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SYNTHESIS OF BENZO[G]QUINOXALINE-5,10-DIONE BASED PYRAZOLINE DERIVATIVES AND THEIR ANTIMYCOBACTERIAL ACTIVITY

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SYNTHESIS OF BENZO[G]QUINOXALINE-5,10-DIONE BASED PYRAZOLINE DERIVATIVES AND THEIR ANTIMYCOBACTERIAL ACTIVITY

Shiv Kumar *1, 2, Nitin Kumar 3 and Sushma Drabu 4

Faculty of Pharmacy 1, Uttrakhand Technical University, Dehradun - 248007, Uttrakhand, India.

Department of Pharmacy 2, Government Polytechnic, Uttawar, Palwal - 121103, Haryana, India.

Oxford College of Pharmacy 3, Masoori Industrial Area, U.P.S.I.D.C., M.G. Road, Ghaziabad - 201001, Uttar Pradesh, India.

Maharaja Surajmal Institute of Pharmacy 4, Janak Puri, New Delhi - 110058, New Delhi, India.

ABSTRACT: Eleven new compounds belonging to series 7-[5-(substituted) phenyl - 4, 5-dihydro-1H-pyrazol-3-yl]-2,3-diphenyl-5H, 10H - benzo[g] quinoxaline - 5, 10 - dione  (Compound 7a-k) were synthesized by multistep synthetic scheme. The newly synthesized compounds were screened for their in-vitro antimycobacterial activity against Mycobacterium tuberculosis H37Rv by L.J. Slope (Conventional) Method. Compound 7j having 4-CH3 at phenyl ring attached to 5-position of pyrazoline ring and compound 7i having 3,4-(OCH3)2 group on the above mentioned position have been observed as most and least active antimycobacterial compounds respectively.

Keywords:

Quinoxaline, Benzo[g] quinoxaline-5,10-dione, Pyrazoline, Antimycobacterial

INTRODUCTION: Nitrogen containing benzene fused heterocyclic ring, quinoxaline is the important components of antibiotics viz. hinomycin, levomycin and actinoleutin, that are inhibitors of gram positive bacteria and various transplantable tumours 1 - 7. Quinoxaline derivatives have also been observed to exhibit wide range of pharmacological activities like antifungal 8 - 10, antibacterial 11 - 12, antitubercular 8 - 9, 11, 13 - 15 etc. In literature, various methods have been explained for synthesis of quinoxaline ring systems by reaction of ortho-phenylenediamine with various α, β-dicarbonyl moieties 16, oximes 17 - 18, phenacyl bromides via oxidative cyclization19, ethyl pyruvate and α-bromo ketones in presence of FeCl3 20, α-hydroxylimino ketone derivatives 21 etc.

Synthesis of various fused quinoxalines by intramolecular cyclization of NH and N-alkyl quaternary salts of 2-quinoxaline-2-carboxyl aldehyde hydrazones have also been reported 22. Various methods for synthesis of benzo[g] quinoxaline scaffold include Bis-SRN1 Methodology 23, regiospecific displacement 24, reaction of diethylester of naphthalenebis(oxamate) with tert-BuNH2 25, Diels-Alder Condensation 6 etc.

Tuberculosis (TB) is one of the major cause for death now-a-days worldwide. Quinoxaline ring containing antileprotic and antitubercular drug clofazimine (CZM) is widely used for treatment of multidrug resistant tuberculosis. In Mycobacterium tuberculosis, CZM is reduced by NADH-dehydrogenase (NDH-2) in order to release reactive oxygen species and reoxidized by O2 26. CZM also competes with mycobacterial menaquinone (MK-4) for its reduction by NDH-2 27.

MATERIALS AND METHODS: Chemistry: Melting points were determined in open capillary tubes and are uncorrected. All the Fourier-Transform Infra-Red (FT-IR) spectra were recorded using KBr pellets on Shimdazu FT-8400 Spectrophotometer. The 1H- NMR and 13C-NMR spectra were recorded on Bruker-Spectrospin DCX NMR spectrometer using tetramethylsilane (TMS) as an internal standard. Chemical shifts (δ) are expressed in ppm. The purity of the compounds was checked by thin layer chromatography (TLC) on Merck Silica Gel 60F254 precoated sheets using Toluene: Ethylacetate: Formic acid (5:4:1) solution as mobile phase (solvent).

FIG. 1: REACTION SCHEME

General Procedure for the Synthesis of Titled Compounds:

2, 3-Dichloronaphthalene (1): 2, 3-dihydroxy naphthalene (5 gm) was dissolved in phosphorus oxychloride (90 ml) in parts at 0° - 5°C with occasionally stirring and refluxed for about 4 hours till the appearance of clear dark pinkish solution. The solution was cooled and poured into ice-cold water. A dark pinkish solid appeared and was filtered. The solid was dried and recrystallized with dimethylformaide (DMF). Pinkish crystalline solid; yield 85%; Rf 0.72; mp 185°C; FT-IR (vmax, cm-1): 756 (ortho-disubstituted aromatic ring), 856 (meta-disubstituted aromatic ring), 1160 (C-Cl, aryl), 1384 (C=C, sp2, aromatic); 1H-NMR (CDCl3, 300 MHz, δ): 8.16-8.20 (q, 2H, A2B2 pattern, Ar-H, J=5-6 Hz), 7.74-7.79 (m, 2H, Ar-H, J=4.5-6 Hz), 7.50-7.53 (m, 2H, Ar-H, J=1-4 Hz).

2,3-Diaminonaphthalene (2): Compound 1 (2 gm) was dissolved in absolute ethanol and ammonium chloride (1.5 gm),  dil. HCl (in catalytic amount) and excess of strong ammonia solution were added and then refluxed for 6 hours on water bath till dark greenish colour permanently persists. Reaction solution was cooled and kept in deep freezer for overnight. Greenish crystalline solid was filtered, dried and recrystallized with methanol. Dark greenish crystals; yield 75%; Rf 0.89; mp 150°C;  FT-IR (vmax, cm-1): 758, 854, 1473 (aromatic =C-N), 1500 (aromatic C=C), 1681 (N-H), 3049 (N-H); 1H-NMR (CDCl3, 500 MHz, δ): 7.45-7.46 (dd, 2H, Ar-H, J=3.5-4 Hz), 7.12-7.14 (dd, 2H, Ar-H, J=3-3.5 Hz), 7.09 (s, 2H, Ar-H), 7.05 (s, 4H, Ar-NH2).

2,3-Diphenylbenzo[g]quinoxaline (3): Equimolar quantities of compound 2 (0.001 mol) and benzil (0.001 mol) were dissolved in ethanol (30 ml) and refluxed for 2 hours. Reaction solution was cooled and kept for overnight. Yellow crystalline solid was filtered, dried and recrystallized with ethanol: methanol solution (1:1). Yellow crystalline solid; yield 72%; Rf 0.83; mp 170°C; FT-IR (vmax, cm-1): 725 (mono-substituted aromatic ring), 785, 820, 875, 1475, 1510, 1660 (quinoxaline C=N); 1H-NMR (DMSO-d6, 500 MHz, δ): 8.73-8.77 (m, 10H, Ar-H, J=2.5-4 Hz), 8.28 (s, 2H, Ar-H), 8.03-8.07 (m, 4H, Ar-H, J=2.5-4 Hz).

