Cambridge, MA (May 30)—Genzyme (www.genzyme.com) agreed to buy its US partner Bioenvision (New York, www.bioenvision.com) in an all-cash transaction. Genzyme will pay $5.60 per share to acquire Bioenvision—roughly 6.7% more than Bioenvision’s closing price last Friday. The acquisition’s total value is approximately $345 million. Genzyme is pursuing the deal to gain exclusive rights to clofarabine, a cancer drug the companies developed together.

Genzyme markets clofarabine as “Clolar” in the United States and Canada to treat relapsed and refractory pediatric acute lymphoblastic leukemia (ALL) patients. The United States and the European Union granted clofarabine orphan-drug status for ALL and acute myeloid leukemia (AML). Genzyme seeks to expand clofarabine’s use into adult populations, especially to treat AML.

Bioenvision markets clofarabine in Europe and also markets “Modrenal” (trilostane), a postmenopausal breast-cancer drug approved in the United Kingdom.

Both companies’ boards of directors approved the transaction, which is scheduled to be completed in July and subject to customary closing conditions.

Steven Rouhandeh, a significant Bioenvision shareholder, and his investment vehicles SCO Capital Partners and SCO Securities said on Wednesday they opposed the deal. In a letter to Bioenvision’s board, Rouhandeh claimed the offer “does not adequately reflect the long-term value of Bioenvision’s drug pipeline.” SCO Capital Partners owned 13.4% of Bioenvision’s outstanding common stock as of May 3, according to a regulatory filing.