High field 1H- and 13C-nmr assignments of grayanotoxins I, IV, and XIV isolated from Kalmia angustifolia.

Grayanotoxins I [2], IV [3], and XIV [4] were isolated from Kalmia angustifolia var. caroliniana, a North American member of the Ericaceae. Their structures were established from physical and spectral data (mp, ir, [alpha]D, uv, cd, ms, 1H and 13C nmr). High field 1H- and 13C-nmr assignments were made for each compound using 1D and 2D nmr techniques including extensive 1H single-frequency spin-decoupling and nOe difference experiments, one-bond and long-range (COLOC) carbon-hydrogen correlations, and the INADEQUATE carbon-carbon correlation experiment. This is the first report of the presence of grayanotoxins IV and XIV in this source, of complete high field (500 MHz) 1H-nmr assignments for any grayanoid, and of 13C-nmr assignments for grayanotoxins IV and XIV. For grayanotoxin I, ambiguities in the literature 13C-nmr assignments have been removed by definitive assignments made through the use of the INADEQUATE experiment.