Synthesis of benzo[g]quinoxaline-5,10-dione based pyridine derivatives and their antimycobacterial activity

Article abstract of DOI:10.13005/ojc/330230

Thirteen new compounds belonging to series 2-amino-6-(5,10-dioxo-2,3-diphenyl-5,10-dihydrobenzo[g]quinoxalin-7-yl)-4-(substituted)phenylpyridine-3-carbonitrile (6a-m) were synthesized by multistep synthetic scheme. The newly synthesized compounds were screened for their antimycobacterial activity by L.J. Slope (Conventional) Method. Compound 6h with 4-N(CH₃)₂ group at phenyl ring of above mentioned position has been reported as most active antimycobacterial compound and compound 6k with 4-CH₃ substitution at phenyl above mentioned position has been reported as the least active antimycobacterial compound.

Full text of DOI:10.13005/ojc/330230

ISSN: 0970-020 X
CODEN: OJCHEG
2017, Vol. 33, No. (2):
Pg. 821-828
ORIENTAL JOURNAL OF CHEMISTRY
An International Open Free Access, Peer Reviewed Research Journal
www.orientjchem.org
Synthesis of Benzo[g]quinoxaline-5,10-dione Based
Pyridine Derivatives and their Antimycobacterial Activity
SHIV KUMAR1*, NITIN KUMAR2 and SUSHMA DRABU3
1Faculty of Pharmacy, Uttrakhand Technical University, Dehradun-248007, India.
2Oxford College of Pharmacy, Masoori Industrial Area, U.P.S.I.D.C., M.G. Road,
Ghaziabad-201001, India.
3Maharaja Surajmal Institute of Pharmacy, Janak Puri, New Delhi-110058, India.
*Corresponding author E-mail: shiv_hamdard@yahoo.co.in
http://dx.doi.org/10.13005/ojc/330230
(Received: January 11, 2017; Accepted: March 25, 2017)
ABSTRACT
Thirteen new compounds belonging to series 2-amino-6-(5,10-dioxo-2,3-diphenyl-
5,10-dihydrobenzo[g]quinoxalin-7-yl)-4-(substituted)phenylpyridine-3-carbonitrile (6a-m) were
synthesized by multistep synthetic scheme. The newly synthesized compounds were screened for
their antimycobacterial activity by L.J. Slope (Conventional) Method. Compound 6h with 4-N(CH3)2
group at phenyl ring of above mentioned position has been reported as most active antimycobacterial
compound and compound 6k with 4-CH3 substitution at phenyl above mentioned position has been
reported as the least active antimycobacterial compound.
Keywords: Quinoxaline, Benzo[g]quinoxaline-5,10-dione, Pyridine, Antimycobacterial.
INTRODUCTION
estimated 9.6 million new TB cases were reported
and 1.5 million deaths were caused due to TB
worldwide16. Quinoxaline ring is also a an important
part of antileprotic drug clofazimine (CZM) which
is also widely indicated for treatment of multidrug
resistant tuberculosis.InMycobacterium tuberculosis,
CZM is reduced by NADH-dehydrogenase (NDH-2)
to release reactive oxygen17 and CZM also act as
competitor with menaquinone (MK-4), which acts
as a key factor for its reduction by NDH-218. First
line antitubercular drug isoniazid (INH) and second
line antitubercular drug ethionamide (Etm) are
derivatives of six membered nitrogen containing
Quinoxaline and pyridine derivatives
constitute the important part of various antibiotics
viz. hinomycin, levomycin and actinoleutin that
inhibit the growth various bacteria and are found
to be cytotoxic against various transplantable
tumours1-7. Quinoxaline derivatives also exhibited a
wide range of biological activities viz. antifungal8-10
antibacterial11-12, antitubercular8-9,12-15
,
.
Tuberculosis (TB) is a major health problem
worldwide now-a-days. In year 2014, there were an

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pyridine ring. Isoniazid and Ethionamide, after 756 (ortho-disubstituted phenyl ring), 856 (meta-
bioactivation by mycobacterial catalase-peroxidase disubstituted phenyl ring), 1160 (aryl C-Cl), 1384
enzyme complex, inhibit synthesis of mycolic acids19- (aromatic C=C); 1H-NMR (CDCl3 300 MHz) d : 8.16-
23, that are important components of mycobacterial 8.20 (q, J=5-6 Hz, A2B2 pattern, 2H, Ar-H), 7.74-7.79
cell wall.
