of shares of common stock issued and outstanding at the end of the period. The unaudited pro forma equivalent per share financial information for each company is computed by multiplying the Holdco unaudited pro forma combined per share amounts by the respective exchange ratio (0.20 shares of Holdco common stock for each share of Idera common stock and 0.50 shares of Holdco common stock for each share of BioCryst common stock).

BioCryst-Historical
  Three Months Ended
March 31, 2018
  Year Ended
December 31, 2017
 

Loss per common share:

             

Basic

  $ (0.26 ) $ (0.78 )

Diluted

  $ (0.26 ) $ (0.78 )

Book value per share of common stock

  $ 0.63   $ 0.85  

Dividends per share of common stock

         

 

Idera-Historical
  Three Months Ended
March 31, 2018
  Year Ended
December 31, 2017
 

Loss per common share:

             

Basic

  $ (0.10 ) $ (0.42 )

Diluted

  $ (0.10 ) $ (0.42 )

Book value per share of common stock

  $ 0.46   $ 0.55  

Dividends per share of common stock

         

 

Holdco pro forma combined amounts
  Three Months Ended
March 31, 2018
  Year Ended
December 31, 2017
 

Earnings (Loss) per common share:

             

Basic

  $ (0.43 ) $ (1.65 )

Diluted

  $ (0.43 ) $ (1.65 )

Book value per share of common stock

  $ 6.19     N/A  

Dividends per share of common stock

    N/A     N/A  

 

BioCryst unaudited pro forma equivalent per share data
  Three Months Ended
March 31, 2018
  Year Ended
December 31, 2017
 

Earnings per common share:

             

Basic

  $ (0.77 ) $ (2.70 )

Diluted

  $ (0.77 ) $ (2.70 )

Book value per share of common stock

  $ 11.61     N/A  

Dividends per share of common stock

    N/A     N/A  

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CAUTIONARY STATEMENT REGARDING FORWARD-LOOKING STATEMENTS

        This joint proxy statement/prospectus and the documents incorporated by reference into this joint proxy statement/prospectus contain, in addition to historical information, forward-looking statements within the meaning of the federal securities law regarding, among other things, future events or the future financial performance of Idera and BioCryst. Such statements are based upon current plans, estimates and expectations that are subject to various risks and uncertainties. The inclusion of forward-looking statements should not be regarded as a representation that such plans, estimates and expectations will be achieved. Words such as "anticipate," "expect," "project," "intend," "believe," "may," "will," "should," "plan," "could," "target," "contemplate," "estimate," "predict," "potential" and words and terms of similar substance used in connection with any discussion of future plans, actions or events identify forward-looking statements.

        Forward-looking statements relating to the transactions contemplated by the merger agreement include, but are not limited to: statements about the benefits of the transactions contemplated by the merger agreement between Idera and BioCryst, including future financial and operating results; Idera's and BioCryst's plans, objectives, expectations and intentions; the expected timing of completion of the transactions contemplated by the merger agreement; and other statements relating to the mergers that are not historical facts. Forward-looking statements are based on information currently available to Idera and BioCryst and involve estimates, expectations and projections. Investors are cautioned that all such forward-looking statements are subject to risks and uncertainties, and important factors could cause actual events or results to differ materially from Idera's and BioCryst's plans. With respect to the transactions contemplated by the merger agreement between Idera and BioCryst, these factors, in addition to those set forth under "Risk Factors," beginning on page 22 of this joint proxy statement/prospectus, could include, but are not limited to: Idera or BioCryst may be unable to obtain stockholder approval as required for the mergers; conditions to the closing of the mergers may not be satisfied; the mergers may involve unexpected costs, liabilities or delays; the effect of the announcement of the mergers on the ability of Idera or BioCryst to retain and hire key personnel and maintain relationships with patients, doctors and others with whom Idera or BioCryst does business, or on Idera's or BioCryst's operating results and business generally; Idera's or BioCryst's respective businesses may suffer as a result of uncertainty surrounding the mergers and disruption of management's attention due to the mergers; the outcome of any legal proceedings related to the mergers; Idera or BioCryst may be adversely affected by other economic, business, and/or competitive factors; the occurrence of any event, change or other circumstances that could give rise to the termination of the merger agreement; risks that the mergers disrupt current plans and operations and the potential difficulties in employee retention as a result of the mergers; the risk that Idera or BioCryst may be unable to obtain governmental and regulatory approvals required for the transactions, or that required governmental and regulatory approvals may delay the transactions or result in the imposition of conditions that could reduce the anticipated benefits from the transactions contemplated by the merger agreement or cause the parties to abandon the transactions contemplated by the merger agreement; risks that the anticipated benefits of the mergers or other commercial opportunities may otherwise not be fully realized or may take longer to realize than expected; the impact of legislative, regulatory, competitive and technological changes; risks relating to the value of the new holding company shares to be issued in the mergers; expectations for future clinical trials, the timing and potential outcomes of clinical studies and interactions with regulatory authorities; other risks to the consummation of the mergers, including the risk that the mergers will not be consummated within the expected time period or at all; the risk that the credit ratings of the combined company or its subsidiaries may be different from what the companies expect; economic and foreign exchange rate volatility; the continued strength of the medical and pharmaceutical markets; the timing, success and market reception for Idera's and BioCryst's products; the possibility of new technologies outdating Idera's or BioCryst's products; continued support of Idera's or BioCryst's products by influential medical professionals; reliance on and integration of information technology systems; the risks associated with assumptions the parties make in

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connection with the parties' critical accounting estimates and legal proceedings; and the potential of international unrest, economic downturn or effects of currencies, tax assessments, tax adjustments, anticipated tax rates, raw material costs or availability, benefit or retirement plan costs, or other regulatory compliance costs.

        Additional factors that may affect the future results of Idera and BioCryst are set forth in their respective filings with the SEC, including each of Idera's and BioCryst's most recently filed Annual Report on Form 10-K and any amendments thereto, subsequent Quarterly Reports on Form 10-Q, Current Reports on Form 8-K and other filings with the SEC, which are available on the SEC's website at www.sec.gov. See in particular Item 1A of Idera's Annual Report on Form 10-K for the fiscal year ended December 31, 2017 under the heading "Risk Factors" and Item 1A of BioCryst's Quarterly Report on Form 10-Q for the three months ended March 31, 2018, under the heading "Risk Factors." The risks and uncertainties described above and in Idera's most recent Annual Report on Form 10-K and BioCryst's most recent Quarterly Report on Form 10-Q, are not exclusive and further information concerning Idera and BioCryst and their respective businesses, including factors that potentially could materially affect their respective businesses, financial condition or operating results, may emerge from time to time. Readers should also carefully review the risk factors described in other documents that Idera and BioCryst file from time to time with the SEC.

        Many of these risks, uncertainties and assumptions are beyond Idera's or BioCryst's ability to control or predict. Because of these risks, uncertainties and assumptions, you should not place undue reliance on these forward-looking statements. Furthermore, forward-looking statements speak only as of the information currently available to the parties on the date they are made, and neither Idera nor BioCryst undertakes any obligation to update publicly or revise any forward-looking statements to reflect events or circumstances that may arise after the date of this communication. Nothing in this communication is intended, or is to be construed, as a profit forecast or to be interpreted to mean that earnings per Idera share or BioCryst share for the current or any future financial years or those of the combined company, will necessarily match or exceed the historical published earnings per Idera share or BioCryst share, as applicable. Neither Idera nor BioCryst gives any assurance (1) that either Idera, BioCryst or the combined company will achieve its expectations, or (2) concerning any result or the timing thereof, in each case, with respect to any regulatory action, administrative proceedings, government investigations, litigation, warning letters, consent decree, cost reductions, business strategies, earnings or revenue trends or future financial results. All subsequent written and oral forward-looking statements concerning Idera, BioCryst, the transactions contemplated by the merger agreement, the combined company or other matters and attributable to Idera or BioCryst or any person acting on their behalf are expressly qualified in their entirety by the cautionary statements above.

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RISK FACTORS

        In addition to the other information included and incorporated by reference in this joint proxy statement/prospectus, including the matters addressed in the section entitled "Cautionary Statement Regarding Forward-Looking Statements," you should carefully consider the following risks before deciding how to vote. In addition, you should read and consider the risks associated with each of the businesses of Idera and BioCryst because these risks will also affect the combined company. These risks can be found in the Annual Report on Form 10-K for the fiscal year ended December 31, 2017, in the case of Idera, and in the Annual Report on Form 10-K for the fiscal year ended December 31, 2017, and any amendments thereto, in the case of BioCryst, as such risks may be updated or supplemented in each company's subsequently filed Quarterly Reports on Form 10-Q or Current Reports on Form 8-K, which are incorporated by reference into this joint proxy statement/prospectus. You should also read and consider the other information in this joint proxy statement/prospectus and the other documents incorporated by reference in this joint proxy statement/prospectus. See the section entitled "Where You Can Find More Information" beginning on page 172 of this joint proxy statement/prospectus.

Risk Factors Relating to the Mergers

BioCryst stockholders and Idera stockholders cannot be sure of the value of the merger consideration they will receive.

        BioCryst stockholders and Idera stockholders will receive a fixed number of shares of Holdco common stock in the BioCryst merger and the Idera merger, respectively, rather than a number of shares of Holdco common stock with a particular fixed market value. The market values of BioCryst common stock and Idera common stock at the effective time may vary significantly from their prices on the date prior to the date the merger agreement was executed, the date of this joint proxy statement/prospectus or the date on which BioCryst stockholders and Idera stockholders vote on the proposal to adopt the merger agreement. Because the exchange ratios are fixed and will not be adjusted to reflect any changes in the market prices of BioCryst common stock or Idera common stock, the market value of the Holdco common stock issued in the BioCryst merger or the Idera merger, as applicable, and the BioCryst common stock and Idera common stock surrendered in the BioCryst merger and the Idera merger, respectively, may be higher or lower than the values of these shares on earlier dates. All of the merger consideration to be received by BioCryst stockholders and Idera stockholders will be Holdco common stock (other than cash in lieu of fractional shares received by BioCryst stockholders and Idera stockholders). At the time of the special meetings, BioCryst stockholders and Idera stockholders will not know or be able to determine the value of the Holdco common stock they may receive upon completion of the mergers. Changes in the market prices of BioCryst common stock and Idera common stock may result from a variety of factors that are beyond the control of BioCryst or Idera, including changes in their respective businesses, operations and prospects, regulatory considerations, governmental actions, and legal proceedings and other developments. Market assessments of the benefits of the mergers, the likelihood that the mergers will be completed and general and industry-specific market and economic conditions may also have an effect on the market price of BioCryst common stock and Idera common stock. Changes in market prices of BioCryst common stock and Idera common stock may also be caused by fluctuations and developments affecting industry-specific and general economic and market conditions and may have an adverse effect on BioCryst common stock and Idera common stock prior to the consummation of the mergers.

        Neither BioCryst nor Idera is permitted to terminate the merger agreement solely because of changes in the market prices of either party's common stock. In addition, the market values of BioCryst common stock and Idera common stock may vary significantly from the date of the special meetings to the date of the completion of the mergers. You are urged to obtain up-to-date prices for BioCryst common stock and Idera common stock. There is no assurance that the mergers will be completed, that there will not be a delay in the completion of the mergers or that all or any of the anticipated benefits of the mergers will be obtained. For ranges of historic prices of BioCryst common stock and Idera common stock, see "Comparative Stock Price Data and Dividends" beginning on page 154 of this joint proxy statement/prospectus.

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The market price for Holdco common stock may be affected by factors different from those that historically have affected BioCryst common stock and Idera common stock.

        Upon completion of the mergers, holders of shares of BioCryst common stock (other than any shares held in treasury), holders of shares of Idera common stock (other than any shares held in treasury) and holders of Idera preferred stock will become holders of shares of Holdco common stock. BioCryst and Idera each have businesses that differ from each other. Accordingly, the results of operations of Holdco will be affected by some factors that are different from those currently affecting the results of operations of each of BioCryst and Idera. For a discussion of the businesses of BioCryst and Idera and of some important factors to consider in connection with those businesses, see the documents incorporated by reference in this joint proxy statement/prospectus and referred to under "Where You Can Find More Information" beginning on page 172 of this joint proxy statement/prospectus.

Any delay in completing the mergers may reduce or eliminate the benefits expected to be achieved thereunder.

        The mergers are subject to a number of conditions beyond BioCryst's and Idera's control that may prevent, delay or otherwise materially adversely affect their completion. We cannot predict whether and when these other conditions will be satisfied. Any delay in completing the mergers could cause the combined company not to realize, or to be delayed in realizing, some or all of the synergies and other benefits that we expect to achieve if the mergers are successfully completed within their expected time frame. See "The Merger Agreement—Conditions to Completion of the Mergers" beginning on page 131 of this joint proxy statement/prospectus.

BioCryst and Idera will be subject to business uncertainties while the mergers are pending, which may cause a loss of management personnel and other key employees which could adversely affect the future business and operations of the combined company.

        Uncertainty about the completion or effect of the mergers may affect the relationship between BioCryst and Idera and their respective patients, doctors, licensors and licensees and may have an adverse effect on BioCryst and/or Idera, and consequently on the combined company. These uncertainties may cause patients, doctors, licensors and others that deal with the parties to seek to change existing business relationships with them and to delay or defer decisions concerning BioCryst or Idera. Changes to existing business relationships, including termination or modification, could negatively affect each of BioCryst's and Idera's revenues, earnings and cash flow, as well as the market price of its common stock.

        BioCryst and Idera are dependent on the experience and industry knowledge of their respective officers and other key employees to execute their business plans. The combined company's success after the mergers will depend in part upon the ability of BioCryst and Idera to retain key management personnel and other key employees. Current and prospective employees of BioCryst and Idera may experience uncertainty about their roles within the combined company following the mergers, which may have an adverse effect on the ability of each of BioCryst and Idera to attract or retain key management and other key personnel. If key employees depart because of issues related to the uncertainty and difficulty of integration or a desire not to remain with the businesses, the combined company's business following the consummation of the mergers could be negatively impacted. Accordingly, no assurance can be given that the combined company will be able to attract or retain key management personnel and other key employees of BioCryst and Idera to the same extent that BioCryst and Idera have previously been able to attract or retain their own employees. A failure by BioCryst, Idera or, following the completion of the mergers, the combined company to attract, retain and motivate executives and other key employees during the period prior to or after the completion of the mergers could have a negative impact on their respective businesses.

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BioCryst and Idera will be subject to certain contractual restrictions while the mergers are pending.

        The merger agreement restricts each of BioCryst and Idera from making certain acquisitions and divestitures, entering into certain contracts, incurring certain indebtedness and expenditures, paying dividends, repurchasing or issuing securities outside of existing equity award programs, and taking other specified actions, if outside the ordinary course of business consistent with past practice, until the earlier of the completion of the mergers or the termination of the merger agreement without the consent of the other party. These restrictions may prevent BioCryst and/or Idera from pursuing attractive business opportunities that may arise prior to the completion of the mergers and could have the effect of delaying or preventing other strategic transactions. Adverse effects arising from the pendency of the mergers could be exacerbated by any delays in consummation of the mergers or the termination of the merger agreement. See the section entitled "The Merger Agreement—Conduct of Business Pending the Effective Time" beginning on page 120 of this joint proxy statement/prospectus.

Third parties may terminate or alter existing contracts or relationships with BioCryst or Idera.

        Each of BioCryst and Idera has contracts with doctors, vendors, landlords, licensors, joint venture partners, and other business partners which may require BioCryst or Idera, as applicable, to obtain consent from these other parties in connection with the mergers. If these consents cannot be obtained, the counterparties to these contracts and other third parties with which BioCryst and/or Idera currently have relationships may have the ability to terminate, reduce the scope of or otherwise materially adversely alter their relationships with either or both parties in anticipation of the mergers, or with the combined company following the mergers. The pursuit of such rights may result in BioCryst, Idera or the combined company suffering a loss of potential future revenue or incurring liabilities in connection with a breach of such agreements and may lose rights that are material to its business. Any such disruptions could limit the combined company's ability to achieve the anticipated benefits of the mergers. The adverse effect of such disruptions could also be exacerbated by a delay in the completion of the mergers or the termination of the merger agreement.

Idera or BioCryst may waive one or more of the closing conditions without re-soliciting stockholder approval.

        Idera or BioCryst may determine to waive, in whole or in part, one or more of the conditions to its obligations to consummate the mergers. Idera or BioCryst currently expect to evaluate the materiality of any waiver and its effect on Idera stockholders or BioCryst stockholders, as applicable, in light of the facts and circumstances at the time to determine whether any amendment of this joint proxy statement/prospectus or any re-solicitation of proxies or voting cards is required in light of such waiver. Any determination whether to waive any condition to the mergers or as to re-soliciting stockholder approval or amending this joint proxy statement/prospectus as a result of a waiver will be made by Idera or BioCryst, as applicable, at the time of such waiver based on the facts and circumstances as they exist at that time.

The merger agreement may be terminated in accordance with its terms and the mergers may not be completed.

        The completion of the mergers is subject to the satisfaction or waiver of a number of conditions. Those conditions include: (i) the adoption of the merger agreement by the affirmative vote of the holders of a majority of all issued and outstanding shares of Idera common stock and BioCryst common stock, respectively, entitled to vote thereon; (ii) the authorization of the shares of Holdco common stock to be issued to Idera stockholders and BioCryst stockholders for listing on the Nasdaq, subject to official notice of issuance; (iii) the effectiveness of the registration statement of which this joint proxy statement/prospectus forms a part and the absence of any stop order in respect thereof; (iv) the absence of certain governmental restraints or prohibitions preventing consummation of the mergers; (v) the receipt of certain regulatory approvals under competition laws, including the termination or expiration of the waiting period under the HSR Act; (vi) the truth and correctness of

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the representations and warranties made by both parties (generally subject to certain materiality and material adverse effect qualifiers); (vii) the receipt by both parties of a certificate certifying that the aforementioned representations and warranties conditions and performance conditions have been satisfied; (viii) the performance by Idera and BioCryst of their respective obligations under the merger agreement in all material respects; (ix) the receipt by BioCryst of an opinion from Skadden to the effect that the BioCryst merger will qualify as a "reorganization" within the meaning of Section 368(a) of the Code or, alternatively, the mergers together will be treated as an "exchange" described in Section 351 of the Code; and (x) the receipt by Idera of an opinion from Latham to the effect that the mergers together will be treated as an "exchange" described in Section 351 of the Code.