2,3-Diphenylbenzo[g]quinoxaline-5,10-dione (4): Compound 3 (1.2 gm) was dissolved in glacial acetic acid (30 ml) and added to a solution of chromium trioxide (1.1 gm) in 12 ml of glacial acetic acid : water solution (1:1). This solution was heated at 80 °C for 2 hours and then poured into ice-chilled water (1500 ml). Resulting solid was filtered, dried and recrystallized with methanol. White solid; yield 65%; Rf 0.78; mp 162oC; FT-IR (vmax, cm-1): 718, 795, 875, 1450, 1594 (aromatic C=C), 1676 (quinoxaline C=N); 1H-NMR (CDCl3, 500 MHz, δ): 8.13-8.15 (d, 2H, Ar-H, J=8.5 Hz), 7.85-7.88 (t, 4H, Ar-H, J=2.5-10.5 Hz), 7.81-7.82 (d, 2H, Ar-H, J=8 Hz), 7.50-7.53 (t, 6H, Ar-H, J=7.5 Hz).

7-Acetyl-2,3-diphenylbenzo[g]quinoxaline-5, 10-dione (5): Anhydrous aluminium trichloride (1 gm) was dissolved in carbon tetrachloride (30 ml). Acetyl chloride (2 ml) was added to it under cold conditions (0° - 5°C). Compound 4 (120 mg) was dissolved in this solution and stirred at room temperature for 6 hours. Yellow crystalline solid was filtered, dried and recrystallized with chloroform. Yellow crystalline solid; yield 48%; Rf 0.74; mp 225°C; FT-IR (vmax, cm-1): 725, 775, 810, 875, 1450 (aromatic =C-N), 1500 (aromatic C=C), 1593 (cyclic >C=O), 1672 (quinoxaline C=N), 1974 (aromatic >C=O), 3063 (C-H, CH3); 1H-NMR (CDCl3, 500 MHz, δ): 7.97-7.98 (d, 4H, Ar-H, J=8 Hz), 7.65-7.68 (t, 3H, Ar-H, J=7.5 Hz), 7.50-7.53 (t, 6H, Ar-H, J=7.5-8 Hz), 7.26 (s, 3H, CH3CO)

Synthesis of 7  -[3-(substituted) phenylprop – 2 -enoyl]-2,3-diphenyl-5H,10H-benzo[g] quinoxaline -5,10-dione (Compound 6a-k): Compound 5 (0.01 mol) and appropriate benzaldehyde derivative (0.15 mol) were dissolved in methanol saturated with KOH and stirred at 0°- 5 °C till the solid appeared. Reaction time may vary from 15 minutes to 4 hours. Solid was filtered, dried and recrystallized with methanol: ethanol (1:1) solution.

7-[3-phenylprop-2-enoyl]-2,3-diphenyl-5H, 10H-benzo[g]quinoxaline - 5, 10-dione (6a): Yellow solid; yield 65%;  Rf 0.78; mp 156°C; FT-IR (vmax, cm-1): 750 (mono-substituted aromatic ring), 783 (ortho-disubstituted aromatic ring), 972 (meta-disubstituted aromatic ring), 980 (>C-C=C), 1290 (C=N), 1384 (C-N), 1483 (Ar-C=O), 1581 (enoyl >C=O), 1620 (cyclic >C=O), 1680 (>C=O, conjugated with phenyl); 1H-NMR (DMSO-d6, 500 MHz, δ): 8.14 (bs, 3H, Ar-H), 7.88 (bs, 5H, Ar-H), 7.74-7.76 (d, 2H, CH=CH, J=12 Hz), 7.35-7.65 (m, 10H, Ar-H); MS-ESI: 492.1 (m/z, M+); Analysis calculated for C33H20N2O3: C, 80.47; H, 4.09; N, 5.69; O, 9.75. Found: C, 80.45; H, 4.07; N, 5.70; O, 9.77.

7-[3-(4-chlorophenyl)prop-2-enoyl]-2,3-diphenyl -5H, 10H-benzo[g]quinoxaline-5,10-dione (6b): Yellow solid; yield 65%; Rf  0.75; mp 185°C; FT-IR (vmax, cm-1): 723, 780, 972, 980, 1172 (aryl C-Cl), 1290, 1382, 1485, 1590, 1620, 1680; 1H-NMR (DMSO-d6, 500 MHz, δ): 8.11-8.15 (m, 1H, CH=CH*-CO-, J=2.5-7.5 Hz,), 8.05-8.07 (d, 1H, *CH=CH-CO-, J=8 Hz,), 7.91-7.97 (m, 3H, Ar-H, J=7.5-16 Hz), 7.77-7.88 (m, 4H, Ar-H, J=3-11 Hz,), 7.45-7.56 (m, 5H, Ar-H, J=2.5-15.5 Hz), 7.32-7.38 (m, 5H, Ar-H, J=5-7 Hz); 13C-NMR (DMSO-d6, 125 MHz, δ):  189.50, 188.96, 167.55, 161.86, 153.55, 142.00, 138.29, 135.48, 135.39, 134.18, 134.13, 133.41, 131.31, 131.17, 131.04, 130.91, 130.71, 130.17, 129.86, 129.68, 129.53, 129.41, 129.29, 129.25, 129.20, 128.88, 128.53, 126.70, 127.24, 114.89; MS-ESI: 526.1 (m/z, M+); Analysis calculated for C33H19ClN2O3: C, 75.21; H, 3.63; Cl, 6.73; N, 5.32; O, 9.11. Found: C, 75.20; H, 3.64; Cl, 6.72; N, 5.31; O, 9.11.

7-[3-(4-hydroxyphenyl)prop – 2 - enoyl] - 2, 3-diphenyl - 5H, 10H -benzo[g] quinoxaline-5, 10-dione (6c): Red Solid; yield 62%;  Rf 0.78; mp 180°C; FT-IR (vmax, cm-1): 690, 780, 880, 960, 980, 1199 (phenolic C-O), 1290, 1384, 1483, 1581, 1680, 1749, 3078 (phenolic C-O-H);  1H-NMR (DMSO-d6, 500 MHz, δ): 8.11-8.16 (m, 1H, CH=CH*-CO-, J=2.5-8 H), 8.01 (s, 1H, Ar-H), 7.82-7.88 (m, 5H, Ar-H, J=2-11 Hz), 7.53-7.56 (t, 1H, *CH=CH-CO-, J=7.5 Hz), 7.41-7.47 (m, 5H, Ar-H, J=3-12 Hz), 7.33-7.38 (m, 2H, Ar-H, J=5-7.5 Hz), 7.00-7.04 (dd, 4H, Ar-H, J=8.5 Hz), 5.83-5.86 (dd, 1H, Ar-OH, J=8 Hz); MS-ESI: 508.1 (m/z, M+); Analysis calculated for C33H20N2O4: C, 77.94; H, 3.96; N, 5.51; O, 12.58. Found: C, 77.93; H, 3.97; N, 5.50; O, 12.57.

