Design And Synthesis Of Novel Naphthalimide Azoles And Their Related Antimicrobial Researches

Naphthalimide compounds are an important type of nitrogen-containing aromatic heterocycles with cyclic double imides and naphthalene framework. This π-sufficient large conjugated planar structure enables naphthalimide derivatives to readily interact with various biological cations, anions, small molecules and macromolecules such as DNAs, enzymes and recetors in living organism via noncovalent bonds, therefore exhibiting extensive potentiality in relatively medicinal applications. Currently, some naphthalimides as anticancer agents have been entered into clinical trials and other naphthalimide-based medicinal developments as potential drugs for treatment of various diseases including bacterial and fungal infections, the diagnosis and detection of life important species etc., are actively and unprecedentedly expanding. Meanwhile, azoles have also been frequently employed in medicinal chemistry and material chemistry resulting from their electron-rich nitrogen heterocycle. This structural characteristic makes their derivatives to easily bind with diverse biological molecules via noncovalent bonds to produce broad bioactivities. So far, lots of azole-based drugs possessing satisfactory pharmacological and biochemical properties have been extensively used in clinic, such as Sulfathiazole, Fluconazole and Ethoxzolamide.In this thesis, based on the current situation in the researches of naphthalimide compounds and azoles, a series of novel azolyl naphthalimides were designed and synthesized. All the newly synthesized compounds were characterized by modern spectra and were evaluated for their antibacterial and antifungal activities. The preliminary structure-activity relationships, preparative methods, conditions were discussed. Further antimicrobial mechanisms of the synthesized active compound were investigated by fluorescence and UV-vis absorption spectroscopy. The main work was summarized as follows:(1) Preparation of novel Schiff base-linked imidazolyl naphthalimides: Commercially available 4-bromo-1,8-naphthalic anhydride was reacted with hydrazine hydrate to afford intermediate II–1 in high yield, and then II–1 was further N-alkylated with three alicyclic amines in ethylene glycol monomethyl ether at 125 oC under a nitrogen atmosphere to produce naphthalimides II–2a-c respectively. The condensation of alicyclic amine-appended naphthalimides II–2a-c and 2-butyl-5-chloro-1H-imidazole-4-carbaldehyde in the presence of nitrogen using phosphorus pentoxide as dehydrating agent formed target imidazoles II–3a-c. The N-alkylation of 2-butyl-5-chloro-1H-imidazole-4-carbaldehyde with alkyl or substituted benzyl halides in the presence of potassium carbonate gave the target imidazolyl aldehydes II–5a-e and II–6a-k in good yields and then further condensation with naphthalimide II–2c afforded target compounds II–7a-e and II–8a-k with yields of 28% to 52%. For comparison, unsubstituted imidazolyl naphthalimide II–4 was also synthesized by directly coupling compound II–1 with 2-butyl-5-chloro-1H-imidazole-4-carbaldehyde under same conditions.(2) Preparation of novel azole-appended naphthalimides: Commercially available 4-bromo-1,8-naphthalic anhydride was reacted with pyrrolidine, piperidine, morpholine and diethanolamine to afford intermediates III–1a–d with high yields of 90-95%, and then further N-alkylated with 2-aminothiazole, 4-amino-1,2,4-triazole, 2-aminobenzaothiazole in DMF at 153 oC under nitrogen atmosphere in the presence of zinc acetate to produce correspounding azolyl naphthalimides III–2a–d, III–3a–c and III–4a–c with considerable yields of 42-56%.(3) All the new compounds were characterized by 1H NMR, 13 C NMR, IR, MS and HRMS spectra.(4) In vitro antibacterial and antifungal activity study demonstrated that compound II–7e, with prominent MIC value of 0.01 μmol/m L against E. coli(JM109), 10-fold more potent than clinical drug Chloromycin, had immense potentiality to be developed as anti-E. coli(JM109) agent. Compound II–8i could effectively inhibit the growth of some tested strains among all the tested compounds, especially for MRSA(MIC = 0.003 μmol/m L), which was superior to the reference drugs Chloromycin(MIC = 0.05 μmol/m L) and Norfloxacin(MIC = 0.02 μmol/m L). Imidazolyl naphthalimides II–7a, II–7d and II–7e displayed specific anti-C. utilis potency at the concentrations of 0.003-0.88 μmol/m L, particularly compound II–7d(MIC = 0.003 μmol/m L), which was 10-fold more active than the reference Fluconazole. Noticeably, 4-nitrobenzyl compound II–8i gave moderate to good antifungal activity towards most of the tested fungi, particularly C. albicans(MIC = 0.003 μmol/m L) and C. utilisi(MIC = 0.01 μmol/m L), and also encouraged us with great interest to carry out relational biological assays of highly bioactive compound II–8i to further explore their possible preliminary mechanism of action and pharmaceutical properties.(5) Diethanolamine-appended thiazole III–2d could effectively inhibit the growth of Gram-positive bacteria and Gram-negative bacteria, and gave the best anti-P. aeruginosa activity(MIC = 0.003 μmol/m L), about 33-fold and 16-fold more potent than clinical drug Chloromycin(MIC = 0.10 μmol/m L) and Norfloxacin(MIC = 0.05 μmol/m L). Triazole III–3b showed comparable or even stronger inhibitory potency against E. coli(JM109)(MIC = 0.005 μmol/m L) than reference drugs, and for morpholine substituted compound III–3c, it gave obvious anti-P. aeruginosa potency with MIC value of 0.005 μmol/m L, which was 20-fold and 10-fold more potent than Chloromycin and Norfloxacin. Triazole naphthalimide III–3b(MIC = 0.09 μmol/m L) and thiazolyl naphthalimide III–2d(MIC = 0.17 μmol/m L) displayed considerable anti-A. flavus potency, about 9-fold and 5-fold more potent than Fluconazole(MIC = 0.84 μmol/m L).(6) The preliminary structure-activity relationships showed that long hydrophobic alkyl chain(over ten carbons) should be beneficial to regulate the flexibility of the imidazole-naphthalimide system and their antimicrobial potency. The introduction of benzyl ring with electro-donating or electro-withdrawing moieties did not exert significantly effect on antimicrobial activity.(7) Bacterial membrane permeabilization assays of compound II–8i manifested it was able to effectively permeate the membranes of Gram-positive(MRSA) and Gram-negative(B. proteus) bacteria. Bacterial resistance assays of compound II–8i against MRSA indicated that MRSA had more difficulty developing resistance against compound II–8i than the control drug Norfloxacin. Time-kill kinetic assays against MRSA manifested compound II–8i could rapidly kill the tested strains. Moreover, preliminary research revealed that compound II–8i could form a steady complex with calf thymus DNA by intercalation mode. These results suggested that compound II–8i could serve as a promising anti-MRSA candidate.(8) Azole-appended naphthalimide III–2d could effectively intercalate into calf thymus DNA and form III–2d–DNA complex, which might could further inhibit DNA replication and exert antimicrobial potency.(9) Absorption spectra to various metal ions, Ni2+-titration induced the fluorescence spectra and electrostatic potential of compound III–2d further confirmed its enormous potentiality as metal ions probe with considerable antimicrobial potency, and the thiazolyl and carbonyl groups might be the recognition sites.Fifty four compounds were successfully synthesized in this thesis. Twenty nine compounds were new, including twenty Schiff base linked imidazolyl naphthalimides, three thiazolyl naphthalimides, three triazolyl naphthalimides, three benzothiazolyl naphthalimides.