(m, J=4.5-6 Hz, 2H, Ar-H), 7.50-7.53 (m, J=1-4 Hz,
2H, Ar-H)
EXPERIMENTAL
Synthesis of 2,3-Diaminonaphthalene (2)
Chemistry
Compound 1 (2 gm) was dissolved in
Melting points were measured in open absolute ethanol. Ammonium chloride (1.5 gm),
capillary tubes and are uncorrected. All the Fourier- dil. HCl (in catalytic amount) and excess of strong
Transform Infra Red (FT-IR) spectra were recorded ammonium solution were added to it and refluxed
on Shimdazu FT-8400 Spectrophotometer using KBr for 6 h on water bath till appearing of permanent dark
pallets.The1H-NMRspectrawererecordedonBruker- greenish colour.After completion of reaction, solution
Spectrospin DCX NMR spectrometer using DMSO-d6 was cooled and kept in deep freezer for overnight.
and CDCl3 as solvents and tetramethylsilane (TMS)
as an internal standard (Chemical shifts expressed in
d/ppm The purity of the compounds was checked by recrystallized with methanol. Dark greenish crystals;
thin layer chromatography (TLC) on Merck Silica Gel Yield 75%; Rf 0.89, Rf 0.82; mp 150oC; IR (nmax
60F254 precoated sheets usingToluene :Ethylacetate KBr, cm-1): 758, 854, 1473 (aromatic =C-N), 1500
Greenish crystals were filtered, dried and
,
: Formic acid (5:4:1) solution as mobile phase.
(aromatic C=C), 1681 (N-H), 3049 (N-H); 1H-NMR
(CDCl3 500 MHz): 7.45-7.46 (dd, J=3.5-4 Hz, 2H,
Ar-H), 7.12-7.14 (dd, J=3-3.5 Hz, 2H, Ar-H), 7.09 (s,
Synthesis of 2,3-Dichloronaphthalene (1)
2,3-dihydroxynaphthalene (5 gm) was Ar-H, 2H), 7.05 (s, Ar-NH2,4H).
dissolved in phosphorusoxychloride (90 mL) in parts
at 0o-5oC with occasionally stirring and refluxed for 2,3-Diphenylbenzo[g]quinoxaline (3)
about 4 h till the appearance of clear dark pinkish
Equimolar quantities of compound 2
solution. This solution was cooled and poured (0.001 mol) and benzil (0.001 mol) were dissolved in
into ice-cold water. A dark pinkish solid appeared ethanol (30 mL) and refluxed for 2 h.After completion
and was filtered, dried and recrystallized with of reaction, reaction mixture was cooled, kept for
dimethylformaide (DMF). Pinkish crystalline solid; overnight, yellow crystalline solid was filtered, dried
Yield 85%; Rf 0.72; mp 185oC. IR (nmax, KBr, cm-1): and recrystallized with ethanol : methanol (1:1)
N
NH
OH
OH
Cl
Cl
2
(iii)
(ii)
(i)
N
NH
2
(3)
(2)
(1)
(iv)
O
Compound
R
O
O
6a
6b
6c
6d
H
N
N
N
(v)
4-Cl
H
C
3
4-OH
N
O
4-NO2
O
(4)
(5)
(vi)
6e
4-OCH3
6f
3-OH-4-OCH3
2-Cl
O
6g
6h
N
4-N(CH3)2
N
6i
4-CF3
N
O
R
6j
3,4-(OCH3)2
4-CH3
NC
NH
2
6k
6l
(6a...)
4-NH2
6m
2-OH
Reagents & Conditions : (i) POCl3, Reflux for 4 h (ii) NH4Cl, NH3 in excess, EtOH, Reflux at water-bath for 6 h
(iii) Benzil, EtOH, Reflux for 2 h (iv) CrO3/AcOH, Reflux for 2 h (v) CH3COCl, CCl4, AlCl3, Reflux for 6 h (vi)
Malononitrile, R-C6H4-CHO, CH3OONH4, NH3, EtOH, dil. HCl, Reflux for 48-50 h
Fig. 1: Reaction Scheme

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KUMAR et al., Orient. J. Chem., Vol. 33(2), 821-828 (2017)
mixture. Yellow crystalline solid;Yield 72%; Rf 0.83;
mp 170oC; IR (nmax,KBr, cm-1) : 725, 785, 820, 875,
1475, 1510 (aromatic C=C), 1660 (quinoxaline
C=N);1H-NMR (DMSO-d6 500 MHz) d:8.73-8.77 (m,
J=2.5-4 Hz, 10H, Ar-H), 8.28 (s, 2H, Ar-H), 8.03-8.07
(m, 4H, J=2.5-4 Hz, Ar-H).
Equimolar quantities of compound 5
(0.01 mol), appropriate benzaldehyde (0.01 mol),
ammonium acetate (2 gm) and malononitrile (0.01
mol) and were dissolved in ethanol (30 mL) and
was refluxed under anhydrous conditions for 48-50
h till the permanent appearance of crystalline solid.
Solid was filtered, dried and recrystallized with
chloroform.
