Synthesis and antibacterial activity of novel phosphorylated flavonoid derivatives

GRAPHICAL ABSTRACT ABSTRACT Fifteen novel phosphonate derivatives containing a flavonoid unit were designed and synthesized, based on the connection method of active fragments. The target compounds were characterized by 1H NMR, 13C NMR, 13P NMR, ESI-MS, IR, and elemental analysis. Bioassay results indicated that some of the compounds possessed an excellent inhibition activity (≥57.38%) against Xanthomonas oryzae pv.oryzae (Xoo) at a concentration of 100 µg/mL, with 50% effective concentration (EC50) values ranging from 40.29 to 66.87 µg/mL, which are superior to the commercial antibacterial agent bismerthiazol (88.51 µg/mL). Compound (2-(3-Bromophenyl)-4-oxo-4H-chromen-3-yl) diethyl phosphonate (2f) and compound (2-(4-(tert-butyl) phenyl)-4-oxo-4H-chromen-3-yl) diethyl phosphonate (2h) display better inhibition rates against Xoo even at a concentration of 50 µg/mL. Moreover, a few compounds exhibited moderate inhibitory activities against Xanhomonas axonopodis pv.citri (Xac).