Design And Synthesis Of Novel Quinolone-3-Azoles And Their Antimicrobial Researches

Quinolone is a class of synthetic antibacterial agents containing benzopyridone acid structure and is widely used for the treatment of infectious diseases caused by Gram-positive bacteria,Gram-negative bacteria and anaerobic bacteria due to oral and parenteral activitives,broad antibacterial profiles,clinically achievable doses,relatively low drug resistance level,unique molecular mode of action,easy synthesis methods,better safety and many other advantages.However,along with the overuse of them and the emergence of new harmful pathogens,quinolone resistance has become increasingly serious which will limit their clinical utility.Thus,discovery of novel quinolone antibacterial agents with low bacterial resistance,excellent pharmacological properties and high potency is an important topic in the antimicrobial field.Azoles are important structural fragments which been extensively employed in drug design and synthesis.Many azole-based compounds such as aminothiazole and metronidazole derivatives have been successfully developed as clinical drugs for the treatment of various diseases such as antibacterial,anti-parasitic,anti-inflammatory and anticancer.In particular,as antimicrobial agents,a lot of aminothiazole and metronidazole derivatives such as Ceftazidime,Cefazoxime,Aztreonam,Ornidazole and Ouconazole play an important role in the fight against infectious diseases.The success of these drugs in the clinical leads to of a large number of highly active analogues.One of the most common methods of obtaining such new molecules is the introduction of aminothiazole or metronidazole fragments into existing drugs to improve biological activity and to construct novel biologically active molecules.Therefore,this thesis employed quinolone as the lead compound,based on the resistance mechanism and the principle of drug design to modify 3-position of quinolone.A series of novel quinolone-3-aminothiazole compounds and quinolone-3-metronidazole compounds were designed and synthesized and the antimicrobial activity of the target compounds was evaluated and structure-activity relationship was analyzed.The biocompatibility and resistance of highly active molecules were studied.The quantum mechanical properties of highly active molecules were explored to explain the biological properties of highly active molecules from the molecular level.The antimicrobial mechanism of high active molecules were explored.The main work is summarized as follows:(1)Synthesis of quinolone-3-azole compounds(A)Synthesis of novel quinolone-3-amidothiazoles: Dehydration condensation reaction occurred by triethyl orthoformate,ethyl acetate and ethyl acetoacetate as starting materials,and compound II-1 was obtained in a high yield,followed by nucleophilic substitution reaction with 2,4-difluoroaniline to give compound II-2 at a yield of about 80%.The resulting compound II-2 was cyclized under a diphenyl ether as a solvent at 250 oC to give 3-acetyl quinolone II-3,which was then N-alkylated and N-aryl with different alkyl halides and benzyl halides to give compounds II-4a–h and II-7a–f,which were bromitated by bromine with acetic acid as solvent at roo m temperature to obtain compounds II-5a–h and II-8a–f.Finally,compounds II-5a–h and II-8a–f were cyclized with thiourea in ethanol at 60 oC to give quinolone-3-aminothiazoles II-6a–h and II-9a–f with the yields ranging from 50% to 60%.(B)Synthesis of novel quinolone-3-metronidazoles: Starting from ethyl acetoacetate,triethoxymethane was condensed with acetic anhydride at 130 oC to produce ethyl 2-(ethoxymethylene)-3-oxobutanoate II-1 in 70% yield.The reaction of intermediate II-1 with various substituted anilines in the absence of solvent gave phenylamino butanoates III-1a–k at 130 oC in 90–95% yields,and then were further cyclized in phenoxybenzene under reflux to produce the desired 3-acetyl quinolones III-2a–k in moderate yields ranging from 42% to 56%.The compounds III-2a–k was subjected to N-alkylation with bromoethane in DMF as solvent and potassium carbonate as base to give the compounds III-3a–k,which then were further brominated b y bromine in acetic acid to obtain dibromo compounds III-4a–k.The dibromo compounds were then treated with THF as the solvent,triethylamine as base and triethyl phosphite as reduction agent to give the monobromo compounds III-5a–k.2-Methyl-5-nitroimidazole was reacted with potassium carbonate in DMF at 70 oC for 1 hour,then the mixture temperature was lowered down to 0 oC and monobromo quinolones III-5a–k were added to the mixture to produce 2-methyl-5-nitroimidazole-substituted quinolones III-6a–k in 90–95% yields,which then were reduced by sodium borohydride in ethanol at 0 oC to give target quinolone-3-metronidazoles III-7a–k with yields of 40–52%.Further,the target compound III-7j was reacted with the different cyclic amine under the conditions of using DMSO as the solvent,potassium carbonate as the base and Cu2 O as the catalyst to obtain the target compounds III-8a–c.(2)All the target compounds were confirmed by IR,NMR and HRMS spectroscopy.(3)Antimicrobial activity analysis of novel quinolone-3-azole compounds(A)Antimicrobial activity analysis of quinolone-3-aminothiazoles: N-1-Propargyl-modified quinolone-3-aminothiazole II-9f showed good broad-spectrum and strong antibacterial activity.The inhibitory ability of compound II-9f against B.typhi was the strongest among all the target compounds(MIC = 1 μg/mL)and the activity was 32 times and 4 times higher than that of the reference drugs Chloramphenicol and Norfloxacin,respectively.In addition,MRSA was also very sensitive to compound II-9f(MIC = 8 μg/mL)than Norfloxacin.In addition,the compound exhibited relatively or even better activity against S.dysenteriae and P.aeruginosa compared to the two reference drugs.Compound II-9f(MIC = 8 μg/mL)also had better anti-A.flavus activity compared to the reference drug Fluconazole(MIC = 256 μg/mL).(B)Antibacterial activity analysis of novel quinolone-3-metronidazoles: Compound III-8c displayed relatively good broad-spectrum and efficient antibacterial activities.In particular,the minimum inhibitory concentration of compound III-8c for all bacteria was almost not more than 16 μg/mL.For S.aureus strains,compound III-8c displayed remarkable inhibition with MIC value of 1 μg/mL,2-fold more potent tha n Norfloxacin(MIC = 4 μg/mL).Furthermore,MRSA was also quite sensitive to compound III-8c(MIC = 4 μg/mL)than Norfloxacin(MIC = 8 μg/mL).The anti-S.dysenteriae potency of compound III-8c with an excellent MIC value of 2 μg/mL was the strongest among the target compounds,which was 8-fold more potent than reference drug Norfloxacin.(4)Drug resistance research found MRSA showed no resistance to highly active molecules II-9f,III-7k and III-8c.Bactericidal kinetic assay revealed that compound II-9f had a rapid killing effect on MRSA.Cytotoxicity experiment in vitro suggested that highly active molecules II-9f,III-7k and III-8c had no cytotoxicity.(5)Bacterial membrane permeabilization showed the active molecule II-9f had a certain effect on the bacterial membrane of Gram-positive bacteria(MRSA)and Gram-negative bacteria(B.typhi).Molecular docking indicated that compound II-9f could interacte with topoisomerase IV-DNA complexe through hydrogen bonds and hydrophobic interactions.Preliminary studies showed that compound II-9f could intercalate into calf thymus DNA to form a stable complex that might block DNA replication and exert a strong biological activity.Enzyme inhibitory activity experiment found that compound III-8c had an excellent ability to inhibit topoisomerase IV.HSA binding behavior found that the main forces between them were hydrogen bonds and hydrophobic interactions.In this thesis,fifty-eight compounds were synthesized including 28 quinolone-3-aminothiazoles and 30 quinolone-3-metronidazoles.