Synthesis and biological evaluation of benzimidazole-linked 1,2,3-triazole congeners as agents
© Harkala et al., licensee Springer. 2014
Received: 14 October 2014
Accepted: 30 October 2014
Published: 2 December 2014
Benzimidazoles and triazoles are useful structures for research and development of new pharmaceutical molecules and have received much attention in the last decade because of their highly potent medicinal activities.
A simple and efficient synthesis of triazole was carried out by treatment of 2-(4-azidophenyl)-1H-benzo[d]imidazole (6) with different types of terminal alkynes in t-BuOH/H2O, sodium ascorbate, and Zn(OTf)2, screened for cytotoxicity assay and achieved good results. A series of new benzimidazole-linked 1,2,3-triazole (8a-i) congeners were synthesized through cyclization of terminal alkynes and azide. These synthesized congeners 8a-i were evaluated for their cytotoxicity against five human cancer cell lines. These benzimidazole-linked 1,2,3-triazole derivatives have shown promising activity with IC50 values ranging from 0.1 to 43 μM. Among them, the compounds (8a, 8b, 8c, and 8e) showed comparable cytotoxicity with adriamycin control drug.
In conclusion, we have developed a simple, convenient, and an efficient convergent approach for the synthesis of benzimidazole-linked 1,2,3-triazole congeners as agents.
In addition, triazoles also display wide spectrum of biological activities and are widely employed as pharmaceuticals and agrochemicals. Triazoles are reported to possess antibacterial, antifungal, and antihelminthic activities -. They have been regarded as an interesting unit in terms of biological activity ,, and some of them have also shown significant anticancer activity in many of the human cell lines .
In view of the biological importance of benzimidazole and 1,2,3-triazoles, to know the combined effect of both benzimidazole and 1,2,3-triazole moieties, it was considered worthwhile to synthesize certain new chemical entities having benzimidazole and 1,2,3-triazole pharmacophores in a single molecular framework, and here we have used Zn(OTf)2 catalyst instead of CuSO4. All of these congeners have been evaluated for their anticancer activity against a panel of five human cancer cell lines (Figure 1).
All chemicals and reagents were obtained from Aldrich (Sigma-Aldrich, St. Louis, MO, USA) and Lancaster (Alfa Aesar, Johnson Matthey Company, Ward Hill, MA, USA) and were used without further purification. Reactions were monitored by TLC and performed on silica gel glass plates containing 60 F-254, and visualization on TLC was achieved by UV light or iodine indicator. 1H and 13C NMR spectra were recorded on Gemini Varian-VXR-unity (Palo Alto, California) (300 and 100 MHz) instrument. Chemical shifts (d) are reported in ppm downfield from internal TMS standard. ESI spectra were recorded on Micromass, Quattro LC (McKinley Scientific, Sparta, NJ, USA) using ESI + software with capillary voltage 3.98 kV and ESI mode positive ion trap detector. Melting points were determined with an electrothermal melting point apparatus and are uncorrected.
A mixture of the O-phenylenediamine (3) (500 mg, 3.64 mmol) and the 4-aminobenzoic acid (4) (394 mg, 3.64 mmol) was dissolved in sufficient quantity of polyphosphoric acid (PPA). The mixture was heated slowly to 250°C for 4 h, permitted to cool to room temperature, quenched with excess of 10% Na2CO3 solution, and extracted with ethyl acetate. Then, the mixture was dried over anhydrous Na2SO4, and the crude product was purified by column chromatography with ethyl acetate/hexane (6:4) to afford pure compound 5, 946 mg in 97% yield. Mp: 209°C to 211°C, 1H NMR (300 MHz, DMSO-d6): δ 6.68 (d, 2H, J =7.3 Hz), 7.14 (br s, 2H), 7.50 (br s, 2H), 7.85 (d, 2H, J =7.1 Hz). IR (neat, cm−1): γmax 404.3; 501.4; 537.9; 607.7; 742.3; 833.4; 960.1; 1,009.1; 1,108.6; 1,178.6; 1,225.7; 1,272.2; 1,397.2; 1,444.1; 1,499.2; 1,612.4; 1,701.4; 2,750.1; 2,853.1; 2,921.8; 3,355.4; 3,435.0; MS (ESI): 210 [M + H]+.
