NEW XENICANE AND HYDROAZULENOID DITERPENES FROM AN AUSTRALIAN COLLECTION OF DICTYOTA-DIVARICATA

Seven new diterpenes and one already known diterpene have been isolated from the brown alga, Dictyota divaricata, collected from the Great Barrier Reef region of northern Australia. Of the novel diterpenes, five are xenicane derivatives (1-5) and two are hydroazulenoid diterpenes (6 and 7). The structures of 1, [(2R, 3RS, 4S, 6E, 9E, 10R)-17, 4-hydroxyxenic-6, 9, 13-trien-1-al-18-oic acid lactone], 2, [(2R, 3R, 6E, 9E, 10R)-17-xenic-6, 9, 13-trien-1-al-18-oic acid lactone], 3, [(2R 3R, 4S,, 6R, 7R, 9E, 10R)-17, 6, 7-epoxyxenic-4-hydroxy-9, 13-dien-1-al-18-oic acid lactone], 4, [(2R, 3R, 4S,, 6E, 9E, 10R)-17-acetoxyxenic-4-hydroxy-6, 9, 13-trien-1, 2-dial], 5, [17-acetoxy-4-alpha-hydroxycrenulide], 6, [deacetoxydictyol H], and 7, [2-hydroxydictyoxide] were assigned by interpretation of their spectral parameters and by comparison with published data of selected known compounds.