3.1. Chemistry
Melting points were measured with an X-4 digital micro melting point apparatus (Shanghai Jingke Co. Ltd, Shanghai, China) and are uncirrected. 1H-NMR spectra were measured with a Bruker ARX (400 MHz) spectrometer and 13C-NMR with a Bruker AV (150 MHz) instrument (Bruker, Karlsruhe, Germany). Chemical shifts are recorded in δ units using tetramethylsilane as the standard (NMR peak description: s, singlet; d, doublet; t, triplet; q, quartet; m, multiplet; br, broad peak). Low resolution mass spectrometry (MS) were recorded with an Agilent 1100 ion trap liquid chromatography-mass spectrometer (Agilent, Santa Clara, CA, USA). Organic solutions were dried over anhydrous sodium sulfate during workup. Column chromatography was carried out on a Combiflash Rf+ preparative liquid chromatograph (Teledyne ISCO, NE, USA). Silica gel 60 (200–300 mesh) and TLC were purchased from Qingdao Haiyang Chemical Co. Ltd. (Qingdao, China) All commercial reagents and solvents were used without further purification unless otherwise noted. The purity of all compounds screened in biological assays was >95% pure as judged by HPLC. HPLC analysis were obtained on an L-2400 system (Hitachi, Kyoto, Japan) using a AichromBond-AQ C18 column (150 mm × 4.6 mm, 5 μm) with a 1.5 mL/min flow rate using acetonitrile and water solution (v/v = 70:30) as the eluent over 30 min.
The original figures of
1H-NMR,
13C-NMR and MS of all the target compounds as the
Supplementary Materials are available online.
3.1.1. General Procedure for the Synthesis of 6a–6o
(1H-Benzo[d]imidazol-2-yl) methanol (1): To a solution of 1,2-diaminobenzene (10.0 g, 92.6 mmol), in 4 N HCl (80 mL), glycolic acid (20.0 g, 263 mmol) was added and stirred for 4 h at 100 °C and monitored by TLC. After complete conversion of starting material, cooled the solution to room temperature, the pH of the solution was adjusted to 8 with a 2 mol/L aqueous sodium hydroxide solution, the precipitate was filtered and dried to afford 1 as white solid in 88.0% yield. LC-MS m/z: 149.2 [M + H]+.
1H-Benzo[d]imidazole-2-carbaldehyde (2): To a solution of 1 (5.0 g, 34 mmol) in DCM was added MnO2 (1.3 g, 6.8 mmol). The resulting solution was stirred at 40 °C for 2 h and monitored by TLC. After complete conversion of starting material, reaction mixture was cooled to room temperature, filtered and concentrated in vacuo to obtain 2 as white solid in 85.0% yield. LC-MS m/z: 147.1 [M + H]+.
Methyl (E)-3-(1H-benzo[d]imidazol-2-yl) acrylate (3): To a solution of methyl diethylphosphonoacetate (3.17g, 15.0 mmol) in dry THF (40 mL) was added sodium carbonate (3.79 g, 27.4 mmol), the mixture was stirred for 30 min at room temperature prior to the addition of compound 2 (2.0 g, 13.7 mmol). The mixture was stirred and refluxed for 24 h under an argon atmosphere and monitored by TLC. After complete conversion of starting material, the reaction mixture was filtered, the filtrate was concentrated and re-dissolved by ethyl acetate, and then washed with saturated NaCl solution and dried over anhydrous sodium sulfate, concentrated in vacuo and purified by flash silica gel column (PE/EA = 4/1, v/v) to obtain 3 as white solid in 87.5% yield. LC-MS m/z: 203.1 [M + H]+.
(E)-3-(2-(3-Methoxy-3-oxoprop-1-en-1-yl)-1H-benzo[d]imidazol-1-yl) propanoic acid (4): To a solution of 3 (0.4 g, 2.0 mmol) in DMF (10 mL) and acetone (40 mL) was added 3-bromopropionic acid (1.2 g, 8.0 mmol) and a solution of K2CO3 (5.5 g, 40 mmol) in water (0.8 mL), the mixture was stirred at 70 °C for 4 h. After complete conversion of starting material, the reaction mixture was cooled to room temperature, concentrated in vacuo and redissolved in water (50 mL). The resulting solution was adjusted to pH 5 with a 6 N HCl at 0 °C, and then extracted with ethyl acetate, the organic layers combined and washed with saturated NaCl, dried over anhydrous sodium sulfate, filtered, and concentrated in vacuo to obtain 4 as a white solid in 82.5% yield. LC-MS m/z: 273.1 [M − H] −.
