Oscillapeptin J, a new grazer toxin of the freshwater cyanobacterium Planktothrix rubescens

Oscillapeptin J (1), a new and highly potent crustacean. grazer toxin, was isolated from the axenic cyanobacterium Planktothrix rubescens, which frequently forms blooms in freshwater lakes. Chemical and spectroscopic analyses, including high resolving MS and two-dimensional NMR, were used to elucidate the compound's structure as a depsiheptapeptide of the oscillapeptin type. Strict application of a bioassay-guided isolation procedure proved this compound to be one of the major causative agents (besides [D-Asp(3),-(E)-Dhb(7)]microcystin-RR) of the acute grazer toxicity of P. rubescens from Lake Zurich. The LC50 value of oscillapeptin J as determined for the freshwater crustacean Thamnocephalus platyurus was 15.6 muM.