Abstract
Background
Based on bioisosteric similarities with thiacetazone, a series of 7-chloro-4-aminoquinoline derivatives have been designed and synthesized. The target compounds were elucidated by NMR, mass, and FTIR spectral data. All synthesized compounds were evaluated for their in vitro antitubercular activity against Mycobacterium tuberculosis H37Rv (MTB), and human dermal fibroblast cell lines were used to assess toxicity of selected ligands.
Results
All of the designed compounds showed inhibition of MTB with MIC of 1.56–50 μM. Among the tested compounds, 7c and 7g proved to be most potent MTB inhibitors (MIC = 1.56 μM).
Conclusions
The outcome of present study suggests that most of the synthesized compounds are sensitive to Mycobacterium tuberculosis and showed acceptable range for molecular parameters. Thus, 7-chloro-4-aminoquinolines could be a useful lead for the development of new MTB inhibitory agents.
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Background
Tuberculosis (TB) is considered to be the most widespread and lethal communicable disease in the world. TB is caused by an infection with the slow-growing Mycobacterium tuberculosis (MTB). According to the World Health Organization, there were an estimated 10.0 million new TB cases in 2017 with 1.3 million TB deaths. In addition, more than 65% of the world’s TB cases occur in Southeast Asia, the West Pacific, and Africa [1]. Commonly used TB treatment regimen DOTS (directly observed therapy short-course) requires taking INH, PZA, and RIF for 60 days followed by an additional 120 days of treatment with INH and RIF [2, 3]. Due to the resistance acquired by the Mycobacterium tuberculosis against various first-line drugs [4], there is a need to find new and better drug candidates for the treatment. Quinoline and analogs have always attracted the attention of industrial and academic personnel. It is being reported as having many interesting biological properties such as antimalarial [5, 6], cytotoxic [7, 8], anti-inflammatory [9, 10], antiviral [11, 12], antimicrobial [13, 14], antifungal [15], anti-Alzheimer [16], antiprotozoal [17], and antitubercular [18] activities. Quinoline is a basic pharmacophore used for the design of antitubercular agents, like mefloquine, ciprofloxacin, moxifloxacin, and bedaquiline which are already in the market [18]. Furthermore, thiosemicarbazone and semicarbazone derivatives are frequently used scaffolds in biology-orientated synthesis which possess a huge variety of pharmacological activities including an antibacterial, antifungal, antitubercular, and anticancer activity [19, 20].
In view of the above observations, the diverse pharmacological activities of these pharmacophores prompted us to synthesize the target compounds, presuming that their hybrid in a one-structural entity could potentially yield new heterocyclic compounds with significant synergistic antitubercular properties. Hence, with an aim to develop promising antitubercular agents, a series of novel 7-chloro-N-phenylquinolin-4-amine derivatives containing thiosemicarbazone and semicarbazone [19, 20], scaffolds were designed and synthesized (Fig. 1). In the present study, all target ligands are screened for their in vitro antitubercular activity against Mycobacterium tuberculosis H37Rv (MTB), and human dermal fibroblast cell line were used for toxicity study.
Design strategy for the quinoline analogs containing thiosemicarbazone/semicarbazone scaffolds
Method
Synthesis of thiosemicarbazide and semicarbazide derivatives
An equimolar amount of thiosemicarbazide or semicarbazide hydrochloride (20 mmol) and substituted α,β-unsaturated ketones (4a-i, and 5a-i) (20 mmol) [21] were dissolved in isopropyl alcohol, and glacial acetic acid (0.1 ml) was used as a catalyst. The mixture was stirred at 85 °C for 36 h. On completion of the reaction, as monitored by TLC, the reaction mixture was cooled. Precipitate was filtered by suction and washed with cooled isopropyl alcohol and solvent ether. The structures of target compounds were established by using different spectroscopic techniques.
Antitubercular activity assay
Microplate alamar blue assay (MABA) method [22, 23] was adopted to evaluate antitubercular activities (Additional file 1).
Cytotoxic assay
MTT (3-(4, 5-dimethylthiazo-2-yl)-2,5-diphenyl-tetrazolium bromide) [24] assay protocol was used to assess the toxicity studies of selected analogs.
Results
Synthesis and spectral data
((E)-1-(4-((7-chloroquinolin-4-yl)amino)phenyl)-3-(p-tolyl)allylidene)hydrazinecarbothioamide(6a)
Yield: 55%; m.p.: 196–198 °C; IR (KBr cm−1): 3362 (NH2), 1593 (C=C), 1351 (C=S), 1170 (OCH3); 1H-NMR (400 MHz, DMSO-d6) δ (ppm) = 2.62 (s, 3H, CH3), 7.05 (s, 1H, ArH), 7.37 (d, 2H, J = 8.4 Hz, ArH), 7.56 (m, 4H, ArH), 7.72–7.69 (m, 3H, ArH, -C=HC-), 7.83 (d, 1H, J = 15.6 Hz, -C=HC-), 7.85 (s, 1H, NH2), 7.88 (s, 1H, NH2), 7.91 (s, 1H, ArH), 8.18 (s, 1H, ArH), 8.42 (s, 1H, ArH), 8.55 (s, 1H, ArH), 9.95 (s, 1H, NH), 10.83 (s, 1H, =N-NH-C); LC-MS M/Z: 473 [M + H]+.
2-((E)-1-(4-((7-chloroquinolin-4-yl)amino)phenyl)-3-(4-methoxyphenyl)allylidene)hydrazinecarbothioamide(6b)
Yield: 53%; m.p.: 190–192 °C; IR (KBr cm−1): 3367 (NH2), 1593 (C=C), 1350 (C=S), 1172 (OCH3); 1H-NMR (400 MHz, DMSO-d6) δ (ppm) 3.82 (s, 3H, OCH3), 7.02 (s, 1H, ArH), 7.34 (d, 2H, J = 8.4 Hz, ArH), 7.53 (m, 4H, ArH), 7.70–7.63 (m, 3H, ArH, -C=HC-), 7.85 (d, 1H, J = 15.6 Hz, -C=HC-), 7.87 (s, 1H, NH2), 7.89 (s, 1H, NH2), 7.88 (s, 1H, ArH), 8.18 (s, 1H, ArH), 8.40 (s, 1H, ArH), 8.58 (s, 1H, ArH), 9.93 (s, 1H, NH), 10.81 (s, 1H, =N-NH-C); LC-MS M/Z: 489 [M + H]+.
2-((E)-1-(4-((7-chloroquinolin-4-yl)amino)phenyl)-3-(3,4-dimethoxyphenyl)allylidene)hydrazinecarbothioamide(6c)
Yield: 56%; m.p.: 148–150 °C; IR (KBr cm−1): 3367 (NH2), 1265 (OCH3), 1350 (C=S); 1H-NMR (400 MHz, DMSO-d6) δ (ppm) = 3.81 (s, 3H, OCH3), 3.86 (s, 3H, −OCH3), 7.02 (s, 1H, ArH), 7.45 (s, 1H, ArH), 7.38 (s, 1H, ArH), 7.53 (m, 3H, ArH), 7.72–7.69 (m, 3H, ArH, -C=HC-), 7.85 (d, 1H, J = 15.6 Hz, -C=HC-), 7.91 (s, 1H, NH2), 7.96 (s, 1H, NH2), 7.98 (s, 1H, ArH), 8.23 (s, 1H, ArH), 8.47 (s, 1H, ArH), 8.61 (s,1H, ArH), 9.91 (s, 1H, NH), 10.82 (s, 1H, =N-NH-C); LC-MS M/Z: 519 [M + H]+.
