Concert Pharmaceuticals and GlaxoSmithKline Form Alliance to Develop Novel Deuterium Modified Drugs

Concert Pharmaceuticals and GlaxoSmithKline (NYSE: GSK) announced today that they will collaborate to develop and commercialize deuterium-containing medicines. The deal includes three of Concert’s research and development programs; namely, CTP-518, a protease inhibitor for the treatment of HIV expected to enter Phase I clinical trials in the second half of 2009, a preclinical compound for chronic renal disease, and a third research product in Concert’s pipeline. Concert will also provide GSK with deuterium-modified versions of three GSK pipeline compounds for GSK to develop.

Under the terms of the agreement, Concert will receive $35 million in upfront payments, including a $16.7 million equity investment by GSK. Concert is eligible to receive milestones and tiered, double-digit royalties based on deuterium-containing products arising from the Concert pipeline programs. In addition, Concert is eligible to receive milestones as well as royalties on the sales of deuterium-containing products arising from the GSK pipeline compounds. Overall, Concert has the potential to receive in excess of $1 billion in total milestone and upfront payments from GSK spread across all programs.

For each Concert pipeline program, Concert will have responsibility for research and development activities through completion of pre-agreed clinical trials. After the completion of such clinical trials for each program, or earlier if it chooses, GSK may elect to obtain an exclusive, worldwide license to product candidates within the program. At such time, GSK will assume responsibility for development and commercialization. Concert will retain full rights to further develop and commercialize its product candidates in any program GSK chooses not to license.

“This agreement marks GSK’s continued efforts to access the best science and technology platforms worldwide,” said Patrick Vallance, Senior Vice-President Drug Discovery, GSK. “We believe Concert’s approach to deuterium modification of medicines has broad potential to enhance certain drug properties and result in innovative new medicines.”

“We are pleased to collaborate with GSK and to advance innovative small molecule drug candidates using our deuterium chemistry approach,” said Roger Tung, Ph.D., President and Chief Executive Officer of Concert Pharmaceuticals. “This collaboration is a major step forward in our strategy to advance a broad pipeline of novel deuterium-modified therapeutics.”

About CTP-518

CTP-518 is a novel HIV protease inhibitor developed from Concert’s deuterium chemistry platform by replacing certain key hydrogen atoms of atazanavir with deuterium. Concert has demonstrated in pre-clinical studies that selective deuterium modification of atazanavir fully retains its antiviral potency but can markedly slow hepatic metabolism, thereby increasing half life and plasma trough levels. As a result, CTP-518 could potentially avoid the need to use a protease inhibitor boosting agent such as ritonavir. Current standard of care is to co-administer HIV protease inhibitors with ritonavir. However, significant complications are associated with ritonavir. Importantly, because the relationship between atazanavir trough plasma levels and clinical virological response is well-established, Phase 1 testing is expected to provide clinical validation of CTP-518. CTP-518 has the potential to be the first HIV protease inhibitor to eliminate the need to co-dose with a boosting agent.

About Deuterium

Deuterium is a safe, non-radioactive relative of hydrogen that can be isolated from sea water and has been used extensively in human metabolic and clinical studies. Since deuterium is an isotope of hydrogen, deuterium-containing compounds are expected to have similar pharmacological activity as their hydrogen analogs. However, as deuterium is heavier than hydrogen, it therefore forms a stronger chemical bond to a carbon atom of a molecule. The stronger chemical bond obtained by selective deuterium modification may substantially improve the drug’s metabolic properties, potentially resulting in better safety, tolerability and/or efficacy.

About Concert

Concert Pharmaceuticals is a clinical stage biotechnology company focused on the application of deuterium chemistry to create novel small molecule drugs. Concert’s approach leverages known activity and safety of existing drugs to reduce time, risk and expense of drug research and development. The Company has a broad research pipeline encompassing many therapeutic areas including renal disease, infectious disease, and cardiovascular disease, among others. Its lead development candidate is the HIV protease inhibitor CTP-518. Founded in 2006, Concert has raised more than $96 million from leading venture capitalists and institutional investors. For more information on Concert Pharmaceuticals, please visit www.concertpharma.com.

About GSK

GlaxoSmithKline – 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 further information please visit www.gsk.com

Cautionary Statement

Under the safe harbor provisions of the U.S. Private Securities Litigation Reform Act of 1995, GSK cautions investors that any forward-looking statements or projections made by GSK, including those made in this announcement, are subject to risks and uncertainties that may cause actual results to differ materially from those projected. Factors that may affect GSK's operations are described under 'Risk Factors' in the 'Business Review' in the company' s Annual Report on Form 20-F for 2008.

CoNCERT and CoNCERT Pharmaceuticals are trademarks of Concert Pharmaceuticals, Inc