Cocrystal structure of the covalent adduct of 2 bound to SARS CoV-1 3CLpro (PDB code 6XHO). The Connolly surface for the inhibitor binding pocket is shown in gray. The bonds are represented as the dashed lines, with the bond length measured between heavy atoms. The views are centered on warhead with active-site interactions and of complete inhibitor–protein interactions depicted.