Synthesis of some novel 2,4-disubstituted thiazoles as possible antimicrobial agents

Article abstract of DOI:10.1080/10426500701641049

A series of 4-aryl-2-(3-methyl-7-substituted quinoxaline-2-one-1-yl)-1,3- thiazoles (6a-l) and 4-substituted alkyl-2-(3-methyl-7-substituted quinoxaline-2-one-1-yl)-1,3-thiazoles (8a-i) were synthesized in good yield by condensing 2-(3-methyl-7-substituted l,2-oxoquinoxalin-1(2H)-yl)ethanethioamides (5a-c) with substituted phenacyl bromide and dichloroacetone followed by treatment with secondary amines, respectively. The intermediates, 5a-c were conveniently obtained by reacting phosphorus pentasulphide with 2-(3-methyl-7-substituted-2-oxoquinoxalin-1(2H)-yl) acetamides (4a-c) which in turn were synthesized from ethyl (3-methyl-7-substituted-2-oxoquinoxalin-1(2H)- yl) acetates (3a-c) by aqueous ammonia treatment. The newly synthesized compounds were characterized by IR, 1H NMR, 13C NMR, and Mass spectral and elemental analyses. These compounds were screened for in vitro antibacterial activity against five pathogenic strains and antifungal activity against four fungi. Preliminary results revealed that some of the synthesized compounds showed promising antimicrobial activity. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/10426500701641049

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Phosphorus, Sulfur, and Silicon
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Synthesis of Some Novel 2,4-
Disubstituted Thiazoles as
Possible Antimicrobial Agents
Shivananda Wagle a b , Airody Vasudeva Adhikari b
Nalilu Suchetha Kumari c
&
a Strides Research and Specialty Chemicals Ltd. ,
New Mangalore, 575011, India
b Department of Chemistry , National Institute
of Technology Karnataka , Surathkal, Mangalore,
575025, India
c Department of Biochemistry , Justice K. S. Hegde
Medical Academy , Deralakatte, Mangalore, India
Published online: 09 May 2008.
To cite this article: Shivananda Wagle , Airody Vasudeva Adhikari & Nalilu Suchetha
Kumari (2008) Synthesis of Some Novel 2,4-Disubstituted Thiazoles as Possible
Antimicrobial Agents, Phosphorus, Sulfur, and Silicon and the Related Elements,
183:5, 1285-1300, DOI: 10.1080/10426500701641049
To link to this article: http://dx.doi.org/10.1080/10426500701641049
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Phosphorus, Sulfur, and Silicon, 183:1285–1300, 2008
Copyright © Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500701641049
Synthesis of Some Novel 2,4-Disubstituted Thiazoles as
Possible Antimicrobial Agents
Shivananda Wagle,1,2 Airody Vasudeva Adhikari,2
and Nalilu Suchetha Kumari3
1Strides Research and Specialty Chemicals Ltd., New Mangalore
575011, India
2Department of Chemistry, National Institute of Technology Karnataka,
Surathkal, Mangalore, 575025, India
3Department of Biochemistry, Justice K. S. Hegde Medical Academy,
Deralakatte, Mangalore, India
A series of 4-aryl-2-(3-methyl-7-substituted quinoxaline-2-one-1-yl)-1,3-thiazoles
(6a–l) and 4-substituted alkyl-2-(3-methyl-7-substituted quinoxaline-2-one-1-yl)-
1,3-thiazoles (8a–i) were synthesized in good yield by condensing 2-(3-methyl-7-
substituted l,2-oxoquinoxalin-1(2H)-yl)ethanethioamides (5a–c) with substituted
phenacyl bromide and dichloroacetone followed by treatment with secondary
amines, respectively. The intermediates, 5a–c were conveniently obtained by re-
acting phosphorus pentasulphide with 2-(3-methyl-7-substituted-2-oxoquinoxalin-
1(2H)-yl) acetamides (4a–c ) which in turn were synthesized from ethyl (3-methyl-7-
substituted-2-oxoquinoxalin-1(2H)-yl) acetates (3a–c) by aqueous ammonia treat-
1
13
ment. The newly synthesized compounds were characterized by IR, H NMR,
C
NMR, and Mass spectral and elemental analyses. These compounds were screened
for in vitro antibacterial activity against five pathogenic strains and antifungal ac-
tivity against four fungi. Preliminary results revealed that some of the synthesized
compounds showed promising antimicrobial activity.
Keywords 2,4-Disubstituted thiazoles; 3,7-Dimethyl quinoxalines; antibacterial; anti-
fungal activity; phenacyl bromide
Received 18 June 2007; accepted 30 July 2007.
The authors are grateful to the Head, SAIF, CDRI, Lucknow and the Head, NMR
Research Centre IISc, Bangalore for providing NMR and mass spectral data. They are
also thankful to the Heads of Department of Chemistry, NITK, Department of Biochem-
istry, KSHMA, Strides Research and Specialty Chemicals Ltd, Mangalore for providing
necessary laboratory facilities.
Address correspondence to Airody Vasudeva Adhikari, Department of Chemistry, Na-
tional Institute of Technology Karnataka, Surathkal, Mangalore 575025, India. E-mail:
avadhikari123@yahoo.co.in
1285

