A systematic re-study on gorgonian Muricella sibogae from South China Sea yielded 10 eunicellin-based diterpenoids including two new ones, sibogins C and D (1 and 2). Their structures were elucidated by extensive spectroscopic analyses (1D and 2D NMR, IR and MS) and by comparison with data reported in literatures. All the isolates were tested for cytotoxic and antifouling activities. Compounds 3 and 5 showed significant antifouling activity against the green mussel Perna viridis, and especially 3 was suggested as a potent low-toxic antifouling agent with a large LC50/EC50 value of 18.6. This was the first report on the antifouling activity of the eunicellin-type diterpenoids against the green mussel.
Keywords: Muricella sibogae; antifouling activity; cytotoxicity; eunicellin-based diterpenoids; gorgonian.