Synthesis and In Vitro Antifungal Evaluation of 1,3,5-Trisubstituted-2-Pyrazoline Derivatives

Pyrazolines, the well-known five-membered nitrogen-containing heterocyclic compounds, have received considerable interests in the fields of medicinal and agricultural chemistry because of their broad spectrum of biological activities. To discover more potent antifungal compounds, a series of structurally related 1,3,5-trisubstituted-2-pyrazoline derivatives have been synthesized by introducing furan rings regarded as bioactive substructure into the scaffold of pyrazolines and tested for their activities against six plant pathogenic fungi in vitro. The preliminary bioassays indicated that almost all synthesized compounds had displayed variable growth inhibitory effects on the tested pathogenic fungi. In particular, compounds 4, 7, 9, 12, 18, 19, and 38 displayed excellent antifungal activities against Rhizoctonia solani and their inhibition of growth reached 100% at the concentration of 20 mg/L. Additionally, compounds 9 and 19 bearing two furan rings, respectively, at site 3 and site 5 of the pyrazoline cycle showed the strongest activities against R. solani (the EC50 were 3.46 mg/L and 3.20 mg/L). The bioactivity results provide good starting templates for further structural optimization of pyrazoline derivatives.