4 NEW CYTOTOXIC CYCLIC HEXAPEPTIDES AND HEPTAPEPTIDES FROM THE MARINEASCIDIAN 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, in cluding the absolute configuration of all amino acids, was elucidated by spectroscopic analysis, mainly NMR data, and degradation experiment s. All four compounds exhibit mild cytotoxicity against several tumor cells. Obtaining four new cyclic peptides from two D. molle collection s, which add to the two earlier reported cyclic peptides from an Austr alian and Philippine D. molle, supports the notion that these compound s originate from prokaryotic algal symbionts. (C) 1998 Elsevier Scienc e Ltd. All rights reserved.