Synthesis And Biological Activities Of Substituted Aldehyde Thiosemicarbazone Derivatives

Phytopathogenic fungi have become the deadly disease in agriculture due to their strong infection and hard to control. Pencycuron and Maneb, two widely used nitrogen-containing fungicides and containing the active group-NH-CH=, showed the good selectivity, high activity and low toxicity. Therefore, a series of substituted aldehyde thiosemicarbazone derivatives were prepared. Meanwhile, their biological activities were tested, and their structure-activity relationships were described. The results were obtained as follows:1. Twenty substituted aldehyde thiosemicaebazone derivatives were synthesized. And the reaction conditions were optimized. Their structures were characterized by mp, 1H NMR and IR. Especially the steric configuration of compound 3b was determined by X- ray diffraction.2. At a concentration of 100 μg/mL, the antifungal activities of all compounds were evaluated against four phytopathogenic fungis such as Valsa mali, Fusarium oxysporum sp.niveum, Fusarium solani and Colletotrichum gloeosporioides. Compounds 3d, 3e, 3g, 3i and3 r showed good antifungal activity against V. mali; compounds 3d, 3e, 3g, 3h and 3r showed good antifungal activity aganist F. oxysporum; compounds 3d, 3e, 3g, 3i and 3r showed good antifungal activity aganist F. solani; compounds 3a, 3d, 3e, 3f, 3g, 3h, 3i, 3r and 3t showed good antifungal activity aganist C. gloeosporioides. Moreover, the EC50 values of compound3 r aganist three phytopathogenic fungis(e.g., V. mali, F. solani and C. gloeosporioides) were also obtained.3. The stomach toxicity of all compounds was tested against third-instar larvae of Mythimna separata Walker. Among all derivatives, compounds 3e, 3g, 3h, 3i, 3o, 3p, 3n, 3l,and 3r exhibited the stomach toxicity.4. The structure-activity relationships of twenty substituted aldehyde thiosemicaebazones as antifungal agents were observed: introduction of the methyl group on the phenyl ring could lead to more potent compounds than those containing the hydroxyl group(e.g., 3d and 3e Vs.3b and 3c); introduction of a halogen atom on the phenyl ring could result in the potent compounds(e.g., 3f, 3g and 3h); introduction of a double bond between a substituted aldehyde and a thiosemicaebazone group could sharply increase the antifungal activities of the corresponding compound(e.g., 3r Vs. 3q).