General experimental
All chemicals were purchased from Aldrich Chemical Company and used without any further purification unless otherwise specified. All prepared compounds were characterized by 1H-NMR, 13C-NMR, IR spectroscopy, elemental analysis, and melting point. Nuclear Magnetic Resonance spectra were recorded on Varian Gemini 2000, 300 MHz instrument and on Bruker DPX-300 MHz instruments. Infrared spectra were recorded in KBr on a Shimadzu 820 PC FT-IR spectrometer. All 1H-NMR experiments were reported in δ units, parts per million (ppm) downfield from tetramethylsilane (TMS). All 13C-NMR spectra were reported in ppm relative to deuterochloroform (77.0 ppm). All melting points were determined in an open capillary tube and are uncorrected. At least two measurements were carried out for each compound. Elemental analyses were carried out with Elementar Vario EL III elemental analyzer. TLC analysis was performed on silica gel plates pre-coated with Merck Kieselgel 60 F254 and visualization was done using UV lamp. Sample purifications were performed using flash chromatography with silica gel (100-200) mesh.
General Procedure
Preparation of curcumin-based heterocyclic compounds
The general experimental procedure for the preparation of compounds shown in
Figure 1 was as follows: In a round bottom flask equipped with magnetic stirring bar and a condenser, curcumin (1.5 mmole, 0.5 g) was dissolved in acetic acid (or polyphosphoric acid (PPA)) (8 mL). The desired hydrazine (1.5 mmole) or amine was added to the solution of curcumin in acid. The produced solution was refluxed for 6-12 h. The progress of the reaction was monitored by TLC. After complete conversion, the mixture was cooled to room temperature and concentrated
in-vacuo and redissolved in ethyl acetate (150 mL). The ethyl acetate layer was washed with saturated solution of NaHCO
3 and saturated solution of NaCl, dried over Na
2SO
4 and concentrated
in-vacuo. The produced solid was collected by suction filtration and purified by flash chromatography (hexane : EtOAC (6 : 4)). In case where PPA was used, reaction mixture was diluted with water, extracted with ethyl acetate and then the product was purified as shown before.
1-phenyl-3,5-bis-2-(4-hydroxy-3-methoxystyryl)-1H-pyrazole (2a)
Curcumin (1.5 mmole, 0.5 g) was dissolved in glacial acetic acid (8.0 mL) and then, phenyl hydrazine hydrochloride (1.5 mmole, 0.25 g) was added. Produced solution was refluxed for about 6 h. Yield 71.6% (0.48 g), mp 127-129°C, IR (KBr ): vmax cm-1 3600 (-C-OH), 3350 (–C–NH), 3100, 1620 (-C=N), 1600, and 1080 (C-O ether) of (–O-CH3). 1H-NMR (300 MHz, CDCl3) δ ppm: 3.90 (s, 6H, OCH3), 6.05 (s, 2H, OH), 6.80 (s, 1H, C4-H), 7.02 (d, 2H, J = 14.8 Hz, C2-H and, C6-H), 7.10 (d, 2H, J = 14.8 Hz, C1-H and C7-H), 7.15–7.32 (m, 8H, Ar-H), 7.45 (m, 2H, Ar-H), 7.72 (m, 1H, Ar-H). 13C NMR (300 MHz, CDCl3) δ ppm: (300 MHz, CDCl3): 56.05, 56.09, 101.22, 110.02, 110.98, 112.57, 115.97, 116.14, 117.64, 120.67, 125.24, 128.17, 128.29, 128.84, 129.02, 129.06, 129.08, 131.22, 133.34, 139.72, 142.82, 147.20, 147.74, 148.2, 148.33, 151.54, 161.00. Anal. Calcd for C27H24N2O4: C 73.62, H 5.49, N 6.36. Found: C 73.43, H 5.42, N 6.48.
1-(2,4-dinitrophenyl)-3,5-bis-2-(4-hydroxy-3-methoxystyryl)-1H-pyrazole (2b)
Curcumin (1.5 mmole, 0.5 g) was dissolved in glacial acetic acid (8.0 mL), and to it was added 2,4-dinitrophenyl hydrazine hydrochloride (1.5 mmole, 0.355 g). Produced solution was refluxed for about 12 h (Yield 55 (0.43 g), mp 192-195°C).
