Rapid and Green One-Pot Synthesis in Water: Accessing Polypeptides with Two Disulfide Bridges

Regioselective assembly of multiple disulfide bonds in peptides remains a formidable challenge in synthetic peptide chemistry. In this work, a rapid, eco-friendly one-pot strategy for the regioselective synthesis of polypeptides bearing two disulfide bonds was developed. The first disulfide bond was formed via hydrogen peroxide-mediated oxidation of dithiol precursors in water, and the second was subsequently established through iodine-triggered deprotection of two acetamidomethyl (Acm) groups under acidic conditions. Using this protocol, a series of bioactive bicyclic peptides with diverse disulfide topologies were efficiently synthesized, with overall isolated yields ranging from 54% to 74%. Remarkably, this method exhibits excellent tolerance toward Trp- and Tyr-containing peptides with no detectable oxidative byproducts; nevertheless, it cannot be applied to Met-bearing peptides, as the thioether side chain of methionine undergoes preferential oxidation. In contrast to previously reported one-pot synthetic methodologies, this approach eliminates buffers and metallic reagents, simplifies the reaction workflow, and employs pure water as the exclusive solvent alongside inexpensive, commercially available reagents. Accordingly, it serves as a mild, efficient, and environmentally benign alternative for the synthesis of two-disulfide-bridged peptides.