Design And Synthesis Of Novel Quinazolinones And Their Antimicrobial Investigation

Quinazolinones are a class of nitrogen-containing heterocyclic compounds with wide biological activities.Quinazolinone nucleus exsits in many natural alkaloids including luotonin,dichroine,glycosminine etc.Owning to the easy structural modification,high efficiency,low toxicity,unique action mode and broad spectrum of biological activities etc.,quinazolinones have been extensively used as medicines and pesticides.Quinazolinone derivatives such as methaqualone(anticonvulsant drug),raltitrexed(anticancer drug)and ketanserin(antihypertensives drug)have been widely used in clinic.Therefore,the design,synthesis and biological activity research of quinazolinones has become one of the hot spots in medicical area.With the extensive use or even abuse of quinolone antibiotics in recent years,the problem of bacterial resistance is becoming more and more serious.The development of new and effective antimicrobial drugs has become a global concern.Quinazolinone is structurally similar to quinolone and it has shown great development potentiality.Studies have shown azole alcohols and imines have displayed promising antimicrobial activities.Therefore,much effort has been devoted to the design and synthesis of these compounds as potent antimicrobial molecules.It has been reported that azoles have shown potential biological activities.In recent years,the investigation based on imidazoles,triazoles,and tetrazoles is becoming an extremely active area.Azoles can interact with different enzymes and receptors,DNA and RNA in the organism.Therefore,they possess huge medicinal develepment potency.Especially in antimicrobial area,such as metronidazole as the imidazole derivative,fluconazole,terconazole,itraconazole as triazole derivatives and cephalosporins as tetrazole derivatives have already gained great success in the treatment of various infectious diseases,which encourages numerous scientists to concentrate on azole-based drug development and their medicinal application.On the basis of the current situation in the research of quinazolinones and our work in the heterocyclic chemistry,a series of novel quinazolinone compounds were designed and synthesized.The preparative methods and conditions of the target compounds were explored.All target compounds were evaluated for their antibacterial and antifungal activities in vitro and the preliminary structure-activity relationships(SARs)were also disscussed.The antimicrobial mechanism of the highly active target molecule was investigated by fluorescence and UV-vis absorption spectroscopy.The main work was summarized as follows:(1)2-Amino-4-chlorobenzoic acid and formamidine acetate as the starting materials and methoxyethanol as solvent,compound II-2 was efficiently synthesized through cyclization.Subsequently,compound II-2 reacted with ?-cholroacetone or 2-chloro-1-(2,4-difluorophenyl)ethan-1-one to afford compound II-3a–b,which could gave intermediate II-4a–b when reacted with trimethylsulfoxonium iodide through cyclization reaction.Compounds II-4a–b then reacted with different azoles to obtain azolyl alcohols II-5–9.All target compounds were confirmed by 1H NMR,13 C NMR,IR and HRMS spectra.The antibacterial and antifungal activities in vitro of target molecules were evaluated and the SARs were also investigated.Triazole alcohol II-5a showed low antibacterial activity toward the bacteria that was tested.However,the replacement of methyl group in target compound II-5a with 2,4-difluorobenzene moiety gave albaconazole analog II-5b,and it showed higher antibacterial activity toward A.baumannii.This revealed that the introduction of 2,4-difluorobenzene group was helpful to improve the antibacterial efficacy.Benzimidazole alcohol II-6a displayed potential efficacy against A.baumannii with an MIC value of 0.043 ?mol/mL.Benzimidazole derivative II-6b(MIC = 0.161 ?mol/mL)showed 4-fold more potent efficacy against S.aureus ATCC 29213 than compound II-6a(MIC = 0.694 ?mol/mL).The substitution of methyl group in compound II-6a with 2,4-difluorobenzene moiety gave derivative II-6c,and it displayed good activity against clinical drug resistant bacteria K.pneumoniae and bacteria P.aeruginosa with MIC values of 0.008 and 0.017 ?mol/mL,respectively.The introduction of two methyl groups at the 5,6-positions on benzimidazole ring of compound II-6c yielded analog II-6d,and it showed 4-fold more potential anti-S.aureus ATCC 29213 efficacy than azolyl alcohol II-6c with an MIC value of 0.008 ?mol/mL.Imidazole deirvative II-7b displayed very high antibacterial activity toward clinical drug resistant bacteria P.aeruginosa with MIC value of 0.002 ?mol/mL,which was 12.5-fold more potent than standard drug norfloxacin.Compound