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S. Wagle et al.
INTRODUCTION
The thiazoles and their derivatives are found in many natural and
synthetic products with a wide spectrum of biological activities such
as antibacterial,1 antifungal,2 anti-inflammatory,3,4 antifilarial, and
antitumor activity.5 A survey of literature reveals that a number of
2,4-disubstituted 1,3-thiazoles were reported to exhibit antibacterial,
antifungal, antiviral, analgesic, anti-inflammatory, antitumor, and cy-
totoxic activities.6−8 On the other hand, many quinoxaline deriva-
tives have been shown to possess a variety of pharmacological prop-
erties such as antibacterial, antifungal, antiturberculosis, analgesic,
and anti-inflammatory activities.9−14 Encouraged by the above reports,
we planned to synthesize a series of new thiazoles containing biologi-
cally active 3-methyl-7-substituted quinoxalin-2-one moiety at position
2, and substituted aryl/alkyl group at position 4, with the hope that
the resulting molecules would exhibit enhanced biological activity. The
present communication reports the multi-step synthesis of the title
compounds (6a-l) and (8a-i) from 3,7-dimethylquinoxalin-2(1H)-ones
and investigation of their in vitro antibacterial and antifungal activity
against pathogenic strains.
RESULTS AND DISCUSSION
The synthetic route followed for obtaining the title compounds is
outlined in the Scheme-1. The intermediates, 3-methyl-7-substituted
quinoxalin-2(1H)-ones (2a–c), prepared by condensing 4-substituted
1,2-phenylene diamine with pyruvic acid was readily converted to ethyl
(3-methyl-7-substituted-2-oxoquinoxalin-1(2H)-yl) acetates (3a-c) by
reacting with ethyl chloroacetate in presence of dry acetone and
potassium carbonate. The compounds 3a–c, on treatment with aque-
ous ammonia gave 2-(3-methyl-7-substituted-2-oxoquinoxalin-1(2H)-
yl) acetamides (4a–c), which on reaction with phosphorous pentasul-
phide in tetrahydrofuran at 50◦C afforded 2-(3-methyl-7-substituted-
2-oxoquinoxalin-1(2H)-yl) ethanethioamides (5a–c) in good yield. The
target molecules 4-aryl-2-(3-methyl-7-substituted quinoxaline-2-one-
1-yl)-1,3-thiazoles (6a–l) were synthesized by the reaction of 5a–c
with various phenacyl bromides in refluxing ethanol medium. Fur-
ther, the compounds 5a–c were readily converted to 4-(chloromethyl)-
2-(3-methyl-7-substituted quinoxaline-2-one-1-yl)-1,3-thiazoles (7a–c)
by refluxing with 1,3-dichloroacetone in methylisobutylketone. The ti-
tle compounds, 4-substituted- 2-(3-methyl-7-substituted quinoxaline-
2-one-1-yl)-1,3-thiazoles (8a–i) were prepared by the condensation of
various secondary amines with 7a–c in the presence of a base.

