Grassypeptolides A− C (1− 3), a group of closely related bis-thiazoline containing cyclic depsipeptides, have been isolated from extracts of the marine cyanobacterium Lyngbya confervoides. Although structural differences between the analogues are minimal, comparison of the in vitro cytotoxicity of the series revealed a structure− activity relationship. When the ethyl substituent of 1 is changed to a methyl substituent in 2, activity is only ...
