General

Analytical grade chemicals were purchased from Lova Chemie PVT LTD and used without additional purification. Melting points were determined by Thiele tube expressed in °C. The progress of the reactions were monitored with TLC and spots were visualized using UV light at 254 nm. Silica gel (60–120 mesh, Merck) has been used for column chromatography. The synthesized compounds were characterized on the basis of physical and spectral analysis. The UV–Vis spectra of synthesized compounds were recorded on Double-beam UV–Vis spectrophotometer using DCM and MeOH as blank solvents and λmax values were expressed by nm. The 1H and 13C NMR spectra of the synthesized compounds were recorded on Bruker avance 400 MHz NMR spectrophotometer using chloroform-d or methanol-d4 as the solvent and the values are expressed in δ ppm.

Experimental procedures

The synthesis of the compounds synthesized in the present work was in accordance with the protocol reported by Zeleke et al. [18] with slight modifications.

Synthesis of N-(4-flouro phenyl) acetamide (3)

4-Fluoro aniline (15 mL), acetic anhydride (22 mL), zinc powder (0.1 g, 0.0016 mmol) and glacial acetic acid (23 mL) were added in 250 mL round bottom flask. The mixture was boiled by refluxing using water condenser for 2 h. Then, it was cooled to room temperature and poured into 200 mL of crushed ice water. The solid product, N-(4-flouro phenyl) acetamide was collected by suction filtration. White crystal; yield 19.69 g (81.2%); mp 154–156 °C.

Synthesis of 2-chloro-6-fluoro quinoline-3-carbaldehyde (4)

N,N-dimethylformamide (29.9 mL) was added to a 100 mL round-bottom flask guarded with drying tube; it was cooled to 0 °C using ice bath. Then, phosphorus oxychloride (84.3 mL) was added dropwise to it from dropping funnel guarded by drying tube while being stirred by magnetic stirrer. This addition was done for 30 min. Then N-(4-flouro phenyl) acetamide (19.69 g, 0.00012 mmol) was added to it after 5 min. The dropper funnel was replaced by air condenser with guarding tube at its end and the mixture was heated for 22 h on oil bath at 85–90 °C. Then it was cooled to room temperature, poured into a beaker containing 400 mL crushed ice water, and stirred for 20 min. The yellow solid product was collected by suction filtration and washed with 100 mL cold water. The crude yield was 16.4 g (60.8%) and was recrystallized from ethyl acetate. yellow crystal; mp 160_162 °C; yield 15.5 g (57.5%); Rf 0.72 (n-hexane:EtOAc, 4:1); 1H NMR (400 MHz, CDCl3): δ 9.36 (1H, s, H-9), 7.54 (1H, s, H-4), 6.85 (1H, dd, J = 12.8 Hz and 3.2 Hz, H-7), 6.47 (1H, d, J = 12 Hz, H-8), 6.32 (1H, d, J = 8.4 Hz, H-5); 13C NMR (101 MHz, CDCl3): δ 189.1 (C-9), 162.2 (C-6), 148.6 (C-2), 143.9 (C-8a), 139.7 (C-4), 130.77 (C-8), 130.0(C-4a), 127.6 (C-3), 123.8 (C-7), 111.2 (C-5).

Synthesis of 6-fluoro-2-methoxy quinoline-3-carbaldehyde (5)

The methanol (10 mL), N,N-dimethylformamide (13 mL), 2-chloro-6-flouro quinoline-3-carbaldehyde (0.5 g, 0.00024 mmol) and potassium carbonate (0.57 g, 0.00041 mmol) were added to A 100 mL two-neck round bottom flask. The mixture was refluxed in water bath for 4 h with the progress monitored with TLC. After completion of the reaction, methanol was removed by distillation, cooled to room temperature and then added to 100 mL ice-cold water. The solid product was collected by fractional distillation and washed with excess ice-cold water. Yellow powder; yield 75.2%; mp 158–160 °C; Rf 0.78 (n-hexane:EtOAc,4:1); 1H NMR (400 MHz, CDCl3): δ 10.46 (1H, s, H-9), 8.50 (s, 1H, H-4), 7.83 (1H, d, J = 9.2 Hz, H-8), 7.51 (2H, m, H-5 and H-7), 4.17 (3H, s, OMe); 13CNMR (101 MHz, CDCl3): δ 189.1 (C-9), 160.7 (C-2), 158.0 (C-6), 146.0 (C-8a), 139.0 (C-4), 129.4 (C-8), 124.7 (C-4a), 122.2 (C-7), 120.7 (C-3), 112.7 (C-5), 54.0 (C-11).

