Oak Hill Bio and Research Alliance Corporation III Announce Business Combination Agreement to Create Publicly Listed Rare Disease Biotechnology Company to Advance Antisense Oligonucleotide Therapy Rugonersen for Angelman Syndrome

• Transaction to provide Oak Hill Bio with approximately $175 million in gross proceeds, including $75 million of cash in Research Alliance Corporation III’s (Nasdaq: RACC) (“RACC”) trust account that is fully backstopped by RA Capital Management and a $100 million committed private financing.
• Together with Oak Hill Bio’s recent $32.5 million Series A financing, the transaction is expected to provide cash runway for development of rugonersen, a potential best-in-class antisense oligonucleotide (ASO) for the treatment of Angelman syndrome, through Phase 3 readout and potential new drug application (NDA) submission in 2H2029.
• Current RACC Director and former Avidity Biosciences CFO Mike MacLean to remain on the Board of the combined company post-closing.
• Business combination expected to close by year-end 2026, and the combined company expected to trade on the Nasdaq Capital Market under the ticker symbol “OAKH”.

CAMBRIDGE, Mass. and NEW YORK, July 27, 2026 — OHB Pediatrics Ltd. d/b/a Oak Hill Bio, a clinical-stage rare disease therapeutics company, and RACC, a special purpose acquisition company (SPAC) sponsored by RA Capital Management, today announced that they have entered into a definitive business combination agreement. In connection with consummation of the transaction, which is expected to close by year-end 2026 subject to customary closing conditions, RACC would redomesticate as a Delaware corporation and be renamed Oak Hill Bio, Inc., and its shares of common stock would be listed on the Nasdaq Capital Market under the ticker symbol “OAKH”.

Oak Hill Bio is developing rugonersen, an investigational ASO therapy for the treatment of Angelman syndrome, in the pivotal Phase 3 BEACON clinical trial (NCT07605429) which dosed its first patient in July 2026. Angelman syndrome is a devastating neurodevelopmental disorder affecting approximately 30,000 diagnosed patients in the U.S. and European Group of Five countries (“EU5”) with no approved disease-modifying therapies. Rugonersen was originally developed by Roche as a highly potent and specific therapy to restore neuronal UBE3A expression, acting as a potential disease modifying treatment, and was licensed by Oak Hill Bio from Roche in February 2025. Several former members of the rugonersen program have joined Oak Hill Bio to lead further development.

“We are excited to announce a business combination with Research Alliance Capital III and partnering with RA Capital,” said Josh Distler, Chief Executive Officer of Oak Hill Bio. “The resources provided by this amazing group of investors will enable us to continue to aggressively develop rugonersen. We have dosed the first patient in the Phase 3 BEACON trial and look forward to evaluating the potential of rugonersen to meaningfully impact the lives of patients living with Angelman syndrome and their families.”

“Oak Hill Bio combines compelling science, a management team with a broad range of experience, and an extremely promising rare disease asset, making for a solid foundation for continued success,” said Matthew Hammond, Partner at RA Capital and CEO and Director of RACC. “We are excited to lead this transaction and support Oak Hill Bio as the team brings rugonersen into pivotal development and towards a potential registration for a best-in-class treatment for Angelman syndrome.”

Summary of the Transaction

The proposed transaction is expected to provide Oak Hill Bio with approximately $175 million in gross proceeds before transaction expenses, including $75 million of cash in RACC’s trust account that is fully backstopped by RA Capital and a $100 million committed private financing. Of the $100 million private financing, $45 million was funded by RA Capital at signing pursuant to a SAFE investment in Oak Hill Bio, with the remaining amount expected to be funded at closing through an oversubscribed PIPE in RACC at $10.00 per share. Participants in the PIPE include Oak Hill Bio’s Series A investors, including Balyasny Asset Management, Janus Henderson Investors, KCap Biotechnology Fund, and venBio, as well as new investors ADAR1 Capital Management; Affinity Asset Advisors, LLC; Ally Bridge Group; BVF Partners, Great Point Partners, LLC, Logos Capital, SilverArc Capital, and Trails Edge Capital Partners.

Oak Hill Bio and RACC’s respective boards have unanimously approved the proposed transaction. Oak Hill Bio’s management team will lead the combined company post-combination, with Oak Hill Bio Chief Executive Officer Josh Distler serving as CEO of the combined company. Current RACC Director and former Avidity Biosciences CFO Mike MacLean to remain on the Board of the combined company post-closing. Mr. MacLean brings a proven track record of financial and operational expertise to support Oak Hill Bio's next phase of growth.

The business combination is expected to close by year-end 2026, subject to customary closing conditions, including approval by shareholders and regulatory bodies.

Additional information about the transaction will be provided in a Current Report on Form 8-K to be filed by RACC with the Securities and Exchange Commission (the "SEC") and will be available at the SEC's website at www.sec.gov.

Advisors

Leerink Partners, UBS Investment Bank, Wells Fargo Securities, and LifeSci Capital are serving as joint placement agents in connection with the PIPE financing. Leerink Partners also acted as an exclusive financial advisor to RACC. Goodwin Procter LLP is serving as legal counsel to Oak Hill Bio. Cooley LLP is serving as legal counsel to RACC. Kirkland & Ellis LLP is serving as legal counsel to the placement agents.

