Osamu Kirino

Quantitative structure-activity relationships of the fungicidal methyl N-phenylcarbamates☆

Abstract For 69 methyl N -phenylcarbamates having various benzene ring substituents, the fungicidal activity was determined against Botrytis cinerea resistant to benzimidazole fungicides by the agar medium dilution method. The structure-activity relationships were analyzed quantitatively using such physicochemical substituent parameters as hydrophobic π, steric B 5 , and HB (hydrogen bonding) with the Hansch-Fujita method (C. Hansch and T. Fujita, J. Amer. Chem. Soc. 86 , 1616 1964). The hydrophobicity of substituents was favorable to the acitivity. The effect was position-specific, the importance being in the order of ortho ≅ meta > para . The activity was related parabolically to the maximum width of one of the m -substituents having the larger dimension. The hydrogen acceptability of p -substituents enhanced the activity. The preventive activity of compounds against gray mold of cucumber caused by the resistant B. cinerea , which was determined by the foliar application in pot tests, was dependent on the magnitude of the fungicidal activity and hydrophobicity of the compounds as analyzed by the adaptive least-squares method.

Quantitative structure-activity relationships for antifungal 3-(3,5-dichlorophenyl)-2,4-imidazolidinediones

The antifungal activity of 441-acyl derivatives of 3-(3,5-dichlorophenyl)-2,4-imidazol- idinedione against Botrytis cinerea, and of 10 1-sulfonyl compounds against Aiternaria kikuchi- ana were assayed by the agar medium dilution method. The structure-activity relationships for the substituents of the acyl and sulfonyl moieties were analyzed with such physicochemical parameters as hydrophobic π, inductive electronic σ1, and steric E′cs and B1 values by multiple regression. The activity of the acyl derivatives against B. cinerea was related parabolically to the hydrophobicity of the substituents. The stronger the electron-donating power, the larger the overall steric bulkiness, and the smaller the minimum width in the direction perpendicular to the bond axis of the substituents, the greater was the activity. The activity of the sulfonyl derivatives against A. kikuciana was related only to the hydrophobicity of the substituents.