GlaxoSmithKline acquires Sirtris Pharmaceuticals, Inc., a world leader in sirtuin research and development

Issued – Friday 6 June 2008, London, UK, Philadelphia, PA, Cambridge, MA

GlaxoSmithKline (GSK) announced today that it has completed its acquisition of Sirtris Pharmaceuticals, Inc. (Sirtris) for approximately USD720 million (or approx. GBP362 million) through a cash tender offer of USD22.50 (or approx. GBP11.33) per share.

Through the acquisition of Sirtris, GSK has significantly enhanced its metabolic, neurology, immunology and inflammation research efforts by establishing a presence in the field of sirtuins, a recently discovered class of enzymes that is believed to be involved in the ageing process.

Sirtris will become part of GSK’s Drug Discovery organisation, while continuing to operate from laboratories in Cambridge, Massachusetts as an autonomous drug discovery unit. Christoph Westphal, CEO and Vice Chair of Sirtris, and the management team will continue to lead this autonomous unit.

About GSK
GSK – one of the world’s leading research-based pharmaceutical and healthcare companies – is committed to improving the quality of human life by enabling people to do more, feel better and live longer. For company information including a copy of this announcement and details of the company’s updated product development pipeline, visit GSK at www.gsk.com.

About Sirtris Pharmaceuticals
Sirtris Pharmaceuticals is a biopharmaceutical company focused on discovering and developing proprietary, orally available, small molecule drugs with the potential to treat diseases associated with aging, including metabolic diseases such as Type 2 Diabetes. Our drug candidates are designed to mimic certain beneficial health effects of calorie restriction, without requiring a change in eating habits, by activation of sirtuins, a recently discovered class of enzymes that the Company believes control the aging process. Sirtris Pharmaceuticals is engaged in human clinical trials for Type 2 Diabetes, and is planning similar trials in cancer, another age-related disease. Sirtris is also engaged in a human clinical trial for MELAS, a mitochondrial disorder. The company’s headquarters are in Cambridge, Massachusetts. On June 2, 2008, GlaxoSmithKline plc announced the successful completion by an indirect wholly-owned subsidiary of a tender offer to purchase all of the outstanding shares of Sirtris common stock. Approximately 97% of Sirtris's outstanding shares were tendered in the offer.

This press release contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. Such statements include, but are not limited to, the potential therapeutic effects of SIRT1 activators including NCEs for diseases of aging, such as Type 2 Diabetes; the success of SIRT1 activators as therapies for diseases, such as Type 2 Diabetes; the progress and results of preclinical and clinical studies of SIRT1 activators, such as SRT501 and Sirtris’ NCEs; and the potential of sirtuin modulators to receive regulatory approval. These forward-looking statements about future expectations, plans and prospects of Sirtris Pharmaceuticals involve significant risks, uncertainties and assumptions, including risks related to the lack of results that would provide a basis for predicting whether any of the Company’s product candidates will be safe or effective, or receive regulatory approval, the possibility that results of pre-clinical studies are not necessarily predictive of clinical trial results, the Company’s potential inability to initiate and complete pre-clinical studies and clinical trials for its product candidates, the fact that none of the Company’s product candidates has received regulatory approvals, the potential inability of the Company to gain market acceptance of the Company’s product candidates, and those other risks factors that can be found in the Company’s filings with the Securities and Exchange Commission. Actual results may differ materially from those Sirtris Pharmaceuticals contemplated by these forward-looking statements. Sirtris Pharmaceuticals does not undertake to update any of these forward-looking statements to reflect a change in its views or events or circumstances that occur after the date of this release.

Enquiries:
UK Media enquiries:
Philip Thomson
(020) 8047 5502

Claire Brough
(020) 8047 5502

Alice Hunt
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Gwenan White
(020) 8047 5502

US Media enquiries:
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Mary Anne Rhyne
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European Analyst/Investor enquiries:
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(020) 8047 5564

Sally Ferguson
(020) 8047 5543

Gary Davies
(020) 8047 5503

US Analyst/ Investor enquiries:
Frank Murdolo
(215) 751 7002

Tom Curry
(215) 751 5419