Synthesis and antimicrobial activity of novel imidazo[1,2-a]pyridinopyrimidine-2,4,6(1H,3H,5H)-triones and thioxopyrimidine-4,6(1H,5H)diones

Article abstract of DOI:10.1007/s11164-015-2130-2

A novel series of imidazo[1,2-a]pyridinopyrimidine-2,4,6(1H,3H,5H)-triones and thioxopyrimidine-4,6(1H,5H)diones were synthesized via multistep synthesis starting from 2-aminopyridine on cyclisation with phenacyl bromide followed by Vilsmeier-Haack and Kn

Full text of DOI:10.1007/s11164-015-2130-2

Res Chem Intermed
DOI 10.1007/s11164-015-2130-2
Synthesis and antimicrobial activity of novel
imidazo[1,2-a]pyridinopyrimidine-2,4,6(1H,3H,5H)-
triones and thioxopyrimidine-4,6(1H,5H)diones
G. Rajitha1 V. Ravibabu1 G. Ramesh1
B. Rajitha1
•
•
•
Received: 12 March 2015 / Accepted: 3 June 2015
Ó Springer Science+Business Media Dordrecht 2015
Abstract A novel series of imidazo[1,2-a]pyridinopyrimidine-2,4,6(1H,3H,5H)-
triones and thioxopyrimidine-4,6(1H,5H)diones were synthesized via multistep
synthesis starting from 2-aminopyridine on cyclisation with phenacyl bromide
followed by Vilsmeier–Haack and Knoevenagel condensation reactions. Structures
of all the newly synthesized compounds were confirmed by their spectral and
analytical studies. All the synthesized compounds were screened for their in vitro
antimicrobial activity. Antibacterial activity results revealed that compounds 5f, 5i,
and 5j have shown promising activity against S. pyogenes with ZOI ranging from 19
to 20 mm, compound 5g against P. aeruginosa (ZOI 19 mm) and 5f and 5h against
S. aureus (ZOI 17, 18 mm) have shown good antibacterial activity. Among barbi-
turic acid and thiobarbituric acid derivatives, thiobarbituric acid derivatives have
shown maximum antibacterial activity. None of the compounds were found to be
active at 150 lg/mL concentration against tested fungal strains.
Keywords Antimicrobial activity Á Barbituric acid Á Imidazo[1,2-a]pyridine Á
Thiobarbituric acid
Electronic supplementary material The online version of this article (doi:10.1007/s11164-015-2130-2)
contains supplementary material, which is available to authorized users.
&
B. Rajitha
rajitabhargavi@yahoo.com
1
Department of Chemistry, National Institute of Technology, Warangal 506004,
Telangana, India
123

G. Rajitha et al.
Introduction
Antibiotics have revolutionized medical care in the twentieth century, these are the
most important weapons aiding humans against a number of infectious diseases.
Bacterial resistance to antibiotics is of grave concern in the medical community as
many species of bacteria have evolved resistance to certain antibiotics and synthetic
agents. Therefore, there is a rapidly growing global crisis in the clinical
management of life-threatening infectious disease caused by multidrug-resistant
strains of the Gram-positive pathogens Streptococcus, Staphylococcus, as well as
the Gram-negative pathogens such as Salmonella, and certain Pseudomonas strains.
For example, distribution of methicillin resistant Staphylococcus aureus (MRSA)
strains has increased [1, 2]. Moreover, the high level of inherent antibiotic resistance
in P. aeruginosa makes treatment of these infections problematic [3]. Therefore, the
development of new, alternative, more effective antimicrobial agents with a broad
spectrum of activities is one of the major challenges in drug discovery.
During recent years, there have been intense investigations on imidazopyridine.
Literature survey revealed that imidazopyridines are pharmacologically important
scaffolds that are known to exhibit a broad spectrum of biological activities like
inhibitors of aromatase estrogen production suppressors [4], thromboxane syn-
thetase [5], HCV replication [6], as well as melatonin receptor ligands [7], DNA
directed alkylating [8], and cardiotonic agents [9]. This heterocyclic scaffold is also
known to exhibit a variety of biological activities such as anticancer [10],
anticoccodial [11], anticandidal [12], anticonvulsant [13], anti-inflammatory [14],
antimicrobial [15], antioxidant [16], antitubercular [17], hypnoselective, anxiose-
lective [18], and antiviral [19] activities. The scaffold also has a high affinity to
human b-amyloid plaques [20]. In addition, imidazopyridines are the major class of
non-benzodiazepines, acting upon various central nervous systems (CNS) disorders.
