Philip S. Magee

New aspects of organophosphorus pesticides. II. Structure and bioactivity of Orthene® insecticide analogs

O,S-Dimethyl phosphoramidothioate was jointly commercialized in the United States as Monitor® Insecticide1 by Chevron Chemical Company and Chemagro, and as Tamaron in Europe by Farbenfabriken Bayer. This exceptional insecticide/acaricide was discovered in 1964 by Lorenz at Bayer (Shrader et al. 1972) and by Magee (1967 Patent-Monitor, 1972 Patent-Orthene) at Chevron Chemical. Both groups carried out extensive modifications within the class leading to subsequent patents. Based on simplicity, efficacy and economics, Monitor Insecticide survived as the most important member of its class and became a commercial reality in 1970. It has many virtues as a systemic broad-spectrum insecticide of good residual life and is expected to have a world-wide impact on many important crops. Hammann (1970) described the bioactivity of Monitor Insecticide in some detail. While safe to handle due to moderate dermal toxicity [LD50 (rats) 110 mg/kg (Hammann 1970)], Monitor and all of its simple analogs have relatively high oral toxicity [LD50 (rats) 20 mg/kg].

PARAMETER FOCUSING — A NEW QSAR TECHNIQUE

Parameter Focusing is an experimental plotting technique that can reliably identify the two most important parameters controlling bioactivity. Focusing in the pattern recognition sense will occur for any related set of reasonable size whenever a distinctive subset of highly active members can be defined. This subset will occupy a relatively small and exclusive area within the total parameter space. Parameter Focusing complements regression analysis but has some useful advantages when the data are not suitable for regression. The biodata are used only for the purpose of identifying the most active subset and do not appear in the experimental plots. The nature of substituent constants and their distribution as individual sets provides a basis for the success of the method.