Flavonol derivatives containing piperazine and quinoxaline fragments: synthesis and antifungal activity

A series of flavonol derivatives containing piperazine and quinoxaline had been designed and synthesized. The biological activity test results showed that some of the target compounds had good antifungal activity against various fungi. N5 had the best antifungal activity against Phomopsis sp (P.s.) and Phytophthora capsica (P.c.). The half maximal effective concentration (EC₅₀) was 12.9 and 25.8 μg/mL against P.s. and P.c., respectively, which were better than azoxystrobin (Az, 25.4 and 71.1 μg/mL). In addition, the protective and curative activities of N5 against kiwifruit were 85.9 and 67.0% at 200 μg/mL in vivo, which were better than that of Az (65.9 and 57.0%). The protective and curative activities against chili leaves were 80.6 and 66.5% at 200 μg/mL, which were better than that of Az (77.6 and 60.0%). The scanning electron microscopy (SEM) experiment showed that the action of N5 caused the mycelium to bend and fold, changed its morphology and caused damaged to the mycelium. Through the measurement of relative conductivity, leakage of cytoplasmic contents and determination of malondialdehyde (MDA) content indicated that N5 could damage the integrity of pathogenic fungal cell membranes, change the permeability of cell membranes, and affect the normal growth of mycelium.