Discovery and structure-activity relationship studies of novel tetrahydro-β-carboline derivatives as apoptosis initiators for treating bacterial infections

Developing and excavating new agrochemicals with highly active and safe is an important tactic for protecting crop health and food safety. In this paper, to discover the new bactericide candidates, we designed, prepared a new type of 1,2,3,4-tetrahydro-β-carboline (THC) derivatives and evaluated the in vitro and in vivo bioactivities against the Xanthomonas oryzae pv. oryzae (Xoo), Xanthomonas axonopodis pv. citri (Xac), and Pseudomonas syringae pv. actinidiae (Psa). The in vitro bioassay results exhibited that most title molecules possessed good activity toward the three plant pathogenic bacteria, the compound A17 showed the most active against Xoo and Xac with EC50 values of 7.27 and 4.89 μg mL-1 respectively, and compound A8 exhibited the best inhibitory activity against Psa with EC50 value of 4.87 μg mL-1. Pot experiments showed that compound A17 exhibited excellent in vivo antibacterial activities to manage rice bacterial leaf blight and citrus bacterial canker, with protective efficiencyes of 52.67 and 79.79% at 200 μg mL-1, respectively. Meanwhile, compound A8 showed good control efficiency (84.31%) against kiwifruit bacterial canker at 200 μg mL-1. Antibacterial mechanism suggested that these compounds could interfere with the balance of the redox system, damage the cell membrane, and induce the apoptosis of Xoo cells. Taken together, our study revealed that tetrahydro-β-carboline derivatives could be a promising candidate model for novel broad-spectrum bactericides.