ABSOLUTE-CONFIGURATION OF HYDROAZULENOID DITERPENES BASED ON CIRCULAR-DICHROISM

The structure of a new hydroazulenoid diterpene, 9-epi-dictyol B(1), isolated from the brown alga Glossophora kuntii, was proposed on the basis of its spectral data and confirmed by chemical transformations. Absolute stereochemistry studies, based on the CD exciton chirality method, of the new diterpenoid 9-epi-dictyol B (1) as well as those of the previously reported dictyotadiol (6) led to the determination of the absolute configuration of the new compound 9-epi-dictyol B(1) and revisions of absolute configurations of previously reported diterpenoids dictyotriols C (2), D (3), and E (4), dictyol B (5), and dictyotadiol (6). The cause of previous erroneous results is discussed and indeed points to the extreme care which must be exercised by anyone using this method.