The organocatalytic site-selective monoacylation of avermectin B2a, an insecticidal and anti-parasitic drug, was accomplished. Although an acetylation of avermectin B2a using a 4-dimethylaminopyridine (DMAP) as a catalyst gave poor site-selectivity, use of our organocatalyst increased site-selectivity of the acylation at the C-5-OH as well as the yield of monoacetate. This catalyst was also eff...

4'-Modified avermectin derivatives were designed and synthesized. Some of the new synthetic compounds showed excellent in vivo bioactivity against cabbage larvae when compared to commercially available avermectin B1a. In this synthesis, uncommon thioglycosyl sugar donors, prepared from the hydrolysis of natural antibiotics, proved compatible with sugar-macrolide synthesis in the presence of N-i...

Response surface methodology was employed to optimize the composition of medium for the production of avermectin B1a by Streptomyces avermitilis 14-12A in shaker flask cultivation. Corn starch and yeast extract were found to have significant effects on avermectin B1a production by the Plackett-Burman design. The steepest ascent method was used to access the optimal region of the medium composit...

I. Biosynthesis of Avermectins A. Incorporation of Labeled Precursors B. Biosynthetically Blocked Mutants and Characteristics of Each Step in Avermectin Biosynthetic Pathway 1. aveA {aveAI and aveAIh step for polyketide synthase) 2. aveB (step for glycosylation) 3. aveC (step for C22~23-dehydration) 4. aveD (step for C5 O-methylation) 5. aveE (step for furan ring formation at C6 to C8a) 6. aveF...

The level of activity of avermectin B O-methyltransferase, the enzyme which catalyzes the conversion of avermectin B components to avermectin A components, was analyzed in a series of "Streptomyces avermitilis" mutants selected for increased production of the avermectins. In all of the mutants, increased avermectin production was accompanied by increased avermectin B O-methyltransferase activit...

results however the maximum production of avermectin b1b (17 mg/l) was obtained by using sm2 growth medium containing soluble corn starch, yeast extract, kcl, caco3 and mgso4 which was detected qualitatively by using tlc and quantitatively by hplc. conclusions maximum production was observed with initial medium ph of 7, 10% inoculum size with incubation temperature of 31°c for 10 days of fermen...

When given to sheep as a single oral dose at 0.1 mg/kg, the B(1a) component of the avermectins caused a reduction of >95% in the numbers of Haemonchus contortus, Ostertagia circumcincta (including inhibited L(4) larvae), Trichostrongylus axei, Trichostrongylus colubriformis, Cooperia oncophora, and Oesophagostomum columbianum. When given to cattle as a single oral dose at 0.1 mg/kg, avermectin ...

Second-stage juveniles (I2) of Meloidogyne arenaria consumed more oxygen (P </= 0.05) than M. incognita J2, which in turn consumed more than M. javanica J2 (4,820, 4,530, and 3,970 mul per hour per g nematode dryweight, respectively). Decrease in oxygen consumption depended on the nematicide used. Except for aldicarb, there was no differential sensitivity among the three nematode species. Meloi...

1. Ivermectin belongs to the macrocyclic lactone class of endectocides and consists of a mixture of two homologous compounds, 22,23-dihydroavermectin B1a (H2B1a, not less than 80%) and 22,23-dihydroavermectin B1b (H2B1b, not more than 20%). Avermectins are potent anthelmintic, insecticidal and acaracidal compounds which, by increasing the membrane permeability to chloride ions, mediate the para...

BACKGROUND Secondary metabolite production from wild strains is very low for economical purpose therefore certain strain improvement strategies are required to achieve hundred times greater yield of metabolites. Most important strain improvement techniques include physical and chemical mutagenesis. Broad spectrum mutagenesis through UV irradiation is the most important and convenient physical m...