αβ,α'β'-Diepoxyketones are mechanism-based inhibitors of nucleophilic cysteine enzymes.

Epoxides are an established class of electrophilic alkylating agents that react with nucleophilic protein residues. We report αβ,α'β'-diepoxyketones (DEKs) as a new type of mechanism-based inhibitors of nucleophilic cysteine enzymes. Studies with the L,D-transpeptidase Ldt from and the main protease from SARS-CoV-2 (M) reveal that following epoxide ring opening by a nucleophilic cysteine, further reactions can occur, leading to irreversible alkylation.