| Since the emergence of antibiotics,the problem of bacterial resistance has become more and more serious.Today,the prevalence of bacterial resistance has significantly reduced the possibility of effective treatment of infections with antibiotics and increased the morbidity and mortality of common bacterial diseases.At the same time,the clinical channels for discovery of new antibacterial drugs are almost exhausted,and antibiotic resistance has become one of the top ten global public health threats.In view of the above situation,it is extremely urgent to solve the problem of bacterial multidrug resistance by developing antibacterial drugs with new mechanisms of action.AcrB transporter protein is an important component of AcrAB-TolC efflux pump.It is widely distributed on the cell membrane surface of Gram-negative bacteria and has a wide range of substrate specificity.It can actively expel almost all types of antimicrobial agents and other harmful substances.This efflux function of AcrB is an important reason for bacterial resistance.Due to the continuous pumping of antibacterial drugs,they cannot accumulate to an effective concentration in the bacterial body and cannot also play an antibacterial role.However,if the function of AcrB inhibited or interfered,bacterial resistance can be reversed,allowing the accumulation of antibacterial drugs in the bacteria to kill them.Therefore,AcrB is an important and ideal target for reversing bacterial resistance.In this thesis,a series of quinoline-4(1H)-one derivatives were designed and synthesized using AcrB as the target and the active compound A3 proved by our group as a lead compound,the structural characteristics of the flavonoid nucleus as a reference.Through the determination of intrinsic antibacterial activity and reversal of drug resistance activity,11 compounds with antibacterial sensitizing activity were obtained.The mechanism of the active compounds was further elucidated by Nile red efflux inhibition experiment,outer membrane permeability experiment and inner membrane depolarization experiment.The results showed that the MIC values of the tested compounds except HB11 and HB12 against wild-type E.coli BW25113 strains were all greater than 512 μg/mL indicating they did not have intrinsic antibacterial activity.There are 4 compounds in HA series and 7 compounds in HB series exhibiting antibacterial sensitizing activity against wild-type E.coli BW25113 strain.Among them,HA3 could increase the sensitivity of erythromycin by 2-fold at 128 μg/mL and HB3 could increase the sensitivity of erythromycin,chloramphenicol and levofloxacin by more than 4-,2-and 2-fold at the concentration of 256 μg/mL,respectively,showing a certain broad spectrum.The result of Nile Red efflux inhibition activity showed that almost all of the tested compounds could completely inhibit the efflux of Nile Red at a concentration of 128 μg/mL.The results of bacterial outer membrane permeability and inner membrane depolarization experiments,indicated that all test compounds had no effect on the inner and outer membranes of wild type strains.Therefore,compounds HA3,HA4,HB3,HB4 and HB5 are AcrB efflux pump inhibitors in the full sense.In conclusion,a series of novel quinoline-4(1H)-one derivatives have be obtained as AcrB inhibitors,which not only provides a direction for the development of new efflux pump inhibitors,but also further deepens our understanding and cognition of the structure of AcrB protein,and providing new ideas for the treatment of multidrug resistant infections. |
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