Isolation and structures of five microcystins from a Russian Microcystis aeruginosa strain CALU 972.

Five microcystins were obtained from Microcystis aeruginosa strain CALU 972 isolated from a hepatotoxic water bloom collected in Lake Kroshnosero (Russia). The structure of a new toxin (1) was determined as [Dha7]microcystin-YR by amino acid analyses and fast atom bombardment mass spectrometry, and the toxins 2, 3, 4, and 5 were assigned the structures as [Dha7]microcystin-LR, [D-Asp3,Dha7]microcystin-LR, [Dha7]microcystin-RR, and [D-Asp3,Dha7]microcystin-RR, respectively, by direct comparison with authentic samples.