7-[3-(4-nitrophenyl)prop-2-enoyl]-2,3- diphenyl-5H,10H-benzo[g] quinoxaline-5,10-dione (6d): Brown solid; yield 55%; Rf  0.78; mp 160°C; FT-IR (vmax, cm-1): 680, 783, 837, 972, 1080, 1290, 1380, 1404 (-NO2, sym.), 1483, 1560 (-NO2, asym.), 1581, 1645, 1701; 1H-NMR (DMSO-d6, 500 MHz, δ): 8.11-8.15 (dd, 4H, Ar-H, J1=7.5 Hz, J2=3.5 Hz), 7.81-7.88 (m, 5H, Ar-H, J=3-10.5 Hz), 7.78 (s, 1H, Ar-H), 7.69-7.72 (d, 2H, CH=CH-CO-, J=15.5 Hz), 7.62-7.65 (t, 2H, Ar-H, J=7-7.5 Hz), 7.45-7.56 (m, 5H, Ar-H); MS-ESI: 537.2 (m/z, M+); Analysis calculated for C33H19N3O5: C, 73.74; H, 3.56; N, 7.82; O, 14.88. Found: C, 73.72; H, 3.57; N, 7.83; O, 14.87.

7-[3-(4-methoxyphenyl) prop-2-enoyl] - 2, 3-diphenyl-5H,10H-benzo[g] quinoxaline - 5, 10-dione (6e): White solid; yield 43%;  Rf 0.70; mp 160°C; FT-IR (vmax, cm-1): 680, 783, 840, 965, 980, 1130 (C-O-C, sym.), 1263 (C-O-C, asym.), 1290, 1380, 1483, 1580, 1616, 1640; 1H-NMR (DMSO-d6, 500 MHz, δ): 8.11-8.15 (m, 1H, CH=CH-CO, J=3.5-7.5 Hz), 7.98 (s, 1H, Ar-H), 7.77-7.88 (m, 5H, Ar-H, J=1.5-15.5 Hz), 7.64-7.72 (m, 1H, Ar-H, J=8-15.5 Hz), 7.41-7.46 (m, 5H, Ar-H, J=2.5-12 Hz), 7.33-7.38 (m, 1H, Ar-H, J=5-7.5 Hz), 7.02-7.04 (d, 2H, Ar-H, J=8.5 Hz), 6.83-6.85 (d, 2H, Ar-H, J=8.5 Hz), 5.82-5.85 (dd, 1H, CH=CH, J1=J2= 7 Hz), 3.68 (s, 3H, CH3O); MS-ESI: 522.2 (m/z, M+); Analysis calculated for C34H22N2O4: C, 78.15; H, 4.24; N, 5.36; O, 12.25. Found: C, 78.14; H, 4.26; N, 5.34; O, 12.24.

7-[3-(3-hydroxy-4-methoxyphenyl)prop-2-enoy]-2,3-diphenyl-5H,10H-benzo[g]quinoxaline-5,10-dione (6f): Yellow solid; yield 50%; Rf 0.80; mp 155°C; FT-IR (vmax, cm-1): 680, 742, 891, 964, 972, 1114 (C-O-C, sym.), 1163 (C-O, phenolic), 1226 (C-O-C, asym.), 1288, 1377, 1498, 1595, 1608, 1629, 3064 (O-H, phenolic); 1H-NMR (DMSO-d6, 500 MHz, δ): 9.60 (s, 1H, Ar-H), 8.52 (s, 1H, Ar-OH), 8.11-8.15 (q, 2H, Ar-H, J=3-7.5 Hz), 7.78-7.87 (m, 3H, Ar-H, J=3-15.5 Hz), 7.69-7.72 (d, 1H, Ar-H, J=16 Hz), 7.62-7.65 (t, 1H, Ar-H, J=7-7.5 Hz), 7.53-7.56 (t, 1H, CH=CH*-CO, J=7-7.5 Hz), 7.45-7.46 (d, 2H, Ar-H, J=7 Hz), 7.32-7.37 (m, 3H, Ar-H, J=5-7.5 Hz), 7.28-7.29 (d, 1H, *CH=CH-CO, J=7.5 Hz), 7.23 (s, 1H, Ar-H), 6.99-7.01 (d, 1H, Ar-H, J=8.5 Hz), 6.80-6.82 (d, 1H, Ar-H, J=8 Hz), 3.74-3.80 (d, 3H, CH3O, J=2.5 Hz); 13C-NMR (DMSO-d6, 125 MHz, δ): 189.98, 189.51, 166.15, 161.86, 153.54, 149.80, 144.53, 140.92, 139.23, 138.28, 133.41, 130.91, 130.30, 130.17, 129.28, 129.25, 129.22, 128..88, 128.53, 127.75, 125.55, 119.96, 116.39, 114.89, 110.30, 55.85; MS-ESI: 538.2 (m/z, M+); Analysis calculated for C34H22N2O5: C, 75.83; H, 4.12; N, 5.20; O, 14.85. Found: C, 75.82; H, 4.11; N, 5.21; O, 14.85.

7-[3-(2-chlorophenyl)prop-2-enoyl]-2,3-diphenyl -5H,10H-benzo[g]quinoxaline-5,10-dione(6g): Red solid; yield 60%; Rf  0.82; mp 140°C; FT-IR (vmax, cm-1): 690, 780, 838, 970, 990, 1089 (C-Cl, aryl), 1247, 1375, 1473, 1577, 1614, 1640; 1H-NMR (DMSO-d6, 500 MHz, δ): 8.12-8.16 (m, 1H, Ar-H, J=3.5-7.5 Hz), 8.05-8.06 (d, 1H, Ar-H, J=7.5 Hz), 7.82-7.88 (m, 2H, Ar-H, J=2.5-8.5 Hz), 7.78-7.80 (d, 1H, Ar-H, J=7 Hz), 7.62-7.75 (m, 2H, Ar-H, J=7.5-16.5 Hz), 7.46-7.56 (m, 3H, Ar-H, J=6.5-20.5 Hz), 7.31-7.38 (m, 3H, Ar-H, J=1.5-8 Hz), 7.20-7.29 (m, 2H, Ar-H, J=6-9.5 Hz), 6.99-7.01 (d, 2H, CH=CH-CO, J=8 Hz), 6.86-6.91 (q, 1H, Ar-H, J=7-12.5 Hz), 6.57-6.64 (m, 1H, Ar-H, J=4.5-8.5 Hz); MS-ESI: 526.2 (m/z, M+); Analysis calculated for C33H19ClN2O3: C, 75.21; H, 3.63; Cl, 6.73; N, 5.32; O, 9.11. Found: C, 75.20; H, 3.62; Cl, 6.74; N, 5.32; O, 9.12.

7-[3-(4-trifluoromethyl)phenylprop-2-enoyl]-2,3-diphenyl-5H,10H-benzo[g] quinoxaline - 5, 10-dione (6h): Brown solid; yield 42%;  Rf 0.78; mp 152°C; FT-IR (vmax, cm-1): 680, 783, 837, 972, 1018, 1263, 1290 (aryl C-F), 1380, 1483, 1581, 1680; 1H-NMR (DMSO-d6, 500 MHz, δ):  7.95-7.97 (d, 4H, Ar-H, J=7.5 Hz), 7.61 (s, 1H, Ar-H), 7.53-7.58 (q, 2H, Ar-H, J=7.5-9.5 Hz), 7.45-7.50 (q, 5H, Ar-H, J=7-8 Hz), 7.27-7.33 (m, 5H, Ar-H, J=1.5-12 Hz), 7.38-7.41 (d, 2H, CH=CH-CO, J=16.5 Hz); 13C-NMR (DMSO-d6, 125 MHz, δ):   189.51, 188.15, 170.12, 161.87, 153.56, 146.27, 140.93, 138.29, 136.73, 133.42, 132.11, 131.32, 130.92, 130.18, 129.68, 129.58, 129.29, 129.26, 129.22, 128.88, 128.75, 128.61, 127.76, 120.36, 114.89-119.98 (t, CF3), 113.71; MS-ESI: 560.1 (m/z, M+); Analysis calculated for C34H19F3N2O3: C, 72.85; H, 3.42; F, 10.17; N, 5.00; O, 8.56. Found: C, 72.84; H, 3.41; F, 10.18; N, 4.99; O, 8.57.

