Design And Synthesis Of Novel Quinazolinone Azoles And Their Antimicrobial Study

Quinazolinones are important nitrogen-containing heterocyclic compounds with benzopyrimidone structures. Many natural alkaloids such as dichroine, luotonin and glycosminine contain the skeleton of quinazolinones. Due to the easy structural modification, quinazolinones display wide application potentials, especially in the field of medicine, because of their broad bioactive spectrum, low toxicity, high efficiency, unique action mode etc., quinazolinone compounds have attracted much attention. Numerous quinazolinone compounds such as methaqualone and methaqualone topiramate(anticonvulsant drugs), ketanserin(antihypertensives drug) and raltitrexed(anticancer drug) have been widely used in clinic to treat various diseases, which engaged lots of related workers in design, synthesis and biological activity research of quinazolinones in the medical field.In recent years, the irrational use of quinolone antibiotics caused the frequent incidents of drug-resistant strains. This growing drug resistance requests the urgent development of new antimicrobial drugs, which has become an important issue around the world. Quinazolinones as important derivatives of antimicrobial quinolones have shown their great potentiality. Many studies have shown that the 2- and 3-positions of quinazolinone are important modificarion sites for the antimicrobial activity, and these sites are easy to be modified. Therefore, a lot of researchers have been engaged in modifying these sites to screen the antimicrobial molecules, and numerous outstanding achievements have been achieved.It is well known that the reasearches of azole compounds including imidazoles, triazoles and tetrazoles are remarkably active. In medical field, azoles compounds can react with different kinds of enzymes and acceptors in organisms and show widely biological activity. A large number of clinical applications of azole compounds have been obtained in respect to antimicrobial field. For instance, clotrimazole, miconazole, oxiconazole and other imidazole drugs, some triazole drugs such as fluconazole, terconazole, itraconazole and many cephalosporins containing tetrazole structure have already been used in clinic for the treatment of various infectious diseases. All the mentioned above have shown the great exploitation value and extensively potential application of the azole compounds as antimicrobial agnets.In this thesis, based on the current situation in the research of quinazolinone compounds and our group’s research for the antimicrobial heterocyclic compounds, a series of novel quinazolinones were designed and synthesized through introducing azole heterocyclic group to the 2- or 3-position of quinazolinone. The preparative methods and conditions of some target compounds were discussed. All newly synthesized compounds were evaluated for their antibacterial and antifungal activities in vitro and the preliminary structure-activity relationships were also disscussed. Further antimicrobial mechanism of the highly active compounds was investigated by fluorescence and UV-vis absorption spectroscopy. The main work was summarized as follows:(1) The preparation of target compound II: Using 2-amino-4-chlorobenzoic acid and formamidine acetate as the starting materials and methoxyethanol as the solvent, compound II–1 was efficiently synthesized through cyclization. Subsequently, compound II–1 as the nucleophilic reagent reacted with ethyl chloroacetate to afford compound II–2, which could provide the intermediate II–3 after reacting with hydrazine hydrate. The shiff base-intermediate II–4 could be obtained through the dehydration of compound II–3 and 2-butyl-4-chloro-5-formylimidazole, using ethanol as the solvent. And finally, a series of shiff base based quinazolinone derivatives, including target compounds II–5a–h and II–6a–l, were synthesized through reacting compound II–4 with various bromoalkanes and benzyl haloids, using acetonitrile as solvent and K2CO3 as catalyst.(2) The preparation of target compound III: Commercially available 2-amino-4-chlorobenzoic acid was reacted with chloroacetonitrile in the presence of sodium alkoxide via cyclization to produce chloromethyl intermediate compound III–1 in high yield, and then intermediate compound III–2 was effectively prepared though introduction of nitro group in the 6-position of III–1 via nitratlon reaction. At last, the target quinazolinone-derived azoles including target compounds III–3a–i with no substituent at 6-position, 6-nirto-substituted compounds III–6a–c, amino-azole derivatives III–4a–c and III–7a–c, mercapto-azole derivatives III–5a–d and III–8a–d were obtained by the nucleophilic substitution of intermediates III–1 or III–2 with azole compounds such as imidazole, benzimidazole, triazole, tetrazole, thiazole.