Discovery of α-Ketoamide inhibitors of SARS-CoV-2 main protease derived from quaternized P1 groups

Although the SARS-CoV-2 pandemic has ended, multiple sporadic cases still exist, posing a request for more antivirals. The main protease (M^pro) of SARS-CoV-2, a key enzyme for viral replication, is an attractive target for drug development. Here, we report the discovery of a new potent α-ketoamide-containing M^pro inhibitor, N-((R)-1-cyclohexyl-2-(((R)-3-methoxy-1-oxo-1-((1-(2-oxo-2-((thiazol-2-ylmethyl)amino)acetyl)cyclobutyl)amino)propan-2-yl)amino)-2-oxoethyl)-4,4-difluorocyclohexane-1-carboxamide (20j). This compound presented promising enzymatic inhibitory activity against SARS-CoV-2 M^pro with an IC₅₀ value of 19.0 nM, and an excellent antiviral activity in cell-based assay with an EC₅₀ value of 138.1 nM. This novel covalent inhibitor may be used as a lead compound for subsequent drug discovery against SARS-CoV-2.