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Twenty-nine N-[5-(substituted phenyl)-1, 3, 4-thiadiazol-2-yl] benzamides with various substituents on both benzene rings were synthesized. Most of them inhibited the incorporation of N-acetyl-[1-14C]glucosamine into cultured rice stem borer (Chilo suppresssalis WALKER) integument in the presence and absence of a metabolic inhibitor for oxidative degradation, piperonyl butoxide. Variations in the activity under each experimental condition were quantitatively analyzed with physicochemical substituent parameters and regression analyses. After the separation of the hydrophobic effect, para substituents on the benzene ring at the 5-position of the thiadiazole ring showed peculiar electronic and steric effects on the inhibitory activity. The greater the inductive component of the electron-withdrawing property and the molecular hydrophobicity, the higher the activity. Introduction of electron-donating groups such as OMe and Me at the ortho position of the benzoyl moiety seemed to be favorable to the activity. A limited number of compounds showed larvicidal activity against the insects via topical application. * Quantitative Structure-Activity Studies of Insect Growth Regulators (Part XII). For the previous paper, see Ref. 14).

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