A new meroditerpenoid dimer from an undescribed Philippine marine sponge of the genus Strongylophora

An undescribed Philippine marine sponge of the genus Strongylophora yielded a new meroditerpenoid-strongylophorine dimer (1) and the known meroditerpenoids, strongylophorine-2 (2), strongylophorine-3 (3), and strongylophorine-4 (4). The structures of the compounds were established on the basis of NMR spectroscopic and mass spectrometric data. The position of the inter-unit linkage in the new compound was elucidated after methylation and 1D H-1 NOE difference experiments. This is the first report wherein the H-1 and C-13 NMR data of the strongylophorine congeners are fully and unambiguously assigned on the basis of 2D NMR spectroscopy. Compounds 2 and 3 exhibited slight activity against Micrococcus luteus and Salmonella typhii, respectively. Compound 3 was active against the phytopathogenic fungus Cladosporium cucumerinum and also against the neonate larvae of the polyphagous pest insect Spodoptera littoralis (EC50 of 69 [+/-0.48 (S.E.)] ppm) when incorporated into artificial diet. Compound 1 was found to be the most active in the brine shrimp lethality test with a LC50 of 10.5 [+/-0.43 (S.E.)] mu g/mL.