Abstract
Background: Azocalix[4] arene derivative based on 2,6-diamino pyridine has been synthesized from diazo-coupling reaction between tetradiazonium salt of calix[4]arene and 2,6-diaminopyridine, and characterized by various spectroscopic methods such as IR, 1HNMR, 13CNMR and Mass spectroscopy. Antibacterial behavior of the product was studied based on reference Gram-positive and Gramnegative bacteria, Disk diffusion assay method and macrodilution experiment. Antibacterial activities were evaluated both in solid and liquid phases.
Methods: At 0°C an aqueous HCl solution (3%) was added to a solution of 5, 11, 17, 23-tetraamino- 25, 26, 27, 28-tetrapropoxycalix[4]arene (76.4 mg, 0.12 mmol in 4 ml THF. Then, a solution of NaNO2 (43 mg, 0.61 mmol in 3 ml H2O) was added slowly at 0°C. The reaction mixture was stirred at room temperature for 1h. Then, a solution of 2, 6-diamino pyridine (133.14 mg, 1.22 mmol) in 2 ml pyridine and 4 ml THF was added dropwise. After 12 h at room temperature, the reaction mixture was poured slowly into H2O (100ml). The precipitate was filtered, washed with water and dried. Results: In this work 5, 11, 17, 23-tetrakis [3-(2,6-diaminopyridine)azo]-25, 26, 27, 28-tetrapropoxy calix [4]arene 5 has been prepared by diazo coupling of calixarene at the upper rim. It has been preferred to have the calix[4]arene scaffold preorganized in cone conformation. The structure of Azo-calixarene derivative 5 was identified by 1H NMR & 13C NMR, FT-IR and UV-vis spectroscopy. The UV absorption spectra of 5 was measured in the wavelength range of 250-600 nm in DMSO against DMSO blank, which gave absorption maxima peak at 427 nm arising from π to π* transition of the –N=N-bond. The cone conformation of 5 was confirmed by its NMR spectra that exhibits two pairs of doublets at 3.35 and 4.45 ppm for the bridge methylene protons of ArCH2Ar in 1H NMR spectra and singlet at 31 ppm for the ArCH2Ar bridge carbons in the 13C NMR spectra. Antibacterial test of 5 was carried out in comparison with phenazopyridine 6 which is a well-known anitibacterial azo compound against two gram negative reference strains Pseudomonas aeruginosa and Escherichia coli two gram-positive reference strains, Staphylococcus aureus and Bacillus cereus Bacteria. Antibacterial activities were evaluated in solid phase. Disk diffusion assay method was performed on Mueller-Hinton agar with sterile 6 mm diameter disk impregnated with different quantities of compounds 5 and 6. The petridishes were incubated at 37°C, and the diameters of the zone inhibition were measured at 24h of incubation, according to Finegold and Baron Method. Conclusion: In summary, the present paper reports the synthesis of new azocalixarene derivative 5 by diazo-coupling. Antibacterial activities were evaluated on Mueller-Hinton agar by using disk diffusion assay. The results showed strong activities towards the Gram- Positive bacteria Bacillus cereus. The resistance shown by P.aeruginosa to the compound 5 showed mild activities against Escherichia coli.Keywords: Azo-calixarene, antibacterial activity, 2, 6-diamino-pyridine, Mueller-Hinton, gram-positive bacteria, gram-negative bacteria.
Graphical Abstract
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