Design, Synthesis, and Antifungal Activities of Novel Aromatic Carboxamides Containing a Diphenylamine Scaffold

A series of novel N-(2-(phenylamino)-4-fluorophenyl)-pyrazole-4-carboxamides 1–15 and aromatic carboxamides with a diphenylamine scaffold 16–29 were designed, synthesized, and evaluated for their antifungal activities. In vitro experiments showed that compound 6 (EC₅₀ = 0.03 mg/L) was superior to bixafen (EC₅₀ = 0.04 mg/L) against Rhizoctoinia solani and compound 6 (IC₅₀ = 1.41 mg/L) was close to bixafen (IC₅₀ = 1.22 mg/L) against succinate dehydrogenase from R. solani. Additionally, in vivo pot experiments showed that compound 6 (EC₅₀ = 1.93 mg/L) was better than bixafen (EC₅₀ = 3.72 mg/L) and close to thifluzamide (EC₅₀ = 1.83 mg/L) against R. solani. In vivo field trials showed that compound 6 at 200 g ai ha–¹ had 64.10% control efficacy against rice sheath blight after 21 days with two sprayings, close to thifluzamide (71.40%). Furthermore, molecular docking showed that compound 6 anchors in the binding site of SDH.