        These conditions to the closing may not be fulfilled and, accordingly, the mergers may not be completed. In addition, if the mergers are not completed by July 21, 2018, either Idera or BioCryst may choose not to proceed with the mergers and to terminate the merger agreement, and the parties can mutually decide to terminate the merger agreement at any time prior to the consummation of the mergers, before or after the required Idera stockholder and BioCryst stockholder approvals. In addition, Idera or BioCryst may elect to terminate the merger agreement in certain other circumstances. If the merger agreement is terminated, Idera and BioCryst may incur substantial fees in connection with termination of the merger agreement, will not recognize the anticipated benefits of the mergers and each party may be adversely affected by a number of factors including the inability to pursue other beneficial opportunities and the focus of their respective managements on the mergers for an extended period of time rather than on management opportunities or other issues. The market price of Idera common stock and/or BioCryst common stock might decline as a result of any such failures to the extent that the current market prices reflect a market assumption that the mergers will be completed. See the section entitled "The Merger Agreement—Termination of the Merger Agreement" beginning on page 133 of this joint proxy statement/prospectus.

BioCryst and Idera will incur significant transaction costs in connection with the mergers.

        BioCryst and Idera have incurred and expect to incur a number of nonrecurring costs associated with the mergers. These costs and expenses include financial advisory, legal, accounting, consulting and other advisory fees and expenses, reorganization and restructuring costs, severance/employee benefit-related expenses, public company filing fees and other regulatory expenses, printing expenses and other related charges. Some of these costs are payable by BioCryst and Idera regardless of whether the mergers are completed.

Lawsuits have been filed against BioCryst and Idera challenging the mergers and an adverse ruling may prevent the mergers from being completed.

        Three putative class action lawsuits have been brought by three stockholders of Idera and/or BioCryst challenging the mergers and seeking, among other things, injunctive relief to enjoin the defendants from completing the mergers on the agreed-upon terms. Additional lawsuits may be filed against BioCryst, Idera and/or their respective directors or officers in connection with the mergers. See "The Mergers—Litigation Related to the Mergers" beginning on page 115 of this joint proxy statement/prospectus for more information about the lawsuits that have been filed related to the mergers.

        One of the conditions to the closing of the mergers is the absence of any law, order, injunction, decree, statute, rule or regulation by a governmental entity that prohibits, restrains or makes illegal the consummation of the mergers. Consequently, if a settlement or other resolution is not reached in the lawsuits referenced above and the plaintiffs secure injunctive or other relief prohibiting, delaying or otherwise adversely affecting the parties' ability to complete the mergers, then such injunctive or other relief may prevent the mergers from becoming effective within the expected time frame or at all.

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Failure to complete the mergers could negatively impact the stock prices and the future business and financial results of BioCryst and Idera.

        Completion of the mergers is not assured and is subject to risks, including the risks that approval of the transactions by BioCryst stockholders and Idera stockholders or by governmental entities will not be obtained or that certain other closing conditions will not be satisfied. If the mergers are not completed, the ongoing businesses and financial results of BioCryst and/or Idera may be adversely affected and BioCryst and/or Idera will be subject to several risks, including the following:

        If the mergers are not completed, BioCryst and Idera cannot assure their stockholders that these risks will not materialize and will not materially adversely affect the businesses, financial results and stock prices of BioCryst or Idera.

The merger agreement contains provisions that could discourage a potential competing acquirer of either BioCryst or Idera.

        The merger agreement contains "no shop" provisions that generally restrict each of BioCryst's and Idera's ability to solicit, initiate or knowingly encourage and induce, or take any other action designed to facilitate competing third-party proposals relating to a merger, reorganization or consolidation of the company or an acquisition of the company's stock or assets. Further, even if the BioCryst board or the Idera board withdraws or qualifies its recommendation with respect to the mergers, BioCryst or Idera, as the case may be, will still be required to submit each of their merger-related proposals to a vote at their respective special meetings. In addition, the other party generally has an opportunity to offer to modify the terms of the merger agreement in response to any competing acquisition proposals before the board of directors of the company that has received a third-party proposal may withdraw or qualify its recommendation with respect to the mergers. In addition, under specified circumstances, BioCryst or Idera may be required to pay a termination fee of $25 million and a fixed reimbursement amount of $6 million if the mergers are not consummated. See the sections entitled "The Merger Agreement—No Solicitation of Competing Proposals," "The Merger Agreement—Termination of the Merger Agreement" and "The Merger Agreement—Expenses and Termination Fees; Liability for Breach" beginning on pages 123, 133 and 134, respectively, of this joint proxy statement/prospectus for a discussion of these provisions.

        These provisions could discourage a potential third-party acquirer that might have an interest in acquiring all or a significant portion of BioCryst or Idera from considering or proposing that acquisition, even if it were prepared to pay consideration with a higher per share cash or market value than the market value of Holdco shares to be received in the mergers or might result in a potential third-party acquirer proposing to pay a lower price to the stockholders than it might otherwise have proposed to pay because of the added expense of the $25 million termination fee and a fixed expense reimbursement amount of $6 million that may become payable in certain circumstances.

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        If the merger agreement is terminated and either BioCryst or Idera determines to seek another business combination, it may not be able to negotiate a transaction with another party on terms comparable to, or better than, the terms of the mergers.

The fairness opinions obtained by the BioCryst board and the Idera board from their financial advisors will not reflect changes in circumstances between signing the merger agreement and the completion of the mergers.

        Neither the BioCryst board nor the Idera board has obtained an updated fairness opinion as of the date of this joint proxy statement/prospectus from J.P. Morgan, BioCryst's financial advisor, or Goldman Sachs, Idera's financial advisor.

        Changes in the operations and prospects of BioCryst or Idera, general market and economic conditions and other factors that may be beyond the control of BioCryst and Idera, and on which the fairness opinions were based, may alter the value of BioCryst or Idera or the prices of shares of BioCryst common stock or Idera common stock by the time the mergers are completed. The opinions do not speak as of the time the mergers will be completed or as of any date other than the dates of such opinions. Because neither BioCryst nor Idera anticipates asking its financial advisor to update its opinion, the January 21, 2018 opinions do not and will not address the fairness of the exchange ratios, from a financial point of view, at the time the mergers are completed. The Goldman Sachs and J.P. Morgan opinions are attached as Annexes B and C, respectively, to this joint proxy statement/prospectus. For a description of the opinion that the BioCryst board received from its financial advisor and a summary of the material financial analyses provided to the BioCryst board in connection with rendering such opinion, please refer to "The Mergers—Opinion of BioCryst's Financial Advisor—J.P. Morgan" beginning on page 94 of this joint proxy statement/prospectus. For a description of the opinion that the Idera board received from its financial advisor and a summary of the material financial analyses provided to the Idera board in connection with rendering such opinion, please refer to "The Mergers—Opinion of Idera's Financial Advisor—Goldman Sachs" beginning on page 84 of this joint proxy statement/prospectus. For a description of the other factors considered by the BioCryst board in determining to approve the merger agreement and the mergers, please refer to "The Mergers—BioCryst's Reasons for the Mergers; Recommendation of the BioCryst Board" beginning on page 71 of this joint proxy statement/prospectus. For a description of the other factors considered by the Idera board in determining to approve the mergers, please refer to "The Mergers—Idera's Reasons for the Mergers; Recommendation of the Idera Board" beginning on page 67 of this joint proxy statement/prospectus.

Executive officers and directors of each of BioCryst and Idera and certain affiliates of the executive officers and directors of Idera have certain interests in the mergers that may be different from, or in addition to, the interests of BioCryst stockholders and Idera stockholders generally.

        BioCryst's executive officers and Idera's executive officers negotiated the terms of the merger agreement. For additional information on these interests, see "The Mergers—Interests of BioCryst Directors and Executive Officers in the Mergers" and "The Mergers—Interests of Idera Directors, Executive Officers and Certain of their Affiliates in the Mergers" beginning on pages 106 and 99, respectively, of this joint proxy statement/prospectus.

        Immediately following the effective time of the mergers, the board of the combined company will be comprised of nine members, consisting of: Mr. Milano, currently a director and the chief executive officer of Idera; Mr. Geraghty, currently the chairman of the Idera board; Dr. Gowen, currently a director of Idera; Dr. Goldberg, currently a director of Idera; Mr. Stonehouse, currently a director and the chief executive officer of BioCryst; Mr. Ingram, currently the chairman of the BioCryst board, who will serve as the chairman of the board of the combined company; Dr. Hutson, currently a director of BioCryst; Mr. Lee, currently a director of BioCryst; and one person to be mutually agreed by the Idera board and the BioCryst board who is not an officer, director or affiliate of either Idera or BioCryst.

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        The BioCryst and Idera boards were aware of these interests at the time each approved the mergers and the transactions contemplated by the merger agreement. These interests, including the continued employment of certain executive officers of BioCryst and Idera by the combined company, the continued positions of certain directors of BioCryst and Idera as directors of the combined company and the indemnification of former directors and officers by the combined company, may cause BioCryst's and Idera's directors and executive officers to view the proposal to adopt the merger agreement differently and more favorably than you may view it. See "The Mergers—Interests of BioCryst Directors and Executive Officers in the Mergers—Continued Service with the Combined Company," "The Mergers—Employee Benefits," "The Mergers—Interests of Idera Directors, Executive Officers and Certain of their Affiliates in the Mergers—Employee Benefits" and "The Mergers—Interests of Idera Directors, Executive Officers and Certain of their Affiliates in the Mergers—Indemnification and Insurance" beginning on pages 106, 112, 103 and 103, respectively, of this joint proxy statement/prospectus for more information.

Current BioCryst stockholders and Idera stockholders will have a reduced ownership and voting interest in Holdco after the mergers compared to their respective interest in Idera or BioCryst.

        Current holders of BioCryst common stock and Idera common stock have the right to vote in the election of the board of directors and on other matters affecting BioCryst and Idera, respectively. Upon the completion of the mergers, each Idera stockholder and each BioCryst stockholder who receives shares of Holdco common stock will become a stockholder of the combined company with a percentage ownership of the combined company that is smaller than such stockholder's percentage ownership of Idera or BioCryst, respectively. It is currently expected that the Idera stockholders immediately prior to the effective time of the mergers as a group will receive shares in the mergers constituting approximately 48.4% of the shares of combined company common stock immediately after the mergers, and the BioCryst stockholders immediately prior to the effective time of the mergers as a group will receive shares in the mergers constituting approximately 51.6% of the shares of combined company common stock immediately after the mergers, each calculated on a fully diluted basis using the treasury stock method.

Shares of Holdco common stock to be received by BioCryst stockholders in the BioCryst merger and Idera stockholders in the Idera merger will have rights different from the shares of BioCryst common stock and Idera common stock, respectively.

        Upon completion of the mergers, BioCryst stockholders and Idera stockholders will no longer be BioCryst stockholders and/or Idera stockholders, as applicable, but will instead be Holdco stockholders. The rights of former BioCryst stockholders and Idera stockholders who become Holdco stockholders will be governed by the Holdco charter and the amended and restated bylaws of Holdco (the "Holdco bylaws"), each of which will be adopted, effective upon the effective time, in substantially the form attached as Annex D and Annex E, respectively, to this joint proxy statement/prospectus. The rights associated with shares of Holdco common stock are different from the rights associated with shares of BioCryst common stock or Idera common stock. See "Comparison of Rights of Idera Stockholders, BioCryst Stockholders and Holdco Stockholders" beginning on page 164 of this joint proxy statement/prospectus.

BioCryst stockholders and Idera stockholders will not be entitled to appraisal rights in the mergers.

        Appraisal rights are statutory rights that, if applicable under law, enable stockholders to dissent from an extraordinary transaction, such as a merger, and to demand that the corporation pay the fair value for their shares as determined by a court in a judicial proceeding instead of receiving the consideration offered to stockholders in connection with the extraordinary transaction. Under the DGCL, stockholders do not have appraisal rights if the shares of stock they hold, as of the record date

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for determination of stockholders entitled to vote at the meeting of stockholders to act upon a merger, are either (i) listed on a national securities exchange or (ii) held of record by more than 2,000 holders. Notwithstanding the foregoing, appraisal rights are available if stockholders are required by the terms of the merger agreement to accept for their shares anything other than (a) shares of stock of the surviving corporation, (b) shares of stock of another corporation that will either be listed on a national securities exchange or held of record by more than 2,000 holders, (c) cash instead of fractional shares or (d) any combination of clauses (a) through (c).

        Because BioCryst common stock is listed on the Nasdaq, a national securities exchange, and is expected to continue to be so listed on the record date for the BioCryst special meeting, and because BioCryst stockholders will receive shares of Holdco common stock in the BioCryst merger, which is expected to be listed on the Nasdaq upon the effective time, BioCryst stockholders will not be entitled to appraisal rights in the BioCryst merger with respect to their shares of BioCryst common stock. Similarly, Idera common stock is listed on the Nasdaq and is expected to continue to be so listed on the record date for the Idera special meeting. Because holders of Idera common stock and Idera preferred stock will also receive shares of Holdco common stock in the Idera merger, holders of Idera common stock and Idera preferred stock will also not be entitled to appraisal rights in the Idera merger with respect to their shares of Idera common stock or Idera preferred stock, respectively.

Risk Factors Relating to the Combined Company Following the Mergers

The combined company may be unable to integrate successfully the businesses of BioCryst and Idera and realize the anticipated benefits of the mergers.

        The success of the mergers will depend, in large part, on the ability of the combined company to realize the anticipated benefits, including cost savings, from combining the businesses of BioCryst and Idera. To realize these anticipated benefits, the businesses of BioCryst and Idera must be integrated successfully. This integration will be complex and time consuming. The failure to successfully integrate and manage the challenges presented by the integration process may result in the combined company not fully achieving the anticipated benefits of the mergers. Potential difficulties the combined company may encounter as part of the integration process, many of which may be beyond the control of management, include the following:

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        In addition, BioCryst and Idera have operated and, until the completion of the mergers, will continue to operate independently. It is possible that the integration process could result in:

The market price of Holdco's common stock may be volatile, and holders of Holdco's common stock could lose a significant portion of their investment due to drops in the market price of Holdco's common stock following completion of the mergers.

        The market price of the combined company's common stock may be volatile, and following completion of the mergers stockholders may not be able to resell their Holdco common stock at or above the price at which they acquired the common stock pursuant to the merger agreement or otherwise due to fluctuations in its market price, including changes in price caused by factors unrelated to the combined company's operating performance or prospects.

        Specific factors that may have a significant effect on the market price for Holdco's common stock include, among others, the following:

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The future results of the combined company will suffer if the combined company does not effectively manage its operations following the mergers.

        The combined company's future success depends, in part, upon its ability to manage the combined businesses of Idera and BioCryst, which will pose substantial challenges for management, including challenges related to the management and monitoring of new operations. There can be no assurances that the combined company will be successful or that it will realize the expected operating efficiencies, cost savings and other benefits currently anticipated from the mergers.

The combined company is expected to incur substantial expenses related to the mergers and the integration of BioCryst and Idera.

        The combined company is expected to incur substantial expenses in connection with the mergers and the integration of BioCryst and Idera. There are a large number of processes, policies, procedures, operations, technologies and systems that must be integrated, including purchasing, accounting and finance, payroll, research and development and benefits. While BioCryst and Idera have assumed that a certain level of expenses would be incurred, there are many factors beyond their control that could affect the total amount or the timing of the integration expenses. Moreover, many of the expenses that will be incurred are, by their nature, difficult to estimate accurately. These expenses could, particularly in the near term, exceed the savings that the combined company expects to achieve from the elimination of duplicative expenses and the realization of economies of scale and cost savings. These integration expenses likely will result in the combined company taking significant charges against earnings following the completion of the mergers, and the amount and timing of such charges are uncertain at present.

Holdco has no operating or financial history and the unaudited pro forma combined financial information included in this joint proxy statement/prospectus are preliminary. Therefore, the actual financial condition and results of operations of Holdco after the mergers may differ materially.

        Holdco has been recently incorporated in connection with the mergers and has no operating history or revenues. This joint proxy statement/prospectus includes unaudited pro forma condensed combined financial statements for Holdco as of the year ended December 31, 2017, that combines the audited historical consolidated financial statements of BioCryst for the year ended December 31, 2017 with the audited historical financial statements of Idera for the year ended December 31, 2017, and unaudited pro forma condensed combined financial statements for Holdco as of the three months ended March 31, 2018 that combines the unaudited historical consolidated financial statements of BioCryst for the three months ended March 31, 2018 with the unaudited historical financial statements of Idera for the three months ended March 31, 2018, in each case, adjusted to give effect to the mergers, and should be read in conjunction with such financial statements and accompanying notes which are incorporated by reference in this joint proxy statement/prospectus. The unaudited pro forma condensed combined balance sheet of Holdco as of March 31, 2018 combines the audited historical balance sheets of BioCryst and Idera as of March 31, 2018 and gives pro forma effect to the mergers as if they had been consummated on March 31, 2018. The unaudited pro forma condensed combined statement of operations for the year ended December 31, 2017 and for the three months ended March 31, 2018 combines the BioCryst audited consolidated statements of operations and the Idera audited statements of operations for the fiscal year ended December 31, 2017, and the BioCryst unaudited consolidated statements of operations and the Idera unaudited statements of operations for the three months ended March 31, 2018, in each case, giving effect to the mergers as if they had been consummated on January 1, 2017. The pro forma financial statements are presented for illustrative

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purposes only, are based on certain assumptions, address a hypothetical situation and reflect limited historical financial data. The pro forma financial statements do not include, among other things, estimated cost or growth synergies, adjustments related to restructuring or integration activities, future acquisitions or disposals not yet known or probable, including those that may be required by regulatory or governmental authorities in connection with the mergers, or impacts of merger-related change in control provisions that are currently not factually supportable and/or probable of occurring. Therefore, the pro forma financial statements are presented for informational purposes only and are not necessarily indicative of what the combined company's actual financial condition or results of operations would have been had the mergers been completed on the dates indicated. Accordingly, Holdco's business, assets, results of operations and financial condition may differ significantly from those indicated by the pro forma combined financial information included in this joint proxy statement/prospectus. For more information, see "Selected Unaudited Pro Forma Condensed Combined Financial Information of Idera and BioCryst" beginning on page 141 of this joint proxy statement/prospectus.

The financial analyses and forecasts considered by BioCryst and Idera and their respective financial advisors may not be realized, which may adversely affect the market price of Holdco common stock following the completion of the mergers.

