Synthesis and biological evaluation of 4-methyl-1,2,3- thiadiazole-5-carboxaldehyde benzoyl hydrazone derivatives

To find new lead compounds with high biological activity, a series of novel 4-methyl-1,2,3-thiadiazole-5- carboxaldehyde benzoyl hydrazone derivatives were designed and synthesized. Their structures were confirmed by ¹H NMR, ¹³C NMR, IR spectrum and elemental analysis. Preliminary bioassay indicated that the title compounds exhibited moderate to strong fungicidal activity against six fungi in vitro at 50 μg/mL. Moreover, some of the title compounds exhibited good curative activity against TMV in vivo at 500 μg/mL. The structure-activity relationship analysis of compounds against Valsa mali showed that compounds containing halogen at the para position on phenyl exhibited the best activity. Especially compound 8k showed broad spectrum fungicidal activities against Valsa mali, Botrytis cinerea, Pythium aphanidermatum, Rhizoctonia solani, Fusarium moniliforme and Alternaria solani with the EC₅₀ values of 8.20, 24.42, 15.80, 40.53, 41.48, and 34.16 μg/mL, respectively.