Synthesis of 2,3-Diphenylbenzo[g]quinoxaline-
5,10-dione (4)
Compound 3 (1.2 gm) was dissolved in
2-Amino-6-(5,10-dioxo-2,3-diphenyl-5,10-
dihydrobenzo[g]quinoxalin-7-yl)-4-phenyl
pyridine-3-carbonitrile (6a)
glacial acetic acid (30 mL) and chromium trioxide
(1.1 gm) in 12 mL of glacial acetic acid : water (1:1)
solution was added to it. This solution was refluxed
at 80oC for 2 h and then poured into ice-chilled
water (1500 mL). Resulting solid was filtered, dried,
recrystallized with methanol.White solid;Yield 65%;
Rf 0.78; mp 162oC; IR (nmax, KBr, cm-1): 718, 795,
875, 1450, 1594 (>C=O, cyclic, conjugated), 1676;
1H-NMR (CDCl3 500 MHz) d: 8.13-8.15 (d, 2H, J=8.5
Hz, Ar-H), 7.85-7.88 (t, J=2.5-10.5 Hz, 4H, Ar-H),
7.81-7.82 (d, J=8 Hz, 2H, Ar-H), 7.50-7.53 (t, J=7.5
Hz, 6H, Ar-H); Elemental Anal. Found (Calcd.) for
C24H14N2O2: Found: C, 79.42 (79.55); H 3.91 (3.89);
N 7.68 (7.73); O 8.95 (8.83).
Yellow crystalline solid;Yield 74%; Rf 0.84;
mp 230oC; IR (nmax, KBr, cm-1): 719, 756, 820, 875,
1296 (C=N, pyridine), 1384 (C-N), 1608 (>C=O,
cyclic, conjugated), 1642 (N-H, primary amine,
bend), 1697 (C=N, quinoxaline), 2358 (C-N, nitrile),
3417 (N-H, primary amine, str.);1H-NMR (CDCl3 500
MHz) d: 12.47 (s, 1H, Ar-H), 11.91 (s, 2H, Ar-H),
11.73 (bs, 2H, Ar-NH2), 9.03-9.04 (d, J=5 Hz, 1H,
Ar-H), 8.01-8.02 (d, 2H, J=8 Hz, Ar-H), 7.75-7.79
(t, J=8-12 Hz, 3H, Ar-H), 7.59-7.63 (t, J=8.5-9.5 Hz,
4H, Ar-H), 7.12-7.30 (m, J=7.5-14.5 Hz, 6H, Ar-H);
MS-ESI: 555.05 (m/z, M+); Elemental Anal. Found
(Calcd.)for C36H21N5O2 : C, 77.80 (77.83); H, 3.82
(3.81); N, 12.60 (12.61); O, 5.76 (5.76).
Synthesis of 7-Acetyl-2,3-diphenylbenzo[g]
quinoxaline-5,10-dione (5)
Anhydrous aluminium trichloride (1 gm)
was dissolved in carbon tetrachloride (30 mL) and
acetyl chloride (2 mL) was added to it under cold
conditions (0o-5oC). Compound 4 (120 mg) was
added and stirred at room temperature for 6 h.Yellow
crystalline solid was filtered, dried and recrystallized
with chloroform.
2-Amino-(4-chlorophenyl)-6-{5,10-dioxo-2,3-
diphenyl-5H,10H-benzo[g]quinoxalin-7-yl}
pyridine-3-carbonitrile (6b)
Yellow crystalline solid;Yield 80%;Rf 0.80;
mp 232oC; IR (nmax, KBr, cm-1): 723, 760, 819, 875,
1162 (aryl C-Cl), 1284, 1383, 1592, 1645, 1697,
2363, 3404; 1H-NMR (DMSO-d6 500 MHz) d: 8.73-
8.77 (m, J=2.5-4 Hz, 10H, Ar-H), 8.03-8.07 (m,
J=3.0-3.5 Hz, 4H, Ar-H), 7.70-7.78 (q, J=7.5-15 Hz,
1H, Ar-H), 7.36-7.38 (d, J=8.5 Hz, 1H, Ar-H), 7.28-
7.30 (d, J=7.5 Hz, 1H, Ar-H), 7.16-7.19 (t, J=8-7.5
Hz, 1H, Ar-H), 6.94-6.96 (d, J=8 Hz, 2H, Ar-NH2);
MS-ESI: 589.08 (m/z, M+); Elemental Anal. Found
(Calcd.) for C36H20ClN5O2 : C, 73.27 (73.28); H, 3.43
(3.42); Cl, 5.98 (6.01); N, 11.89 (11.87); O, 5.42
(5.42).
