Structure and total synthesis of cyclodidemnamide B, a cycloheptapeptide from the ascidian Didemnum molle

A new cycloheptapeptide, cyclodidemnamide B (1), has been isolated from the marine ascidian Didemnum molle, collected at Ibo island, Mozambique. The structure of the bisthiazole-containing macrocyclic peptide was initially assigned using 2D NMR analysis and data comparisons with cyclodidemnamide. The absolute configuration was deduced after hydrolysis and characterization of degradation residues by chiral HPLC analysis. The total synthesis served as an unambiguous structural and stereochemical proof.