Secondary Metabolites Of Three Strains Of Endolichenic Fungi

Lichens are a special kind of biological communities formed by fungi and algae. The history of the study about endolichenic fungi is not very long, while chemical studies of them have led to the discovery of many bioactive and chemically novel natural products. Therefore the study of the metabolites of endolichenic fungi have a great potential for development.In this study, endolichenic fungi were cultured using PDA medium and the cytotoxicity and antifungal activity of the crude extracts were evaluated. By the initial bioassay, three strains of fungi:Floricola striata (No.8462b), Nectria sp. (No.4695c), and Phialocephala sp. (No.4695b) were selected for amplified fermentation in rice culture medium. The fermentation products extracted from ethyl acetate were fractionated using column chromatography on silica gel, Sephadex LH-20, ODS, as well as RP HPLC. A total of 40 secondary metabolites including terphenyls, α-pyrones, perylene quinones, steroids and fatty acid compounds were obtained by separation and purification, and 17 of them were new ones. The structures of these compounds were determined by mass spectrometry, nuclear magnetic resonance techniques, X-ray diffraction analysis, circular dichroism analysis, together with chemical derivatizations. These metabolites were evaluated for their cytotoxicity activity and inhibitory activity against the fungus Candida albicans. Some of the metabolites showed strong activity. Further analysis revealed that compound floricolin C (3) induced cell membrane damage resulted in the death of Candida albicans cells.Chemical studies of three strains of endolichenic fungi have produced many new metabolites, and some of them possess significant activity. These results imply that the endolichenic fungi could be an important source of bioactive natural products and needs further development and utilization.