Synthesis and Structural Revision of the Cyclic Hexapeptide Dimers Antatollamides A and B.

The synthesis and structural revision of the dimerized cyclic hexapeptides antatollamides A () and B () are reported. These are unique peptides with two proline residues and bicyclic peptides combined by a disulfide bond. Cyclization and disulfide bond formation of the linear peptide led to antatollamide A (). However, the H and C NMR spectra of synthetic antatollamide A () were not consistent with those of isolated antatollamide A (). Meanwhile, the NMR spectra of the monomeric cyclic hexapeptide (Pro-Pro-Phe-dCys-Ile-Val) () and the isolated antatollamide A () were identified completely. In addition, we found that isolated antatollamide B () is (Pro-Pro-dPhe-dCys-Ile-Val) ().