Secondary structure peptide mimetics: Design, synthesis, and evaluation ofbeta-strand mimetic thrombin inhibitors

Constrained dipeptide mimetic templates were designed to mimic the secondar y structure of peptides in a beta-strand conformation. Two templates corres ponding to the D-Phe-Pro portion of the thrombin inhibitor D-Phe-Pro-ArgCH( 2)Cl were synthesized and converted into nine alpha-ketoamide and alpha-ket oheterocycle inhibitors of thrombin. Additionally, a template corresponding to L-Phe-Pro was synthesized and converted to a thrombin inhibitor. The in vitro inhibition of thrombin by these compounds was determined, and those corresponding to the D-Phe-Pro were found to be more potent inhibitors than the L-Phe-Pro mimetic. The alpha-ketoamides were found to be more potent t han the alpha-ketoheterocycles but had much slower on rates. By comparison of a series of alpha-ketoamide analogues, it is apparent that the there is a preference for binding of bulky hydrophobic substituents in the P' portio n of the thrombin active site. Three of the inhibitors (MOL098, MOL144, and MOL174) were screened against a series of coagulation and anticoagulation enzymes and found to be selective for inhibition of the coagulation enzymes . Two of the inhibitors were tested in in vitro models of intestinal absorp tion and found to have low absorption potential. The compounds were then te sted in vivo in both rats and primates, and one of them (MOL144) was approx imately 25% absorbed in both species. This study has delineated the synthes is of constrained dipeptide beta-strand mimetics and validated the potentia l for compounds of this type as potent thrombin inhibitors and possible dru g leads.