Site-Specific Dual Functionalization of Cysteine Residue in Peptides and Proteins with 2-Azidoacrylates

Herein, we report use of 2-azidoacrylates to perform site-specific dual functionalization of the cysteine residue of peptides and bovine serum albumin (BSA), a native protein containing one free cysteine residue. The sulfhydryl group of the cysteine residue could be conjugated with 2-azidoacrylates bearing various functionalities, such as fluorescent dyes under physiological aqueous buffer conditions, to afford peptide and protein conjugates anchoring an azide moiety. Successive azide–alkyne cycloaddition enables installation of the second functionality, thus affording dual-functionalized peptide- and protein-based materials.