ISOLATION AND IDENTIFICATION OF 12 MICROCYSTINS FROM 4 STRAINS AND 2 BLOOM SAMPLES OF MICROCYSTIS SPP - STRUCTURE OF A NEW HEPATOTOXIN

Sixteen microcystins, cyclic heptapeptide hepatotoxins, were isolated and purified by high performance liquid chromatography (HPLC) and thin layer chromatography (TLC) from four hepatotoxic strains and two Micr ocystis spp. bloom samples originating from five different lakes in Fi nland. The structures of a new [Dha(7)]MCYST-FR and 11 known microcyst ins MCYST-LR, [D-Asp(3)]MCYST-LR, [Dha(7)]MCYST-LR, [D-Asp(3),Dha(7)] MCYST-LR, MCYST-RR, [D-Asp(3)]MCYST-RR, [Dha(7)]MCYST-RR, [D-Asp(3),Dh a(7)]MCYST-RR, [L-Ser(7)]MCYST-RR, MCYST-YR and [Dha(7)] MCYST-YR were assigned based on amino acid analysis, fast atom bombardment mass spe ctrometry (FARMS) and tandem FABMS. Four other new compounds allowed o nly determination of their molecular formulas and amino acid component s because of inadequate amounts obtained. [Dha7]MCYST-RR was found mos t frequently in these samples as the main toxin.