Studies On The Secondary Metabolites From Four Actinomycetes Strains

Natural products and their derivatives are important sources of drug discovery,and many natural products have good biological activity.However,as people continue to explore natural products,it is becoming more and more difficult to find new compounds with biological activity.Although people have isolated a large number of compounds from microorganisms,many microorganisms have a large number of gene clusters in silence.Therefore,the use of molecular biology methods to activate typical silent gene clusters has gradually become an important means for the development of new drugs.In this study,four strains of AHBA-positive genes,Streptomyces sp.QH13,Streptomyces sp.134,Micromonospora sp.HK160111,and Micromonospora sp.FXY120 were used as research materials to study their secondary metabolites.A total of 39 compounds were isolated by column chromatographyon Sephadex LH-20,RP-18,Si gel and HPLC.The structures of compounds were identified by UV,MS,NMR,and X-ray single crystal diffraction techniques,of which 17 were new compounds,including 3 ansatrienols and 11 pentaketide ansamycin compounds.Streptomyces sp.QH13 was isolated from soilof Qinghai,China.Dr.Li Xiaomanx,construct a mutant strain Streptomyces sp.XZQH13OE△astC△astF2by double-knocked the astC and astF2 genes in QH13.Five ansatrienin analogues were obtained from the YMG agar medium of Streptomyces sp.XZQH130E△astC△astF2,including three ansatrienin analogues,namely,ansatrienols 1-K(3-5).Proposed biosynthetic pathways of ansatrienols in XZQU130E△astC△astF2 based on the structure of these compounds.Compounds CF1 and CF2 had no hydroxyl substitution at the C-19 position,confirming that the gene astF2 is responsible for the hydroxylation at the C-19 position.A total of 12 compounds were isolated from YMG medium of Streptomyces sp.134,including 4 divergolide compounds and 8 other small molecule compounds.134-G(11)was a degradation product of divergolide compounds.Micromonosporasp.HK160111 was isolated from the intertidal soil collected at Xiamen,Fujian.PCR screening revealed that it contains ahybrid PKS-NRPS gene clusters,predicted to produce novol pentaketide ansamycins.Overexpression of positive regulator gene mas 13 obtained the mutant strain HK160111mas13OE.A total of 11pentaketide ansamycins compounds were isolated from YMG medium of Micromonosporasp.HK160111 mas13OE,including 3 ring-opened pentaketide ansamycins.The absolute configuration of the compounds Microansamycins A-C(18-20)and E(22)was determined by single crystal X-Ray diffraction,and the configuration of the other compounds was deduced from the absolute configuration of the four compounds.Proposed biosynthetic pathways of microansamycin compounds based on their structural characteristics.The antioxidant activity of microansamycins A-I(18-26)was evaluated by DPPH method.All compounds showed antioxidant activity,of which Microansamycin D(22)had the best antioxidant activity with IC50 of 0.85 mmol/L.Micromonospora sp.FXY120 was isolated from the intertidal soil collected at Xiamen,Fujian.PCR screening revealed that it contains atypical PKS gene clusters.The mutants FXY120GC1-LuxR and FXY120GC3-SARP were constructed by overexpressing the positive regulator factors LuxR and SARP,respectively.Through the isolation of the secondary metabolites of YMG medium of the mutants FXY120GC1-LuxR and FXY120GC3-SARP,11 compounds were obtained,including 5 polyketides(34-38)and a new 7-membered lactam Compound(39).