Structure-activity relationships of the avermectins and milbemycins
1997
Fisher, M.H.
In 1976 scientists at Merck & Co. Inc. discovered a complex of eight closely related natural products, subsequently named avermectins, in a culture of Streptomyces avermitilis MA-4680 (NRRL8165) originating from an isolate by the Kitasato Institute from a soil sample collected at Kawana, Ito City, Shizuoka Prefecture, Japan. They are among the most potent anthelmintic, insecticidal and acaricidal compounds known. The avermectins are structurally related to another group of natural products, the milbemycins, the first examples of which were described by Japanese workers. Avermectin B1, under the non-proprietary name abamectin, is widely used as an agricultural miticide and its 22,23-dihydro derivative, ivermectin is used world wide as a broad spectrum parasiticide in animals and in man. More recently, a new avermectin, doramectin, has been prepared by directed biosynthesis and developed for similar use in animals. Three milbemycins are used for animal health, milbemycin D, milbemycin oxime and moxidectin. This presentation describes some of the structure-activity relationships between the avermectins and milbemycins and an intensive synthetic program on 4"-deoxy-4"epiamino avermectins culminating in two novel compounds in development, emamectin benzoate as an agricultural insecticide and eprinomectin as a broad spectrum endectocide for use in animals. Mode of action studies have revealed a glutamate-gated chloride channel from C. elegans proposed to be the target site for both avermectins and milbemycins.
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