BioCryst Pharmaceuticals Inc美股招股说明书(2025-12-18版)

Dear Stockholders of Astria Therapeutics, Inc.: On October14, 2025, BioCryst Pharmaceuticals, Inc., a Delaware corporation (“BioCryst”), Axel Merger Sub, Inc., a Delaware corporation and whollyowned subsidiary of BioCryst (“Merger Sub”), and Astria Therapeutics, Inc., a Delaware corporation (“Astria”), entered into an Agreement and Plan of Merger (as itmay be amended from time to time, the “Merger Agreement”). Pursuant to the Merger Agreement, Merger Sub will merge with and into Astria, with Astria survivingand becoming a wholly owned subsidiary of BioCryst (the “Merger”). If the Merger is completed, each share of common stock, par value $0.001 per share, of Astria (“Astria Common Stock”), excluding shares held by BioCryst,Astria or their wholly owned subsidiaries or dissenting stockholders, that is issued and outstanding immediately prior to the effective time of the Merger (the“Effective Time”), will be converted into the right to receive (i) 0.59 (the “Exchange Ratio”) of a share of common stock, par value $0.01per share, of BioCryst (the“BioCryst Common Stock”) and, if applicable, cash in lieu of fractional shares and (ii)$8.55 in cash, without interest (the “Per Share Cash Amount”), subject toadjustment as described below and subject to applicable withholding taxes (the consideration described in the foregoing clauses (i)and (ii), collectively, the “MergerConsideration”). Astria’s SeriesX Preferred Shares, the Astria Pre-Funded Warrants and the Astria Common Warrants (each as defined elsewhere in this proxystatement/prospectus) will be treated as described elsewhere in this proxy statement/prospectus. If the aggregate number of shares of BioCryst Common Stock to be issued or issuable in connection with the Merger (including with respect to SeriesXPreferred Shares, Astria Pre-Funded Warrants and Astria Common Warrants other than Elected Warrants (as defined elsewhere in this proxy statement/prospectus)and without giving effect to any demands for appraisal of shares of Astria Common Stock) would exceed 19.9% of the shares of BioCryst Common Stock issued andoutstanding immediately prior to the Effective Time (the “Maximum Share Number”), (i) the Exchange Ratio will be reduced to the minimum extent necessary suchthat the aggregate number of shares of BioCryst Common Stock to be issued in connection with the Merger does not exceed the Maximum Share Number and (ii)the Per Share Cash Amount will be correspondingly increased to offset such adjustment as described in this proxy statement/prospectus. Although the Exchange Ratio is fixed, the market value of the stock component of the Merger Consideration will fluctuate with the market price of BioCrystCommon Stock. Furthermore, the Exchange Ratio may be subject to adjustment, as described above. As such, the market value of the stock component of theMerger Consideration at the Effective Time will not be known at the time Astria’s stockholders vote on the Merger. Shares of BioCryst Common Stock are listed on The Nasdaq Global Select Market under the symbol “BCRX” and shares of Astria Common Stock are listedon The Nasdaq Global Market under the symbol “ATXS.” The following table sets forth the closing sale prices per share of BioCryst Common Stock and AstriaCommon Stock on October13, 2025, the last trading day before the public announcement of the signing of the Merger Agreement, and on December17, 2025, thelatest practicable trading day before the printing date of this proxy statement/prospectus. The table also shows the implied value of the Merger Considerationpayable for each share of Astria Common Stock on October13, 2025 and on December17, 2025.We urge you to obtain current market quotations for BioCrystCommon Stock and Astria Common Stock. In connection with the Merger, BioCryst may issue up to 19.9% of the shares of BioCryst Common Stock issued and outstanding immediately prior to theEffective Time. Based on 210,739,061 shares of BioCryst Common Stock outstanding as of December 9, 2025, that Maximum Share Number is 42,126,738 shares. Astria will hold a special meeting of its stockholders in connection with the Merger (the “Special Meeting”). BioCryst and Astria cannot complete the Mergerunless Astria’s stockholders adopt the Merger Agreement (the “Merger Proposal”). The Astria board of directors (the “Astria Board”) is providing this proxystatement/prospectus to solicit your proxy to vote on the Merger Proposal and related matters. In addition, this proxy statement/prospectus is also being delivered toAstria’s stockholders as BioCryst’s prospectus for its offering of BioCryst Common Stock in connection with the Merger. The Special Meeting will be held on January 21, 2026 at 9:00 a.m., Eastern Time, at 22 Boston Wharf Road, 10th Floor, Boston, Massachusetts 02210. Your vote is very important. BioCryst and Astria cannot complete the Merger unless Astria’s stockholders approve the Merger Proposal. To ensureyour representation at the Special Meeting, p