Deprotection of S-Acetamidomethyl and 1,3-Thiazolidine-4-Carbonyl Protecting Groups from Cysteine Side Chains in Peptides by -[PtX(CN)]: One-Pot Regioselective Synthesis of Disulfide Bonds.

In this study, we developed an efficient approach for disulfide bond formation in peptides utilizing the Pt(IV) complex -[PtBr(CN)] to mediate Acm and Thz deprotections. [PtBr(CN)] can oxidatively deprotect two Acm groups or deprotect one Thz group and one Acm group to directly form an intramolecular disulfide bond in peptides. Several disulfide-containing peptides with excellent yields were achieved via the deprotection method in an aqueous medium under aerobic conditions. Kinetic studies indicated that the dominant path of the reaction is of first-order in both [Pt(IV)] and [peptide]; moreover, the deprotection rate increased dramatically with the addition of NaBr. A mechanism including a bromide-bridge-mediated electron transfer process was proposed. Apamin, α-conotoxin SI, and the parallel homodimer of oxytocin, all containing two disulfide bonds, were synthesized regioselectively through a one-pot method by the combined use of the above deprotection approach with oxidants l-methionine selenoxide and [PtBr(CN)]. All of the reactions were completed within 30 min to afford good yields for these peptides.