Design, Synthesis, and Antibacterial Activity of Novel Paeonol Derivatives Containing Piperazine Moiety

Currently, there is a lack of effective antibacterial agents against citrus canker, rice bacterial stripe disease, and leaf blight. Paeonol derivatives containing a piperazine moiety were synthesized and studied their antibacterial activity against <i>Xanthomonas oryzae</i> pv. <i>oryzae</i> (<i>Xoo</i>), <i>Xanthomonas oryzae</i> pv. <i>oryzicola</i> (<i>Xoc</i>), and <i>Xanthomonas axonopodis</i> pv. <i>citri</i> (<i>Xac</i>). Some compounds exhibited excellent antibacterial activity against <i>Xoo</i>. Using a three-dimensional quantitative structure-activity relationship (3D-QSAR) model, the optimal compound <b>P5</b> was identified with the 50% effective concentration of 6.9 μg/mL against <i>Xoo</i>. It demonstrated superior <i>in vitro</i> antibacterial activity compared to the positive controls, bismerthiazol (47.2 μg/mL) and thiodiazole copper (96.9 μg/mL). Notably, molecular docking revealed that <b>P5</b> fully occupies the FtsZ binding pocket through hydrogen bonding and hydrophobic interactions, thereby enhancing its anti-<i>Xoo</i> activity. Subsequently, through a 100 ns molecular dynamics (MD) simulation, the stability of the binding between compound <b>P5</b> and the FtsZ protein was confrmed. Scanning electron microscopy showed that <b>P5</b> induces membrane collapse in <i>Xoo</i> cells. Concurrently, <b>P5</b> enables effective detection of plant bacteria by inducing fluorescence quenching through coaggregation, allowing bacterial imaging under a green fluorescence channel. <i>In vivo</i> testing confirmed that <b>P5</b> outperformed commercial thiodiazole copper in controlling <i>Xoo</i>. Mechanistic studies revealed that <b>P5</b> integrates into bacterial membranes, disrupts membrane structure, inhibits biofilm formation, and thus exerts antibacterial effects, indicating its potential as a promising pathogen-control agent.