2-((E)-1-(4-((7-chloroquinolin-4-yl)amino)phenyl)-3-(3,4,5-trimethoxyphenyl)allylidene)hydrazinecarbothioamide(6d)
Yield: 66%; m.p.: 138–140 °C; IR (KBr cm−1): 3343 (NH2), 1593 (C=C), 1352 (C=S), 1128 (OCH3), 1128 (OCH3); 1H-NMR (400 MHz, DMSO-d6) δ (ppm) = 3.76 (s, 3H, OCH3), 3.86 (s, 6H, -OCH3), 6.42 (s, 1H, ArH), 7.27 (d, 2H, J = 8.4 Hz ArH), 7.42 (s, 1H, ArH), 7.52 (s, 1H, ArH), 7.71–7.64 (m, 3H, ArH, -C=HC-), 7.89 (d, 1H, J = 15.6 Hz, -C=HC-), 7.92 (s, 1H, NH2), 7.95 (s, 1H, NH2), 7.98(s, 1H, ArH), 8.23 (s, 1H, ArH), 8.40 (s, 1H, ArH), 8.59 (s, 1H, ArH), 9.68 (s, 1H, NH), 10.72 (s, 1H, =N-NH-C); LC-MS M/Z: 549 [M + H]+.
2-((E)-3-(4-chlorophenyl)-1-(4-((7-chloroquinolin-4-yl)amino)phenyl)allylidene)hydrazinecarbothioamide(6e)
Yield: 73%; m.p.: 142–144 °C; IR (KBr cm−1): 3365 (NH2), 1554 (C=C), 1350 (C=S); 1H-NMR (400 MHz, DMSO-d6) δ (ppm) = 7.08 (s, 1H, ArH), 7.51–7.749 (m, 3H, ArH, -C=HC-), 7.62 (d, 2H, J = 8.8 Hz, ArH), 7.70 (d,1H, J = 15.6 Hz -C=HC-), 7.78 (s, 1H, ArH), 7.89 (s, 1H, NH2), 7.91 (s, 1H, NH2), 7.95 (s, 1H, ArH), 8.01 (d, 2H, J = 8.4 Hz, ArH), 8.20 (d, 2H, J = 8.8 Hz, ArH), 8.41 (s, 1H, ArH), 8.62 (s, 1H, ArH), 10.08 (s, 1H, NH), 11.06 (s, 1H, =N-NH-C); LC-MS M/Z: 494 [M + H]+.
2-((E)-1-(4-((7-chloroquinolin-4-yl)amino)phenyl)-3-(4-fluorophenyl)allylidene)hydrazinecarbothioamide(6f)
Yield: 58%; m.p.: 178–180 °C; IR (KBr cm−1): 3354 (NH2), 1575 (C=C), 1351 (C=S); 1H-NMR (400 MHz, DMSO-d6) δ (ppm) = 7.01 (s, 1H, ArH), 7.32–7.24 (m, 3H, ArH, -C=HC-), 7.52 (d, 2H, J = 8.8 Hz, ArH), 7.64 (d,1H, J = 15.6 Hz -C=HC-), 7.66 (s, 1H, NH2), 7.75 (s, 1H, NH2), 7.98 (s, 1H, ArH), 7.98–7.95 (m, 3H, ArH), 8.23–8.20 (m, 2H, ArH), 8.46 (s, 1H, ArH), 8.60 (s, 1H, ArH), 10.02 (s, 1H, NH), 11.03 (s, 1H, =N-NH-C); LC-MS M/Z: 477 [M + H]+.
2-((E)-3-(4-bromophenyl)-1-(4-((7-chloroquinolin-4-yl)amino)phenyl)allylidene)hydrazinecarbothioamide(6 g)
Yield: 66%; m.p.: 186–188 °C; IR (KBr cm−1): 3375 (NH2), 1580 (C=C), 1352 (C=S); 1H-NMR (400 MHz, DMSO-d6) δ (ppm) = 6.53 (s, 1H, ArH), 6.86 (d, 1H, J = 15.6 Hz, -C=HC-), 6.99 (d, 1H, J = 12.6 Hz, -C=HC-), 7.07 (s, 1H, ArH), 7.30 (s, 1H, ArH), 7.47 (s, 1H, ArH), 7.62 (s, 1H, NH2), 7.77–7.70 (m, 4H, ArH,), 7.81 (s, 1H, NH2) 7.85 (d, 2H, J = 8.4 Hz, ArH), 8.20 (s, 1H, ArH), 8.30 (s, 1H, ArH), 8.51 (s, 1H, ArH), 10.10 (s, 1H, NH), 11.07 (s, 1H, =N-NH-C); LC-MS M/Z: 538 [M + H]+.
2-((E)-1-(4-((7-chloroquinolin-4-yl)amino)phenyl)-3-(4-nitrophenyl)allylidene)hydrazinecarbothioamide(6 h)
Yield: 47%; m.p.: 216–218 °C; IR (KBr cm−1): 3361 (NH2), 1540 (C=C), 1350 (C=S); 1H-NMR (400 MHz, DMSO-d6) δ (ppm) = 7.20 (d, 1H, J = 5.6 Hz, ArH), 7.23–7.10 (m, 4H, ArH, NH2), 7.47 (d, 2H, J = 8.8 Hz, ArH), 7.71–7.60 (m, 3H, ArH, -C=HC-), 7.96 (s, 1H, NH2), 8.13 (s, 1H, ArH), 8.26 (s, 1H, ArH), 8.44–8.38 (m, 4H, ArH), 9.87 (s, 1H, NH), 11.69 (s, 1H, =N-NH-C); LC-MS M/Z: 504 [M + H]+.
2-((E)-1-(4-((7-chloroquinolin-4-yl)amino)phenyl)-3-(4-hydroxyphenyl)allylidene)hydrazinecarbothioamide(6i)
Yield: 50%; m.p.: 230–232 °C; IR (KBr cm−1): 3365 (NH2), 1567 (C=C), 1353 (C=S); 1H-NMR (400 MHz, DMSO-d6) δ (ppm) = 7.20 (s, 1H, ArH), 7.27 (d, 2H, J = 8.8 Hz, ArH), 7.45–7.40 (m, 3H, ArH, CH=C), 7.73–7.61 (m, 3H, ArH, -C=HC-), 7.93 (s, 1H, NH2), 7.96 (s, 1H, NH2), 8.13 (s, 1H, ArH), 8.25 (d, 1H, ArH), 8.44–8.38 (m, 4H, ArH), 9.86 (s, 1H, NH), 9.88 (s, 1H, OH), 11.55 (s, 1H, =N-NH-C); LC-MS M/Z: 475 [M + H]+.
