Antifouling Eunicellin-Type Diterpenoids from the Gorgonian Astrogorgia sp.

Twelve new eunicellin-based diterpenoids, astrogorgins B-M (1-12), were isolated from a Chinese gorgonian Astrogorgia sp., together with ophirin, muricellin, astrogorgin, calicophirins A and B, and 14-deacetoxycalicophirin B. The structures of the new compounds were elucidated by extensive spectroscopic analysis and by comparison with data reported in the literature. Significant antifouling activity was observed for 14-deacetoxycalicophirin B against the larval settlement of the barnacle Balanus amphitrite at nontoxic concentrations with an EC50 = 0.59 mu g/mL, while the other analogues were effective within an EC50 range of 5.14-17.8 mu g/mL.