Insecticide Metabolism and Mode of Action

The metabolism, both in vitro and in vivo, of the chiral isomers of the phosphonodithioate insecticide fonofos was examined. The absolute configurations of the fonofos isomers and relevant oxidation products were established by x—ray diffraction analysis and chemical correlation. Oxidation of fonofos to the corres— ponding oxon in the presence of mouse liver mixed—function oxidase occurred predom— inantly with retention of configuration. The difference in toxicities of the fonofos enantiomers to insects and mammals is rationalized in terms of stereo— selectivity in target site inhibition by the oxon, stereoselectivity in fonofos to fonofos oxon conversion and detoxication by other enzymes.