2-((E)-1-(4-((7-chloroquinolin-4-yl)amino)phenyl)-3-(p-tolyl)allylidene)hydrazinecarboxamide(7a)
Yield: 72%; m.p.: 148–150 °C; IR (KBr cm−1): 3425 (NH2), 1693 (C=O); 1H-NMR (400 MHz, DMSO-d6) δ (ppm) 2.88 (s, 3H, CH3), 6.51 (s, 2H, NH2), 6.83–6.81 (d, 2H, J = 8.8 Hz, ArH), 6.86 (s, 1H, ArH), 6.90 (s, 1H, ArH), 7.60 (d, 2H, J = 8.8, ArH), 7.73 (d, 1H,, J = 15.6 Hz, -C=HC-), 7.83 (d, 1H, J = 15.6 Hz, -C=HC-), 7.85 (s, 1H, ArH), 7.93 (d, 2H, J = 8.4 Hz, ArH), 8.06 (d, 2H, J = 8.4 Hz, ArH), 8.57 (s, 1H, ArH), 8.69 (s, 1H, ArH), 9.41 (s, 1H, NH), 10.91(s, 1H, =N-NH-C); LC-MS M/Z: 457 [M + H]+.
2-((E)-1-(4-((7-chloroquinolin-4-yl)amino)phenyl)-3-(4-methoxyphenyl)allylidene)hydrazinecarboxamide(7b)
Yield: 65%; m.p.: 238–240 °C; FTIR (KBr) cm−1: 3450 (NH2), 1685 (C=O), 1251 (OCH3); 1H-NMR (400 MHz, DMSO-d6) δ (ppm) = 3.72 (s, 3H, OCH3), 6.48 (s, 2H, NH2), 6.88 (d, 2H, J = 8.8 Hz, ArH), 6.96 (s, 1H, ArH), 7.13 (d, 2H, J = 8.8, ArH), 7.51 (d, 2H, J = 8.4 Hz, ArH), 7.75 (d, 1H, J = 15.6 Hz, -C=HC-), 7.78 (d, 1H, J = 15.6 Hz, -C=HC-), 7.85 (s, 1H, ArH), 7.93 (d, 2H, J = 8.8 Hz, ArH), 8.0 (s, 1H, ArH), 8.54 (s, 1H, ArH), 8.72 (s, 1H, ArH), 9.38 (s, 1H, NH), 10.76 (s, 1H, =N-NH-C); LC-MS M/Z: 473 [M + H]+.
2-((E)-1-(4-((7-chloroquinolin-4-yl)amino)phenyl)-3-(3,4-dimethoxyphenyl)allylidene)hydrazinecarboxamide(7c)
Yield: 56%; m.p.: 214–216 °C; IR (KBr cm−1): 3442 (NH2), 1681 (C=O), 1255 (OCH3); 1H-NMR (400 MHz, DMSO-d6) δ (ppm) = 3.72 (s, 3H, OCH3), 3.81 (s, 3H, -OCH3), 6.50 (s, 2H, NH2), 6.81 (s, 1H, ArH), 7.20–6.96 (m, 3H, J = 8.4, ArH), 7.53 (d, 2H, J = 8.8 Hz, ArH), 7.79 (d, 1H, J = 15.6 Hz, -C=HC-), 7.81 (d, 1H, J = 15.6 Hz, -C=HC-), 7.85 (s, 1H, ArH), 7.95 (d, 2H, J = 8.4 Hz, ArH), 8.07 (s, 1H, ArH), 8.56 (s, 1H, ArH), 8.72 (s, 1H, ArH), 10.20 (s, 1H, NH), 10.81 (s, 1H, =N-NH-C); LC-MS M/Z: 503 [M + H]+.
2-((E)-1-(4-((7-chloroquinolin-4-yl)amino)phenyl)-3-(3,4,5-trimethoxyphenyl)allylidene)hydrazinecarboxamide(7d)
Yield: 52%; m.p.: 238–240 °C; IR (KBr cm−1): 3442 (NH2), 1671 (C=O), 1251 (OCH3); 1H-NMR (400 MHz, DMSO-d6) δ (ppm) = 3.82 (s, 6H, OCH3), 3.87 (s, 3H, OCH3), 6.49 (s, 2H, NH2), 6.76 (s, 1H, ArH), 6.88 (s, 1H, ArH), 7.54 (d, 2H, J = 8.8 Hz, ArH), 7.71 (s, 1H, ArH), 7.81 (d, 1H, J = 15.6 Hz, -C=HC-), 7.83 (d, 1H, J = 15.6 Hz, -C=HC-), 7.93 (d, 2H, J = 8.8, ArH), 8.02 (s, 2H, ArH), 8.54 (s, 1H, ArH), 8.76 (s, 1H, ArH), 10.09 (s, 1H, NH), 11.02 (s, 1H, =N-NH-C); LC-MS M/Z: 533 [M + H]+.
2-((E)-3-(4-chlorophenyl)-1-(4-((7-chloroquinolin-4-yl)amino)phenyl)allylidene)hydrazinecarboxamide(7e)
Yield: 45%; m.p.: 174–176 °C; IR (KBr cm−1): 3335 (NH2,), 1680 (C=O), 1226 (C-N); 1H-NMR (400 MHz, DMSO-d6) δ (ppm) = 6.48 (s, 2H, NH2), 7.22 (s, 1H, Ar-H), 7.54 (d, 2H, J = 8.4, Ar-H), 7.62 (d, 2H, J = 8.4 Hz, Ar-H), 7.76 (s, 1H, Ar-H), 7.87 (d, 1H, J = 15.6 Hz, −CH=C), 7.89 (d, 1H, J = 15.6 Hz, −CH=C), 7.95 (d, 2H, J = 8.8, Ar-H), 7.99 (s, 1H, Ar-H), 8.05 (s, 1H, Ar-H), 8.29 (d, 2H, J = 8.8 Hz, Ar-H), 8.62 (s, 1H, Ar-H), 10.17 (s, 1H, NH), 10.76 (s, 1H, =N-NH-C); LC-MS M/Z: 477 [M + H]+.
2-((E)-1-(4-((7-chloroquinolin-4-yl)amino)phenyl)-3-(4-fluorophenyl)allylidene)hydrazinecarboxamide(7f)
Yield: 70%; m.p.: 230–232 °C; IR (KBr cm−1): 3433 (NH2), 1686 (C=O), 1370 (C-N); 1H-NMR (400 MHz, DMSO-d6) δ (ppm) = 6.54 (s, 2H, NH2), 7.22 (s, 1H, ArH), 7.44 (d, 2H, J = 8.4, ArH), 7.52 (d, 2H, J = 8.8 Hz, ArH), 7.73 (d, 1H, J = 15.6 Hz, -C=HC-), 7.76 (s, 1H, A-H), 7.83 (d, 1H, J = 15.6 Hz, -C=HC-), 7.91 (d, 2H, J = 8.8, ArH), 7.7 (s, 1H, ArH), 7.80–7.85 (m, 3H, ArH), 8.01 (s, 1H, ArH), 10.11 (s, 1H, −NH), 10.41 (s, 1H, =N-NH-C); LC-MS M/Z: 461 [M + H]+.
