STRUCTURE BASED DESIGN OF THROMBIN ACTIVE-SITE INHIBITORS. John S. Sack¹, Shari L. Ohringer¹, ChiehYing Y. Chang^1, Mary F. Malley², Lydia Tabernero^1,3 and Howard M. Einspahr^1, Departments of Macromolecular Crystallography¹ and Solid State Chemistry^2, Bristol-Myers Squibb Pharmaceutical Research Institute, P.O Box 4000, Princeton, NJ 08543-4000 U.S.A. ³Current address: Department of Biological Sciences, Lilly Hall of Life Sciences, Purdue University , West Lafayette, IN 47907 USA.

Human thrombin, an important enzyme in the blood coagulation response, has been crystallized in the presence of a variety of high affinity, synthetic active-site inhibitors. X-ray crystallography has been used to determine the orientations of the inhibitors in the thrombin active site and the modes of inhibitor binding. Knowledge of the specifics of inhibitor binding proved useful in the design of successively more potent inhibitors.

Our laboratory used high molecular weight polyethylene glycol precipitations at acidic pH to produce crystalline ternary complexes of thrombin with active site inhibitors and an exosite blocking agent. This inhibitor design effort will be described in the context of the overall thrombin effort in the pharmaceutical community. In our case, the most important contributions were to examine those structures that did not fit the expected structure-activity relationships. It was by analyzing these structures that we were able to provided the chemists with new and useful design information.