Interestingly, several imidazopyridine-based drugs such as zolpidem, alpidem, and
saripidem, exhibit potency against pentylenetetrazole (PTZ)-induced seizures [21].
The chemical structure of some important imidazo[1,2-a]pyridine-based CNS
agents are given in Fig. 1. On the other hand, barbiturate derivatives also possess
several biological activities such as anticancer [22], antiviral [23, 24], sedative,
hypnotic, antispasmodic, anticonvulsant, and local anesthesia [25], as well as anti-
inflammatory [26] activities. Prompted by the above facts and in continuation of our
work on barbiturates [27, 28], herein we report the synthesis of novel pyrimidine
Fig. 1 Imidazo[1,2-a]pyridine-based CNS agents
123

Synthesis and antimicrobial activity of novel…
derivatives via Knovenagel condensation reaction between imidazo[1,2-a]pyridine-
3-carbaldehyde and barbiturates and evaluation of their in vitro antimicrobial
activity.
Results and discussion
Chemistry
The target compounds, imidazo[1,2-a]pyridinopyrimidine-2,4,6(1H,3H,5H)-triones
(5a–e) and thioxopyrimidine-4,6(1H,5H)diones (5f–j) were synthesized in good
yields, via Knoevenagel condensation of imidazo[1,2-a]pyridine-3-carbaldehydes
(4a–f) with barbituric acid and thiobarbituric acid. The intermediate imidazo[1,2-
a]pyridine-3-carbaldehydes (4a–f) were prepared by cyclization of 2-aminopyridine
(1) with phenacylbromides (2a–c). The formed imidazo[1,2-a]pyridines in Vilsmeier-
Haack reaction gave imidazo[1,2-a]pyridine-3-carbaldehydes (4a–f) [13]. A general
approach to synthesize the designed compounds is outlined in Scheme 1.
All the synthesized compounds were characterized by IR, NMR, and mass
spectral data. In IR spectra, appearance of a broad band ranging from 3382 to
3475 cm-1 attributed to NH group of the barbituric acid and thiobarbituric acid.
Bands at 1759–1650 cm-1 stretching frequencies correspond to the C=O groups of
barbituric acid. In thiobarbiturates C=S stretching frequency was observed in the
range of 1246–1292 cm-1. In 1H NMR spectra absence of aldehyde proton signal at
d 9.78 and presence of a signal in the range of d 8.19–8.63 ppm (C=C–H) supports
Scheme 1 Synthesis of imidazo[1,2-a]pyridinopyrimidine-2,4,6(1H,3H,5H)-triones (5a–e) and
thioxopyrimidine-4,6(1H,5H)diones (5f–j)
123

G. Rajitha et al.
the formation of compounds (5a–j). The NH signals of barbituric acid were detected
in the 11.20–11.43 ppm range, while the NH signal in thiobarbituric acid was
observed in the 11.31–11.64 ppm range. 13C-NMR signal at d 161.55–163.52 ppm
assign the C=O groups in barbituric acid, whereas the signal at 178.01 ppm is
attributed to the C=S group in the thiobarbiturc acid derivative. Molecular ion peak
from the mass spectrum as well as elemental analyses further confirmed the
formation of the product (Table 1).
Biological assay
Antimicrobial activity
In vitro antimicrobial activity of all the newly synthesized compounds was carried
out by using agar well diffusion assay [29, 30]. In vitro antibacterial activity was
studied against Gram-positive organisms such as Staphylococcus aureus, Strepto-
coccus pyogenes, and Gram-negative bacteria such as Pseudomonas aeruginosa and
Klebsiella pneumoniae, and in vitro antifungal activity against fungal strains such as
Candida albicans, Fusarium oxysporum, Aspergillus niger, and Aspergillus
candidus fungal strains. Antibacterial activity was determined in terms of zone of
inhibition (ZOI in mm) at 150 lg/mL concentration and minimum inhibitory
concentration (MIC in lg/mL). Antifungal activity was determined in terms of zone
of inhibition. Streptomycin for bacteria and clotrimazole for fungi are taken as
standard drugs at 30 lg/mL.