7-[3-(3,4-dimethoxyphenyl)prop-2-enoyl] - 2, 3-diphenyl-5H,10H-benzo[g] quinoxaline - 5, 10-dione (6i): Brick red solid; yield 68%;  Rf 0.75; mp. 170°C; FT-IR (vmax, cm-1): 680, 740, 840, 972, 980, 1112 (C-O-C, sym.), 1253 (C-O-C, asym.), 1290, 1382, 1480, 1581, 1640, 1680; 1H-NMR (DMSO-d6, 500 MHz, δ):  8.05-8.07 (d, 3H, Ar-H, J=7.5 Hz), 7.77-7.78 (d, 4H, Ar-H, J=8 Hz), 7.60-7.73 (m, 6H, Ar-H, J=7-15.5 Hz), 7.30-7.35 (m, 2H, CH=CH-CO, J=6.5-9.5 Hz), 6.96-6.98 (d, 3H, Ar-H, J=8.5 Hz), 3.87 (s, 6H, OCH3); MS-ESI: 552.2 (m/z, M+); Analysis calculated for C35H24N2O5: C, 76.08; H, 4.38; N, 5.07; O, 14.48. Found: C, 76.07; H, 4.39; N, 5.06; O, 14.48.

7-[3-(4-methylphenyl)prop-2-enoyl] - 2, 3 - di phenyl-5H,10H-benzo[g]quinoxaline-5, 10-dione (6j): White solid; yield 40%;  Rf 0.70; mp 144°C; FT-IR (vmax, cm-1): 710, 783, 877, 972, 980, 1290, 1382, 1483, 1581, 1640, 1680, 2356 (C-H, CH3); 1H-NMR (DMSO-d6, 500 MHz, δ);  7.80-7.88 (m, 5H, Ar-H, J=4-11.5 Hz), 7.77 (s, 1H, Ar-H), 7.70-7.73 (m, 2H, Ar-H, J=4-8 Hz), 7.62-7.67 (q, 1H, CH=CH*-CO), 7.45-7.47 (d, 1H, *CH=CH-CO, J=7 Hz), 7.34-7.39 (m, 5H, Ar-H, J=6.5-7.5 Hz), 6.99-7.00 (d, 4H, Ar-H, J=9 Hz), 3.80 (s, 3H, CH3); MS-ESI: 506.1 (m/z, M+); Analysis calculated for C34H22N2O3: C, 80.62; H, 4.38; N, 5.53; O, 9.48. Found: C, 80.61; H, 4.39; N, 5.51; O, 9.49.

7-[3-(4-aminophenyl)prop-2-enoyl]-2,3-diphenyl -5H, 10H-benzo[g] quinoxaline- 5, 10 - dione (6k): Light yellowish solid; yield 66%;  Rf 0.79; mp 134°C;  FT-IR (vmax, cm-1): 692, 765, 813, 831, 1012, 1290, 1382, 1463, 1585, 1614 (N-H, 1°amine, bend), 3139 (N-H, 1°amine, str.); 1H-NMR (DMSO-d6, 500 MHz, δ);  7.96 (s, 1H, Ar-H), 7.82-7.90 (m, 5H, Ar-H, J=2-10.5 Hz), 7.41-7.47 (m, 5H, Ar-H, J=3.5-8.5 Hz), 7.34-7.38 (m, 1H, CH=CH*-CO, J=4.5-8 Hz), 7.02-7.04 (d, 1H, Ar-H, J=8.5 Hz), 6.92-6.94 (d, 2H, Ar-H, J=9 Hz), 6.83-6.85 (d, 1H, Ar-H, J=8.5 Hz), 6.61-6.63 (d, 2H, Ar-H, J=8.5 Hz), 5.77-5.80 (dd, 1H, *CH=CH-CO, J1=J2 =3 Hz), 3.78-3.87 (m, 2H, NH2, J=5.5-11.5 Hz); MS-ESI: 507.1 (m/z, M+); Analysis calculated for C33H21N3O3: C, 78.09; H, 4.17; N, 8.28; O, 9.46. Found: C, 78.08; H, 4.17; N, 8.26; O, 9.47.

Synthesis of 7-[5-(substituted) phenyl - 4, 5-dihydro-1H-pyrazol-3-yl]-2,3-diphenyl-5H, 10H-benzo[g]quinoxaline-5,10-dione (7a-k):Compound 6(a-k) (0.005 mol) and hydrazine hydrate (1 ml) were refluxed in absolute ethanol under anhydrous conditions till the solid appeared with brisk bumping. Solid was filtered, dried and recrystallized.

7-[5-phenyl-4,5-dihydro-1H-pyrazol-3-yl] - 2, 3-diphenyl-5H,10H-benzo[g] quinoxaline - 5, 10 -dione (7a): White solid, yield 55%, mp 136°C, Rf 0.70; FT-IR (vmax, cm-1): 696, 757, 829, 985, 1147 (=N-N, pyrazoline), 1353 (C-N, pyrazoline), 1379, 1583 (C=N, pyrazoline), 1656, 1749, 2358 (C-C, cyclic, pyrazoline), 3058 (N-H, pyrazoline); 1H-NMR (DMSO-d6, 500 MHz, δ): 8.59 (s, 1H, Ar-H), 7.86-7.95 (m, 5H, Ar-H), 7.72-7.75 (d, 1H, Ar-H, J=11 Hz), 7.64-7.67 (t, 1H, Ar-H, J=7-7.5 Hz), 7.54-7.57 (t, 2H, pyrazoline-H, J=7.5-8 Hz), 7.32-7.46 (m, 10H, Ar-H), 7.23-7.24 (d, 1H,. pyrazoline-H, J=7.5 Hz), 6.83-6.88 (q, 1H, pyrazoline-N-H, J=5.5-8.5 Hz); 13C-NMR (DMSO-d6, 125 MHz, δ):  189.68, 176.58, 155.40, 153.56, 144.53, 143.47, 140.93, 139.24, 138.01, 135.12, 133.66, 131.36, 131.14, 131.03, 130.92, 130.18, 129.41, 129.40, 129.29, 129.26, 129.16, 129.01, 128.98, 128.54, 127.59, 127.39, 125.75,  122.52, 63.31, 42.86; MS-ESI: 506.5 (m/z, M+); Analysis calculated for C33H22N4O2: C, 78.25; H, 4.38; N, 11.06; O, 6.32. Found: C, 78.15; H, 4.41; N, 10.98; O, 6.46.

