Synthesis and Optimization of Small Molecule Inhibitors of Prostate Specific Antigen.

Semen liquefaction is a postejaculation process that transforms semen from a gel-like (coagulated) form to a water-like consistency (liquefied). This process is primarily regulated by serine proteases from the prostate gland, most prominently, prostate-specific antigen (PSA; KLK3). Inhibiting PSA activity has the potential to impede liquefaction of human semen, presenting a promising target for nonhormonal contraception in the female reproductive tract. This study employed triazole B1 as a starting compound. Through systematic design, synthesis, and optimization, we identified compound 20 (CDD-3290) as a 216 nM inhibitor of PSA with better stability in media than triazole B1. Further, we also evaluated the selectivity profile of compound 20 (CDD-3290) by testing against closely related proteases and demonstrated excellent inhibition of PSA versus α-chymotrypsin and elastase and similar potency versus thrombin. Thus, compound 20 is an improved PSA inhibitor that can be tested for efficacy in vitro or in the female reproductive tract.