Diastereomeric Resolution Yields Highly Potent Inhibitor of SARS-CoV-2 Main Protease

Abstract

SARS-CoV-2 is the causative agent behind the COVID-19 pandemic. The main protease (M^pro, 3CL^pro) of SARS-CoV-2 is a key enzyme that processes polyproteins translated from the viral RNA. M^pro is therefore an attractive target for the design of inhibitors that block viral replication. We report the diastereomeric resolution of the previously designed SARS-CoV-2 M^pro α-ketoamide inhibitor <b>13b</b>. The pure (<i>S,S,S</i>)-diastereomer, <b>13b-K</b>, displays an IC₅₀ of 120 nM against the M^pro and EC₅₀ values of 0.8-3.4 μM for antiviral activity in different cell types. Crystal structures have been elucidated for the M^pro complexes with each of the major diastereomers, the active (<i>S,S,S</i>)-13b (<b>13b-K</b>), and the nearly inactive (<i>R,S,S</i>)-13b (<b>13b-H</b>); results for the latter reveal a novel binding mode. Pharmacokinetic studies show good levels of <b>13b-K</b> after inhalative as well as after peroral administration. The active inhibitor (<b>13b-K</b>) is a promising candidate for further development as an antiviral treatment for COVID-19.