(E)-3-(1-(3-oxo-3-(piperidin-1-yl)propyl)-1H-benzo[d]imidazol-2-yl)acrylic acid (6a): To a mixture of compound 4 (0.47 g, 1.73 mmol) and piperidine (0.16 g, 1.9 mmol) in dried DCM (50 mL) was added 4-methylmorpholine (0.97 mL) followed by HOBt (0.47 g 3.46 mmol) at 0 °C, and EDCI (0.66 g, 3.46 mmol) was added in batches. After stirring for 30 min, the mixture was warmed to room temperature and stirred overnight. The reaction mixture was washed by saturated NaCl solution three times and dried over anhydrous sodium sulfate, concentrated and purified by flash silica gel column (PE/EA = 1/3, v/v), the residue was dissolved in THF (6 mL), then lithium hydroxide solution (3.5 mmol/mL, 1.6 mL) was added dropwise. The resulting solution was stirred at room temperature for 6 h then concentrated in vacuo, and the residue re-dissolved by water and acidified with 2N HCl to pH 5 at 0 °C. Filtered and dried to obtain the desired compounds 6a as white solid in 58.5% yield. m.p.: 128–130 °C. 1H-NMR (DMSO-d6) δ: 12.74 (s, 1H), 7.79 (d, J = 15.4 Hz, 1H), 7.67 (m, 1H), 7.66 (m, 1H), 7.33 (m, J = 9.04 Hz, 2H), 6.90 (d, J = 15.4 Hz, 1H), 4.60 (t, J = 6.6 Hz, 2H), 3.34 (t, J = 5.44 Hz, 2H), 3.21 (t, J = 5.4 Hz, 2H), 2.84 (t, J = 6.7 Hz, 2H), 1.47 (m, J = 5.32 Hz, 2H), 1.32 (m, J = 3.9 Hz, 2H), 1.26 (m, J = 7.4 Hz, 2H). LC-MS m/z: 328.2 [M + H]+.
(E)-3-(1-(3-Morpholino-3-oxopropyl)-1H-benzo[d]imidazol-2-yl) acrylic acid (6b): Compound 6b was prepared from 4 and morpholine in a similar manner as compound 6a. White solid. Yield 51.2%. m.p.: 207–209 °C. 1H-NMR (DMSO-d6) δ: 12.81 (s, 1H), 7.79 (d, J = 15.4 Hz, 1H), 7.66 (t, J = 7.36 Hz, 2H), 7.28 (m, J = 7.2, 3.6 Hz, 2H), 6.91 (d, J = 15.4 Hz, 1H), 4.61 (t, J = 6.7 Hz, 2H), 3.44 (t, J = 9.36 Hz, 2H), 3.37 (t, J = 4.16Hz, 4H), 3.26 (t, J = 9.36 Hz, 2H), 2.86 (t, J = 6.7 Hz, 2H). LC-MS m/z: 330.1 [M + H]+.
(E)-3-(1-(3-Oxo-3-(phenylamino)propyl)-1H-benzo[d]imidazol-2-yl)acrylic acid (6c): Compound 6c was prepared from 4 and aniline in a similar manner as compound 6a. White solid. Yield 59.5%. m.p.: 228–230 °C. 1H-NMR (DMSO-d6) δ: 12.89 (s, 1H), 9.95 (s, 1H), 7.81 (d, J = 15.4 Hz, 1H), 7.67 (t, J = 8.9 Hz, 2H), 7.46 (d, J = 8.0 Hz, 2H), 7.30 (t, J = 7.5 Hz, 1H), 7.24 (t, J = 7.8 Hz, 3H), 7.00 (t, J = 7.4 Hz, 1H), 6.91 (d, J = 15.4 Hz, 1H), 4.71 (t, J = 6.3 Hz, 2H), 2.85 (t, J = 6.4 Hz, 2H). LC-MS m/z: 336.1 [M + H]+.
(E)-3-(1-(3-Oxo-3-(p-tolylamino)propyl)-1H-benzo[d]imidazol-2-yl)acrylic acid (6d): Compound 6d was prepared from 4 and p-toluidine in a similar manner as compound 6a. White solid. Yield 54.1%. m.p.: 221–222 °C. 1H-NMR (DMSO-d6) δ: 12.93 (s, 1H), 9.88 (s, 1H), 7.80 (d, J = 15.4 Hz, 1H), 7.67 (t, J = 7.8 Hz, 2H), 7.35 (d, J = 8.4 Hz, 2H), 7.30 (t, J = 7.5 Hz, 1H), 7.24 (t, J = 7.5 Hz, 1H), 7.04 (d, J = 8.3 Hz, 2H), 6.91 (d, J = 15.4 Hz, 1H), 4.70 (t, J = 6.4 Hz, 2H), 2.83 (t, J = 6.4 Hz, 2H), 2.21 (s, 3H). LC-MS m/z: 350.1 [M + H]+.
(E)-3-(1-(3-((4-Methoxyphenyl)amino)-3-oxopropyl)-1H-benzo[d]imidazol-2-yl)acrylic acid (6e): This compound was prepared from 4 and 4-methoxyaniline in a similar manner as compound 6a. White solid. Yield 53.6%. m.p.: 215–217 °C. 1H-NMR (DMSO-d6) δ: 12.80 (s, 1H), 9.80 (s, 1H), 7.81 (d, J = 15.4 Hz, 1H), 7.67 (t, J = 7.3 Hz, 2H), 7.36 (d, J = 8.9 Hz, 2H), 7.32 (s, 1H), 7.25 (t, J = 7.6 Hz, 1H), 6.90 (d, J = 15.4 Hz, 1H), 6.82 (d, J = 8.9 Hz, 2H), 4.70 (t, J = 6.2 Hz, 2H), 3.69 (s, 3H), 2.80 (t, J = 6.3 Hz, 2H). LC-MS m/z: 366.1 [M + H]+.
