Indole is considered as the chief constituent of the alkaloids present in plants (Somei & Yamada, 2003; Gupta et al., 2007). It contains versatile biological activities such as antiviral potential (Cihan-Üstündağ et al., 2019; Xu & Lv, 2009; Ran et al., 2010; Ghosh et al., 2008; Williams et al., 2004), anticancer activity (Gaikwad et al., 2019; El Sayed et al., 2018; Sreenivasulu et al., 2019; Andreani et al., 2008; Slater et al., 2001), antimicrobial study (Chodvadiya et al., 2019; Shirinzadeh et al., 2018; Mathada & Mathada, 2009; Gurkok et al., 2009), antimycobacterial activity (Cihan-Üstündağ et al.; Karah et al., 2007), free radical scavenging activity and antifungal potential (Demurtas et al., 2019; Dekker et al., 1975). The most important pharmacological activities of drugs containing indole moiety are antimicrobial activity and free radical scavenging activity. There are several indole containing structures which are reported by researchers as a good antimicrobial and antifungal agents. Among them, ethyl-3-Indolylacrylate, 5-Bromo-3-(2-Cyanovinyl) indole and 3-(2-Nitrovinyl)indole were those compounds that were active against microbes (Whitehead & Whitesitt, 1974). Haloindoles were found to be effective in between the concentration of 10–100
The purity of all the synthesized derivatives was determined by thin-layer chromatography on pre-coated silica gel aluminum sheets (Type 60 GF254, Merck) and detection of the spots was done by iodine vapors and UV-Lamp. The melting point was determined by the melting point apparatus and all the melting points were uncorrected. The FTIR spectra were recorded on 470-Shimadzu FTIR spectrophotometer and wavenumber values were expressed in cm−1. NMR spectra were recorded in DMSO-
The mixture of 4-Nitrophenylhydrazine (15 g, 98.03 mmol) and 2-Aminoacetophenone (13.23 g, 98.03 mmol) was refluxed in acetic acid/ethanol mixture for 3 h to give 4-Nitro substituted phenyl hydrazone of 2-Aminoacetophenone. Methanesulfonic acid (220 ml) was heated to 80 °C and phosphorus pentoxide (30 g) was added very slowly with stirring till its complete dissolution (mixture A). The 4-Nitro substituted phenylhydrazone of 2-Aminoacetophenone (20 g) was added slowly to mixture A. The temperature of the reaction was maintained between 80 and 100 °C. Then the solution was heated further at 80 °C for half an hour. Then the reaction mixture cooled to room temperature and then it was poured over crushed ice already containing sodium hydroxide. Then the solid precipitate was filtered, it was washed thoroughly with water, and it was dried to give the crude product which was recrystallized from ethanol. (Yield: 16.20 g, 90 %, M.P. 140–142 °C)
Compound
(Yield: 12.47 g, 75 %, M.P. 200–202 °C)
Phosphorous oxychloride (9.72 g, 63.52 mmol) was added slowly to
(11.44 g, 83 %, M.P. 233–235 °C)
An equimolar mixture of 10-nitro-
Compound 3b (1 g) was refluxed with Aniline (0.31 g).
(Yield: 1.05 g, 84 %); M.P. 251–252 °C; Brown color
FTIR (νmax, cm−1) 3107 (Aromatic C-H str.), 2938 (Aliphatic C-H str.), 1600 (C=N str.), 1540, 1515 (Aromatic C=C ring str.), 1493, 1350 (N=O str.), 1329 (Aromatic C-N str.); 1H NMR (300 MHz, DMSO-
Compound 3b (1 g) was refluxed with 2-Chloroaniline (0.43 g).
(Yield: 1.13 g, 82%); M.P. 256–257 °C; Reddish brown color
FTIR (νmax, cm−1) 3050 (Aromatic C-H str.), 2800 (Aliphatic C-H str.), 1600 (C=N) str.), 1544,1492 (Aromatic C=C ring str.), 1451, 1364 (N=O str.), 1330 (Aromatic C-N str.); 750 (C-Cl str.); 1H NMR (300 MHz, DMSO-
Compound 3b (1 g) was refluxed with 3-Chloroaniline (0.43 g).
