Abstract
Quantitative structure-activity relationships (QSAR) analyses of fungicidal activity of 3-chloro-2-[N-(3-substituted-2, 6-dinitro-4-trifluoromethylphenyl)] amino-5-trifluoromethylpyridines against Sphaerotheca fuliginea, Pyricularia oryzae and Rhizoctonia solani were carried out and the results were compared. In the case of S. fuliginea, a usual QSAR equation with Hammett's electronic parameter (σm) and hydrophobicity (π) was obtained, suggesting that the uncoupling mechanism might be involved in the mode of action. In the cases of P. oryzae and R. solani, QSAR equations were consisted of σm, π and the activity rank against Botrytis cinerea as independent variables, indicating both of uncoupling and SH-inhibition were working in the action mechanism. Molecular orbital calculations clarified that the charge delocalization coupled with structural relaxations of the torsion angles between the C-N-C plane and the benzene and pyridine rings were responsible for strong acidity of fluazinam even in the less polar environment, which was reported as an important feature of shuttle-type uncoupling mechanism. More than one mode of action may be working behind the broad fungicidal spectrum of fluazinam.