Novel 2,4-Disubstituted Thiazole
1287
SCHEME 1
The structural assignments to the new compounds were based on
their elemental analysis and spectral (IR, 1H NMR, 13C NMR and
Mass) data. The formation of 3,7-dimethylquinoxalin-2(1H)-one (2a)
1
was confirmed by its H NMR and IR spectra. FTIR spectrum showed
absorption bands at 3224, 1680, 1544 cm−1 owing to NH, >C O, and

1288
S. Wagle et al.
>C C< groups respectively. Further, 1H NMR spectrum of 2a showed
two sharp singlets at δ 2.37 and δ 2.50 indicating the presence of two
methyl groups. The appearance of two doublets at δ 7.15 and δ 7.27
was due to one aromatic proton and a –NH group respectively and two
singlets at δ 7.48 and 7.55 was due to two aromatic protons of quinoxa-
line ring. In the mass spectrum, it appeared molecular ion peak at m/z
175 (100%), which matches with its molecular formula C10H10N2O. The
compound 3a, obtained by condensing 2a with ethyl chloroacetate, was
confirmed by recording its NMR and IR spectra. A quatrate at δ 4.24 and
a triplet at 1.30 clearly indicate the formation of ester. The mass spec-
trum of 3a showed a molecular ion peak at m/z 261 (M+1,100%), which
matches with its molecular formula C14H16N2O3. The formation of 4a
was confirmed by its IR and 1H NMR spectral data. Its FTIR spectrum
showed strong peaks at 3340 and 1743 cm−1‘ indicating the presence
1
of NH2 and >C O groups respectively while its H NMR spectrum
showed a peak at δ 6.65 confirming the presence of NH2 group. The
mass spectrum showed a molecular ion peak at m/z 232 (M+1, 100%)
which matches with its molecular formula C12H13N3O2. The structure
of thioamide 5a was confirmed by recording the FAB mass spectra. It
showed the molecular ion peak at m/z 248 (M+1, 80%), which is consis-
tent with its molecular.
1
Formations of thiazoles are confirmed by IR, H NMR, 13C NMR,
and Mass spectral studies. In the IR spectrum of compounds 6a, the
typical absorption bands due to CS and NH2 groups of thioamide 5a
were absent. The absorption bands corresponding to C N stretching of
thiazole ring appeared at 1611–1602 cm−1. Further, the mass spectrum
of 6a showed a molecular ion peak at m/z 407 (M + 1,100%), which is
in consistent with its molecular formula C12H18N4O3S. Similarly, the
formation of chloroalkyl thiazole 7a was confirmed by its IR spectral re-
sults. In the IR spectrum of compound 7a, the typical absorption bands
due to CS and NH2 groups of thioamide 5a were absent. Further, in
its mass spectrum, a molecular ion peak appeared at m/z 320 (M+1,
100%), which matches with its molecular formula C15H14ClN3OS. Phys-
ical data and results of elemental analysis of 6a–l and 8a–i are listed
in Table I and Table II, respectively.
All the title compounds were screened for their in vitro activity
against bacterial and fungal pathogens. Antibacterial activity was de-
termined against Gram positive and Gram negative bacteria by serial
plate dilution method.15,16 The investigation of antibacterial screen-
ing (Table III) revealed that most of the newly synthesized compounds
showed moderate to good inhibition at 1.56-25 µg/ml in DMSO.
The compounds 6a, 6c, 6e, 8a, 8b, and 8h were found to be active
against all the microbes studied. They manifested zone of inhibition

