Studies On The Secondary Metabolites From Xylaria Sp.YM 311647 And Synsepalum Dulcificum Leaves

The research content of this paper includes two parts.The first part is the study of the bioactive substances of the solid fermentation product of Xylaria sp.YM 311647.The second part is the study of chemical constituents of Synsepalum dulcificum leaves.The specific results are as follows:In our previous work,a series of new guaiane sesquiterpenes and isopimarane diterpenes were obtained from the liquid fermentation products of the endophytic fungus Xylaria sp.YM 311647 of Azadirachta indica,indicating its potential to produce new bioactive compounds.In order to further explore the diversity of secondary metabolites of this strain and obtain more diverse new active substances,the chemical components of fermentation products of the strain YM 311647 were further studied by means of solid culture in this paper.Five new compounds were isolated and identified from rice solid fermentation of the strain,which were named as xylariosides A-E（1-5）.Compounds 1-3 are guaiane sesquiterpene glycosides,which are rarely reported in microbial resources.Compounds 4 and 5 are polyhydroxylated ergostane glycosides,in which 4 was bearing an unusual seven-membered A-ring lactone.Synsepalum dulcificum is belonging to the genus Synsepalum in the family of Sapotaceae.Currently,it is mainly focused on the application of its fruit in food and medicine.It has been reported that the leaves of Synsepalum dulcificum possess antioxidant,antimicrobial,anti-tumor,cholesterol-lowering and diabetes treatment effects,but few systematic studies on effective substances have been carried out.Therefore,in this paper,the chemical study of Synsepalum dulcificum leaves was conducted in order to explore its antioxidant and antimicrobial components.Twenty-nine compounds were isolated and identified from the ethyl acetate extract of Synsepalum dulcificum leaves,among which 3-O-b-D-xylopyranosyl-（1→3）-b-D-glucopyranosyl protobassic acid methyl ester（6）is a new triterpenoid saponin and（+）-isolarisiresinol-2′-O-β-D-glucopyranoside（7）is a new lignan glycoside.All the isolated compounds were obtained from Synsepalum dulcificum for the first time.The main types of these compounds are flavonoids,flavonoid glycosides,lignans,triterpenoids,triterpenoid saponins,megastigmane glycosides,and cerebrosides.The antimicrobial and antioxidant activities of some obtained compounds were detected.Antimicrobial assay showed that compounds 4 and 5 from Xylaria sp.YM311647 exhibited strong antifungal activity.The MIC value of compound 4 against Gibberella saubinetii YM 3042,Curvularia lunata YM 3034,and Colletotrichum gloeosporioides YM 3012 were 4,4,8μg/m L,respectively,which were comparable to the positive control nystatin.Compound 5 displayed potent inhibitory activity against Alternaria alternata YM 3073 and Curvularia lunata with MIC values of 8μg/m L.As for the compounds derived from Synsepalum dulcificum leaves,compound 9 had strong inhibitory activity against Gibberella saubinetii and methicillin-resistant Staphylococcus aureus YM 3106,with MIC values of 8μg/m L.Compound 10 showed obvious inhibitory activity against methicillin-resistant Staphylococcus aureus and Salmonella typhimurium YM 3115,with MIC values of 8 and 16μg/m L,respectively.In DPPH free radical assay and ABTS⁺scavenging assay,compounds 23,24,30 and 31 showed strong antioxidant activity.In DPPH test,their IC₅₀values were 0.27,0.43,0.45 and0.90μg/m L,respectively.In ABTS⁺test,their IC₅₀values were 4.84,3.33,6.86 and6.83μg/m L,respectively.Most of the other compounds showed moderate activity.Reviewing the whole thesis,a total of 7 new compounds were obtained from the fermentation products of Xylaria sp.YM 311647 and Synsepalum dulcificum leaves,including three guaiane-type sesquiterpenoid glycosides rarely obtained from microbial resources,two steroidal saponins（one containing an unusual seven-membered A-ring lactone）,one triterpenoid saponin and one lignan glycoside.Compared with liquid fermentation,new antimicrobial guaiane-type sesquiterpenoid glycosides and steroidal saponins were produced by solid fermentation of the strain YM 311647.The bioactivity test showed that four compounds showed potent antimicrobial activity and four compounds showed strong antioxidant activity.By means of solid fermentation,the types and quantity of secondary metabolites of the new structures were further enriched.This research revealed the structural types of chemical components of Synsepalum dulcificum leaves,and identified compounds 9 and 10 as the main antimicrobial components and compounds 23,24,30 and 31 as the main antioxidant components.