Tamandarins A and B: New cytotoxic depsipeptides from a Brazilian ascidianof the family Didemnidae

The structures of two new, naturally occurring cytotoxic depsipeptides, tam andarins A and B (1 and 2), are presented. The tamandarins were isolated fr om an unidentified Brazilian marine ascidian of the family Didemnidae. The structures of the new cytotoxins were assigned by interpretation of FABMS d ata and by extensive 2D NMR analyses. The absolute configurations of the ta mandarins were assigned by acid and alkaline hydrolysis to yield their corr esponding amino acids, which were then analyzed as their Marfey derivatives . The cytotoxicity of tamandarin A (1) was evaluated against various human cancer cell lines and shown to be slightly more potent than didemnin B. A. qualitative discussion of the conformation of tamandarin A (1) in solution, obtained from NMR J-value data, variable temperature experiments, and NOES Y/ROESY data, is included.