7-[5-(4-chlorophenyl)-4,5-dihydro-1H-pyrazol-3-yl]-2,3-diphenyl-5H, 10 H-benzo[g]quinoxaline -5,10-dione (7b): Yellow solid, yield 68%, mp 184°C, Rf 0.86; FT-IR (vmax, cm-1): 684, 759, 840, 1018, 1176 (=N-N, pyrazoline, C-Cl, aryl), 1342, 1384, 1593, 1610, 1749, 2360, 3168; 1H-NMR (DMSO-d6, 500 MHz, δ): 8.14-8.15 (d, 1H, pyrazoline-H, J=6.5 Hz), 8.05 (s, 1H, Ar-H), 7.88 (bs, 2H, Ar-H), 7.74-7.75 (d, 4H, Ar-H, J=7.5 Hz), 7.44-7.47 (t, 1H, pyrazoline-H, J=6-7.5 Hz), 7.34-7.36 (d, 4H, Ar-H, J=8 Hz), 7.23-7.25 (d, 3H, Ar-H, J=8 Hz), 7.11-7.13 (d, 3H, Ar-H, J=8.5 Hz), 5.86-5.89 (dd, 2H, pyrazoline-H, J1= J2= 3 Hz); 13C-NMR (DMSO-d6, 125 MHz, δ): 191.49, 189.68, 161.14, 153.55, 150.48, 144.53, 140.93, 139.24, 138.00, 135.11, 133.66, 131.14, 130.91, 130.17, 129.40, 129.29, 129.26,  129.01, 128.53, 125.80, 124.12, 122.51, 115.85, 115.95, 110.46, 56.03, 55.97; MS-ESI: 540.2 (m/z, M+); Analysis calculated for C33H21ClN4O2: C, 73.26; H, 3.91; Cl, 6.55; N, 10.36; O, 5.91. Found: C, 73.20; H, 3.96; Cl, 6.42; N, 10.38; O, 6.04.

7-[5-(4-hydroxyphenyl)-4,5-dihydro-1H-pyrazol-3-yl]-2,3-diphenyl-5H,10H-benzo[g]quinoxaline-5,10-dione (7c): White solid, yield 65%, mp 174°C, Rf 0.79; FT-IR (vmax, cm-1): 684, 759, 840, 1018, 1145, 1249 (C-O, phenolic), 1342, 1384, 1593, 1610, 1747, 2360, 3170, 3375 (O-H, phenolic); 1H-NMR (DMSO-d6, 500 MHz, δ): 8.14-8.15 (q, 1H, Ar-OH, J=1.5-3.5 Hz), 8.02 (s, 1H, Ar-H), 7.85-7.86 (t, 5H, Ar-H, J=2-6 Hz), 7.73-7.76 (d, 1H, Ar-H, J=15 Hz), 7.64-7.67 (t, 1H, pyrazoline-H, J=2-8.5 Hz), 7.54-7.57 (t, 1H, Ar-H, J1=J2= 7.5 Hz), 7.41-7.47 (m, 5H, Ar-H, J=5-10 Hz), 7.32-7.38 (m, 2H, pyrazoline-H, J=2-8.5 Hz), 7.03-7.04 (d, 2H, Ar-H, J=8.5 Hz), 6.83-6.85 (d, 2H, Ar-H, J=8.5 Hz), 5.83-5.86 (q, 1H, pyrazoline-H, J=3-8 Hz); MS-ESI: 522.3 (m/z, M+); Analysis calculated for C33H22N4O3: C, 75.85; H, 4.24; N, 10.72; O, 9.19. Found: C, 75.88; H, 4.21; N, 10.65; O, 9.26.

7-[5-(4-nitrophenyl)-4,5-dihydro - 1H - pyrazol-3-yl]-2,3-diphenyl-5H,10H-benzo[g]quinoxaline-5,10-dione (7d): Dark brown solid, yield 48%, mp 148°C, Rf 0.76; FT-IR (vmax, cm-1): 684, 759, 840, 995, 1176, 1342, 1382, 1461 (-NO2, sym.), 1512 (-NO2, asym.), 1593, 1610, 1725, 2536, 3170; 1H-NMR (DMSO-d6, 500 MHz, δ): 8.13-8.15 (d, 3H, Ar-H, J=6.5 Hz), 7.88-7.95 (q, 4H, Ar-H, J=3-19 Hz), 7.72-7.75 (d, 1H, pyrazoline-N-H, J=9.5 Hz), 7.64-7.67 (t, 1H, Pyrazoline-H, J1= J2=7 Hz), 7.55-7.58 (t, 2H, pyrazoline-H, J1=J2=7.5 Hz), 7.33-7.47 (m, 10H, Ar-H); MS-ESI: 551.4 (m/z, M+); Analysis calculated for C33H21N5O4: C, 71.86; H, 3.84; N, 12.70; O, 11.60. Found: C, 71.84; H, 3.89; N, 12.66; O, 11.61.

7-[5-(4-methoxyphenyl)-4,5-dihydro-1H-pyrazol -3-yl]-2,3-diphenyl-5H,10H-benzo[g]quinoxaline -5,10-dione (7e): Light silver solid, yield 72%, mp 164°C, Rf 0.71; FT-IR (vmax, cm-1): 688, 759, 833, 1006, 1126 (C-O-C, sym.), 1166, 1288 (C-O-C, asym.), 1359, 1388, 1585, 1614, 1740, 2360, 3136; 1H-NMR (DMSO-d6, 500 MHz, δ): 8.14-8.157 (d, 1H, Ar-H, J=8 Hz), 7.91-7.96 (q, 1H, Ar-H, J=2.5-16.5 Hz), 7.85-7.88 (q, 4H, Ar-H, J=2-8.5 Hz), 7.82 (s, 1H, Ar-H), 7.61-7.70 (m, 1H, pyrazoline-H, J=2.5-9 Hz), 7.32-7.57 (m, 10H, Ar-H, J=4.5-17 Hz), 6.92-6.94 (d, 2H, pyrazoline-H, J=8.5 Hz), 6.61-6.73 (m, 3H, Ar-OCH3, J=8.5-18 Hz), 5.77- 5.80 (dd, 1H, pyrazoline-N-H, J1=J2=2.5 Hz); MS-ESI: 536.2 (m/z, M+); Analysis calculated for C34H24N4O3: C, 76.11; H, 4.51; N, 10.44; O, 8.95. Found: C, 76.07; H, 4.55; N, 10.40; O, 8.98.

7-[5-(3-hydroxy-4-methoxyphenyl)-4, 5-dihydro-1H-pyrazol-3-yl]-2,3-diphenyl - 5H, 10H - benzo [g]quinoxaline-5,10-dione (7f): Red solid, yield 72%, mp 156°C, Rf 0.75; FT-IR (vmax, cm-1): 702, 790, 819, 979, 1116 (C-O-C, sym.), 1172, 1253 (C-O-C, asym.), 1292 (C-O, phenolic), 1342, 1373, 1591, 1654, 1899, 2347, 3072, 3386 (O-H, phenolic); 1H-NMR (DMSO-d6, 500 MHz, δ): 8.14-8.15 (d, 1H, Ar-H, J=6.5 Hz), 8.03 (s, 1H, Ar-H), 7.85-7.95 (m, 5H, Ar-H, J=7-19 Hz), 7.55-7.58 (t, 1H, pyrazoline-H, J1=J2=7.5 Hz), 7.43-7.47 (q, 5H, Ar-H, J=6.5-8 Hz), 7.33-7.38 (m, 1H, Ar-H, J=6.5-7 Hz), 6.83-6.85 (d, 1H, Ar-H, J=8 Hz), 6.76 (s, 1H, Ar-H), 6.56- 6.57 (d, 1H, Ar-H, J=7.5 Hz), 5.83-5.86 (dd, 1H, pyrazoline-N-H, J1=J2=3 Hz), 3.81-3.87 (q, 2H, pyrazoline-H, J=6.5-11 Hz), 3.33 (s, 3H, OCH3), 3.12-3.16 (dd, 1H, Ar-OH, J1=J2=3 Hz); MS-ESI: 552.1 (m/z, M+); Analysis calculated for C34H24N4O4: C, 73.90; H, 4.38; N, 10.14; O, 11.58 Found: C, 73.88; H, 4.39; N, 10.08; O, 11.35.

