Synthesis, Crystal Structure and Biological Activity of a New 4,5-Diaryl-1H-imidazole Derivative①

CAIZhi-Qing MA Wei-Ying LIU Ju HU Zhi-Qun HOU Ling WANG Jin-Y

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Synthesis, Crystal Structure and Biological Activity of a New 4,5-Diaryl-1-imidazole Derivative①

CAIZhi-Qianga②MA Wei-YingaLIU JubHU Zhi-QuanaHOU LingaWANG Jian-Yaa

a(111003)b(110036)

A new 4,5-diaryl-1-imidazole was synthesized and characterized by1H NMR, ESI-MS, elemental analysis and FT-IR. The crystal structure of the title compound (C19H16Cl2N2O2,M= 375.24) has been determined by single-crystal X-ray diffraction. Crystal parameters: mono- clinic system, space group21/,= 14.349(3),= 8.7918(18),= 15.352(3) ?,= 108.56(3)°,= 1836.1(6) ?3,= 4,(000) = 776,D= 1.357 g/cm3,= 0.368 mm-1, the final= 0.0502 and= 0.1066 for 2324 observed reflections with> 2(). A total of 16117 reflections were collected, of which 3615 were independent (int= 0.0595). The preliminary bioassay suggested that the title compound exhibits distinct effective inhibition on the proliferation of cancer cell lines.

4,5-diaryl-1-imidazole, anti-cancer activity, synthesis, crystal structure

1 INTRODUCTION

Substituted imidazoles are important and useful skeletons in organic synthesis and medicine che- mistry[1, 2]. 4,5-diaryl-1-imidazole and its derivati- ves play important roles in Na+channel blockers[3], p38MAP kinase inhibitors[4-7]and B-Raf kinase inhibitors[8], 4,5-diaryl-1-imidazoles have also been shown to be potent cytotoxic agents mimicking the activity of combretastatin A-4 which inhibits the polymerization of tubulin[9], and 2-substituted 4,5- diaryl-1-imidazoles have been identified as COX-2 inhibitors[10]and as human CB1 receptor inrever- sible agonists[11].

To find more novel anti-cancer candidates with unexpected biological activity, our group has focu- sed on the synthesis and characterization of various 4,5-diaryl-1-imidazole derivatives and their biological activities. In this paper, a new 4,5-diaryl- 1-imidazole by a two-step synthesis method was obtained from the mixture of ethanol:acetone = 1:1 (v:v = 1:1) and the molecular structure was determined by X-ray diffraction. The biological tests suggested the compound displayed distinct effective inhibition on the proliferation of cancer cell lines. The synthetic procedure for the title compound is shown in Scheme 1.

2 EXPERIMENTAL

2. 1 Materials and methods

All melting points were taken on a Beijing Taike X24 microscopy melting point apparatus and uncorrected. The infrared spectra were recorded on a Perkin-Elmer Spectrum one FT-IR spectrometer using KBr pellets.1H NMR spectrum was recorded on a Bruker AV-600MHz instrument with TMS as internal standard with chemical shifts () expressed in ppm. MS spectra were recorded by Finnigan Trace Ms mass spectrometer; and Elementar Vario EL III elemental analyzer was used for elemental analysis. Crystallographic data of the compounds were collected on a Rigaku saturn diffractometer. All starting materials and reagents were obtained from commercial supplies without further purifica- tion. 1,2-bis(4-chlorophenyl)ethane-1,2-dione (1) was synthesized according to the literature[12].

Scheme 1. Synthesis route of the title compound 3

2. 2 Synthesis of 4,5-bis(4-chlorophenyl)-1H-imidazole

A mixture of 1,2-bis(4-chlorophenyl)ethane-1,2- dione 1 (10.0 g, 35.8mmol), hexamethylenete- tramine (10.0g, 71.6 mmol) and ammonium acetate (13.8 g, 179.0 mmol) in 60 mL of aceticacid was mixed in a round-bottomed flask. The reaction mixture was heated in an oil bath at the given tem- perature for 12 h. After cooling to room temperature, the reaction mixture was concentrated to 20 mL and extracted with ethyl acetate (100 mL × 3). Subse- quently, the organic phase was washed with brine, dried over Na2SO4and filtered, and the solvent was removed under reduced pressure. The residue was purified by recrystallization from hexane/ethyl acetate = 1/2 to afford 4,5-bis(4-chlorophenyl)-1- imidazole 2 as white solid (6.7 g, yield 64.7%). m.p: 253～256 ℃. IR (KBr, cm-1): 3436, 3088, 3051, 3031, 1734, 1652, 1510, 1493, 1474.1H-NMR (600MHz, DMSO-d6): 12.59(s, 1H, active-H); 7.81(s, 1H, imidazole-H); 7.38(m, 8H, Ar-H).