Yellow crystalline solid;Yield 48%; Rf 0.74;
mp 225oC; IR (nmax, KBr, cm-1): 725, 775, 810, 875,
1450, 1500, 1593 (>C=O, cyclic, conjugated), 1672
(C=N, quinoxaline), 1974 (>C=O, aliphatic), 3063
(C-H, sp3, CH3); 1H-NMR (CDCl3 500 MHz) d: 7.97-
7.98 (d, J=8 Hz, 4H, Ar-H), 7.65-7.68 (t, J=7.5 Hz,
3H, Ar-H), 7.50-7.53 (t, 6H, J=7.5-8 Hz, Ar-H), 7.26
(s, 3H, CH3CO);MS-ESI:404.14 (m/z, M+);Elemental
Anal.Found (Calcd.) for C26H16N2O3 :C 77.23 (77.22);
H 3.98 (3.99); N 6.97 (6.93); O 11.82 (11.87).
2-Amino-6-{5,10-dioxo-2,3-diphenyl-5H,10H-
benzo[g]quinoxalin-7-yl}-4-(4-hydroxyphenyl)
pyridine-3-carbonitrile (6c)
Yellow crystalline solid;Yield 72%; Rf 0.78;
mp 250oC; IR (nmax, KBr, cm-1) : 718, 765, 827, 895,
1256 (phenolic C-O phenolic), 1351, 1402, 1596,
Synthesis of 2-amino-6-(5,10-dioxo-2,3-
diphenyl-5,10-dihydrobenzo[g]quinoxalin-7-yl)-
4-(substituted) phenylpyridine-3-carbonitrile
(6a-m)

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1679, 1683, 2358, 3146, 3367 (O-H phenolic); 1H- (C-O, phenolic), 1342, 1424 (C-N), 1611, 1660, 1673,
NMR (DMSO-d6 500 MHz) d: 9.12 (s, 1H, Ar-H), 2360, 3326, 3381 (O-H, phenolic); 1H-NMR (CDCl3
8.72-8.76 (m, J=2.5-4 Hz, 10H, Ar-H), 8.56-8.58 (d, 500 MHz) d: 7.80-7.81 (d, J=7 Hz, 10H, Ar-H), 7.96-
J=9 Hz, 1H, Ar-H), 8.48-8.49 (d, J=9 Hz, 1H, Ar-H), 7.97 (d, J=7.5 Hz, 1H, Ar-OH), 7.09 (s, 2H, Ar-NH2),
7.99-8.11 (t, J=3-5 Hz, 1H, Ar-H), 7.68-7.72 (dd, J=9 7.33-7.36 (t, J=7.5-8 Hz, 3H, Ar-H), 7.48-7.51 (t,
Hz, 2H, Ar-H), 7.44-7.49 (dd, J=9 Hz, 2H, Ar-H), 6.98 J=2.5-7.5 Hz, 2H, Ar-H), 7.63-7.66 (t, J=7-8 Hz, 1H,
(s, 2H, Ar-NH2), 6.86-6.88 (t, J=3-4 Hz, 1H, Ar-OH); Ar-H), 7.16-7.20 (t, J=7.5-8.5 Hz, 1H, Ar-H), 3.31 (s,
MS-ESI: 571.11 (m/z, M+); Elemental Anal. Found 3H, Ar-OCH3); MS-ESI:601.16 (m/z, M+);Elemental
(Calcd.) for C36H21N5O3 : C, 75.62 (75.65); H, 3.69 Anal.Found (Calcd.) for C37H23N5O4 :C, 73.85 (73.87);
(3.70); N, 12.27 (12.25); O, 8.39 (8.40).
H, 3.86 (3.85); N, 11.65 (11.64); O, 10.63 (10.64).
2-Amino-6-{5,10-dioxo-2,3-diphenyl-5H,10H- 2-Amino-4-(2-chlorophenyl)-6-{5,10-dioxo-
benzo[g]quinoxalin-7-yl}-4-(4-nitrophenyl) 2,3-diphenyl-5H,10H-benzo[g]quinoxalin-7-yl}
pyridine-3-carbonitrile (6d)
Yellow crystalline solid; Yield 68%; mp
pyridine-3-carbonitrile (6g)
White crystalline solid;Yield 66%; Rf 0.72;
210oC; Rf 0.80; IR (nmax, KBr, cm-1): 720, 758, 811, mp 180oC; IR (nmax, KBr, cm-1): 736, 761, 815, 892,
854, 1284, 1383 (-NO2, sym.), 1410, 1545 (-NO2, 1164 (aryl C-Cl), 1311, 1363, 1591, 1662, 2356,
1
1
asym.), 1594, 1669, 1684, 2359, 3335; H-NMR 3305; H-NMR (DMSO-d6 500 MHz) d: 8.74-8.76
(DMSO-d6 500 MHz) d:9.23-9.27 (dd, J=9.5 Hz, 2H, (q, J=2.5-3.5 Hz, 4H, Ar-H), 8.04-8.07 (m, J=3.5-5
Ar-H), 9.11-9.11 (d, J=3 Hz, 1H, Ar-H), 8.87-8.92 (dd, Hz, 10H, Ar-H), 7.96 (s, 1H, Ar-H), 7.91-7.93 (t,
J=9 Hz, 2H, Ar-H), 8.82-8.86 (m, J=2.5-5 Hz, 10H, J=2.5–8.5 Hz, 1H, Ar-H), 7.68-7.71 (d, 2H, Ar-NH2),
Ar-H), 8.76-8.78 (d, J=11 Hz, 1H, Ar-H), 8.68-8.70 7.51-7.53 (d, J=8.5 Hz, 1H, Ar-H), 7.37-7.39 (d, J=8
(d, J=11 Hz, 1H, Ar-H), 8.59-8.60 (t, J=3-4.5 Hz, 1H, Hz, 1H, Ar-H); MS-ESI: 589.14 (m/z, M+); Elemental
Ar-H), 7.01 (s, 2H, Ar-NH2); MS-ESI: 600.14 (m/z, Anal. Found (Calcd.) for C36H20ClN5O2 : C, 73.28
M+); Elemental Anal. Found (Calcd.) for C36H20N6O4 (73.28); H, 3.41 (3.42); Cl, 6.00 (6.01); N, 11.88
: C, 71.98 (71.99); H, 3.34 (3.36); N, 14.02 (13.99); (11.87); O, 5.42 (5.42).
