GlaxoSmithKline commences tender offer to acquire Sirtris Pharmaceuticals

GlaxoSmithKline plc (GSK) announced today that Fountain Acquisition Corporation, a wholly-owned subsidiary of GSK, is commencing a cash tender offer to purchase all outstanding shares of common stock of Sirtris Pharmaceuticals, Inc. (Nasdaq: SIRT) (Sirtris), for $22.50 in cash without interest and less any required withholding taxes. The tender offer is being made pursuant to a previously announced definitive agreement dated April 22, 2008 among Sirtris, Fountain Acquisition Corporation and SmithKline Beecham Corporation, a wholly-owned subsidiary of GSK.

The Sirtris board of directors has unanimously determined that the merger agreement, the tender offer and the merger are advisable and are fair to, and in the best interests of, Sirtris and Sirtris’ stockholders and unanimously recommends that Sirtris’ stockholders tender their shares in the offer.

The tender offer will expire at 12:00 midnight on Friday, May 30, 2008, unless extended in accordance with the merger agreement and the applicable rules and regulations of the Securities and Exchange Commission (SEC). The offer is subject to customary conditions, including the acquisition by GSK of a majority of the outstanding shares of Sirtris common stock on a fully diluted basis.

GSK today will file with the SEC a tender offer statement on Schedule TO setting forth in detail the terms of the tender offer. Sirtris today will file with the SEC a solicitation/recommendation statement on Schedule 14D-9 setting forth in detail, among other things, the recommendation of Sirtris’ board of directors that Sirtris’ stockholders accept the tender offer and tender their shares pursuant to the tender offer. Questions and requests for assistance may be directed to the Information Agent for the offer, MacKenzie Partners, Inc., at (212) 929-5500 or (800) 322-2885 (toll free).