Urethanyl-3-amidinophenylalanine derivatives as inhibitors of factor Xa. X-ray crystal structure of a trypsin/inhibitor complex and modeling studies

Hydrophobic urethanyl derivatives of 3-amidinophenylalanine methyl ester we re found to be relatively potent and selective factor Xa inhibitors. These compounds consist of the arginine-mimetic 3-benzamidino group as Fl residue and of hydrophobic residues as potential interaction partners for the S3/S 4 aryl binding site of the enzyme. Attempts to possibly identify their bind ing mode to factor Xa via the X-ray crystal structure of a trypsin/inhibito r complex and analogy modeling on the crystal structure of factor Xa failed . However, synthesis of enantiomerically pure (R)- and (S)-derivatives, com bined with modeling experiments, led to an hypothetical non-substrate like binding mode, which was fully confirmed by the remarkably inhanced inhibito ry potency of derivatives in which the methyl ester was replaced by arylami des for interactions with the S3/S4 enzyme binding subsites. With adamantyl oxycarbonyl-(R)-3-amidinophenylalanine-phene-thylamide a nanomolar inhibito n was obtained, thus indicating this new class of factor Xa inhibitors as a highly promising lead structure.