        In performing their financial analyses and rendering their opinions regarding the fairness, from a financial point of view, of the BioCryst exchange ratio and Idera exchange ratio, as applicable, each of the respective financial advisors to BioCryst and Idera relied on, among other things, internal standalone financial analyses and forecasts as separately provided to each respective financial advisor by BioCryst and Idera. See "The Mergers—Certain Financial Forecasts Utilized by the BioCryst Board and BioCryst's Financial Advisor in Connection with the Mergers" and "The Mergers—Certain Financial Forecasts Utilized by the Idera Board and Idera's Financial Advisor in Connection with the Mergers" beginning on pages 80 and 76, respectively, of this joint proxy statement/prospectus. These analyses and forecasts were prepared by, or as directed by, the managements of BioCryst or Idera, as applicable. Since the forecasts cover a long period of time, the forecasts by their nature are unlikely to anticipate each circumstance that will have an effect on the commercial value of BioCryst's and Idera's product candidates and become subject to greater uncertainty with each successive year. None of these analyses or forecasts were prepared with a view towards public disclosure or compliance with the published guidelines of the SEC, GAAP, or the guidelines established by the American Institute of Certified Public Accountants for preparation and presentation of financial forecasts. These projections are inherently based on various estimates and assumptions that are subject to the judgment of those preparing them. These projections are also subject to significant economic, competitive, industry and other uncertainties and contingencies, all of which are difficult or impossible to predict and many of which are beyond the control of BioCryst and Idera. There can be no assurance that BioCryst's or Idera's financial condition or results of operations will be consistent with those set forth in such analyses and forecasts, which could have a material impact on the market price of Holdco common stock following the mergers.

Other Risk Factors of Idera and BioCryst

        Idera's and BioCryst's businesses are and will be subject to the risks described above. In addition, Idera's and BioCryst's businesses are, and will continue to be, subject to the risks described in Part I, Item 1A of Idera's Annual Report on Form 10-K for the fiscal year ended December 31, 2017 and described in Item 1A of BioCryst's Quarterly Report on Form 10-Q for the three months ended March 31, 2018, and any amendments thereto, each as updated by subsequent Quarterly Reports on Form 10-Q and Current Reports on Form 8-K, all of which are or will be filed with the SEC and incorporated by reference into this joint proxy statement/prospectus. See "Where You Can Find More Information" beginning on page 172 of this joint proxy statement/prospectus for the location of information incorporated by reference in this joint proxy statement/prospectus.

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THE COMPANIES

Nautilus Holdco, Inc.

        Nautilus Holdco, Inc. is a Delaware corporation and wholly owned subsidiary of BioCryst formed for the sole purpose of becoming the parent entity of each of Idera and BioCryst following the mergers. At the effective time of the mergers, Nautilus Holdco, Inc., will be renamed "Valenscion Incorporated."

Idera Pharmaceuticals, Inc.

        Idera is a clinical-stage biopharmaceutical company focused on the discovery, development and commercialization of novel oligonucleotide therapeutics for oncology and rare diseases. Idera uses two distinct proprietary drug discovery technology platforms to design and develop drug candidates: its Toll-like receptor, or TLR, targeting technology and its nucleic acid chemistry technology (formerly referred to as Idera's third generation antisense, or 3GA technology). Idera developed these platforms based on its scientific expertise and pioneering work with synthetic oligonucleotides as therapeutic agents. Using its TLR targeting technology, Idera designs synthetic oligonucleotide-based drug candidates to modulate the activity of specific TLRs. Using its nucleic acid chemistry technology, Idera is developing drug candidates to turn off the messenger RNA, or mRNA, associated with disease causing genes. Idera believes that its nucleic acid chemistry technology may potentially reduce the immunotoxicity and increase the potency of earlier generation antisense and RNA interference, or RNAi, technologies.

        Idera's business strategy is focused on the clinical development of drug candidates for oncology and rare diseases characterized by small, well-defined patient populations with serious unmet medical needs. Idera believes that it can develop and commercialize these targeted therapies on its own. To the extent Idera seeks to develop drug candidates for broader disease indications, it has entered into and may explore additional collaborative alliances to support development and commercialization.

        Idera's common stock is traded on the Nasdaq under the symbol "IDRA." The principal executive offices of Idera are located at 167 Sidney Street, Cambridge, Massachusetts 02139, and its telephone number is (617) 679-5500. Idera maintains another office at 505 Eagleview Boulevard, Suite 212, Exton, Pennsylvania 19341.

BioCryst Pharmaceuticals, Inc.

        BioCryst is a biotechnology company that designs, optimizes and develops novel small molecule drugs that block key enzymes involved in the pathogenesis of diseases. BioCryst focuses on the treatment of rare diseases in which significant unmet medical needs exist and align with BioCryst's capabilities and expertise. BioCryst integrates the disciplines of biology, crystallography, medicinal chemistry and computer modeling to discover and develop small molecule pharmaceuticals through the process known as structure-guided drug design. Structure-guided drug design is a drug discovery approach by which BioCryst designs synthetic compounds from detailed structural knowledge of the active sites of enzyme targets associated with particular diseases. BioCryst uses X-ray crystallography, computer modeling of molecular structures and advanced chemistry techniques to focus on the three-dimensional molecular structure and active site characteristics of the enzymes that control cellular biology. Enzymes are proteins that act as catalysts for many vital biological reactions. BioCryst's goal generally is to design a compound that will fit in the active site of an enzyme and thereby prevent its catalytic activity.

        BioCryst's common stock is traded on the Nasdaq under the symbol "BCRX."

        The principal executive offices of BioCryst are located at 4505 Emperor Blvd., Suite 200, Durham, North Carolina 27703, and its telephone number is (919) 859-1302.

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Island Merger Sub, Inc.

        Island Merger Sub, Inc. is a Delaware corporation and wholly owned subsidiary of Holdco formed for the sole purpose of effecting the Idera merger.

Boat Merger Sub, Inc.

        Boat Merger Sub, Inc. is a Delaware corporation and wholly owned subsidiary of Holdco formed for the sole purpose of effecting the BioCryst merger.

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THE BIOCRYST SPECIAL MEETING

        This joint proxy statement/prospectus is being provided to BioCryst stockholders as part of a solicitation of proxies by the BioCryst board for use at the BioCryst special meeting and at any adjournments or postponements of such special meeting. This joint proxy statement/prospectus provides BioCryst stockholders with information they need to know to be able to vote or instruct their vote to be cast at the BioCryst special meeting or any adjournment or postponement thereof and should be read carefully in its entirety. In addition, this joint proxy statement/prospectus constitutes a prospectus for Holdco in connection with the issuance by Holdco of its common stock pursuant to the merger agreement.

Date, Time and Place

        The BioCryst special meeting is scheduled to be held at 4505 Emperor Blvd., Suite 200, Durham, North Carolina 27703 on July 10, 2018 at 10:00 a.m., Eastern Time, subject to any adjournments or postponements thereof.

Purpose of the BioCryst Special Meeting

        At the BioCryst special meeting, BioCryst stockholders will be asked to consider and vote on:

        Completion of the mergers is conditioned on, among other things, approval by BioCryst stockholders of the proposal to adopt the merger agreement.

Recommendation of the BioCryst Board

        BioCryst's board unanimously determined that the merger agreement and the transactions contemplated thereby, including the mergers and the compensatory arrangements between BioCryst and its named executive officers, are fair, advisable and in the best interests of BioCryst and its stockholders and approved the execution, delivery and performance by BioCryst of the merger agreement and the consummation of the transactions contemplated thereby, including the mergers.

        The BioCryst board unanimously recommends that BioCryst stockholders vote "FOR" the proposal to adopt the merger agreement, "FOR" the proposal to approve, on a non-binding advisory basis, the compensation that may become payable to BioCryst's named executive officers that is based on or otherwise relates to the mergers and "FOR" the proposal to adjourn the BioCryst special meeting, if necessary or appropriate, to solicit additional proxies if there are not sufficient votes to adopt the merger agreement.

        This joint proxy statement/prospectus contains important information regarding these proposals and factors that BioCryst stockholders should consider when deciding how to cast their votes. BioCryst stockholders are encouraged to read carefully this joint proxy statement/prospectus in its entirety, including the annexes to and documents incorporated by reference into this joint proxy/prospectus, for

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more detailed information regarding the merger agreement and the transactions contemplated thereby, including the mergers.

Attendance at the BioCryst Special Meeting

        Only BioCryst stockholders of record as of the close of business on the BioCryst record date, beneficial owners as of the close of business on the BioCryst record date, holders of valid proxies for the BioCryst special meeting and invited guests of BioCryst may attend the BioCryst special meeting, and admission will be on a first-come, first-serve basis.

        All attendees should be prepared to present government-issued photo identification (such as a driver's license or passport) for admittance. The additional items, if any, that attendees must bring depend on whether they are stockholders of record, beneficial owners or proxy holders.

        No cameras, recording equipment or other electronic devices will be allowed in the meeting room. Failure to provide the requested documents at the door or failure to comply with the procedures for the BioCryst special meeting may prevent stockholders from being admitted to the BioCryst special meeting.

        BioCryst is able to provide reasonable assistance to help persons with disabilities participate in the BioCryst special meeting if BioCryst is notified in writing in advance of requested accommodations. Please write to BioCryst's principal executive offices at 4505 Emperor Blvd., Suite 200, Durham, North Carolina 27703, Attention: Corporate Secretary.

BioCryst Record Date; Stockholders Entitled to Vote

        Only holders of record of BioCryst common stock at the close of business on May 29, 2018, the record date for the BioCryst special meeting, will be entitled to notice of, and to vote at, the BioCryst special meeting or any adjournments or postponements thereof.

        As of the close of business on the BioCryst record date, there were 98,821,091 shares of BioCryst common stock issued and outstanding, held by 171 holders of record. A complete list of registered BioCryst stockholders entitled to vote at the BioCryst special meeting will be available for inspection at the principal place of business of BioCryst at 4505 Emperor Blvd., Suite 200, Durham, North

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Carolina 27703 during regular business hours for a period of no less than 10 days before the BioCryst special meeting and at the place of the BioCryst special meeting during the meeting.

BioCryst Voting and Support Agreement

        Simultaneously with the execution of the merger agreement, each of BioCryst and Idera entered into a voting and support agreement with affiliates of Baker Brothers. Baker Brothers is the beneficial owner of approximately 14% of issued and outstanding BioCryst common stock and approximately 18% of issued and outstanding Idera common stock. Pursuant to the voting and support agreements, Baker Brothers has agreed, among other things, to vote its shares of BioCryst common stock and Idera common stock in favor of the adoption of the merger agreement at each of the BioCryst special meeting and the Idera special meeting, respectively. In addition, Baker Brothers has agreed to be present at each of the BioCryst special meeting and the Idera special meeting for purposes of establishing a quorum.

Voting by BioCryst's Directors and Executive Officers

        At the close of business on the BioCryst record date, directors and executive officers of BioCryst and their affiliates were entitled to vote 1,225,516 shares of BioCryst common stock, or approximately 1% of the shares of BioCryst common stock issued and outstanding on that date. We currently expect that BioCryst's directors and executive officers will vote their shares in favor of each proposal being submitted to a vote of the BioCryst stockholders at the BioCryst special meeting, although no director or officer has entered into any agreement obligating him or her to do so.

Quorum

        In order for business to be conducted at the BioCryst special meeting, a quorum must be present. A quorum requires the presence, in person or by proxy, of a majority of the issued and outstanding shares of BioCryst common stock entitled to vote at the BioCryst special meeting. For purposes of determining whether there is a quorum, all shares that are present will count towards the quorum, which will include proxies received but marked as abstentions and will exclude broker non-votes. Broker non-votes occur when a beneficial owner holding shares in "street name" does not instruct the broker, bank or other nominee that is the record owner of such stockholder's shares on how to vote those shares on a particular proposal.

        If a quorum is not present, the BioCryst special meeting may be adjourned by the vote of the holders of a majority of the shares of BioCryst common stock present or represented by proxy and entitled to vote, to reconvene at the same or another place. If a quorum is present at the BioCryst special meeting but there are not sufficient votes at the time of the BioCryst special meeting to adopt the merger agreement, then BioCryst stockholders may be asked to vote on the BioCryst adjournment proposal. Notice need not be given of any such adjourned meeting if the time and place thereof are announced at the meeting at which the adjournment is taken.

Required Vote

        The adoption of the merger agreement requires the affirmative vote of the holders of a majority of the issued and outstanding shares of BioCryst common stock entitled to vote on the proposal. Failures to vote, abstentions and broker non-votes will have the effect of a vote against the proposal. Pursuant to the voting and support agreement, Baker Brothers has agreed to vote in favor of the proposal to adopt the merger agreement.

        Approval of, on a non-binding advisory basis, the compensation that may become payable to BioCryst's named executive officers that is based on or otherwise relates to the mergers requires the affirmative vote of the holders of a majority of the shares of BioCryst common stock present, in person

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or represented by proxy, at the BioCryst special meeting and voting on the proposal, although such vote will not be binding on BioCryst, the BioCryst board or any of its committees, or, following completion of the mergers, the combined company. Abstentions, failures to vote (i.e., not submitting a proxy and not voting in person) and broker non-votes will have no effect on the proposal, assuming a quorum is present.

        Approval of the BioCryst adjournment proposal requires the affirmative vote of the holders of a majority of the shares of BioCryst common stock present, in person or represented by proxy, at the BioCryst special meeting and voting on the proposal. Abstentions, failures to vote (i.e., not submitting a proxy and not voting in person) and broker non-votes will have no effect on the outcome of the BioCryst adjournment proposal, assuming a quorum is present. Brokers, banks and other nominees do not have discretionary authority to vote on the adjournment proposal and will not be able to vote on the adjournment proposal absent instructions from the beneficial owner.

How to Vote

        BioCryst stockholders of record as of the close of business on the BioCryst record date may have their shares voted by submitting a proxy or may vote in person at the BioCryst special meeting by following the instructions provided in the one-page notice regarding the Internet availability of proxy materials. BioCryst recommends that BioCryst stockholders entitled to vote submit a proxy even if they plan to attend the BioCryst special meeting.

        BioCryst stockholders who hold their shares beneficially in "street name" and wish to submit a proxy must provide instructions to the broker, bank, trustee or other nominee that holds their shares of record as to how to vote their shares with respect to all proposals to be voted on at the BioCryst special meeting. BioCryst stockholders who hold their shares beneficially and wish to vote in person at the BioCryst special meeting must obtain a "legal proxy."

        BioCryst stockholders of record may submit a proxy in one of three ways or vote in person at the BioCryst special meeting:

        BioCryst stockholders are encouraged to submit a proxy promptly. Each valid proxy received in time will be voted at the BioCryst special meeting according to the choice specified, if any. Executed

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but uninstructed proxies (i.e., proxies that are properly signed, dated and returned but are not marked to tell the proxies how to vote) will be voted in accordance with the recommendations of the BioCryst board. However, if you previously submitted a proxy for the BioCryst special meeting originally scheduled for May 9, 2018, which proxy has not subsequently been revoked, and are a holder of record on May 29, 2018 and you do not want to change or revoke your proxy, you do not need to take any action. Accordingly, BioCryst intends to vote such proxy at the BioCryst special meeting on July 10, 2018, as directed by your previously submitted proxy.

Shares Held in Street Name

        BioCryst stockholders who hold shares of BioCryst common stock in a stock brokerage account or through a bank, broker or other nominee ("street name" stockholders) who wish to vote at the BioCryst special meeting should be provided a voting instruction form by the institution that holds their shares. If this has not occurred, contact the institution that holds your shares. A number of banks and brokerage firms participate in a program that also permits "street name" stockholders to direct their vote by telephone or over the Internet. If your shares are held in an account at a bank or brokerage firm that participates in such a program, you may direct the vote of these shares by telephone or over the Internet by following the voting instructions enclosed with the proxy form from the bank or brokerage firm. The Internet and telephone proxy procedures are designed to authenticate stockholders' identities, to allow stockholders to give their proxy voting instructions and to confirm that those instructions have been properly recorded. Votes directed by telephone or over the Internet through such a program must be received by 11:59 p.m., Eastern Time, on July 9, 2018. Directing the voting of your shares will not affect your right to vote in person if you decide to attend the BioCryst special meeting; however, you must first obtain a signed and properly executed legal proxy from your bank, broker or other nominee to vote your shares held in "street name" at the BioCryst special meeting. Requesting a legal proxy prior to the deadline described above will automatically cancel any voting directions you have previously given by telephone or over the Internet with respect to your shares. However, if you are a BioCryst stockholder as of the revised May 29, 2018 record date who previously provided voting instructions to your bank, broker or other nominee, and do not wish to change your vote, you will not need to provide voting instructions again and your BioCryst shares will be voted at the rescheduled July 10, 2018 BioCryst special meeting in accordance with your original voting instructions.

        In accordance with the rules of the Nasdaq, brokers, banks and other nominees who hold shares of BioCryst common stock in "street name" for their customers do not have discretionary authority to vote the shares with respect to the proposal to adopt the merger agreement, the BioCryst merger-related compensation proposal, or the BioCryst adjournment proposal. Accordingly, if brokers, banks or other nominees do not receive specific voting instructions from the beneficial owner of such shares, they may not vote such shares with respect to these proposals. Under such circumstance, a broker non-vote would arise. Broker non-votes, if any, will not be considered present at the special meeting for purposes of determining whether a quorum is present at the special meeting, will have the same effect as a vote "AGAINST" the proposal to adopt the merger agreement and, assuming a quorum is present, will have no effect on the BioCryst merger-related compensation proposal or on the BioCryst adjournment proposal. Thus, for shares of BioCryst common stock held in "street name," only shares of BioCryst common stock affirmatively voted "FOR" the proposal to adopt the merger agreement will be counted as a vote in favor of such proposal.

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Proxies and Revocation

        BioCryst stockholders of record may revoke their proxies at any time before their shares are voted at the BioCryst special meeting in any of the following ways:

        BioCryst beneficial owners may change their voting instruction by submitting new voting instructions to the brokers, banks or other nominees that hold their shares of record or by requesting a "legal proxy" from such broker, bank or other nominee and voting in person at the BioCryst special meeting.

        BioCryst stockholders that hold their shares in "street name" through a broker, bank or other nominee will need to follow the instructions provided by their broker, bank or other nominee in order to revoke their proxies or submit new voting instructions.

Tabulation of Votes

        BioCryst has appointed Alane Barnes to serve as the Inspector of Election for the BioCryst special meeting. Alane Barnes will, among other things, determine the number of shares of BioCryst common stock represented at the BioCryst special meeting to confirm the existence of a quorum, determine the validity of all proxies and ballots and independently tabulate affirmative and negative votes and abstentions.

Solicitation of Proxies

        BioCryst is making this proxy solicitation both through the mail and Internet, although proxies may be solicited by personal interview, telephone, facsimile, letter, e-mail or otherwise. Certain of BioCryst's directors, officers and other employees, without additional compensation, may participate in the solicitation of proxies. BioCryst will pay the cost of this solicitation, including the reasonable charges and expenses of brokerage firms and others who forward solicitation materials to beneficial owners of BioCryst common stock. BioCryst has retained Innisfree M&A Incorporated, 501 Madison Avenue, 20th floor, New York, New York 10022 to act as proxy solicitor in conjunction with the meeting. We have agreed to pay that firm approximately $18,500 plus reasonable out of pocket expenses for their services.

