4 NEW BIOACTIVE LOBANE DITERPENES OF THE SOFT CORAL LOBOPHYTUM-PAUCIFLORUM FROM MINDORO, PHILIPPINES

The marine soft coral Lobophytum pauciflorum collected from Mindoro Is land, Philippines, yielded four new lobane diterpene derivatives: the acetate congeners of epoxylobatrienol and lobatrienediol (2 and 7, res pectively), a methoxyl congener of lobatetraene (10), and an oxepin co ngener of lobatrienetriol (11), and six known derivatives (1, 3-6, and 8). The structures of the new compounds were unambiguously establishe d on the basis of NMR spectroscopic (H-1, C-13, COSY, H-1-detected dir ect, and long-range C-13-H-1 correlations) and mass spectrometric (EIM S) data. All of the compounds were active against the phytopathogenic fungus Cladosporium cucumerinum. Compound 1 was found to be active aga inst the Gram-positive bacteria Bacillus subtilis and the yeast Saccha romyces cerevisiae. The isolated lobane diterpenes were also active in the brine shrimp lethality test. In the latter bioassay, compounds 8 and 10 were the most active congeners with LC50's of 0.64 and 4.18 mu g/mL, respectively.