Design And Synthesis Of Novel Carbazole Ethanols And Their Antimicrobial Study

Carbazoles are an important type of nitrogen-containing heterocycles with large π-conjugated system and strong charge-transport abilities.This special rigid fused ring endows carbazoles with distinct various functions,properties and biological activities,such as antioxidant,antitumor,anti-inflammatory,antimicrobial and so on,thus holding great potentiality in medicinal field.Much literature has reported that carbazoles also display good inhibitory effect against biomicromolecules and cell membrane,which indicates the promising future of carabzole in biochemistry.Furthermore,carbazole ring could be easily mofidied by introducing different functional groups.The synthesis of carbazole derivatives and the exploration of their novel applications have become increasingly attractive.All the above mentioned show the enormous potentiality of carbazole-based compounds in medicinal chemistry,which encourage much special interest in exploiting carbazole derivatives as biological agents.Azole compounds as electron-rich nitrogen heterocycles have been widely applied in clinical medicinal field and have been extensively investigated as antibacterial and antifungal drugs.Some azole compounds such as metronidazole,sulconazole,fluconazole,ceforanide,ceftizoxime,oxazolidones,sulfaphenazole have been employed in clinic to treat various types of microbial infections,which insprires the further development of azole-based antimicrobial agents.A large number of alcohols from natural and artificial source with potent antimicrobial potentiality in daily life have long been employed as disinfectants with advantages of ubiquity,convenience and high efficiency and especially aminoalcohols have been announced with prominent antibacterial potencies.Additionally,azole ethanol as a combination of alcohol and azole ring has showed excellent inhibitory efficacies against bacteria and fungi,which quickly diverts a great deal of scientific effort towards the development and extensive use of other hydroxyethyl azoles in clinic to treat pathogenic infections.The conjugation of azole ethanols with carbazoles as antimicrobial agents has been reported actively,which is a beneficial way to afford multi-targeting agents with a view of overcoming drug resistance.In this thesis,based on the situation in the researches of carbazoles and azoles in recent years,a series of novel azolyl carbazole compounds were designed and synthesized.These novel compounds were evaluated for their antimicrobial activity,and preliminary structure-activity relationships were also discussed and summarized.Cytotoxicity and time-killing ability of some highly active target compounds were evaluated to predict their pharmacokinetic behaviors.The preliminary antibacterial mechanism was also discussed.The main work was summarized as follows:(1)Preparation of new carbazole-derived azolyl ethanols: Intermediates II-2a-g were prepared by the nucleophilic substitution of substituted carbazoles II-1a-e respectively with epichlorohydrin in N,N-dimetylformamide,which were further reacted with various azoles under basic condition to give corresponding carbazole derivatives II-3-6,where compounds II-3f-g and II-4f were obtained from the ring opening reaction of triazole and imidazole with the chlorination and bromination products of Ⅱ–2a respectively.Seven carbazolyl epoxides and fifteen novel carbazole-derived azolyl ethanols were synthesized.(2)Preparation of carbazole-derived fluconazole analogs: Intermediates III-2a-e were prepared by the Friedel-Crafts acylation of substituted benzenes III-1a-e respectively with chloroacetyl chloride in dichloromethane,which were further reacted with triazole under basic condition to give corresponding N-alkylated triazole derivatives III-3a-e through nucleophilic substitution.The epoxidation of intermediates ITI-3a-e with excessive trimethyl iodide in dichloromethane afforded epoxides III-4a-e,which were further subjected to ring opening reaction with a variety of carbazoles in the presence of sodium hydride in DMF to prepare the target carbazole-based fluconazole analogs III-5a-j and III-6.Five chloroacetophenones,ten triazolyl benzene intermediates and eleven novel carbazole-derived fluconazole analogs were synthesized.(3)The structures of the new compounds were characterized by 1H NMR,13 C NMR,IR and HRMS spectra.(4)The antibacterial and antifungal results indicated that some synthesized carbazole derivatives in series II and III showed moderate to good antibacterial or antifungal activities against the tested strains.Particularly,triazolyl carbazole II-3f was found to be the most potential one against E.faecalis with an MIC value of 2 μg/m L,being 2-fold more potent than norfloxacin,and it also displayed superior anti-S.aureus ATCC 29213(MIC = 4 μg/m L)activity to norfloxacin,which exhibited its broad antifungal spectrum.Some of fluconazole analogs in series III could effectively inhibit the growth of the some tested fungal strains,and the substituents in benzene ring and carbazole scaffold as well as the conjugated system exerted obvious effect on the biologal activity of target molecules.Notably,3,6-dibromocarbazole derivative Ⅲ–5d could effectively inhibit the growth of all the tested fungal strains with MIC values in the range of 2–32 μg/m L.Especially,it revealed comparable anti-C.albicans potencies(MIC = 4 μg/m L)to fluconazole.Compound Ⅲ–5d could also inhibit the growth of C.tropicals at a concentration of 4 μg/m L,being 2-fold more potent than fluconazole.These indicated that molecule Ⅲ–5d had the potency to be a lead compound in the development of more effective board-spectrum antifungal agents.(5)Drug resistance test showed that compounds Ⅱ–3f and Ⅲ–5d did not obviously trigger the development of resistance in bacteria and fungi,respectively.They could also interact with cell membrane in different manner,thus displaying repressive activities.UV-vis and fluorescence spectrum study found that compounds Ⅱ–3f and Ⅲ–5d could intercalate into DNA to further block DNA replication,which might be a factor to exert their antimicrobial activity.Molecular docking demonstrated that Ⅱ–3f and Ⅲ–5d could form compound-enzyme complex with DNA gyrase and CYP51,respectively,which were beneficial to exert the pharmaceutical effect of bioactive molecules.(6)Time kinetics indicated the highly active molecule Ⅱ–3f had a rapidly killing effect towards E.faecalis and possessed low cytotoxicity against normal mammalian cells RAW264.7.Fungicial ability evaluation showed that compounds Ⅲ–5d exhibited strong fungi-killing action against all of the treated fungi.Compound Ⅲ–5d mainly showed a synergism with fluconazole to enhance antifungal efficacy and broaden anfungal spectrum.Moreover,the theoretical prediction of other ADME properties manifested that the higher antifungal activity of compound Ⅲ–5d may be on the basis of appropriate log P and p Ka values.Binding investigations of Ⅲ–5d with HSA guided the further design,synthesis and modification of drug molecules.(7)Forty eight compounds were successfully synthesized in this thesis,in which twenty six compounds were new.Some of the target compounds exhibited superior antibacterial or antifungal potentialities to clinical antibiotics.Biological study found that the synthesized carbazole ethanols could enhance membrane permeability or depolarize membrane potential to exert membrane activity,and even intercalate into DNA.Moreover,these compounds had low possibility to induce resistance in bacterial or fungal strains and were competent to potentiate the inhibitory actition of clinical drugd.These biological researches indicated that the new carbazole ethanols had the potency to be leading compounds in the development of more effective board-spectrum antibacterial and antifungal agents.