Direct Editing of Cysteine to Electrophilic Alkyl Halides in Peptides.

Functional group conversion is a cornerstone of modern synthetic chemistry. Many strategies routinely employed for small-molecule transformations are unsuitable for modifying biomacromolecules, including peptides. Here, we describe a simple but chemoselective approach that directly converts the nucleophilic cysteine carbon-thiol side chain into an electrophilic carbon-halogen bond under mild conditions, compatible with diverse peptides. The incorporation of this versatile synthetic handle facilitates a range of subsequent transformations that are rarely, if ever, applied to complicated peptides. We envision that this side-chain editing methodology will open a broad expanse of unexplored peptide chemical space, which will concomitantly unlock applications for an entire class of new biomacromolecules.