Sosei declined to specify the deal size, but Senior Vice President Hironoshin Nomura said it could be similar to previous contracts with AstraZeneca Plc and Teva Pharmaceutical Industries Ltd that were in the $500 million range.

Sosei will join with Aditum Bio to form a new company named Tempero Bio to develop a drug pipeline from the compound known as HTL0014242, the companies said in a release. The drug is a selective mGlu5 negative allosteric modulator (NAM) and is now in phase 1 trials in the United States for the treatment of anxiety and substance abuse disorders.

Oakland, California-based Aditum is headed by ex-Novartis CEO Joe Jimenez and Mark Fishman, the founding president at the Novartis Institutes for Biomedical Research.

The partnership represents a new tack for Sosei, which typically does research and development for larger pharma companies in exchange for fees and royalties.

As the drug goes through trials and regulatory review, Sosei will seek to exit the investment by listing Tempero Bio or selling it off, Nomura said.

"We think the value of this pipeline programme is very high," Nomura said. "That's why we are taking the risk."

(Reporting by Rocky Swift in Tokyo)

By Rocky Swift