Antifouling metabolites from the mangrove plant Ceriops tagal

The new diterpene methoxy-ent-8(14)-pimarenely-15-one ( 1) and three known metabolites: ent-8(14)-pimarene-15R, 16-diol(2), stigmasterol ( 3) and beta-sitosterol ( 4), were isolated from the roots of the mangrove plant Ceriops tagal. Their structures and relative stereochemistry were elucidated by means of extensive NMR, IR and MS analysis. Compounds 1, 2, 3 and 4 exhibited significant antifouling activities against cyprid larvae of the barnacle Balanus albicostatus Pilsbry, with EC50 values of 0.32 +/- 0.01, 0.04 +/- 0.00, 4.05 +/- 0.15 and 18.47 +/- 0.40 mu g/cm(2), respectively, whereas their toxicities towards cyprids were very low, with LC50 values all above 10 mu g/cm(2)