Synthesis, fungicidal activity, and QSAR of pyridazinonethiadiazoles

A series of novel 5-[l-aryl-1,4-dihydro-6-methylpyridazin-4-one-3-yl]-2-,arylamino-1,3,4-thiadiazoles, related to the fungicidal activity, were synthesized and tested in vivo against wheat leaf rust, Puccinia recondita. The preliminary bioassay indicated that they exhibited fungicidal activity and the activity was influenced by the nature of the substituents. A quantitative structure-activity relationship study showed that the hydrophobicity (Sigmapi) is a major positive parameter in affecting the activity; the electronic parameters (Sigmasigma, SigmaF) are the major negative parameters in affecting the activity. Especially, introducing an ortho substituent with an inductively electron-donating property is favorable to the activity.