General
Melting points were determined in open capillary tubes on a MPA120-Automated Melting Point apparatus and are uncorrected. The1H and13C NMR spectra were recorded on a Bruker Heaven 11400 (400 MHz) spectrometer using TMS as internal standard and the chemical shifts are expressed in ppm. All the metal triflates, indole, N-methylaniline, and aldehydes were purchased from Sigma-Aldrich. The products were purified by column chromatography using silica gel (60-120 mesh, S. D. Fine, India). The bacterial cultures (Bacillus subtilis MTCC 121, Staphylococcus aureus MTCC 96 and Escherichia coli MTCC 1652) were procured from Microbial Type Culture Collection, Institute of Microbial Technology, Chandigarh, India. Dimethyl sulfoxide (DMSO) and chloramphenicol (standard broad spectrum antibiotic) were used as negative and positive controls, respectively. The experiments were carried out in triplicates.
General procedure for preparation of 3-aminoalkylated indoles (4)
To a solution of N-methylaniline (114 mg, 1.2 mmol) and a benzaldehyde (1.0 mmol) in acetonitrile (10 mL), AgOTf (30 mg) was added. The reaction mixture was stirred at room temperature. After 30 min, indole or N-methylindole (0.71 mmol) was added to the reaction and the mixture was allowed it to stir for an additional 90 min. The progress of reaction was monitored by TLC. After completion of the reaction, solvent was removed under reduced pressure. To the residue, diethyl ether was added and filtered. The filtrate was dried over anhydrous sodium sulfate and concentrated to obtain the crude product, which was purified by column chromatography on silica gel (100-200 mesh) using ethyl acetate/hexane as eluents to yield a pure product (4a-4r). All the compounds were characterized by ESI-MS,1H NMR, and13C NMR spectroscopic data.
N-((4-Chlorophenyl)(1H-indol-3-yl)methyl)-N-methylbenzenamine (4a)
Brown solid, m.p. 183-185°C;1H NMR (400 MHz, CDCl3): δ 7.98 (s, 1H), 7.37 (d, J = 4.0 Hz, 2H), 7.27-7.16 (m 5H), 7.03 (d, J = 8.0 Hz, 3H), 6.57 (d, J = 8.0 Hz, 3H), 5.55 (s, 1H), 2.83 (s, 3H);13C NMR (100 MHz, DMSO-d
6): δ 147.5, 141.6, 137.0, 135.5, 132.9, 129.8, 129.1, 129.0, 127.3, 124.2, 121.9, 120.8, 120.2, 119.3, 113.1, 111.2, 47.6, 31.0, 21.1; ESI-MS (m/z): 346.9975 [M + H]+.
N-((1H-Indol-3-yl)(p-tolyl)methyl)-N-methylbenzenamine (4b)
Brown solid, m.p. 136-138°C;1H NMR (400 MHz, DMSO-d
6): δ 10.62 (s, 1H), 7.31 (d, J = 8.0 Hz 1H), 7.07-6.98 (m, 7H), 6.92-6.90 (m, 1H), 6.62-6.61 (m, 1H), 6.43 (d, J = 8.4 Hz, 2H), 5.46 (s, 1H), 5.40 (s, 1H), 2.49-2.48 (m, 3H), 2.24 (s, 1H);13C NMR (100 MHz, DMSO-d
6): δ 147.6, 141.7, 136.7, 135.4, 133.2, 129.7, 128.9, 128.8, 127.2, 123.9, 121.9, 120.9, 120.1, 119.3, 112.4, 111.0, 47.6, 31.0, 21.1; ESI-MS (m/z): 327.0665 [M + H]+.
N-((1H-Indol-3-yl)(4-methoxyphenyl)methyl)-N-methylbenzenamine (4c)
Brown solid, m.p. 177-179°C;1H NMR (400 MHz, CDCl3): δ 7.93 (s, 1H), 7.42-7. 26 (m, 3H), 7.16 (d, J = 7.6 Hz, 3H), 7.06-6.98 (m, 3H), 6.83 (d, J = 7.6, 2H), 6.56 (d, J = 8.0 Hz, 3H), 5.54 (s, 1H), 3.80 (s, 3H), 2.83 (s, 3H);13C NMR (100 MHz, CDCl3): δ 168.98, 157.90, 147.56, 136.99, 133.29, 129.85, 129.65, 127.13, 123.90, 121.97, 120.16, 119.27, 113.56, 112.40, 110.97, 55.21, 47.13, 30.95; ESI-MS (m/z): 343.0446 [M + H]+.
