Studies On The Secondary Metabolites Of A Medicinal Plant And Its Endophytic Fungus

Three chapters are included in this dissertation.The first chapter mainly describes the chemical constituents including their pharmacological activities of the traditional Chinese medicinal plant Phyllanthus glaucus.The second chapter mainly describes the chemical and pharmacological investigation on the endophytic fungus Aspergillus micronesiensis.The last chapter describes the progress of aspochalasins and its related merocytochalasans.The roots of the traditional medicinal plant Phyllanthus glaucus have been used to treat rheumatic arthritis and infantile malnutrition for a long history.The chemical constituents of Phyllanthus glaucus were studied.As a result,39 compounds(1-30)were isolated and identified,among which 20 were new compounds(1a/1b-8a/8b,22-25).Interestingly,most of the isolated lignans were obtained as a mixture of enantiomers.During our experiments,eight pairs of new lignan enantiomers were obtained(1a/1b-8a/8b),the absolute configurations were determined by analysis of their experimental ECD spectra.The antioxidant activities of 1a/1b-8a/8b were evaluated using DPPH free radical scavenging assay,and the results demonstrated that compounds 1b and 3b showed potent DPPH radical scavenging activities with IC50 values of 5.987 and 9.641 ?g/m L,respectively.Besides,we obtained three unusual phenylacetylene-bearing 3,4-seco-cleistanthane diterpenoids(22-24),their structures with absolute configurations were determined by single-crystal X-ray diffraction.Compounds 22-24 showed moderate anti-inflammatory activities by decreasing the level of TNF-? and IL-1? in the LPS-stimulated RAW 264.7 cells.The endophytic fungus Aspergillus micronesiensis was derived from the root of Phyllanthus glaucus.In the current study,79 compounds were isolated and elucidated,including 71 cytochalasans(31-101)and eight epicoccine derivatives(101-109),and 45 of them were new compounds(31-47,50-55,62-69,72-82,87,88,and 96)including 17 new skeletal compounds.The cytochalasans could be divided into four classes according to their structure characteristics: cytochalasan homodimer(31),cytochalasan heterotrimers(32-49),cytochalasan heterotetramers(50-52),cytochalasan heterodimers(53-61),and aspochalasins(62-101).Compound 31 is the first example of cytochalasan homodimer,which is composed by two aspochalasin monomers through a C-20/C-20' linkage.The structure with absolute configuration was unambiguously determined by single X-ray diffraction.Compounds 32-36 represent a new subclass of cytochalasan heterotrimers containing two types of aspochalasins,which belong to 5/6/11-type aspochalasin and 5/6/12-type aspochalasin,respectively.The structure with absolute configuration of 32 was unambiguously determined by single X-ray diffraction.Compounds 37-39 represent an unprecedented type of cytochalasan heterotrimers with new fusion patterns between two aspochalasins and the epicoccine unit,among them,37 and 38 possess an undecacyclic 5/6/11/5/5/6/6/5/11/6/5 ring system,and 39 has an additional furan ring with a dodecacyclic 5/6/11/5/5/6/6/5/5/11/6/5 ring system.The structure with absolute configuration of 37 was unambiguously determined by single X-ray diffraction.Compounds 41-45 share identical carbon skeleton with that of asperchalasine A(48)but possesses a mirror-image configuration at the epicoccine moiety.Their structures were unambiguously determined by the single X-ray diffraction experiments of 41 and 43.Specially,compounds 45 and 46 are the first cytochalasan heterotrimers with a ?5 double bond.Compounds 50-52 are rare cytochalasan heterotetramers with different structures from asperflavipine A.A tiny crystal of 50 was obtained,and the X-ray diffraction of 50 confirmed its structure.Compounds 62–69 are aspochalasins with a C-21 ester carbonyl.The CH3-25 in compound 62 is located at C-16 rather than at C-14 in the common aspochalasin skeleton,endowing 62 with a new carbon skeleton.The structure with absolute configuration of 62 was unambiguously determined by single X-ray diffraction.Compounds 63 and 64 are the first examples of aspochalasins with an unprecedented 5/6/6/8 tetracyclic ring system.Compounds 67 and 68 possess a long open-chain system,and their absolute configurations were discussed by comparing the NMR data of the hydrolysis and methyl esterification products of 65 and 66.Compound 72 is the first example of aspochalasin composed by an 8-oxa-bicyclo[3.2.1]octane unit and an isoindole moiety which connect to each other through a carbon-carbon single bond.Compounds 73 and 74 are the first examples of 17,18-secoaspochalasins.Compounds 75 and 76 are first examples of aspochalasins with a cysteine residue connecting at C-20 through a S atom.Compound 96 is the first example of aspochalasin with an unprecedented 5/6/5/8 ring system.The cytotoxic and anti-microbial activities of parts of the cytochalasans were evaluated,and it was demonstrated that many of the merocytochalasans were cytotoxic,most of the aspochalasins with a C-21 ester carbonyl were inactive,and compounds 75 and 76 with a cysteine residue were the most active among these aspochalasins.Moreover,compound 38 was twice as potent as the model compounds cytochalasins B and D,and its IC50 value against HL60 cells was 1.71 ?M.Further analysis of the mechanisms revealed that 38 exhibited cytotoxic activities through apoptosis induction mediated by caspase-3 activation and PARP degradation.Our current study of the secondary metabolites of Aspergillus micronesiensis not only greatly enriches the structural diversity but also provides deeper insight into the biological property of cytochalasans.It is of great significance in further study on cytochalasans.