Neurotoxic meroditerpenoids from the tropical marine brown alga Stypopodium flabelliforme.
Sabry OM, Andrews S, McPhail KL, Goeger DE, Yokochi A, LePage KT, Murray TF, Gerwick WH.
Brine shrimp toxicity and TLC analysis guided the isolation of five new and biologically active meroditerpenoids [2beta,3alpha-epitaondiol (1), flabellinol (2), flabellinone (3), stypotriolaldehyde (4), and stypohydroperoxide (5)] along with five known compounds from the marine brown alga Stypopodium flabelliforme collected in Papua New Guinea. The planar structures of compounds 1-5 were determined by extensive spectroscopic analysis (1D and 2D NMR, LRMS, HRMS, IR, and UV), while relative configuration was determined by 1D and 2D NOE experiments. X-ray crystallography confirmed the relative configuration of 2beta,3alpha-epitaondiol (1), and the modified Mosher's ester method was used to establish its absolute configuration. All of the new metabolites were moderately toxic to murine neuro-2a cells (LC50 2-25 microM), and three [2beta,3alpha-epitaondiol (1), flabellinol (2), and flabellinone (3)] possessed potent sodium channel blocking activity. Stypotriolaldehyde (4) had a biphasic effect on the concentration of intracellular Ca2+ in rat cerebellar granule neurons (CGN). The previously known compound, stypoldione (6), also modulated intracellular calcium concentration and was cytotoxic in CGN. Metabolites 2beta,3alpha-epitaondiol (1), flabellinol (2), and flabellinone (3) displayed moderate cytotoxicity to the NCI-H460 human lung cancer cell line.