Expedited Approach toward the Rational Design of Noncovalent SARS-CoV-2 Main Protease Inhibitors

The main protease (M^pro) of SARS-CoV-2 is a validated antiviral drug target. Several M^pro inhibitors have been reported with potent enzymatic inhibition and cellular antiviral activity, including GC376, boceprevir, calpain inhibitors II, and XII, with each containing a reactive warhead that covalently modifies the catalytic Cys145. Coupling structure-based drug design with the one-pot Ugi four-component reaction, we discovered one of the most potent noncovalent inhibitors, 23R (Jun8-76-3A) that is structurally distinct from the canonical M^pro inhibitor GC376. Significantly, 23R is highly selective compared with covalent inhibitors such as GC376, especially toward host proteases. The cocrystal structure of SARS-CoV-2 M^pro with 23R revealed a previously unexplored binding site located in between the S2 and S4 pockets. Overall, this study discovered 23R, one of the most potent and selective noncovalent SARS-CoV-2 M^pro inhibitors reported to date, and a novel binding pocket in M^pro that can be explored for inhibitor design.