IR: vmax cm-1 3610 (-C-OH), 3050, 1635, (-C=N), 1590, 1080 (C-O ether), 1520, 1350.
1H-NMR (300 MHz, CDCl3) δ ppm: 3.78 (s, 3H, OCH3), 3.80 (s, 3H, OCH3), 6.16 (s, 2H, OH),
6.80 (s, 1H, C-4H), 6.83 (m, 4H, C1-H, C2-H, C6-H, and, C7-H), 6.90 (m, 1H, Ar-H), 7.10 (d, 2H, Ar-H), 7.20 (d, 2H, Ar-H), 7.40 (d, 1H, Ar-H), 8.00 (d, 1 H, J = 9.43 Hz, Ar-H containing NO2), 8.43 (dd, 1H, J = 2.64 Hz, 9.43 Hz, Ar-H containing NO2), 8.90 (d, 1H, J = 2.64 Hz, Ar-H containing NO2). 13C NMR (300 MHz, CDCl3) δ ppm: 56.15, 56.23, 102.07, 110.00, 110.94, 111.28, 111.72, 116.11, 116.89, 121.59, 121.86, 123.63, 126, 83, 127.91, 128.43, 128.92, 130.23, 133.07, 135.18, 135.69, 147.16, 144.89, 145.48, 146.23, 148.23, 148.42, 154.02. Anal. Calcd for C27H22N4O8: C 61.13, H 4.18, N 10.56. Found: C 61.59, H 4.32, N 10.66.
1-(2-pyridyl)-3,5-bis-2-(4-hydroxy-3-methoxystyryl)-1H-pyrazole (2c)
Curcumin (1.5 mmole, 0.5 g) was dissolved in glacial acetic acid (8.0 mL), to it was added 2-hydrazinopyridin (1.5 mmole, 0.164 g). Produced solution was refluxed for 12 h. Yield 89.5 (0.6 g), mp 122-125°C IR: vmax cm-1 3550 (-C-OH), 3050, 1640, (-C=N), 1590, 1080 (C-O ether), 1520, 1350. 1H NMR (400 MHz, DMSO-d6) δ: 3.78 (s, 6H, 2OCH3), 6.13 (2H, OH), 6.65 (s, 1H, C4-H), 6.78 (m, 4H), 6.95 (m, 4H), 7.13 (m, 2H), 7.35 (d, 1H), 7.63 (d, 1H), 7.72 (t, 1H), 8.21 (d, 1H). 13C NMR (400 MHz, DMSO-d6) δ: 56.17,101.33, 102.45, 110.135, 110.87, 111.79, 115.56, 116.21, 117.50, 120.62, 122.37, 123.68, 126.69, 127.51, 128.85, 132.38, 132.79, 141.17, 144.02,, 147.81, 148.41, 150.08, 152.20, 163.37, 183.64. Anal. Calcd for C26H23N3O4: C 70.73, H 5.25, N 9.50, Found: C 70.62, H 5.27, N 9.56.
| Compound | MIC (mg/mL) | MBC (mg/mL) |
|---|
| curcumin | 1 | 1 |
| 2a | 0.25 | 1 |
| 2b | 0.25 | 1 |
| 2c | 0.0625 | 1 |
| 2d | 0.0625 | 1 |
| 2e | 0.0625 | 1 |
| 3 | 0.25 | 1 |
| 4 | 0.0019 | 0.0075 |
| 5 | 0.0625 | |
1-(2-furyl)-3,5-bis((E)-4-hydroxy-3-methoxystyryl)-1H-pyrazol (2d)
Curcumin (1.5 mmole, 0.5 g) was dissolved in glacial acetic acid (8.0 mL) and to it, was added 2-Furoichydrazide (1.5 mmole, 0.2 g). Produced solution was refluxed for 12 h. Yield 81 (0.52 g), mp 138-141°C, IR: vmax cm-1 3605 (-C-OH), 3030, 1673 (–C=O amido), 1640 ( -C=N), 1590, 1080 (C-O ether), 1520, 1320 (C-O of the five-member ring). 1H-NMR (400 MHz, DMSO-d6) δ: 3.78 (s, 6H, OCH3), 6.01 (s, 2H, OH), 6.50-7.32 (m, 13 H), 7.52 (dd, 1H, J= 16.15Hz). 13C-NMR (400 MHz, DMSO-d6) δ: 56.03, 99.79, 101.4, 111.74, 112.43, 115.18, 116.01, 116.14, 116.37, 120.56, 121.52, 123.67, 126.74, 128.79, 130.06, 141.18, 146.32, 146.67, 148.32, 148.46, 149.89, 157.70, 183.30. Anal. Calcd for C25H22N2O5: C 69.76, H 5.15, N 6.51. Found: C 69.66, H 5.18, N 6.62.
