Antifouling Metabolites from the Mangrove Plant Ceriops tagal

The new diterpene methoxy-ent-8(14)-pimarenely-15-one (1) and three knownmetabolites: ent-8(14)-pimarene-15R,16-diol (2), stigmasterol (3) and β-sitosterol (4), wereisolated from the roots of the mangrove plant Ceriops tagal. Their structures and relativestereochemistry were elucidated by means of extensive NMR, IR and MS analysis.Compounds 1, 2, 3 and 4 exhibited significant antifouling activities against cyprid larvaeof 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 μg/cm2, respectively, whereas their toxicities towards cypridswere very low, with LC50 values all above 10 μg/cm2.