7-[5-(2-chlorophenyl)-4,5-dihydro-1H-pyrazol-3-yl]-2,3-diphenyl-5H,10H-benzo[g]quinoxaline-5, 10-dione (7g): Brown solid, yield 72%, mp 158°C, Rf 0.79; FT-IR (vmax, cm-1): 703, 775, 831, 983, 1174, 1209 (C-Cl, aryl), 1334, 1384, 1600, 1654, 1917, 2374, 3058; 1H-NMR (DMSO-d6, 500 MHz, δ): 8.02 (s, 1H, Ar-H), 7.92-7.97 (d, 1H, Ar-H, J=22 Hz), 7.83-7.86 (t, 5H, Ar-H, J=6-9 Hz), 7.42-7.47 (t, 5H, Ar-H, J=8.5-15.5 Hz), 7.32-7.37 (m, 1H, Ar-H, J=4.5-8.5 Hz), 7.03- 7.04 (d, 1H, Ar-H, J =9 Hz), 6.93-6.94 (d, 2H, Ar- H, J=9 Hz), 6.83-6.85 (d, 1H, Ar-H, J=8.5 Hz), 6.61-6.63 (d, 2H, pyrazoline-H, J=9 Hz), 5.83-5.86 (dd, 1H, pyrazoline-N-H, J1=J2=3 Hz), 5.78-5.80 (dd, 1H, pyrazoline-H, J1=7.5 Hz, J2=8 Hz); MS-ESI: 540.2 (m/z, M+); Analysis calculated for C33H21ClN4O2: C, 73.26; H, 3.91; Cl, 6.55; N, 10.36; O, 5.91. Found: C, 73.20; H, 3.99; Cl, 6.60; N, 10.40; O, 5.81.

7-[5-(4-trifluoromethylphenyl)-4,5-dihydro- 1H -pyrazol-3-yl]-2,3-diphenyl - 5H, 10H - benzo [g] quinoxaline-5,10-dione (7h): Dark brown solid, yield 67%, mp 180°C, Rf 0.81; FT-IR (vmax, cm-1): 696, 757, 831, 1072, 1093, 1263 (C-F, aryl), 1353, 1384, 1583, 1670, 1876, 2393, 3143; 1H-NMR (DMSO-d6, 500 MHz): 8.14-8.15 (t, 1H, pyrazoline-H, J=4-8 Hz), 8.11 (s, 1H, Ar-H), 7.81-7.95 (m, 4H, Ar-H, J=3.5-9.5 Hz), 7.54-7.67 (m, 2H, Ar-H, J=2-9 Hz), 7.31-7.49 (m, 10H, Ar-H, J=5.5-10 Hz), 7.10-7.14 (t, 2H, pyrazoline-H, J=8-10.5 Hz), 5.88-5.91 (dd, 1H, pyrazoline-N-H, J1=J2=3.5 Hz); MS-ESI: 574.1 (m/z, M+); Analysis calculated for C34H21F3N4O2: C, 71.08; H, 3.68; F, 9.92; N, 9.75; O, 5.57. Found: C, 71.11; H, 3.65; F, 9.90; N, 9.75; O, 5.59.

7-[5-(3,4-dimethoxyphenyl)-4, 5 - dihydro - 1H -pyrazol-3-yl]-2,3-diphenyl - 5H, 10H -benzo [g] quinoxaline-5,10-dione (7i): Light silver solid, yield 72%, mp 164°C, Rf 0.71; FT-IR (vmax, cm-1): 688, 763, 840, 1026, 1139 (C-O-C, sym.), 1166, 1307 (C-O-C, asym.), 1350, 1382, 1587, 1680, 1753, 2302, 3149; 1H-NMR (DMSO-d6, 500 MHz, δ): 8.59 (s, 1H, Ar-H), 8.13-8.14 (d, 2H, Ar-H, J=3 Hz), 7.86-7.95 (m, 3H, Ar-H, J=3-20.5 Hz), 7.64-7.75 (m, 2H, pyrazoline-H), 7.32-7.47 (m, 10H, Ar-H), 7.23-7.24 (d, 1H, pyrazoline-H, J=8 Hz), 6.86-6.88 (d, 1H, pyrazoline-H, J=8 Hz), 4.34 (s, 3H, OCH3), 3.81 (s, 3H, OCH3); MS-ESI: 566.4 (m/z, M+); Analysis calculated for C35H26N4O4: C, 74.19; H, 4.63; N, 9.89; O, 11.29. Found: C, 74.20; H, 4.65; N, 9.85; O, 11.30.

7-[5-(4-methylphenyl)-4,5-dihydro-1H - pyrazol-3-yl]-2,3-diphenyl-5H,10H-benzo[g]quinoxaline-5,10-dione (7j): Red  solid, yield 69%, mp 164°C, Rf 0.73; FT-IR (vmax, cm-1): 688, 763, 838, 1004, 1157, 1352, 1377, 1583, 1612, 1810, 2374, 2835 (C-H, sp3, CH3), 3155; 1H-NMR (DMSO-d6, 500 MHz, δ): 8.11-8.15 (q, 4H, Ar-H, J=3.5-8.5 Hz), 7.78-7.85 (q, 6H, Ar-H, J=3.5-15.5 Hz), 7.69-7.72 (d, 2H, Ar-H, J=15.5 Hz), 7.62-7.65 (t, 2H, pyrazoline-H, J=7-7.5 Hz), 7.53-7.56 (t, 4H, Ar-H, J=7.5 Hz), 7.45-7.47 (d, 1H, Ar-H, J=7 Hz), 7.34-7.35 (d, 1H, pyrazoline-H, J=7.5 Hz), 6.99-7.01 (d, 1H, pyrazoline-H, J=9 Hz), 3.80 (s, 3H, CH3); 13C-NMR (DMSO-d6, 125 MHz, δ): 207.01, 176.37, 155.45, 153.56, 144.53, 139.24, 133.66, 131.85, 130.92, 130.17, 129.74, 129.40, 129.29,  129.26, 129.01, 128.94, 128.53,  128.51, 127.81, 127.61, 122.51, 62.68, 42.68, 21.54; MS-ESI: 520.2 (m/z, M+); Analysis calculated for C34H24N4O2: C, 78.44; H, 4.65; N, 10.76; O, 6.15. Found: C, 78.40; H, 4.66; N, 10.78; O, 6.16.

