Chloromethyl ketone (CMK) inhibitor complex. Apo Mpro crystals grown under pH 6.0 were soaked in a number of different
small-molecule inhibitors. The best results were obtained by using a 5.0-mM solution of the substrate-analogue CMK inhibitor
(9), Cbz–Val–Asn–Ser–Thr–Leu–Gln–CMK in 7.5% PEG