Rhodium-Catalyzed Synthesis of Peptide Polysulfides by Insertion of Sulfur into Unprotected Peptide Disulfides

A rhodium-catalyzed insertion of sulfur into unprotected peptide disulfides in aqueous solvents has been developed, which yields mixtures of trisulfides and tetrasulfides. This method can be applied to peptides containing amino acids such as Gly, Phe, Tyr, Ser, Met, Asp, Gln, and Lys and provides polysulfides with various amino acid residues without being affected by functional groups. A reaction can be conducted on a gram scale. Vasopressin can also be converted into its corresponding polysulfides.