In vitro antibacterial activity results (Table 2) revealed that compounds 5f, 5i,
and 5j show promising activity against S. pyogenes with ZOI ranging from 19 to
20 mm with MIC 50 lg/mL, compound 5g against P. aeruginosa has also shown
maximum antibacterial activity with ZOI 19 mm, MIC 50 lg/mL. Compounds 5h,
5f against S. aureus also have shown good antibacterial activity with ZOI 18,
17 mm, MIC 50 lg/mL. Thus, antibacterial activity results showthat, among
barbituric acid and thiobarbituric acid derivatives, thiobarbituric acid derivatives
Table 1 Synthesis of
imidazo[1,2-
Anolog
R
R1
R2
Time (h)
Yielda (%)
a]pyridinopyrimidine-
2,4,6(1H,3H,5H)-triones (5a–e)
and thioxopyrimidine-
4,6(1H,5H)diones (5f–j)
5a
5b
5c
5d
5e
5f
H
H
Cl
2
92
88
89
86
89
94
92
90
89
91
H
H
Br
2.5
2.5
3
H
Cl
Cl
H
CH3
Br
H
CH3
H
Br
3
H
CH3
Cl
2
5g
5h
5i
H
H
2
Reaction condition: Compounds
4a–f (1 mmol), barbituric acid/
thiobarbituric acid (1 mmol),
EtOH, Cat. AcOH, Reflux 2–3 h
H
H
Br
2.5
3
H
Cl
Cl
Br
5j
H
CH3
2.5
a
Isolated yields
123

Synthesis and antimicrobial activity of novel…
Table 2 Antibacterial activity of imidazo[1,2-a]pyridinopyrimidine-2,4,6(1H,3H,5H)-triones (5a–e) and
thioxopyrimidine-4,6(1H,5H)diones (5f–j)
S. no
Anolog
S. aureus
S. pyogenes
P. aeruginosa
K. pneumoniae
ZOI
MIC
ZOI
MIC
ZOI
MIC
ZOI
MIC
1
5a
8
10
8
200
200
200
200
200
50
10
8
200
200
200
200
200
50
8
8
200
200
200
200
200
100
50
9
8
200
200
200
200
200
100
100
100
100
100
50
2
5b
3
5c
10
10
8
10
8
10
8
4
5d
8
5
5e
10
17
15
18
14
15
22
10
13
19
14
15
14
20
8
6
5f
19
13
15
20
19
21
12
14
13
16
14
22
7
5g
100
50
100
100
50
8
5h
100
100
100
12.5
9
5i
100
100
25
10
11
5j
50
Streptomycin
12.5
Zone of inhibition values (mm) for analogs (5a–j) and positive control drugs (Streptomycin) were
measured at 150 and 30 lg/mL, respectively. MIC values were given in lg/mL. Bacterial strains: S.
aureus—Staphylococcus aureus, S. pyogenes—Streptococcus pyogenes, P. aeruginosa—Pseudomonas
aeruginosa and K. pneumoniae—Klebsiella pneumonia
(5f–j) have maximum antibacterial activity. Remaining compounds have shown
moderate activity. None of the compounds were found to be active at 150 lg/mL
concentration against tested fungal strains.
Conclusion
In conclusion, we have synthesized a novel series of imidazo[1,2-a]pyridinopy-
rimidine-2,4,6(1H,3H,5H)-triones and thioxopyrimidine-4,6(1H,5H)-diones and
evaluated for their antimicrobial activity. Compound 5f, 5i, and 5j against S.
pyogenes, compound 5g against P. aeruginosa and compound 5f, 5h against S.
aureus have shown promising antibacterial activity with ZOI ranging from 17 to
20 mm. Compounds derived from thiobarbituric acid (5f–j) have shown better
antibacterial activity than the compounds derived from barbituric acid. None of the
compounds have shown antifungal activity.
Experimental
Materials and methods
All the reagents were purchased from Aldrich/Merck and used without further
purification. Melting points were determined in open capillaries using a Stuart
SMP30 apparatus and are uncorrected. The progress of the reactions, as well as
123

G. Rajitha et al.
purity of the compounds, was monitored by thin layer chromatography (TLC) with
F254 silica gel precoated sheets using hexane/ethyl acetate (7/3) as eluent. IR spectra
were recorded on a Perkin–Elmer 100S spectrophotometer using KBr pellet. NMR
spectra were recorded on Bruker 400 MHz spectrometer using DMSO-d6 as solvent
and TMS as internal standard. Elemental analyses were performed on a Carlo Erba
model EA1108, and mass spectra were recorded on a Jeol JMSD-300 spectrometer.
