GlaxoSmithKline to buy Sirtris for $720M

British drug giant GlaxoSmithKline PLC has agreed to acquire Sirtris Pharmaceuticals Inc. of Cambridge for $720 million.

Glaxo said it would keep Sirtris (NASDAQ: SIRT) as an autonomous unit of its drug discovery business and plans to retain Sirtris CEO Christoph Westphal and the rest of the company's employees. The British pharmaceutical firm (NYSE: GSK) plans to begin a tender offer of $22.50 per share of Sirtris common stock in May and close the deal in the second quarter of 2007. Sirtris's stock closed at $12.23 per share Tuesday.

Sirtris has gained wide recognition for its experimental, anti-aging treatments. The firm has a pipeline of small-molecule drugs that target genes linked to enzymes called sirtuins that are believe to have anti-aging effects and could be used to treat diabetes, cancer and other major diseases.

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With 57 employees, the biotech firm reported a 2007 net loss of $31.1 million and no revenue. Glaxo said it would maintain Sirtris' operations in Cambridge.