3 DEHYDROBUTYRINE-CONTAINING MICROCYSTINS FROM NOSTOC

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