2. 3 Synthesis of ethyl 2-(4,5-bis(4-chloro-phenyl)-1H-imidazol-1-yl)acetate

A mixture of 4,5-bis(4-chlorophenyl)-1-imida- zole 2 (1.0 g, 3.5 mmol), ethyl 2-chloroacetate (512 mg, 4.2 mmol), KI (580 mg, 3.5 mmol) and K2CO3(966 mg, 7.0 mmol) in 15 mL of DMF was mixed in a round-bottomed flask. The reaction mixture was heated in an oil bath at the given temperature for 6 h. After cooling to room temperature, the reaction was quenched by the addition of saturated aqueous NaHCO3, and the aqueous phase was extracted with ethyl acetate (100 mL × 3). Subsequently, the organic phase was washed with brine, dried over Na2SO4and filtered, and the solvent was removed under reduced pressure. The residue was purified by separation on a silicagel column with ethylacetate- petroleumether (1/1) as the eluent to afford pure ethyl 2-(4,5-bis(4-chlorophenyl)-1-imidazol-1-yl)acetate 3 as white solid (1.0 g, yield 76.0%). m.p: 138～140 ℃. IR (KBr. cm-1): 2964, 2933, 1748, 1503, 1474, 1375, 1213.1H-NMR(600 MHz, DMSO-d6): 7.86(s, 1H, imidazole-H); 7.54(d, 2H,= 8.4Hz, Ar-H); 7.36(d, 2H,= 8.4 Hz, Ar-H); 7.29(m, 4H, Ar-H); 4.78(s, 2H, -COCH2); 4.01(q,= 7.2Hz, 2H, -CH2); 1.05(t,= 7.2Hz, 3H, -CH3). ESI-MS: m/z = 375.2 [M]+. Elemental analysis calcd. (%) for C19H16Cl2N2O2: C, 60.81; H, 4.30; N, 7.47. Found (%): C, 60.95; H, 4.06; N, 7.53.

2. 4 Crystal structure determination

The white powder of the title compound was dissolved in ethylanol/acetone mixed solvents = 1:1 (V/V). After slowly evaporating the solvents for several days, some single crystals suitable for X-ray analysis were obtained. A colourless crystal with dimensions of 0.20mm × 0.18mm × 0.12mm was selected for data collection which was performed on a Rigaku saturn diffractometer equipped with a graphite-monochromatic Moradiation (= 0.71073 ?) by using anscan mode at 293(2) K. A total of 16117 reflections were collected in the range of 2.35<<26.07° (index ranges: –15≤≤17, –10≤≤10, –18≤≤18) and 3615 were independent (int= 0.0595), of which 2324 observed reflections with> 2() were used in the structure determina- tion and refinements. The structure was solved by direct methods with SHELXS-97 program[13]and expanded by Fourier technique. The non-hydrogen atoms were refined anisotropically. The hydrogen atoms bound to carbon were determined with theore- tical calculations and those attached to nitrogen and oxygen were determined with successive difference Fourier syntheses. The structure was refined by full-matrix least-squares techniques on2with SHELXL-97[14]. The final refinement gave= 0.0502 and= 0.1066 (= 1/[2(F2) + (0.0574)2], where= (F2+ 2F2)/3),= 1.009, (Δ/)max= 0.004, (Δ)max= 0.214 and (Δ)min= –0.192 e/?3.

