The Study On Second Metabolites And Activity From Streptomyces Avermitilis NEAU1069-3

Microbial metabolites attract more and more attention as potential pesticides due to their potential bioactivity and low toxicity to non-target animals and humans. Some microbial metabolites, for example avermectins, milbemycins, have been commercialized and considered to be the most widely used drugs in animal health and agriculture. During the course of the screening program for new natural pesticides and antiparasitic veterinary drugs, two new macrocyclic lactones, three milbemycins, six new doramectin congeners have been isolated from Streptomyces avermitilis NEAU1069. To screen for more bioactive compounds, a mutant S. avermitilis NEAU1069-3 was obtained by UV treated and two new doramectin analogs were isolated from its fermentation broth. In the further work to explore the chemical diversity of the constituent of S. avermitilis NEAU1069-3. Herein, we describe the fermentation, isolation, structural elucidation and insecticidal activity of those compounds.Thirty liters of broth from 300 producing fermentations was produced by large-scale fermentation of the Streptomyces avermitilis NEAU 1069-3. 10 compounds(1-10) were extracted and isolated by using silica gel column, Sephadex LH-20,HPLC and other chromatographic skills. Then, 1D and 2D NMR, as well as HRESIMS, IR, UV, 1H-1H COSY, HMBC and HMQC were used to determine the structure of those compounds. At last, we found that 2 compounds are novel compounds, 23, 24-didehydro-13α-hydroxy milbemycin A3(1) and 24,30-didehydro-13α-hydroxy milbemycin A3(2). The remaining 8 are already known compounds, 13β-hydroxy Milbemycin D(3), 13β-hydroxy Milbemycin A4(4), 13β-hydroxy Milbemycin A3(5), 13α,24-dihydroxy Milbemycin A4(6), 13β,30-dihydroxy Milbemycin A4(7), 13β-hydroxy-14,15-epoxy Milbemycin A4(8), 13β-hydroxy-5-oxo-5-deoxyMilbemycin A4(9),Milbemycin A3(10).The insecticidal activities of compounds 1 and 2 against Brevicoryne brassicae(L.) were tested by the leaf dip method. The insecticidal capacities of the two compounds were compared with milbemycin A3/A4. In this technique, the aphids were collected from insectides-free flowering Chinese cabbage and reared at room temperature. Serial dilutions(five concentrations) of each compound were prepared in distilled water for use in the bioassays. leaf discs with a diameter of approximately 35 mm were prepared from cabbage leaves and dipped for 30 s in various concentrations of the 3 compounds. Leaf discs dipped only in distilled water conducted as controls. The dried leaf discs were then transferred to Petri dishes, and 80-90 aphids were put in each dish. The mortality of aphids was recorded after 24 h. The mortality of the treated compound was corrected using the control mortality, and the LC50 values were calculated from the corrected data. The bioassays were conducted simultaneously on three replications for each concentration. Compared with milbemycins A3/A4, the results demonstrated that compounds 1 and 2 have good aphidicidial activities and would be a potential insecticide.