Long-range carbon-proton coupling constants for stereochemical assignment of acyclic structures in natural products: Configuration of the C5-C9 portion of maitotoxin

Long-range carbon-proton coupling constants ((2,3)J(CH)) were measured for maitotoxin (MTX), one of the largest natural non-biopolymers, by hetero-half filter experiments and phase-sensitive HMBC with use of 9 mg of a 4% C-13-enriched sample. The necessary coupling constants within the terminal acyclic portions of MTX, where NOE analysis was not successful owing to the presumed coexistence of multiple conformers, were thus obtained for the resultant elucidation of relative configurations for the acyclic stereogenic centers to be 5R*, 7R*, 8R*, and 9S*.