Secondary Metabolites Of Symbionts From Illigera Rhodantha

Symbionts supposed to have special biogenetic pathway due to the unique habitats and long-time co-evolution with their host have become a promising resource of numerous structurally diverse secondary metabolites with remarkable bio-activities. The dissertation presents the structure elucidation and bioactivity evaluation of secondary metabolites produced by five fungal strains isolated from the flower and seed of I, rhodantha Hance. The crude extracts derived from the cultures of the five symbionts were repeatedly fractionated by a combination of chromatographies over normal-and reverse-phase ODS silica gel, gel filtration over Sephadex LH-20 and HPLC to give a total of 39 compounds. The thirty-five compounds of which 14 are new were elucidated by spectroscopic analyses including UV, IR, MS, CD, 1D and 2D NMR, and single-crystal X-ray diffraction. Furthermore, some of the natural products were found to have acetylcholine inhibitory or antibacterial activities. Specifically:Lasiodiplodia sp. F2 was an endophytic fungus isolated from the flower of I. rhodantha. The liquid fermentation, followed extraction and fractionation, gave 9 compounds including 3 known and 6 new caged and oxidized sulfureous diketopiperazines compounds were elucidated. Compound 5 showed antibacterial activity against a panel of target bacteria (IC50:0.12-0.25μM).Repeated fractionation of the extract from endophytic fungus Phomopsis sp. S12 afforded 8 diterpenes including 4 new compounds. Compounds 10 showed significant acetylcholinesterase inhibitory activity with an IC50 value of 40 nM well comparable to that of huperzine A (IC50:25 nM).The endophytic fungus Nigrospora Oryzae S4 dwelling in the seed of I. rhodantha was shown to be capable of producing 7 compounds including two new polyketides. Strains IFB-S11 and IFB-F3 were also endophytic fungi isolated from the Ⅰ. rhodantha. Repeated fractionation of the extract from IFB-S11, afforded 8 compounds including 2 new compounds. From the liquid fermentation of IFB-F3,7 compounds were isolated and 5 compounds were elucidated.Furthermore, natural bioactive products from endophytic fungus were reviewed briefly.