General procedure for the synthesis of 2-(4-substituted-phenyl)-imidazo[1,2-
a]pyridines (3a–f)
4-Substituted phenacylbromide (2a–c, 0.1 mol) was added to a solution of
substituted 2-amino pyridine (1a–c, 0.1 mol) in 15 mL of ethanol, and the reaction
mixture was stirred at reflux temperature for 6 h. The progress of the reaction was
checked by TLC. After completion of the reaction, the mixture was cooled, and the
solid was separated, filtered, and dried in vacuum to obtain analytically pure product
in good yields.
General procedure for the synthesis of 2-(4-substituted-phenyl)-imidazo[1,2-
a]pyridin-3-carbaldehydes (4a–f)
Vilsmeyer reagent was prepared at 0–5 °C by dropping phosphorus oxychloride
(11 mL), into a stirred solution of DMF (8 mL). Compound (3a–f, 3 mmol) was
suspended in CHCl3 (15 mL) and dropped into the Vilsmeier reagent, while
maintaining stirring and cooling for half an hour. The mixture so obtained was
refluxed for 6 h, and the solution was evaporated to dryness in vacuum. The residue
was treated with cold water, solid thus obtained was filtered and crystallized from
methanol.
General procedure for the synthesis of imidazo[1,2-a]pyridinopyrimidine-
2,4,6(1H,3H,5H)-triones (5a–e)
A mixture of imidazo[1,2-a]pyridine-3-carbaldehydes (4a–e, 1 mmol) and barbi-
turic acid (1 mmol) were taken in 10 mL of ethanol, and a catalytic amount of
acetic acid was added and refluxed for 2–3 h. The progress of the reaction was
monitored by TLC. After completion of the reaction, the solid was separated out,
filtered, and washed with hot ethanol, which afforded the analytically pure product
in good yields.
5-((2-(4-Chlorophenyl)imidazo[1,2-a]pyridin-3-yl)methylene)pyrimidine-2,4,6(1H,
3H,5H)-trione (5a)
Orange solid, Yield: 90 %; mp: 347 °C; IR (KBr, tmax
,
cm-1): 3468 (NH), 3184–3033 (CH), 1759, 1697 (C=O), 755 (C–Cl); H NMR
(400 MHz, DMSO-d6): d 7.19 (t, J = 6.8 Hz, 1H), 7.64–7.71 (m, 3H), 7.78 (d,
J = 8.4 Hz, 2H), 7.88 (d, J = 8.8 Hz, 1H), 7.99 (d, J = 6.8 Hz, 1H), 8.20 (s, 1H),
11.25 (s, 1H), 11.37 (s, 1H); 13C NMR (100 MHz, DMSO-d6): d 113.24, 114.78,
116.52, 118.44, 128.89, 129.65, 131.06, 131.24, 131.82, 134.46, 134.89, 148.04,
1
123

Synthesis and antimicrobial activity of novel…
150.36, 152.47, 161.55, 163.52; MS (ESI) m/z: 367 [M ? H]?; Anal. calcd. for
C18H11ClN4O3: C, 58.95; H, 3.02; N, 15.28. Found: C, 58.81; H, 3.23; N, 15.45.
5-((2-(4-Bromophenyl)imidazo[1,2-a]pyridin-3-yl)methylene)pyrimidine-2,4,6(1H,
3H,5H)-trione (5b)
Orange solid, Yield: 87 %; mp: 369 °C; IR (KBr, tmax
,
cm-1): 3475 (NH), 3181–3032 (CH), 1756, 1697 (C=O), 655 (C–Br); H NMR
(400 MHz, DMSO-d6): d 7.19 (t, J = 6.8 Hz, 1H), 7.69 (t, J = 8.4 Hz, 3H), 7.78
(d, J = 8.4 Hz, 2H), 7.88 (d, J = 8.8 Hz, 1H), 7.99 (d, J = 6.8 Hz, 1H), 8.19 (s,
1H), 11.26 (s, 1H), 11.38 (s, 1H); MS (ESI) m/z: 412 [M ? H]?; Anal. calcd. for
C18H11BrN4O3: C, 52.57; H, 2.70; N, 13.62. Found: C, 52.39; H, 2.51; N, 13.83.
