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