Synthesis And Bioactivity Of Novel Glycyrrhetinic Acid Derivatives With Isopropanolamine Substructure

18?-glycyrrhetinic acid?GA?is a pentacyclic triterpenoid isolated from the natural product glycyrrhiza species,which has a broad spectrum of biological activities,such as antibacterial,anti-inflammatory,anti-virus,anti-tumor,and so on.In addition to the abundant resources of glycyrrhiza species,it has been a research hotspot.Three aspects were mainly studied in this thesis.The first one is synthesis and biological activity research the 18?-glycyrrhetinic acid derivatives containing isopropanolamine substructure,the second is the possible pharmacophore were evaluated by corresponding structural modification and structure-activity relationship analysis,the last one is the mechanism of excellent antibacterial compounds was preliminarily studied.1.Based on 18?-glycyrrhetinic acid with piperazine group introduced into C-30,31 derivatives(I₁-I₃₁)of 18?-glycyrrhetinic acid-30-piperazine containing isopropanolamine substructure were designed and synthesized,and 2718?-glycyrrhetinic acid-30-ester derivatives(II₁-II₂₇)containing isopropanolamine substructure were designed and synthesized,and their structures were characterized by ¹H NMR,¹³C NMR and HRMS.The biological activities of all the title compounds against Xanthomonas oryzae pv.oryzae?Xoo?,Xanthomonas axonopodis pv.Citri?Xac?were examined using the turbidimeter test in vitro.Biological activity test results showed that some of title compounds were attached with potent antibacterial capacity against the two plant pathogens,providing the minimum EC₅₀ values of 2.28 and 0.93?g/m L,respectively.Those data were substantially superior to bismerthiazol?92.6?g/m L?,and thiodiazole copper?121.8 and 77.0?g/m L?.In addition,The curative and protection activities in potted plants of compounds I₃,I₁₃,II₆,and II₁₆ against rice bacterial leaf blight were determined.Results showed that I₃,I₁₃,II₆,and II₁₆ exerted prominently therapeutic and preventive effects at 200?g/m L with the control efficiencies in the range of 50.19%-53.70%and 50.57%-53.06%,respectively.Those values clearly outperformed those of commercial agents BT?33.43%and 39.86%?and TC?42.39%and 37.07%?.2.Compounds I₃,I₁₃,II₆,and II₁₆ possessing excellent antibacterial competences were selected as the reference substances by corresponding structural modification and structure-activity relationship analysis to explore the possible pharmacophore.For18?-glycyrrhetinic acid-30-piperazine derivatives I₃ and I₁₃,first of all,the GA skeleton and the latter nitrogen-containing pattern play an important synergistic effect in promoting the more interactions with the bacterial target species.Secondly,the two hydroxyl groups and nitrogen-containing heterocyclic scaffolds at the tail were recommended in maximally functioning the antibacterial power.Finally,the fixed configuration in target compounds could improve the anti-Xoo activity,while the racemic style was beneficial to the anti-Xac activity.For 18?-glycyrrhetinic acid-30-ester derivatives II₆ and II₁₆,the GA skeleton was essential for the biological actions;while the latter generated hydroxyl group and the absolute configuration could launch various degrees of influence toward bioactivity.3.Flow cytometry was exploited to investigate the apoptotic actions of pathogens induced by the corresponding bioactive compounds I₃,II₁₆?for Xoo?and I₁₃,II₆?for Xac?.Scanning electron microscope?SEM?imaging technique was used to find that the addition of compounds I₃,II₁₆?for Xoo?and I₁₃,II₆?for Xac?resulted in partial folding or rupture of the pathogen cell membrane.The accumulation of reactive oxygen species?ROS?was detected by fluorescent probe method,and the ROS content in pathogens increased after the interaction with compounds I₃?for Xoo?and I₁₃?for Xac?.At the same time,fluorescence-enhanced images of reactive oxygen species?ROS?in pathogenic bacteria were observed by fluorescence imaging microscopy after the stimulation of compound I₃?for Xoo?.