1289

1290

Novel 2,4-Disubstituted Thiazole
1291
TABLE III Antibacterial Activity of Compounds 6a–l and 8a–i
Compound
Escherichia coli K.pneumoniae
S. aureus
P. aeruginosa
6a
6b
6c
6d
6e
6f
6g
6h
6i
6j
6k
6l
8a
8b
8c
8d
6.25(16–20)
12.5(16–20)
6.25(16–20)
12.5(16–20)
6.25(16–20)
12.5(11–15)
12.5(11–15)
6.25(16–20)
12.5(16–20)
25(<10)
12.5(16–20)
25(<10)
6.25(16–20)
6.25(16–20)
12.5(11–15)
25(<10)
6.25(16–20)
12.5(16–20)
6.25(11–15)
25(<10)
6.25(16–20)
12.5(16–20)
25(<10)
6.25(16–20)
6.25(16–20)
12.5(11–15)
12.5(16–20)
12.5(16–20)
6.25(16–20)
6.25(16–20)
12.5(16–20)
6.25(16–20)
12.5(16–20)
6.25(16–20)
12.5(16–20)
6.25(16–20)
12.5(11–15)
6.25(23–27)
6.25(16–20)
12.5(16–20)
6.25(16–20)
12.5(16–20)
6.25(16–20)
12.5(16–20)
12.5(16–20)
12.5(16–20)
25(<10)
6.25(16–20)
12.5(16–20)
6.25(16–20)
12.5(16–20)
12.5(11–15)
25(<10)
12.5(11–15)
6.25(16–20)
12.5(11–15)
25(<10)
12.5(16–20)
25(<10)
6.25(16 -20)
−
12.25(16–20)
12.5(16–20)
6.25(16–20)
25(<10)
12.5(11–15)
25(<10)
6.25(16-20)
6.25(16–20)
6.25(16–20)
12.5(16–20)
6.25(16–20)
12.5(16–20)
6.25(16–20)
12.5(16–20)
6.25(16–20)
6.25(16–20)
25(<10)
8e
8f
8g
8h
6.25(16–20)
25(<10)
25(<10)
6.25(16–20)
12.5(16–20)
6.25(30–40)
6.25(16–20)
12.5(16–20)
12.5(16–20)
1.56(22–30)
8i
Standard
6.25(25–33)
(Ciprofloxacin)
The MIC values were evaluated at concentration range, 1.56-25 µg/ml. The figures
in the table show the MIC values and the corresponding zones of inhibition (in mm).
up to 16–20 mm at concentration of 6.26 mg/ml, which are compara-
ble to standard. Amongst the tested compounds, 6h and 8h displayed
considerable activity against E.coli and K.pneumoniae with zone of in-
hibition 16–20mm at 6.25 mg/ml, whereas compounds 6d, 6g, 6k, 6l, 8c
and 8e exhibited good activity against S. aureus with zone of inhibition
16–20 mm diameter at 6.25 mg/ml. The compounds 6b, 6g, 6i, and 8g
demonstrated good activity (inhibition zone of 16-20 mm at 6.25 mg/ml)
against P. aeruginosa.
The test results measured at four different concentrations reveal
that presence of halogen and N-methyl piperazino substitutions in the
aromatic ring system caused increase in activity mainly because of
their structural similarities with the standard drug. As reported in
the literature,17 presence of active groups like NH2, F, Cl, CH3,
CONH2 in a molecule enhances its antimicrobial activity probably due
to the enhancement of the rate of electron flow in chloroplasts concomi-
tant with an inhibition of phosphorylation. Thus, it has been concluded

1292
S. Wagle et al.
TABLE IV Antifungal Activity of Compounds 6a–l and 8a–i
Compound
Trichophyton Asp. Fumigatus Can. Albicans Penicillium
6a
6b
6c
6d
6e
6f
6g
6h
6i
6j
6k
6l
8a
8b
8c
8d
6.25(16–20)
12.5(11–15)
12.5(11–15)
12.5(11–15)
6.25(16–20)
12.5(11–15)
6.25(16–20)
12.5(16–20)
12.5(16–20)
6.25(16–20)
12.5(11–15)
12.5(16–20)
12.5(11–15)
6.25(16–20)
12.5(11–15)
12.5(11–15)
25(<10)
12.5(16–20)
6.25(16–20)
12.5(11–15)
6.25(16–20)
6.25(16–20)
12.5(16–20)
6.25(16–20)
25(<10)
12.5(16–20)
6.25(16–20)
12.5(16–20)
12.5(11–15)
6.25(16–20)
12.5(11–15)
12.5(11–15)
12.5(11–15)
12.5(11–15)
6.25(16–20)
12.5(11–15)
6.25(16–20)
12.5(16–20)
3.125(27–33)
6.25(16–20) 6.25(16–20)
6.25(16–20) 25(<10)
12.5(16–20) 12.5(16–20)
12.5(16–20) 12.5(16–20)
6.25(16–20) 12.5(16–20)
12.5(16–20) 6.25(16–20)
12.5(16–20) 12.5(16–20)
12.5(11–15) 6.25(16–20)
12.5(16–20)
12.5(16–20) 6.25(16–20)
25(<10) 12.5(16–20)
25(<10)
12.5(11–15) 12.5(16–20)
6.25(16–20) 12.5(11–15)
6.25(16–20) 6.25(16–20)
12.5(11–15) 12.5(11–15)
12.5(16–20) 6.25(16–20)
8e
8f
8g
8h
12.5(11–15)
12.5(16–20) 12.5(11–15)
25(<10) 12.5(11–15)
12.5(11–15) 6.25(16–20)
12.5(11–15) 25(<10)
3.125(25–30) 6.25(25–30)
25(<10)
12.5(11–15)
12.5(11–15)
6.25(16–20)
25(<10)
8i
Standard
6.25(20–27)
(Ciclopirixolamine)
The MIC values were evaluated at concentration range, 1.56-25 µg/ml. The figures in
the table show the MIC values and the corresponding zones of inhibition (in mm).
that amongst the various tested thiazoles, compounds containing 4-
methyl, 4-chloro, 4-amine, and 3-amide groups on phenyl moiety at
position 4 and 7-methyl quinoxaline at position 2 of thiazole ring have
demonstrated encouraging results, which are comparable to the stan-
dard drug.
Similarly, the investigation of antifungal activity (Table IV) revealed
that all the newly synthesized compounds showed moderate to good
inhibition at 1.56–25 µg/ml in DMSO. The compounds 6a, 6e, 6j, 8b
and 8h exhibited good activity against all the four fungal strains, while
the compounds 6g, 6b, 6d, 8a and 8f were found to be active against
Trichophyton and Asp.Fumigatus (inhibitory zone 16–20 mm at 6.25
mg/ml), whereas the compounds 6b, 6f, 8a, and 8d displayed good activ-
ity against Can.Albicans and Penicillium (inhibitory zone 16–20 mm at
6.25 mg/ml). Therefore, it can be concluded that presence of 4-hydroxy,
3-amide groups on phenyl ring and 4-N-methyl piperazine through
methylene link at position 4, in addition to 7-methyl quinoxaline at

