Quantitative structure-activity studies of pyrethroids: 10. Physicochemical substituent effects of substituted benzyl pyrethrates on symptomatic and neurophysiological activities

Abstract

The lethal and convulsive activities against American cockroaches and the knockdown activity against house flies of meta-substituted benzyl (1 R)- trans-pyrethrates and related compounds were measured under conditions where metabolic factors were minimized. The neuroexcitatory and blocking activities in central nerve preparations from the cockroaches were also measured with an extracellular recording technique. Variations in these activities were analyzed quantitatively by use of physicochemical substituent parameters and regression analysis, and the results were compared with those obtained from substituted benzyl (1 R)- trans-chrysanthemates. The most important parameters that governed these activities of the pyrethrates were hydrophobicity and the steric dimensions represented by the STERIMOL width and length of the aromatic substituents. The result was similar to that of the chrysanthemates. The relationships between the whole-body toxicities and the neurophysiological activities were also analyzed quantitatively. The cockroach toxicities could be analyzed by the neuroblocking activity index when the transport factor was separated by use of the hydrophobicity parameter. The house fly knockdown activity could also be analyzed in this way, but both neurophysiological activity indices were needed in the analysis.