(3) All structures of these new compounds were confirmed by the spectral methods including 1H NMR, 13 C NMR, IR, MS, and HRMS.(4) The preparative condition(solvent and catalyst) of quinazolinone-based azole compounds III–3–8 was also explored. The study found that the yields of compounds III–3a–i and III–6a–c were the highest under the condition of DMF as solvent and potassium carbonate or sodium hydride as catalyst. In addition, the optimization condition of desired compounds III–4a-c and III–7a–c was co-catalyzed by TEA and catalytic amount of DMAP in dichloromethane. Moreover, compounds III–5a–d and III–8a–d were efficiency obtained in ethanol and catalyzed by TEA.(5) The antibacterial and antifungal activities of target compounds II and intermediates were evaluated in vitro and the structure-activity relationships were also discussed. The results showed that most target compounds exerted poor effects against four gram-positive bacteria, six gram-negative bacteria, and five fungi. Some target compounds exhibited comparative antimicrobial activity as the clinical agents, which were worth of further investigation. These antimicrobial activity data were in accordance with the values of Clog P. The introduction of imidazole ring is of great importance for antimicrobial effect. For instance, compound II–5d–e showed moderate effect against fungi, and the antibacterial activity of compound II–6i with the MIC value of 8–16 μg/m L was as strong as the reference agent Chloramphenicol.(6) Additionally, the interaction between compound II–6i and calf thymus DNA was detected via UV spectra, which preliminarily indicated that the antimicrobial mechanism of target compounds II–6i is via interacting with DNA to form complex through intercalation binding.(7) The prepared intermediates and target compounds III were evaluated for their in vitro antibacterial and antifungal activities. The relationship between structure and antimicrobial activity was explored. The biological assays indicated that some target compounds such as III–3e, III–3g–h, III–5c and III–8d showed strong antibacterial effects against Micrococcus luteus, Staphylococcus aureus and Escherichia coli, whose MIC values reached 2-8 μg/m L. In terms of antifungal activity, imidazole derivatives III–3a, III–3c–d and III–5a showed good antifungal activity against Candida albicans and S. cerevisiae with MIC values ranging from 1 to 8 μg/m L. Noteworthly, the mercaptotriazole derivative III–8c showed an excellent antimicrobial ability against all the tested bacteria and fungi with MIC values between 2 and 16 μg/m L. The preliminary structure-activity relationships showed that the antibacterial activities of triazoles were better than imidazoles, and tetrazoles were the most worst. In addition, the introduction of 6-nitro group broadened the antimicrobial spectrum. However, the introduction of nitro group, thioether bond and N-H bond had little effect on the antibacterial and/or antifungal activity.(8) The interactions of the highly active target compound III–8c with calf thymus DNA were studied by UV spectroscopy. The results revealed that compound III–8c could interact with DNA through intercalative mode confirmed by competing experiment of III–8c with neutral red(NR), which preliminarily suggested that its proposed antibacterial mechanism might be the obstruction of bacterial DNA replication.(9) The fluorescence quenching mechanism of III–8c–HSA system was explored through fluorescence spectroscopy. The number of binding sites, binding constants and thermodynamic parameters suggested that the III–8c–HSA binding process was spontaneous and the main binding forces for the association of compound III–8c–HSA were hydrogen bonds and van der Waals forces.Fifty two compounds were successfully synthesized in this thesis, forty seven compounds were new. In the charpter two, there were four intermediates II–1–4, eight N-alkyl target compounds II–5a–h and twelve N-benzyl target compounds II–6a–l. In the charpter three, there were two intermediates III–1–2 and twenty six target compounds including III–3a–I, III–4a–c, III–5a–d, III–6a–c, III–7a–c and III–8a–d.