(E)-3-(1-(3-((4-Chlorophenyl)amino)-3-oxopropyl)-1H-benzo[d]imidazol-2-yl)acrylic acid (6f): Compound 6f was prepared from 4 and 4-chloroaniline in a similar manner as compound 6a. White solid. Yield 54.8%. m.p.: 158–160 °C. 1H-NMR (DMSO-d6) δ: 10.23 (s, 1H), 7.67 (d, J = 15.3 Hz, 1H), 7.64 (t, J = 8.2 Hz, 2H), 7.52 (d, J = 8.8 Hz, 2H), 7.30 (d, J = 8.8 Hz, 2H), 7.25 (t, 1H), 7.22(t, J = 7.1 Hz, 1H), 6.95 (d, J = 15.3 Hz, 1H), 4.68 (t, J = 6.2 Hz, 2H), 2.86 (t, J = 6.3 Hz, 2H). LC-MS m/z: 370.1 [M + H]+.
(E)-3-(1-(3-((4-Bromophenyl)amino)-3-oxopropyl)-1H-benzo[d]imidazol-2-yl)acrylic acid (6g): Compound 6g was prepared from 4 and 4-bromoaniline in a similar manner as compound 6a. White solid. Yield 48.0%. m.p.: 192–194 °C. 1H-NMR (DMSO-d6) δ: 10.18 (s, 1H), 7.66 (d, J = 15.6 Hz, 1H),7.64 (t, J = 5.5 Hz, 2H), 7.46 (m, J = 6.7 Hz, 4H), 7.26 (t, J = 7.2 Hz, 1H), 7.22 (t, J = 7.2 Hz, 1H), 6.94 (d, J = 15.6 Hz, 1H), 4.68 (t, J = 5.8 Hz, 2H), 2.86 (t, J = 5.8 Hz, 2H). LC-MS m/z: 414.0 [M + H]+.
(E)-3-(1-(3-((3-Bromophenyl)amino)-3-oxopropyl)-1H-benzo[d]imidazol-2-yl)acrylic acid (6h): Compound 6h was prepared from 4 and 3-bromoaniline in a similar manner as compound 6a. White solid. Yield 58.9%. m.p.: 209–210 °C. 1H-NMR (DMSO-d6) δ: 12.46 (s, 1H), 10.15 (s, 1H), 7.80 (s, 1H), 7.78 (d, J = 15.4 Hz, 1H), 7.67 (t, J = 6.9 Hz, 2H), 7.36 (d, J = 6.56 Hz, 1H), 7.30 (t, J = 7.24 Hz, 1H), 7.24 (t, J = 7.68 Hz, 1H), 7.21 (d, J = 6.28 Hz 1H), 7.20 (s, 1H), 6.92 (d, J = 15.4 Hz, 1H), 4.71 (t, J = 6.3 Hz, 2H), 2.86 (t, J = 6.3 Hz, 2H). LC-MS m/z: 416.1 [M + H]+.
(E)-3-(1-(3-((3,5-dimethoxyphenyl)amino)-3-oxopropyl)-1H-benzo[d]imidazol-2-yl)acrylic acid (6i): Compound 6i was prepared from 4 and 3,5-dimethoxyaniline in a similar manner as compound 6a. White solid. Yield 53.1%. m.p.: 203–204 °C. 1H-NMR (DMSO-d6) δ: 12.81(s, 1H), 9.90 (s, 1H), 7.81 (d, J = 15.4 Hz, 1H), 7.67 (t, J = 7.5 Hz, 2H), 7.31 (t, J = 7.5 Hz, 1H), 7.25 (t, J = 7.8 Hz, 1H), 6.91 (d, J = 15.4 Hz, 1H), 6.87 (s, 1H), 6.71 (s, 2H), 4.70 (t, J = 6.4 Hz, 2H), 3.67 (s, 6H), 2.82 (t, J = 6.4 Hz, 2H). LC-MS m/z: 396.1 [M + H]+.
(E)-3-(1-(3-((4-Bromobenzyl)amino)-3-oxopropyl)-1H-benzo[d]imidazol-2-yl)acrylic acid (6j): Compound 6j was prepared from 4 and (4-bromophenyl)methanamine in a similar manner as compound 6a. White solid. Yield 55.8%. m.p.: 210–212 °C. 1H-NMR (DMSO-d6) δ: 12.78 (s, 1H), 8.42 (t, J = 5.9 Hz, 1H), 7.77 (d, J = 15.4 Hz, 1H), 7.72–7.66 (m, 1H), 7.66–7.58 (m, 1H), 7.35 (d, J = 8.4 Hz, 2H), 7.33–7.22 (m, 2H), 6.89 (d, J = 15.4 Hz, 3H), 4.65 (t, J = 6.3 Hz, 2H), 4.11 (d, J = 5.8 Hz, 2H), 2.68 (t, J = 6.3 Hz, 2H). LC-MS m/z: 430.1 [M + H]+.