N-((1H-Indol-3-yl)(phenyl)methyl)-N-methylbenzenamine (4d)
Brown solid, mp 189-191°C;1H NMR (400 MHz, DMSO-d
6): δ 10.01 (s, 1H), 7.57 (s, 1H), 7.35 (d, J = 8.0 Hz, 1H), 7.26-7.20 (m, 4H), 7.17-7.14 (m, 2H), 7.09-6.86 (m, 3H), 6.60 (d, J = 2.0 Hz, 3H), 5.53 (s, 1H), 2.79 (s, 3H);13C NMR (100 MHz, CDCl3): δ 147.7, 144.9, 133.0, 130.1, 129.8, 129.0, 128.2, 127.2, 124.0, 122.0, 120.7, 120.1, 119.3, 112.4, 111.0, 48.0, 31.0; ESI-MS (m/z): 313.0450 [M + H]+.
N-((1H-Indol-3-yl)(4-hydroxy phenyl)methyl)-N-methylbenzenamine (4e)
Brown solid, m.p. 139-140°C;1H NMR (400 MHz, CDCl3): δ 7.929 (s, 3H), 7.41-7.01 (m, 7H), 6.75-6.57 (m, 4H), 5.84 (s, 1H), 5.31 (s, 1H), 2.83 (s, 3H);13C NMR (100 MHz, CDCl3): δ 153.8, 136.8, 133.5, 130.5, 130.1, 129.9, 127.1, 123.9, 123.6, 122.0, 120.0, 119.3, 115.1, 112.3, 111.1, 47.1, 39.5, 31.0; ESI-MS (m/z): 329.0347 [M + H]+.
N-((4-Hydroxy-3-bromophenyl)(1H-indol-3-yl)methyl)-N-methylbenzenamine (4f)
Brown solid, m.p. 187-189°C;1H NMR (400 MHz, CDCl3): δ 7.97 (s, 1H), 7.38-7.19 (m, 4H), 7.08-6.93 (m, 5H), 6.59 (s, 3H), 5.50 (s, 1H), 2.84 (s, 3H);13C NMR (100 MHz, CDCl3): δ 150.3, 147.6, 138.5, 136.9, 132.0, 129.7, 129.6, 127.0, 123.9, 123.6, 122.6, 122.1, 119.9, 119.4, 115.7, 112.6, 111.1, 110.1, 46.9, 31.0; ESI-MS (m/z): 406.9101 [M + H]+.
N-((1H-Indol-3-yl)(3-methoxyphenyl)methyl)-N-methylbenzenamine (4g)
Brown solid, m.p. 136-139°C;1H NMR (400 MHz, CDCl3): δ 7.939 (s, 2H), 7.43-7.22 (m, 3H), 7.20-7.17 (m, 3H), 7.08-6.86 (m, 2H), 6.84-6.81 (m, 2H), 6.57 (d, J = 7.6 Hz, 2H), 5.56 (s, 1H), 3.75 (s, 3H), 2.83 (s, 3H);13C NMR (100 MHz, CDCl3): δ 159.5, 148.5, 147.6, 146.5, 145.8, 136.7, 132.9, 129.7, 127.1, 123.9, 123.6, 122.0, 121.6, 120.1, 120.0, 115.0, 112.5, 111.2, 110.1, 55.5, 48.0, 31.0; ESI-MS (m/z): 343.0968 [M + H]+.
N-((1H-Indol-3-yl)(2,4-dimethoxyphenyl)methyl)-N-methylbenzenaminen (4h)
Brown solid, m.p. 123-126°C;1H NMR (400 MHz, CDCl3): δ 7.91 (s, 1H), 7.34-7.27 (m, 2H), 7.16-6.92 (m, 4H), 6.57-6.37 (m, 4H), 5.59 (s, 1H), 3.79 (s, 6H), 2.83 (s, 3H);13C NMR (100 MHz, CDCl3): δ 159.9, 157.9, 147.3, 136.8, 130.2, 130.0, 129.7, 125.7, 125.0, 123.9, 121.8, 120.2, 119.1, 112.4, 112.3, 110.9, 103.8, 95.6, 55.7, 55.3, 39.1, 31.1; ESI-MS (m/z): 373.0427 [M + H]+.
