ISOLATION AND IDENTIFICATION OF 8 MICROCYSTINS FROM 13 OSCILLATORIA-AGARDHII STRAINS AND STRUCTURE OF A NEW MICROCYSTIN

Microcystins (cyclic heptapeptide hepatotoxins), isolated from 13 fres hwater Oscillatoria agardhii strains from eight different Finnish lake s by high-performance liquid chromatography, were characterized by ami no acid analysis, fast atom bombardment mass spectrometry (FABMS), and tandem FABMS (FABMS/collisionary-induced dissociation/MS). All strain s produced two to five different microcystins. In total, eight differe nt compounds, of which five were known microcystins, were isolated. Th e known compounds identified were [D-Asp3]MCYST (microcystin)-LR, [Dha 7]MCYST-LR, [D-Asp3]MCYST-RR, [Dha7]MCYST-RR, and [D-Asp3,Dha7]MCYST-R R. This is the first time that isolation of these toxins from Oscillat oria spp., with the exception of [D-Asp3]MCYST-RR, has been reported. Three of the strains produced a new microcystin, and the structure was assigned as [D-Asp3,Mser7]MCYST-RR. The structures of two new microcy stins, produced as minor components by one Oscillatoria strain, could not be determined because of the small amounts isolated from the cells . Four strains produced [Dha7]MCYST-RR as the main toxin, but [D-Asp3] MCYST-RR was clearly the most abundant and most frequently occurring t oxin among these isolates of O. agardhii.