(E)-3-(1-(3-((4-Bromophenethyl)amino)-3-oxopropyl)-1H-benzo[d]imidazol-2-yl)acrylic acid (6k): Compound 6k was prepared from 4 and 2-(4-bromophenyl)ethan-1-amine in a similar manner as compound 6a. White solid. Yield 59.9%. m.p.: 203–205 °C. 1H-NMR (DMSO-d6) δ: 12.82(s, 1H), 8.00 (t, J = 5.4 Hz, 1H), 7.71–7.59 (m, 3H), 7.34 (d, J = 8.3 Hz, 2H), 7.31–7.21 (m, 2H), 6.93 (d, J = 15.5 Hz, 1H), 6.89 (d, J = 8.3 Hz, 2H), 4.59 (t, J = 6.2 Hz, 2H), 3.12 (dd, J = 12.7, 6.7 Hz, 2H), 2.56 (t, J = 6.3 Hz, 2H), 2.46 (t, J = 7.1 Hz, 2H). 13C-NMR (DMSO-d6) δ 169.3, 167.2, 148.1, 142.7, 138.8, 135.3, 131.0, 130.9, 128.5, 127.1, 123.1, 122.7, 119.4, 119.1, 111.1, 40.1, 36.0, 34.1, 30.5. LC-MS m/z: 442.0 [M + H]+.
(E)-3-(1-(3-((4-Methoxybenzyl)amino)-3-oxopropyl)-1H-benzo[d]imidazol-2-yl)acrylic acid (6l): Compound 6l was prepared from 4 and (4-methoxyphenyl)methanamine in a similar manner as compound 6a. White solid. Yield 54.3%. m.p.: 203–205 °C. 1H-NMR (DMSO-d6) δ: 12.85 (s, 1H), 8.32 (t, J = 5.7 Hz, 1H), 7.78 (d, J = 15.4 Hz, 1H), 7.69 (d, J = 7.16 Hz, 1H), 7.63 (d, J = 7.16 Hz, 1H), 7.29 (m, J = 7.1 Hz, 2H), 6.89 (d, J = 8.6 Hz, 3H), 6.75 (d, J = 9.1 Hz, 2H), 4.65 (t, J = 6.3 Hz, 2H), 4.08 (d, J = 5.7 Hz, 2H), 3.70 (s, 3H), 2.66 (t, J = 6.3 Hz, 2H). 13C-NMR (DMSO-d6) δ 169.2, 166.9, 158.1, 147.7, 142.7, 135.4, 130.9, 129.6, 128.5, 125.4, 123.3, 122.8, 119.5, 113.6, 111.2, 55.0, 41.6, 40.1, 36.0. LC-MS m/z: 380.1 [M + H]+.
(E)-3-(1-(3-((4-Methoxyphenethyl)amino)-3-oxopropyl)-1H-benzo[d]imidazol-2-yl)acrylic acid (6m): Compound 6m was prepared from 4 and 2-(4-methoxyphenyl)ethan-1-amine in a similar manner as compound 6a. White solid. Yield 51.9%. m.p.: 219–220 °C. 1H-NMR (DMSO-d6) δ: 12.85 (s, 1H), 8.32 (t, J = 5.7 Hz, 1H), 7.78 (d, J = 15.4 Hz, 1H), 7.69 (d, J = 7.48,1H), 7.62 (d, J = 7.64 Hz, 1H), 7.31 (t, J = 7.12 Hz, 2H), 7.26 (t, J = 7.12 Hz, 2H), 6.91 (d, J = 15.4 Hz, 1H), 6.87 (d, J = 8.56 Hz, 2H), 6.73 (d, J = 8.64 Hz, 2H), 4.60 (t, J = 6.3 Hz, 2H), 3.68 (s, 3H), 3.08(q, J = 6.76 Hz, 2H), 2.57 (t, J = 6.24 Hz, 2H), 2.42 (t, J = 7.24 Hz, 2H). LC-MS m/z: 394.1 [M + H]+.
(E)-3-(1-(3-((3,5-Dichlorophenyl)amino)-3-oxopropyl)-1H-benzo[d]imidazol-2-yl)acrylic acid (6n): Compound 6n was prepared from 4 and 3,5-dichloroaniline in a similar manner as compound 6a. White solid. Yield 51.7%. m.p.: 152–154 °C. 1H-NMR (DMSO-d6) δ: 10.48 (s, 1H), 7.63 (d, J = 7.88 Hz, 2H), 7.60 (d, J = 15.3 Hz, 1H), 7.54 (d, J = 1.5 Hz, 2H), 7.26 (t, J = 7.0 Hz, 1H), 7.23 (s, 1H), 7.20 (t, J = 7.3 Hz, 1H), 6.92 (d, J = 15.3 Hz, 1H), 4.67 (t, J = 6.1 Hz, 2H), 2.86 (t, J = 6.3 Hz, 2H). LC-MS m/z: 404.0 [M + H]+.
