Design, Synthesis And Antibacterial Activity Of Novel Derivatives Based On 1,2,3,4-tetrahydro-β-carboline Unit

1,2,3,4-tetrahydro-β-carboline（THC）alkaloids are mainly derived from plants,marine species,etc.THC and its derivatives have a spectrum of biological activities,such as anticancer,antioxidant,antibacterial,antiviral and antimalarial activities.Based on the previous work of our research group,novel 1,2,3,4-tetrahydro-β-carboline derivatives were designed and prepared in this paper to structurally modify THC,and all compounds were structurally characterized by ¹H NMR,¹³C NMR and high-resolution mass spectrometry（HRMS）.The target compounds were evaluated by turbidimetric method against rice leaf blight（Xanthomonas oryzae pv.oryzae,Xoo）,citrus ulcer（Xanthomonas axonopodis pv.citri,Xac）and kiwi ulcer（Pseudomonas syringae pv.actinidiae,Psa）,the best active compounds were selected for in vivo pot experiments,and the antibacterial mechanisms of the highly active compounds were further investigated.In order to investigate the effect of the C1,N2,C3,and C6 positions of THC on antibacterial activity,we designed a series of compounds A,B,C,D,E,and F,and found that 1,2,3,4-tetrahydro-β-carboline with a substitution at the C1 position exhibits high antibacterial activity.Compound A8 and A17 exhibited better anti Xoo,Xac,and Psa activities,with EC₅₀ values of 13.3,2.49,and 4.87?g/m L and 7.27,4.89,and 20.1?g/m L,respectively,significantly superior to the control drugs TC(EC₅₀ values of40.05,89.43,and 184.21?g/m L,respectively)and BT(EC₅₀ values of 58.01,37.58,and 182.45?g/m L,respectively).Pot experiments showed that compounds A17 and F3 exhibited excellent protective and therapeutic effects on rice bacterial blight and citrus canker disease.At200?g/m L,the protective effects were 52.67%,79.79%,53.87%,87.43%,and the therapeutic effects were 43.07%,26.64%,38.32 and 29.40%,respectively,higher than the activity of the control drug TC（anti Xoo,protection:38.20%,treatment:35.28%;anti Xac,protection:82.88%,treatment:26.64%）;Compound A8 also showed good protective and therapeutic effects on kiwifruit canker disease at 200?g/m L（84.31%and 64.71%,respectively）,superior to the activity of the control drug TC（80.39%and62.75%）.Changes in cell membrane integrity were clearly observed by AO/EB double fluorescence staining,indicating that compound A17 or F3 induced apoptosis in Xoo cells;compound A17 or F3 showed enhanced ROS fluorescence after incubation with Xoo cells,suggesting that the compound may disrupt the redox system of Xoo cells,triggering the production of ROS and disrupting the bacterial membrane,which leads to apoptosis of Xoo cells;using electron scanning microscope imaging（SEM）,it was found that compound A17 or F3-induced ROS could cause damage to the Xoo cell membrane.