| It is high-pressured, high-salted, anerobiousand closed-ray in seawater environments. Marine organisms in seawater environments have developed various mechanisms to face the tough competitive situations such as attack and defense, prey and anti-prey, allelopathy and symbiosis, and fight for food and spaces. Marine invertebrates can survive in the highly competitive and hostile environments, mainly relying on their chemical defensive system by accumulating a series of defensive chemicals in their bodies or releasing the compounds to their surroundings. Gorgonians are inferior invertebrates living in the highly competitive and hostile environments, which make chemists, biologists, pharmacologists have great interest.In this paper, the allelopathicsubstances from the gorgonian Dichotella gemmacea (valenciennes) and Echinogorgia sassapo reticulate (Esper) were investigated according to the methodology of chemical ecology combining with modern technology of marine natural products.The bioactive secondary metabolites were isolated and elucidated from the two corals by the methods of chromatography and spectroscopy.48 compounds in total, of which 28 from gorgonian D.gemmacea(valenciennes)and 21 from E. sassapo reticulate (Esper),were isolated from the organic extracts of the corals by repeated column chromatography on silica gel, Sephadex LH-20, TLC and HPLC. By a variety of spectra including MS,NMR and IR,the structures of 32 compounds were elucidated,of which 20 from D.gemmacea and 12 from Echinogorgia sassapo reticulate (Esper).They were compound 1, compound 2, compound 3, compound 4, compound 5, juncin H (6), Juncin K (7), junceols A (8), Junceeuohdes D (9), praelohde (10),β,20β-Epoxy-4-deacetoxyjunceellolide D (11), Junceellin (12), cholesterol (13), (22E,24R)-cerevisterol (14), (22E,24R)-24-methyl-Sa-cholesta-7,22-diene-3β,5α-diol (15), (24R)-24-methyl-5acholest-7-ene-3β,5α,6β-triol (16), Junceelloside C (17), saringosterol (18), Stearic Acid (19), Chimyl alcohol (20), uridine (21), 2'-deoxythymidine (22),2'-de-oxyuridine (23), uracil (24), batyl alcohol (25), 1-O-eicosanylglycerol (26), 11,13-dihydro-7,11-dehydro-3-desoxy-zaluzalanin C (27), dibutyl phthalate (28), butyl 2-methylbutyl phthalate (29), (22E)-5α-cholest-22-ene-3α,5α,6β-triol (30), (22E,24S)-24-methyl-5a-cholesta-7,22-diene-3β,5α,6β,9-tetraol (31), (24S)-methylene cholestane-3β,5α,6β,18-tetrol (32). Compounds 1-5 were novel compounds and Most compounds except compounds 9 and 12 were isolated from the genus of Dichotella for the first time. The biological activities of the crude extracts and the compounds from the corals were evaluated primarily on the models of lethal to brine shrimp (Artimia salina), toxicity toward embryo of zebrafish Danio rerio and antifouling activities against the larval settlement of barnacle Balanus amphitrite. At the concentration of 50μg/mL, compounds 6,9,10,11 and 12 showed strong lethal activity to brine shrimp A. salina with the lethality rate of 60%,65%,75%,55% 85%, respectively. Compounds 9 and 10 also showed toxicity toward embryo of zebrafish Danio rerio and strong antifouling activities against the larval settlement of barnacle Balanus amphitrite. The bioassay of pure compounds isolated from the corals indicated that Briarane-type diterpenoids showed strong inhibition against brine shrimp.These compounds were deduced primarily as the allelopathicsubstances in the gorgonian D.gemmacea.This study provided a basis for the research on the chemical defense substances and mechanisms of the corals.The strategy and methodology of marine chemical ecology to find chemical defensive compounds should besignificance and inspire to screening and discovery for bioactive natural products even for lead compounds from marine bioresources.
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