(E)-3-(1-(3-((2,4,6-Trimethylphenyl)amino)-3-oxopropyl)-1H-benzo[d]imidazol-2-yl)acrylic acid (6o): Compound 6o was prepared from 4 and 2,4,6-trimethylaniline in a similar manner as compound 6a. White solid. Yield 55.5%. m.p.: 275–278 °C. 1H-NMR (DMSO-d6) δ: 9.17 (s, 1H), 7.73(d, J = 15.2 Hz, 1H), 7.65 (t, J = 8.3 Hz, 2H), 7.26 (dq, J = 7.2, 6.0 Hz, 2H), 6.93(d, J = 15.2 Hz, 1H), 6.76(s, 2H), 4.68 (t, J = 6.1 Hz, 2H), 2.88 (t, J = 6.2 Hz, 2H), 2.16 (s, 3H), 1.73 (s, 6H). 13C-NMR (DMSO-d6) δ 168.0, 167.2, 148.0, 142.8, 135.3, 135.3, 134.7, 132.1, 129.1, 128.1, 126.6, 123.2, 122.7, 119.4, 111.3, 40.1, 35.6, 20.4, 17.6. LC-MS m/z: 378.1 [M + H]+.
3.1.2. General Procedure for the Synthesis of 7a–7c
To a solution of compounds 6d, 6f or 6o (0.29 mmol) in methanol (5 mL) was added Pd/C (5%, 31 mg, 0.14 mmol). The mixture was stirred and subjected to an atmosphere of hydrogen for 3 h at room temperature. After the start material was completed, the mixture was filtered and the filtrate was concentrated in vacuo to obtain the desired compounds 7a–7c.
3-(1-(3-Oxo-3-(p-tolylamino)propyl)-1H-benzo[d]imidazol-2-yl)propanoic acid (7a): Compound 7a was prepared from 6d using the general procedure as a white solid. Yield 98.0%. m.p.: 66–68 °C. 1H-NMR (DMSO-d6) δ: 12.28 (s, 1H), 9.95 (s, 1H), 7.54 (dd, J = 11.4, 7.8 Hz, 2H), 7.38 (t, J = 11.6 Hz, 2H), 7.18 (t, J = 7.1 Hz, 1H), 7.13 (t, J = 7.5 Hz, 1H), 7.07 (d, J = 8.3 Hz, 2H), 4.51 (t, J = 6.8 Hz, 2H), 3.13 (t, J = 7.0 Hz, 2H), 2.82 (t, J = 6.9 Hz, 4H), 2.22 (s, 3H). LC-MS m/z: 352.1 [M + H]+.
3-(1-(3-((4-Chlorophenyl)amino)-3-oxopropyl)-1H-benzo[d]imidazol-2-yl)propanoic acid (7b): Compound 7b was prepared from 6f using the general procedure as a white solid. Yield 95.0%. m.p.: 66–68 °C. 1H-NMR (DMSO-d6) δ: 12.28 (s, 1H), 10.15 (s, 1H), 7.54 (m, 4H), 7.33 (d, J = 7.9 Hz, 2H), 7.18 (t, J = 7.5 Hz, 1H), 7.13 (t, J = 7.4 Hz, 1H), 4.51 (d, J = 6.0 Hz, 2H), 3.60 (d, J = 6.1Hz, 2H), 3.12 (d, J = 6.2 Hz, 2H), 2.84 (d, J = 6.7 Hz, 2H). LC-MS m/z: 372.1 [M + H] +.
3-(1-(3-(Mesitylamino)-3-oxopropyl)-1H-benzo[d]imidazol-2-yl)propanoic acid (7c): Compound 7c was prepared from 6o using the general procedure as a white solid. Yield 94.0%. m.p.: 222–224 °C. 1H-NMR (DMSO-d6) δ: 12.25 (s, 1H), 9.19 (s, J = 8.1 Hz, 1H), 7.54 (dd, J = 7.3, 4.0 Hz, 2H), 7.21–7.10 (m, 2H), 6.77 (s, 2H), 4.50 (t, J = 6.6 Hz, 2H), 3.14 (t, J = 7.1 Hz, 2H), 2.86 (t, J = 6.6 Hz, 2H), 2.81 (t, J = 7.1 Hz, 2H), 2.17 (t, J = 4.3 Hz, 3H), 1.81 (s, 6H). LC-MS m/z: 380.2 [M + H]+.
3.1.3. General Procedure for the Synthesis of 13a–13j
1H-Benzo[d]imidazole-2-carboxylic acid (8): To a mixture of 1 (6.0 g, 40.5 mmol) and K2CO3 (4.3 g, 31.2 mmol) in 100 mL water was added KMnO4 (6.4 g, 40.5 mmol) in batches, the mixture was refluxed for 1h. After complete conversion of starting material, the reaction mixture was filtered; the pH of the filtrate was adjusted to 5 with 6N HCl at 0 °C. Filter and dried to obtain 8 as white solid in 45.0% yield. LC-MS m/z: 161.5 [M − H]−.