2. 5 Biological activity determination

The cell line UKF-NB-3 was derived from bone marrow metastases of a patient with stage IV neuro- blastoma who had relapsed. Cells were cultured in RPMI 1640 medium supplemented with 15% fetal calf serum, 2 mM glutamine, 100 IU/mL penicillin, and 100 μg/mL streptomycin in a humidified atmosphere with 5% CO2at 37 ℃. Nutlin-3 and compound 3 were dissolved in absolute ethanol and stored as a 10 mM stock solution in 100 μL aliquots at –20 ℃, respectively. Cell viability was inves- tigated using the MTT assay.

Anticancer activity was determined by Methyl Thiazolyl Tetrazolium (MTT) bioassay in three cell lines UKF-NB-3, A549 and H1299, with the data shown in Table 1. Nutlin-3 was employed as control in this assay. Results indicated that compound 3 inhibited UKF-NB-3 cell lines with almost similar IC50values of13.25 ± 0.16 μg/mL (5.20 ± 0.24 μg/mL for nutlin-3). Additionally, in A549 cells, compound 3 possessed IC50values of 87.09 ± 0.06 μg/mL compared with 11.13 ± 0.21 μg/mL from nutlin-3. However, neither compound 3 nor nutlin-3 showed any significant activity towards H1299 cell line with IC50values more than 100 μg/mL. These results suggested that compound 3 is more sensitive than nutlin-3 to control the anticancer activity, but the activity is relatively weaker. Further structure optimization may result in more active anticancer compounds.

Table 1. Anti-cancer Activity of the Title Compound

3 RESULTS AND DISCUSSION

The named compound 3 was prepared according to Scheme 1.The molecular structures of the target compounds were analyzed by ESI-MS, elemental analysis,1H NMR spectroscopy, infrared spectro- scopy (IR) and single-crystal X-ray diffraction analysis. Based on the IR spectrum of this com- pound, two sharp intense peaks were observed at 2964 and 2933 cm-1due to the presence of sym- metrical and asymmetrical C–H stretching vibrations on the OCH2CH3. The peak at 1748 cm?1results from the C=O stretching vibration of ester, and that at 1213 cm?1is duo to the C–O stretching vibration of ester. The absorption at 1375 cm?1is the(C–H) bending vibration of ethyl in the compound. The IR spectrum confirmed the proposed structure of this compound.

The molecular structure and unit cell crystal packing of the compound are presented in Figs. 1 and 2, respectively. The selected bond lengths and bond angles of this compound are listed in Table 2. As shown in Table 2, the bond lengths and bond angles in the phenyl and imidazol rings are generally normal. The O(1)–C(17) bond in 1.195(3) ? belongs to the typical C=O double bond. All N–C bond lengths are between 1.304(3) and 1.452(3) ?, which is shorter than the isolated N–C single bond (1.4710 ?) and longer than the double bond (1.2730 ?). The bond angles of phenyl ring vary from 117.1(2) to 122.0(2)° with the average of 120°. The torsion angles C(1)–C(2)–C(3)–Cl(1), C(10)–C(11)–C(12)– Cl(2) and N(1)–C(7)–C(8)–N(2) are –179.13(19)°, 179.21(19)° and 0.5(2)°, respectively. From these results, it is known that all the bond lengths and bond angles are in normal ranges[15]. The single- crystal X-ray study revealed a centrosymmetric dimer formation in the crystal lattice, as illustrated in Fig. 2. According to theH(4)···O(1)length (2.494 ?), the imidazole and amide groups of the two mole- cules interacted with a centrosymmetric manner by non-classical C(4)–H(4)···O(1) hydrogen-bonding interactions.

Table 2. Selected Bond Lengths (?) and Bond Angles (°)

Fig. 1. Molecular structure of the title compound, showing displacement ellipsoids drawn at the 30% probability level

Fig. 2. Packing of the title compound

4 CONCLUSION

In summary, a novel compound 2-(4,5-bis(4- chlorophenyl)-1-imidazol-1-yl)acetate was obtai- ned in a two-step synthesis method, and its structure was characterized by IR, ESI-MS, elemental analy- sis and1H-NMR. Single-crystal X-ray diffraction analysis reveals that the molecular structure of 3 is essentially as expected and confirms the formu- lation of the compound. The structure of compound 3 waits for further medications, in expectation of improved activities.

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19 February 2014;

12 May 2014 (CCDC 987018)

the National Undergraduate Training Programs for Innovation and Entrepreneurship (No. 101422013067)

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