Secondary Metabolites Of Aspergillus Ochraceus Associated With Dichotella Gemmacea Under Biomimetic Culture

Coral-associated microorganism is a rich source of secondary metabolites with diverse structures and biological activities, but researches on secondary me tabolites of coral-associated microorganism are rarely reported. A study is carri-ed out to investigate the bioactive lead compounds derived from coral-associate d microorganism. This thesis describes the study of the secondary metabolites produced by a coral-associated fungus under different environmental stresses. St udies include isolation of associated microorganism from coral samples and acti vity screening, selecting talented strains and effects of environmental stress on secondary metabolites, bioassay-guided fractionation, structural elucidation and c ytotoxicity evaluation of pure compounds.78 fungal strains were isolated from 12 coral samples which were collected from the seashore of Linggao and Sanya in Hainan Province.3 strains were picked out based on the cytotoxic assay using the P388 cell line by the SRB method and on the HPLC and TLC chemical screening. Among them, a strain which was identified as Aspergillus ochraceus LCJ11-102 isolated from Dichotella gemmacea was selected for further study of its secondary metabolites.After investigating effects of different environmental stresses on secondary metabolites of LCJ11-102, large-scale fermentations of two different environments were performed to obtain the active extracts. By means of chromatography over silica gel column, Sephadex LH20, preparative TLC and semi-preparative HPLC,22 (1-22) and 5 compounds (23-27) were isolated from the two different cultures.By means of physic-chemical properties and spectral analysis (IR, UV, MS, NMR, X-ray, etc.), structures of 28 pure compounds were respectively determined. Among them there are 6 new compounds, including 3 lactone derivatives (2,16,18), 3 circumdatin (19,20,21) derivatives and 1 sterol derivative (4).The antibacterial activity of these compounds was evaluated by paper disk method. Compounds 1,4,13,14,16,17,18 all showed moderately antibacterial activity against Staphylococcus aureus,Blastomyces albicans,Bacillus subtilis and Bacillus aerogenes. Compound 5 showed fairly strong antibacterial activity against Blastomyces albicans. The cytotoxicity of these compounds against several cancer cell lines was evaluated by SRB and MTT method. Only compound 4 and 11 exhibited cytotoxicity against HL-60 cells with IC50 36μM and 12μM.Summarily, this work obtained 3 talented strains from coral-associated microorganism by integrated screening, and 27 compounds were obtained from cultures of LCJ11-102 under different environmental stresses, including 7 new compounds. This study provides novel structure types for natural product chemistry and bioactive template compounds for exploring new drugs. It also proves that coral-associated microorganism is an affluent resource and the method we used is effective in looking for new bioactive secondary metabolites from coral-associated microorganism.