Synthesis of 2-ethoxy-6-flouro- quinoline-3-carbaldehyde (6)

A 2-chloro-6-flouro quinoline-3-carbaldehyde (0.5 g, 0.00026 mmol), potassium carbonate (0.6 g, 0.00043 mmol), ethanol (10 mL) and N,N-dimethylformamide (10 mL) were added to 100 mL two-neck round-bottom flask and the necks were snug with water condenser and stopper. The mixture was refluxed for 4 h whereby the progress was monitored with TLC. At the end, the ethanol was removed by distillation, and the remaining cooled mixture was poured into 100 mL crushed ice water. The solid mass was collected by suction filtration. Yield 72.3%; white powder; mp 184–186 °C, Rf 0.64 (n-hexane:EtOAc, 4:1); 1H NMR (400 MHz, CDCl3): δ 10.51 (1H, s, H-9), 8.52 (1H, s, H-4), 7.84 (1H, dd, J = 8.4 Hz and 1.6 Hz, H-7), 7.49 (2H, m, H-5 and H-8), 4.64 (2H, q, J = 7.1 Hz, H-10), 1.52 (3H, t, J = 7.1 Hz, H-11); 13C NMR (101 MHz, CDCl3): δ 189.3 (C-9), 160.6 (C-2), 158.0 (C-6), 145.9 (C-8a), 138.7(C-4), 129.3 (C-8), 124.6 (C-4a), 122.1 (C-7), 120.4 (C-3), 112.7 (C-5), 62.7 (C-10), 14.3 (C-11).

Synthesis of 6-fluoro-2-thiocyanatoquinoline-3-carbaldehyde (7)

Potassium thiocyanate (0.24 g, 0.00025 mmol), 2-chloro-8-methyl quinoline-3-carbaldehyde (0.4 g, 0.00020 mmol),and potassium carbonate (0.65 g, 0.00047 mmol) were added to 100 mL two-neck round-bottom flask containing N,N-dimethylformamide (20 mL). One of its necks was connected to a condenser, and the other was closed with glass stopper and then refluxed for 5 h and progress was checked by TLC. It was cooled to room temperature and poured into 50 mL crushed ice water. The solid product was collected with suction filtration and washed with 10 mL cold water. Yield 67%; Gray powder; mp 156–158 °C; Rf 0.49 (DCM:Methanol, 99:1); 1H NMR (400 MHz, DMSO-d6): δ 10.24 (1H, s, H-9), 8.48 (1H, s, H-4), 7.81 (1H, dd, J = 9.2 Hz and 2.4 Hz, H-7), 7.57 (1H, m, H-8), 7.37 (1H, m, H-8); 13C NMR (101 MHz, DMSO-d6): δ 190.2 (C-9), 161.6 (C-2), 158.7 (C-6), 156.2 (C-8a), 142.0 (C-4), 138.4 (C-4a), 126.9 (C-3), 122.5 (C-8), 119.1 (C-10), 117.8 (C-7), 115.6 (C-5).

Synthesis of 2-chloro-6-fluoroquinoline-3-carboxylic acid (8)

Sodium hydroxide solution (1 mL, 10%) was added to a suspensions of 2-chloro-6-fluoroquinoline-3-carbaldehyde (0.5 g, 0.00026 mmol) in water (20 mL). Then, saturated solution of potassium permanganate was added dropwise until a definite purple color remained after quivering the solution. The mixture was acidified with 10% of sulfuric acid and oxalic acid was added to destroy the excess permanganate solution. The carboxylic acid precipitate was collected by suction filtration. 63.1% yield, Yellow powder, mp 200–202 °C; Rf 0.67 (n-hexane:EtOAc, 4:1); 1H NMR (400 MHz, CDCl3): δ 11.00 (1H, s, H-9), 9.13 (1H, s, H-4), 8.51 (1H, d, J = 11.3 Hz, H-8), 8.06 (1H, d, J = 3 Hz, H-5), 7.72 (1H, dd, J = 8.2 Hz, H-7); 13C NMR (101 MHz, CDCl3): δ 179.9 (C-9) 153.3 (C-6), 140.5 (C-2), 137.7 (C-8a), 130.5 (C-4), 122.2 (C-8), 118.2 (C-3 and C-4a), 114.8 (C-7), 103.7 (C-5)

Synthesis of 2-((2-hydroxyethyl) amino)-3-(-2-(ethylideneamino) ethanol quinoline (9)

2-Chloroquinoline-3-carbaldehyde (0.5 g, 0.00026 mmol) was added to ethanolamine (8 mL) in 100 mL round bottom flask and heated in oil bath at 100 °C for 2 h after cooling to ambient temperature, it was poured into 100 mL crushed ice water the precipitate was collected by suction filtration and allowed to dry in air. Yield 63.6%; yellow powder; mp 150–152 °C; Rf 0.57 (DCM:methanol, 99:1); 1H NMR (400 MHz, DMSO-d6): δ 9.49 (1H, s, H-9), 8.48 (1H, s, H-4), 8.18 (1H, d, J = 2.3 Hz, H-5), 7.52 (3H, m, H-7, H-8 and NH), 4.88 (2H, m, H-11), 3.5 (6H, bro. s, H-12, H-15 and H-16); 13C NMR (101 MHz, DMSO-d6): δ 163.7 (C-9), 158.3 (C-2), 155.0 (C-6), 145.3 (C-8a), 142.2 (C-4), 127.8 (C-8), 122.2 (C-4a), 122.1 (C-3), 120.6 (C-7), 111.9 (C-5), 63.6 (C-11), 61.2 (C-16), 60.3 (C-12), 43.4 (C-15).

