Antibacterial Activity of Novel 18 β -Glycyrrhetinic Hydrazide or Amide Derivatives

T hrough a facile structural modification on the natural bioactive ingredient 18β-glycyrrhetinic acid(GA), a series of novel GA hydrazide or amide derivatives was obtained, and their final molecular frameworks were characterized by NMR and HRMS analysis. Antibacterial bioassays revealed that some of the GA hydrazide or amide derivatives were able to suppress the growth of three tested plant pathogens. Particularly, compound 3 c exhibited excellent in vitro activity against Xanthomonas oryzae pv. Oryzae ( Xoo ), Pseudomonas syringae pv. actinidiae ( Psa ), and Xanthomonas axonopodis pv. citri ( Xac ), providing the EC 50 values of 5.89, 16.1, and 3.64 µg/mL, respectively. The data were better than those of the positive controls thiodiazole copper(92.7, 77.8, and 89.9 µg/mL, respectively) and bismerthiazol(31.1, 125.6, and 77.4 µg/mL, respectively). In addition, in vivo experiments suggested that, compared with thiodiazole copper(41.93% and 39.73%, respectively), compound 3 c exerted prominently curative and protective activities against rice bacterial leaf blight at 200 µg/mL with the control effects of 52.36% and 51.40%, respectively. Given these obtained results, GA hydrazide or amide derivatives could serve as the feasible leads for exploring highly bioactive substrates.