Cysteine and Selenocysteine Deprotection Chemistry in Peptide Synthesis

One of the most challenging areas in the field of peptide science is the chemistry of cysteine and the need for multiple protecting groups that can be removed orthogonally to facilitate regioselective disulfide bond formation. This article reviews the methods and reagents used to remove the various protecting groups of cysteine derivatives with subsequent disulfide bond formation used in peptide synthesis. Also reviewed is the related amino acid selenocysteine, which requires benzyl-type protecting groups during synthesis. As these benzyl groups are difficult to remove using older methods, we highlight the use of electrophilic, aromatic disulfides for the removal of selenocysteine (and cysteine) protecting groups with concomitant disulfide and diselenide bond formation.