Synthesis of Novel Thrombin Inhibitors. Use of Ring-Closing Metathesis Reactions for Synthesis of P2 Cyclopentene- and Cyclohexenedicarboxylic Acid Derivatives

The thrombin inhibitory tripeptide d-Phe-Pro-Arg has been mimicked using either cyclopentenedicarboxylic derivatives or a cyclohexenedicarboxylic derivative as surrogate for the P2 proline. In the P3 position, tertiary amides were optimized as d-Phe P3 replacements. The P1 arginine was, in all compounds, substituted with the more rigid and biocompatible 4-aminomethylbenzamidine. One of the novel inhibitors was cocrystallized with alpha-thrombin and subjected to X-ray analysis. From analysis of the X-ray crystal structure, new ligands were designed leading to significantly improved binding affinity, the lead candidate exhibiting an in vitro IC(50) of 49 nM.