Adjournments

        If a quorum is not present, the BioCryst special meeting may be adjourned by the vote of the holders of a majority of the shares of BioCryst common stock present or represented by proxy and entitled to vote, to reconvene at the same or another place. If a quorum is present at the BioCryst special meeting but there are not sufficient votes at the time of the BioCryst special meeting to adopt the merger agreement, then BioCryst stockholders may be asked to vote on the BioCryst adjournment

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proposal. Notice need not be given of any such adjourned meeting if the time and place thereof are announced at the meeting at which the adjournment is taken.

Householding of Special Meeting Materials

        The SEC has adopted rules that permit companies and intermediaries such as banks, brokers or nominees to satisfy delivery requirements for proxy statements and annual reports with respect to two or more stockholders sharing the same address by delivering a single proxy statement or annual report, as applicable, addressed to those stockholders. This process, which is commonly referred to as "householding," reduces the volume of duplicate information received at your household and helps reduce BioCryst's expenses. Unless BioCryst has received contrary instructions, BioCryst may send a single copy of this joint proxy statement/prospectus and notice to any household at which two or more stockholders with the same surname reside if BioCryst believes the stockholders are members of the same family. Each stockholder in the household will continue to receive a separate proxy card. We will promptly deliver a separate copy of our proxy statement to any stockholder upon written request to BioCryst Pharmaceuticals, Inc., Attention: Corporate Secretary, 4505 Emperor Blvd., Suite 200, Durham, North Carolina 27703, telephone: (919) 859-1302. Any stockholder who wants to receive separate copies of our proxy statement or annual report to stockholders in the future, or any stockholder who is receiving multiple copies and would like to receive only one copy per household, should contact the stockholder's bank, broker or other nominee, or the stockholder may contact BioCryst at the above address and phone number.

Questions and Additional Information

        BioCryst stockholders may contact BioCryst's proxy solicitor, Innisfree M&A Incorporated, with any questions about the proposals or how to vote or to request additional copies of any materials at:

LOGO

Innisfree M&A Incorporated
501 Madison Avenue, 20th floor
New York, New York 10022
Stockholders May Call Toll Free: 888-750-5834
Banks & Brokers May Call Collect: 212-750-5833

        BioCryst stockholders should not return their stock certificates or send documents representing BioCryst common stock with the proxy card. If the mergers are completed, the exchange agent for the BioCryst merger will send to BioCryst stockholders a letter of transmittal and related materials and instructions for exchanging shares of BioCryst common stock.

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BIOCRYST PROPOSALS

BioCryst Proposal 1: The BioCryst Merger Proposal

        BioCryst stockholders are asked to approve the proposal to adopt the merger agreement. For a summary and detailed information regarding this proposal, see the information about the mergers and the merger agreement throughout this joint proxy statement/prospectus, including the information set forth in sections entitled "The Mergers" and "The Merger Agreement" beginning on pages 53 and 116, respectively, of this joint proxy statement/prospectus. A copy of the merger agreement is attached as Annex A to this joint proxy statement/prospectus.

        Pursuant to the merger agreement, approval of this proposal by BioCryst stockholders is a condition to the consummation of the mergers. If this proposal is not approved, the mergers will not be consummated.

        BioCryst is requesting that BioCryst stockholders approve the proposal to adopt the merger agreement. Approval of this proposal requires the affirmative vote of the holders of a majority of the issued and outstanding shares of BioCryst common stock entitled to vote on the proposal at the BioCryst special meeting.

Recommendation of the BioCryst board

        The BioCryst board unanimously recommends that BioCryst stockholders vote "FOR" the proposal to adopt the merger agreement.

BioCryst Proposal 2: The BioCryst Merger-Related Compensation Proposal

        BioCryst stockholders are asked to approve, on a non-binding advisory basis, the compensation that may become payable to BioCryst's named executive officers that is based on or otherwise relates to the mergers. For a summary and detailed information regarding this proposal, see the information about the mergers and the merger agreement throughout this joint proxy statement/prospectus, including the information set forth in the section entitled "The Mergers—Interests of BioCryst Directors and Executive Officers in the Mergers" beginning on page 106 of this joint proxy statement/prospectus.

        Pursuant to the Dodd-Frank Wall Street Reform and Consumer Protection Act of 2010 and Rule 14a-21(c) of the Exchange Act, BioCryst is seeking non-binding, advisory stockholder approval of the compensation of BioCryst's named executive officers that is based on or otherwise relates to the mergers as disclosed in the section entitled "The Mergers—Interests of BioCryst Directors and Executive Officers in the Mergers" beginning on page 106 of this joint proxy statement/prospectus. The proposal gives BioCryst's stockholders the opportunity to express their views on the merger-related compensation of BioCryst's named executive officers.

        Accordingly, BioCryst is requesting stockholders to adopt the following resolution, on a non-binding, advisory basis:

        BioCryst stockholders should note that the BioCryst merger-related compensation proposal is merely an advisory vote, which will not be binding on BioCryst or the BioCryst board. Further, the underlying plans and arrangements are contractual in nature and not, by their terms, subject to stockholder approval. Accordingly, regardless of the outcome of the advisory vote, if the mergers are

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consummated, the eligibility of the BioCryst named executive officers for such payments and benefits will not be affected by the outcome of the advisory vote.

        The proposal to approve, on a non-binding advisory basis, the compensation that may be paid or become payable to BioCryst's named executive officers in connection with the mergers is a vote separate and apart from the vote on the proposal to adopt the merger agreement. Accordingly, a BioCryst stockholder may vote to approve one proposal and not the other. Approval of the BioCryst merger-related compensation proposal is not a condition to the completion of the mergers.

Recommendation of the BioCryst board

        The BioCryst board unanimously recommends a vote "FOR" the approval of the BioCryst merger-related compensation proposal.

BioCryst Proposal 3: The BioCryst Adjournment Proposal

        BioCryst stockholders are asked to vote on a proposal to adjourn the BioCryst special meeting, if necessary or appropriate, to solicit additional proxies in favor of the merger agreement proposal if there are not sufficient votes at the time of such adjournment to adopt the merger agreement.

Recommendation of the BioCryst board

        The BioCryst board unanimously recommends a vote "FOR" the BioCryst adjournment proposal.

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THE IDERA SPECIAL MEETING

        This joint proxy statement/prospectus is being provided to the Idera stockholders as part of a solicitation of proxies by the Idera board for use at the Idera special meeting to be held at the time and place specified below and at any properly convened meeting following any adjournments or postponements thereof. This joint proxy statement/prospectus provides Idera stockholders with the information they need to know to be able to vote or instruct their vote to be cast at the Idera special meeting.

Date, Time and Place

        The Idera special meeting is scheduled to be held at Idera's offices located at 505 Eagleview Boulevard, Suite 212, Exton, Pennsylvania 19341 on July 10, 2018 at 10:00 a.m., Eastern Time, subject to any adjournments or postponements thereof.

Purpose of the Idera Special Meeting

        At the Idera special meeting, Idera stockholders will be asked to consider and vote on:

        Completion of the mergers is conditioned on, among other things, approval by the Idera stockholders of the proposal to adopt the merger agreement.

Recommendation of the Idera Board

        The Idera board has unanimously approved the merger agreement and determined that the merger agreement and the transactions contemplated thereby, including the mergers and the compensatory arrangements between Idera and its named executive officers, are advisable, fair to and in the best interests of Idera and its stockholders.

        The Idera board unanimously recommends that Idera stockholders vote "FOR" the proposal to adopt the merger agreement and "FOR" the proposal to approve, on a non-binding advisory basis, the compensation that may become payable to Idera's named executive officers that is based on or otherwise relates to the mergers.

Idera Record Date; Stockholders Entitled to Vote

        Only holders of record of Idera common stock at the close of business on May 29, 2018, the record date for the Idera special meeting, will be entitled to notice of, and to vote at, the Idera special meeting or any adjournments or postponements thereof.

        At the close of business on the Idera record date, 217,310,991 shares of Idera common stock were issued and outstanding and held by 91 holders of record. Holders of record of Idera common stock on the Idera record date are entitled to one vote per share at the special meeting on each proposal. A list of Idera stockholders will be available for review for any purpose germane to the Idera special meeting at Idera's executive offices and principal place of business at the office of Idera's Assistant Secretary, 505 Eagleview Boulevard, Suite 212, Exton, Pennsylvania 19341, during regular business hours for a period of 10 days before the special meeting. The list will also be available at the Idera special meeting for examination by any stockholder of record present at the Idera special meeting.

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Idera Voting and Support Agreement

        Simultaneously with the execution of the merger agreement, each of BioCryst and Idera entered into a voting and support agreement with affiliates of Baker Brothers. Baker Brothers is the beneficial owner of approximately 14% of issued and outstanding BioCryst common stock and approximately 18% of issued and outstanding Idera common stock. Pursuant to the voting and support agreements, Baker Brothers has agreed, among other things, to vote its shares of BioCryst common stock and Idera common stock in favor of the adoption of the merger agreement at each of the BioCryst special meeting and the Idera special meeting, respectively. In addition, Baker Brothers has agreed to be present at each of the BioCryst special meeting and Idera special meeting for purposes of establishing a quorum.

Voting by Idera's Directors and Executive Officers

        At the close of business on the Idera record date, directors and executive officers of Idera and their affiliates were entitled to vote 39,424,036 shares of Idera common stock, or approximately 18% of shares of Idera common stock issued and outstanding on that date. We currently expect that Idera's directors and executive officers will vote their shares in favor of each proposal being submitted to a vote of the Idera stockholders at the Idera special meeting, although no director or officer has entered into any agreement obligating him or her to do so.

Quorum

        No business may be transacted at the Idera special meeting unless a quorum is present. Stockholders who hold shares representing at least a majority of the issued and outstanding shares of common stock entitled to vote at the Idera special meeting must be present in person or represented by proxy to constitute a quorum for the transaction of business at the meeting. If a quorum is not present, the special meeting may be adjourned by the chairman of the Idera special meeting to allow additional time for obtaining additional proxies. At any subsequent reconvening of the special meeting, all proxies will be voted in the same manner as they would have been voted at the original convening of the special meeting, except for any proxies that have been effectively revoked or withdrawn prior to the subsequent meeting.

        Abstentions (shares of Idera common stock for which proxies have been received but for which the holders have abstained from voting or as to which the holder attends the Idera special meeting in person but does not vote) will be included in the calculation of the number of shares of Idera common stock represented at the special meeting for purposes of determining whether a quorum has been achieved. However, broker non-votes will not be included in the calculation of the number of shares of Idera common stock represented at the Idera special meeting for purposes of determining whether a quorum has been achieved.

        If a quorum is not present, the Idera special meeting may be adjourned by the chairman of the Idera special meeting, to reconvene at the same or another place, and notice need not be given of any such adjourned meeting if the time and place thereof are announced at the meeting at which the adjournment is taken.

Required Vote

        The adoption of the merger agreement requires the affirmative vote of the holders of a majority of the issued and outstanding shares of Idera common stock entitled to vote on the proposal. Failures to vote, abstentions and broker non-votes will have the effect of a vote against the proposal. Pursuant to the voting and support agreement, Baker Brothers has agreed to vote in favor of the proposal to adopt the merger agreement.

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        Approval of, on a non-binding advisory basis, the compensation that may become payable to Idera's named executive officers that is based on or otherwise relates to the mergers requires the affirmative vote of the holders of a majority of the shares of Idera common stock represented in person or by proxy at the Idera special meeting and voting on the proposal, although such vote will not be binding on Idera, the Idera board or any of its committees, or, following completion of the mergers, the combined company. Abstentions, failures to vote (i.e., not submitting a proxy and not voting in person) and broker non-votes will have no effect on the proposal, assuming a quorum is present.

Failure to Vote, Broker Non-Votes and Abstentions

        Under the rules of the Nasdaq, banks, brokers or other nominees holding shares of record may vote those shares in their discretion on certain routine proposals when they do not receive timely voting instructions from the beneficial holders. A broker non-vote occurs under these Nasdaq rules when a bank, broker or other nominee holding shares of record is not permitted to vote on a non-routine matter without instructions from the beneficial owner of the shares and no instruction is given.

        In accordance with these Nasdaq rules, banks, brokers and other nominees who hold shares of Idera common stock in "street name" for their customers, but do not have discretionary authority to vote the shares, may not exercise their voting discretion with respect to the proposal to adopt the merger agreement. Accordingly, if banks, brokers or other nominees do not receive specific voting instructions from the beneficial owner of such shares, they may not vote such shares with respect to the proposal to adopt the merger agreement and will have the same effect as a vote "AGAINST" the proposal to adopt the merger agreement. For shares of Idera common stock held in "street name," only shares of Idera common stock affirmatively voted "FOR" the proposal to adopt the merger agreement will be counted as a favorable vote for such proposal. Abstaining from voting, or failing to provide voting instructions to your bank, broker or other nominee, will have the same effect as a vote "AGAINST" the proposal to adopt the merger agreement.

        Abstentions, failures to attend the Idera special meeting (in person or by proxy) and vote and broker non-votes will have no effect on the Idera merger-related compensation proposal.

How to Vote

        Whether or not you plan to attend the Idera special meeting, please vote your shares. If you are a registered or "record holder," which means your shares are registered in your name with Computershare Trust Company, N.A., Idera's transfer agent and registrar, you may vote in person at the Idera special meeting or by proxy. If your shares are held in "street name," which means your shares are held of record in an account with a broker, bank or other nominee, you must follow the instructions from your broker, bank or other nominee in order to vote.

        In addition, if you are a registered stockholder, please be prepared to provide proper identification, such as a driver's license. If you hold your Idera shares in "street name," you will need to provide proof of ownership, such as a recent account statement or letter from your bank, broker or other nominee, along with proper identification.

        Idera stockholders of record may submit a proxy in one of three ways or vote in person at the Idera special meeting:

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        Idera stockholders are encouraged to submit a proxy promptly. Your proxy will only be valid if you complete and return the proxy card, vote by telephone or vote over the internet at or before the Idera special meeting. The persons named in the proxy card will vote the shares you own in accordance with your instructions on your proxy card, in your vote by telephone or in your vote over the internet. If you return the proxy card, vote by telephone or vote over the internet, but do not give any instructions on a particular matter described in this joint proxy statement/prospectus, the persons named in the proxy card will vote the shares you own in accordance with the recommendations of the Idera board. However, if you previously submitted a proxy for the Idera special meeting originally scheduled for May 9, 2018, which proxy has not subsequently been revoked, and are a holder of record on May 29, 2018 and you do not want to change or revoke your proxy, you do not need to take any action. Accordingly, Idera intends to vote such proxy at the Idera special meeting on July 10, 2018, as directed by your previously submitted proxy.

Voting of Idera Common Stock Held in Street Name

        If you hold Idera shares through a bank, broker or other nominee, you may instruct your bank, broker or other nominee to vote your Idera shares by following the instructions that the bank, broker or nominee provides to you with these materials. Most banks and brokers offer the ability for stockholders to submit voting instructions by mail by completing a voting instruction card, by telephone and via the Internet. If you do not provide voting instructions to your bank, broker or other nominee, your Idera shares will not be voted on any proposal as your bank, broker or other nominee does not have discretionary authority to vote on any of the proposals to be voted on at the Idera special meeting. However, if you are an Idera stockholder as of the revised May 29, 2018 record date who previously provided voting instructions to your bank, broker or other nominee, and do not wish to change your vote, you will not need to provide voting instructions again and your Idera shares will be voted at the rescheduled July 10, 2018 Idera special meeting in accordance with your original voting instructions.

        Even if your shares are held in street name, you are welcome to attend the Idera special meeting. If your shares are held in street name, you may not vote your shares in person at the Idera special meeting unless you obtain a proxy, executed in your favor, from the holder of record (i.e., your bank, broker or other nominee). If you hold your shares in street name and wish to vote in person, please contact your bank, broker or other nominee before the Idera special meeting to obtain the necessary proxy from the holder of record.

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How Proxies are Counted

        All shares represented by properly executed proxies received in time for the Idera special meeting will be voted at the meeting in the manner specified by the stockholders giving those proxies. Properly executed proxies that do not contain voting instructions will be voted "FOR" each of the proposals.

        Only shares affirmatively voted for the proposal, and properly executed proxies that do not contain voting instructions, will be counted as favorable votes for the proposal to adopt the merger agreement. Abstentions and broker non-votes will have the same effect as votes "AGAINST" the proposal to adopt the merger agreement. Abstentions, failures to vote and broker non-votes will have no effect on the proposal to approve, on a non-binding advisory basis, the compensation that may become payable to Idera's named executive officers that is based on or otherwise relates to the mergers. However, because none of the proposals to be voted on at the Idera special meeting are routine matters for which brokers may have discretionary authority to vote, Idera does not expect any broker non-votes at the special meeting.

Revocation of Proxies

        If you are the record holder of Idera common stock, you can change your vote or revoke your proxy at any time before your proxy is voted at the special meeting. You can do this by:

        A registered stockholder may revoke a proxy by any of these methods, regardless of the method used to deliver the stockholder's previous proxy.

        Written notices of revocation and other communications with respect to the revocation of proxies should be addressed as follows:

Idera Pharmaceuticals, Inc.
167 Sidney Street
Cambridge, Massachusetts 02139
Attention: Assistant Secretary

        Please note that if your shares are held in "street name" through a broker, bank or other nominee, you may change your vote by submitting new voting instructions to your broker, bank or nominee in accordance with its established procedures. If your shares are held in the name of a broker, bank or other nominee and you decide to change your vote by attending the Idera special meeting and voting in person, your vote in person at the Idera special meeting will not be effective unless you have obtained and present an executed proxy issued in your name from the record holder (your broker, bank or other nominee).

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Tabulation of Votes

        Idera has appointed Robert Doody to serve as the inspector of election for the Idera special meeting. Robert Doody will, among other things, determine the number of shares of Idera common stock represented at the Idera special meeting to confirm the existence of a quorum, determine the validity of all proxies and ballots and independently tabulate affirmative and negative votes and abstentions.

Solicitation of Proxies

        Idera is soliciting proxies for its special meeting from its stockholders. Idera will pay its own cost of soliciting proxies, including the cost of mailing this joint proxy statement/prospectus, from its stockholders. In addition to solicitation by use of the mails, proxies may be solicited by Idera's directors, officers and employees in person or by telephone or other means of communication. These persons will not receive additional compensation, but may be reimbursed for reasonable out-of-pocket expenses in connection with this solicitation.

        Idera has retained the services of MacKenzie Partners, Inc. to assist in the solicitation of proxies for an estimated fee not to exceed $17,500, plus reimbursement of out-of-pocket expenses. Idera will make arrangements with brokerage houses, custodians, nominees and fiduciaries to forward proxy solicitation materials to beneficial owners of shares held of record by them. Idera will also reimburse these brokerage houses, custodians, nominees and fiduciaries for their reasonable out-of-pocket expenses incurred in forwarding the proxy materials.

