Structure/function aspects of neutral P1 residue peptide inhibitors of thrombin

Control of thrombin by its inhibition in indications such as myocardial infarction, unstable angina or stroke has been demonstrated to be therapeutically valuable. However restoration of hemostasis by targeting thrombin while avoiding its fellow serine proteinases, (e.g. plasmin, trypsin), remains a challenge of medicinal chemistry. Tripeptide-boronates and -phosphonates with neutral P1 side chains meet these criteria. Development of novel, high yielding chemical routes furnishes a wide range of un-natural P1 functionalities, demonstrating that this indeed is a class effect with selectivity conferred by the uncharged P1 residue. For example N-benzyloxycarbonyl-D-phenylalanylprolyl-1- (3-methoxypropyl) boroglycine ester (1) has a Ki value for thrombin of 7 nM and greater than two order of magnitude higher with all other serine proteinases tested. The ester group determines the kinetics of inhibition by tripeptide phosphonates, with diphenylphosphonates being slow tight binding inhibitors, showing 50% reversibility of inhibition. Therefore this design of inhibitors offers a facile strategic approach to development as thrombin specific pharmaceutical agents.