1-carbohydrazidyl-3,5-bis-2-(4-hydroxy-3-methoxystyryl)-1H-pyrazole (2e)
Curcumin (1.5 mmole, 0.5 g) was dissolved in glacial acetic acid (8.0 mL), to it was added carbohydrazide (1.5 mmole, 0.135 g). Produced solution was refluxed for 12 h. Yield 88.6 (0.0.56 g), mp 151-154°C, IR: vmax cm-1 3605 (-C-OH), 3320, 3275, 3190 (–C–NH), 3020, 1635 (-C=N), 1600, 1080 (C-O ether).1H-NMR (400 MHz, DMSO-d6) δ: 3.78 (s, 3H, OCH3), 4.32 (s, 2H, NH), 6.01 (s, 2H, OH), 6.50-7.40 (m, 11H), 8.80 (s, H, NH). 13C-NMR (400 MHz, DMSO-d6): 56.07, 56.12, 100.1, 110.6, 116.08, 116.24,120.30, 120.66, 123.16, 123.34, 128.62, 129.81, 130.4, 131.03, 143.78, 144.70, 147.13, 147.51, 147.50, 150.69, 151.13, 161.06. Anal. Calcd for C22H22N4O5: C 62.55, H 5.25, N 13.26. Found: C 62.63, H 5.25, N 13.37.
3,5-bis-2-(4-hydroxy-3-methoxystyryl)-isoxazole (3) Curcumin (1.5 mmole, 0.5 g) was dissolved in glacial acetic acid (8.0 mL) and to it, was added hydroxylamine hydrochloride (1.5 mmole, 0.11g). Produced solution was refluxed for 12 h. Yield 72.0 (0.4 g), mp 116-119°C, IR: 3570 (-C-OH), 3030, 1605, 1586 (-C=N), 1330 (C-O of the five-member ring) cm-1. 1H-NMR (400 MHz, DMSO-d6): 1H-NMR: δ 3.85 (s, 6H, 2OCH3), 6.25 (s, 2H, OH), 6.71 (s, 1H, C4-H), 6.84-7.01 (m, 3H), 7.04-7.15 (m, 4H), 7.26 (m, 3H). 13C-NMR (300 MHz, CDCl3) δ ppm: 56.14, 56.18, 98.33, 110.56, 110.82, 113.12, 113.43, 115.98, 116.11, 116.24, 121.8, 122.16, 127.49, 127.83, 129.22, 135.27, 135.98, 148.22, 148.42, 162.70, 168.84. Anal. Calcd for C21H19NO5: C 69.03, H 5.24, N 3.38. Found: C 68.89, H 5.21, N 3.41.
3,5-bis-2-(4-hydroxy-3-methoxystyryl)-3,6-dihydro-2H-1,4-diazepine (4) Curcumin (1.5 mmole, 0.5 g) was dissolved in glacial acetic acid (8.0 mL) and then, ethylenediamine (1.5 mmole, 0.1 mL) was added to the solution. Produced solution was refluxed for 4 h. Yield 76.3 (0.45), mp 65-68°C (hydrated) IR: vmax cm-1 3605 (-C-OH), 3020, 1640 (-C=N), 1600, 1080 (C-O ether). 1H-NMR (400 MHz, DMSO-d6) δ: 3.16 (s, 2H, CH2), 3.764 (s, 4H, CH2CH2); 3.78 (s, 6H, OCH3), 5.72 (s, 2H, OH), 6.85 (m, 2H), 6.91 (d, 2H, J = 15.2 Hz), 7.05 (d, 2H, J = 12.1 Hz), 7.20 (s, 2H), 7.40- 7.60 (m, 2H). 13C-NMR (400 MHz, DMSO-d6) δ: 24.50, 48.30, 56.40, 112.90, 116.30, 120.60, 122.40, 127.80, 129.30, 148.20, 149.30, 165.80. LC/MS [M + 1] for C23H24N2O4 Calcd 393.0, found: 394.0. Anal. Calcd for C23H24N2O4: C 70.39, H 6.16, N 7.14. Found: C 70.33, H 6.21, N 7.19. The differences in the [M+1] values could be due to the protonation of compound 4 during LC/MS analysis, since mobile phase used in the analysis was an acidic solution of aqueous methanol.
