Isolation And Characterizantion Of The Secondary Metabolites From Genetically Engineered Streptomyces Avermitilis TM24 With Insecticidal And Acaricidal Activities

Polyketides represent an important class of biologically active and structurally diverse compounds found in nature.They are biosynthesized from acyl CoA precursors by polyketide synthases?PKSs?.The use of combinatorial biosynthesis to form hybrid PKSs is considered as an excellent approach for the development of novel polyketides.This paper describes a preliminary study on the active ingredients of genetically engineered strain Streptomyces avermitilis TM24,including the isolation and identification of metabolites from S.avermitilis TM24 and the acaricidal and nematicidal activities of the obtained compounds.1.Isolation and identification of the secondary metabolites of S.avermitilis TM24.The resulted cultural broth?30 L?of S.avermitilis TM24 was filtered,and ethanol was used to extract the mycelia.By filtration,extraction and concentration,the 258 goily residue was obtained.Twelve compounds were isolated and purified by silica gel column chromatography?100-200 mesh?,gel column chromatography?Sephadex LH-20?and HPLC?C-18 and C-3 columns?.The structures of the compounds were elucidated on the basis of NMR,HRESIMS,IR,UV spectroscopic analysis.The twelve compounds including tenvermectin A,tenvermectin B and the other 10 compounds were new sixteen-membered macrolactone compounds.The ten new compounds were assigned as:Tenvermectin F?1?,Tenvermectin G?2?,Tenvermectin H?3?,Tenvermectin I?4?,Tenvermectin K?5?,Tenvermectin L?6?,Tenvermectin Monosaccharide A?7?,Tenvermectin Monosaccharide B?8?,Tenvermectin Monosaccharide C?9?,Tenvermectin Monosaccharide D?10?.2.The insecticidal and acaricidal activities of the obtained compounds.The insecticidal and acaricidal activities of the compounds against Bursaphelenchus xylophilus,Tetranychus cinnabarinus and Plutella xylostella were evaluated.The LC₅₀ values of tenvermectin A,tenvermectin B,milbemycin A4and 1-8 against Tetranychus cinnabarinus were 0.0043,0.0049,0.0210,0.0022,0.0172,0.0248,0.0297,0.0723,0.0193,0.0266 and 0.0776 mg/L,respectively,while the LC₅₀ values of 9 and 10 were more than0.2000 mg/L.The LC₅₀ values of tenvermectin A,tenvermectin B,milbemycin A4 and 1-9 against Bursaphelenchus xylophilus were 3.45,2.17,4.04,28.60,17.11,12.23,19.92,4.56,38.56,4.30,20.19and 8.34 mg/L,while the LC₅₀ value of 10 was more than 100 mg/L.Compounds 1-10 shown lower biological activity against Plutella xylostella.3.Comparing the insecticidal and acaricidal activities and molecular structure of the compounds,the different groups of the tenvermectins C-5,C-13,C-24 and C-25 have a great influence on the insecticidal activity.Tenvermectins that lack a furan moiety showed weak nematicidal activities.The research results provided a theoretical foundation and scientific basis for the development of genetic engineering strain.