Hymerhabdrin A, a novel diterpenoid with antifouling activity from the intertidal sponge Hymerhabdia sp.

Hymerhabdrin A (1), a diterpenoid possessing a novel 6/6/5 fused-ring skeleton, together with four known sterols were isolated from an intertidal marine sponge Hymerhabdia sp. Their structures were elucidated by extensive spectroscopic methods, and the relative and absolute configurations of 1 were determined by NOESY analysis and electronic circular dichrosim calculations, respectively. Hymerhabdrin A (1) exhibited significant antifouling activity against Balanus amphitrite larval with LC50 (lethal concentration 50) value of 3.6 µg ml-1.