N-Methyl-N-((1-methyl-1H-indol-3-yl)(phenyl)methyl)benzenamine (4i)
Brown solid, mp 189-191°C;1H NMR (400 MHz, CDCl3): δ 7.28-7.22 (m, 8H), 7.04 (d, J = 8.0 Hz, 4H), 6.58-6.45 (m, 3H), 5.59 (s, 1H), 3.71 (s, 3H), 2.84 (s,3H);13C NMR (100 MHz, CDCl3): δ 129.73, 128.97, 128.71, 128.35, 128.18, 125.94, 124.55, 122.32, 121.67, 121.52, 121.52, 120.18, 119.04, 118.72, 112.37, 109.06, 94.27, 47.90, 32.68, 30.93. ESI-MS (m/z): 327.055 [M + H]+.
N-((4-Chlorophenyl)(1-methyl-1H-indol-3-yl)methyl)-N-methylbenzenamine (4j)
Brown solid, m.p. 208-210°C;1H NMR (400 MHz, CDCl3): δ 7.29-7.18 (m, 7H), 7.03 (d, J = 8.0 Hz, 3H), 6.57 (d, J = 4.0 Hz, 4H), 6.42 (s, 1H), 5.54 (s, 1H), 3.71 (s, 3H), 2.84 (s, 3H);13C NMR (100 MHz, CDCl3): δ 147.8, 143.5, 137.5, 132.5, 131.6, 130.9, 130.3, 130.2, 129.7, 129. 6, 128.7, 128.5, 128.3, 121.7, 120.5, 118.9, 118.6, 112.6, 112.4, 109.2, 47.3, 32.7, 30.9. ESI-MS (m/z): 361.002 [M + H]+.
N-Methyl-N-((1-methyl-1H-indol-3-yl)(p-tolyl)methyl)benzenamine (4k)
Brown solid, m.p. 202-204°C;1H NMR (400 MHz, CDCl3): δ 7.31-7.26 (m, 3H), 7.19-7.01 (m, 8H), 6.57 (d, J = 8.0 Hz, 2H), 6.46 (s, 1H), 5.56 (s, 1H), 3.71 (s, 3H), 2.84 (s, 3H), 2.35 (s, 3H);13C NMR (100 MHz, CDCl3): δ 147.6, 142.0, 137.5, 135.3, 133.9, 129.7, 128.9, 128.8, 128.7, 127.5, 121.5, 120.2,119.2, 118.7, 112.4, 109.0, 47.5, 32.7, 31.0, 21.1; ESI-MS (m/z): 341.066 [M + H]+.
N-((1H-indol-3-yl)(3-nitrophenyl)methyl)-N-methylbenzenamine (4l)
Brown solid, m.p. 193-194°C;1H NMR (400 MHz, CDCl3): δ 8.13-8.07 (m, 3H), 7.59 (d, J = 8.0 Hz, 1H), 7.46-7.38 (m, 2H), 7.21 (d, J = 8.0 Hz, 2H), 7.06-7.02 (m, 3H), 6.66-6.57 (m, 3H), 5.68 (s, 1H), 2.84 (s, 3H);13C (100 MHz, CDCl3): δ 148.1, 147.8, 146.8, 136.5, 134.9, 130.9, 129.4, 128.8, 126.4, 123.8, 123.5, 122.1, 121.1, 119.4, 119.4, 119.1, 112.3, 112.2, 111.0, 47.5, 30.6; ESI-MS (m/z): 358.007 [M + H]+.