1
5-((6-Chloro-2-(p-tolyl)imidazo[1,2-a]pyridin-3-yl)methylene)pyrimidine-2,4,6(1H,
3H,5H)-trione (5c)
Orange solid, Yield: 88 %; mp: 311 °C; IR (KBr, tmax
,
cm-1): 3460 (NH), 3194–3057 (CH), 1740, 1692 (C=O), 775 (C–Cl); H NMR
(400 MHz, DMSO-d6): d 2.39 (s, 3H), 7.39 (d, J = 8.0 Hz, 2H), 7.86 (t,
J = 8.4 Hz, 4H), 8.19 (s, 1H), 8.58 (s, 1H), 11.43 (s, 2H); MS (ESI) m/z: 381
[M ? H]? Anal. calcd. for C19H13ClN4O3: C, 59.93; H, 3.44; N, 14.71. Found: C,
59.77; H, 3.30; N, 14.93.
1
5-((2-(4-Bromophenyl)-6-chloroimidazo[1,2-a]pyridin-3-yl)methylene)pyrimidine-
2,4,6(1H,3H,5H)-trione (5d) Orange solid, Yield: 86 %; mp: 349 °C; IR (KBr,
t
max, cm-1): 3383 (NH), 3191–3059 (CH), 1739, 1690 (C=O), 816 (C–Cl), 599 (C–
1
Br); H NMR (400 MHz, DMSO-d6): d 7.14 (d, J = 8.8 Hz, 2H), 7.68–7.71 (m,
3H), 7.87 (d, J = 9.2 Hz, 1H), 8.12 (s, 1H), 8.19 (s, 1H), 11.31 (s, 1H), 11.37 (s,
1H); MS (ESI) m/z: 446 [M ? H]? Anal. calcd. for C18H10BrClN4O3: C, 48.51; H,
2.26; N, 12.57. Found: C, 48.39; H, 2.13; N, 12.75.
5-((2-(4-Bromophenyl)-7-methylimidazo[1,2-a]pyridin-3-yl)methylene)pyrimidine-
2,4,6(1H,3H,5H)-trione (5e) Orange solid, Yield: 91 %; mp: 317 °C; IR (KBr,
1
t
max, cm-1): 3473 (NH), 3180–3031 (CH), 1754, 1697 (C=O), 654 (C–Br); H
NMR (400 MHz, DMSO-d6): d 2.43 (s, 3H), 7.67 (s, 1H), 7.77 (d, J = 8.4 Hz, 2H),
7.87 (t, J = 8.0 Hz, 2H), 8.17 (d, J = 8.8 Hz, 1H), 8.48 (s, 1H), 8.53 (d,
J = 6.8 Hz, 1H), 11.20 (s, 1H), 11.33 (s, 1H); MS (ESI) m/z: 426 [M ? H]?; Anal.
calcd. for C19H13BrN4O3: C, 53.67; H, 3.08; N, 13.18. Found: C, 53.81; H, 3.25; N,
13.03.
General procedure for the synthesis of imidazo[1,2-a]pyridinothioxopyrimidine-4,6
(1H,5H)diones (5f–j)
A mixture of imidazo[1,2-a]pyridine-3-carbaldehydes (4a–d, 4f, 1 mmol) and
thiobarbituric acid (1 mmol) were taken in 10 mL of ethanol, and a catalytic amount
of acetic acid was added and refluxed for 2–3 h. The progress of the reaction was
monitored by TLC. After completion of the reaction, the solid was separated out,
filtered, and washed with hot ethanol, which afforded the analytically pure product
in good yields.
