Discovery of Novel Pentacyclic Triterpene Acid Amide Derivatives as Excellent Antimicrobial Agents Dependent on Generation of Reactive Oxygen Species.

Developing new agricultural bactericides is a feasible strategy for stopping the increase in the resistance of plant pathogenic bacteria. Some pentacyclic triterpene acid derivatives were elaborately designed and synthesized. In particular, compound A 22 exhibited the best antimicrobial activity against Xanthomonas oryzae pv. oryzae ( Xoo ) and Xanthomonas axonopodis pv. citri ( Xac ) with EC 50 values of 3.34 and 3.30 mg L -1 , respectively. The antimicrobial mechanism showed that the compound A 22 induced excessive production and accumulation of reactive oxygen species (ROS) in Xoo cells, leading to a decrease in superoxide dismutase and catalase enzyme activities and an increase in malondialdehyde content. A 22 also produced increases in Xoo cell membrane permeability and eventual cell death. In addition, in vivo experiments showed that A 22 at 200 mg L -1 exhibited protective activity against rice bacterial blight (50.44%) and citrus canker disease (84.37%). Therefore, this study provides a paradigm for the agricultural application of pentacyclic triterpene acid.