In vitro antitubercular and antimicrobial activities of 1-substituted quinoxaline-2,3(1H,4H)-diones

Article abstract of DOI:10.1016/j.bmcl.2009.10.026

1-((Substituted)methyl)quinoxaline-2,3(1H,4H)-dione (2a-e) and 1-((substituted)acryloyl)quinoxaline-2,3(1H,4H)-dione (4a-c) were synthesized from quinoxaline-2,3(1H,4H)-dione 1 and evaluated for their antimicrobial activities. Results of the antitubercular screening against Mycobacterium tuberculosis H₃₇Rv showed that the compounds 2b, 3, and 4a were the most effective, with minimum inhibitory concentrations of 8.012, 8.561, and 8.928 μg/ml, respectively. All the compounds exhibited significant antibacterial and considerable antifungal activities.

Full text of DOI:10.1016/j.bmcl.2009.10.026

Bioorganic & Medicinal Chemistry Letters 20 (2010) 406–408
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
In vitro antitubercular and antimicrobial activities of 1-substituted
quinoxaline-2,3(1H,4H)-diones
b
c
P. Ramalingam a, , S. Ganapaty , Ch. Babu Rao
*
a Raghavendra Institute of Pharmaceutical Education and Research, Anantapur, Andhra Pradesh 515 721, India
b University College of Pharmaceutical Sciences, Andhra University, Visakhapatnam, Andhra Pradesh 530 003, India
c Siddharth Institute of Pharmacy, Nalanda Educational Institutions, Kantepudi, Guntur District, Andhra Pradesh 522 438, India
a r t i c l e i n f o
a b s t r a c t
Article history:
1-((Substituted)methyl)quinoxaline-2,3(1H,4H)-dione (2a–e) and 1-((substituted)acryloyl)quinoxaline-
2,3(1H,4H)-dione (4a–c) were synthesized from quinoxaline-2,3(1H,4H)-dione 1 and evaluated for their
antimicrobial activities. Results of the antitubercular screening against Mycobacterium tuberculosis H37Rv
showed that the compounds 2b, 3, and 4a were the most effective, with minimum inhibitory concentra-
Received 24 February 2009
Revised 5 October 2009
Accepted 6 October 2009
Available online 12 October 2009
tions of 8.012, 8.561, and 8.928
lg/ml, respectively. All the compounds exhibited significant antibacterial
and considerable antifungal activities.
Keywords:
Ó 2009 Elsevier Ltd. All rights reserved.
Quinoxaline-2,3(1H,4H)-diones
Antitubercular
Antibacterial
Antifungal
Tuberculosis is one of the world’s most infectious diseases, kill-
ing 2 million peoples every year out of 2 billion infected individu-
als. Often tuberculosis is accompanied by AIDS and exists as
multidrug resistant tuberculosis (MDR-TB) or as extensively/extre-
mely resistant tuberculosis (XTR-TB), where neither standard anti-
tubercular drug nor any of the regimens are potentially effective.1
Owing to the ineffective remedy and risk in the treatment option,
by 2020, the global burden of tuberculosis is estimated to be 2.3
million, of which 99% will be in developing countries (WHO,
1997). In 2000, the global alliance for tuberculosis drug develop-
ment was established to accelerate the development of new antitu-
bercular agents and ensure their availability and affordability in
high-epidemic countries. For the first time in the last few decades,
under the guidance of global alliance and pharmaceutical compa-
nies, 20 new molecules were developed with promising character-
istics during in vitro and in vivo animal studies.2 However these
molecules were not brought to the realization and precluded their
future development. Hence, the search for new and potent antitu-
bercular agents is gaining interest
In view of the literature regarding antimicrobial potency of
quinoxaline and its mode of action that prevent DNA-directed
RNA synthesis by virtue of binding to CpG site on DNA, the quinox-
aline nucleus is focused on synthesizing newer derivatives to
explore potent antitubercular moiety for the present epidemics
of tuberculosis.6 In continuation of our earlier communi-
cations,7–9 herein we synthesize 1-((substituted)methyl)quinoxa-
line-2,3(1H,4H)-dione (2a–e) as mannich base and 1-((substituted)
acryloyl)quinoxaline-2,3(1H,4H)-dione (4a–c) as chalcones and
subsequently evaluate their antitubercular, antibacterial, and anti-
fungal activities.
The synthesis of the compounds was carried as outlined in
Scheme 1. The starting compound, quinoxaline-2,3(1H,4H)-diones
(1) was synthesized by Phillips condensation10 and obtained as
white silky needle crystals with good yield. 1-((Substituted)methyl)
quinoxaline-2,3(1H,4H)-diones (2a–e) were obtained as mannich
bases by acid-catalyzed mannich condensation reaction.11 The re-
sulted synthon structures were supported by the 1H resonance
around d 5.0 ppm and 13C resonance around d 58 ppm for the
methylene linkage (–N–CH2–) of quinoxaline-heteryl moiety. The
intermediate 1-acetylquinoxaline-2,3(1H,4H)-dione (3) was syn-
thesized by conventional acetylating procedure by refluxing in acet-
ylating mixture. The yielded product was purified from byproducts
by n-hexane precipitation followed by chromatographic techniques
and was authenticated by the presence of absorption band at
2984 cmÀ1, 1H resonance around d 3 ppm, and 13C resonance around
d 21 ppm for the methyl group (–COCH3). 1-((substituted)acry-
loyl)quinoxaline-2,3(1H,4H)-diones (4a–c) were prepared as chal-
cones by reacting with appropriate aldehyde by conventional
Nitrogen-containing heterocycles are indispensable structural
units for medicinal chemists. Among the various heterocyclic com-
pounds, quinoxalines form an attractive biologically active mole-
cule as these are a part of various antibiotics such as hinomycin,
levomycin, and actinoleutin3,4 that are known to possess other bio-
logical potentials such as adenosine receptor antagonist, antican-
cer, antihelmintic, antidepressant, and anti-inflammatory.5
* Corresponding author. Tel.: +91 9985184448.
E-mail address: rammpharm@rediffmail.com (P. Ramalingam).
0960-894X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2009.10.026

