Phthalimide derivatives as a new class of papain-like protease inhibitors in SARS-CoV-2.

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) papain-like cysteine protease (PLpro) represents one of only two essential cysteine proteases involved in the regulation of viral replication. It, therefore, qualifies as a promising therapeutic target for the development of antiviral agents. We identified a previously synthesized protease inhibitor, resulting from an earlier project, as a PLpro inhibitor and crafted a structure-activity relationship around the hit, leading to the more potent inhibitors ZHAWOC6941 (17h) and ZHAWOC25153 (17o) displaying IC values of 8 and 7 µM, respectively. The two compounds represent a new class of PLpro inhibitors and, with single-digit micromolar IC values, are comparable to inhibitors found in the literature.