123

G. Rajitha et al.
2-Thioxo-5-((2-(p-tolyl)imidazo[1,2-a]pyridin-3-yl)methylene)dihydropyrimidine-
4,6(1H,5H)-dione (5f)
Red solid, Yield: 94 %; mp: 339 °C; IR (KBr, tmax
,
cm-1): 3410 (NH), 3090 (CH), 1650 (C=O), 1292 (C=S); H NMR (400 MHz,
DMSO-d6): d 2.38 (s, 3H), 7.31 (brs, 1H), 7.38 (d, J = 8.0 Hz, 2H), 7.72 (brs, 1H),
7.84 (t, J = 8.0 Hz, 2H), 8.20 (d, J = 7.6 Hz, 1H), 8.63 (s, 1H), 8.76 (d,
J = 6.8 Hz, 1H), 11.32 (s, 1H), 11.43 (s, 1H); MS (ESI) m/z: 363 [M ? H]?; Anal.
calcd. for C19H14N4O2S: C, 62.97; H, 3.89; N, 15.46. Found: C, 62.81; H, 3.73; N,
15.63.
1
5-((2-(4-Chlorophenyl)imidazo[1,2-a]pyridin-3-yl)methylene)-2-thioxodihydropy-
rimidine-4,6(1H,5H)-dione (5g) Red solid, Yield: 92 %; mp: 303 °C; IR (KBr,
t
max, cm-1): 3467 (NH), 3114 (CH), 1683, 1651 (C=O), 1286 (C=S), 769 (C–Cl);
1H NMR (400 MHz, DMSO-d6): d 7.25 (t, J = 6.8 Hz, 1H), 7.35 (brs, 1H), 7.65 (d,
J = 8.4 Hz, 2H), 7.75–7.81 (m, 2H), 7.92–8.02 (m, 2H), 8.19 (s, 1H), 11.43 (s, 2H);
MS (ESI) m/z: 383 [M ? H]?; Anal. calcd. for C18H11ClN4O2S: C, 56.47; H, 2.90;
N, 14.64. Found: C, 56.59; H, 2.79; N, 14.50.
5-((2-(4-Bromophenyl)imidazo[1,2-a]pyridin-3-yl)methylene)-2-thioxodihydropy-
rimidine-4,6(1H,5H)-dione (5h) Red solid, Yield: 89 %; mp: 315 °C; IR (KBr,
t
max, cm-1): 3450 (NH), 3115 (CH), 1686, 1645 (C=O), 1286 (C=S), 527 (C–Br);
1H NMR (400 MHz, DMSO-d6): d 7.25 (t, J = 6.8 Hz, 1H), 7.35 (s, 1H), 7.71–7.80
(m, 3H), 7.92 (t, J = 8.4 Hz, 2H), 8.01 (d, J = 6.8 Hz, 1H), 8.19 (s, 1H), 11.42 (s,
2H); 13C NMR (100 MHz, DMSO-d6): d 113.75, 114.36, 116.47, 119.17, 127.99,
128.72, 131.52, 131.85, 131.95, 132.32, 135.13, 148.48, 153.64, 159.50, 161.86,
178.01; MS (ESI) m/z: 428 [M ? H]?; Anal. calcd. for C18H11BrN4O2S: C, 50.60;
H, 2.59; N, 13.11. Found: C, 50.48; H, 2.75; N, 13.27.
5-((2-(4-Bromophenyl)-6-chloroimidazo[1,2-a]pyridin-3-yl)methylene)-2-thioxodi-
hydropyrimidine-4,6(1H,5H)-dione (5i) Red solid, Yield: 91 %; mp: 299 °C; IR
(KBr, tmax, cm-1): 3382 (NH), 3057 (CH), 1651, 1623 (C=O), 1246 (C=S), 767 (C–
1
Cl), 520 (C–Br); H NMR (400 MHz, DMSO-d6): d 7.13–7.19 (m, 2H), 7.70–7.77
(m, 3H), 7.90 (d, J = 9.2 Hz, 1H), 8.12 (s, 1H), 8.23 (s, 1H), 11.42 (s, 1H), 11.64 (s,
1H); MS (ESI) m/z: 462 [M ? H]?; Anal. calcd. for C18H10BrClN4O2S: C, 46.82;
H, 2.18; N, 12.13. Found: C, 46.66; H, 2.31; N, 12.31.
