Design And Synthesis Of Tetrazole Compounds As Antimicrobial Agents And Their Interaction With Calf Thymus DNA And Human Serum Albumins

Tetrazole is an important five-membered aromatic heterocycle poly-nitrogen electron-rich planar structural feature. This unique structure endows tetrazole derivativesto readily bind with various enzymes or receptors in organisms via weak interactions such as coordination bonds, hydrogen bonds, cation-π,π-π stacking, hydrophobic effect, van der Waals force and so on, thus displaying a broad spectrum of biological activities in pharmaceutical fields. More and more tetrazole compounds with diversity of drug administration, good pharmacokinetics property and less adverse effects are frequently employed clinical drugs or as candidates for the therapy of various types of diseases. The tetrazole ring is also an important isostere of triazole, carboxy amide moiety etc. in designing various new types of drug molecules. Moreover, it can be used as an attractive linker to combine or stable different pharmacophore fragments to generate special functional molecules. In this thesis, based on the recent advances in the research and development of tetrazole derivatives, a series of tetrazole tertiary amine derivatives and tetrazole Fluconazole analogues were designed and synthesized, and also their antimicrobial activities were evaluated. The main contents are as follows:(1) The target tetrazole tertiary amine derivatives were synthesized via N-alkylation and cyclization reactions from commercially available substituted anilines and chloroacetonitrile. All the newly synthesized compounds were characterized by lH NMR,13C NMR, IR, MS and HRMS spectra. The in vitro bioactive assay manifested that most compounds exhibited good or even excellent antifungal activity in comparison with antibacterial activity. Halobenzyl tertiary amine tetrazole derivatives exerted relatively better activities in inhibiting the growth of tested strains in comparison with alkyl compounds. Particularly, compound89g displayed the best antifungal activity and broad spectrum, and it was more sensitive to C. albicans with MIC value of2μg/mL, which was almost equipotent to the reference drug Fluconazole. Furthermore, compound89g gave the most potent antimicrobial effciencies with MIC value of16mg/mL against A. flavus, which was16-fold more active than Fluconazole. The combination of high bioactive compound89g with antibacterial Chloromycin, Norfloxacin or antifungal Fluconazole respectively showed better antimicrobial efficiency with less dosage and broad antimicrobial spectrum than the separated use of them alone, and these combined systems were more sensitive to methicillin-resistant MRSA and Fluconazole-insensitive A. flavus. The Lipophilicity/hydrophilicity (log p) of the compounds89and91was calculated experimentally by traditional saturation shake flask approach, and the results suggested that suitable lipophilicity/hydrophilicity be necessary for good antimicrobial activities. The ionization constants (pKa) of them were also determined by UV-vis absorption spectroscopic method to evaluate the antimicrobial activity. In addition, the interaction of compound89g with calf thymus DNA demonstrated that this compound could effectively intercalate into DNA to form a compound89g-DNA complex that might block DNA replication and thereby exert good antimicrobial activity.(2) A series of novel tetrazole Fluconazole analogues were synthesized respectively from commercially available substituted benzenes and amino tetrazole. The newly synthesized compounds were characterized by1H NMR,13C NMR, IR, MS and HRMS spectra. Bioactive assay indicated that tetrazole Fluconazole analogues showed moderate or even excellent antifungal activity against all the tested strains. Especially, compounds96b-c and100displayed excellent anti-A.flavus activity (MIC=1-8μg/mL) in comparison with Fluconazole (MIC=256μg/mL). The antibacterial evaluation in vitro showed that compounds95a,95c,95e,95g and96only exhibited anti-S. aureus and anti-B. proteus activities. The introduction of piperazine and carboxy amide moieties, which yielded compound100, resulted in moderate antibacterial activity against the tested strains. The quenching mechanism, binding constants, binding sites and thermodynamic parameters of the interaction between the most bioactive compound96b with HSA were obtained by Fluorescence and UV-vis absorption spectroscopic method. The results indicated that electrostatic interaction played major roles in the strong association of tetrazole96b and HAS.