O, 10.65 (10.66).
2-Amino-4-[4-(dimethylamino)phenyl]-6-{5,10-
2-Amino-6-{5,10-dioxo-2,3-diphenyl-5H,10H- dioxo-2,3-diphenyl-5H,10H-benzo[g] quinoxalin-
benzo[g]quinoxalin-7-yl}-4-(4-methoxyphenyl) 7-yl}pyridine-3-carbonitrile (6h)
pyridine-3-carbonitrile (6e)
Lemon crystalline solid, yield 76%; Rf
White crystalline solid;Yield 74%; Rf 0.78; 0.80; mp 185oC; IR (nmax, KBr, cm-1): 723, 759, 819,
mp 200oC; IR (nmax, KBr, cm-1): 719, 758, 826, 853, 837, 1325, 1411, 1593, 1647, 2360, 2958 (C-H, sp3,
1130 (C-O-C, sym.), 1253 (C-O-C, asym.), 1340, CH3), 3282; 1H-NMR (DMSO-d6 500 MHz) d: 8.73-
1420, 1595, 1645, 1677, 2360, 3315; 1H-NMR 8.77 (m, J=3-4 Hz, 10H, Ar-H), 8.03-8.07 (m, J=3-4
(DMSO-d6 500 MHz) d: 8.73-8.76 (m, J=2.5-4 Hz, Hz, 4H, Ar-H), 8.28 (s, 1H, Ar-H), 7.93 (s, 1H, Ar-H),
10H, Ar-H), 8.03-8.07 (m, J=3-4 Hz, 4H, Ar-H), 7.74 7.65 (s, 1H, Ar-H), 7.28 (s, 1H, Ar-H), 7.14 (s, 2H,
(s, 1H, Ar-H), 7.67 (s, 1H, Ar-H), 7.44-7.46 (d, J=7.5 Ar-NH2), 3.49 (s, 6H, N-CH3); MS-ESI: 598.31 (m/z,
Hz, 1H, Ar-H), 7.28-7.30 (d, J=7.5 Hz, 1H, Ar-H), M+); Elemental Anal. Found (Calcd.) for C38H26N6O2
7.13-7.17 (t, 2H, Ar-NH2), 3.91 (s, 3H, Ar-OCH3) ; : C, 76.22 (76.24); H, 4.37 (4.38); N, 14.05 (14.04);
MS-ESI: 585.13 (m/z, M+); Elemental Anal. Found O, 5.34 (5.35).
(Calcd.) for C37H23N5O3 : C, 75.90 (75.89); H, 3.95
(3.96); N, 11.97 (11.96); O, (8.18) 8.20.
2-Amino-6-{5,10-dioxo-2,3-diphenyl-5H,10H-
benzo[g]quinoxalin-7-yl}-4-[4-(trifluoromethyl)
2-Amino-6-{5,10-dioxo-2,3-diphenyl-5H,10H- phenyl]pyridine-3-carbonitrile (6i)
benzo[g]quinoxalin-7-yl}-4-(3-hydroxy-4-
methoxyphenyl)pyridine-3-carbonitrile (6f)
Brown crystalline solid;Yield 78%;Rf 0.80;
mp 178oC; IR (nmax, KBr, cm-1): 723, 741, 843, 863,
Brown crystalline solid;Yield 72%;Rf 0.81; 1285 (C-F), 1320, 1420, 1603, 1645, 1675, 2365,
mp 210oC;IR (nmax, KBr, cm-1): 720, 757, 838, 865, 3236;1H-NMR (DMSO-d6 500 MHz) d:8.73-8.77 (m,
1124 (C-O-C, sym.), 1252 (C-O-C, asym.), 1295 J=3-4 Hz, 4H, Ar-H), 8.28 (s, 1H, Ar-H), 8.03-8.07

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(m, J=3-4.5 Hz, 10H, Ar-H), 7.73-7.84 (d, J=8.5
zHzHHHHz, 1H, Ar-H), 7.35-7.37 (d, J=8 Hz, 1H,
Ar-H), 7.76 (s, 1H, Ar-H), 7.02-7.03 (d, J=4.5 Hz, 2H,
Ar-NH2); MS-ESI: 623.14 (m/z, M+); Elemental Anal.
