Mr. Greg Mayes reports

REUNION NEUROSCIENCE ANNOUNCES US$13.1 MILLION TAKE-PRIVATE TRANSACTION WITH MPM BIOIMPACT

Reunion Neuroscience Inc. has entered into a definitive arrangement agreement dated May 31, 2023, with MPM BioImpact, a world-leading biotechnology investment firm, whereby affiliates of MPM would acquire Reunion in an all-cash transaction valued at approximately $13.1-million (U.S.) by way of a statutory plan of arrangement under the Canada Business Corporations Act.

Pursuant to the terms and conditions of the arrangement agreement, all holders of outstanding common shares of Reunion will be entitled to receive $1.12 (U.S.) in cash for each share held immediately prior to the effective time of the arrangement. Based on the Bank of Canada daily exchange rate as of the close of business on May 31, 2023, this would be approximately $1.52 per share in Canadian dollars, representing a premium of approximately 43.1 per cent over the trailing 30-trading-day volume-weighted average price.

Reunion's board of directors, after consultation with its financial and legal advisers and acting on the unanimous recommendation of a special committee of independent directors of Reunion, has determined that the arrangement is in the best interests of the company and is fair to shareholders. The board unanimously recommends that shareholders vote in favour of the arrangement at a special meeting of shareholders expected to be held on or around July 12, 2023 (including any adjournment or postponement thereof). The company has fixed a record date of June 12, 2023, for purposes of determining shareholders entitled to receive notice of, to attend and to vote at the meeting.

"We believe that this all-cash transaction maximizes value and is in the best interest of our shareholders," said Greg Mayes, president and chief executive officer of Reunion. "We are thrilled that MPM recognizes the value and differentiation of our clinical pipeline and look forward to working with them to bring this transaction to a close for the benefit of Reunion's shareholders."

"MPM BioImpact is excited to partner with Reunion and for the opportunity to develop next-generation solutions for underserved mental health conditions," added Ansbert Gadicke, managing partner, MPM BioImpact. "This transaction reflects MPM BioImpact's strategy of investing in breakthrough science and innovative products that can address the world's greatest unmet medical needs."

The arrangement

Completion of the arrangement will, among other things, require the approval by at least two-thirds (66-2/3rds per cent) of the votes cast by the shareholders at the meeting. Certain shareholders, and all of the company's officers and directors, representing in aggregate approximately 34 per cent of the issued and outstanding shares, have entered into voting and support agreements with MPM in support of the arrangement.

Completion of the arrangement remains subject to the satisfaction (or waiver) of a number of conditions precedent, including, but not limited to the following material conditions:

• Approval of the shareholders at the meeting;
• Obtaining all applicable regulatory approvals, including approval of the Ontario Superior Court of Justice (Commercial List) of the arrangement;
• The net cash held by the company being equal to or greater than $8-million (U.S.) as of the close of business on the third business day immediately prior to closing of the arrangement (subject to reduction under certain circumstances);
• The performance or completion in all material respects with all obligations required to be performed by the company and MPM under the arrangement agreement.

Subject to the satisfaction or waiver of the conditions precedent for completion of the arrangement, the arrangement is expected to close in the calendar third quarter of 2023. Upon completion of the transaction, Reunion will no longer be traded or listed on any public securities exchange and will be wholly owned by affiliates of MPM.

The foregoing summary is qualified in its entirety by the provisions of the respective documents. Reunion will file a material change report in respect of the arrangement; and copies of the arrangement agreement, the plan of arrangement and the forms of voting support agreements will be filed with the applicable Canadian securities regulators and will be available for review on SEDAR. Full details of the arrangement will be included in a management information circular from Reunion that is expected to be filed on SEDAR and mailed to shareholders on or around June 21, 2023.

Advisers

Oppenheimer & Co. Inc. is serving as exclusive financial adviser to the special committee of the board of directors of Reunion; PI Financial Corp. rendered a fairness opinion to Reunion; and Bennett Jones LLP and Morgan Lewis & Bockius LLP are serving as legal advisers. McCarthy Tetrault LLP and Wilmer Cutler Pickering Hale and Dorr LLP are serving as legal advisers to MPM.

Poster presentation at ASCP

On Thursday, June 1, 2023, Dr. Robert Alexander, Reunion's chief medical officer, will present the company's first-in-human phase 1 final analysis with RE104 at this year's American Society of Clinical Psychopharmacology (ASCP) annual meeting. Key findings include:

• RE104 was generally well tolerated with robust pharmacodynamic (PK) effects observed at doses greater than or equal to 33 milligrams that closely aligned with the PK profile of its pro-drug, 4-OH-DiPT (isoprocin).
• Drug effect questionnaire and mystical effect questionnaire scores observed at these dose levels indicate the potential for therapeutic effect.
• The mean duration of experience with RE104 at these dose levels was 3.7 hours, representing a shorter duration of action when compared with psilocybin but with the same intensity and quality of experience.
• The adverse event profile of RE104 was similar to that of psilocybin, with no serious adverse events.
• These data informed the dose selection of 33 milligrams of RE104 for a randomized, placebo-controlled phase 2 trial in women with moderate to severe postpartum depression, with trial initiation planned for the second half of 2023.

About Reunion Neuroscience Inc.

Reunion is committed to developing innovative therapeutic solutions for underserved mental health conditions. The company's lead asset, RE104, a proprietary, novel, serotonergic psychedelic compound and the only 4-OH-DiPT pro-drug in clinical development, is being developed as a potential treatment for postpartum depression that could provide rapid symptom relief and durable efficacy. RE104 is protected under U.S. patent No. 11,292,765 issued on April 5, 2022 (priority June 30, 2020), with claims for composition of matter, methods of manufacturing, formulations and methods of use for a genus of hemi-ester tryptamines, including RE104, which could provide protection out to June 30, 2041. Reunion is also developing the RE200 series, which includes preclinical compounds with enhanced receptor selectivity to address additional therapeutic applications.

About MPM BioImpact

MPM is a world-leading biotechnology investment firm with three decades of experience creating and investing in innovative biotechnology companies seeking to deliver transformative therapies to patients in the areas of highest unmet medical need. MPM strives to power novel medical breakthroughs that transform patients' lives. It invests across the biotech landscape with its early-stage venture capital funds and with impact funds investing in both private and public companies.

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