2-((E)-3-(4-bromophenyl)-1-(4-((7-chloroquinolin-4-yl)amino)phenyl)allylidene)hydrazinecarboxamide(7 g)
Yield: 51%; m.p.: 244–246 °C; IR (KBr cm−1): 3452 (NH2,), 1680 (C=O), 1251 (C-N); 1H-NMR (400 MHz, DMSO-d6) δ (ppm) = 6.52 (s, 2H, NH2), 7.16 (s, 1H, ArH), 7.61(d, 2H, J = 8.4, ArH), 7.68 (d, 2H, J = 8.4 Hz, ArH), 7.74 (d, 1H, J = 15.6 Hz, -C=HC-), 7.78 (s, 1H, ArH), 7.81 (d, 1H, J = 15.6 Hz, -C=HC-), 7.90 (d, 2H, J = 8.0, ArH), 8.00 (s, 1H, ArH), 8.06 (s, 1H, ArH), 8.27 (d, 2H, J = 8.8 Hz, ArH), 8.62 (s, 1H, ArH), 10.18 (s, 1H, NH), 10.83 (s, 1H, =N-NH-C); LC-MS M/Z: 522 [M + H]+.
2-((E)-1-(4-((7-chloroquinolin-4-yl)amino)phenyl)-3-(4-nitrophenyl)allylidene)hydrazinecarboxamide(7 h)
Yield: 70%; m.p.: 196–198 °C; IR (KBr cm−1): 3398 (NH2), 1675 (C=O), 1585 (NO2), 1371 (C- N); 1H-NMR (400 MHz, DMSO-d6) δ (ppm) = 6.50 (s, 2H, NH2), 7.20 (s, 1H, ArH), 7.42 (d, 2H, J = 8.8 Hz, ArH), 7.62 (d, 2H, J = 8.8 Hz, ArH), 7.80 (d, 1H, J = 15.6 Hz, -C=HC-), 7.83 (d, 1H, J = 15.6 Hz, -C=HC-), 7.9 (s, 1H, ArH), 8.02 (d, 2H, J = 8.4, ArH), 8.16 (s, 1H, ArH), 8.29 (d, 2H, J = 8.4 Hz, ArH), 8.53 (s, 1H, ArH), 8.62 (s, 1H, ArH), 10.30 (s, 1H, NH), 10.76 (s, 1H, =N-NH-C); LC-MS M/Z: 488 [M + H]+.
2-((E)-1-(4-((7-chloroquinolin-4-yl)amino)phenyl)-3-(4-hydroxyphenyl)allylidene)hydrazinecarboxamide(7i)
Yield: 45%; m.p.: 240–242 °C; IR (KBr cm−1): 3360 (NH2), 1680 (C=O), 1251 (C-N); 1H-NMR (400 MHz, DMSO-d6) δ (ppm) = 6.53 (s, 2H, NH2), 7.23 (s, 1H, ArH), 7.56 (d, 2H, J = 8.8 Hz, ArH), 7.68 (d, 2H, J = 8.8 Hz, ArH), 7.78 (d, 1H, J = 15.6 Hz, -C=HC-), 7.81 (d, 1H, J = 15.6 Hz, -C=HC-), 7.7 (s, 1H, ArH), 8.0 (d, 2H, J = 8.2, ArH), 8.16 (s, 1H, ArH), 8.26 (d, 2H, J = 8.4 Hz, ArH), 8.51 (s, 1H, ArH), 8.60 (s, 1H, ArH), 9.89 (s, 1H, OH), 10.32 (s, 1H, NH), 10.71 (s, 1H, =N-NH-C); LC-MS M/Z: 459 [M + H]+.
2-((E)-1-(3-((7-chloroquinolin-4-yl)amino)phenyl)-3-(p-tolyl)allylidene)hydrazinecarbothioamide(8a)
Yield: 50%; m.p.: 238–240 °C; IR (KBr cm−1): 3350 (NH2), 1575 (C=C), 1352 (C=S), 1261 (C-N); 1H-NMR (400 MHz, DMSO-d6) δ (ppm) = 2.62 (s, 3H, CH3), 6.99 (s, 1H, ArH), 7.20–7.15 (m, 4H, ArH), 7.25 (d, 1H, J = 15.6 Hz, -C=HC-), 7.37 (d, 2H, J = 8.4 Hz, ArH), 7.50 (d, 1H, J = 15.6 Hz, -C=HC-), 7.59 (d, 2H, J = 8.4 Hz, ArH), 7.76 (s, 1H, ArH), 7.85 (s, 1H, NH2), 7.88 (s, 1H, NH2), 7.92 (s, 1H, ArH), 8.26 (s, 1H, ArH), 8.46 (s, 1H, ArH), 9.25 (s, 1H, NH), 11.25 (s, 1H, =N-NH-C); LC-MS M/Z: 473 [M + H]+.
2-((E)-1-(3-((7-chloroquinolin-4-yl)amino)phenyl)-3-(4-Methoxyphenyl)allylidene)hydrazinecarbothioamide(8b)
Yield: 43%; m.p.: 210–212 °C; IR (KBr cm−1): 3365 (NH2), 1568 (C=C), 1350 (C=S), 1255 (OCH3); 1H-NMR (400 MHz, DMSO-d6) δ (ppm) = 3.81 (s, 3H, OCH3), 7.42–7.35 (m, 4H, ArH), 7.67–7.58 (m, 3H, ArH, −NH2), 7.71 (s, 1H, NH2), 7.72 (s, 1H, ArH), 7.73 (d, 1H, J = 15.6 Hz, -C=HC-), 7.76 (d, 1H, J = 15.6 Hz, -C=HC-), 7.84 (d, 2H, J = 8.8 Hz, ArH), 7.93 (s, 1H, ArH), 8.04 (s, 1H, ArH), 8.43 (s, 1H, ArH), 8.50 (s, 1H, ArH), 9.26 (s, 1H, NH), 11.75 (s, 1H, =N-NH-C); LC-MS M/Z: 489 [M + H]+.
2-((E)-1-(3-((7-chloroquinolin-4-yl)amino)phenyl)-3-(3,4-dimethoxyphenyl)allylidene)hydrazinecarbothioamide(8c)
Yield: 41%; m.p.: 120–122 °C; IR (KBr cm−1): 3655 (NH2), 1516 (C=C), 1313 (C=S), 1267 (C-N), 1560 (C=C), 1183 (OCH3); 1H-NMR (400 MHz, DMSO-d6) δ (ppm) = 3.81 (s, 3H, OCH3), 3.84 (s, 3H, −OCH3), 7.39 (s, 1H, ArH), 7.41 (s, 1H, ArH), 7.65 (s, 1H, −NH2), 7.70–7.66 (m, 3H, ArH), 7.73 (d, 1H, J = 15.6 Hz, -C=HC-), 7.80 (d, 1H, J = 15.6 Hz, -C=HC-), 7.92–7.85 (m, 3H, ArH), 7.94 (s, 1H, ArH), 8.01 (s, 1H, ArH), 8.1 (s, 1H, −NH2), 8.14 (s, 1H, ArH), 8.49 (s, 1H, ArH), 9.71 (s, 1H, NH), 11.95 (s, 1H, =N-NH-C); LC-MS M/Z: 519 [M + H]+.
