New Haven, CT and London, U.K., – April 14, 2008 – Rib-X Pharmaceuticals, Inc. (“Rib-X” or the “Company”), a development-stage company focused on the discovery and development of novel antibiotics for the treatment of antibiotic-resistant infections, and the Laboratory of Molecular Biology of the Medical Research Council (MRC) today announced they have renewed their research collaboration agreement in the area of ribosome and antibiotic structure and function for an additional year. Under the terms of the Agreement, Rib-X and the MRC will continue to jointly explore the high resolution crystal structure of the 70S ribosome.

"Using information discovered about the ribosome during our first year of work with the MRC, Rib-X has been able to advance the iterative intelligent discovery engine that the Company developed to design novel antibiotic scaffolds which circumvent the mechanisms employed by resistant bacteria,” said Erin Duffy, Ph.D., Rib-X’s Vice President of Structure-Based Drug Design. "This is a natural extension of our relationship with MRC, which will build upon Dr. Venki Ramakrishnan’s discovery of the structure of the full 70S ribosome and, in turn, increase our understanding, on an atomic level, of the binding properties of antibiotics to the 50S subunit of the ribosome.”

About Rib-X Pharmaceuticals, Inc.
Rib-X Pharmaceuticals is a product-driven small molecule drug discovery and development company focused on the structure-based design of new classes of antibiotics. The Company's underlying drug discovery engine capitalizes on its proprietary high-resolution crystal structure of the ribosome, which performs an essential role in the fundamental process of protein synthesis. Many known, commercially valuable antibiotics bind to the ribosome, including those used to treat both community-acquired and hospital-acquired pathogens. The Company's integrated research strategy, which combines state of the art, proprietary computational analysis, X-ray crystallography, medicinal chemistry, microbiology and biochemistry, allows it to rapidly synthesize new agents designed to avoid typical antibiotic resistance mechanisms. Rib-X's iterative intelligent engine has yielded several distinctive new antibiotic classes. The Company currently has two programs in human clinical trials, the RX-1741 designer oxazolidinone program as an oral/IV agent to treat serious hospital Gram-positive infections and the RX-3341 program, a next generation fluoroquinolone, active against a broad spectrum of bacteria, including methicillin-resistant Staphylococcus aureus. Additionally, the Company has multiple drug discovery programs. The first of these programs is focused on design and development of an orally active macrolide for community use for treatment of skin infections, including those caused by MRSA. The second discovery program is directed towards identifying a new chemical class of antibiotics active against multi-drug resistant Gram negative bacteria.

About the Medical Research Council
The Medical Research Council is dedicated to improving human health through excellent science. It invests on behalf of the UK taxpayer. Its work ranges from molecular level science to public health research, carried out in universities, hospitals and a network of its own units and institutes. The MRC liaises with the Health Departments, the National Health Service and industry to take account of the public's needs. The results have led to some of the most significant discoveries in medical science and benefited the health and wealth of millions of people in the UK and around the world. For more information about the Medical Research Council, visit www.mrc.ac.uk

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