Adjournments

        If a quorum is not present, the Idera special meeting may be adjourned by the chairman of the Idera special meeting, to reconvene at the same or another place, and notice need not be given of any such adjourned meeting if the time and place thereof are announced at the meeting at which the adjournment is taken.

Householding of Special Meeting Materials

        The SEC has adopted rules that permit companies and intermediaries such as banks, brokers or nominees to satisfy delivery requirements for proxy statements and annual reports with respect to two or more stockholders sharing the same address by delivering a single proxy statement or annual report, as applicable, addressed to those stockholders. This process, which is commonly referred to as "householding," reduces the volume of duplicate information received at your household and helps reduce Idera's expenses. Unless Idera has received contrary instructions, Idera may send a single copy of this joint proxy statement/prospectus and notice to any household at which two or more stockholders with the same surname reside if Idera believes the stockholders are members of the same family. Each stockholder in the household will continue to receive a separate proxy card. We will promptly deliver a separate copy of our proxy statement to any stockholder upon written request to Idera Pharmaceuticals, Inc., Attention: Investor Relations, 167 Sidney Street, Cambridge, Massachusetts 02139, or request via telephone: 1-877-888-6550 or email at ir@iderapharma.com. Any stockholder who wants to receive separate copies of our proxy statement or annual report to stockholders in the future, or any stockholder who is receiving multiple copies and would like to receive only one copy per household, should contact the stockholder's bank, broker or other nominee, or the stockholder may contact Idera at the above address and phone number.

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Questions and Additional Information

        If you need assistance in completing your proxy card, have questions regarding the Idera special meeting or would like additional copies of any materials, Idera stockholders may contact Idera's proxy solicitor, MacKenzie Partners, Inc. at:

LOGO

1407 Broadway, 27th Floor
New York, New York 10018
Stockholders May Call Toll-Free: 800-322-2885
Banks and Brokers May Call Collect: 212-929-5500
Email: proxy@mackenziepartners.com

        Idera stockholders should not return their stock certificates or send documents representing shares of Idera stock with the proxy card. If the mergers are completed, the exchange agent for the Idera merger will send to Idera stockholders a letter of transmittal and related materials and instructions for exchanging shares of Idera stock.

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IDERA PROPOSALS

Idera Proposal 1: The Idera Merger Proposal

        Idera stockholders are asked to approve the proposal to adopt the merger agreement. For a summary and detailed information regarding this proposal, see the information about the mergers and the merger agreement throughout this joint proxy statement/prospectus, including the information set forth in sections entitled "The Mergers" and "The Merger Agreement" beginning on pages 53 and 116, respectively, of this joint proxy statement/prospectus. A copy of the merger agreement is attached as Annex A to this joint proxy statement/prospectus.

        Pursuant to the merger agreement, approval of this proposal by Idera stockholders is a condition to the consummation of the mergers. If this proposal is not approved, the mergers will not be consummated.

        Idera is requesting that Idera stockholders approve the proposal to adopt the merger agreement. Approval of this proposal requires the affirmative vote of the holders of a majority of the voting power of all shares of Idera common stock entitled to vote at the Idera special meeting.

Recommendation of the Idera Board

        The Idera board unanimously recommends that Idera stockholders vote "FOR" the proposal to approve the mergers.

Idera Proposal 2: The Idera Merger-Related Compensation Proposal

        Idera stockholders are asked to approve, on a non-binding advisory basis, the compensation that may become payable to Idera's named executive officers that is based on or otherwise relates to the mergers. For a summary and detailed information regarding this proposal, see the information about the mergers and the merger agreement throughout this joint proxy statement/prospectus, including the information set forth in the section entitled "The Mergers—Idera Stockholder Advisory Vote on Merger-Related Compensation for Idera's Named Executive Officers Proposal" beginning on page 103 of this joint proxy statement/prospectus.

        Pursuant to the Dodd-Frank Wall Street Reform and Consumer Protection Act of 2010 and Rule 14a-21(c) of the Exchange Act, Idera is seeking non-binding, advisory stockholder approval of the compensation of Idera's named executive officers that is based on or otherwise relates to the mergers as disclosed above in the section entitled "The Mergers—Idera Stockholder Advisory Vote on Merger-Related Compensation for Idera's Named Executive Officers Proposal" beginning on page 103 of this joint proxy statement/prospectus. The proposal gives Idera's stockholders the opportunity to express their views on the merger-related compensation of Idera's named executive officers.

        Accordingly, Idera is requesting stockholders to adopt the following resolution, on a non-binding, advisory basis:

        Idera stockholders should note that the Idera merger-related compensation proposal is merely an advisory vote, which will not be binding on Idera or the Idera board. Further, the underlying plans and arrangements are contractual in nature and not, by their terms, subject to stockholder approval. Accordingly, regardless of the outcome of the advisory vote, if the mergers are consummated, the

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eligibility of the Idera named executive officers for such payments and benefits will not be affected by the outcome of the advisory vote.

        The proposal to approve, on a non-binding advisory basis, the compensation that may be paid or become payable to Idera's named executive officers in connection with the mergers is a vote separate and apart from the vote on the proposal to adopt the merger agreement. Accordingly, an Idera stockholder may vote to approve one proposal and not the other. Approval of the Idera merger-related compensation proposal is not a condition to the completion of the mergers.

Recommendation of the Idera Board

        The Idera board unanimously recommends a vote "FOR" the approval of the Idera merger-related compensation proposal.

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THE MERGERS

        The following is a description of the material aspects of the mergers, including the merger agreement. While we believe that the following description covers the material terms of the mergers, the description may not contain all of the information that is important to you. We encourage you to read this joint proxy statement/prospectus carefully and in its entirety, including the merger agreement which is attached as Annex A to this joint proxy statement/prospectus, for a more complete understanding of the mergers.

Effects of the Mergers

        Upon the terms and subject to the conditions of the merger agreement and in accordance with the DGCL, at the effective time of the mergers, Merger Sub A, a wholly owned subsidiary of Holdco and a party to the merger agreement, will merge with and into Idera. Idera will survive the merger as a wholly owned subsidiary of Holdco. Upon the terms and subject to the conditions of the merger agreement and in accordance with the DGCL, at the effective time of the mergers, Merger Sub B, a wholly owned subsidiary of Holdco and a party to the merger agreement, will merge with and into BioCryst. BioCryst will survive the merger as a wholly owned subsidiary of Holdco. As a result, among other things, Holdco will become the ultimate parent of Idera, BioCryst and their respective subsidiaries. The mergers will become effective at the time at which the certificates of merger have been duly filed with the Secretary of State of the State of Delaware or at any later date or time mutually agreed to in writing by Idera and BioCryst and specified in the certificates of merger in accordance with the DGCL.

        At the effective time of the mergers, each issued and outstanding share of Idera common stock (other than shares held by Idera, BioCryst, Holdco, Merger Sub A or Merger Sub B, or any subsidiary of each of the aforementioned entities, or by Idera as treasury shares, which will cease to remain outstanding and will be canceled and retired and cease to exist) will be converted into the right to receive 0.20 fully paid and nonassessable shares of Holdco common stock, with cash paid in lieu of fractional shares.

        At the effective time of the mergers, each issued and outstanding share of Idera preferred stock (other than shares held by Idera, BioCryst, Holdco, Merger Sub A or Merger Sub B, or any subsidiary of each of the aforementioned entities, or by Idera as treasury shares, which will cease to remain outstanding and will be canceled and retired and cease to exist) will be converted into the right to receive a number of fully paid and nonassessable shares of Holdco common stock equal to (i) $1.00 divided by the 20-trading-day average trading price of Idera common stock, ending with the trading day prior to the third day prior to the closing date, multiplied by (ii) 0.20, with cash paid in lieu of fractional shares.

        At the effective time of the mergers, each issued and outstanding share of BioCryst common stock (other than shares held by Idera, BioCryst, Holdco, Merger Sub A, or Merger Sub B, or any subsidiary of each of the aforementioned entities, or by BioCryst as treasury shares, which will cease to remain outstanding and will be canceled and retired and cease to exist) will be converted into the right to receive 0.50 fully paid and nonassessable shares of Holdco common stock, with cash paid in lieu of fractional shares.

        The exchange ratios are fixed and will not be adjusted to reflect stock price changes prior to the closing of the mergers.

        Idera and BioCryst are working to complete the mergers as soon as practicable and expect the closing of the mergers to occur in the third quarter of 2018. However, the mergers are subject to the satisfaction or waiver of certain conditions, and it is possible that factors outside the control of Idera and BioCryst could result in the mergers being completed at a later time or not at all.

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Background of the Mergers

        The BioCryst board and Idera board, together with their respective management, regularly reviews their respective company's discovery and development programs, business opportunities and potential transactions to strengthen their respective position and enhance stockholder value. Each of them also, from time to time in the past, has had informal discussions with a number of participants in the biopharmaceutical industry relating to potential transactions or relationships, including mergers, collaborations, partnerships, combination studies, licensing and other arrangements.

        In early February 2016, BioCryst announced the results of its Avoralstat in hereditary angioedema OPuS-2 (Oral ProphylaxiS-2) clinical trial and that BioCryst would not be moving forward with further clinical trials for Avoralstat. At a meeting of the BioCryst board held at that time to review the OPuS-2 results, the BioCryst board noted the early stage of clinical development for BioCryst's follow-on lead compound, BCX-7353, and discussed potential opportunities for risk diversification to increase the number of potential product candidates that could advance through clinical trials, including potential strategic opportunities such as mergers, bolt-on acquisitions or in-licensing transactions with other participants in the biopharmaceutical industry.

        In early March 2016, Mr. Stonehouse, chief executive officer of BioCryst, called the chief executive officer of a privately held biopharmaceutical company ("Company A") to discuss developments in the biopharmaceutical industry generally. On the call, each expressed their mutual interest in learning more about the other company's clinical development programs, and the two agreed to meet in person later that month. Following the call, on March 11, 2016, Company A and BioCryst entered into a non-disclosure agreement which included a standstill provision that is inoperative in circumstances where BioCryst enters into a merger agreement with a third party or is the subject of a tender offer, and does not prohibit Company A from requesting that the BioCryst board waive the restrictions in the standstill provision. Beginning in mid-March 2016 and continuing through April 2016, Company A and BioCryst conducted due diligence on each other.

        On March 29, 2016, Mr. Stonehouse and three independent directors of BioCryst met with the chief executive officer and senior management of Company A, together with their respective legal and financial advisors, to learn more about each company's programs. They discussed whether to explore a potential business combination that would be structured as a stock-for-stock transaction based on the relative values of the two companies. Representatives of BioCryst and Company A also discussed their respective views on the values of BioCryst and Company A. Over the next several weeks diligence was conducted by both companies. In late April 2016, the chief executive officer of Company A called Mr. Stonehouse and informed him that Company A was not interested in pursuing a business combination transaction at that time because Company A's due diligence review of BioCryst, given the lack of clinical data on BCX-7353, did not support the relative valuation levels previously discussed by representatives of Company A and BioCryst.

        On May 24, 2016, the BioCryst board held a regularly scheduled meeting, which was also attended by members of BioCryst management and representatives of an advisor engaged by BioCryst to assist in identifying potential strategic opportunities, such as mergers, bolt-on acquisitions and in-licensing transactions. The BioCryst board discussed potential opportunities for risk diversification and the desired criteria for a counterparty, including that the counterparty have a focus on chronic orphan and rare diseases and near term clinical catalysts. Following a review of potential counterparties, the BioCryst board instructed BioCryst management to do further analysis on the various biopharmaceutical companies discussed by the BioCryst board, in order to identify strategic opportunities that could enhance stockholder value and provide risk diversification.

        On June 10, 2016, following an introduction by a BioCryst board member, Mr. Stonehouse called the chief executive officer of a large publicly traded biopharmaceutical company ("Company B") who expressed interest in discussing their respective businesses. Following this call, Mr. Stonehouse and the

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chief executive officer of Company B agreed to meet in person to discuss potential opportunities for a strategic transaction between the two companies. Mr. Stonehouse and the chief executive officer of Company B met on June 22, 2016 and on July 26, 2016 and discussed a transaction proposed by the chief executive officer of Company B in which Company B would acquire BioCryst for cash. On July 27, 2016, BioCryst and Company B entered into a non-disclosure agreement, which included a standstill provision that is inoperative in circumstances where BioCryst enters into a merger agreement or is the subject of a tender offer and does not prohibit Company B from requesting that the BioCryst board waive the restrictions in the standstill. BioCryst made an online data room available to Company B, and Company B and its advisors conducted preliminary due diligence on BioCryst. In early August the chief executive officer of Company B called Mr. Stonehouse and told him that Company B was no longer interested in pursuing a transaction with BioCryst because, based on the advice of Company B's financial advisor, Company B believed it would need to provide a meaningful premium to BioCryst stockholders to successfully conclude a deal, and Company B was not willing to pay a price for BioCryst that provided a meaningful premium to BioCryst stockholders based on the trading price of BioCryst common stock at the time.

        On August 5, 2016, the BioCryst board held a special telephonic meeting. At the meeting, Mr. Stonehouse informed the BioCryst board of Company B's decision to terminate discussions at that time. The BioCryst board also discussed whether to explore other potential sale transactions, and the BioCryst board's belief that other potential purchasers were not likely to appropriately value BioCryst until more data was available from clinical trials. The BioCryst board instructed management to continue analyzing strategic opportunities that would enhance stockholder value and provide risk diversification.

        As a follow up to an informal meeting at an investor conference in June 2016, Mr. Stonehouse and Mr Milano, chief executive officer of Idera, spoke by telephone in July 2016 and discussed developments in the biopharmaceutical industry generally and their mutual interest in learning more about the clinical and discovery programs of each other's company. Mr. Milano and Mr. Stonehouse met in person in August 2016 and discussed their respective companies, whether a combination of the two companies could enhance stockholder value for each respective company, and whether to explore a potential business combination at that time.

        The BioCryst board held a regularly scheduled meeting on September 27 and 28, 2016, and conducted its annual strategic review which included an update from BioCryst management on developments in BioCryst's clinical programs and a discussion of potential strategic combination opportunities and opportunities for diversification through bolt-on acquisitions of companies with an orphan/rare disease focus. The BioCryst board discussed the status of the clinical program for BCX-7353 in hereditary angioedema, which had begun enrolling patients in August 2016, and determined that further efforts with respect to strategic opportunities should be considered, but meaningful progress was unlikely until closer to the time that additional data would be available from the BCX-7353 APeX-1 study.

        On October 27, 2016, as a follow up to the discussions between Mr. Stonehouse and Mr. Milano during the summer of 2016, Mr. Stonehouse and Lynne Powell, Senior Vice President and Chief Commercial Officer of BioCryst, met with Mr. Milano and Clayton Fletcher, Senior Vice President of Business Development and Strategic Planning of Idera, and discussed their respective company's clinical development and preclinical programs. Each of BioCryst and Idera concluded at that time that each party should focus its efforts on further progressing its own clinical development efforts for its lead products, and not to pursue a potential business combination, with Mr. Milano and Mr. Stonehouse leaving open the possibility of further discussions after additional data was available from their respective company's clinical development efforts.

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        In December 2016, the CEO of a privately held biopharmaceutical company ("Company C") called Mr. Stonehouse, and, in light of the anticipated announcement of additional data from the BCX-7353 APeX-1 study, expressed an interest in exploring a possible strategic transaction with BioCryst. On December 22, 2016, BioCryst and Company C entered into a non-disclosure agreement which did not include a standstill provision. Mr. Stonehouse and members of BioCryst management met with members of Company C management in January 2017 and discussed their respective company's clinical development programs. Shortly thereafter, Company C informed Mr. Stonehouse that Company C was not interested in pursuing a transaction with BioCryst, and there were no further discussions between Company C and BioCryst following that meeting.

        In January 2017, Mr. Stonehouse attended an industry conference and had informal meetings with representatives of several biopharmaceutical companies, including the CEO of a private biopharmaceutical company ("Company D"). Mr. Stonehouse met again with the CEO of Company D on February 13, 2017 and discussed their mutual interest in exploring a strategic combination, following such time as data from the clinical trials for BCX-7353 in hereditary angioedema became available.

        On February 27, 2017, BioCryst announced positive results from an interim analysis of its Phase 2 APeX-1 clinical trial for BCX-7353 in hereditary angioedema.

        In February 2017, following the announcement of the interim results of the Phase 2 APeX-1 clinical trial for BCX-7353, representatives of a mid-size publicly traded biopharmaceutical company ("Company E") contacted Mr. Stonehouse and indicated Company E's interest in exploring a potential business combination transaction with BioCryst, following the availability of final results from the BCX-7353 APeX-1 Phase 2 trial expected in late 2017.

        Also in February 2017, in a discussion with an investment banker, Idera became aware of a privately held rare disease company ("Company F") that was considering its strategic alternatives, including a possible sale of Company F. After a discussion at the March 7, 2017 regularly scheduled Idera board meeting, the Idera board requested that Mr. Milano follow up on this possible acquisition opportunity. In April 2017, the CEO of Company F called Mr. Milano to discuss a possible strategic transaction with Idera. During May 2017, Idera and Company F entered into a non-disclosure agreement and Mr. Milano and members of Idera management met telephonically with members of Company F management to discuss the lead asset of Company F.

        On May 9, 2017, BioCryst and Company E entered into a non-disclosure agreement which did not include a standstill provision. BioCryst made an online data room available to Company E, and throughout the summer of 2017, Company E conducted a due diligence review of BioCryst, and members of Company E management and Mr. Stonehouse engaged in preliminary discussions regarding possible terms of a potential strategic transaction, including a stock-for-stock merger transaction.

        During the months of May and June 2017, Idera management, along with the Idera board, had a series of informational meetings to discuss a possible merger agreement with Company F. Shortly thereafter, Company F informed Mr. Milano that Company F was pursuing a different strategic alternative and would not continue to pursue a transaction with Idera.

        In August 2017, the chairman of Company D called Mr. Stonehouse and informed him that Company D remained interested in discussing a transaction with BioCryst.

        On September 5, 2017, BioCryst announced the final results from the BCX-7353 Phase 2 trial, which showed a positive treatment effect, and announced plans to meet with the Food and Drug Administration and the European Medicines Agency during the fourth quarter of 2017 to finalize plans for Phase 3 study of BCX-7353.

        On September 10, 2017, Idera announced final results from the dose-selection phase of an ongoing Phase 1/2 trial investigating IMO-2125, Idera's intratumorally-delivered Toll-like Receptor, or TLR,

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9 agonist, in combination with ipilimumab (Yervoy®), manufactured by Bristol-Myers Squibb, which demonstrated positive and encouraging response data in anti-PD-1 refractory melanoma.