P. Ramalingam et al. / Bioorg. Med. Chem. Lett. 20 (2010) 406–408
407
H
H
N
N
O
O
O
(CH3CO)2O /
CH3COOH
N
N
H
O
3
1
O
CH3
R-H / HCHO/
DMF
R-CHO /
EtOH / NaOH
H
H
N
N
O
O
O
N
N
O
4(a-c)
2(a-e) H2C
R
O
R
2e
N
2d
2c
2a
2b
N
O
O
N
N
N
N
NH
N
R =
N(C6H5)2
H3C
O
4b
4c
4a
OCH3
CH3
R =
N
OH
CH3
Scheme 1.
route. The structures were supported by the additional maxima in
UV spectrum at 254 nm for unsaturated carbonyl chromophore (Ta-
ble 1), 1H signal around d 5–6 (dd) ppm, disappearance of 13C reso-
nance for the methyl group (–CH3), and appearance of two 13C
resonances around d 110 ppm. The compounds’ molecular weight
and molecular formula were supported by mass spectral data and
elements analytical data.
E. coli, P. vulgaris, and P. aeruginosa (Gram-negative bacteria) and
for their antifungal activity against A. Niger and C. albicans by agar
plate disk diffusion method.11 The antitubercular screening was
performed by Alamar blue assay12 against Mycobacterium tubercu-
losis H37Rv and the results are represented in Table 2. The obtained
results revealed that the nature of substituents on the cyclic nitro-
gen of quinoxaline may have a considerable impact on the antitu-
bercular, antibacterial, and antifungal activities of the parent
pharmacophore. Introduction of heteryl-substituted methyl side
All the synthesized compounds were evaluated for their in vitro
antibacterial activity against S. aureus (Gram-positive bacteria),
Table 1
Physical data of the compounds 2a–e, 3, and 4a–c
Compound
Molecular formula
Molecular weight
Melting point (°C)
% Yield
kmax (nm)
Rf* value
2a
2b
2c
2d
2e
3
4a
4b
4c
C21 H17N3O2
C13 H12N4O3
C19 H11N3O4
C15 H11N5O2
C16 H12N4O2
C10H8 N2O3
C17H12 N2O3
C18H14 N2O5
C19H17 N3O3
343.352
272.260
321.260
293.280
292.292
204.182
292.289
338.314
335.35
290–291
273–274
>300
65
55
47
60
48
45
63
52
64
257
249
253
278
269
250
278
284
318
0.689
0.603
0.620
0.682
0.487
0.714
0.533
0.757
0.679
>300
256–258
230–231
281–282
101–102
98–100
*
Mobile phase: benzene/methanol/water (7:2:1).

408
P. Ramalingam et al. / Bioorg. Med. Chem. Lett. 20 (2010) 406–408
Table 2
Antitubercular and antimicrobial activities of the synthesized compounds
Compound
Antibacteriala
P. vulgaris
Antifungala
C. albicans
M. tuberculosis H37 Rv (MIC in lg/ml)
S. aureus
E. coli
P. aeruginosa
A. Niger
2a
2b
2c
2d
2e
3
4a
4b
26
33
29
29
36
20
20
16
18
24
00
30
37
30
39
33
24
26
16
33
25
00
30
32
31
34
32
26
30
18
33
34
00
35
39
34
39
35
29
29
18
31
22
00
28
23
23
28
25
20
24
16
00
21
00
20
21
23
20
18
00
18
10
00
13
00
9.920
8.012
10.593
10.775
10.245
8.561
8.928
10.775
16.447
—
4c
Stdb
Blankc
00
a
The antibacterial and antifungal activities are the average results of triplicate experiments and reported as zone of inhibition in millimeter at a test concentration of
g/disk.
Nalidixic acid (50
100
l
b
l
g/disk) and clotrimazole (50
lg/disk) were used, respectively, for antibacterial and antifungal activities.
c
Dimethyl formamide for bacteria and fungi, and dimethyl sulfoxide for mycobacteria were used as blank solvents.
(2a–e) chain at quinoxalines-2,3(1H,4H)-dione exhibited signifi-
cant antimicrobial potential against bacteria than against fungi.
Among the series, 1-((3-methyl-5-oxo-4,5-dihydro-1H-pyrazol-4-
yl)methyl)quinoxaline-2,3(1H,4H)-dione (2b) showed predomi-
nant antitubercular activity with the minimum inhibitory concen-
(TAACF) through research and development contract with US Na-
tional Institute of Allergy and Infectious Disease (NIAID) for provid-
ing antimycobacterial data.
References and notes
tration of 8.012
between 8.928 and 10.775
16.447 g/ml among the compounds synthesized. However, the
introduction of chalcones moiety at parent quinoxaline decreased
the antimicrobial activity toward all the test microbes impartially,
whereas heteryl substitution with ethylene linkage resulted in a
significant enhancement in the antibacterial activity with moder-
ate enhancement against antifungal activity.
l
g/ml, while the rest of the compounds showed
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Acknowledgments
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The authors are thankful to the Indian Institute of Chemical
Technology (IICT), Hyderabad, India, and to Laila Impex Pvt. Ltd,
Vijayawada, India, for their support in spectral studies and to
Tuberculosis Antimicrobial Acquisition Coordinating Facility