Novel 2,4-Disubstituted Thiazole
1293
position 2 of thiazole ring enhanced the antifungal activity of the title
compounds. Further, it is interesting to note that compounds 6a, 6e,
8b, and 8h displayed both antibacterial and antifungal activities.
EXPERIMENTAL
General
Melting points were determined by open capillary and are uncorrected.
The IR spectra (in KBr pellets) were recorded on a Shimadzu FT-IR 157
1
spectrophotometer. H NMR spectra were recorded either on Perkin-
Elmer EM-390 (300 MHz) and Bruker WH-200 (400 MHz) spectrom-
eters using TMS as an internal standard. 13C NMR spectra were ob-
tained on a Perkin-Elmer (Model RB-12, 100 MHz) spectrometer. All
chemical shifts are reported in ppm downfield from tetramethylsilane.
The mass spectra were recorded on a Jeol JMS-D 300 mass spectrom-
eter (FAB) operating at 70eV. Elemental analysis was performed on
Flash E A 1112 Thermo Electron Corporation CHNS analyzer. The pu-
rity of the compounds was checked by thin layer chromatography (TLC)
on Merck silica gel 60 F254 precoated sheets using hexane and ethyl ac-
etate 4:1, v/v. Starting materials were purchased from Aldrich Chemical
Company or Spectrochem Chemical Company and used without further
purification. All solvents were of analytical grade and freshly distilled
prior to use.
Chemistry
2-(3-Methyl-7-substituted-2-oxoquinoxalin-1(2H)-yl)
acetamide (4a–c)
A mixture of ethyl (3-methyl-7-substituted-2-oxoquinoxalin-1(2H)-
yl) acetate (3a–c) (25 g, 96.15 mmol), and aqueous ammonia (100 ml)
was stirred at 40◦C for 8–10 h. Progress of the reaction was monitored
by TLC (ethyl acetate/hexane, 1:1, v/v). After completion of the reaction,
the mixture was cooled to 10◦C and filtered. The product was thoroughly
washed with cold water to remove trace of ammonia and finally dried
at 60–70◦C under vacuum.
4a. Off-white solid. Yield: 20.5 g (92.7%), M.p., 218–220◦C. MS (m/z,
%): 232 (M+1, 100), 231(M+, 30), 187(40), 173(15), 157(40), 150(40),
147(10), 121(20), 102(40). 1H-NMR (DMSO-d6) δ: 7.25 (s, 1H, CH), 7.12–
7.14 (d, 1H, J = 8.8 Hz), 6.65 (s, 2H, NH2), 6.50–6.52 (d, 1H, J = 8.8 Hz),
4.71 (s, 2H, CH2), 2.55 (s, 3H, CH3), 2.46 (s, 3H, CH3). 13C NMR (DMSO):
20.60 (CH3), 21.85 (CH3-), 53.18, 118.88, 123.03, 123.21, 133.45, 135.64,
137.25, 159.93 (C O), 164.92 (N C CH3), 171.66 (C O). Anal. Calcd.