1H-Benzo[d]imidazole-2-carboxamide (9): A solution of 8 (3.0 g, 18.6 mmol) in SOCl2 (30 mL) was stirred at 70 °C for 4 h. The mixture was cooled to room temperature, concentrated in vacuo and aqueous ammonia (150 mL) was added. The resulting solution was stirred at 70 °C for 5 h, then cooled and water (50 mL) was added and stirred at room temperature for additional 1 h. Filtration and drying gave 9 as a yellow solid in 51.4% yield. LC-MS m/z: 162.1 [M + H]+.
1H-Benzo[d]imidazole-2-carbothioamide (10): To a solution of 9 (3.0 g, 18.6 mmol) in THF (70 mL) was added Lawesson’s reagent (7.5 g, 18.6 mmol). The resulting solution was stirred at 66 °C for 5 h. After complete conversion of the starting material, the reaction mixture was concentrated in vacuo and the residue was redissolved in DCM (500 mL), the solution was washed with saturated NaCl solution three times, dried over anhydrous sodium sulfate, concentrated and purified by flash silica gel column chromatography (DCM:MeOH = 100:1) to obtain 10 as yellow solid in 61.2% yield. LC-MS m/z: 178.2 [M + H]+.
Ethyl 2-(1H-benzo[d]imidazol-2-yl)thiazole-4-carboxylate (11): A solution of ethyl 3-bromo-2-oxopropanoate (3.0 g, 16.9 mmol) and 10 (3.0 g 16.9 mmol) in ethanol (150 mL) was stirred at 66 °C for 5 h. After complete conversion of the starting material, the reaction mixture was concentrated in vacuo, and then purified by silica gel column chromatography (DCM:MeOH= 250:1) to obtain 11 as white solid in 95.0% yield. LC-MS m/z: 274.3 [M + H]+.
3-(2-(4-(Ethoxycarbonyl)thiazol-2-yl)-1H-benzo[d]imidazol-1-yl)propanoic acid (12): To a solution of 11 (1.0 g, 3.70 mmol) in mixture of DMF (20 mL) and acetone (100 mL), 3-bromopropionic acid (2.2 g, 14.8 mmol) and a solution of K2CO3 (10.0 g, 72.4 mmol) in water (2 mL) was added, the mixture was stirred at 70 °C for 4 h. After complete conversion of the starting material, the reaction mixture was concentrated in vacuo and redissolved in water (80 mL). The resulting solution was acidified to pH 5 with 6 N HCl at 0 °C, and then extracted with ethyl acetate, the organic layers combined and washed with saturated NaCl and dried over anhydrous sodium sulfate, filtered, and concentrated in vacuo to give 12 as white solid in 65.0% yield. LC-MS m/z: 344.1 [M − H]−.
2-(1-(3-Oxo-3-(phenylamino)propyl)-1H-benzo[d]imidazol-2-yl)thiazole-4-carboxylic acid (13a): To a mixture of compounds 12 (500 mg, 1.45 mmol), 4-methylmorpholine (0.8 mL, 4.25 mmol) and aniline (161 mg, 1.74 mmol) in dried DCM was added HOBt (389 mg, 2.90 mmol) at 0 °C, and then EDCI (557 mg, 2.90 mmol) was added in batches. The resulting solution was warmed to room temperature after stirring for 30 min at 0 °C. The reaction mixture was washed with water three times and saturated NaCl solution once. The organic layer was dried over anhydrous sodium sulfate, concentrated and purified by flash silica gel column chromatography (PE/EA = 4/1, v/v), and then the residue was re-dissolved in THF (15 mL), and lithium hydroxide solution (3.5 mmol/mL, 5 mL) was added dropwise. The resulting solution was stirred at room temperature for 6 h. After the reaction was completed, the reaction mixture was concentrated in vacuo, and the residue dissolved in water and acidified with 2 N HCl to pH 5 at 0 °C, filtered and dried to obtain the desired compound 13a as a white solid in 56.1% yield. m.p.: 226–228 °C. 1H-NMR (DMSO-d6) δ: 13.23 (s, 1H), 9.88 (s, 1H), 8.64 (s, 1H), 7.77 (d, J = 8.2 Hz, 1H), 7.73 (d, J = 8.0 Hz, 1H), 7.43 (d, J = 7.9 Hz, 2H), 7.36 (t, J = 7.5 Hz, 1H), 7.29 (t, J = 7.5 Hz, 1H), 7.22 (t, J = 7.8 Hz, 2H), 6.99 (t, J = 7.3 Hz, 1H), 5.15 (t, J = 6.6 Hz, 2H), 2.96 (t, J = 6.6 Hz, 2H). 13C-NMR (DMSO-d6) δ 168.7, 161.9, 159.3, 148.6, 144.1, 142.0, 138.8, 136.1, 130.8, 128.6, 124.1, 123.2, 123.1, 119. 6, 119.2, 111.7, 41.3, 36.8. LC-MS m/z: 391.0 [M − H]−.
