7-DESMETHYL-MICROCYSTIN-RR, A HEPATOTOXIN FROM A WATERBLOOM OF MICROCYSTIS-AERUGINOSA

A peptide toxin was isolated from a waterbloom of Microcystis aeruginosa from Lake Froylandsvatn in Norway. The isolation procedure included liquid and solid phase extraction and reversed phase high performance liquid chromatography. Amino acid analysis yielded D-glutamic acid, D-erythro-beta-methylaspartic acid and D-alanine in equimolar and L-arginine in twofold molar ratios. The presence of dehydroalanine was confirmed by hydrogenation and subsequent amino acid analysis with combined gas liquid chromatography/mass spectrometry. Investigation of the toxin with fast atom bombardment mass spectrometry showed a nominal relative molecular mass of 1023. 3-Amino-9-methoxy-2,6,8-trimethyl-10-phenyl-4,6-decadienoic acid (Adda) was identified by H-1 NMR and H-1, H-1 COSY spectroscopy. The structure of the toxin was elucidated as 7-desmethyl-microcystin-RR.