1294
S. Wagle et al.
for C12H13N3O2: C, 62.27; H, 5.62; N, 18.16; Found: C, 62.40; H, 5.72;
N, 18.54%.
4b. Off-white solid. Yield: 16.5 g (74.8%), M.p., 220–222◦C. MS (m/z,
%): 218 (M+1, 100), 217(M+, 30), 187(20), 157(40), 150(10), 147(30),
1
121(20), 102(40), 79(20). H-NMR (DMSO-d6) δ: 8.11-8.13 (d, 1H, CH,
J = 7.65 Hz), 7.48-7.52 (t, 1H, J = 7.68 Hz), 7.18–7.14 (t, 1H, CH,
J = 7.65 Hz), 6.73–6.70 (d, 1H, CH, J = 7.50 Hz), 6.54 (s, 2H, NH2), 4.78
(s, 2H, NH2), 2.50 (s, 3H, CH3).13C NMR (DMSO): 20.64 (CH3), 53.18,
117.19, 122.48, 127.92, 129.36, 135.64, 137.09, 159.93 (C=O), 164.90
(N C CH3), 171.66 (C O). Anal. Calcd. for C11H11N3O2 : C, 60.76; H,
5.06; N, 19.33; Found: C, 60.48; H, 5.16; N, 19.63%
4c. Beige colored solid. Yield: 17.25 g (78%), M.p., 216–218◦C. MS
(m/z, %): 252(M+1, 80), 251(M+, 30), 235(80), 234(20), 207(40), 179(60),
120(20), 105(10), 95(20). 1H-NMR (DMSO-d6) δ: 7.51–7.49 (d, 1H, CH,
J = 8.50 Hz), 7.46 (s, 1H), 6.98-7.00 (d, 1H, CH, J = 8.50 Hz), 6.65
(s,2H, NH2), 4.74 (s, 2H, CH2), 2.46(s, 3H, CH3).13C NMR (DMSO):
20.60 (CH3), 53.18, 116.21, 122.68, 125.27, 132.30, 134.81, 135.85,
160.06 (C=O), 164.92 (N=C-CH3), 171.61 (C O). Anal. Calcd. for
C11H10ClN3O2 : C, 52.45; H, 3.97; N, 16.68; Found: C, 52.60; H, 4.08; N,
16.90%.
2-(3-Methyl-7-substituted-2-oxoquinoxalin-1(2H)-yl)
ethanethioamide (5a–c)
To a solution of 2-(3-methyl-7-substituted-2-oxoquinoxalin-1(2H)-yl)
acetamide (4a–c) (20 g, 86.6 mmol) in tetrahydrofuran (50 ml), phos-
phorous pentasulphide (38.5 g, 171 mmol) was slowly added at 50◦C
over a period of 2 h while stirring. The resulting slurry was further
stirred at 50–55◦C for 2 h, and the reaction mass was poured into ice-
cold water. The precipitated solid was filtered, washed with water and
dried at 50–60o under vacuum. The product was recrystallized from
ethyl acetate.
5a. Brown colored solid. Yield: 14.5 g (68%), M.p., 212–214◦C. MS
(m/z, %): 248 (M+1, 80), 247(M+, 50), 187(25), 173(30), 157(40), 147(10),
1
121(20), 102(40). H-NMR (DMSO-d6) δ: 7.70 (s, 1H, CSNH2), 7.25 (s,
1H, CH), 7.12–7.14 (d, 1H, J = 8.8 Hz), 6.96 (s, 1H, CSNH2), 6.50–6.52
(d,1H, J = 8.8), 4.88 (s, 2H, CH2), 2.50(s, 3H, CH3), 2.42 (s, 3H, CH3).
Anal. Calcd. for C12H13N3OS : C, 58.21; H, 5.25; N, 16.97; Found: C,
58.24; H, 5.20; N, 16.90%.
5b. Brown colored solid. Yield: 13.6 g (63.5%), M.p., 210–212◦C.
MS (m/z, %): 234 (M+1, 100), 235(M+, 80), 173(40), 157(40), 121(30),