2-((E)-1-(3-((7-chloroquinolin-4-yl)amino)phenyl)-3-(3,4,5-trimethoxyphenyl)allylidene)hydrazinecarbothioamide(8d)
Yield: 60%; m.p.: 240–242 °C; IR (KBr cm−1): 3352 (NH2), 1560 (C=C), 1352 (C=S), 1246 (C-N), 1182 (OCH3); 1H-NMR (400 MHz, DMSO-d6) δ (ppm) = 3.70 (s, 3H, OCH3), 3.84 (s, 6H, OCH3), 7.22 (s, 1H, ArH), 7.64–7.58 (m, 4H, ArH), 7.67 (s, 1H, ArH), 7.71(d, 1H, J = 15.6, -C=HC-), 7.84 (s, 1H, NH2), 7.85 (d, 1H, J = 15.6, -C=HC-), 7.91 (s, 1H, NH2), 7.97 (s 2H, ArH), 8.02 (s, 1H, ArH), 8.43 (s, 1H, ArH), 8.51 (s, 1H, ArH), 9.28 (s, 1H, NH), 10.96 (s, 1H, =N-NH-C); LC-MS M/Z: 549 [M + H]+.
2-((E)-3-(4-chlorophenyl)-1-(3-((7-chloroquinolin-4-yl)amino)phenyl)allylidene)hydrazinecarbothioamide(8e)
Yield: 66%; m.p.: 212–214 °C; IR (KBr cm−1): 3338 (NH2), 1597 (C=C), 1350 (C=S), 1261 (C-N); 1H-NMR (400 MHz, DMSO-d6) δ (ppm) = 7.21 (s, 1H, ArH), 7.46 (d, 1H, J = 15.6 Hz, -C=HC-), 7.52 (d, 2H, J = 8.4 Hz, ArH), 7.59 (d,1H, J = 15.6 Hz, -C=HC-), 7.61 (d, 2H, J = 8.4 Hz, ArH), 7.79–7.63 (m, 4H, ArH), 7.81 (s, 1H, NH2), 7.85 (s, 1H, ArH), 7.93 (s, 1H, NH2), 8.20 (s, 1H, ArH), 8.24 (s, 1H, ArH), 8.47(s, 1H, ArH), 9.29 (s, 1H, NH), 11.12 (s, 1H, =N-NH-C); LC-MS M/Z: 494 [M + H]+.
2-((E)-1-(3-((7-chloroquinolin-4-yl)amino)phenyl)-3-(4-fluorophenyl)allylidene)hydrazinecarbothioamide(8f)
Yield: 60%; m.p.: 234–236 °C; IR (KBr cm−1): 3358 (NH2), 1591 (C=C), 1350 (C=S); 1H-NMR (400 MHz, DMSO-d6) δ (ppm) = 7.21 (s, 1H, ArH), 7.41–7.34 (m, 4H, ArH), 7.48 (d,1H, J = 15.6 Hz, -C=HC-), 7.57 (d, 2H, J = 8.4 Hz, ArH), 7.63 (d, 2H, J = 8.4 Hz, ArH), 7.76 (d, 1H, J = 15.6 Hz, -C=HC-), 7.88 (s, 1H, NH2), 7.83 (s, 1H, ArH), 7.95 (s, 1H, NH2), 8.22 (s, 1H, ArH), 8.31 (s, 1H, ArH), 8.45 (s, 1H, ArH), 9.25 (s, 1H, NH), 11.22 (s, 1H, =N-NH-C); LC-MS M/Z: 477 [M + H]+.
2-((E)-3-(4-bromophenyl)-1-(3-((7-chloroquinolin-4-yl)amino)phenyl)allylidene)hydrazinecarbothioamide(8 g)
Yield: 55%; m.p.: 238–240 °C; IR (KBr cm−1): 3364 (NH2), 1575 (C=C), 1355 (C=S); 1H-NMR (400 MHz, DMSO-d6) δ (ppm) = 7.21 (s, 1H, ArH), 7.45–7.37 (m, 4H, ArH), 7.48 (d, 1H, J = 15.6 Hz, -C=HC-), 7.53 (d, 2H, J = 8.4 Hz, ArH), 7.68 (d, 2H, J = 8.4 Hz, ArH), 7.75 (d, 1H, J = 15.6 Hz, -C=HC-), 7.83 (s, 1H, NH2), 7.91 (s, 1H, ArH), 7.96 (s, 1H, NH2), 8.14 (s, 1H, ArH), 8.23 (s, 1H, ArH), 8.46 (s, 1H, ArH), 9.23 (s, 1H, NH), 11.21 (s, 1H, =N-NH-C); LC-MS M/Z: 538 [M + H]+.
2-((E)-1-(3-((7-chloroquinolin-4-yl)amino)phenyl)-3-(4-nitrophenyl)allylidene)hydrazinecarbothioamide(8 h)
Yield: 47%; m.p.: 218–220 °C; IR (KBr cm−1): 3356 (NH2), 1593 (NO2), 1550 (C=C), 1350 (C=S); 1H-NMR (400 MHz, DMSO-d6) δ (ppm) = 7.20 (s, 1H, ArH), 7.52–7.43 (m, 4H, ArH), 7.56 (d, 2H, J = 8.4 Hz, ArH), 7.61 (d, 1H, J = 15.6 Hz, -C=HC-), 7.64 (d, 2H, J = 7.6 Hz, ArH), 7.69 (d, 1H, J = 15.6 Hz, -C=HC-), 7.72 (s, 1H, NH2), 7.96 (s, 1H, NH2), 8.16 (s, 1H, ArH), 8.31 (s, 1H, ArH), 8.36 (s, 1H, ArH), 8.48 (s, 1H, ArH), 9.68 (s, 1H, NH), 11.23 (s, 1H, =N-NH-C); LC-MS M/Z: 504 [M + H]+.
2-((E)-1-(3-((7-chloroquinolin-4-yl)amino)phenyl)-3-(4-hydroxyphenyl)allylidene)hydrazinecarbothioamide(8i)
Yield: 57%; m.p.: 250–242 °C; IR (KBr cm−1): 3478 (OH), 3360 (NH2), 1590 (C=C), 1361 (C=S), 1265 (C-N); 1H-NMR (400 MHz, DMSO-d6) δ (ppm) = 7.2 (s, 1H, ArH), 7.20–7.15 (m, 4H, ArH), 7.25 (d, 1H, J = 15.6 Hz, -C=HC-), 7.38 (d, 2H, J = 8.4 Hz, ArH), 7.50 (d, 1H, J = 15.6 Hz, -C=HC-), 7.61 (d, 2H, J = 8.4 Hz, ArH), 7.76 (s, 1H, ArH), 7.87 (s, 1H, NH2), 7.93 (s, 1H, NH2), 7.97 (s, 1H, ArH), 8.31 (s, 1H, ArH), 8.43 (s, 1H, ArH), 9.35 (s, 1H, NH), 9.98 (s, 1H, OH), 11.22 (s, 1H, =N-NH-C); LC-MS M/Z: 475 [M + H]+.
