Studies On The Bioactive Natural Products From Three Fungi And Caesalpinia Decapetala,and The Biosynthesis Research Of Terrein

This thesis is divided into four chapters.The first two chapters mainly describe the chemical constituents and their bioactivities from three fungi,including Aspergillus rugulosus,an endophytic fungus from the mouldy Viburnum cylindricum Buch,Aspergillus sp.TJ23,an endophytic fungus from the Hypericum perforatum L,and a fungus of marine origin,Aspergillus terreus,as well as the Chinese medicinal plant,Caesalpinia decapetala,respectively.The third chapter mainly demonstrates the research on the biosynthesis of the terrein,a secondary metabolite of Aspergillus terreus.The fourth chapter summarizes the research progress of terrein,including isolation,structural elucidation,bioactivities,biosynthesis,and chemical synthesis.A total of 93 compounds,including 29 undescribed natural products,were isolated and further identified from three fungi and C.decapetala by a various of chromatographic methods,including silica gel column,ODS C-18 reversed phase column,MCI column,Sephadex LH-20,thin layer plate(TLC),semi-preparative HPLC and so on.Structures of the isolates were determined by NMR data analysis,HRESIMS,IR and UV spectra analysis,ECD calculations,X-ray single crystal diffraction analysis,and other modern natural products research methods.The main types of these compounds were polyketides,diterpenoids,meroterpenoids,steroids,lignans,and authraquinones.In chapter 1,the in vitro bioactive assays demonstrated that compound 1 displayed remarkable immunosuppressive effect on murine splenocytes and human T cells stimulated by anti-CD3/anti-CD28 monoclonal antibodies,with the effective concentration at the grade of n M.Compound 5 significantly inhibited BACE1,with IC50 value of 11.42?M.Conpound6 was a potential inhibitor of PBP2a,and worked synergistically with the?-lactam antibiotics oxacillin and piperacillin against MRSA,with the MIC value of 1?g/m L and the?FIC value less than 0.5.PBP2a was presumed to be the target of 6 supported by inverse virtual docking and MST assay.In addition,6 could induce irregular membrane damage and disruption exhibited by the TEM images.Compound 8 could function as a potential hypoglycemic agent,with pronounced efficacy than metformin.The underlying mechanism of 8 was explored by Kyoto Encyclopedia of Genes and Genomes(KEGG)pathway analysis,Gene Ontology(GO)function enrichment,the protein interaction network,eventually the potential target verified by q RT-PCR.The results suggested that 8 exhibited the hypoglycemic activity by activating the insulin signaling pathway.Moreover,fibroblast growth factor 21(FGF21)was supposed to be a potential target for 8.In chapter 2,we obtained a pair of inseparable epimeric mixtures9/10.The mechanism of conversion of 9/10 was proposed as the intramolecular hemiacetal reaction.The in vitro bioactivities showed compounds 1,4,5,7,and 14 exhibited inhibitory activities against the SW1990 human pancreatic cancer cell line with IC50 values ranging from 2.9 to 8.9?M.Additionally,compound 11 displayed moderate antibacterial activity against MRSA with an MIC₅₀ value of 5.99?g·m L^-1.The chapter 3 mainly described the biosynthesis study of terrein,including a combination of heterologous expression in Saccharomyces cerevisiae BJ5464 and Aspergillus nidulans LO8030,genetic knockout,feeding to mutant strain,expressing and purifing protein in Escherichia coli Top10,BL21,Rosetta,chemical derivatization,and biochemical experiments in vitro.The research indicated that there are one or more unstable intermediates involving in the biosynthesis of terrein,and the FAD-dependent monooxygenase Ter C might be the next key catalytic protein.