Found (Calcd.) for C37H20FN5O2 :C, 71.26 (71.27);H,
3.24 (3.23); F, 9.12 (9.14); N, 11.24 (11.23); O, 5.13
(5.13).
6.92-6.93 (t, J=2.5-3 Hz, 4H, Ar-H), 6.89-6.91 (d,
J=10 Hz, 2H, Ar-H), 6.85 (s, 1H, Ar-H), 6.06 (bs, 4H,
Ar-NH2); MS-ESI: 570.18 (m/z, M+); Elemental Anal.
Found (Calcd.) for C36H22N6O2 : C, 75.79 (75.78); H,
3.90 (3.89); N, 14.73 (14.73); O, 5.58 (5.61).
2-Amino-6-{5,10-dioxo-2,3-diphenyl-5H,10H-
benzo[g]quinoxalin-7-yl}-4-(2-hydroxyphenyl)
pyridine-3-carbonitrile (6m)
2-Amino-4-(3,4-dimethoxyphenyl)-6-{5,10-dioxo-
2,3-diphenyl-5H,10H-benzo[g]quinoxalin-7-yl}
pyridine-3-carbonitrile (6j)
Yellow crystalline solid;Yield 72%;Rf 0.86;
mp 220oC; IR (nmax, KBr, cm-1): 725, 760, 820, 870,
1280, 1311 (C-O, phenolic), 1382, 1595, 1650, 2358,
White crystalline solid;Yield 66%; Rf 0.75;
mp 144oC; IR (nmax, KBr, cm-1): 720, 752, 821, 854,
1125 (C-O-C, sym.), 1246 (C-O-C, asym.), 1337,
1
3380 (O-H, phenolic), 3406; H-NMR (DMSO-d6
500 MHz) d: 8.78 (bs, 1H, Ar-H), 8.64-8.66 (d, J=10
Hz, 1H, Ar-H), 8.56-8.59 (t, J=4-10 Hz, 1H, Ar-H),
8.48-8.50 (t, J=4-5 Hz, 1H, Ar-H), 8.22-8.31 (m,
J=2.5-8.5 Hz, 10H, Ar-H), 7.12-7.18 (m, J=2.5-10
Hz, 4H, Ar-H), 6.94 (bs, 2H, Ar-NH2), 6.86-6.87
(d, J=3 Hz, 1H, Ar-OH); MS-ESI: 571.14 (m/z, M+);
Elemental Anal. Found (Calcd.) for C36H21N5O3 : C,
1
1418, 1608, 1645, 1682, 2357, 3246; H-NMR
(DMSO-d6 500 MHz) d: 8.98 (s, 1H, Ar-H), 8.83-
8.94 (m, J=3.5-12 Hz, 10H, Ar-H), 8.11-8.12 (d,
J=8 Hz, 1H, Ar-H), 8.01-8.03 (d, J=8 Hz, 1H, Ar-H),
7.92-7.94 (d, J=8.5 Hz, 1H, Ar-H), 7.83 (bs, 2H, Ar-
NH2), 7.24-7.26 (d, J=10 Hz, 1H, Ar-H), 7.21-7.31
(d, J=9.5 Hz, 1H, Ar-H), 6.91-6.93(d, J=10 Hz, 1H,
Ar-H), 3.38 (s, 6H, Ar-OCH3); MS-ESI: 615.19 (m/z,
M+); Elemental Anal. Found (Calcd.) for C38H25N5O4
: C, 74.16 (74.14); H, 4.07 (4.09); N, 11.38 (11.38);
O, 10.39 (10.40).