(Yield: 1.16 g, 85 %); M.P. 254–255 °C; Dark brown color
FTIR (νmax, cm−1) 3029 (Aromatic C-H str.), 2929 (Aliphatic C-H str.), 1590 (C=N str.), 1500, 1458 (Aromatic C=C ring str.), 1554, 1326 (N=O str.), 1238 (Aromatic C-N str.), 752 (C-Cl str.); 1H NMR (300 MHz, DMSO-
Compound 3b (1 g) was refluxed with 4-Chloroaniline (0.43 g).
(Yield: 1.13 g, 83 %); M.P. 253–254 °C; Reddish brown color
FTIR (νmax, cm−1) 3046 (Aromatic C-H str.), 2928 (Aliphatic C-H str.), 1624 (C=N str.), 1590, 1500 (Aromatic C=C ring str.), 1550, 1350 (N=O str.), 1283 (Aromatic C-N str.), 750 (C-Cl str.); 1H NMR (300 MHz, DMSO-
Compound 3b (1 g) was refluxed with 2-Nitroaniline (0.47 g).
(Yield: 1.12 g, 80 %); M.P. 245–246 °C; Grey color
FTIR (νmax, cm−1) 3020 (Aromatic C-H str.), 2954 (Aliphatic C-H str.), 1620 (C=N str.), 1585,1450 (Aromatic C=C ring str.), 1520, 1322 (N=O str.), 1220 (C-N str.); 1H NMR (300 MHz, DMSO-
Compound 3b (1 g) was refluxed with 3-Nitroaniline (0.47 g).
(Yield: 1.18 g, 84 %); M.P. 250–252 °C; Greyish green color
FTIR (νmax, cm−1) 3046 (Aromatic C-H str.), 2958 (Aliphatic C-H str.), 1651 (C=N str.), 1574, 1419 (Aromatic C=C ring str.), 1508, 1360 (N=O str.), 1174 (C-N str.); 1H NMR (300 MHz, DMSO-
Compound 3b (1 g) was refluxed with 4-Nitroaniline (0.47 g).
(Yield: 1.22 g, 87 %); M.P. 252–253 °C; Reddish brown color
FTIR (νmax, cm−1) 3085 (Aromatic C-H str.), 2937 (Aliphatic C-H str.), 1670 (C=N str.), 1610,1421 (Aromatic C=C ring str.), 1554, 1326 (N=O str.), 1292 (C-N str.); 1H NMR (300 MHz, DMSO-
Compound 3b (1 g) was refluxed with 4-Fluoroaniline (0.37 g).
(Yield: 1.06 g, 81 %); M.P. 258–259 °C; Grey color
FTIR (νmax, cm−1) 3080 (Aromatic C-H str.), 2920 (Aliphatic C-H str.), 1606 (C=N str.), 1558, 1325, (N=O str.), 1433, 1421 (Aromatic C=C ring str.), 1292 (Aromatic C-N str.), 1180 (C-F str.); 1H NMR (300 MHz, DMSO-
Compound 3b (1 g) was refluxed with 4-Bromoaniline (0.59 g).
(Yield: 1.30 g, 85 %); M.P. 240–241 °C; Dark brown color
FTIR (νmax, cm−1) 3073 (Aromatic C-H str.), 2927 (Aliphatic C-H str.), 1613 (C=N str.), 1588,1458 (Aromatic C=C ring str.), 1518, 1323, (N=O str.) 1232 (Aromatic C-N str.), 609 (C-Br str.); 1H NMR (300 MHz, DMSO-
3b (1 g) was refluxed with 2-Chloro-4-nitroaniline (0.58 g).
(Yield: 1.33 g, 88 %); M.P. 256–257 °C; Reddish brown color
FTIR (νmax, cm−1) 3028 (Aromatic C-H str.), 2853 (Aliphatic C-H str.), 1642 (C=N str.), 1563, 1430 (Aromatic C=C ring str.), 1523,1308 (N=O str.), 1283 (C-N str.), 752 (C-Cl str.); 1H NMR (300 MHz, DMSO-
Compound 3b (1 g) was refluxed with 4-Chloro-2-nitroaniline (0.58 g).
