Contract analysis

I. Purpose of Memorandum Calderwood & Harkness LLP (the "Firm") has been asked by the Special Committee of the Board of Directors (the "Special Committee") of Penterra Pharmaceuticals Corp. (NYSE: PPHR) ("Penterra"), a Delaware corporation headquartered at 400 Innovation Drive, Suite 1200, Princeton, NJ 08540, to serve as independent counsel in connection with the Special Committee's evaluation of a proposed related-

II. Background on the Proposed Engagement A. Penterra Pharmaceuticals Corp. Penterra Pharmaceuticals Corp. is a publicly traded specialty pharmaceutical company focused on the oncology and immunology therapeutic areas. Penterra's common stock is listed on the New York Stock Exchange under the ticker symbol PPHR. As of June 1, 2023, Penterra has an approximate market capitalization of $4.72 billion. For fiscal year 20

III. Scope of Conflicts Search The Firm conducted its conflicts search on May 30–31, 2023, using the Firm's centralized conflict-checking database (the "Conflicts System"). The Conflicts System was searched against all parties to the proposed transaction, their known affiliates, key individuals, advisors, and counterparty counsel. The search utilized both exact-match and fuzzy-match algorithms and included searches o

1. Penterra Pharmaceuticals Corp., including all known subsidiaries and affiliates (including but not limited to Penterra Oncology, Inc., Penterra Immunology Holdings, LLC, and Penterra International S.à r.l.).

2. Special Committee Members (individually): (a) Diane Prescott (b) James Okafor (c) Dr. Helen Ng B. Target Company and Affiliates The following entities and individuals were searched in connection with the target company:

1. Caliston BioSciences, Inc.

2. Dr. Nadia Sorensen — Co-Founder and CEO of Caliston; 14.2% equity holder.

3. Dr. Raj Malhotra — Co-Founder and CSO of Caliston; 9.8% equity holder.

4. Dr. Evan Whitmore — Head of Clinical Development and board member of Caliston; spouse of Penterra director Angela Whitmore. C. Interested Parties / Conflicted Individuals The following individuals were searched as interested or conflicted parties:

1. Dr. Marcus Hale — individually, in his capacity as the holder of a 28.5% equity interest in Caliston, and in his capacity as Chairman and CEO of Penterra.

2. Angela Whitmore — Penterra director; EVP, Commercial Operations; non-independent due to spousal relationship with Dr. Evan Whitmore of Caliston.

3. Raymond Tusk — Penterra director; non-independent; appointed at the nomination of Dr. Hale. D. Key Caliston Stockholders The following institutional stockholders and their principals were searched:

1. Ridgeline Ventures, LP — 22.3% equity interest in Caliston; managing partner: Ava Lindström. The search included Ridgeline Ventures, LP, Ridgeline Ventures Management, LLC (its general partner), and Ava Lindström individually.

2. Meridian Life Sciences Fund III, LP — 18.7% equity interest in Caliston; managing partner: Tomás Reyes. The search included Meridian Life Sciences Fund III, LP, Meridian Life Sciences Capital, LLC (its general partner), and Tomás Reyes individually. E. Counterparty Counsel and Financial Advisors The following counterparty professional advisors were searched:

1. Whitfield Graves LLP — counsel to Caliston; lead partner: Kenneth Pratt; One Federal Street, Suite 2600, Boston, MA 02110. The search included the firm and Kenneth Pratt individually.

2. Fendowell Sinclair & Co. — financial advisor to Caliston; lead banker: Sandra Wu; 200 Clarendon Street, 50th Floor, Boston, MA 02116. The search included the firm and Sandra Wu individually. F. Other Transaction Parties and Advisors The following additional transaction parties, advisors, and service providers were searched:

1. Alcott, Barringer & Cole LLP — Penterra's regular outside counsel; recused from Special Committee matters; lead M&A partner: Victoria Shen.

2. Thorngate Partners LLC — prospective independent financial advisor to the Special Committee; Managing Director: Gregory Ashford; 590 Madison Avenue, 22nd Floor, New York, NY 10022.

3. Greystone National Bank, N.A. — administrative agent for Penterra's $1.5 billion revolving credit facility; 383 Madison Avenue, New York, NY 10179.

4. Harwick & Tolliver LLP — Penterra's independent auditor; 30 Rockefeller Plaza, New York, NY 10112.

5. Brentmoor Advisors LLP — Caliston's independent auditor; 125 Summer Street, Suite 800, Boston, MA 02110.

6. Northpoint Specialty Insurance Company — directors and officers liability insurance carrier (Policy No. NSI-DO-2023-88412); 100 Constitution Plaza, Hartford, CT 06103.

7. Columnar Trust Services, Inc. — Penterra's transfer agent; 6201 15th Avenue, Brooklyn, NY 11219.

8. Hargrove Proxy Advisors, Inc. — potential proxy solicitor; 17 Ashbury Asset Advisors, Suite 1100, New York, NY 10004. In total, the conflicts search encompassed more than forty-five individual names and entity names, including all known variants, former names, and abbreviations, as reflected in the complete search report attached as Attachment A.

IV. Results of Conflicts Search The results of the comprehensive conflicts search conducted on May 30–31, 2023, are summarized below by category of party. For each category, the Firm reports whether any current or prior attorney-client relationships, any adverse representations, any co-counsel or opposing-counsel relationships, or any other potential conflicts were identified. A. Penterra Pharmaceuticals Corp. and It

V. Analysis of Independence Requirements A. The Heightened Independence Standard The Firm's proposed role as independent counsel to the Special Committee requires the Firm to be free from any conflicts of interest — whether actual or potential, whether arising from current or prior professional relationships, financial interests, personal connections, or other circumstances — that could impair the Firm's ability to r

Section 144 of the Delaware General Corporation Law (the "DGCL") further provides a framework for evaluating transactions involving interested directors and officers, permitting such transactions to stand if approved by a majority of disinterested directors or stockholders upon full disclosure, or if the transaction is fair to the corporation at the time it is authorized. In this context, the independence of the Spec

VI. Engagement Team Confirmation In addition to the entity- and party-level conflicts search described above, the Firm has conducted individual conflicts clearance for each member of the proposed engagement team. Each team member has been individually cleared through the Conflicts System and has confirmed, through personal attestation, that he or she has no personal, financial, familial, or social relationship with a

VII. Conclusion and Clearance Based on the comprehensive conflicts search conducted on May 30–31, 2023, and the analysis set forth in this memorandum, the Firm's Conflicts Committee confirms that no conflicts of interest exist that would prevent Calderwood & Harkness LLP from accepting the engagement as independent counsel to the Special Committee of Penterra Pharmaceuticals Corp. in connection with the Special Commi

VIII. Approval / Sign-Off The undersigned hereby confirm the accuracy and completeness of the foregoing conflicts clearance memorandum and request approval from the Conflicts Committee for acceptance of the proposed engagement. CONFLICTS COMMITTEE APPROVAL: APPROVED: By: ________ Name: ________ Title: Chair, Conflicts Committee / Firm General Counsel Calderwood & Harkness LLP Date: ________ RESPONSIBLE PARTNER CONFIR