Synthesis of 6-fluoro-N-phenyl-3-((phenylimino) methyl) quinolin-2-amine (10)

2-Chloroquinoline-3-carbaldehyde (0.5 g, 0.00026 mmol), aniline (8 mL) and acetic acid (9 mL) refluxed for 25 min. After cooled to ambient temperature, it was poured into 100 mL crushed ice water and precipitate was collected by suction filtration and allowed to dry in air. Yield 1.09 g (70%); Yellow powder; mp 162_164 °C; Rf 0.5 (n-hexane:EtOAc, 4:1); 1H NMR (400 MHz, DMSO-d6): δ 9.93 (1H, s, H-4), 7.59 (2H, bro s, H -8 and H-9), 7.57 (2H, m, H-5 and H-7), 7.00–7.29 (10H, t, phenyl), 7.26 (1H, dd, J = 7.6 Hz, H-7); 13C NMR (101 MHz, DMSO-d6): δ 161.9 (C-9), 157.3, 145.9, 153.9, 153.8, 153.7, 142.9, 140.8, 140.7, 124.9, 124.8, 120.7, 120.6, 118.4, 118.3, 116.4, 109.6, 109.4

Synthesis of 2-methoxyquinoline-3-carboxylic acid (15)

Sodium hydroxide solution (1 mL, 10%) was added to a suspension of 2-chloroquinoline-3-carbaldehyde (0.5 g, 0.00028 mmol) in water (20 mL). Then, saturated solution of potassium permanganate in water was added dropwise until a definite purple color remained after shaking the solution. The mixture was acidified with 10% of sulfuric acid to which oxalic acid was added to get rid off the excess permanganate solution. The carboxylic acid precipitate was collected by suction filtration. 60.1% yield, white powder, mp 205–207 °C; Rf 0.71 (n-hexane:EtOAc, 4:1) and then a 100 mL two-neck round-bottom flask was charged with methanol (10 mL) N,N-dimethylformamide (13 mL), 2-chloroquinoline-3-carboxylic acid (0.5 g) and potassium carbonate (0.57 g); the mixture was refluxed using water condenser for 5 h; and the progress of the reaction was monitored with TLC. After completion of the reaction, methanol was removed by distillation; the mixture was cooled to room temperature, and then added to 100 mL ice-cold water. The solid product was collected by fractional distillation and washed with excess ice cold water. The amount of product was 0.42 g. White powder; yield 76.2%; mp 192–194 °C; Rf 0.75 (n-hexane:EtOAc, 4:1); 1H NMR (400 MHz, CDCl3): δ 10.44 (1H, s, H-9), 8.54 (1H, s, H-4), 7.83 (2H, bro d, H-5 and H-8), 7.72 (1H, bro s, H-7), 7.41 (1H, bro s, H-8), 4.75 (3H, s, H-10); 13C NMR (101 MHz, CDCl3): δ 185.3 (C-9), 157.1 (C-2), 144.9 (C-8a), 135.9 (C-4), 128.5 (C-7), 125.7 (C-5), 123.2 (C-8), 121.0 (C-6), 120.3 (C-4a), 115.9 (C-3), 49.8 (C-10).

Synthesis of methyl 2-chloroquinoline-3-carboxylate (16)

A 100 mL two-neck round-bottom flask was charged with methanol (6 mL), chloroquinoline-3-carbaldehyde (0.5 g, 0.00026 mmol), and sulfuric acid (2 mL); wherein the mixture was refluxed using water condenser for 2 h and progress was monitored with TLC. After finale of the reaction, methanol was detached by distillation, the mixture was allowed to cool to room temperature, and then added to 100 mL ice-cold water. The solid violet product was collected and washed with excess ice cold water. The amount of product was 0.37 g. yellow powder; yield 60.7%; mp196–198 °C; Rf 0.66 (DCM:Methanol, 99:1); 1H NMR (400 MHz, CDCl3): δ 7.45 (H, s, H-4), 7.03 (1H, bro s, H-8), 6.92 (1H, bro s, H-5), 6.77 (1H, bro s, H-7), 6.65 (1H, bro s, H-6), 3.65 (3H s, OMe); 13C NMR (101 MHz, CDCl3): δ 166.2 (C-9), 142.0 (C-2), 134.8 (C-8a), 132.3 (C-4), 126.8 (C-7), 123.3 (C-5, 8), 119.4 (C-3,C-4a), 56.05 (OMe).