N-((5-Bromo-1H-indol-3-yl)(phenyl)methyl)-N-methylbenzenamine (4m)
Brown solid, m.p. 207-209°C;1H NMR (400 MHz, CDCl3): δ 8.07 (s, 1H), 7.39 (s, 1H), 7.27-7.23 (m, 7H), 7.02 (d, J = 8.0 Hz, 2H), 6.58 (d, J = 8.0 Hz, 3H), 5.52 (s, 1H), 2.83 (s, 3H);13C NMR (100 MHz, CDCl3): δ 147.5, 144.3, 135.4, 132.7, 129.7, 128.9, 128.3, 126.2, 125.2, 125.0, 122.5, 120.4, 112.7, 112.5, 47.7, 31.1; ESI-MS (m/z): 390.9823 [M + H]+ and 392.9105 [M + 2 + H]+.
N-((5-Methoxy-1H-indol-3-yl)(4-methoxyphenyl)methyl)-N-methylbenzenamine (4n)
Brown solid, m.p. 203-205°C;1H NMR (400 MHz, DMSO-d
6): δ 10.62 (s, 1H), 7.24-7.20 (m, 3H), 7.09 (d, J = 4.0 Hz, 1H), 6.91 (d, J = 8.0 Hz, 1H), 6.81 (d, J = 8.0 Hz, 2H), 6.77 (s, 1H), 6.70-6.66 (m, 3H), 6.60-6.53 (m, 1H), 6.43 (d, J = 8.0 Hz, 1H), 5.66 (s, 1H), 3.68 (s, 3H), 3.44 (s, 3H), 2.48 (s, 3H);13C NMR (100 MHz, DMSO-d
6): δ 157.8, 153.1, 137.7, 132.3, 129.9, 129.7, 129.4, 127.4, 124.7, 118.5, 113.8, 112.5, 111.9, 111.0, 102.0, 55.7, 55.4, 47.0, 30.4; ESI-MS (m/z): 373.1681 [M + H]+.
N-((5-Methoxy-1H-indol-3-yl)(p-tolyl)methyl)-N-methylbenzenamine (4o)
Brown solid m.p. 197-199°C;1H NMR (400 MHz, DMSO-d
6): δ 10.60 (s, 1H), 7.21 (d, J = 4.0 Hz, 3H), 7.06 (d, J = 8.0 Hz, 3H), 6.91 (d, J = 4.0 Hz, 1H), 6.77 (s, 1H), 6.69-6.66 (m, 3H), 6.59-6.52 (m, 1H), 6.42 (d, J = 8.0 Hz, 1H), 5.66 (s, 1H), 3.57 (s, 3H), 2.48 (s, 3H), 2.23 (s, 3H);13C NMR (100 MHz, DMSO-d
6): δ 153.1, 148.9, 142.5, 135.0, 132.3, 129.5, 129.1, 128.9, 128.7, 127.5, 124.7, 118.3, 112.4, 111.9, 110.9, 102.0, 55.7, 47.4, 30.4, 21.1; ESI-MS (m/z): 357.1747 [M + H]+.
N-((5-Bromo-1H-indol-3-yl)(p-tolyl)methyl)-N-methylbenzenamine (4p)
Brown solid, m.p. 195-197°C;1H NMR (400 MHz, DMSO-d
6): δ 11.02 (s, 1H), 7.29 (d, J = 8.0 Hz, 1H), 7.19 (d, J = 4.0 Hz, 1H), 7.11 (d, J = 4.0 Hz, 1H), 7.08-7.00 (m, 4H), 6.89 (d, J = 4.0 Hz, 2H), 6.75 (d, J = 8.0 Hz, 1H), 6.68 (d, J = 4.0 Hz, 1H), 6.42 (d, J = 8.0 Hz, 2H), 5.39 (s, 1H), 2.48 (s, 3H), 2.22 (s, 3H);13C NMR (100 MHz, DMSO-d
6): δ 148.7, 142.4, 135.7, 135.3, 131.7, 129.4, 129.2, 128.7, 126.0, 123.9, 121.7, 119.4, 114.0, 112.0, 111.3, 47.0, 30.4, 21.1; ESI-MS (m/z): 405.0683 [M + H]+ and 407.072 [M + 2 + H]+.
