Secondary Metabolites Of Gorgonian From Nanhai Coral Reef And Their Antifouling Activity On Barnacle

In marine environment, many invertebrates, such as gorgonians and soft corals, develop chemical defensive system by antifeedant, anti-biofouling, ichthyootoxin and other ecological effects. Therefore, it should be practical significance for screening for anti-biofouling agents from marine natural products under the guidance of chemical ecology effects. In present study, secondary metabolites with antifouling activity from gorgonian coral collected from Chinese tropical coral reef were screened and evaluated with the antifouling model of inhibition the larval settlement,of barnacle.Under the guidance of antifouling activity on barnacle, the bioactive secondary metabolites from gorgonian Dichotella gemmacea (Valenciennes), collected from Weizhou island coral reef, were isolated by column chromatography on silica gel, Sephadex LH-20, ODS, and semi-preparative HPLC, and identified by spectroscopy of NMR, MS, IR, and UV. Total of 21 compounds have been isolated and identified, including 7 brianane diterpenoids including juncin D (1), juncin P (2), juncin R (3), juncin S (4), gemmacolide C (5), junceelolide D (6) and junceellin (7), 5 steroids including cholesterol (8), ergosterol peroxide (9), cerevisterol (10), junceelloside C (11) and junceelloside D (12), 2 glycerol ethers including 2-hydroxy-3-[(1-oxooctadecyl)oxy]propyl ester (13) and (R)-1-O-nonadecyl-3-O-hexadecanoyl glycerol (14), and 1,2-benzenedicarboxylic acid (15). Compounds 1, 3, 4, 5, 6, 7, 9, 10, 11, 12 were obtained from D. gemmacea for the frist time.The bioactivities of the secondary metabolites from gorgonian D. gemmacea were evaluated by the model of antifouling activity on barnacle combined with the models of lethal activity to brine shrimp and zebrafish toxicity. The result indicated that brianane diterpenoids 1, 2 and 6 inhibited the settlement of the larval of barnacle Balanus amphitrite with inhibition rate of 100% at a concentration of 10μg/mL. Compounds 2 and 6 showed strong inhibition to barnacle B. amphitrite with EC50 values of 0.77μg/mL and 0.80μg/mL, respectively. Meanwhile, compound 2 also showed lethality to brine shrimp Artemia salina with a lethal rate of 85% at 50μg/mL. Compound 6 showed potent toxicity to the embryos of zebrafish Danio rerio with a lethality LC₅₀ of 51.4μg/mL, teratogenesis EC₅₀ of 41.6μg/mL, and eggs coagulation EC₅₀ of 56.5μg/mL. In addition, the compounds of steroid 9 and steroid saponin 11 exhibited moderate inhibition to barnacle B. amphitrite.In present study, from the viewpoint of marine chemical ecology, the secondary metabolites with antifouling effects were isolated and screened from gorgonian under the guidance of antifouling activity to barnacle. And the chemical ecology effects of the natural products were investigated, which should provide the basic data for the research and development of marine natural antifouling agents.