Novel 18β-glycyrrhetinic acid amide derivatives show dual-acting capabilities for controlling plant bacterial diseases through ROS-mediated antibacterial efficiency and activating plant defense responses

Natural products have long been a crucial source of, or provided inspiration for new agrochemical discovery. Naturally occurring 18β-glycyrrhetinic acid shows broad-spectrum bioactivities and is a potential skeleton for novel drug discovery. To extend the utility of 18β-glycyrrhetinic acid for agricultural uses, a series of novel 18β-glycyrrhetinic acid amide derivatives were prepared and evaluated for their antibacterial potency. Notably, compound 5k showed good antibacterial activity in vitro against Xanthomonas oryzae pv. oryzae (Xoo, EC50=3.64 mg L–1), and excellent protective activity (54.68%) against Xoo in vivo. Compound 5k induced excessive production and accumulation of reactive oxygen species in the tested pathogens, resulting in damaging the bacterial cell envelope. More interestingly, compound 5k could increase the activities of plant defense enzymes including catalase, superoxide dismutase, peroxidase, and phenylalanine ammonia lyase. Taken together, these enjoyable results suggested that designed compounds derived from 18β-glycyrrhetinic acid showed potential for controlling intractable plant bacterial diseases by disturbing the balance of the phytopathogen’s redox system and activating the plant defense system.