Novel 2,4-Disubstituted Thiazole
1295
102(40), 91(20). Anal. Calcd. for C11H11N3OS: C, 56.58; H, 4.71; N,
18.00; Found: C, 56.60; H, 4.75; N, 18.08%.
5c. Pale yellow colored solid. Yield: 14.2 g (66.6%), M.p., 206–208◦C.
MS (m/z, %): 268 (M+1, 50), 267(M+, 50), 147(40), 121(20), 91(25),
73(15). Anal. Calcd. for C11H10ClN3OS: C, 49.30; H, 3.73; N, 15.68;
Found: C, 49.26; H, 3.70; N, 15.60%.
4-Aryl-2-(3-methyl-7-substituted quinoxaline-2-one-
1-yl)-1,3-thiazoles (6a-l)—General Procedure
An equimolar mixture of appropriate thioamide 5a–c (10 mmol)
and substituted phenacylbromide (10 mmol) in ethanol (10 ml) was
refluxed for 6 h. Then the reaction mixture was cooled to room temper-
ature. The solid separated was filtered and recrystallized from chloro-
form/dimethyl formamide.
6a. MS (m/z, %): 407(M+1, 100), 406(M+, 60), 207(40), 179(60),
1
105(10), 91(20). H-NMR (DMSO-d6) δ: 13.21 (s, 1H, OH), 8.15 (s, 2H,
NH2), 7.96–7.98 (d, 1H, CH, J = 8.50 Hz), 7.88–7.89 (d, 1H), 7.65 (s, 1H),
7.39 (s, 1H), 7.05–7.07 (d, 1H, CH, J =8 .50 Hz), 6.84–6.86 (d, 1H), 6.58–
6.60 (d, 1H), 4.31 (s, 2H, CH2), 2.55 (s, 3H, CH3), 2.46(s, 3H, CH3).13C
NMR (DMSO): 21.08 (CH3), 21.85 (CH3), 40.42, 118.87, 119.61, 122.80,
123.00, 124.02, 128.11, 128.20, 128.88, 133.48, 134.18, 135.58, 137.02,
152.80, 160.25, 163.07, 163.12, 163.74, 165.84.
6b. MS (m/z, %): 382(M+1, 80), 381(M+, 60), 179(25), 105(10), 91(10).
1H-NMR (DMSO-d6) δ: 7.83(d, 2H, p-chlorophenyl, J = 5.20 Hz), 7.50
(s, 1H, thiazole), 7.40 (s, 1H), 7.34 (d, 2H, p-chlorophenyl, J = 5.20 Hz),
6.84–6.86 (d, 1H), 6.60-6.62 (d, 1H), 4.76 (s, 2H, CH2), 2.60 (s, 3H, CH3),
2.49(s, 3H, CH3).
6e. IR (KBr) γ /cm−1: 1580 (C N), 1540 (C C), 1070 (C S), 815, 710.
MS (m/z, %): 393(M+1, 100), 392(M+, 60), 207(50), 179(30), 105(20),
91(20), 73(25).
6g. MS (m/z, %): 348(M+1, 70), 347(M+, 20), 207(20), 179(30),
105(20), 91(10). 1H-NMR (CDCl3) δ: 7.89 (d, 1H, CH, J = 7.65 Hz ), 7.81
(d, 2H, p-methylbenzene, J = 8.30 Hz), 7.43 (d, 2H, p-methylbenzene,
J = 8.30 Hz), 7.30 (s, 1H, thiazole), 7.25–7.28 (m, 2H, quinoxaline pro-
tons), 6.62 (d, 1H, quinoxaline, J=7.50 Hz), 4.03 (s, 2H, CH2), 2.48 (s,
3H, CH3), 2.37(s, 3H, CH3).13C NMR (DMSO): 20.60 (CH3), 21.22 (CH3),
51.76, 116.31, 117.46, 122.46, 125.26, 127.56, 128.99, 129.41, 130.72,
134.41, 134.76, 136.71, 137.08, 143.54, 162.79, 167.53.
6j. IR (KBr) γ /cm−1: 1600 (C N), 1530 (C C), 1070 (C S), 820, 707
MS (m/z, %): 403(M+1, 80), 402(M+, 30), 395(10), 391(10), 339(15),

