Disulfide bond formation in S-Acetamidomethyl cysteine-containing peptides by the combination of silver trifluoromethanesulfonate and dimethylsulfoxide / aqueous HCl

S-Acetamidomethyl (Acm) cysteine was found to be converted quantitatively to cystine by deprotection of the Acm group with silver trifluoromethanesulfonate (AgOTf) followed by dimethylsulfoxide (DMSO) / aqueous hydrochloric acid (HCl) treatment. No significant side reactions were observed with oxidation-sensitive amino acids such as Met, Tyr, and Trp under these reaction conditions. This method has been applied successfully to the syntheses of oxytocin and a Trp-containing peptide, urotensin II.