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MediChem Life Sciences and Rigel Pharmaceuticals Enter into Structural Proteomics Agreement Focused on Ubiquitin Ligases

Chicago and South San Francisco - September 05, 2001

MediChem Life Sciences (NASDAQ: MCLS) and Rigel Pharmaceuticals (NASDAQ: RIGL), both drug discovery companies, announced today that they have entered into a two-year collaborative agreement in structural proteomics for new drug development initially focused on the area of ubiquitin ligases. Ubiquitin ligase activity is involved in cell division and the progression of certain cancers and has become an important new area of research in the field of oncology.

Under the terms of the agreement, scientists at MediChem’s Emerald BioStructures structural proteomics division will express, purify and co-crystallize important protein complexes that are part of Rigel’s anti-cancer program focusing on ubiquitin ligases. When the co-crystallizations are complete, MediChem will utilize Argonne National Laboratory’s Advanced Photon Source (APS) to collect the data necessary to determine the structures of the protein complexes at near-atomic resolution. MediChem will also co-crystallize several of Rigel’s small molecule drug leads with the protein complexes. This will provide Rigel researchers with a detailed three-dimensional picture of their drug leads bound to the target protein complexes. This structural information will be used to further optimize the chemical properties of Rigel’s drug leads.

“Our technology platform in structural proteomics enables our scientists to make complex scientific discoveries in a high-throughput fashion,” said Michael T. Flavin, Ph.D., President and CEO of MediChem. “The three-dimensional structures that MediChem provides will enable Rigel to create more effective drugs by more fully understanding the interaction of their target proteins and drug leads.”

“Ubiquitin ligase activity has become a very important and promising area of discovery research for cancer therapeutics and Rigel is proud of its leading position in this area," said Donald G. Payan, M.D., Chief Scientific Officer and Executive Vice President for Rigel. "We are developing small molecule drugs based on these protein targets and already have inhibitors of several classes of ubiquitin ligases, some of which have shown potent activity in animal models of cancer. The structural information that we gain through our collaboration with MediChem will have a significant impact on the outcome of our drug discovery programs and should help Rigel retain its leadership position in this area.”

Rigel will pay MediChem for research conducted by MediChem’s scientists during the collaboration. MediChem will also receive milestone payments for completion of specified scientific achievements, and retain rights to certain technology, data and improvements to MediChem’s structural proteomics technology platform. Rigel will also grant MediChem a right of discussion on all future medicinal chemistry partnering opportunities as related to the targets researched during this collaboration.

MediChem Life Sciences (www.medichem.com) is a drug discovery company that combines the power of structural proteomics with medicinal chemistry to deliver more effective drugs and drug targets. MediChem’s technology platform includes a broad range of integrated R&D capabilities. MediChem partners with pharmaceutical and biotechnology companies in addition to conducting proprietary research.

Rigel Pharmaceuticals (www.rigel.com) is a drug discovery and development company that uses advanced functional genomics tools to discover novel drug targets. Rigel's technology is designed to identify molecules which play an important role in regulating a human cell's response to disease by testing a very large number of proteins in a very large number of cells to determine which proteins will change the cell's response to the disease. Rigel currently has programs in asthma/allergy, autoimmunity, transplant rejection, rheumatoid arthritis, inflammatory bowel disease, chronic bronchitis, cancerous tumor growth and hepatitis C. Rigel has multi-year collaborations with Pfizer Inc., Cell Genesys, Inc., Janssen Pharmaceutica N.V. and Novartis Pharma A.G. Rigel is based in South San Francisco, California.

In addition to any historical information presented herein, this release contains forward-looking statements regarding the future activities of MediChem and Rigel within the meaning of the Private Securities Litigation Reform Act of 1995 and such statements involve a high degree of risk and uncertainty.. Many possible factors could affect future results and performance of the services and technologies of MediChem and Rigel, such that actual results and performance may differ materially. If the services and technologies of MediChem or Rigel fail to perform as expected or if there is lower demand for these than expected, the financial condition and operating results of the two companies may be materially and adversely affected. The financial condition and operating results of MediChem and Rigel may also be materially and adversely affected by a number of other factors, including, but not limited to, adverse changes in competitive and economic conditions, or difficulties and adverse actions by third parties and licensors, as well as other risks identified in MediChem’s registration statement on Form S-1 filed with the Securities and Exchange Commission and in Rigel’s Annual Report on Form 10-K for the year ended December 31, 2000 and subsequent filings made with the Securities and Exchange Commission from time to time. The information in this press release is current as of its release date and neither MediChem nor Rigel intends to update the forward-looking information contained herein.