Cocrystal structure of the covalent adduct of 4 bound to SARS CoV-2 3CLpro (6XHM). The Connolly surface for the inhibitor binding pocket is shown in gray. The bonds are represented as dashed lines, with the bond length between heavy atoms depicted. The schematic rendering of the active site with dashed lines represented as hydrogen bonds with key residues and curved lines to show S1 and S2 binding pockets is depicted.