Contract analysis

I. IDENTIFICATION OF SELLING STOCKHOLDERS The Selling Stockholders, and the number of shares of Common Stock being sold by each in the base offering, are as follows: The Option Shares, if any, will be sold by the Selling Stockholders in proportions to be determined in accordance with the terms of the Underwriting Agreement upon the exercise of the Underwriters' over-allotment option.

II. DOCUMENTS EXAMINED In connection with the opinions expressed herein, we have examined originals or copies, certified or otherwise identified to our satisfaction, of the following documents:

1. The Restated Certificate of Incorporation of the Company, as amended through the date hereof, as filed with the Secretary of State of the State of Delaware (the "Certificate of Incorporation");

2. The Amended and Restated Bylaws of the Company, as currently in effect (the "Bylaws");

3. Resolutions of the Board of Directors of the Company duly adopted at a meeting held on September 8, 2023, relating to the offering of the Securities and the Company's cooperation therewith, including the authorization of the execution and delivery of the Underwriting Agreement and related documents (the "Board Resolutions");

4. The Underwriting Agreement dated October 12, 2023, among the Company, the Selling Stockholders, and the several Underwriters;

5. The Company's Registration Statement on Form S-3 (File No. 333-274851), as filed with the Securities and Exchange Commission (the "SEC") under the Securities Act of 1933, as amended (the "Securities Act"), and declared effective by the SEC on August 22, 2023 (the "Registration Statement"), including the base prospectus contained therein (the "Base Prospectus"), together with all exhibits thereto and documents inco

6. The Preliminary Prospectus Supplement dated October 2, 2023, relating to the offering of the Securities, as filed with the SEC (the "Preliminary Prospectus Supplement");

7. The Final Prospectus Supplement dated October 12, 2023, relating to the offering of the Securities, as filed with the SEC pursuant to Rule 424(b)(5) under the Securities Act (the "Prospectus Supplement" and, together with the Base Prospectus, the "Prospectus");

8. The Issuer Free Writing Prospectus in the form of a Pricing Term Sheet dated October 12, 2023, as filed with the SEC pursuant to Rule 433 under the Securities Act (the "Pricing Term Sheet");

9. A certificate of good standing with respect to Penterra Pharmaceuticals Corp. issued by the Secretary of State of the State of Delaware, dated October 16, 2023 (the "Good Standing Certificate");

10. An Officer's Certificate of the Company dated October 17, 2023, executed by Dr. Marco Castellano, Chief Executive Officer of the Company, and Lisa Hargrove, Chief Financial Officer of the Company (the "Officer's Certificate");

11. A Secretary's Certificate of the Company dated October 17, 2023, executed by David Orenstein, General Counsel and Corporate Secretary of the Company, certifying as to the incumbency of officers, the Certificate of Incorporation, the Bylaws, and the Board Resolutions (the "Secretary's Certificate");

12. Stock records and transfer agent records of Pinnacle Trust & Transfer Co., in its capacity as the transfer agent and registrar for the Common Stock of the Company, with respect to the Shares and the Option Shares; and

13. Such other documents, records, certificates, corporate proceedings, and instruments as we have deemed necessary or appropriate as a basis for the opinions expressed herein. The documents described in items (1) through (4) above are hereinafter referred to collectively as the "Transaction Documents." The Registration Statement, the Base Prospectus, the Preliminary Prospectus Supplement, the Prospectus Supplement,

III. ASSUMPTIONS In rendering the opinions set forth herein, we have, with your consent and without independent investigation or verification, assumed the following: (a) The genuineness of all signatures on all documents examined by us (other than signatures of persons signing on behalf of the Company); (b) The authenticity and completeness of all documents submitted to us as originals; (c) The conformity to the orig

IV. OPINIONS Based upon and subject to the foregoing, and subject to the qualifications and limitations set forth in Section V below, we are of the opinion that: Opinion 1 — Due Incorporation and Good Standing The Company has been duly incorporated and is validly existing as a corporation in good standing under the laws of the State of Delaware. In rendering this opinion, we have relied exclusively upon the Good Stan

V. QUALIFICATIONS AND LIMITATIONS The foregoing opinions are subject to the following qualifications and limitations: (a) Governing Law Limitation. Our opinions are limited solely to the laws of the State of New York, the General Corporation Law of the State of Delaware (including the statutory provisions thereof, all applicable provisions of the Delaware Constitution, and reported judicial decisions interpreting the

VI. RELIANCE AND BENEFIT This opinion letter is furnished to the Underwriters solely for their benefit in connection with the offering of the Securities and may not be relied upon by any other person or entity without our prior written consent. Without limiting the foregoing, this opinion letter may not be quoted in whole or in part, referred to in any report or document, or furnished to any other person or entity, w