DITERPENES FROM THE BROWN ALGA DICTYOTA-DIVARICATA OF THE INDIAN-OCEAN

The brown alga Dictyota divaricata from the coasts of the Andaman and Nicobar Islands in the Indian Ocean yielded one known and 11 new diterpenes of which four are dolabellanes, six are dolastanes, and one is a novel aromatic isodolastane. The structures of (1R*,3E,6S*,7E,11S*)-6-hydroxydolabella-3,7,12-triene, (1S*,3S*,4R*,6S*,7E,11S*)-3,4-epoxy-6-hydroxydolabella-7,12-diene, (1R*,3Z,7E,11S*,12S*)-12-hydroxydolabella-3,7-dien-2-one, (1R*,3Z,7Z,11S*,12S*)-12-hydroxydolabella-3,8-dien-2-one, (1S*,11S*)-3,4;7,8-diepoxy-18-hydroxydolabella-12-ene, (5S*,8S*,9S*,12R*,13R*,14R*)-9,13-dihydroxydolasta-1,3-diene, (5S*,8S*,9S*,12R*,13R*,14R*)-13-acetoxy-9-hydroxydolasta-1,3-diene, (5R*,8S*,9S*,12R*,14S*)-9-hydroxydolasta-1,3-dien-13-one, (5R*,8S*,9S*,12R*,13S*,14S*)-9,13-dihydroxydolasta-1,3-diene, and (8S*,9S*,12R*)-9-hydroxyisodolasta-1,3,5(14)-trien-13-one were established by interpretation of spectral data and chemical interconversions. Two stereoisomers of (8S*,9S*,12S*)-9-hydroxydolasta-1,3-diene were isolated but their stereochemistries could not be completely elucidated.