Secondary Metabolites Of An Endophytic Fungus Stagonospora Sp. Inhabiting In Desert Plant Bassia Dasyphylla

Fungal secondary metabolites(SMs),especially those with novel structural features,are the important sources for drugs and pesticides.Due to the special living environment of desert plants(such as large temperature difference,strong light,water shortage,high salinity and poor nutrition,et al),endophytic fungi get limited nutrition and living space from their host plants.Thus,the intra-specific or inter-specific competition is more intense,and the interaction or antagonism between endophytic fungi and host plants is also more close or intense.This will lead these unique member of endophytic fungi to produce potent unique structural secondary metabolites with diverse chemical ecological/biological activities or information exchange functions.Therefore,an endophytic fungus(Stagonospora sp.)inhabiting in desert plants from special bioenvironment was selected to find new or novel bioactive secondary metabolites.This study will provide scientific basis for the resource development of desert plants derived endophytic fungi,and those discovered secondary bioactive metabolites will also provide more candidates for new drug innovation.The results were as follows:1 Secondary metabolites of the solid fermentation products of this fungus were isolated by silica gel column chromatography,Sephadex LH-20 gel column chromatography,thin layer chromatography and semi-preparative high-performance liquid chromatography.The structures were identified by multiple spectroscopic methods(¹H NMR,¹³C NMR,¹H-¹H COSY,HSQC,HMBC,NOESY,IR,UV,CD,X-ray,HR-ESI-MS)and the modified Mosher reaction.Fourteen compounds(1-14)were isolated and identified from the Et OAc extraction of the Stagonospora sp.,among which compounds 1,2 and 12 were new compounds.It is the first time to isolate and identify a new skeleton compound stagonspirone(1),four usnic acid analogs(2-5),seven anthraquinone compounds(6-10 and 12-13),a phenolic hydroxyl compound(11)and a sesquiterpene compound(14)from the secondary metabolites of the endophytic fungus Stagonospora sp..Stagonspirone(1)has a unique 6/5/5/6-fused polyketide core and spiro-ring system,which are rare in nature.Due to the optical rotation value of 1 was near zero,and its CD spectrum displayed no Cotton effects,which implied that it is a pair of enantiomers(1/1').It is the first attempt to use the combination of chemical derivatization methods and common semi-HPLC column for separation and absolute configuration of trace compounds,which provided a new way for purification and the stereochemical establishment of trace enantiomers.2 The cytotoxic and anti-plant pathogen activities of some compounds were evaluated by MTT and bacteriostatic experiments,respectively.Their possible biosynthetic pathways were speculated and analyzed.Biological activity test showed that compounds 2-5 displayed certain cytotoxic activities against MGC-803,He La and A549 cancer cell lines,Compound 6significantly inhibited the growth of Hep G2 and HCT116 cancer cell lines.Compouds 7-9displayed strong cytotoxic activities against B16,Hep G2 and HCT116 cancer cell lines.The inhibitory activity of compound 13 on HCT116 cancer cell lines is slightly stronger than that of the positive control cisplatin.Anti-phytopathogenic activity showed that compounds 6-9 had no significant inhibitory effects on 6(FE-DS-004,FO-DS-001,AA-CZ-012,CS-HJ-008,CG-CZ-015 and FO-CZ-020)plant pathogenic fungi.