Three dehydrobutyrine-containing microcystins from Nostoc

Three cyclic heptapeptide hepatotoxins, [Asp(3), ADMAdda(5), Dhb(7)] microcystin RR, [Asp(3), ADMAdda(5), Dhb(7)] microcystin HtyR and [Asp(3), ADMAdda(5), Dhb(7)] microcystin LR, were isolated from a Nostoc species. Their structures were assigned on the basis of (1)H and (13)C NMR, HR FAB mass spectrometry and amino acid analysis using GC-mass spectrometry on a chiral capillary column. All three microcystins contained dehydrobutyrine (Dhb), instead of dehydroalanine (Dha), D-aspartic acid, instead of D-erythro-beta-methylaspartic acid (D-MeAsp), and 9-acetoxy-3-amino-2,6,8-trimethyl-10-phenyldeca-4,6-dienoic acid (ADMAdda), instead of the corresponding 9-methoxyl derivative (Adda). This is the first report on the identification of Dhb-containing microcystins from Nostoc. (C) 1998 Elsevier Science Ltd. All rights reserved.