Compound 7(k): 7-[5-(4-aminophenyl) - 4, 5-dihydro-1H-pyrazol-3-yl]-2,3-diphenyl- 5H,10H-benzo[g]quinoxaline-5, 10 - dione (7k): Orange solid, yield 70%, mp 158°C, Rf 0.80; FT-IR (vmax, cm-1): 740, 779, 835, 999, 1170, 1377, 1390, 1585, 1602 (>C=O, cyclic, conjugated, 1° amine, N-H, bend), 1757, 2374, 3058 (N-H, pyrazoline), 3236 (1° amine, N-H, str.); 1H-NMR (DMSO-d6, 500 MHz, δ): 7.95-7.97 (bd, 2H, Ar-NH2, J=7.5 Hz), 7.82-7.88 (m, 3H, Ar-H, J=2.5-21.5 Hz), 7.44-7.47 (t, 1H, pyrazoline-H, J=6-7 Hz), 7.32-7.38 (m, 1H, pyrazoline-N-H, J=3-7.5 Hz), 7.23-7.25 (d, 5H, Ar-H, J=8 Hz), 7.02-7.03 (d, 5H, Ar-H, J=8.5 Hz), 6.83-6.84 (d, 4H, Ar-H, J=8.5 Hz), 5.81-5.84 (dd, 2H, pyrazoline-H, J1=J2=2.5 Hz); MS-ESI: 521.5 (m/z, M+); Analysis calculated for C33H23N5O2: C, 75.99; H, 4.44; N, 13.43; O, 6.14. Found: C, 76.01; H, 4.42; N, 13.39; O, 6.18.

In-vitro Antimycobacterial Screening: The newly synthesized compounds were submitted for their antimycobacterial activity against Mycobacterium tuberculosis H37Rv by L.J. Slope (Conventional) Method 28 - 29. Each compound was diluted to obtain 2000 μg/ml concentration (as a stock solution).

Inoculum Size for M. tuberculosis was adjusted to 1 mg/ml. L. J. Medium was used as nutrient medium. Isoniazid (0.20µg/ml) and rifampicin (0.25µg/ml) were used as standard drug.

TABLE 1: ANTIMYCOBACTERIAL SCREENING OF COMPOUNDS (7a-k) AGAINST MYCOBACTERIUM TUBERCULOSIS H37Rv, MIC (μg/ml) (L. J. SLOPE METHOD)

Compound R MIC (μg/mL)
7a H ---
7b 4-Cl 125
7c 4-OH 100
7d 4-NO2 62.5
7e 4-OCH3 250
7f 3-OH-4-OCH3 100
7g 2-Cl 125
7h 4-CF3 250
7i 3,4-(OCH3)2 1000
7j 4-CH3 12.5
7k 4-NH2 250
Rifampicin --- 0.25
Isoniazid --- 0.20 

Primary screen:    500 µg/ml, 250 µg/ml, and 125 µg/ml concentrations of the compounds were considered for primary screening. The compounds found active in primary screening were further tested in second set of dilution against M. tuberculosis. 

Secondary screen:  The compounds found active in primary screening were similarly diluted to obtain 100 µg/ml, 50 µg/ml, 25 µg/ml, 12.5 µg/ml, 6.250 µg/ml, 3.125 µg/ml and 1.5625 µg/ml concentrations and were tested.

Reading Result: The result was expressed in term of Minimum Inhibitory concentration (MIC). The highest dilution inhibiting 99% of M. tuberculosis population was considered as MIC.

RESULT AND DISCUSSION:

Chemistry: 2, 3 - Dihydroxynaphthalene on refluxing with phosphorus oxychloride yields 2, 3-dichloronaphthalene (1). Compound 1 on refluxing with ammonium chloride in excess of ammonia, catalytic amount of dil. HCl and ethanol undergoes amination (nucleophilic substitution) and furnishes 2,3-diaminonaphthalene (2).

Compound 2 on refluxing with equimolar quantity of benzil in ethanol undergoes nucleophilic addition followed by dehydration to yield 2,3-diphenylbenzo[g] quinoxaline (3). Compound 3 undergoes aromatic oxidation on refluxing with equimolar mixture of chromium trioxide and glacial acetic acid in water, furnishes 2,3-diphenylbenzo[g]quinoxaline-5,10-dione (4).

Compound 4 on acetylation reaction with acetylchloride and anhydrous aluminium chloride in carbon tetrachloride yields 7-acetyl - 2, 3-diphenylbenzo[g]quinoxaline-5, 10-dione (5).

Compound 5 on stirring with appropriate substituted benzaldehydes in potassium hydroxide saturated with methanol furnishes 7-[3-(substituted) phenylprop-2-enoyl]-2,3-diphenyl - 5H, 10H-benzo [g]  quinoxaline - 5, 10-dione (6a-k) (Cannizzaro Raction). Compound 6(a-k) were further refluxed with hydrazine hydrochloride in ethanol under anhydrous conditions to furnish 7-[5-(substituted) phenyl-4,5-dihydro-1H-pyrazol-3-yl]-2,3-diphenyl-5H, 10H - benzo [g] quinoxaline - 5, 10 - dione (Compound 7a-k). The structures of all the newly synthesized compounds (7a-k) belonging to series 7-[5-(substituted)phenyl-4,5-dihydro - 1 H-pyrazol-3-yl]-2,3-diphenyl-5H,10H-benzo[g]quinoxaline-5, 10 -dione  (Compound 7a-k) were confirmed by FT-IR, 1H-NMR, MS-ESI spectral data interpretation and their elemental analysis.

FT-IR spectrum of 7-[5-phenyl-4,5-dihydro-1H-pyrazol-3-yl]-2, 3-diphenyl-5H, 10H - benzo [g] quinoxaline-5,10-dione (7a) showed bands at 696 cm-1, 757 cm-1, 829 cm-1, 985 cm-1, 1147 cm-1, 1353 cm-1, 1379 cm-1, 1583 cm-1, 1656 cm-1, 1749 cm-1, 2358 cm-1 and 3058 cm-1  belonging to mono-substituted aromatic ring, ortho-disubstituted aromatic ring, para-disubstituted aromatic ring, meta- disubstituted aromatic ring, = N - N (pyrazoline), C-N (pyrazoline), C-N (quinoxaline), C=N (pyrazoline), >C=O (cyclic, conjugated, C=N (quinoxaline), C-C (cyclic, pyrazoline)  and N-H (pyrazoline) respectively. In 1H-NMR spectrum of compound (7a), a singlet at 8.59 ppm belonging to one aromatic proton present at C-6 of quinoxaline-5,10-dione ring. A multiplet at 7.86-7.95 ppm confirms five aromatic protons of phenyl ring attached to C-5 of pyrazoline ring.

A doublet at 7.72-7.75 ppm with J value of 11 Hz confirmed one aromatic proton at C-9 of quinoxaline-5,10-dione ring. A triplet at 7.64-7.67 ppm with J value 7-7.5 Hz confirmed one aromatic proton at C-8 of quinoxaline-5,10-dione ring. A triplet at 7.54-7.57 ppm with J value 7.5-8 Hz belonged to two protons at C-4 of pyrazoline ring. A multiplet at 7.32-7.46 ppm confirmed ten aromatic protons of two phenyl rings present at C-2 and C-3 of quinoxaline-5,10-dione ring. A doublet at 7.23-7.24 ppm having J value 7.5 Hz belonged to one proton attached to C-5 of pyrazoline ring. A quarlet at 6.83-6.88 ppm with J value 5.5-8.5 Hz belonged to one proton attached at N-1 of pyrazoline ring.

