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Avermectins            Chemical Formula: C48H74O14  

Streptomyces Avermitilis Extract
   
derived from: aglycons   
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Abstract:

Generic companies registering Abamectins, Ivermectins, Milbemectins, Azadirachtins and other botanical insecticides:

We specialize in isolation, purification and certification of active and impurity standards for GLP chemistry packages.
25 years experience with natural products and pharmaceuticals. Call for quotations. State of the art chromatography methods.

For several years Planta Analytica has been helping agrocheical companies to fulfill the regulatory requirements for registering their commercial product. We hav developed several successful strategies to isolate minor (>0.1%) abamectins to use them as the reference standards for quantitative HPLC analyses. We can also0 offer our expertise in identifying various abamectins.

Avermectins were first isolated at Merck Sharp & Dohme Resarch Laboratories (G. Albers-Schonberg, B. H. Arison, J.C.Chabala, A.W. Douglas, R. Eskola, M. H.Fisher, A. Lusi, H. Mrozik, J. L.Smith, and R. L. Tolman “Avermectins. Structure Determination”, J.Am.Chem. Soc. 1981, 103, 4216-4221; see also Antimicrob. Agents Chemother. 15, 361, 368, 372 (1979). Avermectins are a group of fermentation products from a strain of Streptomyces avermitilis possessing potent anthelmintic and insecticidal activities. Presently, avermectins are the active components of some insecticidal and nematocidal products used in agriculture.

Avermectin Chemical Structure
Diagram showing Avermectin Chemical Structure

   

Different fermentation and purification protocols afford commercial avermectin that vary in the composition of minor components. An HPLC gradient of the commercial avermectin from different sources showed that contaminants were grouped into three clusters. At the beginning of the work, the components eluting in a cluster before the main avermectin B1a (code letter: G) were given the codes with a letter K. Two clusters of avermectins eluting after avermectin B1a were given the codes starting with the letters L and M. Table 1 shows the composition of 5 different commercial samples of avermectin and the concentration range for various components.

The goal was to isolate about 10 mg of each avermectin present above 0.1% in the commercial product. In the initial step, the relative concentration of the avermectins was increased by 10-30 times by fractional crystallization (Table 1, colums yellow and tan). The obtained enriched mixture was then subjected to a CPC fractionation in a solvent system containing hexane, ethyl acetate, methanol and water. Table 2 shows the results of this fractionation. Each column in the Table 2 represents composition of the fraction and the concentration of the individual avermectins is expressed as percent of the fraction weight. These fractions had a much simplified composition and their final purification by preparative HPLC on C18 or C8 columns was greatly facilitated. It needs to be mentioned that while the CPC fractionation led to full recovery of the components, the yields from the preparative HPLC usually were in the range of 15 to 75 %.

This is a repeate para for testing only. The goal was to isolate about 10 mg of each avermectin present above 0.1% in the commercial product. In the initial step, the relative concentration of the avermectins was increased by 10-30 times by fractional crystallization (Table 1, colums yellow and tan). The obtained enriched mixture was then subjected to a CPC fractionation in a solvent system containing hexane, ethyl acetate, methanol and water. Table 2 shows the results of this fractionation. Each column in the Table 2 represents composition of the fraction and the concentration of the individual avermectins is expressed as percent of the fraction weight. These fractions had a much simplified composition and their final purification by preparative HPLC on C18 or C8 columns was greatly facilitated. It needs to be mentioned that while the CPC fractionation led to full recovery of the components, the yields from the preparative HPLC usually were in the range of 15 to 75 %.

 
Table 1
Table1
Table 2
Table 2  
 
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