CONFORMATIONAL-ANALYSIS OF NATURAL-PRODUCTS USING LONG-RANGE CARBON-PROTON COUPLING-CONSTANTS - 3-DIMENSIONAL STRUCTURE OF OKADAIC ACID IN SOLUTION

Long-range carbon-proton coupling constants ((2,3)J(C,H)) a,known to d epend on the dihedral angles as is the well-known case with interproto n couplings. The precise measurement of these J values were carried ou t using hetero half-filtered TOCSY and phase-sensitive HMBC on a marin e natural product, okadaic acid. From the obtained values together wit h (3)J(H,H) We disclosed the conformations of okadaic acid in organic and aqueous solutions (CD3OD-CDCl3 or NaOD/D2O), which resembled each other and that obtained for its crystalline o-bromobenzyl ester. The s uccessful result in the present conformational study, even though as a n exmaple, demonstrated this methodology to be powerful in elucidation of conformations and configurations of acyclic or macrocyclic portion s in natural products of this size.