13C-NMR spectrum of compound (7a) showed the prominent peaks at 189.68  ppm (C5, C10 of quinoxaline-5,10-dione ring), 176.58 ppm (C4a, C10a of quinoxaline-5,10-dione ring), 155.40 ppm (C3 of quinoxaline-5,10-dione ring), 153.56 ppm (C2 of quinoxaline-5,10-dione ring), 144.53 ppm (C3 of pyrazoline), 143.47 ppm (C1 of phenyl ring attached to C-3 of quinoxaline-5,10-dione ring), 140.93 ppm (C1 of phenyl ring attached to C-2 of quinoxaline-5,10-dione ring), 139.24 ppm (C1 of phenyl ring attached to C-5 of pyrazoline ring), 138.01 ppm (C5 of phenyl ring attached to C-2 of quinoxaline-5,10-dione ring), 135.12 ppm (C7 of quinoxaline-5,10-dione ring), 133.66 ppm (C5a, C9a of quinoxaline-5,10-dione ring), 131.36 ppm (C2 of phenyl ring attached to C-5 of pyrazoline ring), 131.14 ppm (C4 of phenyl ring attached to C-2 of quinoxaline-5,10-dione ring), 131.03 ppm (C4 of phenyl ring attached to C-3 of quinoxaline-5,10-dione ring), 130.92 ppm (C5 of phenyl ring attached to C-3 of quinoxaline-5,10-dione ring), 130.18 ppm (C6 of phenyl ring attached to C-5 of pyrazoline ring), 129.41 ppm (C2 of phenyl ring attached to C-3 of quinoxaline-5,10-dione ring), 129.40 ppm (C2 of phenyl ring attached to C-2 of quinoxaline-5,10-dione ring), 129.29 ppm (C6 of phenyl ring attached to C-3 of quinoxaline-5,10-dione ring), 129.26 ppm (C6 of phenyl ring attached to C-2 of quinoxaline-5,10-dione ring), 129.16 ppm (C3 of phenyl ring attached to C-2 of quinoxaline-5,10-dione ring), 129.01 ppm (C9 of quinoxaline-5,10-dione ring), 128.98 ppm (C3 of phenyl ring attached to C-3 of quinoxaline-5,10-dione ring), 128.54 ppm (C6 of quinoxaline-5,10-dione ring), 127.59 ppm (C3 of phenyl ring attached to C-5 of pyrazoline ring), 127.39 ppm (C5 of phenyl ring attached to C-5 of pyrazoline ring), 125.75 ppm (C8 of quinoxaline-5,10-dione ring),  122.52 ppm (C4 of phenyl ring attached to C-5 of pyrazoline ring), 63.31 ppm (C5 of pyrazoline ring) and 42.86 ppm (C4 of pyrazoline ring). ESI-MS spectrum of compound (7a) showed M+ peak at 506.5, close to its molecular weight. Similarly, structures of other compounds of the newly synthesized series viz. 7-[5-(substituted) phenyl-4, 5-dihydro-1H-pyrazol-3-yl]-2,3-diphenyl-5H,10H-benzo[g] quinoxaline - 5, 10-dione (7a-k) were confirmed.

Biological Activity (In-vitro Antimycobacterial Screening): The newly synthesized compounds 7b, 7c, 7d, 7e, 7f, 7g, 7h, 7i, 7j and 7k of the series 7-[5-(substituted)phenyl-4,5-dihydro-1H-pyrazol-3-yl]-2,3-diphenyl-5H,10H-benzo[g]quinoxaline - 5, 10-dione  (Compound 7a-k) were screened for their antimycobacterial activity against Mycobacterium tuberculosis H37Rv by L.J. Slope (Conventional) Method to observe the effect of substitution at phenyl ring attached to 5-position of pyrazoline ring attached to C-7 of the series 7-[5-(substituted) phenyl-4,5-dihydro-1H-pyrazol-3-yl]-2,3-diphenyl-5H,10H-benzo[g] quinoxaline - 5, 10 - dione (Compound 7a-k). Isoniazid and Rifampicin were used as standard drugs.

Compound 7j having electron donating 4-CH3 group on phenyl ring attached to the above mentioned position has been observed as the most active antimycobacterial compound. Compounds 7d, 7b, 7g having electron withdrawing 4-NO2, 4-Cl, 2-Cl groups and compounds 7c and 7f  having electron donating 4-OH and 3-OH-4-OCH3 groups respectively on phenyl ring attached to above mentioned position have exhibited significant antimycobacterial activity.

While compounds 7e and 7k having electron donating 4-OCH3 and 4-NH2 groups respectively and compound 7h having electron withdrawing 4-CF3 group on phenyl ring attached to above mentioned position, have exhibited moderate antimycobacterial activity. Compound 7i having electron donating  3, 4-(OCH3)2 group on phenyl ring attached to above mentioned position has been observed as the least active antimycobacterial compound of the newly synthesized series 7-[5-(substituted)phenyl-4,5-dihydro-1H-pyrazol-3-yl]-2,3-diphenyl - 5H, 10H-benzo[g]quinoxaline-5,10-dione  (Compound 7a-k).  

CONCLUSION: After the interpretation of the results obtained after antimycobacterial screening, Structure Activity Relationship (SAR) may be established, for the series 7-[5-(Substituted)phenyl-4,5-dihydro-1H-pyrazol-3-yl]-2,3-diphenyl-5H, 10 H-benzo[g]quinoxaline-5,10-dione  (Compound 7a-k), as “substitution with smaller functional group at the ortho and para-position of phenyl ring attached to 5-position of pyrazoline ring attached to C-7 of 2,3-diphenylbenzo[g] quinoxaline - 5, 10 - dione nucleus increases antimycobacterial activity, while substitution with larger functional groups at the para-position of phenyl ring present at the above mentioned position produces moderate active antimycobacterial compounds. Compounds with more powerful electron donating groups like 3,4-(OCH3)2 group at phenyl ring attached to above mentioned position produces least active anti mycobacterial compound.”

ACKNOWLEDGEMENT: Authors are thankful to Microcare Laboratory and TRC, Surat, Gujarat (India) for providing antimycobacterial activity data and Advanced Instrumentation Research Facilities (AIRF), Jawaharlal Nehru University, New Delhi (India) for providing spectral data.

CONFLICT OF INTEREST: Authors have no conflict of interest.

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    How to cite this article:

    Kumar S, Kumar N and Drabu S: Synthesis of benzo[g]quinoxaline-5,10-dione based pyrazoline derivatives and their antimycobacterial activity. Int J Pharm Sci Res 2018; 9(2): 498-08.doi: 10.13040/IJPSR.0975-8232.9(2).498-08.

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Article Information

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498-508

434

1805

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English

IJPSR

S. Kumar *, N. Kumar and S. Drabu

Department of Pharmacy, Government Polytechnic, Uttawar, Palwal, Haryana, India.

shiv_hamdard@yahoo.co.in

14 May, 2017

23 July, 2017

25 July, 2017

10.13040/IJPSR.0975-8232.9(2).498-08

01 February, 2018

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