Study On Mining Secondary Metabolites From Stereum Hirsutum And Cyathus Stercoreus

This dissertation consists of three chapters.Study on the polyketides and their bioactivities from the lovastatin treated culture broth of the fungus Stereum hirsutum is described in the first chapter.Investigation on sesquiterpenes and their bioactivities from the epigenetic modifier vorinostat modified cultures of the fungus Cyathus stercoreus is discussed in the second chapter.The research progress of the natural products containing orsellinic acid units is summarized in the third chapter.Compounds described in this dissertation were isolated from the culture broths by plenty of chromatographic techniques,including normal-phase silica gel column chromatography（CC）,reverse-phase CC,Sephadex LH-20 gel-filtration CC,medium pressure liquid chromatography,analytical and preparative high performance liquid chromatography（HPLC）.Structural elucidations of the compounds were determined by various spectroscopic methods,such as one-and two-dimension nuclear magnetic resonance spectroscopy（1D and 2D NMR）,high resolution electrospray ionization mass spectrometry（HRESIMS）,ultraviolet and visible spectrum（UV-vis）,chemical calculations,and so on.Previous studies showed that the fungus S.hirsutum HP27 produced many sesquiterpenoids with diverse skeletons,and a small amount of depside polyketides.3-Hydroxymrthylglutaryl-coenzyme A reductase（HMGR）is a rate-limiting enzyme of the mevalonate pathway,which produces isopentenyl diphosphate（IPP）,a key precursor of terpenoids.The lipid regulating agent lovastatin is a competitive inhibitor of HMGR.In an attempt to reduce the production of terpenoids in S.hirsutum,lovastatin was used to modify the cultures of S.hirsutum in this study.The results showed that the yields and types of terpenoids in lovastatin-modified culture broth of S.hirsutum were been significantly reduced,while the yields and types of depside polyketides were been noticeably increased.Totally thirty-eight depsides,including twenty-nine undescribed compounds,were isolated and identified from the lovastatin-treated culture broth of S.hirsutum.The new compounds contained one compound with novel skeleton（1）,two trimers（2-3）,four dimers（4-7）,and a class of depsides comprising three benzene rings（11-18）.It was confirmed by chiral HPLC analysis that compounds 1,6,and 10-13,were racemates.The absolute configurations of the compounds 2,29,31,and 33-35 were determined by comparing the specific optical rotations with the corresponding synthetic analogs.The previously described compound sterenin C（24）showed a weak inhibitory effect on the growth of E.coli ATCC25922 with an MIC₅₀ value of 84.91μM.Additionally,twelve undescribed compounds,2-9,11,13,15,and 35,exhibited significant inhibitory activities against BACE1 with IC₅₀ values ranging from 3.47 to 11.81μM.Therefore,lovastatin is expected to be a general secondary metabolite-mining tool which can be applied to other higher fungi with rich terpenoid production.The histone deacetylase inhibitors（HDACIs）are a kind of epigenetic modifiers which were proved to be effective specialized product-mining tools by rationally regulating the gene expression of ascomycetous biosynthetic pathways.However,the application of HDACIs in mining chemical component from basidiomycetes has not been reported.In this study,vorinostat,a kind of HDACI,was applied to modify the culture broth of the basidiomycete Cyathus stercoreus HFG134.As a result,the diversity of secondary metabolites was significantly increased by comparing with the control group.Thirteen sesquiterpenoids,including nine previously unreported sesquiterpenes,and four reported ones,were isolated from the vorinostat-treated group.The sesquiterpenes consisted of five skeletons,of which compound 9 possessed an unprecedented 14（11→10）abeo-illudalane skeleton.This study suggested that epigenetic modifiers are also an effective tool for specialized metabolite-mining in basidiomycete.In chapter three,the isolation,structural identification,bioactivity,chemical synthesis,and biosynthesis of natural products containing orsellinic acid fragments were summarized.It always served as a build block to furnish complex molecules.These compounds were divided into simple orsellinic acid derivatives,depsides,meroterpenoids,and other types of compounds which were orsellinic acid-azaphilone hybrids,or hybridized with some other molecules in actinomycetes.