O
N
N
N
2-Amino-6-{5,10-dioxo-2,3-diphenyl-5H,10H-
benzo[g]quinoxalin-7-yl}-4-(4-methylphenyl)
pyridine-3-carbonitrile (6k)
O
R
NC
NH
2
Table 1: Antimycobacterial activity of
synthesized compounds against M.
tuberculosis H37Rv by L. J. Slope Method
Yellow crystalline solid;Yield 70%;Rf 0.70;
mp 140oC; IR (nmax, KBr, cm-1): 723, 750, 817, 850,
1328, 1406, 1606, 1650, 2358, 2839 (C-H, sp3, CH3),
3209; 1H-NMR (DMSO-d6 500 MHz) d: 8.88 (s, 1H,
Ar-H), 8.56-8.58 (d, J=10 Hz, 1H, Ar-H), 8.48-8.51
(d, J=10.5 Hz, 1H, Ar-H), 8.42-8.43 (t, J=3.5-4 Hz,
1H, Ar-H), 8.11-8.18 (m, J=2.5-7.5 Hz, 10H, Ar-H),
7.82-7.99 (m, 4H, Ar-H), 6.88 (s, 2H, Ar-NH2), 3.58-
3.59 (t, J=1.5-5 Hz, 3H, CH3); MS-ESI: 569.17 (m/z,
M+); Elemental Anal. Found (Calcd.) for C37H23N5O2
: C, 78.03 (78.02); H, 4.06 (4.07); N, 12.30 (12.29);
O, 5.60 (5.62).
Compound
R
MIC (mg/mL)
6a
6b
6c
6d
6e
6f
6g
6h
6i
6j
6k
6l
H
4-Cl
4-OH
125
62.5
100
500
—-
500
62.5
50
100
250
500
—-
4-NO2
4-OCH3
3-OH-4-OCH3
2-Cl
4-N(CH3)2
4-CF3
2-Amino-4-(4-aminophenyl)-6-{5,10-dioxo-
2,3-diphenyl-5H,10H-benzo[g]quinoxalin-7-yl}
pyridine-3-carbonitrile (6l)
3,4-(OCH3)2
4-CH3
Yellow crystalline solid;Yield 74%; Rf 0.84;
mp 180oC; IR (nmax, KBr, cm-1): 725, 750, 820, 860,
1325, 1415, 1650 (N-H, primary amine, bend), 1658,
2358, 3240; 1H-NMR (DMSO-d6 500 MHz) d: 7.24-
7.26 (q, J=2.5-3 Hz, 10H, Ar-H), 7.01 (s, 1H, Ar-H),
4-NH2
6m
2-OH
—-
Rifampicin
Isoniazid
—-
—-
0.25
0.20

826
75.64 (75.65); H, 3.69 (3.70); N, 12.27 (12.25); O, followed by dehydration to yield 2,3-diphenylbenzo[g]
KUMAR et al., Orient. J. Chem., Vol. 33(2), 821-828 (2017)
8.39 (8.40).
quinoxaline (3). Compound 3 undergoes aromatic
oxidation at C-5 and C-10 on refluxing with equimolar
mixture of chromium trioxide and glacial acetic acid
In-vitro Antimycobacterial Screening
Ten compounds 6a, 6b, 6c, 6d, 6f, 6g, 6h, 6i, in water, till the permanent appearance of dark green
6j and 6k were submitted for their antimycobacterial colour, furnished 2,3-diphenylbenzo[g]quinoxaline-
activity against Mycobacterium tuberculosis H37Rv 5,10-dione (4). Compound 4 on acetylation reaction
(MTCC-200) by L.J. Slope (Conventional) Method24- with acetylchloride and anhydrous aluminium
25. Each compound was diluted to 2000 ìg/mL chloride in carbon tetrachloride yields 7-acetyl-
concentration (as a stock solution). Inoculum Size 2,3-diphenylbenzo[g]quinoxaline-5,10-dione (5).
for Mycobacterium tuberculosis was adjusted to 1 Compound 5 on refluxing with equimolar quantity of
mg/mL. L.J. Medium was used as nutrient medium. substituted aromatic aldehydes, ammonium acetate,
Isoniazid (0.20 µg/mL) and rifampicin (0.25 µg/mL) malononitrile, ammonia and catalytic amount of
were used as standard drug.
dil. HCl undergoes Heitzch-Pyridine synthesis to
yield 2-amino-6-(5,10-dioxo-2,3-diphenyl-5,10-
dihydrobenzo[g]quinoxalin-7-yl)-4-(substituted)
Primary screen
In primary screening, the compounds phenylnicotinonitrile (6a-m). Structure of all newly
were diluted to 500 µg/mL, 250 µg/mL and 125 µg/ synthesized thirteen compounds were confirmed by
mL concentrations. Compounds found active in this FT-IR, 1H-NMR, MS-ESI spectral data interpretation
primary screening were further tested in a second and their elemental analysis.
set of dilution against Mycobacterium tuberculosis.
Biological Activity (In-vitro Antimycobacterial
Secondary screen
The compounds found active in primary
Screening)
The ten newly synthesized compounds
screening were further diluted to 100 µg/mL, 50 µg/ viz. 6a, 6b, 6c, 6d, 6f, 6g, 6h, 6i, 6j and 6k were
mL, 25 µg/mL, 12.5 µg/mL, 6.250 µg/mL, 3.125 µg/ screened for their antimycobacterial screening
mL and 1.5625 µg/mL concentrations.
against Mycobacterium tuberculosis H37Rv by L.J.