(Yield: 1.29 g, 85 %; M.P. 255–256 °C; Light brown color
FTIR (νmax, cm−1) 3023 (Aromatic C-H str.), 2910 (Aliphatic C-H str.), 1612 (C=N str.), 1553, 1423 (Aromatic C=C ring str.), 1513, 1330 (N=O str.), 1285 (C-N str.), 685 (C-Cl str.); 1H NMR (300 MHz, DMSO-
Antibacterial activity for all derivatives was done by agar well diffusion method. Ciprofloxacin was used as the reference compound. One gram-negative bacterium
All the synthesized derivatives were evaluated for their free radical scavenging potential using 0.1 mmol solution of DPPH in methanol. Solutions were kept in darkness for half an hour to form free radicals. Solution of different concentrations were prepared (10, 20, 30, 40 and 50 μg/ml) for test compounds as well as standard. Then, 1 ml of each test compound solution was added with the same volume of DPPH solution, then the mixture was mixed vigorously and kept for half an hour in the darkroom. The absorbance of all solutions was measured at a wavelength of 517 nm. The same procedure was performed in the triplicate manner (n = 3) and the average of the three readings was shown in the results with standard deviation. The same procedure was carried out with the solutions of ascorbic acid. Percent inhibition was calculated using equation 1 (Kaushik et al., 2016; Malviya et al., 2017).
Hydrogen peroxide was used to produce hydroxyl radicals. All the solutions of test and standard compounds were prepared as above and concentrations of hydroxyl radicals were observed at 230 nm (Ningsih et al., 2016). The procedure was performed in a triplicate manner and the average of the three readings was shown in the results with standard deviation. Percent inhibition was calculated using
In the first step, phenyl hydrazone of 2-Aminoacetophenone was synthesized by the reflux of equimolar quantities of 4-Nitrophenyl hydrazine and 2-Aminoacetophenone in acetic acid/ethanol mixture for 3 h. Then, 2-(5-nitro-1
The characterization of all derivatives was done by IR, 1H NMR, 13C NMR, mass spectral data, and elemental analysis. In the IR spectra of compounds
In the 13C NMR spectra of all compounds, carbons present in aromatic rings gave signals in the region of 102–160 ppm. The signal of N-C=N carbon atom of the quinazoline ring was observed at 136 ppm. The signal due to the C-Cl carbon was observed at 127–135 ppm. The signal due to the C-F carbon was observed at 161.40 ppm. The signal due to the C-Br carbon was observed at 121.63 ppm. Mass spectral data and elemental analysis were complying with the structures of all compounds. [M+ 2] peaks were found for compounds having Cl group.
All indoloquinazoline derivatives
The result for antibacterial activity was shown (Table 1), compound
Zone of inhibition values for derivatives (4b1–4b11) at 100 μg/ml and 150 μg/ml
2 | 7 | 3 | 5 | |
2 | 8 | 4 | 9 | |
4 | 8 | 6 | 10 | |
5 | 10 | 4 | 9 | |
3 | 7 | 4 | 9 | |
6 | 10 | 7 | 10 | |
6 | 12 | 7 | 12 | |
5 | 10 | 7 | 13 | |
13 | 18 | 12 | 17 | |