Antibacterial activity

Four pathogenic bacterial strains, two Gram negative (E. coli (ATCC 25922) and Pseudomonas aeruginosa (ATTC 27853)) and two Gram positive bacteria (Staphylococcus aureus (ATCC 6538) and Streptococcus pyogenes (ATTC 19615) were supplied by Adama Regional Microbiology Laboratory. In vitro antibacterial activity of the synthesized compounds was done using paper disc diffusion method following the procedure reported by Zeleke et al. [18].

The bacterial cultures were inoculated into the nutrient broth (inoculation medium) and incubated overnight at 37 °C. Inoculated medium containing 24 h grown culture were added aseptically to the nutrient medium and mixed thoroughly to get a uniform distribution. The solution was poured to 20 mL of sterile MHA in sterile culture plates and allowed to attain room temperature. Sterile paper disc diffusion previously soaked in a known concentration (100 and 200 μg/mL per disc) synthesized compounds and standard drugs was prepared in DMSO using nutrient agar tubes and carefully placed at the center of the labeled seeded plate. The zones of growth inhibition around the disks were measured after 24 h of incubation at 37 °C for bacteria. Samples were analyzed in triplicates and inhibition zones were measured with a ruler and compared with the positive control disk (disk containing ciprofloxacin).

Radical scavenging activity

The radical scavenging activity of the synthesized compounds was evaluated with 1,1-diphenyl-2-picryl hydrazyl (DPPH). In the process, 4 mg/100 mL solution of DPPH in methanol was prepared. Likewise each sample was dissolved in methanol and serially diluted with the DPPH solution to furnish four different concentrations (10, 5, 2.50, 1.25 μg/mL). The mixtures were shaken and allowed to stand at 37 °C for 30 min in dark oven, and absorbance was recorded at 517 nm using double beam UV–Vis spectrophotometer. The radical scavenging activity of ascorbic acid was measured at 2, 1, 0.5 and 0.3 μg/mL. Percentage inhibition of DPPH radical was determined using the following equation:

$$ {text{Percentage inhibition }} = frac{{A_{0} – A_{1} }}{{A_{0} }} times 100 $$

where A0 is the absorbance of control reaction and A1 is the absorbance in the presence of test or standard sample [18].

In silico analysis

In silico molecular docking

The experimental procedure followed for the in silico molecular docking analysis of the synthesized compounds was as reported by Blessy and Sharmila [19] with slight modifications. The interactions of the synthesized compounds with the proteins (PDB ID:6F86 and PDB ID:4FM9) were studied using AutoDock Vina v.1.2.0 [20]. The structures of the compounds synthesized were drawn using ChemOffice tool (ChemDraw 16.0) assigned with proper 2D orientation. The energy of each molecule was minimized using ChemBio3D and were then used as input for AutoDock Vina, in order to carry out the docking simulation. The crystal structures of E. coli gyrase B (PDB ID:6F86) and human topoisomerase IIα (PDB ID:4FM9) were downloaded from protein data bank. The protein preparation was done using the reported standard protocol by removing the co-crystallized ligand, selected water molecules (except 616, 641, and 665), and cofactors; the target protein file was prepared by leaving the associated residue with protein using Auto preparation of target protein file AutoDock 4.2 (MGLTools 1.5.6). The graphical user interface program was used to set the grid box for docking simulations. The grid was set so that it surrounds the region of interest in the macromolecule. The docking algorithm provided with AutoDock Vina v.1.2.0 was used to search for the best docked conformation between ligand and protein. During the docking process, a maximum of nine conformers were considered for each ligand. The conformations with the most favorable (least) free binding energy were selected for analyzing the interactions between the target receptor and ligands by Discovery Studio Visualizer and PyMOL. The ligands are represented in different color; H-bonds and the interacting residues are represented in ball and stick model representation [18].

In silico pharmacokinetics (ADME) and toxicological properties

The structures of synthesized compounds were changed to their canonical simplified molecular input line entry system (SMILES) then submitted to SwissADME tool to estimate in silico pharmacokinetic parameters and other molecular properties based on the methodology reported by Daina et al. and Lipinski [21, 22]. The organ toxicities and toxicological endpoints of the isolated compounds were predicted using PreADMET and OSIRIS Properties. The results were then compared with vosaroxin used as standard clinical drug.

Rights and permissions

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data.

Disclaimer:

This article is autogenerated using RSS feeds and has not been created or edited by OA JF.

Click here for Source link (https://www.biomedcentral.com/)