Quantitative Structure‐Activity Relationships in Insecticidal Pyrethroid Ethers

A series of twenty‐six insecticidal pyrethroid ethers were subjected to multiple regression QSAR analysis. The results indicated that candidate insecticides should have a lipophilicity, as expressed in the log of the calculated octanol/water partition coefficient, of approximately 5.5. There was a general, negative correlation of activity with molar refractivity, suggesting that molecular size, or volume, and polarizability should not be too large for optimum insecticidal activity. The substituents on the aromatic ring adjacent to the cyclopropyl moiety appear to exert their primary influence via electronic effects. For optimum activity strongly electron donating para substituents are required. Electron‐withdrawing or donating effects, size and lipophilicity of the substituents on the cyclopropyl ring appear to influence the insecticidal activity. Substituents which are small, not very polarizable, not very lipid soluble and which have a positive polar electronic substituent constant are likely to be the most effective. This is consistent with the hypothesis of the pyrethroids and other toxins acting at specific receptors adjacent to ion channels embedded in nerve membranes, causing partial blockade of these sodium, or other ion, channels. There were very few changes made to the substituents on the other aromatic ring. The results indicated that electron withdrawing groups were favoured as substituents on that ring.