[D-leu] Microcystin-LR from the cyanobacterium Microcystis RST 9501 and from Microcystis bloom in the Patos Lagoon estuary, Brazil

[D-Leu1]Microcystin-LR was identi®ed as the most abundant microcystin from a laboratory strain of the cyanobacterium Microcystis sp. isolated from a hepatotoxic Microcystis bloom from brackish waters in the Patos Lagoon estuary, southern Brazil. Toxicity of [d-Leu1]microcystin-LR, according to bioassay and protein phosphatase inhibition assay, was similar to that of the commonly-occurring microcystin-LR, which was not detectable in the Patos Lagoon laboratory isolate. This is the ®rst report of a microcystin containing [d-Leu1] in the cyclic heptapeptide structure of these potent cyanobacterial toxins