Fungitoxicity and QSAR of 4-amino-5-substituted aryl-3- mercapto-(4 H )-1,2,4-triazoles

Twenty eight 4-amino-5-substituted aryl-3-mercapto-1,2.4-triazoles have been tested in vitro against Rhizoctonia solani. Scferotium rolfsii, Fusarium oxysporum, Pythium aphanidermatum. Puccinia recondita and Bipolaris sorokiniana. These triazoles have shown very good activity against all the six test fungi, their activity against P. recoitdita and B. sorokiniana have been found cxcellent. The compound. 5-(2-chloro-5-nitrophenyl)-4-amino-3-mcreapto- 1,2,4-triazole 27 exhibits highest activity (ED 50 =12 mg mL -1 ) against P. recondita and the compounds 5-(2-chlorophenyl)-4-amino-3-mercapto-1,2,4-triazole 3 and 5-(4-formylphenyl)-4-amino-3-mercapto-1,2,4-traizole 19 (ED 50 =27 mg mL -1 ) against B. sorokiniana. The quantitative structure activity relationship (QSAR) analyzed using physicochemical parameters for hydrophobic, electronic and steric properties of the molecules by means of multiple regression analysis has revealed different structural requirement for fungicidal activity against different fungi. The position dependent steric effect of the aryl substitucnts is playing an important role in imparting fungicidal activity against all the test fungi. The positive sign with stcric parameter terms indicate that their higher values enhance the fungicidal activity in this series. The other parameters for hydrophobic and electronic effect arc also influencing the fungicidal activity differently against different fungi.