Formation of multiple intramolecular disulfide bonds in peptides using the reagent trans-[Pt(ethylenediamine)2Cl2]2+

The disulfide-bond forming reagent trans-[Pt(en)2Cl2]2+ cleanly, rapidly and quantitatively converts fully reduced α-conotoxin GI and α-conotoxin SI to their three disulfide bond-containing regioisomers in one-step in media of pH 3–7, enabling the convenient synthesis of the three isomers.