Benzotriazole esters (88–91; Figure 26) were discovered as novel nonpeptidic irreversible inhibitors of SARS‐CoV‐1 Mpro. 168  Among them, 91 exhibited the best enzymatic inhibitory activity, but no antiviral activity in cell‐based assays. The covalent binding mode of 91 was confirmed by electrospray ionization mass spectrometry (ESI‐MS) analyses.