2-(1-(3-((3-Bromophenyl)amino)-3-oxopropyl)-1H-benzo[d]imidazol-2-yl)thiazole-4-carboxylic acid (13b): Compound 13b was prepared from 12 and 3-bromoaniline in a similar manner as compound 13a. White solid. Yield 53.0%. m.p.: 210–212 °C. 1H-NMR (DMSO-d6) δ: 9.59 (s, 1H), 8.62 (s, 1H), 7.74 (d, J = 8.1 Hz, 3H), 7.58 (d, J = 7.9 Hz, 1H), 7.37 (t, J = 7.4 Hz, 1H), 7.31 (t, J = 7.5 Hz, 2H), 7.27 (s, 1H), 7.09 (t, J = 7.1 Hz, 1H), 5.15 (t, J = 6.2 Hz, 2H), 3.02 (s, 2H). LC-MS m/z: 469.4 [M − H]−.
2-(1-(3-((2-Bbromophenyl)amino)-3-oxopropyl)-1H-benzo[d]imidazol-2-yl)thiazole-4-carboxylic acid (13c): Compound 13c was prepared from 12 and 2-bromoaniline in a similar manner as compound 13a. White solid. Yield 48.3%. m.p.: 186–188 °C. 1H-NMR (DMSO-d6) δ: 9.59 (s, 1H), 8.62 (s, 1H), 7.74 (d, J = 8.1 Hz, 3H), 7.58 (d, J = 7.9 Hz, 1H), 7.37 (t, J = 7.4 Hz, 1H), 7.31 (t, J = 7.5 Hz, 2H), 7.27 (s, 1H), 7.09 (t, J = 7.1 Hz, 1H), 5.15 (t, J = 6.2 Hz, 2H), 3.02 (s, 2H). LC-MS m/z: 469.4 [M − H]−.
2-(1-(3-((3-Methoxyphenyl)amino)-3-oxopropyl)-1H-benzo[d]imidazol-2-yl)thiazole-4-carboxylic acid (13d): Compound 13d was prepared from 12 and 3-methoxyaniline in a similar manner as compound 13a. White solid. Yield 46.8%. m.p.: 223–225 °C. 1H-NMR (DMSO-d6) δ: 9.92 (s, 1H), 8.62 (s, 1H), 7.77 (d, J = 8.2 Hz, 1H), 7.73 (d, J = 8.0 Hz, 1H), 7.36 (t, J = 7.7 Hz, 1H), 7.29 (t, J = 7.6 Hz, 1H), 7.13 (dd, J = 9.6, 6.6 Hz, 2H), 6.99 (d, J = 8.0 Hz, 1H), 6.58 (d, J = 8.2 Hz, 1H), 6.58 (d, J = 8.2 Hz, 1H), 5.14 (t, J = 6.7 Hz, 2H), 3.68 (s, 3H), 2.95 (t, J = 6.7 Hz, 2H). 13C-NMR (DMSO-d6) δ 169.0, 164.1, 159.4, 159.3, 156.1, 145.2, 142.1, 140.6, 135.9, 129.1, 123.8, 123.6, 122.8, 119.5, 112.5, 110.9, 108.7, 106.1, 55.0, 42.6, 38.2. LC-MS m/z: 421.3 [M − H]−.
2-(1-(3-((3,5-Dimethoxyphenyl)amino)-3-oxopropyl)-1H-benzo[d]imidazol-2-yl)thiazole-4-carboxylic acid (13e): Compound 13e was prepared from 12 and 3,5-dimethoxyaniline in a similar manner as compound 13a. White solid. Yield 43.9%. m.p.: 208–210 °C. 1H-NMR (DMSO-d6) δ: 10.68 (s, 1H), 8.02 (s, 1H), 7.72 (d, J = 10.5 Hz, 2H), 7.35 (t, J = 7.5 Hz, 1H), 7.28 (t, J = 7.6 Hz, 1H), 7.10 (s, 2H), 6.19 (s, 1H), 5.04–4.87 (m, 2H), 3.70 (s, 6H), 3.13–2.97 (m, 2H). 13C-NMR (DMSO-d6) δ 169.3, 164.3, 160.4, 159.7, 156.3, 145.4, 142.3, 141.2, 136.1, 124.0, 123.8, 123.1, 119.7, 111.2, 98.8, 95.5, 55.3, 42.7, 38.4. LC-MS m/z: 451.0 [M − H]−.
2-(1-(3-((3-Nitrophenyl)amino)-3-oxopropyl)-1H-benzo[d]imidazol-2-yl)thiazole-4-carboxylic acid (13f): Compound 13f was prepared from 12 and 3-nitroaniline in a similar manner as compound 13a. White solid. Yield 44.7%. m.p.: 234–236 °C. 1H-NMR (DMSO-d6) δ: 11.64 (s, 1H), 8.92 (s, 1H), 8.30 (d, J = 8.0 Hz, 1H), 8.06 (s, 1H), 7.91 (d, J = 8.1 Hz, 1H), 7.73 (d, J = 8.0 Hz, 2H), 7.59 (t, J = 8.1 Hz, 1H), 7.37 (t, J = 7.6 Hz, 1H), 7.30 (t, J = 7.6 Hz, 1H), 5.01–4.93 (m, 2H), 3.18–3.12 (m, 2H). LC-MS m/z: 436.4 [M − H]−.
