Conformational analysis and absolute stereochemistry of ‘spongian’-related metabolites

New degraded and rearranged diterpenoids, , have been isolated from the Antarctic sponge Dendrilla membranosa. The structure and relative stereochemistry of these compounds were determined by spectroscopic data. The absolute stereochemistry of was determined by spectroscopic data using a chiral reagent. Conformational studies allowed us to assign also the absolute stereochemistry of , as well as those previously isolated spongian-derived metabolites with known relative stereochemistries.