Four new cytotoxic cyclic hexa- and heptapeptides from the marine ascidian Didemnum molle

Two novel cyclic hexapeptides, comoramides A and B and two new cyclic heptapeptides, mayotamides A and B were isolated, separately, from two collections of the compound ascidian Didemmum molle collected at two spots of the lagoon of Mayotte. The structure of all four peptides, including the absolute configuration of all amino acids, was elucidated by spectroscopic analysis, mainly NMR data, and degradation experiments. All four compounds exhibit mild cytotoxicity against several tumor cells. Obtaining four new cyclic peptides from two D. molle collections, which add to the two earlier reported cyclic peptides from an Australian and Philippine D. molle, supports the notion that these compounds originate from prokaryotic algal symbionts. (C) 1998 Elsevier Science Ltd. All rights reserved.