New Haven, CT – April 22, 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, today announced that Graham Johnson, Ph.D., Chief Research Officer and Vice President, Discovery, will be presenting at the Cambridge Healthtech Institute’s 2nd Annual “The Challenge of Antibacterial Development” conference on April 24, 2008 in San Diego, CA.

Dr. Johnson’s presentation, entitled “Using Structure-Based Discovery to Define Novel Macrolide Antibiotics Targeting the 50S Ribosomal Subunit,” will focus on Rib-X’s ability to develop new antibiotic compounds using a drug discovery engine that combines a sophisticated, structure-based drug design approach with computational analyses and proprietary knowledge of the high-resolution crystal structure of the bacterial ribosome. Rib-X’s most advanced discovery program is focused on engineering novel macrolides that overcome multiple forms of bacterial resistance. This discovery program has produced several series of structurally-distinct compounds effective against a wide range of bacteria, including those generally associated with nosocomial Gram-positive infections, community respiratory-tract infections and uncomplicated skin and soft tissue infections (uSSTIs) seen both in the hospital and community settings. Three distinct compound families with drug-like properties are being advanced for Phase 1 studies to commence late in 2008. In his presentation, Dr. Johnson will highlight the Rib-X structure-driven drug discovery approaches yielding this richness of novel, orally bioavailable macrolides.

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 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.

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