        Following the announcement and the subsequent translational medicine presentation at the Society of Immunotherapy of Cancer on November 9, 2017, there was substantial interest in IMO-2125 and Idera engaged in discussions with select parties regarding potential licensing and collaboration arrangements between Idera and such parties, however, none of the parties proposed definitive terms regarding a potential licensing or collaboration arrangement with Idera during the course of discussions with BioCryst regarding the potential business combination.

        On September 12, 2017, a public offering of BioCryst common stock priced at $5.15 per share, which resulted in net proceeds to BioCryst of $85.8 million.

        In mid-September 2017, the CEO of Company A contacted Mr. Stonehouse and indicated that Company A was again interested in exploring a potential business combination transaction with BioCryst. Mr. Stonehouse told the CEO of Company A that he would communicate Company A's renewed interest in a business combination transaction to the BioCryst board.

        On September 19, 2017, the Idera board held a regularly scheduled meeting with members of Idera management in attendance. At the meeting, among other topics discussed, Mr. Milano led a discussion with the Idera board related to the landscape of the biopharmaceutical industry, Idera's stand-alone business plan, the advantages of diversifying Idera's clinical portfolio and various organic and strategic alternatives, including the potential licensing and collaboration arrangements discussed with third parties who had expressed an interest in IMO-2125. As part of this discussion, Mr. Milano presented an overview of BioCryst based on publicly available information. Julian Baker and Kelvin Neu, members of the Idera board, noted that affiliates of Baker Bros. Advisors ("BBA") held a minority interest in BioCryst, and they recused themselves from the portion of the meeting regarding a potential business combination with BioCryst and from future discussions regarding a potential business combination. Beginning at this meeting and continuing until January 21, 2018, Messrs. Baker and Neu were not present for, and did not participate in, any discussions or determinations of the Idera board regarding the potential business combination between BioCryst and Idera. At the conclusion of the discussion, the Idera board determined that Mr. Milano should continue to explore potential licensing or collaboration arrangements and reach out to Mr. Stonehouse to see if there was interest in restarting a discussion regarding a potential stock-for-stock business combination between BioCryst and Idera.

        On September 20, 2017, Mr. Milano and Mr. Stonehouse spoke by telephone and discussed progress in the respective clinical programs of BioCryst and Idera. On the call, Mr. Milano inquired about Mr. Stonehouse's interest in having a further general discussion about recent biopharmaceutical industry developments and the possibility of a potential business combination between BioCryst and Idera. Mr. Stonehouse agreed to an in-person discussion, which was thereafter set for September 26, 2017.

        On September 22, 2017, the chairman of Company D called Mr. Stonehouse and informed him that Company D was not able to consider further discussions at that time because of other corporate priorities of Company D.

        On September 26, 2017, Mr. Milano and Mr. Stonehouse met and discussed the possibility of exploring a potential business combination transaction, given the additional data that was now available from their respective clinical development efforts. Mr. Stonehouse told Mr. Milano that he would discuss the opportunity for a potential business combination between BioCryst and Idera with the BioCryst board.

        On October 2, 2017, Company E informed BioCryst that it was no longer interested in pursuing a merger or acquisition transaction with BioCryst, and was only interested in licensing BCX-7353.

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Mr. Stonehouse informed representatives of Company E that BioCryst was not interested in a licensing transaction, given the recent positive clinical trial results, BioCryst's ability to pursue the commercialization of BCX-7353 without a partner and the desire to preserve upside potential for BioCryst stockholders.

        The BioCryst board held a regularly scheduled board meeting on October 11 and 12, 2017 at which the BioCryst board conducted its annual strategic review of developments in the biopharmaceutical industry as they related to the treatment of rare diseases and potential platforms for developing new treatments, BioCryst's clinical programs, commercialization and launch plans, financial position and potential strategic combination opportunities. At this meeting, members of management of BioCryst presented preliminary internal financial forecasts, which assigned various probabilities to the successful clinical development of BioCryst's pipeline product candidates, and the BioCryst board and members of management discussed refinements to the assumptions underlying such forecasts. Representatives of J.P. Morgan, a financial advisor that BioCryst had retained in considering strategic matters, presented an illustrative valuation of BioCryst based on management's preliminary internal financial forecasts. Mr. Stonehouse informed the BioCryst board of his discussions with Company A and Idera and the interest that each had indicated in exploring a potential strategic transaction with BioCryst. The BioCryst board discussed BioCryst's stand-alone business plan, including its development, commercialization and launch plans for BCX-7353, financing risks, the desirability of diversifying its pipeline of products in development and strategic alternatives that could be available to BioCryst, which included a business combination transaction with Company A, Idera or other biotechnology or pharmaceutical companies in a stock-for-stock transaction. The BioCryst board also discussed whether any biotechnology or pharmaceutical companies would be interested in acquiring BioCryst in a cash transaction, and determined that a stock-for-stock transaction based on the relative values of the constituent companies could be more value-enhancing for BioCryst stockholders than a cash sale transaction in light of the status of BioCryst's development programs, and the BioCryst board's belief that an all-stock transaction would allow BioCryst stockholders to participate in any upside potential for its products while providing diversification. The BioCryst board authorized BioCryst management to exchange information and engage in due diligence with Company A and Idera and pursue further discussions with both companies to explore whether a potential strategic transaction effecting a combination with either party would be value-enhancing to BioCryst stockholders.

        On October 13, 2017, Mr. Stonehouse contacted Mr. Milano to inform him that the BioCryst board was interested in exploring a potential business combination with Idera. They agreed to proceed with preliminary diligence on the other company's respective lead product candidates, with the possibility of additional diligence if it was determined that a potential business combination was likely to be in the best interests of their respective stockholders.

        On October 17, 2017, BioCryst entered into a mutual non-disclosure agreement with Company A, which included a standstill provision that is inoperative in circumstances where BioCryst enters into a merger agreement with a third party or is the subject of a tender offer, and which does not prohibit Company A from requesting that the BioCryst board waive the restrictions in the standstill provision. Company A and BioCryst exchanged confidential information, engaged in management discussions about their respective businesses and conducted due diligence on each other during October and November.

        On October 18, 2017, BioCryst entered into a mutual non-disclosure agreement with Idera, which did not include a standstill provision, following which BioCryst and Idera granted the other party and its representatives access to its respective online data room with materials limited to each company's respective lead product candidates. BioCryst and Idera periodically engaged in management discussions about, and conducted preliminary due diligence with respect to, each company's respective lead product candidates during October and November.

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        On October 25, 2017, a public offering of Idera common stock priced at $1.50 per share, resulting in net proceeds to Idera of $53.8 million.

        On October 26, 2017, members of Idera and BioCryst management and representatives of Goldman Sachs, financial advisor to Idera, and J.P. Morgan met to discuss the two companies' respective clinical and preclinical development programs.

        Beginning on November 13, 2017 and continuing through the signing of the merger agreement, Mr. Milano had periodic discussions with members of the Idera board to provide updates regarding the status of discussions regarding potential licensing or collaboration arrangements and the exploration of the potential business combination with BioCryst. Mr. Stonehouse periodically updated members of the BioCryst board on the status of discussions with Idera.

        On November 22, 2017, the CEO of Company A contacted Mr. Stonehouse to discuss Company A's continued interest in pursuing a stock-for-stock business combination transaction with BioCryst based on the relative values of the companies, as well as the status of the due diligence review being conducted by Company A and BioCryst. Representatives of Company A engaged in discussions with BioCryst management and representatives of J.P. Morgan in late November and early December on due diligence matters. During their discussions, representatives of Company A provided to J.P. Morgan Company A's views on the relative values of BioCryst and Company A, which ascribed a higher value to Company A than to BioCryst.

        On November 28, 2017, the Idera board held a regularly scheduled in-person meeting, with members of Idera management and, for the portion of the meeting regarding the potential business combination, representatives of Goldman Sachs in attendance. At the meeting, Mr. Milano provided an update on the discussions with BioCryst regarding the potential business combination between BioCryst and Idera. At this meeting, members of Idera management reviewed Idera's due diligence to date on BCX-7353, the commercial potential of BCX-7353, and the capital structure and funding requirements, including the potential for raising capital through partnering arrangements. Representatives of Goldman Sachs presented public market perspectives on BioCryst. The Idera board discussed the results of the due diligence review and the strategic rationale for a combination with BioCryst. The Idera board determined that a potential business combination transaction with BioCryst, on the right terms, could be attractive to Idera and its stockholders. The Idera board instructed Idera management to continue its diligence and valuation work on BioCryst.

        Subsequently on November 28, 2017, Mr. Milano contacted Mr. Stonehouse to discuss the status of the parties' mutual due diligence review, and Idera's continued interest in the possibility of a potential stock-for-stock business combination transaction with BioCryst. Mr. Milano and Mr. Stonehouse also discussed potential synergies from combining headquarters and research and development facilities, the relative representation of BioCryst directors and Idera directors on the board of directors of the combined company and perspectives on key management roles. Mr. Milano and Mr. Stonehouse also discussed potential next steps, including completing diligence and pursuing negotiation of a definitive agreement if the two companies' respective boards of directors wished to further pursue a potential business combination.

        On December 6, 2017, the BioCryst board held a special meeting. Also in attendance were members of BioCryst management, representatives of J.P. Morgan and representatives of Skadden, legal advisor to BioCryst. Mr. Stonehouse updated the BioCryst board on discussions with each of Company A and Idera, including discussions between representatives of J.P. Morgan and representatives of Company A with respect to Company A's views on the relative values of BioCryst and Company A, and his discussions with Mr. Milano on the methodology for determining the relative values of BioCryst and Idera, and the corporate governance of a combined BioCryst/Idera entity. At this meeting, members of BioCryst management reviewed BioCryst's due diligence to date on each of Company A and Idera, focusing on the lead programs of each of Company A and Idera, the

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commercial potential of their respective lead programs, and their respective capital structures and funding requirements, including the potential for raising capital through partnering arrangements. Members of BioCryst management reviewed preliminary financial forecasts for the lead programs of Company A, Idera and BioCryst prepared by BioCryst management, which assigned various probabilities to the successful clinical development of the lead product candidates of each company. The BioCryst financial forecasts presented by BioCryst management at the meeting reflected the refinements to probability of success and commercialization assumptions discussed with the BioCryst board at the October 11-12 BioCryst board meeting, and the BioCryst board members discussed further adjustments to the assumptions underlying the forecasts. Representatives of J.P. Morgan presented a preliminary valuation review, based on management's preliminary financial forecasts, with respect only to the lead products of each of Company A, Idera and BioCryst, together with a sensitivity analysis which varied certain assumptions for each of the lead products. The BioCryst board discussed the results of the due diligence review, the preliminary valuation review and the strategic rationale for a combination with each of Idera and Company A. The BioCryst board determined that the preliminary valuation review on Company A did not support the relative valuation levels that Company A had indicated to representatives of J.P. Morgan that it would require in a business combination transaction, and determined that a business combination transaction with Idera, on the right terms, could be attractive to BioCryst and its stockholders. The BioCryst board instructed BioCryst management to continue its diligence and valuation work with respect to Idera only, and to inform Company A that it was not interested in pursuing a transaction with Company A at that time.

        On December 6, 2017, at the instruction of the BioCryst board, Mr. Stonehouse called Company A and informed Company A of the BioCryst board's determination that due diligence and preliminary valuation work on Company A did not support the valuation levels that Company A had previously indicated it would require in a business combination transaction with BioCryst, and that the BioCryst board determined not to further pursue a transaction with Company A at that time. Mr. Stonehouse also called Mr. Milano and informed him of the BioCryst board's interest in pursuing further discussions and due diligence to determine whether an agreement could be reached with respect to a business combination between Idera and BioCryst.

        Beginning the week of December 12, 2017 through January 21, 2018, each of BioCryst and Idera granted the other party and its representatives expanded access to its respective online data room to include materials responsive to due diligence request lists supplied by Idera and BioCryst, respectively, and any further due diligence requests made by either party.

        On December 13, 2017, members of Idera and BioCryst management and representatives of Goldman Sachs and J.P. Morgan held an in-person meeting to discuss each company's respective commercialization plans for its product candidates, status of financial due diligence, and Idera and BioCryst management's respective views on future performance.

        During the month of December 2017 and continuing into January 2018, management of BioCryst and Idera, together with their legal and financial advisors, continued their mutual diligence review and participated in meetings and telephonic conferences where financial, commercial, regulatory, R&D, tax, human resource, chemistry/manufacturing/control (CMC), legal and corporate information was exchanged by the parties. Idera also discussed with BioCryst its plans for potential partnering arrangements involving rights to develop and market one of Idera's lead product candidates in certain jurisdictions.

        On December 15, 2017, the Idera board met with members of Idera management and representatives of Goldman Sachs and Latham, legal advisor to Idera, in attendance. At the meeting, representatives of Latham provided an overview of the duties of the Idera board in evaluating a potential business combination with BioCryst. Idera management, along with representatives of Goldman Sachs and Latham, then provided an update on the status of due diligence, document

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requests and negotiations related to the potential business combination as well as the potential timing for receiving a first draft of the merger agreement from BioCryst. Following the update, Idera management presented an update on the preparation of Idera management's unadjusted financial forecasts and risk-adjusted financial forecasts reflecting Idera management's viewpoints on the likelihood of successful commercialization of Idera's products. The Idera board provided guidance on the assumptions to be used for purposes of Idera management's unadjusted and risk-adjusted financial forecasts and determined that Idera management, together with Idera's legal and financial advisors, should continue discussions and negotiations with BioCryst and provided guidance with respect to such negotiations, including with respect to ownership and governance of the combined company.

        On December 17, 2017, the BioCryst board held a special telephonic meeting, with members of BioCryst management and representatives of J.P. Morgan and Skadden in attendance, to discuss the process for evaluating a potential business combination with Idera, and to receive an update from BioCryst management on BioCryst's ongoing diligence with respect to Idera. BioCryst management updated the BioCryst board on the status of due diligence and information requests by Idera and BioCryst, which included a request to exchange non risk-adjusted forecasts for each company's lead product candidates. The BioCryst board instructed BioCryst management to provide Idera with the non-risk-adjusted forecasts that had previously been reviewed with, and reflected the input of, the BioCryst board, and to continue discussions with Idera regarding the terms of a business combination transaction. Skadden provided the BioCryst board with a summary of the key terms to be included in the initial draft merger agreement, which included a reverse subsidiary merger structure pursuant to which Idera would merge into a newly formed subsidiary of BioCryst with Idera stockholders receiving a fixed number of BioCryst shares in the merger, acceleration and vesting of outstanding options, reciprocal representations, warranties and covenants, mutual non-solicitation provisions and board recommendation requirements, and the obligation to put the merger to a stockholder vote even if the BioCryst board were to change its recommendation, and the BioCryst board instructed Skadden to send the draft merger agreement to Latham.

        On December 18, 2017, Skadden sent the initial draft merger agreement to Latham.

        On December 20, 2017, the BioCryst board held a special telephonic meeting, with members of BioCryst management and representatives of J.P. Morgan and Skadden in attendance. Representatives of Skadden reviewed the terms of the initial draft merger agreement with the BioCryst board. BioCryst management provided the BioCryst board with an update on the mutual due diligence review and discussions with Idera management.

        On December 22, 2017, Mr. Milano and Mr. Stonehouse spoke by telephone and discussed the status of the mutual due diligence review, and the financial analysis being done by both parties, including with respect to each party's development of assumptions to apply to the non-risk adjusted forecasts of the other party and the methodology to be used in determining the appropriate relative ownership of BioCryst stockholders and Idera stockholders in a combined company. On that call, Mr. Milano suggested that the transaction should be structured in a manner in which each of BioCryst and Idera would merge into subsidiaries of a new holding company owned 50% by BioCryst stockholders and 50% by Idera stockholders, reflecting the relative market capitalization based on current trading of the two companies and taking the intrinsic value of the two companies into account. They also discussed issues related to corporate governance, and agreed to speak again regarding those issues at a later date.

        Subsequently on December 22, 2017, the Idera board held a special telephonic meeting, with members of Idera management and representatives of Goldman Sachs and Latham in attendance. At the meeting, Mr. Milano provided an update on the status of negotiations of the potential business combination, including regarding the board of directors of the combined company and the headquarters of the combined company. Representatives of Latham then provided an overview of the draft merger

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agreement received from Skadden, and members of Idera management provided an update on the diligence review of BioCryst. Idera management then reviewed Idera management's unadjusted financial forecasts and risk-adjusted financial forecasts reflecting Idera management's viewpoints on the likelihood of successful commercialization of Idera's products. The Idera board then discussed alternatives to the potential business combination with BioCryst, including remaining as a stand-alone company and exploring potential licensing or partnership transactions. The Idera board instructed Idera management to provide Idera management's unadjusted financial forecasts that had previously been reviewed by the Idera Board to BioCryst, and determined that Idera management, together with Idera's legal and financial advisors, should continue discussions and negotiations with BioCryst and provided guidance with respect to such negotiations, including with respect to ownership of the combined company.

        Later on December 22, 2017, BioCryst and Idera exchanged their respective management's unadjusted financial forecasts.

        During the last two weeks of December 2017, management of BioCryst and Idera, together with their legal and financial advisors, continued to participate in meetings and telephonic conferences relating to due diligence, and discussed the appropriate assumptions to apply to the non-risk adjusted forecasts exchanged by the parties and other valuation topics.

        On December 28, 2017, the BioCryst board held a special telephonic meeting, with members of BioCryst management and representatives of J.P. Morgan, Skadden and Ernst & Young LLP, BioCryst's public accounting firm, in attendance. At the meeting, management of BioCryst reviewed the results of the due diligence review of Idera, including an assessment of Idera's clinical programs and pipeline, the commercial potential of Idera's lead products, accounting and tax matters, and human resource matters. Mr. Stonehouse updated the BioCryst board on his recent discussions with Mr. Milano, which included the parties' respective views on relative values, the appropriate relative ownership of BioCryst stockholders and Idera stockholders in a combined company and the proposed holding company structure to effectuate the transaction. The BioCryst board instructed management and the advisors to continue discussions with Idera and its advisors regarding the terms of a business combination transaction as discussed at the meeting and provided guidance as to the BioCryst board's position that the exchange ratio for the transaction should be based on the relative intrinsic values of the two companies and that BioCryst stockholder ownership in the combined company should be greater than 50% on a fully diluted basis.

        On December 29, 2017, representatives of Goldman Sachs and J.P. Morgan spoke to discuss the potential respective ownership by BioCryst stockholders and Idera stockholders of the combined company following the potential business combination. Representatives of Goldman Sachs indicated that Idera believed the parties needed to further discuss the relative values of the two companies. Representatives of J.P. Morgan indicated that BioCryst believed BioCryst stockholder ownership in the combined company should be greater than 50% on a fully diluted basis.

