Concert Pharmaceuticals Announces Milestone Achievement in GlaxoSmithKline Collaboration

Lexington, MA –- June 20 , 2011 -- Concert Pharmaceuticals, Inc. today announced that it has achieved a milestone in its strategic alliance with GlaxoSmithKline (GSK) for its HIV protease inhibitor (HIV-PI) development program, resulting in a $4 million milestone payment to Concert. The strategic alliance with GSK was formed in 2009. In the HIV development program a number of deuterium modified-versions of atazanavir were evaluated preclinically, and a subset was selected for further testing in early human clinical studies. Based on the human data, CTP-298 was selected as the lead compound for further development. Concert expects the program will advance into initial clinical efficacy trials in HIV-positive patients next year.

"We are very pleased by the continuing progress of our alliance with GSK and their support of CTP-298’s clinical development," said Roger Tung, Ph.D., President and CEO of Concert Pharmaceuticals. "For this contractual milestone our lead candidate met certain clinical criteria that included improved pharmacokinetics, as compared to atazanavir in healthy human subjects. Achieving those criteria demonstrates the potential of selective deuterium substitution to clinically improve compound performance and represents a significant advancement in our program."

The goal of the HIV-PI development program is to create a potent, once-daily protease inhibitor that does not require ritonavir as a pharmacokinetic boosting agent, and that can be dosed as part of a fixed dose combination with other HIV replication inhibitors. Eliminating the need for ritonavir, which is currently co-administered per label with all once-daily HIV protease inhibitors to increase their blood levels, could provide significant advantages over current standard-of-care. To this end, Concert prepared deuterium-modified versions of atazanavir utilizing its DCE Platform™ (deuterium chemical entity platform). Extensive preclinical testing and comparative human pharmacokinetic studies enabled the identification of CTP-298 as an agent that retains atazanavir’s antiviral potency but improves on its pharmacokinetic behavior, in particular raising C24 plasma concentrations.

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, because deuterium is heavier than hydrogen, it forms a stronger chemical bond to carbon. The stronger chemical bond obtained by selective deuterium modification may, in certain cases, substantially improve a 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 applying the company’s DCE Platform™ (deuterated chemical entity platform) to create novel and differentiated small molecule drugs. Concert’s approach leverages decades of pharmaceutical and clinical experience to reduce the time, risk and expense needed to create important new medicines. The Company has a broad research pipeline encompassing many therapeutic areas including antiviral disease, renal disease and CNS disorders, among others. Founded in 2006, Concert has raised more than $110 million of venture and institutional capital. For more information on Concert Pharmaceuticals, please visit www.concertpharma.com.

Concert Pharmaceuticals, the CoNCERT logo and the DCE Platform are trademarks of Concert Pharmaceuticals, Inc.