Slope (Conventional) Method to observe the effect
of substitution at phenyl ring attached to C-4 of
Reading Result
The highest dilution showing at least 99% pyridine ring of 2-amino-6-(5,10-dioxo-2,3-diphenyl-
inhibition was considered as Minimum Inhibitory 5,10-dihydrobenzo[g]quinoxalin-7-yl)-4-(substituted)
Concentration. The inoculum size of test should phenylpyridine-3-carbonitrile (Compound 6a-m).
contain 108 organism/mL.
RESULT and DISCUSSIONS
Chemistry
Isoniazid and Rifampicin were used as standard
drugs.
Unsubstituted phenyl ring (6a) on the
4-position of pyridine ring in above mentioned
Thirteen new compounds belonging to nucleus exhibited moderate antimycobacterial
series 2-amino-6-(5,10-dioxo-2,3-diphenyl-5,10- activity. Substitution with electron donating
dihydrobenzo[g]quinoxalin-7-yl)-4-(substituted) para-dimethylamino group (6h) on the phenyl
phenylpyridine-3-carbonitrile(6a-m) weresynthesized ring present at C-4 of pyridine ring increases
by multistep synthetic scheme (Figure 1). 2,3- antimycobacterial activity and produces the most
Dihydroxynaphthalene on refluxing with phosphorus active antimycobacterial compound of the above
oxychloride yielded 2,3-dichloronaphthalene (1). mentioned newly synthesized series. Substitution
Compound 1 on refluxing with ammonium chloride with electron withdrawing 4-Cl group (6b) and
in excess of ammonia, catalytic amount of dil. HCl 2-Cl (6g) at the phenyl ring also increases the
and ethanol undergoes amination (nucleophilic antimycobacterial activity but lesser than that of
substitution) & furnished 2,3-diaminonaphthalene substitution with para-dimethylamino group (6h).
(2).Compound 2 on refluxing with equimolar quantity Substitution with para-hydroxy (6c) and electron
of benzil in ethanol undergoes nucleophilic addition withdrawing para-trifluoromethyl (6i) at the pheny

827
KUMAR et al., Orient. J. Chem., Vol. 33(2), 821-828 (2017)
ring exhibits moderate activity lesser than that of
compounds 6h, 6g and 6b and more than that of
compound with unsubstituted phenyl ring (6a).
While, substitution with bulky electron withdrawing
group para-nitro (6d), electron donating para-methyl
(6k) and bulky electron donating groups 3-OH-
4-OCH3 (6f) and 3,4-dimethoxy (6j) decreases
the antimycobacterial activity to great extent and
produces the least active compounds of the newly
synthesized series.
7-yl)-4-(substituted)phenylpyridine-3-carbonitrile
(6a-m), which were screened for antimycobacterial
screening against Mycobacterium tuberculosis H37Rv
by L. J. Slope (Conventional) Method, compound 6h
with 4-N(CH3)2 at phenyl ring attached at pyridine
group of 2-amino-6-(5,10-dioxo-2,3-diphenyl-5,10-
dihydrobenzo[g]quinoxalin-7-yl)-4-(substituted)
phenylpyridine-3-carbonitrile (6a-m) exhibited the
maximal potency, while compounds with 4-Cl (6b)
and 2-Cl (6g) substitutions at the above mentioned
position exhibited better antimycobacterial potency
as compared to other compounds. Compounds
with 4-OH (6c), 4-CF3 (6i) and with no substitution
(6a) at phenyl ring of the above mentioned position
exhibited moderate antimycobacterial activity,
while compounds with 3,4-(OCH3)2 (6j), 4-NO2 (6d),
3-OH-4-OCH3 (6f) and 4-CH3 (6k) showed minimal
antimycobacterial potency against Mycobacterium
tuberculosis H37Rv strain under observation.
From the above observations, Structure
Activity Relationship (SAR) may be established as
“substitution with smaller electron withdrawing and
donating groups at the ortho and para positions
of phenyl ring attached to C-4 of pyridine ring,
present at 7-position of 2-amino-6-(5,10-dioxo-2,3-
diphenyl-5,10-dihydrobenzo[g]quinoxalin-7-yl)-4-
(substituted)phenylpyridine-3-carbonitrile increases
antimycobacterial activity, while substitution with
bulky electron donating groups at the phenyl ring
attached to above mentioned position decreases
antimycobacterial activity.”
ACKNOWLEDGEMENT
Authors are grateful 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.
CONCLUSION
Among the newly compounds synthesized
compounds of series phenyl ring of 2-amino-6-(5,10-
dioxo-2,3-diphenyl-5,10-dihydrobenzo[g]quinoxalin-
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