Design and synthesis of novel 2-(6-thioxo-1,3,5-thiadiazinan-3-yl)-N'-phenylacethydrazide derivatives as potential fungicides.

A series of novel 2-(6-thioxo-1,3,5-thiadiazinan-3-yl)-N'-phenylacethydrazide derivatives were designed, synthesized and evaluated for their antifungal activities against Fusarium graminearum (Fg), Rhizoctonia solani (Rs), Botrytis cinerea (Bc) and Colletotrichum capsici (Cc). The bioassay results in vitro showed that most of the title compounds exhibited impressive antifungal activities against the above plant fungi. Particularly, the compounds 5c, 5f, 5g, 5i, 5m and 5p displayed desirable anti-Rs activities, with the corresponding EC50 values of 0.37, 0.32, 0.49, 0.50, 0.46 and 0.45 µg/mL, respectively, which are superior to the positive control carbendazim (0.55 µg/mL). Further in vivo bioassay results showed that the anti-Rs activity of title compound 5f at 200 µg/mL reached 95.84% on detached rice leaves and 93.96% on rice plants. Featuring convenient synthesis, novel structures and desirable antifungal activity, these 2-(6-thioxo-1,3,5-thiadiazinan-3-yl)-N'-phenylacethydrazide derivatives could be further studied as the potential candidates of novel agricultural fungicides.