Novel Flavonol Derivatives Containing Quinoxaline: Insights into the Antifungal Mechanism against Sclerotinia sclerotiorum

Abstract

In this study, 12 pairs of tautomeric flavonol derivatives containing quinoxaline were synthesized. The results of antifungal activity showed that in the enol−keto tautomerism, the target compounds containing keto (Y B series) had better inhibitory activity against Sclerotinia sclerotiorum (S.s.) than compounds containing enol (Y A series). Y B9 showed the strongest antifungal activity against S.s., and the median effective concentration (EC 50 ) value was 1.0 μg/mL, which was better than azoxystrobin (Az, 35.3 μg/mL). In vivo fungal inhibition experiments showed that the protective activity of Y B9 against rape leaves was 83.4% at 200 μg/mL, which was superior to that of Az (70.2%). The activity of succinate dehydrogenase and molecular docking results showed that Y B9 had a stronger antifungal effect than Y A9 . The results of oxalic acid content determination showed that Y B9 could reduce the pathogenic ability of S.s. Then, the inhibitory effect of Y B9 against S.s. was further verified by scanning electron microscopy, fluorescence microscopy, cell membrane permeability, cell content leakage, and malondialdehyde content.