The amine derivative (5) (500 mg, 2.39 mmol) was dissolved in 10% aq HCl at room temperature. This reaction mixture upon cooling to 0°C and addition of a solution of NaNO2 (165 mg, 2.39 mmol) was stirred for 10 min at 0°C to 5°C. Sodium azide (186 mg, 2.87 mmol) was added, and the mixture was stirred at room temperature for 2 h. The reaction was worked up by dilution with ethyl acetate. The organic layer was washed with brine and dried over Na2SO4. After evaporation of the solvent, the crude product was purified by column chromatography with ethyl acetate/hexane (3:7) to afford pure compound 6, 536 mg in 95% yield; Mp: 317°C to 319°C, 1H NMR (300 MHz, DMSO-d6): δ 7.16 to 7.26 (m, 2H), 7.32 (d, 2H, J =9.0 Hz), 7.50 to 7.69 (dd, 2H, J =40.0, 38.5 Hz), 8.22 (d, 2H, J =8.3 Hz), 12.97 (s, 1H). IR (neat, cm−1): γmax 500.6; 541.4; 694.3; 743.3; 838.1; 963.4; 1,011.1; 1,115.8; 1,175.5; 1,283.5; 1,395.2; 1,438.8; 1,485.1; 1,604.6; 1,726.8; 2,120.1; 2,414.9; 2,856.9; 2,918.2; 3,055.5; 3,422.9; MS (ESI): 236 [M + H]+.
A mixture of the corresponding azide 6 (200 mg, 0.85 mmol) and the corresponding alkyne 7a (163 mg, 0.85 mmol) was dissolved in t-BuOH/H2O 1:1 (20 mL). Sodium ascorbate (33 mg, 20 mol%) and Zn(OTf)2 (300 mg, 5 mol%) were added. After stirring for 4 h, water/ice (40 mL) was added. The product was either worked up by filtration, followed by rinsing with aqueous 5% NH3 (×3) and cold ether (×2), or by extraction with dichloromethane (4 × 100 mL). The combined organic layers were washed with aqueous 5% NH3 (3 × 100 mL) and brine (100 mL) and dried over anhydrous MgSO4. The solvent was removed in vacuo, and the crude product was purified by column chromatography with ethyl acetate/hexane (3:7) to afford pure compound 8a, 347 mg in 95% yield. Mp: 270°C to 272°C, 1H NMR (400 MHz, CDCl3): δ 3.71 (s, 3H), 3.89 (s, 6H), 7.24 to 7.28 (m, 4H), 7.63 to 7.66 (m, 2H), 8.17 (d, 2H, J =8.4 Hz), 8.41 (d, 2H, J =8.4 Hz), 9.44 (s, 1H). 13C NMR (100 MHz, CDCl3): δ 57.2, 61.4, 110.2, 114.8, 117.1, 122.1, 123.3, 125.3, 128.4, 129.8, 140.1, 141.8, 143.3, 148.7, 152.4, 154.1; MS (ESI): 428 [M + H]+.
The other derivatives are also prepared according to the same procedure and described in Additional file 1.
In vitro cytotoxicity assay
Cytotoxic activity (IC 50 μM) of compounds 8a-i
Procedure for MTT assay
Toxicity of test compound in cells was determined by MTT assay based on mitochondrial reduction of yellow MTT tetrazolium dye to a highly colored blue formazan product. Cells (1 × 104) (counted by Trypan blue exclusion dye method) in 96-well plates were incubated with compounds with series of concentrations tested for 48 h at 37°C in RPMI/DMEM/MEM with 10% FBS medium. Then, the above media was replaced with 90 μl of fresh serum free media and 10 μl of MTT reagent (5 mg/ml), and plates were incubated at 37°C for 4 h, thereafter the above media was replaced with 200 μl of DMSO and incubated at 37°C for 10 min. The absorbance at 570 nm was measured on a spectrophotometer (SpectraMax, Molecular devices, Sunnyvale, CA, USA). IC50 values were determined from plot: percent inhibition (from control) versus concentration.
We thank the management and principal of the Mahatma Gandhi Institute of Technology and the vice-chancellor and the registrar of JNT University Hyderabad for their encouragement.
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