        Also on December 29, 2017, Latham sent a revised draft of the merger agreement to Skadden, which reflected the holding company structure previously discussed by Mr. Milano and Mr. Stonehouse. Later that day Mr. Milano called Mr. Stonehouse to discuss Idera's views on the methodology for determining relative ownership of BioCryst stockholders and Idera stockholders in a combined company and advised Mr. Stonehouse that Idera believed that the appropriate valuation of the companies should take into account both intrinsic value and their relative market capitalization based on current trading of the two companies. Mr. Milano and Mr. Stonehouse agreed that further review and analysis of the forecasts assumptions was required in order for the parties to refine their respective views on relative valuation, and they agreed to speak again in January when they would both be attending an industry conference.

        On January 3, 2018, the Idera board held a special telephonic meeting, with members of Idera management and representatives of Goldman Sachs and Latham in attendance. At the meeting, Mr. Milano provided an update on the status of negotiations of a potential business combination and considerations on relative valuation of the two companies.

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        On January 9, 2018, Messrs. Stonehouse and Ingram, chairman of the BioCryst board, met with Mr. Milano and James Geraghty, chairman of the Idera board, at an industry conference, and discussed the strategic rationale for, and benefits of, combining BioCryst and Idera, and the proposed corporate governance of the new holding company, including the proposal for a combined company board comprised of four directors from each of the Idera board and the BioCryst board, and one director who was not a BioCryst or Idera director. Mr. Stonehouse and Mr. Milano agreed to speak again later in the week, together with their respective financial advisors, regarding the financial forecasts exchanged between the companies and the assumptions around the major drivers of value.

        On January 11, 2018, Mr. Stonehouse and Mr. Milano, together with members of BioCryst management, Idera management and representatives of J.P. Morgan and Goldman Sachs, met to discuss the financial forecasts of the companies' that the respective managements exchanged. Following the meeting, Mr. Stonehouse and Mr. Milano met separately to discuss the appropriate exchange ratio for the potential business combination between the two companies. Mr. Milano stated that the disinterested members of the Idera board continued to be of the view that the negotiated exchange ratio should take into account both the intrinsic value of the two companies and the recent trading performance of Idera and BioCryst common stock. On January 13, 2018, Mr. Stonehouse and Mr. Milano spoke again by telephone to continue their discussion around the appropriate exchange ratio for the potential business combination.

        Representatives of Latham and Skadden continued to discuss the terms of the merger agreement during this period, including the holding company structure, the treatment of employee equity awards, the circumstances giving rise to a termination fee and the amount of the termination fee. Representatives of Latham and Skadden also discussed potential voting agreements between each of Idera and BioCryst, and affiliates of BBA, pursuant to which affiliates of BBA would agree to vote in favor of the merger agreement at the BioCryst stockholder meeting and at the Idera stockholder meeting, subject to certain exceptions.

        On January 14, 2018, the BioCryst board had a special telephonic meeting, with members of BioCryst management and representatives of J.P. Morgan and Skadden in attendance. At the meeting, Mr. Stonehouse updated the BioCryst board on the status of negotiations with Idera, and Idera's position regarding the exchange ratio. At the meeting, representatives of J.P. Morgan presented their preliminary analysis with respect to the relative values of BioCryst and Idera based on the latest available financial forecasts of BioCryst and Idera prepared by BioCryst management, and reviewed with the BioCryst board the recent trading history of the two companies. The BioCryst board discussed the composition of the board of the combined company, and the roles of Mr. Milano, Mr. Stonehouse and Mr. Ingram in the combined company. The BioCryst board instructed BioCryst management to continue discussions with Idera management on a business combination transaction, but to inform Idera that the exchange ratio should reflect the relative intrinsic values of BioCryst and Idera, and that on this basis the BioCryst board believed that this should yield BioCryst stockholder ownership in the combined company of 52.0% on a fully diluted basis.

        On January 17, 2018, the Idera board held a special telephonic meeting, with members of Idera management and representatives of Goldman Sachs and Latham in attendance. At the meeting, Mr. Milano provided an update on the status of negotiations of the exchange ratio, the board of directors of the combined company and the headquarters of the combined company, as well as the timing for the proposed business combination. Representatives of Latham then provided an overview of the open issues in the draft merger agreement, and members of Idera management provided an update on the diligence review of BioCryst. Idera management and representatives of Goldman Sachs then reviewed certain preliminary financial analyses of Idera, BioCryst and a potential business combination as well as potential strategic alternatives to the potential business combination with BioCryst, including remaining as a stand-alone company, an update to a potential partnership relating to IMO-2125 and a sale of Idera. Following this review, the Idera board confirmed that the potential business combination

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with BioCryst on acceptable terms was preferable to any other strategic alternatives. Mr. Milano then provided an overview of the possible timing and process for signing the merger agreement with BioCryst. The Idera board then instructed Idera management, together with Idera's legal and financial advisors, to continue discussions and negotiations with BioCryst and provided guidance with respect to such negotiations, including with respect to ownership of the combined company.

        Over the next several days, Mr. Stonehouse and Mr. Milano spoke numerous times by telephone to negotiate the appropriate relative ownership of BioCryst stockholders and Idera stockholders in a combined company, during which Mr. Milano objected to the implied premium on the then-prevailing trading price of BioCryst common stock that would result from BioCryst's proposed relative ownership of the combined company. During this period, representatives of Skadden and Latham continued to negotiate the open issues in the merger agreement, which included the circumstances in which a termination fee would be payable and the amount of the termination fee and expense reimbursement in specified circumstances. Representatives of Latham and Skadden also negotiated the terms of voting and support agreements with legal counsel to BBA, pursuant to which affiliates of BBA would agree to vote the Idera and BioCryst shares owned by them in favor of adoption of the mergers at the Idera stockholders meeting and at the BioCryst stockholder meeting. Such discussions among representatives of Latham and Skadden and legal counsel to BBA purposefully excluded the relative valuations of BioCryst and Idera or other terms or conditions of the potential business combination and focused on the principle of securing BBA's voting support in the event that both the BioCryst board and the Idera board approved a potential business combination, and each of BioCryst and Idera received a fairness opinion from their respective financial advisors. Messrs. Baker and Neu did not participate in these negotiations nor were they aware of the terms of the voting and support agreements negotiated, other than being informed that Latham would approach representatives of BBA (excluding Messrs. Baker and Neu) to initiate discussions regarding a voting and support agreement.

        On January 19, 2018, the Idera board held a special telephonic meeting with representatives of each of Idera management, Goldman Sachs and Latham in attendance. In advance of the meeting, the Idera board was provided with, among other things, a near-final draft of the merger agreement and other business combination-related materials. At this meeting, Idera management reviewed with the Idera board the results of the business, financial, accounting and legal due diligence review of BioCryst, provided a detailed overview of BioCryst's business and the strategic rationale for the potential business combination and provided an update on remaining open items related to the potential business combination, including the exchange ratio. Representatives of Latham then reviewed with the Idera board its duties when considering the potential business combination and reviewed the process to date by which the Idera board had overseen negotiations of the potential business combination. Representatives of Latham then discussed amending Idera's bylaws by adopting a forum selection bylaw and amending the adjournment bylaw, and reviewed the next steps and timeline of the potential business combination. Representatives of Latham provided a detailed summary of the business combination documents, including the terms and conditions of the merger agreement, the proposed corporate governance of the combined company and the voting and support agreement proposed to be entered into with BBA. Representatives of Latham noted that all discussions with legal counsel for BBA expressly excluded any discussion with or input from BBA regarding the relative valuation of BioCryst and Idera and other terms of the potential business combination. The Idera board, Idera management and representatives of Goldman Sachs and Latham discussed using volume-weighted average prices of BioCryst common stock and Idera common stock as reference points in negotiating the exchange ratio. The Idera board advised Mr. Milano to propose an exchange ratio to BioCryst ranging from 0.41 to 0.42 holding company shares for each share of Idera and a BioCryst exchange ratio of 1.0 (to be adjusted as appropriate based on any reduced exchange ratio for BioCryst). The Idera board then authorized Idera management, together with Idera's legal and financial advisors, to continue to negotiate the exchange ratio and other remaining open issues.

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        Also on January 19, 2018, the BioCryst board held a special telephonic meeting, with members of BioCryst management and representatives of Skadden in attendance. Representatives of Skadden updated the BioCryst board on the status of negotiations with Idera on the terms of the merger agreement and on the status of negotiations with legal counsel to BBA and the terms of the voting and support agreements. Representatives of Skadden noted that all discussions with legal counsel for BBA expressly excluded any discussion with or input from BBA regarding the relative valuation of BioCryst and Idera and other terms of the potential business combination. Later that day, in a call between Mr. Milano and Mr. Stonehouse, Mr. Milano informed Mr. Stonehouse that he had spoken with Idera directors and that, following such discussions, Mr. Milano believed that the Idera board would be willing to consider an exchange ratio which would imply ownership in the new holding company of 51.2% to 51.5% for BioCryst stockholders on a fully diluted basis and would be consistent with the 30-day volume-weighted average prices of BioCryst common stock and Idera common stock. The parties also discussed the equivalent of a holding company reverse stock split on the call.

        On January 20, 2018, the BioCryst board held a special telephonic meeting, with members of BioCryst management and representatives of Skadden and J.P. Morgan in attendance. Representatives of Skadden reviewed legal matters including directors' fiduciary duties in connection with the proposed transaction with Idera. Representatives of Skadden updated the BioCryst board on the status of negotiations with Idera on the merger agreement and the status of negotiations with BBA on the voting agreement, and also discussed with the BioCryst board a proposed amendment to the BioCryst bylaws to adopt a forum selection bylaw. Mr. Stonehouse updated the BioCryst board on recent discussions with Mr. Milano regarding the appropriate exchange ratio for the transaction, including the suggested adjustment to the BioCryst exchange ratio in order to reduce the number of shares of the new holding company. Representatives of J.P. Morgan reviewed the recent trading history of BioCryst and Idera. The BioCryst board instructed Mr. Stonehouse to make a final proposal to Idera on the Idera exchange ratio of 0.40 holding company shares for each share of Idera and a BioCryst exchange ratio of 1.0 (to be adjusted as appropriate based on any reduced exchange ratio for BioCryst) implying ownership by BioCryst stockholders of approximately 51.6% in the new holding company on a fully diluted basis. Following the BioCryst board meeting, in accordance with the BioCryst board's instructions, Mr. Stonehouse called Mr. Milano and communicated the BioCryst board's position on the appropriate exchange ratio in the merger. Mr. Milano responded that he would discuss BioCryst's final proposal with the Idera board, and confirmed that the Idera board was meeting the following day.

        On the morning of January 21, 2018, Messrs. Baker and Neu met telephonically with members of Idera management as well as representatives of Goldman Sachs, Latham, and BBA in order for Messrs. Baker and Neu to become informed as part of the forthcoming vote of the Idera board regarding the potential business combination and Idera's request that BBA sign a voting and support agreement. Idera management and representatives of Goldman Sachs reviewed certain preliminary financial analyses of Idera, BioCryst and the combined company. Messrs. Baker and Neu, Idera management and representatives of Goldman Sachs, Latham and BBA then discussed the negotiation and diligence process of the potential business combination, Goldman Sachs' preliminary financial analysis of the potential business combination, and the terms and conditions of the proposed merger agreement. During such discussions, Messrs. Baker and Neu asked questions on the overall process and basis of Goldman Sachs' financial analyses, but did not comment or provide any opinion on the relative valuation of BioCryst and Idera or the exchange ratio.

        Subsequently, on January 21, 2018, the Idera board held a special telephonic meeting with representatives of each of Idera management, Goldman Sachs and Latham in attendance. In advance of the meeting, the directors were provided with, among other things, final versions of the merger agreement and the other definitive documents, including the proposed certificate of incorporation of the combined company and the proposed amendments to Idera's bylaws, draft proposed resolutions approving the business combination and financial analyses prepared by Goldman Sachs (based on the

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BioCryst Management Forecasts as adjusted by Idera management). Mr. Milano provided an update on the negotiation of the exchange ratio and reviewed with the Idera board BioCryst's final offer of an exchange ratio of 0.40 holding company shares for each share of Idera and a BioCryst exchange ratio of 1.0 (to be adjusted as appropriate based on any reduced exchange ratio for BioCryst), implying ownership by Idera stockholders of approximately 48.4% in the combined company on a fully diluted basis. Mr. Milano noted that the exchange ratio of 0.40, while implying a premium on the most recent closing price of BioCryst common stock of 14.1%, was consistent with the 30-day volume-weighted average prices of BioCryst common stock and Idera common stock, and representatives of Goldman Sachs and Latham provided their perspectives on the proposed exchange ratio. Mr. Milano then recommended approving the potential business combination with an exchange ratio of 0.40 (to be adjusted as appropriate based on any reduced exchange ratio for BioCryst). At this point, Messrs. Baker and Neu exited the meeting, and, following discussion among the remaining Idera board members, Idera management and representatives of Goldman Sachs and Latham, the Idera board determined to move forward with the exchange ratio of 0.40 (to be adjusted as appropriate based on any reduced exchange ratio for BioCryst). At this point, Messrs. Baker and Neu rejoined the meeting, and Messrs. Baker and Neu each read statements reminding the Idera board of BBA's affiliates' ownership interest in both Idera and BioCryst as well as the personal ownership interest of each of Messrs. Baker and Neu in Idera and BioCryst, with such statements noting the number and type of securities of Idera and BioCryst owned by BBA and its affiliates and each of Messrs. Baker and Neu individually. See "The Mergers—Interests of Idera Directors, Executive Officers and Certain of their Affiliates in the Mergers—Holdings of Baker Brothers as of January 21, 2018" beginning on page 100 of this joint proxy statement/prospectus for more information. The statements also noted that Messrs. Baker and Neu's support of the potential business combination as Idera board members would take into account discussions among members of Idera management, the Idera board, excluding Messrs. Baker and Neu, and Idera's advisors, as well as the financial analyses of Goldman Sachs. Following the statements, the Idera board determined that Messrs. Baker and Neu could participate in the remainder of the meeting. Representatives of Latham then provided an overview of the final merger agreement and a summary of the resolved issues. Representatives of Goldman Sachs then reviewed with the Idera board its financial analysis and rendered to the Idera board an oral opinion of Goldman Sachs, subsequently confirmed by delivery of a written opinion, dated January 21, 2018, to the effect that, as of such date and based upon and subject to the factors and the assumptions set forth in Goldman Sachs' written opinion, the Idera exchange ratio pursuant to the merger agreement was fair from a financial point of view, to the holders (other than BioCryst and its affiliates) of Idera common stock, as more fully described in the section entitled "The Mergers—Opinion of Idera's Financial Advisor—Goldman Sachs" beginning on page 84 of this joint proxy statement/prospectus. A discussion ensued regarding the potential business combination with BioCryst. In the course of its deliberations, the Idera board considered a number of factors, including those described more fully below under the section entitled "The Mergers—Idera's Reasons for the Mergers; Recommendation of the Idera Board" beginning on page 67 of this joint statement/prospectus. Following these discussions, representatives of Latham reviewed resolutions approving the mergers, the merger agreement and the related matters that had been previously distributed to the Idera board. The Idera board unanimously determined that the merger agreement and the transactions contemplated thereby, including the mergers, are advisable, fair to and in the best interests of Idera and its stockholders and authorized the appropriate officers of Idera to execute and deliver the merger agreement, the amendment to Idera's bylaws and related documents.

        On the afternoon of January 21, 2018, Mr. Milano called Mr. Stonehouse and informed him that the Idera board had approved the transaction with the most recent relative exchange ratios as proposed by BioCryst.

        Later that day, a special telephonic meeting of the BioCryst board was held for the purpose of considering approval and adoption of the merger agreement with Idera. Members of BioCryst

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management and representatives of J.P. Morgan and Skadden participated in the meeting. Representatives of Skadden reviewed legal matters including BioCryst directors' duties in connection with the proposed transaction with Idera and reviewed with the BioCryst board key terms of the merger agreement and the voting and support agreements with BBA. Representatives of J.P. Morgan then reviewed with the BioCryst board its financial analysis of the BioCryst exchange ratio in the proposed transaction and delivered to the BioCryst board its oral opinion, which was confirmed by delivery of a written opinion dated January 21, 2018, to the effect that, as of such date and based upon and subject to the assumptions made, procedures followed, matters considered and limitations on the review undertaken by J.P. Morgan in preparing the opinion, the BioCryst exchange ratio in the proposed transaction was fair, from a financial point of view, to the holders of BioCryst common stock, as more fully described in the section entitled "The Mergers—Opinion of BioCryst's Financial Advisor—J.P. Morgan" beginning on page 94 of this joint proxy statement/prospectus. Following the presentation, Mr. Stonehouse provided BioCryst management's view of the proposed transaction, and the BioCryst board discussed the proposed transaction. Following discussion the BioCryst board unanimously approved and adopted the merger agreement, approved the transactions contemplated by the merger agreement and resolved to recommend that BioCryst stockholders approve the merger agreement.

        In the evening of January 21, 2018, the merger agreement and the voting and support agreements were executed by Idera and BioCryst. The transaction was announced by joint press release on the morning of January 22, 2018.

Idera's Reasons for the Mergers; Recommendation of the Idera Board

        In evaluating the mergers, the Idera board consulted with Idera's management and legal and financial advisors, and in reaching its decision to approve the merger agreement and recommend its adoption by Idera stockholders, the Idera board considered a number of factors and a substantial amount of information, including the following:

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        The Idera board also weighed the factors described above against a number of risks and other factors identified in its deliberations as weighing negatively against the mergers:

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        The Idera board also was apprised of certain interests in the mergers of Idera's directors and executive officers that may be different from, or in addition to, the interests of Idera stockholders generally as discussed in "The Mergers—Interests of Idera Directors, Executive Officers and Certain of their Affiliates in the Mergers" beginning on page 99 of this joint proxy statement/prospectus.

        This discussion of the information and factors considered by the Idera board in reaching its conclusions and recommendation summarizes the material factors considered by the board, but is not intended to be exhaustive. In view of the wide variety of factors considered in connection with its evaluation of the mergers and the complexity of these matters, the Idera board did not find it practicable, and did not attempt, to quantify, rank or assign any relative or specific weights to the various factors that it considered in reaching its determination to approve the merger agreement and to recommend that Idera stockholders vote in favor of the proposal to adopt the merger agreement.

        The Idera board conducted an overall review of the factors described above and considered the factors overall to be favorable to and to support its determination. In considering the factors described above, individual members of the Idera board may have given differing weights to different factors.

        The Idera board unanimously approved the merger agreement and determined that the merger agreement and the transactions contemplated thereby, including the mergers, are advisable, fair to and in the best interests of Idera and its stockholders. The Idera board unanimously recommends that Idera stockholders vote "FOR" the proposal to adopt the merger agreement.

