Design, synthesis, fungicidal property and QSAR studies of novel β‐carbolines containing urea, benzoylthiourea and benzoylurea for the control of rice sheath blight

BACKGROUND Rice sheath blight is a globally important rice disease. Unfortunately, this critical disease has not been effectively controlled, and the intensive and continuous use of the same fungicide might increase the risk of resistance development in the pathogen. To discover new active agents against rice sheath blight, in this study, three series of β‐carboline urea, benzoylurea and benzoylthiourea derivatives were designed, synthesized and evaluated for in vitro and in vivo fungicidal activity against Rhizoctonia solani. RESULTS All these compounds (EC50: 0.131–1.227 mmol L−1) exhibited better fungicidal activity than harmine itself (EC50: 2.453 mmol L−1). Significantly, compound 17c (EC50: 0.131 mmol L−1) displayed the best efficacy in vitro and superior fungicidal activity compared with validamycin A (EC50: 0.397 mmol L−1). Moreover, the in vivo bioassay also indicated that compound 17c could be effective for the control of rice sheath blight. CONCLUSION Based on the bioassay result and quantitative structure–activity relationship (QSAR) information, structure modification in β‐carboline warrants further investigation and its benzoylurea derivative 17c, which showed the best fungicidal activities, could emerge as a potential fungicide against rice sheath blight. © 2018 Society of Chemical Industry Design of the novel β‐carboline urea, benzoylurea and benzoylthiourea derivatives.