Benzofurazan derivatives as antifungal agents against phytopathogenic fungi

•Transformation of benzofuroxan to benzofurazan retains the compound activity against phytopathogenic fungi.•However, the benzofurazan derivatives exhibited reduced activity in general.•Highest activity was observed for compounds with 7-nitro derivatives having R1 substituents containing aromatic rings.•Derivatives with substituents at 5,6-ortho position of the benzene ring exhibit moderate efficacy.

A series of benzofurazan derivatives were prepared and evaluated for their biological activities against four important phytopathogenic fungi, namely, Rhizoctonia solani, Sclerotinia sclerotiorum, Fusarium graminearum and Phytophthora capsici, using the mycelium growth inhibition method. The structures of these compounds were characterized by 1H NMR, 13C NMR, and HRMS. N-(3-chloro-4-fluorophenyl)-7-nitrobenzo[c][1,2,5]oxadiazol-4-amine (A3) displayed the maximum antifungal activity against R. solani (IC50 = 1.91 μg/mL), which is close to that of the positive control Carbendazim (IC50 = 1.42 μg/mL). For other benzofurazan derivatives with nitro group at R4 position (A series), 9 out of 30 compounds exhibited high antifungal effect against strain R. solani, with IC50 values less than 5 μg/mL. Most of the derivatives with substituents at R2 and R3 positions (B series) displayed moderate growth inhibition against S. sclerotiorum (IC50 < 25 μg/mL). Also, several benzofuran derivatives with nitro group at R4 position and another conjugated aromatic ring at the R1 position of the phenyl ring displayed high antifungal capability against strain R. solani. Compounds with substituents at R2 and R3 position had moderate efficacy against strain S. sclerotiorum.

Graphical abstractBenzofurazan derivatives with 5 or 6 member aromatic ring at R1 and nitro group at R4 display high antifungal activity against phytopathogenic fungi strain Rhizoctonia solani, compounds with substituents at R2 and R3 position show good activity against strain Sclerotinia sclerotiorum.Figure optionsDownload full-size imageDownload as PowerPoint slide