2-((E)-1-(3-((7-chloroquinolin-4-yl)amino)phenyl)-3-(p-tolyl)allylidene)hydrazinecarboxamide(9a)
Yield: 55%; m.p.: 192–194 °C; IR (KBr cm−1): 3365 (NH2), 1690 (C=O), 1575 (C=C), 1261(C-N); 1H-NMR (400 MHz, DMSO-d6) δ (ppm) = 2.61 (s, 3H, CH3), 6.73 (s, 2H, NH2), 7.16 (s, 1H, ArH), 7.33–7.21 (m, 4H, ArH), 7.36 (d, 1H, J = 15.6 Hz, -C=HC-), 7.41 (d, 2H, J = 8.4 Hz, ArH), 7.53 (d, 1H, J = 15.6 Hz, -C=HC-), 7.61 (d, 2H, J = 8.4 Hz, ArH), 7.82 (s, 1H, ArH), 7.91 (s, 1H, ArH), 8.32 (s, 1H, ArH), 8.41 (s, 1H, ArH), 9.33 (s, 1H, NH), 10.93 (s, 1H, =N-NH-C); LC-MS M/Z: 457 [M + H]+.
2-((E)-1-(3-((7-chloroquinolin-4-yl)amino)phenyl)-3-(4-methoxyphenyl) allylidene)hydrazinecarboxamide(9b)
Yield: 40%; m.p.: 188–190 °C; IR (KBr cm−1): 3365 (NH2), 1685 (C=O), 1590 (C=C), 1235 (OCH3); 1H-NMR (400 MHz, DMSO-d6) δ (ppm) = 3.83 (s, 3H, OCH3), 6.69 (s, 2H, NH2), 7.52–7.43 (m, 4H, ArH), 7.65 (d, 2H, ArH), 7.68 (s, 1H, ArH), 7.71 (d, 1H, J = 15.6 Hz, -C=HC-), 7.75 (d, 1H, J = 15.6 Hz, -C=HC-), 7.81 (d, 2H, J = 8.8 Hz, ArH), 7.93 (s, 1H, ArH), 8.01 (s, 1H, ArH), 8.42 (s, 1H, ArH), 8.47 (s, 1H, ArH), 9.34 (s, 1H, NH), 11.10 (s, 1H, =N-NH-C); LC-MS M/Z: 473 [M + H]+.
2-((E)-1-(3-((7-chloroquinolin-4-yl)amino)phenyl)-3-(3,4-dimethoxyphenyl)allylidene)hydrazinecarboxamide(9c)
Yield: 51%; m.p.: 254–256 °C; IR (KBr cm−1): 3648 (NH2), 1680 (C=O), 1580 (C=C), 1215 (OCH3); 1H-NMR (400 MHz, DMSO-d6) δ (ppm) = 3.86 (s, 3H, OCH3), 3.89 (s, 3H, −OCH3), 6.69 (s, 2H, −NH2), 7.53 (s, 1H, ArH), 7.68–7.59 (m, 3H, ArH), 7.71 (d, 1H, J = 15.6 Hz, -C=HC-), 7.79 (d, 1H, J = 15.6 Hz, -C=HC-), 7.91–7.83 (m, 3H, ArH), 7.94 (s, 1H, ArH), 8.10 (s, 1H, ArH), 8.23 (s, 1H, ArH), 8.49 (s, 1H, ArH), 8.51(s, H, ArH), 9.36 (s, 1H, NH), 11.13 (s, 1H, =N-NH-C); LC-MS M/Z: 503 [M + H]+.
2-((E)-1-(3-((7-chloroquinolin-4-yl)amino)phenyl)-3-(3,4,5-trimethoxyphenyl) allylidene)hydrazinecarboxamide(9d)
Yield: 60%; m.p.: 258–260 °C; IR (KBr cm−1): 3363 (NH2), 1690 (C=O), 1565 (C=C), 1248 (C-N), 1189 (OCH3); 1H-NMR (400 MHz, DMSO-d6) δ (ppm) = 3.76 (s, 3H, OCH3), 3.85 (s, 6H, -OCH3), 6.79 (s, 2H, NH2), 7.41 (s, 1H, ArH), 7.81–7.7 (m, 4H, ArH), 7.92 (s, 1H, ArH), 7.83 (d, 1H, J = 15.6, -C=HC-), 7.87 (d, 1H, J = 15.6, -C=HC-), 7.96 (s 2H, ArH), 8.13 (s, 1H, ArH), 8.41 (s, 1H, ArH), 8.48 (s, 1H, ArH), 9.33 (s, 1H, NH), 10.83 (s, 1H, =N-NH-C); LC-MS M/Z: 533 [M + H]+.
2-((E)-3-(4-chlorophenyl)-1-(3-((7-chloroquinolin-4-yl)amino)phenyl)allylidene)hydrazinecarboxamide(9e)
Yield: 50%; m.p.: 226–228 °C; IR (KBr cm−1): 3354 (NH2), 1686 (C=O), 1583 (C=C), 1270 (C-N); 1H-NMR (400 MHz, DMSO-d6) δ (ppm) = 6.73 (s, 2H, NH2), 7.13 (s, 1H, ArH), 7.48 (d, 1H, J = 15.6 Hz, -C=HC-), 7.53 (d, 2H, J = 8.4 Hz, ArH), 7.58 (d,1H, J = 15.6 Hz, -C=HC-), 7.65 (d, 2H, J = 8.4 Hz, ArH), 7.81–7.75 (m, 4H, ArH), 7.83 (s, 1H, ArH), 8.22 (s, 1H, ArH), 8.35 (s, 1H, ArH), 8.43 (s, 1H, ArH), 9.31 (s, 1H, NH), 10.86 (s, 1H, =N-NH-C); LC-MS M/Z: 477 [M + H]+.
2-((E)-1-(3-((7-chloroquinolin-4-yl)amino)phenyl)-3-(4-fluorophenyl)allylidene)hydrazinecarboxamide(9f)
Yield: 55%; m.p.: 198–200 °C; IR (KBr cm−1): 3360 (NH2), 1685 (C=O), 1595 (C=C); 1H-NMR (400 MHz, DMSO-d6) δ (ppm) = 6.73 (s, 2H, NH2), 7.28 (s, 1H, ArH), 7.45–7.36 (m, 4H, ArH), 7.49 (d,1H, J = 15.6 Hz, -C=HC-), 7.53 (d, 2H, J = 8.4 Hz, ArH), 7.59 (d, 2H, J = 8.4 Hz, ArH), 7.75 (d, 1H, J = 15.6 Hz, -C=HC-), 7.95 (s, 1H, ArH), 8.26 (s, 1H, ArH), 8.35 (s, 1H, ArH), 8.46 (s, 1H, ArH), 9.29 (s, 1H, NH), 10.98 (s, 1H, =N-NH-C); LC-MS M/Z: 461 [M + H]+.
