The Allelopathicsubstances From Gorgonian Dichotella Gemmacea (Valenciennes) And Soft Coral Sinularia Sp. From The South China Sea

Despite lack of efficient physical protection in the highly competitive and hostile environment, the marine invertebrates including gorgonians and soft corals can survive mainly relying on their chemical defensive system by a series of secondary metabolites accumulating in their bodies or releasing to their surroundings. The chemical defensive functions of these secondary metabolites were found to serve as allelopathicsubstances, antifeedant, antimicrobial as well as antifouling agents. These secondary metabolites show significant chemoecological functions in marine environment as well as display strong bioactivities while tested with pharmacological models, such as antitumor and antibacterial activities. The research strategy and methodology of chemical ecology played an edificatory role in the bioactive natural products discovery and new drug lead compounds generation from marine sources.In this paper, the allelopathicsubstances from the gorgonian Dichotella gemmacea (valenciennes) and the soft coral Sinularia sp. 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. 27 compounds in total, of which 15 from gorgonian D. gemmacea (valenciennes) and 12 from soft coral Sinularia sp., 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 17 compounds were elucidated, of which 9 from D. gemmacea and 8 from Sinularia sp. They were compound 1, compound 2, compound 3, 1-(4-hydroxy-5-hydroxymethyl- tetrahydro-furan-2-y1)-5-methyl-1H-pyrimidine-2, 4-dione (4), phthalic acid bis- (2-ethyl-hexyl) ester (5), p-hydroxy-benzoic acid (6),β-naphthaldehyde (7), 11β, 20β- epoxy-4-deacetoxyjunceellolide D (8), junceellolide D (9), 3β-hydroxy-24- methylenecholest-5-en-7-one (10), pregnenolone (11), cembrene A (12), epoxycembrane A (13), 4, 8, 12-trimethyl-1-(1-methylethenyl)-3, 7-cyclo tetradecadien-10-one (14), (3E, 7E, 11E)-11, 12-dihydroxy-1-isopropyl-4, 8, 12- trimethyicyclotetradeca-1, 3, 7-triene (15), 1, 2-benzenedicarboxylic acid, dibutyl ester (16), 2-nonadecanone (17). Compounds 1~3 were novel compounds and compounds 1~9 were all isolated from the genus of Dichotella for the first time.In addition, the petroleum ether fractions from the crud extracts of the corals were analyzed by GC/MS resulting in the identification of 20 compounds from D. gemmacea and 15 compounds from Sinularia sp., respectively. Moreover 6 sterols were also identified by GC/MS from the petroleum ether fraction of Sinularia sp.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), antibacterial and cytotoxin to KB, KBV200, P388 and Bel-7402 cell lines. The petroleum ether fraction of the gorgonian D. gemmacea showed high lethal rate to brine shrimp and strong cytotoxin to KB and KBV200 cells, while the EtOAc fraction showed strong cytotoxic and medium antibacterial activities. The petroleum ether fraction of the soft coral Sinularia sp. exhibited high lethal rate to brine shrimp and strong cytotoxin to KB and KBV200 cells.The bioassay of pure compounds isolated from the corals indicated that the new sterol compound 3 and Briarane-type diterpenoids 8 and 9 showed strong inhibition against brine shrimp. These three compounds were deduced primarily as the allelopathicsubstances in the gorgonian D. gemmacea. Cembrane-type diterpenoids 12 and 13 showed strong inhibition against brine shrimp Artimia salina, both of them being primarily presumed as allelopathicsubstances in the soft coral Sinularia sp.It is the first time to isolate and elucidate the secondary metabolites from 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 be significance and inspire to screening and discovery for bioactive natural products even for lead compounds from marine bioresources.