4-Chloro-N-((4-chlorophenyl)(5-methoxy-1H-indol-3-yl)methyl)benzenamine (4q)
Brown solid, m.p. 190-191°C;1H NMR (400 MHz, DMSO-d
6): δ 11.02 (s,1H), 7.29 (d, J = 4.0 Hz, 1H), 7.19 (s, 1H), 7.11 (d, J = 4.0 Hz, 1H), 7.07 (d, J = 4.0 Hz, 2H), 6.89 (d, J = 4.0 Hz, 2H), 6.83 (d, J = 8.0 Hz, 3H), 6.67 (s, 1H), 6.43 (d, J = 4.0 Hz, 2H), 5.39 (s, 1H), 3.69 (s, 3H), 2.47(s, 3H);13C NMR (100 MHz, DMSO-d
6): δ 157.8, 148.6, 137.4, 135.8, 131.7, 129.8, 129.4, 128.9, 126.0, 123.9, 121.8, 119.3, 114.0, 112.0, 111.1, 55.4, 46.6, 30.4; ESI-MS (m/z): 421.0695 [M + H]+.
N-((4-Chlorophenyl)(5-methoxy-1H-indol-3-yl)methyl)-N-methylbenzenamine (4r)
Brown solid, m.p. 201-203°C;1H NMR (400 MHz, DMSO-d
6): δ 10.60 (s, 1H), 7.31-7.28 (m, 5H), 7.22-7.17 (m, 2H), 6.91 (s, 1H), 6.79 (s, 1H), 6.69 (s, 2H), 6.52 (s, 1H), 6.43 (d, J = 4.0 Hz, 2H), 5.73 (s, 1H), 3.30 (s, 3H), 2.47(s, 3H);13C NMR (100 MHz, DMSO-d
6): δ 153.2, 148.9, 144.6, 132.3, 131.2, 130.8, 130.6, 129.5, 128.4, 127.3, 125.3, 125.2, 124.8, 117.7, 112.6, 112.0, 111.1, 55.7, 47.3, 30.3; ESI-MS (m/z): 377.1223 [M + H]+.
N-((4-chlorophenyl)(5-methoxy-1H-indol-3-yl)methyl)benzenamine (4s)
Brown solid, m.p. 198-201°C;1H NMR (400 MHz, MeOH) δ 7.258-7.164 (m, 6H), 6.95 (d, J = 8.0 Hz, 2H), 6.73-6.55 (m, 3H), 6.53 (d, J = 10.0 Hz, 2H), 5.47 (s, 1H), 3.61 (s, 3H);13C NMR (100 MHz, DMSO-d
6): δ 154.7, 148.3, 141.3, 132.3, 130.9, 129.3, 128.9, 128.7, 128.2, 123.4, 117.5, 112.5, 112.3, 112.1, 110.7, 109.5, 55.3; ESI-MS (m/z): 363.21 [M + H]+, 365.20 [M + H +2]+.
Anti-bacterial assay
Zone of inhibition assay was performed at 128 μg mL-1 concentration for all the compounds (4a-s) using disk diffusion method [17]. For this purpose, Mueller-Hilton (HiMedia, India) agar medium was prepared and sterilized by autoclaving at 121°C at 15 psi for 15 min. The medium was poured into sterile Petri dishes under aseptic conditions using laminar air flow chamber. After the solidification of medium, the suspension of the test organism (106 cfu mL-1) was swabbed onto the individual media plates using a sterile glass spreader. A sterile disk (9-mm diameter) impregnated with compound was placed over media surface and the plates were incubated at 37°C for 18-24 h under dark conditions. The determination as to whether the organism is susceptible, intermediate, or resistant was made by measuring the size of zone of inhibition in comparison with standard antibiotic.
MIC assay was performed to determine the lowest concentration of compound necessary to inhibit a test organism. MIC values were evaluated for all the compounds (4a-t) using broth microdilution method as per the standard guidelines [18]. Assay was carried out for the compounds at 0.5, 1.0, 2.0, 4.0, 8.0, 16.0, 32.0, 64.0, 128.0 μg mL-1 concentrations. A set of tubes containing Muller Hilton broth medium with different concentrations of compounds were prepared. The tubes were inoculated with bacterial cultures (106 cfu mL-1) and incubated on a rotary shaker (180 rpm) at 37°C for 18-24 h under dark conditions. MIC values were defined as lowest concentration of compound that prevented the visible growth of bacteria after the incubation period. All the experiments were performed in three replicates.