Discovery and evaluation of potent P1 aryl heterocycle-based thrombin inhibitors

In an effort to discover potent, clinically useful thrombin inhibitors, a rapid analogue synthetic approach was used to explore the P-1 region. Various benzylamines were coupled to a pyridine/pyrazinone P-2-P-3 template. One compound with an o-thiadiazole benzylic substitution was found to have a thrombin K-i of 0.84 nM. A study of ortho-substituted five-membered-ring heterocycles was undertaken and subsequently demonstrated that the o-triazole and tetrazole rings were optimal. Combination of these potent P-1 aryl heterocycles with a variety of P-2-P-3 groups produced a compound with an extraordinary thrombin inhibitory activity of 1.4 pM. It is hoped that this potency enhancement in P-1 will allow for more diversification in the P-2-P-3 region to ultimately address additional pharmacological concerns.