Structure-based discovery of highly bioavailable, covalent, broad-spectrum coronavirus MPro inhibitors with potent in vivo efficacy

The main protease (M^Pro) of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a validated drug target. Starting with a lead-like dihydrouracil chemotype identified in a large-library docking campaign, we improved M^Pro inhibition >1000-fold by engaging additional M^Pro subsites and using a latent electrophile to engage Cys¹⁴⁵. Advanced leads from this series show pan-coronavirus antiviral activity, low clearance in mice, and for AVI-4773, a rapid reduction in viral titers >1,000,000 after just three doses. Both compounds are well distributed in mouse tissues, including brain, where concentrations >1000× the 90% effective concentration are observed 8 hours after oral dosing for AVI-4773. AVI-4516 shows minimal inhibition of major cytochrome P450s and human proteases. AVI-4516 also exhibits synergy with the RNA-dependent RNA polymerase inhibitor, molnupiravir, in cellular infection models. Related analogs strongly inhibit nirmatrelvir-resistant M^Pro mutant virus. The properties of this chemotype are differentiated from existing clinical and preclinical M^Pro inhibitors and will advance therapeutic development against emerging SARS-CoV-2 variants and other coronaviruses.