Symplostatin 2: a dolastatin 13 analogue from the marine cyanobacterium Symploca hydnoides.

An analogue of dolastatin 13 (2) has been isolated from a marine cyanobacterium, Symploca hydnoides, collected near Guam. This new cyclic depsipeptide contains a L-methionine sulfoxide residue; however, the sulfoxide exists as both R- and S-forms, resulting in the doubling of several signals in the 1H and 13C NMR spectra. Structure elucidation required extensive application of 2-D NMR techniques such as COSY, HMQC, HMBC, and ROESY. The trivial name symplostatin 2 (1) has been assigned to the new metabolite and its isolation from S. hydnoides further supports the proposal that many compounds originally isolated from the sea hare Dolabella auricularia are most probably of cyanobacterial origin.