II-8b also showed high antibacterial activity toward K.pneumoniae and P.aeruginosa with MIC values of 0.074 ?mol/mL.Benzimidazole derivative II-6a exerted potential antifungal activity toward C.albicans ATCC 90023 with an MIC value of 0.174 ?mol/mL.The introduction of two methyl groups at 5,6-positions on benzimidazole in compound II-6a gave derivative II-6b and it displayed 2-fold better antibacterial efficacy than analog II-6a with an MIC value of 0.081 ?g/mL.The replacement of methyl group in compound II-6a with 2,4-difluorobenzene fragment gave analog II-6c,and it exhibited 22-fold more potential anti-C.albicans ATCC 90023 efficacy than compound II-6a.Compound II-6c also exerted significant antifungal activity against C.parapsilosis ATCC 22019 with the MIC value of 0.017 ?mol/mL.The specific interaction of imidazole derivative II-7b with calf thymus DNA was investigated via UV-vis absorption spectroscopy.It was revealed that azolyl alcohol II-7b could intercalate into DNA to form II-7b–DNA complex,which might then block DNA replication exerting high antibacterial and antifungal efifcacies.Molecular docking study showed that compound II-7b could form hydrogen bond with the protein residue of ALA-1120 and ?-? stacking with the DNA base DG-10.The binding energy of the target compound II-7b with DNA was-6.33 kcal/mol.The intercalating binding mode betweent target molecule II-7b and DNA might be an effective way to inhibit bacterial DNA replication,leading to death of the strain.(2)2-Amino-4-chlorobenzoic acid and formamidine acetate as the starting material and 2-methoxyethanol as solvent,intermediate III-2 was obtained via cyclization,and then it was reacted with 2-chloro-1-(2,4-difluorophenyl)ethan-1-one to yield intermediate III-3 through nucleophilic substitution reaction.Compound III-3 was then reacted with hydroxylamine hydrochloride to give Schiff base derivative III-4.At last,the target molecules III-5,III-6 and III-7 was achieved by using compound III-4 and different halogenated hydrocarbons.All target molecules were confirmed by 1H NMR,13 C NMR,IR and HRMS spectra.Intermediates III-3 and III-4 displayed low antibacterial activities.Imine derivative III-5b displayed moderate antibacterial efficacy against S.aureus ATCC 29213,and low antibacterial efficacy toward other tested bacteria.Compound III-5c exhibited good antibacterial efficacy toward clinical drug resistant bacteria K.pneumoniae with the MIC value of 0.17 ?mol/mL.Quinazolinone derivative III-5d exerted high antibacterial activity toward clinical drug resistant bacteria E.coli with an MIC value of 0.08 ?mol/mL.Compound III-5e showed significant antibacterial activity toward Gram-positive bacteria S.aureus with the MIC value of 0.16 ?mol/mL,and at the same time potential activity toward Gram-negative bacteria A.baumanii with the MIC value of 0.04 ?mol/mL.n-Hexyl compound III-5f was found to display highly potent antibacterial activity against A.baumanii with an MIC value of 0.04 ?mol/mL.In addition,the heptyl III-5g and octyl III-5h also exhibited potential anti-A.baumanii activity.The benzyl substituted III-6a showed potential anti-A.baumanii activity(MIC = 0.07 ?mol/mL).4-Chlorobenzyl quinazolinone III-6b exhibited potential anti-A.baumanii efficacy(MIC = 0.02 ?mol/mL),and it also displayed good antibacterial activity toward P.aeruginosa(MIC = 0.13 ?mol/mL).Benzimidazole derivative III-7 was found to show high antibacterial efficacy toward P.aeruginosa and A.baumanii with MIC values of 0.12 and 0.06 ?mol/mL,respectively.Intermediate III-3 displayed good antifungal efficacy agianst C.tropicals with an MIC value of 0.19 ?mol/mL.Oxime derivative III-4 also displayed moderate antifungal efficacy toward C.albicans ATCC 90023 and C.parapsilosis ATCC 22019 with MIC values of 0.18 and 0.09 ?mol/mL,respectively.Imine derivative III-5d exhibited good antifungal activities against C.albicans ATCC 90023 and C.parapsilosis ATCC 22019 with MIC values of 0.16 ?mol/mL.Benzimidazole III-7 was observed to display good antifungal efficacy toward C.tropicals and C.parapsilosis ATCC 22019 with MIC values of 0.12 and 0.06 ?mol/mL,respectively.The interaction between highly activitive target molecule III-6b and A.baumannii DNA was studied via UV spectroscopy method.The results showed that the active molecule III-6b could intercalate into DNA helix structure.The fluorescence quenching mechanism,binding constant,binding site and other thermodynamic parameters of III-6b-HSA complex were studied by fluorescence spectroscopy.The combination of compound III-6b and HSA was spontaneously carried out.Cell membrane permeability assay showed that compound III-6b was effective in penetrating the cell membrane of clinically resistant bacteria A.baumannii.