-- Company to present interim results from phase 2 trial of novel compound RX-1741 --

New Haven, CT – April 3, 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 Albert Collinson, Ph.D., Chief Business Officer, will be presenting at the 10th Annual Superbugs & Superdrugs Conference on April 9, 2008 in London, UK. Dr. Collinson will disclose interim results from Rib-X’s Phase 2 clinical trial of RX-1741 in the treatment of uncomplicated skin and soft tissue infections (uSSTI).

RX-1741 was discovered using Rib-X’s proprietary computational tools and knowledge of the three dimensional structure of the 50S subunit of the ribosome. An oxazolidinone antibiotic that exhibits activity against methicillin-resistant Staphylococcus aureus (MRSA) and other Gram-positive organisms, RX-1741 has demonstrated both wider spectrum and stronger potency of activity than Zyvox® (linezolid), the only currently marketed product in this compound class.

uSSTI Study Design
The uSSTI study is a Phase 2, multicenter, randomized, open-label, comparative study to evaluate the safety and efficacy of RX-1741 versus linezolid in the outpatient treatment of adults with uSSTI. The study assesses the efficacy, safety and tolerability of a once or twice daily dose of RX-1741 compared to a twice daily dose of linezolid. Dosing is given for five to ten days for the treatment of ambulatory patients with uSSTI.

The uSSTI study will enroll approximately 150 patients in study centers across the US. The Company intends to release final data from all patients during the first half of 2008.

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.

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