2-((E)-3-(4-bromophenyl)-1-(3-((7-chloroquinolin-4-yl)amino)phenyl)allylidene)hydrazinecarboxamide(9 g)
Yield: 60%; m.p.: 306–308 °C; IR (KBr cm−1): 3360 (NH2), 1686 (C=O), 1570 (C=C); 1H-NMR (400 MHz, DMSO-d6) δ (ppm) = 6.75 (s, 2H, NH2), 7.14 (s, 1H, ArH), 7.49–7.38 (m, 4H, ArH), 7.52 (d, 1H, J = 15.6 Hz, -C=HC-), 7.63 (d, 2H, J = 8.4 Hz, ArH), 7.71 (d, 2H, J = 8.4 Hz, ArH), 7.79 (d, 1H, J = 15.6 Hz, -C=HC-), 7.93 (s, 1H, ArH), 8.22 (s, 1H, ArH), 8.29 (s, 1H, ArH), 8.45 (s, 1H, ArH), 9.27 (s, 1H, NH), 10.96 (s, 1H, =N-NH-C); LC-MS M/Z: 522 [M + H]+.
2-((E)-1-(3-((7-chloroquinolin-4-yl)amino)phenyl)-3-(4-nitrophenyl)allylidene)hydrazinecarboxamide(9 h)
Yield: 43%; m.p.: 246–248 °C; IR (KBr cm−1): 3360 (NH2), 1690 (C=O), 1595 (NO2), 1565 (C=C); 1H-NMR (400 MHz, DMSO-d6) δ (ppm) = 6.72 (s, 2H, NH2), 7.20 (s, 1H, ArH), 7.53–7.48 (m, 4H, ArH), 7.56 (d 2H, J = 8.4 Hz, ArH), 7.65 (d, 2H, J = 7.6 Hz, ArH), 7.73 (d, 1H, J = 15.6 Hz, -C=HC-), 7.96 (d, 1H, J = 15.6 Hz, -C=HC-), 8.13 (s, 1H, ArH), 8.26 (s, 1H, ArH), 8.33 (s, 1H, ArH), 8.47 (s, 1H, ArH), 9.36 (s, 1H, NH), 10.87 (s, 1H, =N-NH-C); LC-MS M/Z: 488 [M + H]+.
2-((E)-1-(3-((7-chloroquinolin-4-yl)amino)phenyl)-3-(4-hydroxyphenyl)allylidene)hydrazinecarboxamide(9i)
Yield: 43%; m.p.: 234–236 °C; IR (KBr cm−1): 3362 (NH2), 1685 (C=O), 1593 (C=C), 1265(C-N); 1H-NMR (400 MHz, DMSO-d6) δ (ppm) = 6.67 (s, 2H, NH2), 7.10 (s, 1H, ArH), 7.23–7.14 (m, 4H, ArH), 7.27 (d, 1H, J = 15.6 Hz, -C=HC-), 7.49 (d, 2H, J = 8.4 Hz, ArH), 7.62 (d, 1H, J = 15.6 Hz, -C=HC-), 7.73 (d, 2H, J = 8.4 Hz, ArH), 7.98 (s, 1H, ArH), 8.15 (s, 1H, ArH), 8.36 (s, 1H, ArH), 8.46 (s, 1H, ArH), 9.29 (s, 1H, NH), 9.85 (s, 1H, OH), 10.93 (s, 1H, =N-NH-C); LC-MS M/Z: 459 [M + H]+.
Discussions
Chemistry
The reaction sequence employed for synthesis of the title compounds (6a-i), (7a-i), (8a-i), and (9a-i) are illustrated in Scheme 1. Initially, compounds 1-(4-((7-chloroquinolin-4-yl) amino)phenyl)ethanone (2) and 1-(3-((7-chloroquinolin-4-yl)amino) phenyl)ethanone (3) were prepared with slight modification on the basis of the previously reported methods [21]. Their IR spectra showed the appearance of characteristic band at around 3564–3651 cm−1 attributed to amino (NH) group and carbonyl (C=O) stretching frequency at around 1684 cm−1, while their 1H NMR spectrum indicated singlet signal at around δ 11.16 and 11.33 ppm for amine (NH) protons. Further, these compounds were confirmed by D2O exchange experiment. The key intermediate α, β-unsaturated ketones (chalcones) (4a-i) and (5a-i) were synthesized by reacting 1-(4-((7-chloroquinolin-4-yl)amino)phenyl)ethanone (2) or 1-(3-((7-chloroquinolin-4-yl)amino)phenyl)ethanone (3) with appropriate aldehydes by conventional base-catalyzed Claisen-Schmidt condensation. The IR spectra of the compounds (4a-i) and (5a-i) showed new band at 1530 cm−1 attributed to an alkene (C=C) group of α, β-unsaturated ketones. In addition, two sets of protons with a trans coupling constant (J = 16 Hz) were present at δ 7.72 and 8.05 ppm which confirms the completion of Claisen-Schmidt condensation reactions. Reaction of chalcones (4a-i) and (5a-i) with thiosemicarbazide and semicarbazide hydrochloride in dry isopropyl alcohol and the presence of glacial acetic acid for 36 h afforded the target thiosemicarbazone (6a-i) and (8a-i) and semicarbazone (7a-i) and (9a-i) derivatives respectively.
Reagents and conditions: (a) dry methanol, reflux 9–10 h; (b) methanol, NaOH, THF, RT; (c) thiosemicarbazide or semicarbazide hydrochloride, dry isopropyl alcohol, and glacial acetic acid, reflux 36 h
The structures of target compounds were established by using different spectroscopic techniques, including FTIR, NMR, and mass spectroscopy. The FTIR spectra of these compounds showed a medium to strong band for C=N stretch which appeared in the range 1620 to 1560 cm−1, C=S absorption band appeared at 1341 to 1356 cm−1, and semicarbazone derivatives showed C=O absorption band at 1661 to 1690 cm−1. In addition, FTIR spectra showed the appearance of characteristic bands at 3350 and 3290 cm−1 assignable for amino (NH) group, while their proton NMR spectrum indicated singlet at around δ 11.69–11.82 ppm for =N-NH-C- proton. The two amino (-NH2) protons appeared as two singlets in the range at 7.67 and 8.2 ppm. Finally, formation of these compounds was also evidenced by mass spectral data.
