New Diterpenoids from the Soft Corals Xenia Macrospiculata and Xenia obscuronata

Sixteen diterpenoids have been isolated from two soft corals of the Red Sea, Xenia macrospiculata and X. obscuronata. These xenia diterpenoids, many of them novel and reported for the first time, are divided into three subgroups: the xenicins [xeniculin (2), 9-deacetoxy-14,15-deepoxyxeniculin (3), and 9-deacetoxy-14,15- deepoxyxeniculin 7,8-epoxide (4)], the xeniolides [xeniolide-A (6), xeniolide-B (7a), xeniolide-B 9-acetate (7b), 7,8-epoxyxeniolide-B (8), and xenialactol (9a)], and the xeniaphyllanes [xeniaphyllenol (11), 4,5-epoxyxeniaphyllenol (12), isoxeniaphyllenol (13), 4,5-epoxyisoxeniaphyllenol (14), 14,15-xeniaphyllandiol (15a), xeniaphyllandiol 14-acetate (15b), and 4,5-epoxy-14,15-xeniaphyllandiol (16)]. The structures were elucidated from spectral data and chemical transformations. The 13C NMRspectra are fully assigned, and their application to the determination of the xenia diterpenoids is discussed. In addition to the above compounds, another diterpenoid, obscuronatin (23), was isolated and its structure elucidated.