4,4›-((1E,3Z,5Z,6E)-3-(butylamino)-5-(butylimino)hepta-1,3,6,triene-1,7-diyl) bis(2-methoxyphenol) (5) Curcumin (1.5 mmole, 0.5 g) was dissolved in glacial acetic acid (8.0 mL) and to it was added n-butyl amine (3 mmole, 0.25 mL). Produced solution was refluxed for 10 h. Yield 78% (0.56 g), mp 106-109°C IR: vmax cm-1 3605 (-C-OH), 3335 (–C–NH), 3040, 1640 (-C=N), 1600, 1080 (C- O ether). 1H-NMR (400 MHz, DMSO-d6) δ: 0.79 (m, 6H), 1.23 (m, 4H), 1.32-1.41 (m, 4H),1.82 (s, 1H), 2.52 (t, 2H), 2.72 (t, 2H), 3.78 (s, 6H, OCH3), 6.10 (s, 2H, OH), 6.62 (s, 1H, C4-H), 6.84 (m, 4H, C2-H, C6-H), 7.10 (m, 2H), 7.20 (m, 2H), 7.40 (d, 2H). 13C-NMR (400 MHz, DMSO-d6) δ: 13.60, 13.60, 19.20, 19.20, 35.30, 36.10, 44.50, 46.80, 56.20, 56.43, 97.31, 109.74, 111.95, 115.83, 116.12, 116.11, 121.50, 123.80, 125.31, 129.3, 129.31, 135.55,136.26, 148.23, 148.27, 149.92, 149.93, 152.81, 174.65. Anal Calcd for C29H38N2O4: C 72.77, H 8.00, N 5.85. Found: C 72.54, H 8.12, and N 5.76.
Antibacterial activity of materials
Culture media: Mueller-Hinton, Tryptic Soy Broth was obtained from Hylabs, Israel.
Microorganisms used
Bacterial strains used in the study were clinical isolates of Staphylococcus aureus, Escherichia coli, Proteus mirabilis, and Pseudomonas aeroginosa, were all isolated from patients suffering from bacterial infections with the relevant bacteria.
Procedure
These isolates were tested for their susceptibility to the prepared curcumin-based heterocyclics as follows:
Solutions of these derivatives were prepared at concentration of 4 mg per 1 mL of dimethyl sulfoxide (DMSO) solvent, and then incubated for 24 h at 37°C.
Screening the antimicrobial activity
The antibacterial bioactivities of the prepared heterocyclics were screened using the well diffusion method reported in the literature by Perez
et al (
55)
.Three colonies of bacteria were transferred to sterile tubes each containing 5 mL of Tryptic Soy Broth. Turbidity of the bacterial suspensions was then adjusted to reach an optical density equivalent to a 0.5 McFarland standard to give a bacterial suspension of 108 cfu/mL (cfu: colony forming unit). Mueller-Hinton agar plates were inoculated through streaking bacterial swabs over the entire surface of the plates. Produced Plates were allowed to dry at room temperature and 6 mm wells were punched in each plate. In each plate, 50 μL of 4 mg/mL solutions of each curcumin derivatives were added into duplicate wells. Plates were allowed to stand at room temperature to let the tested derivative be diffused into the agar, and afterwards, they were incubated at 37°C for 18 to 24 h. Then, plates were examined for bacterial growth inhibition and zones of inhibition were measured in millimeters.
Determination of minimum inhibitory concentration (MIC)
Two-fold serial dilutions were prepared from the derivative solution in Tryptic Soy Broth. Duplicate tubes of each dilution were inoculated with 5 × 105 of the bacterial strains. All tubes were incubated at 37°C for 18 to 24 h. The highest dilution of the drug that resulted in inhibition of bacterial growth was considered as the MIC.
Determination of minimal bactericidal concentration (MBC)
Subcultures from the above dilutions were done on Muller-Hinton plates and incubated at 37°C for 18 to 24 h. The highest dilution that resulted in total inhibition of bacterial growth was then determined and considered as MBC.