About Oak Hill Bio

Oak Hill Bio is a clinical-stage biotechnology company focused on acquiring and developing promising therapeutics for rare diseases with significant unmet need that have been deprioritized by pharmaceutical companies. The company's lead program is rugonersen (OHB-724), an investigational antisense oligonucleotide (ASO) in Phase 3 clinical development as a potential best-in-class treatment for Angelman syndrome, a devastating neurodevelopmental disorder with no approved disease-modifying therapies.

Oak Hill Bio is the trading name for OHB Pediatrics Ltd. It was formed in 2024 as a subsidiary of Oak Hill Bio Holdings (formerly known as Oak Hill Bio Ltd).

About Angelman Syndrome

Angelman syndrome (AS) is a serious rare genetic neurodevelopmental disorder that causes severe mental and physical impairment and affects approximately 15,000 patients in each of the U.S. and the EU5, with an estimated incidence of 1 in 12,000 to 20,000 live births. AS is characterized by global developmental delay, intellectual disability, epilepsy (90% of cases before age 3 years) with an atypical underlying electroencephalogram (EEG), ataxia, tremor, hyperactivity, limited speech, and sleep dysregulation. Symptoms often emerge during infancy and persist throughout life. Deletions and mutations in the maternal ubiquitin protein ligase E3A (UBE3A) allele cause Angelman syndrome, due to epigenetic silencing of the paternal UBE3A allele by a long non-coding antisense RNA (UBE3A-ATS) in neurons. UBE3A is required for normal brain development and function. Failure to express UBE3A in central nervous system (CNS) neurons leads to a build-up of damaged or unwanted proteins, that if left unchecked, can paralyze normal neuronal maturation, function, and synaptic pruning.

About Rugonersen

Rugonersen is an antisense oligonucleotide (ASO) designed to address the underlying disease biology of Angelman syndrome (AS) by specifically and potently binding the UBE3A-ATS transcript. Rugonersen binding is intended to trigger degradation of the UBE3A-ATS transcript in the CNS and therefore the unsilencing of the UBE3A paternal allele. Rugonersen allows neuronal expression of the paternal wild-type copy of the UBE3A gene, potentially improving neuronal function and development in AS patients.

Rugonersen’s clinical and preclinical data are detailed in the following publications: Hipp, J.F., Bacino, C.A., Bird, L.M. et al. The UBE3A-ATS antisense oligonucleotide rugonersen in children with Angelman syndrome: a Phase 1 trial. Nat Med (2025). https://doi.org/10.1038/s41591-025-03784-7 ; Jagasia et al., Angelman syndrome patient-derived neuron screen leads to clinical ASO rugonersen targeting UBE3A-ATS with long-lasting effect in monkeys, Nucleic Acids Research (2025). https://doi.org/10.1093/nar/gkaf851

About RACC

Research Alliance Corporation III (Nasdaq: RACC) is a special purpose acquisition company incorporated for the purpose of effecting a merger, share exchange, asset acquisition, share purchase, reorganization or similar business combination with one or more businesses or entities. RACC’s sponsor is an affiliate of RA Capital Management, L.P., a leading life sciences focused investment firm. RACC is led by Matthew Hammond, Ph.D., Chief Executive Officer and director and Henry Stusnick, Chief Business Officer and Chief Operating Officer.

Additional Information About the Proposed Transaction and Where to Find It

The proposed transactions will be submitted to shareholders of RACC for their consideration. RACC intends to file a registration statement on Form S-4 with the SEC, which will include a prospectus and preliminary and definitive proxy statements to be distributed to RACC’s shareholders in connection with RACC’s solicitations of proxies from RACC’s shareholders with respect to the proposed transactions and other matters to be described in the registration statement, as well as the prospectus relating to the offer of Oak Hill Bio’s business in connection with the completion of the proposed transactions. After the registration statement has been filed and declared effective, RACC will mail a definitive proxy statement/prospectus and other relevant documents relating to the proposed transactions and other matters to be described in the registration statement to RACC’s shareholders as of a record date to be established for voting on the proposed transactions. Before making any voting or investment decision, RACC’s shareholders, Oak Hill Bio’s shareholders, and other interested persons are urged to read these documents and any amendments thereto, as well as any other relevant documents filed with the SEC by RACC in connection with the proposed transactions and other matters to be described in the registration statement, when they become available because they will contain important information about RACC, Oak Hill Bio and the proposed transactions. Shareholders will also be able to obtain free copies of the preliminary proxy statement/prospectus, the definitive proxy statement/prospectus and other documents filed by RACC with the SEC, once available, without charge, at the SEC’s website located at www.sec.gov, or by directing a written request to Research Alliance Corporation III, 600 Fifth Avenue, 23rd Floor, New York, New York 10020.

Contacts

Oak Hill Bio

Investors

John Fraunces, LifeSci Advisors

jfraunces@lifesciadvisors.com

Media

media@oakhillbio.com