Studies On Bioactive Secondary Metabolites From Three Fungi

Microorganisms,as the large treasury of natural products,constantly have provided us with novel and diverse structures and significant biological activity compounds,which are an important resource for the development of drugs or lead molecules.For the purpose of mining active natural products in plants and microorganisms,three symbiont fungi were selected as the study subjects.Their secondary metabolites were extracted,isolated,and purified using multiple chromatographies,including silica gel,Sephadex LH-20,reversedphase C18,MPLC,and HPLC.23 novel natural products together with 53 known compounds were acquired.Their structures were established by extensive spectral data(1D/2D NMR,MS,IR,and UV).The absolute configurations of novel natural products were deduced by CD,ECD,X-ray diffraction,optical rotations,and chemical reaction.Most of compounds were assessed with various bioactivities and their mechanism of action were investigated.The major results were displayed as follows:1.According to the chemical epigenetic manipulation strategy and OSMAC strategy,18undescribed eremophilane sesquiterpenoids and one novel conjugated unsaturated polyketide fatty acid,together with 23 known metabolites were isolated from the cultures of the fungus Septoria rudbeckiae,a plant pathogenic fungus separated from the halophyte Karelinia caspia.Compounds 1-13 possesses an eremophilane sesquiterpenoids skeleton with the C₉-conjugated unsaturated polyketide fatty acids moiety.Compound 1 represents an unprecedented tetranor-eremophilane sesquiterpenoid with an?,?-unsaturated?-lactone unit bearing a hemiacetal group,and the biosynthetic pathway of 1 was presumed.The absolute configurations of compound 21 was determined by single-crystal X-ray crystallographic analysis,and the absolute configurations of 17 was distributed by chemical reaction and ECD.Compound 11exhibited the significant inhibition of nitric oxide(NO)production in lipopolysaccharide(LPS)-induced BV-2 microglial cells with an IC₅₀ value of 6.0±0.2?M.The activity mechanism of these compound was investigated preliminarily by molecular docking simulation with iNOS.Compound 11 displayed the remarkable protection in H₂O₂-metiated neuronal damage of PC-12 cells,with the cell's survival of 80.5%at a concentration of 10?M,verging on the positive control,glutathione(82.3%).The structure-activity relationship(SAR)analysis indicated the presence of the 3-hydroxy-5,6-dihydronaphthalen-2(4a H)-one unit in the molecules is essential to the improvement of neuroprotective activity and anti-neuroinflammatory activity.Therefore,the eremophilane sesquiterpenoid congeners can be used as the template for compounds development for the treatment of neurodegenerative diseases.Additionally,compound 24 exhibited potent antibacterial activities against Psa and41 displayed remarkable growth inhibition of B.cereus,with the IC₅₀ values of 6.25?M,respectively.2.According to the OSMAC strategy,16 known metabolites were isolated from the cultures of the fungus Alternaria sp.Ctuco36,a plant pathogenic fungus separated from the halophyte Karelinia caspia.Compound 45 exhibited the significant radical-scavenging capacity against DPPH,with IC₅₀ value of 12.6±0.6?M.Meanwhile,compounds 46-48displayed the potent radical-scavenging capacity against DPPH.The structure-activity relationship(SAR)analysis indicated the presence of multiple phenolic hydroxyl groups in the molecules are critical to the improvement of radical-scavenging properties.Additionally,compounds 43 and 44 exhibited the potent inhibition of?-glucosidase activities,with the IC₅₀values of 32.2±0.6?M and 34.7±1.0?M,respectively.Thus,this investigation demonstrated that such metabolites have some development and application value.3.According to the OSMAC strategy and the analyses of HPLC,three undescribed compounds,together with 15 known metabolites were isolated from the cultures of the endolichenic fungus Aspergillus chevalieri SQ-8.Compound 59 represents an unusual phthalide-like derivative with a benzo[c]thiophen-1(3H)-one scaffold.Compounds 64 and 68exhibited the significant inhibition of nitric oxide(NO)production in lipopolysaccharide(LPS)-induced BV-2 microglial cells with an IC₅₀ values of 12.2±0.5?M and 12.8±0.22?M.The structure-activity relationship(SAR)analysis indicated the hydroxyl at C-6 and the aldehyde group at C-1 on the aromatic ring may play a significant role in the activity.Furthermore,the conjugated aliphatic chains can enhance the anti-neuroinflammatory activity of compounds.And the isoprene group at C-6 and the conjugate fragment of the dione piperazine fraction are essential to the anti-neuroinflammatory activity of prenylated indinddione piperazines.The possible anti-inflammatory mechanisms involved were also studied by molecular docking.Compounds 59 and 60 exhibited potent antibacterial activities against two plant pathogens Psa and B.cereus,with the MIC value of 6.25?M.Compounds 59 and 60 were more active and sensitive against Psa and B.cereus than other congeners,this is probably due to their heterocyclic moiety.Compound 62 exhibited the significant radical-scavenging capacity against DPPH,with IC₅₀ value of 10.6±0.1?M.Additionally,compounds 62 and 65exhibited the potent inhibition of?-glucosidase activities,with the IC₅₀ values of 22.5±0.5?M and 19.5±0.6?M,respectively.The structure-activity relationship(SAR)analysis indicated the hydroxyl at C-6 and the aldehyde group at C-1 on the aromatic ring are critical to the improvement of radical-scavenging properties and inhibition of?-glucosidase activity.And alkylated salicylaldehydes were more active on the radical-scavenging properties and inhibition of?-glucosidase activity than prenylated indinddione piperazines.Therefore,this further indicated that the alkylated salicylaldehydes and prenylated indinddione piperazines have diverse biological activities and have promising development and application.4.According to the results of antibacterial assays,four metabolites(compounds 24,41,59,and 60)were chosen to further investigate the antibacterial mechanisms,respectively.Studies on the growth curves,cell membrane permeability and cell morphology have demonstrated that the possible bacteriostatic mechanisms for compounds were to alter the external structure of B.cereus and Psa,and caused the rupture or deformation of the cell membranes,respectively.Thus,this further illustrated that these compounds have the potential to be developed as agricultural fungicides.Overall,these investigations exploited that some novel compounds from three symbiont fungi and endemic Chinese plant Hypericum henryi Levl.et Van,may serve as potential promising candidates for lead compounds of agrochemical bactericides and the treatment of neurodegenerative disease.Therefore,our findings may provide a theoretical foundation for research and development of these bioactive metabolites.