The amino acid cysteine plays an important role in the biological processes of protein chemistry. Through its ability to form disulfide bonds between residues, cysteines contained within a protein can control biochemical redox processes as well as assisting in maintaining the structural integrity of protein tertiary structure. Because of this, a high demand exists for synthetic methodology toward the facile and stepwise manipulation of the oxidative states in multiple cysteine-containing peptides. Numerous thiol blocking strategies have been developed for Solid Phase Peptide Synthesis which allow for orthogonal oxidative exploitation of cysteine pairs within a growing peptide chain. However, for the construction of multiple disulfide-containing peptides, additional degrees of orthogonality are necessary for strict control over sequential disulfide-forming reactions.

A novel and straightforward methodology for the deprotection of p-methoxybenzyl (pMob) and acetamidomethyl (acm) protecting groups is presented in this work. Utilizing a TFA cocktail of 2,2'-dithiobis(5-nitropyridine) (DTNP) and thioanisole, Acm- and/or pMob-protected cysteine-containing peptides are effectively deblocked within two hours at room temperature. The resulting deprotected cysteine emerges from this procedure capped as its S-Npys derivative which is easily reduced to the native sulfhydryl via treatment with excess thiol. This methodology offers an alternative, gentler deprotection protocol for thiol systems than the traditionally toxic and harsh conditions utilized for the removal of these groups (ie: heavy metal salts, HF, I₂, etc). Efforts are ongoing to optimize this methodology to on-resin cysteine deprotection (and subsequent thiol manipulation).