Design, Synthesis, and Biological Activity Studies of Flavonol Derivatives Containing Isopropanolamine and Piperazine

A series of antibacterial compounds incorporating a piperazine-isopropanolamine bifunctional group were designed and synthesized. In vitro activity evaluation revealed that compound Q17 exhibited the most potent inhibitory effects, demonstrating activity far superior to the control agents against both pathogens: its half-maximal effective concentration (EC₅₀) values were as low as 0.9 μg/mL against the bacterium Xanthomonas oryzae pv oryzae (Xoo), significantly better than thiodiazole-copper (TC, EC₅₀ = 29.9 μg/mL); and 9.8 μg/mL against the oomycete Phytophthora capsica (P.c), also significantly superior to azoxystrobin (Az, EC₅₀ = 98.5 μg/mL). Pot trials further demonstrated its outstanding curative and protective efficacy against infections caused by both pathogens. Mechanistic studies indicated that Q17 effectively suppressed virulence factor expression, compromised bacterial membrane integrity, inhibited cellular proliferation, and diminished colonization and infectivity in host plants. Consequently, Q17 represents a promising candidate for controlling crop bacterial diseases.