BioCryst's Reasons for the Mergers; Recommendation of the BioCryst Board

        By unanimous vote, the BioCryst board, at a meeting held on January 21, 2018, determined that the merger agreement and the transactions contemplated thereby, including the mergers, are fair, advisable and in the best interests of BioCryst and its stockholders. In addition, subject to the terms of the merger agreement, the BioCryst board resolved to recommend that the BioCryst stockholders approve the adoption of the merger agreement and the transactions contemplated thereby. THE BIOCRYST BOARD UNANIMOUSLY RECOMMENDS THAT BIOCRYST STOCKHOLDERS VOTE "FOR" THE ADOPTION OF THE MERGER AGREEMENT, "FOR" THE APPROVAL ON A NON-BINDING ADVISORY BASIS, THE COMPENSATION THAT MAY BECOME PAYABLE TO BIOCRYST'S NAMED EXECUTIVE OFFICERS THAT IS BASED ON OR OTHERWISE RELATES TO THE MERGERS AND "FOR" THE ADJOURNMENT OF THE BIOCRYST SPECIAL MEETING, IF NECESSARY OR APPROPRIATE, TO SOLICIT ADDITIONAL PROXIES IF THERE ARE NOT SUFFICIENT VOTES TO ADOPT THE MERGER AGREEMENT.

        In evaluating the merger agreement and the transactions contemplated thereby, the BioCryst board consulted with BioCryst senior management, its outside legal counsel and financial advisors. This explanation of BioCryst's reasons for the mergers and all other information presented in this section should be read in light of the factors discussed in the section entitled "Cautionary Statement Regarding

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Forward-Looking Statements" beginning on page 20 of this joint proxy statement/prospectus. In recommending that BioCryst stockholders vote their shares of BioCryst common stock in favor of adoption of the merger agreement, the BioCryst board considered a number of factors, including the following (not necessarily in order of relative importance):

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        The BioCryst board also considered a number of uncertainties and risks in its deliberations concerning the mergers and the other transactions contemplated by the merger agreement, including the following (not necessarily in order of relative importance):

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The BioCryst board considered all of these factors as a whole and believed that, overall, the potential benefits of the mergers to BioCryst's stockholders outweighed the uncertainties and risks of the mergers.

        The foregoing discussion of factors considered by the BioCryst board is not intended to be exhaustive, but includes the material factors considered by the BioCryst board. In light of the variety of factors considered in connection with its evaluation of the mergers and the complexity of these matters, the BioCryst board did not find it practicable to, and did not, quantify, rank or otherwise assign relative weights to the specific factors considered in reaching its determinations and recommendations. Moreover, each member of the BioCryst board applied his or her own personal business judgment to the process and may have viewed factors differently or given different weight or merit to different factors. The BioCryst board did not undertake to make any specific determination as to whether any factor, or any particular aspect of any factor, supported or did not support its ultimate determination. The BioCryst board based its recommendation on the totality of the information presented. The BioCryst board evaluated the factors described above, among others, and reached the conclusion that it is in the best interests of BioCryst and its stockholders, and declared it advisable, to enter into the merger agreement, and unanimously approved the merger agreement and the transactions contemplated by the merger agreement, including the merger, and resolved to recommend the adoption of the merger agreement by BioCryst stockholders and resolved that the adoption of the merger agreement be submitted to a vote at a meeting of BioCryst stockholders.

Certain Financial Forecasts Utilized by the Idera Board and Idera's Financial Advisor in Connection with the Mergers

        The unaudited prospective financial data presented below includes projections prepared by Idera management. Idera does not, as a matter of course, normally make public long-term projections or publicly disclose financial projections or forecasts as to future performances, revenues, earnings or other results given, among other things, the unpredictability of the underlying assumptions and estimates inherent in preparing financial projections and forecasts. As a result, Idera does not endorse unaudited prospective financial information as a reliable indication of future results.

        The unaudited financial projections concerning Idera and BioCryst set forth below, as well as the synergy estimates and unaudited financial projections for the combined company after the completion of the mergers set forth below, were made available as described below to the Idera board in its review and evaluation of the transactions contemplated by the merger agreement, and to Goldman Sachs for its use and reliance in connection with its financial analyses and opinion to the Idera board described under "The MergersOpinion of Idera's Financial Advisor—Goldman Sachs" beginning on page 84 of this joint proxy statement/prospectus and, in the case of the Idera Unadjusted Management Projections, to BioCryst. The summary of these financial projections is not being included in this joint proxy statement/prospectus to influence the voting decision of any Idera stockholder or BioCryst stockholder

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with respect to the mergers, but instead only because these financial projections were provided to the parties above in connection with the mergers. Idera makes and has made no representation to BioCryst, in the merger agreement or otherwise, concerning the Idera Unadjusted Management Projections, the Idera Adjusted Management Projections, the Idera Adjusted BioCryst Projections or the Combined Company Projections.

Financial Forecasts Related to Idera

        Idera management prepared unaudited unadjusted financial projections for Idera (the "Idera Unadjusted Management Projections") for the fiscal years ending December 31, 2018 through 2030. The Idera Unadjusted Management Projections were based on numerous variables and assumptions including key assumptions around the following: (1) capitalization and expenditure estimates; (2) product pricing and pricing increases; (3) composition of patients, (4) product launch dates and (5) market share. The Idera Unadjusted Management Projections are being described herein solely because they were provided to BioCryst in connection with its review and evaluation of the mergers. The Idera Unadjusted Management Projections are summarized in the following table:

$mm
  2018E   2019E   2020E   2021E   2022E   2023E   2024E  

Total net revenues

              $ 113   $ 229   $ 361   $ 676  

Gross profit

              $ 112   $ 228   $ 359   $ 671  

Ex-U.S. partnership revenue

                  $ 35   $ 19   $ 29  

Operating income

  $ (70 ) $ (71 ) $ (108 ) $ (36 ) $ 67   $ 125   $ 378  

 

$mm
  2025E   2026E   2027E   2028E   2029E   2030E  

Total net revenues

  $ 1,522   $ 2,492   $ 3,257   $ 3,655   $ 4,055   $ 4,570  

Gross profit

  $ 1,500   $ 2,447   $ 3,187   $ 3,560   $ 3,935   $ 4,415  

Ex-U.S. partnership revenue

  $ 64   $ 158   $ 292   $ 372   $ 383   $ 395  

Operating income

  $ 946   $ 1,622   $ 2,218   $ 2,521   $ 2,761   $ 3,066  

        Using the Idera Unadjusted Management Projections, Idera management prepared unaudited financial projections for Idera (the "Idera Adjusted Management Projections") for the fiscal years ending December 31, 2018 through 2030, which were adjusted based on numerous variables, including the following: (1) Idera management's assessment of the probability of success for Idera's products; (2) Idera's federal net operating loss balance and the future usability of such tax attributes; (3) expectations around future equity financings; and (4) capitalization estimates. The Idera board utilized the Idera Adjusted Management Projections in connection with its review and evaluation of the mergers, and Goldman Sachs used the Idera Adjusted Management Projections in connection with its financial analyses and opinion to the Idera board, as described in the section titled "The Mergers—Opinion of Idera's Financial Advisor—Goldman Sachs" beginning on page 84 of this joint proxy

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statement/prospectus. The Idera Adjusted Management Projections are summarized in the following table:

$mm
  2018E   2019E   2020E   2021E   2022E   2023E   2024E  

POS Adjusted Revenue by Product:

                                           

IMO-2125—Melanoma

              $ 75   $ 152   $ 240   $ 252  

IMO-2125—Head & Neck

                          $ 101  

IMO-2125—Bladder

                             

IMO-8400—Dermatomyositis

                          $ 2  

Nucleic acid chemistry compound

                             

POS-adjusted net revenue

              $ 75   $ 152   $ 240   $ 355  

Ex-U.S. partnership revenue

                  $ 17   $ 9   $ 14  

POS-adjusted operating income

  $ (70 ) $ (72 ) $ (109 ) $ (37 ) $ 48   $ 105   $ 280  

Unlevered free cash flow(1)

  $ (73 ) $ (76 ) $ (115 ) $ (45 ) $ 29   $ 72   $ 207  

Tax-effected net operating loss cash savings

                  $ 10   $ 22   $ 57  

Financings

      $ 150   $ 150                  

 

 
  2025E   2026E   2027E   2028E   2029E   2030E  

POS Adjusted Revenue by Product:

                                     

IMO-2125—Melanoma

  $ 264   $ 277   $ 291   $ 305   $ 320   $ 336  

IMO-2125—Head & Neck

  $ 211   $ 331   $ 346   $ 362   $ 379   $ 397  

IMO-2125—Bladder

  $ 131   $ 279   $ 447   $ 476   $ 508   $ 541  

IMO-8400—Dermatomyositis

  $ 11   $ 28   $ 52   $ 80   $ 105   $ 124  

Nucleic acid chemistry compound

  $ 4   $ 15   $ 24   $ 35   $ 45   $ 66  

POS-adjusted net revenue

  $ 620   $ 929   $ 1,159   $ 1,258   $ 1,357   $ 1,464  

Ex-U.S. partnership revenue

  $ 23   $ 47   $ 81   $ 101   $ 104   $ 107  

POS-adjusted operating income

  $ 574   $ 898   $ 1,155   $ 1,268   $ 1,364   $ 1,468  

Unlevered free cash flow(1)

  $ 422   $ 670   $ 879   $ 981   $ 1,056   $ 1,136  

Tax-effected net operating loss cash savings

  $ 1                      

Financings

                         

(1)
Defined as cash provided by operating activities less capital expenditures. Unlevered free cash flow is a non-GAAP financial measure. Unlevered free cash flow does not include tax-effected net operating loss cash savings or financings.

Financial Forecasts Related to BioCryst

        BioCryst management prepared unaudited unadjusted financial projections for BioCryst for the fiscal years ending December 31, 2018 through 2035 for its board of directors (see the section entitled "The Mergers—Certain Financial Forecasts Utilized by the BioCryst Board and BioCryst's Financial Advisor in Connection with the Mergers—Financial Forecasts Related to BioCryst" beginning on page 81 of this joint proxy statement/prospectus), which were provided to Idera management for its review and evaluation of the mergers. Idera management then made adjustments to BioCryst management's projections based on numerous variables (the "Idera Adjusted BioCryst Projections"), including the following: (1) Idera management's assessment of the probability of success for BioCryst's products; and (2) expectations around future equity financings. The Idera board utilized these Idera Adjusted BioCryst Projections in connection with its review and evaluation of the mergers, and Goldman Sachs used the Idera Adjusted BioCryst Projections in connection with its financial analyses and opinion to the Idera board, as described in the section titled "The Mergers—Opinion of Idera's

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Financial Advisor—Goldman Sachs" beginning on page 84 of this joint proxy statement/prospectus. The Idera Adjusted BioCryst Projections are summarized in the following table:

$mm
  2018E   2019E   2020E   2021E   2022E   2023E   2024E   2025E   2026E  

POS Adjusted Revenue by Product:

                                                       

HAE Prophylactic

          $ 21   $ 112   $ 214   $ 331   $ 376   $ 469   $ 492  

HAE Acute

                  $ 8   $ 20   $ 27   $ 30   $ 30  

Rapivab

  $ 2   $ 3   $ 21   $ 21   $ 21   $ 18   $ 18          

Galidsevir

                  $ 20   $ 20   $ 20          

Other development candidate

                      $ 6   $ 27   $ 46   $ 61  

FOP

                      $ 6   $ 13   $ 20   $ 25  

Ex-U.S. product sales

          $ 1   $ 8   $ 22   $ 46   $ 74   $ 97   $ 118  

Royalty and other revenues

  $ 1   $ 1   $ 1   $ 1   $ 1   $ 1   $ 1   $ 1   $ 1  

Research and development reimbursement

  $ 5   $ 6   $ 9   $ 1                      

Milestone receipts

  $ 3                                  

POS-adjusted net revenue

  $ 11   $ 10   $ 52   $ 143   $ 285   $ 447   $ 556   $ 662   $ 728  

POS-adjusted operating income

  $ (91 ) $ (136 ) $ (104 ) $ (3 ) $ 167   $ 338   $ 437   $ 534   $ 593  

Unlevered free cash flow(1)

  $ (92 ) $ (136 ) $ (108 ) $ (12 ) $ 118   $ 251   $ 334   $ 412   $ 462  

Tax-effected net operating loss cash savings

                  $ 28   $ 71   $ 73          

Financings

      $ 150   $ 150                          

 

$mm
  2027E   2028E   2029E   2030E   2031E   2032E   2033E   2034E   2035E  

POS Adjusted Revenue by Product:

                                                       

HAE Prophylactic

  $ 503   $ 523   $ 544   $ 566   $ 588   $ 612   $ 636   $ 662   $ 688  

HAE Acute

  $ 31   $ 32   $ 33   $ 35   $ 36   $ 38   $ 39   $ 41   $ 42  

Rapivab

          $ 2   $ 3   $ 3   $ 3   $ 3          

Galidsevir

                                     

Other development candidate

  $ 72   $ 78   $ 84   $ 87   $ 91   $ 95   $ 98   $ 102   $ 106  

FOP

  $ 28   $ 29   $ 30   $ 31   $ 32   $ 33   $ 34   $ 36   $ 37  

Ex-U.S. product sales

  $ 131   $ 137   $ 145   $ 152   $ 158   $ 164   $ 171   $ 178   $ 185  

Royalty and other revenues

  $ 1                                  

Research and development reimbursement

                                     

Milestone receipts

                                     

POS-adjusted net revenue

  $ 765   $ 799   $ 837   $ 874   $ 909   $ 945   $ 982   $ 1,018   $ 1,059  

POS-adjusted operating income

  $ 625   $ 655   $ 688   $ 720   $ 751   $ 783   $ 816   $ 847   $ 883  

Unlevered free cash flow(1)

  $ 490   $ 514   $ 540   $ 565   $ 590   $ 615   $ 641   $ 666   $ 693  

Tax-effected net operating loss cash savings

                                     

Financings

                                     

(1)
Defined as cash provided by operating activities less capital expenditures. Unlevered free cash flow is a non-GAAP financial measure. Unlevered free cash flow does not include tax-effected net operating loss cash savings or financings.

Financial Forecasts Related to Combined Company

        Using the Idera Adjusted Management Projections and the Idera Adjusted BioCryst Projections, Idera management prepared unaudited financial projections for the combined company (the "Combined Company Projections") after completion of the mergers for the fiscal years ending December 31, 2018 through 2030. The Idera board utilized the Combined Company Projections prepared by Idera's management in connection with its review and evaluation of the mergers, and Goldman Sachs used the Combined Company Projections in connection with its financial analyses and opinion to the Idera board as described in the section titled "The Mergers—Opinion of Idera's Financial Advisor—Goldman

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Sachs" beginning on page 84 of this joint proxy statement/prospectus. The Combined Company Projections are summarized in the following table:

$mm
  2018E   2019E   2020E   2021E   2022E   2023E   2024E  

Pro forma revenue

  $ 11   $ 10   $ 52   $ 218   $ 454   $ 696   $ 925  

Operating income

  $ (161 ) $ (208 ) $ (213 ) $ (40 ) $ 215   $ 443   $ 717  

Operating income with synergies(1)

  $ (151 ) $ (185 ) $ (182 ) $ (9 ) $ 246   $ 474   $ 748  

Unlevered free cash flow

  $ (154 ) $ (189 ) $ (193 ) $ (26 ) $ 171   $ 347   $ 565  

Tax-effected net operating loss cash savings

                  $ 52   $ 83   $ 46  

Financings

      $ 300   $ 300                  

 

$mm
  2025E   2026E   2027E   2028E   2029E   2030E  

Pro forma revenue

  $ 1,306   $ 1,704   $ 2,005   $ 2,158   $ 2,298   $ 2,445  

Operating income

  $ 1,109   $ 1,490   $ 1,780   $ 1,923   $ 2,053   $ 2,188  

Operating income with synergies(1)

  $ 1,140   $ 1,521   $ 1,811   $ 1,954   $ 2,084   $ 2,219  

Unlevered free cash flow(2)

  $ 858   $ 1,156   $ 1,394   $ 1,519   $ 1,620   $ 1,726  

Tax-effected net operating loss cash savings

  $ 3   $ 3   $ 3   $ 3   $ 3   $ 3  

Financings

                         

(1)
Reflects run-rate synergy estimates for the combined company after completion of the mergers for the fiscal years ending December 31, 2018 through 2030, giving effect to the mergers as if they had been consummated as of January 1, 2018, of $30.7 million annually, phased 50% in the year ended December 31, 2018, 90% in the year ended December 31, 2019 and 100% in each year thereafter, with costs to achieve such synergies estimated at $4.5 million in each of the years ending December 31, 2018 and 2019.

(2)
Defined as cash provided by operating activities less capital expenditures. Unlevered free cash flow is a non-GAAP financial measure. Unlevered free cash flow does not include tax-effected net operating loss cash savings or financings.

Certain Financial Forecasts Utilized by the BioCryst Board and BioCryst's Financial Advisor in Connection with the Mergers

        BioCryst does not normally make public long-term projections as to future revenues, earnings or other results due to the uncertainty of the underlying assumptions and estimates. However, in connection with the BioCryst board's review of potential strategic alternatives, BioCryst management provided the BioCryst board and J.P. Morgan with forecasts for the performance of BioCryst's business for the fiscal years 2018 through 2037. These prospective forecasts were based on internal assumptions about the probability of success for product candidates, probability of regulatory approvals, launch timing, pricing, market growth, market share, competition, the commercial life of the product candidates, and other relevant factors related to the commercialization of each of BioCryst's products and product candidates (the "BioCryst Adjusted Management Projections"). In addition, BioCryst management provided forecasts which were not risk adjusted to include a probability of success for BioCryst's product candidates (the "BioCryst Unadjusted Management Projections," and together with the BioCryst Adjusted Management Projections, the "BioCryst Management Projections"). BioCryst management provided Idera solely with the BioCryst Unadjusted Management Projections. The BioCryst Management Projections, which are summarized below, were made available to the BioCryst board for purposes of considering and evaluating the transactions contemplated by the merger agreement, and to J.P. Morgan for use in performing its financial analyses in connection with rendering its fairness opinion, which is attached as Annex C to this joint proxy statement/prospectus. BioCryst makes and has made no representation to Idera, in the merger agreement or otherwise, concerning the BioCryst Management Projections. For purposes of the BioCryst Adjusted Management Projections and

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the "BioCryst Adjusted Idera Projections" (as defined in "The Mergers—Certain Financial Forecasts Utilized by the BioCryst Board and BioCryst's Financial Advisor in Connection with the Mergers—Financial Forecasts Related to Idera"): "EBIT" refers to earnings before interest and tax and "Unlevered free cash flow" refers to tax-affected EBIT, less capital expenditures, plus depreciation, amortization and decreases in net working capital. For more information on J.P. Morgan's fairness opinion, see the section entitled "The Mergers—Opinion of BioCryst's Financial Advisor—J.P. Morgan"