SELECTIVE TOXICITY OF ISOPROPYL PARATHION - EFFECT OF STRUCTURE ON TOXICITY AND ANTICHOLINESTERASE ACTIVITY

Isopropyl parathion and a series of related phosphate, phosphonate, and phosphinate esters containing branched alkyl groups were examined for toxicity to the housefly, honey bee, and white mouse. Anticholinesterase activity and alkaline hydrolysis rates of the esters were also determined. Isopropyl parathion and isopropyl paraoxon were found to be >212- and 17.8-fold more toxic to the housefly than to the honey bee, respectively; both were somewhat less toxic to the white mouse than the corresponding dimethyl and diethyl analogs. A number of other branched alkyl p-nitrophenyl phosphorothioate and phosphonothioate esters also showed selective action, particularly O-ethyl O-p-nitrophenyl isopropylphosphonothioate, which was >39-fold more toxic to the housefly than honey bee. However, the order of toxicity was reversed with the corresponding PO analog. Substantial differences were found in the rates of inhibition of cholinesterase from the two insects by some of the compounds and in the case of isopropyl paraoxon there was reasonable agreement between anticholinesterase activity and toxicity. The over-all data indicate that the selectivity of these esters may be explained only in part by differences in cholinesterase inhibition and that other factors also are involved in their selective action. © 1969, American Chemical Society. All rights reserved.