2-(1-(3-Oxo-3-((3-(trifluoromethyl)phenyl)amino)propyl)-1H-benzo[d]imidazol-2-yl)thiazole-4-carboxylic acid (13g): Compound 13g was prepared from 12 and 3-(trifluoromethyl)aniline in a similar manner as compound 13a. White solid. Yield 47.6%. m.p.: 178–180 °C. 1H-NMR (400 MHz, DMSO-d6) δ: 11.35 (s, 1H), 8.36 (s, 1H), 8.11 (d, J = 7.9 Hz, 1H), 8.05 (s, 1H), 7.72 (dd, J = 7.7, 4.1 Hz, 2H), 7.52 (t, J = 7.8 Hz, 1H), 7.38 (d, J = 7.9 Hz, 1H), 7.36 (d, J = 7.8 Hz, 1H), 7.29 (t, J = 7.5 Hz, 1H), 4.98–4.94 (m, 2H), 3.13 (t, J = 13.1 Hz, 2H). 13C-NMR (150 MHz, DMSO) δ 169.4, 162.1, 159.2, 144.3, 142.1, 139.6, 136.1, 130.3, 129.9, 129.5, 129.2, 125.1, 124.2, 123.3, 123.2, 122.9, 119.7, 115.4, 115.4, 111.6, 41.4, 37.1. LC-MS m/z: 459.1 [M − H]−.
2-(1-(3-Oxo-3-((4-(trifluoromethyl)phenyl)amino)propyl)-1H-benzo[d]imidazol-2-yl)thiazole-4-carboxylic acid (13h): Compound 13h was prepared from 12 and 4-(trifluoromethyl)aniline in a similar manner as compound 13a. White solid. Yield 56.7%. m.p.: 176–178 °C. 1H-NMR (DMSO-d6) δ: 11.36 (s, 1H), 8.13 (d, J = 8.1 Hz, 2H), 8.04 (s, 1H), 7.72 (d, J = 8.3 Hz, 2H), 7.64 (d, J = 8.5 Hz, 2H), 7.36 (t, J = 7.6 Hz, 1H), 7.29 (t, J = 7.6 Hz, 1H), 4.98–4.92 (m, 2H), 3.23-3.09 (m, 2H). 13C-NMR (DMSO-d6) δ 168.8, 161.2, 158.7, 147.8, 143.5, 141.8, 141.4, 135.5, 130.2, 125.3, 124.7, 123.5, 122.9, 122.6, 122.5, 119.0, 118.3, 111.0, 40.5, 36.3. LC-MS m/z: 459.1 [M − H]−.
2-(1-(3-((3,5-Dichlorophenyl)amino)-3-oxopropyl)-1H-benzo[d]imidazol-2-yl)thiazole-4-carboxylic acid (13i): Compound 13i was prepared from 12 and 3,5-dichloroaniline in a similar manner as compound 13a. White solid. Yield 42.6%. m.p.: 192–194 °C. 1H-NMR (DMSO-d6) δ: 10.42 (s, 1H), 8.62 (s, 1H), 7.77 (d, J = 8.2 Hz, 1H), 7.74 (d, J = 8.0 Hz, 1H), 7.47 (d, J = 1.8 Hz, 2H), 7.37 (dd, J = 10.0, 5.3 Hz, 1H), 7.32–7.30 (m, 1H), 7.20 (t, J = 1.8 Hz, 1H), 5.18 (t, J = 6.6 Hz, 2H), 2.97 (t, J = 6.6 Hz, 2H). 13C-NMR (DMSO-d6) δ 168.9, 161.1, 158.7, 147.8, 143.5, 141.3, 140.5, 135.4, 133.3, 130.1, 123.5, 122.5, 121.7, 118.9, 116.6, 111.0, 40.5, 36.3. LC-MS m/z: 459.3 [M − H]−.
2-(1-(3-((3-Fluoro-4-methylphenyl)amino)-3-oxopropyl)-1H-benzo[d]imidazol-2-yl)thiazole-4-carboxylic acid (13j): Compound 13j was prepared from 12 and 3-fluoro-4-methylaniline in a similar manner as compound 13a. White solid. Yield 46.6%. m.p.: 204–206 °C. 1H-NMR (DMSO-d6) δ: 11.08 (s, 1H), 8.03 (s, 1H), 7.80 (d, J = 12.7 Hz, 1H), 7.74-7.65 (m, 2H), 7.61 (d, J = 8.3 Hz, 1H), 7.36 (t, J = 7.6 Hz, 1H), 7.29 (t, J = 7.6 Hz, 1H), 7.16 (t, J = 8.6 Hz, 1H), 5.05–4.87 (m, 2H), 3.14–2.96 (m, 2H), 2.18 (s, 3H). 13C-NMR (DMSO-d6) δ 168.9, 162.3, 160.9, 159.3, 144.3, 142.0, 138.4, 136.0, 131.2, 124.0, 123.0, 119.6, 118.4, 118.3, 115.0, 111.4, 106.2, 106.0, 41.6, 37.2, 13.7. LC-MS m/z: 423.4 [M − H]−.