5-((6-Chloro-2-(p-tolyl)imidazo[1,2-a]pyridin-3-yl)methylene)-2-thioxodihydropy-
rimidine-4,6(1H,5H)-dione (5j) Red solid, Yield: 92 %; mp: 312 °C; IR (KBr,
1
t
max, cm-1): 3461 (NH), 3112 (CH), 1650 (C=O), 1286 (C=S), 767 (C–Cl); H
NMR (400 MHz, DMSO-d6): d 2.41 (s, 3H), 7.39 (d, J = 7.6 Hz, 2H), 7.64 (d,
J = 7.6 Hz, 2H), 7.70 (d, J = 9.6 Hz, 1H), 7.88 (d, J = 9.2 Hz, 1H), 8.13 (s, 1H),
8.23 (s, 1H), 11.31 (s, 1H), 11.38 (s, 1H); MS (ESI) m/z: 397 [M ? H]?; Anal.
calcd. for C19H13ClN4O2S: C, 57.50; H, 3.30; N, 14.12. Found: C, 57.32; H, 3.14;
N, 14.31.
123

Synthesis and antimicrobial activity of novel…
Antibacterial activity
In vitro antibacterial activity was carried out against four pathogenic Gram-positive
(Staphylococcus aureus and Streptococcus pyogenes) and Gram-negative bacteria
(Klebsiella pneumonia and Pseudomonas aeruginosa) by means of agar well
diffusion assay [29, 30]. Streptomycin (30 lg/mL) was used as standard drug. Cell
suspension containing 108 CFU/mL was prepared and evenly spread on the surface
of the agar plates of Mueller–Hinton agar medium using sterile swab sticks. Once
the plates had been aseptically dried, 10 mm wells were bored using a sterile cork
borer. The samples were first dissolved in dimethyl sulfoxide. The sets of five
dilutions (25, 37.5, 75, and 150 lg/mL) of samples were prepared in dimethyl
sulfoxide using nutrient agar tubes for calculating MIC values. The samples were
tested at a concentration of 150 lg/mL for calculating ZOI. The samples were
placed into the wells and the plates were incubated at 37 °C for 24 h for bacterial
strains. Antibacterial activity was evaluated by measuring the zone of inhibition
(mm) and MIC (the lowest concentration of compounds required to inhibit the
growth of the tested microorganisms) values.
Antifungal activity
In vitro antifungal activity was carried out against four pathogenic fungi, Candida
albicans, Fusarium oxysporum, Aspergillus niger, and Aspergillus candidus, by
means of agar well diffusion assay [29, 30]. Clotrimazole was used as standard drug.
Cell suspension containing 105 spore/mL was prepared and evenly spread on the
surface of agar plates of Sabouraud dextrose agar medium using sterile swab sticks.
Once the plates had been aseptically dried, 10 mm wells were bored using a sterile
cork borer. The samples were first dissolved in dimethyl sulfoxide. The samples
(150 lg/mL) were placed into the wells and the plates were incubated at 28 °C for
48 h and the resulting zones of inhibitions were measured.
Acknowledgments The authors are thankful to Siddhardha Busi, Centre for Microbiology, Pondicherry
University, for performing antimicrobial activity. The author, RG, is also thankful to the University
Grants Commission, New Delhi, for providing senior research fellowship.
Conflict of interest The authors have declared no conflict of interest.
References
1. L. Fu, X. Liu, C. Ling, J. Cheng, X. Guo, H. He, S. Ding, Y. Yang, Bioorg. Med. Chem. Lett. 22,
814–819 (2012)
2. A. Siwek, P. Staczek, J. Stefanska, Eur. J. Med. Chem. 46, 5717–5726 (2011)
3. J.R. Govan, V. Deretic, Microbiol. Rev. 60, 539–574 (1996)
4. L.J. Browne, C. Gude, H. Rodriguez, R.E. Steele, A. Bhatnager, J. Med. Chem. 34, 725–736 (1991)
5. N.F. Ford, L.J. Browne, T. Campbell, C. Gemenden, R. Goldstein, C. Gude, J.W. Wasley, J. Med.
Chem. 28, 164–170 (1985)
123

G. Rajitha et al.
6. I. Vliegen, J. Paeshuyse, T. De Burghgraeve, L.S. Lehman, M. Paulson, I.H. Shih, E. Mabery, N.
Boddeker, E. De Clercq, H. Reiser, D. Oare, W.A. Lee, W. Zhong, S. Bondy, G. Purstinger, J. Neyts,
J. Hepatol. 50, 999–1009 (2009)
7. S. El Kazzouli, A. Griffon du Bellay, S. Berteina-Raboin, P. Delagrange, D.H. Caignard, G. Guil-
laumet, Eur. J. Med. Chem. 46, 4252–4257 (2011)
