Novel Morpholinone-Based d-Phe-Pro-Arg Mimics as Potential Thrombin Inhibitors: Design, Synthesis, and X-ray Crystal Structure of an Enzyme Inhibitor Complex Original Research Article

A morpholinone structural motif derived from d(+)- and l(−)-malic acid has been used as a mimic of d-Phe-Pro in the thrombin inhibiting tripeptide d-Phe-Pro-Arg. In place of Arg the more rigid P1 truncated p-amidinobenzylamine (Pab) or 2-amino-5-aminomethyl-3-methyl-pyridine have been utilized. The synthetic strategy developed readily delivers these novel thrombin inhibitors used to probe the α-thrombin inhibitor binding site. The best candidate in this series of thrombin inhibitors exhibits an in vitro IC50 of 720 nM. The X-ray crystal structure of this candidate co-crystallized with α-thrombin is discussed.