Synthesis,Bioactivity Evaluation And Mechanism Study Of Novel Antibacterial Inhibitors

At present the increasing number of drug-resistant bacteria has posed a serious threat to human health.In this environment,we urgently need new drug development strategies or new antibacterial means to fight pathogens.This dissertation develops new antibacterial agents based on novel drug development strategies and photodynamic therapy,and their antibacterial activities and mechanisms are studied.The main work of the thesis is divided into three parts:Part Ⅰ:This part developed 10 novel 1,3,4-oxadiazole-2(3H)-norfloxacin hybrids based on the concept of pharmacophore hybridization.In vitro antibacterial experiments showed that most of the hybrids had better antibacterial activity against gram-negative and gram-positive bacteria than the parent drug(norfloxacin),and their MIC(minimum inhibitory concentration)values were between ≤0.125 and 1 μg/mL.Among them,hybrid 3e had the smallest MIC and MBC(minimum bactericidal concentration)against the tested strains.Time-kill curve analysis showed that 3e could rapidly kill Staphylococcus aureus and Escherichia coli within 2 h,proving its strong bactericidal activity.Cytotoxicity and hemolysis tests showed that all hybrids had good biocompatibility.Molecular docking studies show that all hybrids have higher affinity for DNA topoisomerase Ⅳ than the parent drug,with minimum binding energies ranging from-9.4 to-10.0 kcal/mol.Among all the synthetic hybrids,3e is promising to be a potential candidate for further development of novel an tibiotics.Part two:A series of 1,2,4-triazole-norfloxacin compounds were designed and synthesized with norfloxacin as the core of quinolone,and their antibacterial activities were evaluated in vitro.The newly synthesized compounds were characterized by Fourier transform infrared spectroscopy,proton nuclear magnetic resonance and carbon nuclear magnetic resonance,and electrospray ionization mass spectrometry.Representative compounds from each step of the synthesis were further characterized by X-ray crystallography.The in vitro antibacterial results showed that most of the compounds had better antibacterial activity against gram-positive and gram-negative bacteria than norfloxacin.The 1,2,4-triazole-norfloxacin compounds were 3 2-512-fold more toxic to bacterial cells than to mouse fibroblasts,and none of the compounds were found to be toxic at 64 μg/mL.Rabbit red blood cells produce hemolysis,indicating that they have good biocompatibility.Molecular docking revealed that the compounds had minimal binding energies of-9.4 to-9.7 kcal/mol,suggesting a significant affinity for bacterial topoisomerase Ⅳ.Part Ⅲ:This part designs and develops two novel AIE PSs(photosensitizers with aggregation-induced luminescence properties).Due to the structurally enhanced D-A(donor-acceptor)effect,AIE PSs exhibit efficient near-infrared fluorescence emission as well as efficient 1O2 generation.Pathogen imaging experiments demonstrated that AIE PSs could successfully visualize Staphylococcus aureus,Candida albicans,and dead Escherichia coli.In vitro antibacterial experiments showed that AIE PSs could effectively kill Staphylococcus aureus,Candida albicans and Escherichia coli under light conditions,proving that they have broad-spectrum antimicrobial activity.The bactericidal mechanism of AIE PSs was demonstrated to damage ion channels on the cell membrane of Escherichia coli,severely damage the structure of Staphylococcus aureus and Candida albicans to deform and damage the cell membrane.In vivo antiinfection experiments showed that AIE PSs could accelerate wound healing in bacteriainfected mice.All the results indicated that AIE PSs can be used as effective antibacterial agents for anti-infective therapy.