8. A. Kamal, G. Ramakrishna, M. Janaki Ramaiah, A. Viswanath, A.V. Subba Rao, C. Bagul, D.
Mukhopadyay, S.N.C.V.L. Pushpavalli, M. Pal-Bhadra, Med. Chem. Commun. 4, 697–703 (2013)
9. D. Davey, P.W. Erhardt, W.C. Lumma, J. Wiggins Jr., M. Sullivan, D. Pang, E. Cantor, J. Med.
Chem. 30, 1337–1342 (1987)
10. N. Dahan-Farkas, C. Langley, A.L. Rousseau, D.B. Yadav, H. Davids, C.B. De Koning, Eur. J. Med.
Chem. 46, 4573–4583 (2011)
11. D. Feng, M. Fisher, G.B. Liang, X. Qian, C. Brown, A. Gurnett, P.S. Leavitt, P.A. Liberator, J.
Mathew, A. Misura, S. Samaras, T. Tamas, D.M. Schmatz, M. Wyvratt, T. Biftu, Bioorg. Med.
Chem. Lett. 16, 5978–5981 (2006)
12. Z.A. Kaplancikli, G. Turan-Zitouni, A. Ozdemir, G. Revial, J. Enzyme Inhib. Med. Chem. 23,
866–870 (2008)
13. S. Ulloora, R. Shabaraya, S. Aamir, A.V. Adhikari, Bioorg. Med. Chem. Lett. 23, 1502–1506 (2013)
14. G. Chen, Z. Liu, Y. Zhang, X. Shan, L. Jiang, Y. Zhao, W. He, Z. Feng, S. Yang, G. Liang, A.C.S.
Med, Chem. Lett. 4, 69–74 (2013)
15. T.H. Al-Tel, R.A. Al-Qawasmeh, R. Zaarour, Eur. J. Med. Chem. 46, 1874–1878 (2011)
16. J.S. Biradar, P. Rajesab, S.B. Somappa, J. Chem. 2014, 1–8 (2014)
17. B.O. Kasimogullari, Z. Cesur, Turk. J. Chem. 31, 617–622 (2007)
18. T. Swainston Harrison, G.M. Keating, CNS Drugs 19, 65–89 (2005)
19. K.S. Gudmundsson, J.D. Williams, J.C. Drach, L.B. Townsend, J. Med. Chem. 46, 1449–1455 (2003)
20. L. Cai, J. Cuevas, S. Temme, M.M. Herman, C. Dagostin, D.A. Widdowson, R.B. Innis, V.W. Pike, J.
Med. Chem. 50, 4746–4758 (2007)
21. B.E. Tomczuk, C.R. Taylor Jr., L.M. Moses, D.B. Sutherland, Y.S. Lo, D.N. Johnson, W.B. Kinnier,
B.F. Kilpatrick, J. Med. Chem. 34, 2993–3006 (1991)
22. N.R. Madadi, N.R. Penthala, V. Janganati, P.A. Crooks, Bioorg. Med. Chem. Lett. 24, 601–603
(2014)
23. A. Esanu, BE Patent 902, 232 (1985)
24. A. Esanu, Chem Abstr 104, 130223 (1986)
25. X. Cheng, K. Tanaka, F. Yoneda, Chem. Pharm. Bull. 38, 307–311 (1990)
26. G. Orzalesi, P. Graiteri, S. Seller, Eur. J. Med. Chem. 25, 197–201 (1990)
27. S. Vijaya Laxmi, Y. Thirupathi Reddy, B. Suresh Kuarm, P. Narsimha Reddy, P.A. Crooks, B.
Rajitha, Bioorg. Med. Chem. Lett. 21, 4329–4331 (2011)
28. S. Vijaya Laxmi, B. Suresh Kuarm, B. Rajitha, Med. Chem. Res. 22, 768–774 (2013)
29. S. Mert, R. Kasımogulları, T. Ica, F. Colak, A. Altun, S. Ok. Eur. J. Med. Chem. 78, 86–96 (2014)
30. S. Kaviya, J. Santhanalakshmi, B. Viswanathan, J. Muthumary, K. Srinivasan, Spectrochim. Acta,
Part A 79, 594–598 (2011)
123