Exploration of P1 and P4 modifications of nirmatrelvir: Design, synthesis, biological evaluation, and X-ray structural studies of SARS-CoV-2 Mpro inhibitors.

We report the synthesis, biological evaluation, and X-ray structural studies of a series of SARS-CoV-2 Mpro inhibitors based upon the X-ray crystal structure of nirmatrelvir, an FDA approved drug that targets the main protease of SARS-CoV-2. The studies involved examination of various P4 moieties, P1 five- and six-membered lactam rings to improve potency. In particular, the six-membered P1 lactam ring analogs exhibited high SARS-CoV-2 Mpro inhibitory activity. Several compounds effectively blocked SARS-CoV-2 replication in VeroE6 cells. One of these compounds maintained good antiviral activity against variants of concern including Delta and Omicron variants. A high-resolution X-ray crystal structure of an inhibitor bound to SARS-CoV-2 Mpro was determined to gain insight into the ligand-binding properties in the Mpro active site.