Design, Synthesis, and Characterization of New Quercetin Derivatives: Antibacterial Activity and Mechanism Against...

In order to identify more effective antimicrobial agents against Clavibacter michiganensis subsp. sepedonicus (Cms), which has the capacity to cause severe reductions in potato yields, nine quercetin derivatives (2a-2i) were synthesized. All synthesized derivatives were structurally confirmed by ¹H NMR and ¹³C NMR and HRMS. In comparison with quercetin, the majority of the derivatives (2a, 2b, 2c, 2g, 2h, 2i) exhibited significant antibacterial activity. Among them, compound 2b (7-isopentenyloxy-4'-chloroflavonol) exhibited the highest inhibitory activity against Cms, with DIZ of 16.70 ± 0.35 mm and MIC of 0.08 mg/mL. Furthermore, in in vivo antibacterial activity assay, 2b demonstrated significant protective activity (88.04% ± 3.98%) and therapeutic activity (83.64% ± 10.91%), which were both significantly superior to positive control (71.79% ± 5.64% and 62.55% ± 4.41%, respectively). It was determined that 2b disrupted cell walls, increased cell membrane permeability, and depolarized cell membranes, leading to significant leakage of essential ions from the cells. The activities of various key enzymes were found to be significantly reduced. In summary, the studies demonstrated that 7-isopentenyloxyflavonol derivatives exhibit potent antibacterial activities against Cms, providing some new insights for future applications of 7-isopentenyloxyflavonol derivatives in combating Cms.