THE CRYSTAL STRUCTURE OF HUMAN [[alpha]]-THROMBIN/ LY178550 COMPLEX: 5-AMIDINOINDOLE-4-BENZYLPIPERIDINE NON PEPTIDAL ACTIVE SITE INHIBITOR. Nickolay Y. Chirgadze, Daniel J. Sall, Robert Hermann, David K. Clawson, V. Joe Klimkowski, Gerald F. Smith, Donetta S.Gifford- Moore, William J Coffman, Eli Lilly and Company, Indianapolis, IN USA

Thromboembolic diseases remain a leading cause of mortality and morbidity in developed societies. Thrombin, a trypsin-like serine protease, is a key mediator in such disease states, primarily through fibrin formation and platelet aggregation.¹ In response to the well documented liabilities associated with warfarin,² an industry wide search has been initiated to discover safe and effective, orally active thrombin inhibitors that can be used to treat thrombotic disorders. Over the past few years, a number of very potent and selective inhibitors of thrombin have identified based on the NAPAP, Argatroban (MD-805), or a D-Phe-Pro-Arg structural motifs.³ In general, however, the peptidal nature of these class of agents is prohibitive of high oral bioavailability.

In an effort to identify non peptidal inhibitors of thrombin which might have a more favorable pharmacokinetic profile than their peptide-related counterparts, we have prepared LY178550 as an initial lead for future structure-based drug design studies. Agent LY178550 consists of two primary components: 1) 5-amidinoindole which has been previously employed as an arginine surrogate in the design of inhibitors of arginine endopeptidases,⁴ and 2) a hydrophobic 4-benzylpiperidine tail which has the potential to interact with the well characterized P₃ pocket of the thrombin active site.

A crystal structure of human [[alpha]]-thrombin complexed with LY178550 was determined by X-ray technique at 2.2 Å resolution. A final complex model has crystallographic R-factor of 14.4% with standard deviation from ideal for bond distances of 0.014 Å. A clear well defined electron density was observed for the inhibitor molecule in the active site. The inhibitor main chain has a L-shape and mimics conformation of arginal trypeptides⁵. This poster will describe the X-ray crystallographic study of the interaction of LY178550 with the active site of human [[alpha]]-thrombin.

[1] In The Thrombin;1st ed.; Machovich, R., Ed.; CRC Press Inc.:, 1984.; V1, pp 1-22.

[2] Smith, G. F. et al. Thromb. Res. 1988, 50, 163-174.

[3] Scarborough, R. M., Ann. Rep. Med. Chem. 1995, 30, 71.

[4] Geratz, J. D. et al. Arch. Biochem. Biophys. 1979, 197, 551-559.

[5] Chirgadze, N.Y., et al., Amer Crystallog. Ass Meeting, Aug 9-14, 1992, v.20., 116.