Nazumazoles A-C, Cyclic Pentapeptides Dimerized through a Disulfide Bond from the Marine Sponge Theonella swinhoei.

A mixture of nazumazoles A-C (1-3) was purified from the extract of the marine sponge Theonella swinhoei. The mixture was eluted as an extraordinarily broad peak in the reversed-phase HPLC. The structures of nazumazoles were determined by interpretation of the NMR data and chemical degradations. Nazumazoles contain one residue each of alanine-derived oxazole and α-keto-β-amino acid residue. Nazumazoles exhibited cytotoxicity against P388 cells.