This Amendment No. 1 (this Amendment) amends and supplements the Tender Offer
Statement on Schedule TO filed by (i) Kortex Acquisition Corp., a Delaware corporation (Purchaser) and a wholly owned subsidiary of Sanofi, a French société anonyme (Parent), (ii)
Parent, and (iii) Aventis Inc., a Delaware corporation and a direct wholly owned subsidiary of Parent and direct parent of Purchaser (Aventis) on August 28, 2020 (together with any subsequent amendments or supplements
thereto, including this Amendment, the Schedule TO), relating to the offer by Purchaser to purchase all of the outstanding shares of common stock, par value, $0.0001 per share (the Shares), of Principia
Biopharma Inc., a Delaware corporation (the Company), at a purchase price of $100.00 per Share (the Offer Price) net to the seller in cash, without interest and subject to any withholding of taxes required by
applicable legal requirements, on the terms and subject to the conditions set forth in the Offer to Purchase, as it may be amended or supplemented from time to time, and in the related Letter of Transmittal, as it may be amended or supplemented from
time to time, copies of which are attached to the Schedule TO as Exhibits (a)(1)(A) and (a)(1)(B), respectively.
All information set forth in the Offer
to Purchase, including Schedule I thereto, is incorporated by reference herein in response to Items 1 through 9 and Item 11 of this Schedule TO and is supplemented by the information specifically provided in this Amendment, except as otherwise set
forth below. This Amendment should be read together with the Schedule TO.
Items 1 through 9 and Item 11.
The Offer to Purchase and Items 1 through 9 and Item 11 of the Schedule TO, to the extent such Items incorporate by reference the information contained in the
Offer to Purchase, are hereby amended and supplemented as follows:
1. The subsection captioned Antitrust Compliance under
Section 16 Certain Legal Matters; Regulatory Approvals is hereby amended and supplemented by deleting the second sentence of the second paragraph and replacing it with the following sentence:
Each of Parent and the Company filed their respective Premerger Notification and Report Form under the HSR Act with the FTC and the Antitrust Division
on September 4, 2020 in connection with the purchase of Shares in the Offer and the Merger and the fifteen (15) day waiting period will expire at 11:59 p.m., Eastern Time on September 21, 2020, unless earlier terminated by the FTC and
the Antitrust Division, Parent receives a request for additional information or documentary material prior to that time, or Parent pulls and refiles its notification so as to provide the FTC and Antitrust Division an additional 15 days to review the
transaction.
2. Section 16 Certain Legal Matters; Regulatory Approvals is hereby amended and supplemented by adding the
following to the end of such Section after the subsection captioned State Takeover Laws:
Legal Proceedings Relating to the
Tender Offer. As of September 11, 2020, four complaints were filed in federal courts by purported stockholders of the Company regarding the Merger. The first complaint was filed on an individual basis by the plaintiff on August 28,
2020, and is captioned Elaine Wang v. Principia Biopharma Inc., et al., Case No. 3:20-cv-06085 (N.D. Cal. filed August 28, 2020). The second complaint, filed as a
putative class action on September 1, 2020, is captioned Marcy Curtis v. Principia Biopharma Inc., et al., No.
1:20-cv-01164-UNA (D. Del. filed September 1, 2020). A third complaint was filed on an individual basis by the plaintiff on
September 4, 2020, and is captioned Stephen Bushansky v. Principia Biopharma Inc., et al., Case No. 3:20-cv-06283 (N.D. Cal. filed September 4, 2020). The
fourth complaint was filed by the plaintiff on behalf of himself and all others similarly situated, on September 8, 2020, and is captioned Kelvin Hawkins v. Principia Biopharma Inc., et al., Case No. 1:20-cv-07289 (S.D.N.Y filed September 8, 2020) (collectively, the Federal Complaints). The Federal Complaints name as defendants the Company and each member of the Company Board (the
Principia Defendants). The Curtis complaint additionally names as defendants Parent and Purchaser (the Sanofi Defendants). The Wang, Curtis and Hawkins complaints allege violations of Section 14(d) and
Section 14(e) of the Exchange Act against all Principia Defendants, and assert violations of Section 20(a) of the Exchange Act against the individual Principia Defendants. The Curtis complaint additionally alleges violations of
Section 14(d) and Section 14(e) of the Exchange Act against the Sanofi Defendants and a violation of Section 20(a) of the