Acetogenic isoquinoline alkaloids .96. Circular dichroism of naphthyldihydroisoquinoline alkaloids: Determination of the axial configuration of yaoundamine A

The absolute axial configuration of yaoundamine A, a naphthyldihydroisoquinoline alkaloid recently isolated from Ancistrocladus korupensis, was elucidated by comparison of experimental and theoretical Circular Dichroism (CD) spectra. An extensive semiempirical (AM1) analysis of the conformational properties of yaoundamine A and its atropodiastereomer revealed an interesting long-range mutual interaction of the local conformations in the axis and of the dihydroisoquinoline system via the 8-methoxy group as a ''molecular clutch''. Subsequent calculation and Boltzmann-weighting of single-conformation CD spectra (CNDO/2S - C.I.) gave a thermal average CD spectrum matching the experimental one very closely. (C) 1997 Elsevier Science Ltd.