Synthesis, fungicidal activity and structure-activity relationships of 3-benzoyl-4-hydroxylcoumarin derivatives

To develop a coumarin-based fungicide, a series of 3-benzoyl-4-hydroxylcoumarin derivatives were synthesised and their fungicidal activities were evaluated against typical fungi occurring in Chinese agroecosystems.

Target compounds were characterised through (1) H NMR, (13) C NMR and high-resolution mass spectrometry. The crystal structure of compound III-21 was determined through X-ray diffraction. Bioassay results indicated that most of the target compounds showed good growth inhibition against all of the fungi tested in vitro. EC50 of the target compounds against Physalospora piricola, Rhizoctonia cerealis, Sclerotinia sclerotiorum and Botrytis cinerea indicated that most of the target compounds displayed comparable activity with that of carbindazim and chlorothalonil in vitro. Among these compounds, the analogue 3-(2-bromo-4-chlorobenzoyl)-4-hydroxylcoumarin (III-21) displayed the optimum growth inhibition against R. cerealis (87.5%) and B. cinerea (82.7%) in vivo at 200 µg mL(-1) concentration; thus, this analogue is a potential inhibitor of pathogenic fungi and a new major compound for further optimisation. The results of analysing the structure-activity relationships demonstrated that changes in substituents on benzene ring A of 3-benzoyl-4-hydroxylcoumarin caused different fungicidal activities and provided original information on the preferential conformation to maintain high activities.

The present work demonstrated that 3-benzoyl-4-hydroxylcoumarin derivatives can be used as possible major compounds to develop novel fungicides. © 2015 Society of Chemical Industry.