STRUCTURES AND CONFIGURATIONS OF CIGUATOXIN FROM THE MORAY EEL GYMNOTHORAX-JAVA']JAVANICUS AND ITS LIKELY PRECURSOR FROM THE DINOFLAGELLATE GAMBIERDISCUS-TOXICUS

Ciguatoxin (CTX) is the toxic principle of ciguatera, which is responsible for the most widespread food poisoning of nonbacterial origin. The toxin, isolated from the moray eel Gymnothorax javanicus, and its congener, from the causative dinoflagellate Gambierdiscus toxicus, were used for this study. The structure elucidation was carried out by combined use of Ή NMR 2D correlation and NOE experiments done with no more than 0.35 mg of CTX and 0.74 mg of the congener. Broadening of1Ή NMR signals due to a slow conformational change around a nine-membered ring was sharpened by measurements at -20 °C, in which all3J proton connectivities and NOE's around angular protons were clearly indicated. The structure of CTX, which had a molecular formula of CwHMOl9, was disclosed to be a brevetoxin-type polyether comprising 13 continuous ether rings (7/6/6/7/7/9/7/6/8/6/7/6-spiro-5). The congener was shown to be a less oxygenated analogue of CTX. Their relative stereochemistries, except for C2 of CTX, were clarified by detailed analyses of 'H NMR NOE experiments, MM2 energy calculations, and spectral simulations. © 1990, American Chemical Society. All rights reserved.