Biological activities
Antitubercular activity
The new thiosemicarbazone derivatives (6a-i) and (8a-i) and semicarbazide compounds (7a-i) and (9a-i) were evaluated against Mycobacterium tuberculosis (MTB) H37Rv (ATCC 27294) by using the microplate alamar blue assay (MABA) [22, 23]. The minimum inhibitory concentration (MIC) was determined for each derivative which was measured as the minimum concentration of the compound required to completely inhibit the bacterial growth. Isoniazid, pyrazinamide, and ciprofloxacin were used as standard drugs for comparison. Antitubercular activity results are summarized in Table 1. From the results, it was observed that among the tested compounds, the most active compounds 7c and 7 g exhibited Mycobacterium tuberculosis inhibition at 1.56 μM as compared to standard isoniazid (MIC = 1.56 μM). Three compounds 7a, 7i, and 9a inhibited MTB with MIC value of 6.25 μM, when compared to ciprofloxacin (MIC = 12.5 μM) and pyrazinamide (MIC = 50 μM). Nine compounds 6a, 6b, 6d, 6e, 7d, 7e, 8a, 8b, 9b, and 9c are found to be equally active as ciprofloxacin (12.5 μM). When compared to pyrazinamide (50.0 μM), most of the compounds were found to be more active, though 34 compounds were less potent than the first-line antitubercular drug isoniazid. Further, the following features of structure-activity relationship (SAR) of 7-chloro-N-phenylquinolin-4-amine derivatives (6a-i), (7a-i), (8a-i), and (9a-i) have been drawn against the inhibition of Mycobacterium tuberculosis. The thiosemicarbazide (6a-i) compounds with electron donating groups like 4-CH3 (6a), 4-OCH3 (6b), and 3,4,5-OCH3 (6d) have shown activity at 12.5 μM. When the same methoxy group was substituted at C-3 and C-4 positions (3,4-OCH3), the activity decreased to 25 μM as shown by compound 6c. Substitution of the C-4 position by a hydroxyl group (6i) further decreased the activity to 50 μM. Compounds 6f, 6g, and 6h with electron withdrawing groups like F, Br, and NO2 substituted at the C-4 position showed very weak activity (50 μM). However, the 4-chloro substituted compound 6e showed moderate activity (12.5 μM).
Among the semicarbazones (6a-i), compounds 7c and 7g displayed very promising activity at 1.56 μM, which was higher than the activities shown by their thiosemicarbazone counterparts. Compound 7a with an alkyl substituent (4-CH3) showed better activity at 6.25 μM as compared to 6a, whereas compound 7b with an alkoxy (4-OCH3) substituent displayed decreased activity as compared to 6b. Compounds with 3,4,5-(OCH3)3 group (7d) and 4-Cl group (7e) showed activities at 12.5 μM, similar to 6d and 6e. Compound 7g with an electronegative group at position C-4 proved to be the next most potent molecule by exhibiting inhibitory activity at 1.56 μM. Compounds 7h (4-NO2) and 7i (4-OH) displayed better inhibitory activities (12.5 μM and 6.25 μM) as compared to compounds 6h and 6i (50 μM). In the next series, the compound 8a with an electron donating 4-CH3 group has shown inhibitory activity at 12.5 μM. Other compounds 8b, 8c, and 8d with electron donating groups like 4-OCH3, 3,4-(OCH3)2, and 3,4,5-(OCH3)3 have shown inhibitory activity at 25 μM. Compounds with electron accepting substituents at the C-4 position like Cl (8e), Br (8 g), and NO2 (8 h) also showed activity at 25 μM, whereas compounds 8f (with substituent 4-F) and 8i (with substituent 4-OH) showed inhibitory activity at 50 μM. In these meta-substituted compounds, the most potent compound was 9a with a 4-methyl substituent exhibiting activity at 6.25 μM, which was better than that exhibited by 8a. Compounds 9b and 9c with electropositive substituents like 4-OCH3 and 3,4-OCH3 showed inhibitory activities at 12.5 μM, both being better than compound 8b and 8c with activity at 25 μM. Compounds 9d, 9e, 9g, and 9h displayed activities at 25 μM, which was similar to activities shown by 8d, 8e, 8g, and 8h. Compounds 9f and 9i with electronegative substituents 4-F and 4-OH showed better activities at 25 μM when compared with 8f and 8i. With respect to structure-activity relationship, the study revealed that the nature of carbazide and substituent(s) on the phenyl ring greatly affects the antitubercular activity. Thus, the comparative study of thiosemicarbazones and semicarbazones revealed that in general, semicarbazone compounds exhibited better inhibitory activity against Mycobacterium tuberculosis.
In recent years, drug likeness and rule of five models [25,26,27] are a novel approach for better understanding molecular parameters. The obtained results are showing that most of the synthesized compounds have better predicted value of hydrogen bond acceptor, polar surface area, and hydrogen bond donor. According to Lipinski’s rule of five, a biological therapeutic ligand should have number of hydrogen bond accepter atoms of 10 or less (N or O), number of hydrogen bond donor atoms of 5 or less, log p not more than 5, and molecular weight (MW) of 500 or less. The values of calculated drug scores revealed that most of the synthesized analogs have positive drug likeness score; interestingly, compound 7c exhibited promising inhibitory activity against Mycobacterium tuberculosis and highest drug likeness score Table 2.
Cytotoxicity activity assay
The in vitro cytotoxicity of the active compounds (MIC ≤ 12.5 μM Mycobacterium tuberculosis) was evaluated against normal HDF cell line using 3-(4, 5-dimethylthiazo-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) cell proliferation assay. The graphical representation of the cell growth inhibition by the active compounds at a concentration of 50 μM is shown in Table 3. The assay data revealed that none of the active compounds are toxic to the normal cells thus proving the lack of general toxicity.
Conclusion
In conclusion, a series of 7-chloro-N-phenylquinolin-4-amine derivatives (6a-i), (7a-i), (8a-i), and (9a-i) have been designed and synthesized. All synthesized derivatives underwent in vitro antitubercular evaluation against Mycobacterium tuberculosis H37Rv (MTB), and selected analogs were screened for cytotoxicity against normal HDF cell line by MTT cell proliferation assay. The results displayed that among the tested compounds, the most potent antitubercular activity was displayed by 7c and 7g with MIC = 1.56 μM and with low cytotoxicity. Thus, it can be concluded that 7-chloro-N-phenylquinolin-4-amines could be a promising approach for the design of new MTB inhibitory agents.
Availability of data and materials
All the data generated and analyzed during the study are included in the manuscript.
Change history
04 February 2020
Following publication of the original article [1], the authors reported an error in one of the authors’ names.
Abbreviations
- DOTS:
-
Directly observed therapy short-course
- INH:
-
Isoniazid
- MIC:
-
Minimum inhibitory concentration
- MTB:
-
Mycobacterium tuberculosis
- MTT:
-
3-(4, 5-dimethylthiazo-2-yl)-2,5-diphenyl-tetrazolium bromide
- PZA:
-
Pyrazinamide
- RIF:
-
Rifampicin
- TB:
-
Tuberculosis
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Acknowledgements
The authors are grateful to Principal, KLE College of Pharmacy, Belagavi, for providing necessary facilities for the research. The authors are also grateful to the NMR Research center, IISC, Bangalore, India, for providing the spectral data.
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All authors have read and approved the manuscript. SA designed and outlined and contributed to the characterization of the study. KK, SK, RK, and PS managed the synthetic application. MP, SA, and SS contributed to the analytical work.
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The original version of this article was revised: author Sunil Jalalpure’s name was incorrectly published as Sulin Jalalpure.
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Alegaon, S., Kashniyal, K., Kuncolienkar, S. et al. Synthesis and biological evaluation of some 4-aminoquinoline derivatives as potential antitubercular agents. Futur J Pharm Sci 6, 2 (2020). https://doi.org/10.1186/s43094-019-0016-7
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DOI: https://doi.org/10.1186/s43094-019-0016-7