12 | 15 | 13 | 17 | |
6 | 14 | 8 | 14 | |
20 | 18 |
All the newly synthesized indoloquinazoline derivatives were screened for free radical scavenging activity by DPPH method. Sample solutions were prepared to have concentrations of 10, 20, 30, 40 and 50 μg/ml. Ascorbic acid was taken as a standard antioxidant. Compounds
DPPH free radical scavenging activity of compounds 4b1–4b11
45.8 ± 1.21 | 54.01 ± 1.09 | 61.60 ±0.98 | 66.89 ± 1.23 | 78.01 ± 2.31 | 87.67 | |
17.26 ± 4.36 | 20.98 ± 0.43 | 26.20 ± 0.69 | 36.84 ± 2.86 | 41.26 ± 1.50 | 189.43 | |
4.01 ± 2.43 | 14.75 ± 0.79 | 24.29 ± 1.71 | 35.24 ± 0.89 | 37.94 ± 1.67 | 150.70 | |
14.75 ± 0.42 | 19.67 ± 0.91 | 27.60 ± 0.46 | 32.92 ± 0.75 | 36.64 ± 0.45 | 178.80 | |
7.42 ± 0.75 | 15.66 ± 0.30 | 20.88 ± 0.62 | 30.82 ± 0.45 | 35.13 ± 0.75 | 174.22 | |
16.06 ± 0.45 | 21.68 ± 0.30 | 28.01 ± 0.30 | 34.93 ± 1.08 | 45.98 ± 0.75 | 141.77 | |
4.31 ± 0.75 | 13.65 ± 0.62 | 23.18 ± 1.50 | 26.70 ± 0.75 | 32.92 ± 0.62 | 176.32 | |
50.19 ± 1.05 | 54.71 ± 0.45 | 65.45 ± 0.75 | 73.49 ± 0.90 | 76.70± 0.75 | 25.18 | |
50.59 ± 1.17 | 53.61 ± 0.79 | 57.02 ± 0.62 | 60.94 ± 0.45 | 67.66 ± 0.75 | 28.09 | |
12.74 ± 1.83 | 20.57 ± 0.96 | 28.41 ± 0.75 | 32.92 ± 0.92 | 36.04 ± 0.74 | 158.38 | |
27.40 ± 0.21 | 30.41 ± 0.60 | 33.12 ± 0.79 | 35.63 ± 0.62 | 38.75 ± 0.45 | 203.73 | |
44.67 ± 0.96 | 50.00 ± 0.62 | 56.62 ± 0.82 | 59.83 ± 0.45 | 67.46 ± 0.60 | 44.22 |
All the derivatives were also screened for antioxidant activity by the H2O2 method. Sample solutions were prepared to have concentrations of 10, 20, 30, 40 and 50 μg/ml. Ascorbic acid was taken as a standard antioxidant. Compounds
H2O2 free radical scavenging activity of compounds 4b1–4b11
44.35 ± 1.21 | 55.32 ± 1.34 | 62.09 ± 1.51 | 66.72 ± 1.10 | 77.02 ± 1.33 | 88.23 | |
4.02 ± 0.57 | 10.18 ± 0.75 | 18.11 ± 0.75 | 24.52 ± 0.37 | 32.32 ± 0.57 | 224.22 | |
1.88 ± 0.37 | 7.67 ± 1.32 | 16.98 ± 0.37 | 20.37 ± 0.75 | 26.03 ± 0.75 | 220.12 | |
9.68 ± 0.57 | 20.25 ± 0.57 | 24.02 ± 1.32 | 28.80 ± 0.57 | 34.08 ± 0.94 | 191.10 | |
2.26 ± 0.37 | 8.55 ± 0.94 | 15.34 ± 0.78 | 20.00 ± 0.75 | 28.17 ± 0.94 | 213.82 | |
1.25 ± 0.57 | 7.92 ± 1.13 | 12.20 ± 1.15 | 19.24 ± 0.37 | 23.52 ± 0.78 | 234.89 | |
4.90 ± 0.99 | 10.06 ± 0.57 | 19.37 ± 0.57 | 23.64 ± 0.94 | 28.17 ± 0.57 | 205.62 | |
44.90 ± 0.37 | 54.08 ± 0.57 | 60.37 ± 0.37 | 65.15 ± 0.94 | 76.10 ± 0.94 | 39.46 | |
43.52 ± 0.57 | 54.00 ± 1.15 | 59.11 ± 0.57 | 66.03 ± 0.75 | 72.83 ± 1.13 | 44.47 | |
8.30 ± 0.75 | 13.96 ± 0.37 | 20.12 ± 0.57 | 28.80 ± 0.57 | 30.81 ± 0.57 | 178.53 | |
4.90 ± 0.75 | 8.30 ± 0.37 | 13.20 ± 0.37 | 20.75 ± 0.37 | 24.90 ± 0.75 | 219.88 | |
47.04 ± 0.57 | 53.58 ± 1.13 | 57.10 ± 0.57 | 63.39 ± 0.75 | 74.08 ± 0.57 | 35.61 |
The present study suggests that all the indole derivatives that were containing substituted anilines having electron-withdrawing groups at para positions were reported to have good antioxidant and antibacterial activities. Compounds
Synthesis of some newer