C-13 NMR ASSIGNMENTS OF CIGUATOXIN BY INVERSE-DETECTED 2D-SPECTROSCOPY AND AN EXPLANATION OF NMR SIGNAL BROADENING

C-13 NMR assignments of ciguatoxin were achieved with 1.1 mg of the sample (1-mu-mol). C-13-decoupled HMQC and HSQC spectra revealed 1J(CH) arising from the flexible part of the molecule which yielded no sharp peaks in the 1D C-13 NMR spectrum. These data suggest that contiguous 9- and 7-membered rings (rings F, G) give rise to a slow conformational change, which leads to extreme broadening of both H-1 and C-13 NMR signals.