Azapeptide epoxides (APEs) are another class of SARS‐CoV‐1 Mpro inhibitors, although they were originally developed for clan CD cysteine peptidases. 152 ,  153  The epoxide S,S‐diastereomer 60 (K inact/K i, 1900 (±400) M−1·s−1; Figure 17) exhibited the best inhibitory activity against SARS‐CoV Mpro. 154  The X‐ray structure of Mpro in complex with 60 confirmed the formation of a covalent bond between the cysteine‐S atom and the epoxide C‐3. It is worth noting that the S,S‐configured epoxide is required for the activity.