1296
S. Wagle et al.
273(20), 252(10), 235(30), 207(50), 179(30), 167(20), 120(20), 105(20),
95(20).
6l. IR (KBr) γ /cm−1: 1598 (C N), 1529 (C C), 1078 (C S), 830, 708.
MS (m/z, %): 383(M+1, 50), 382(M+, 30), 339(25), 273(20), 235(30),
1
207(30), 179(20), 167(10), 120(10), 105(5), 95(20). H-NMR (CDCl3)δ:
7.45–7.47 (t, 2H, p-aminiphenyl, J = 9.00 Hz), 7.36 (s, 1H), 7.32 (s,
1H, thiazole), 7.26–7.28 (s, 1H, quinoxaline protons), 7.08-7.10 (d, 1H,
quinoxaline, J = 8.50 Hz), 6.64 (t, 2H, p-aminiphenyl, J = 9.00 Hz), 6.18
(s,2H, NH2), 4.01 (s, 2H, CH2), 2.48 (s, 3H, CH3).13C NMR (DMSO):
20.60 (CH3), 51.78, 115.33, 117.46, 118.86, 122.31, 123.62, 125.25,
128.97, 130.56, 131.93, 133.93, 135.47, 143.54, 148.60, 162.79, 167.53.
4-(Chloromethyl)-2-(3-methyl-7-substituted
quinoxaline-2-one-1-yl)-1,3-thiazoles (7a–c)
A mixture of appropriate thioamide (5a–c) (5a:10 g, 40.48 mmol;
5b:7.5 g, 32.08 mmol; 5c:10 g, 37.38 mmol) and 1,3-dichloroacetone (7.7
g, 60.72 mmol) in methylisobutylketone (MIBK) was refluxed for 5 h.
After completion of the reaction, the mass was poured into chilled water.
The organic layer was separated, washed with water, dried over anhy-
drous sodium sulfate, and finally evaporated to dryness under reduced
pressure. The product was recrystallized from chloroform.
7a. Beige colored solid. Yield: 8.0g (62%), M.p., 180–182◦C. MS (m/z,
%): 320(M+1, 100), 319(M+, 50), 235(40), 234(20), 207(40), 179(60),
1
120(20), 105(10), 95(20). H-NMR (DMSO-d6) δ: 7.74 (s, 1H, thiazole),
7.24 (s, 1H), 6.93-6.95 (d, 1H, CH, J = 8.88 Hz), 6.61-6.64 (d,1H, CH,
J = 8.88 Hz), 5.62 (s, 2H, CH2), 4.39 (s, 2H, CH2), 2.56 (s, 3H, CH3),
2.46 (s, 3H, CH3).13C NMR (DMSO): 20.63 (CH3), 21.85, 36.88, 44.01,
118.59, 121.21, 123.44, 124.32, 133.15, 136.55, 137.67, 137.82, 145.68,
159.03, 165.60. Anal. Calcd for C15H14ClN3OS : C, 56.28; H, 4.37; N,
13.13; Found: C, 56.32; H, 4.30; N, 13.17%.
7b. Off-white solid. Yield: 7.0 g (71.4%), M.p., 190–194◦C. MS (m/z,
%): 306(M+1, 80), 305(M+, 30), 235(20), 207(30), 179(10), 120(20),
105(20), 95(20). 1H-NMR (DMSO-d6) δ: 7.92 (d, 1H, CH, J = 7.65
Hz), 7.72 (s, 1H, thiazole), 7.24–7.33 (m, 2H, 2-CH), 6.69–6.72 (d, 1H,
CH, J = 7.50 Hz), 5.52 (s, 2H, CH2), 4.63 (s, 2H, CH2), 2.54(s, 3H,
CH3).13C NMR (DMSO): 20.72 (CH3), 36.92, 44.01, 116.89, 121.25,
123.64, 128.34, 129.78, 135.36, 137.82, 138.00, 159.09, 165.69. Anal.
Calcd for C14H12ClN3OS : C, 54.94; H, 3.92; N, 13.73; Found: C, 54.98;
H, 3.96; N, 13.82%.
7c. Brown colored powder. Yield: 8.6 g (67.2%), M.p., 178–180◦C. MS
(m/z, %): 341(M+1, 100), 340(M+, 60), 235(80), 234(10), 207(5), 179(40),

Novel 2,4-Disubstituted Thiazole
1297
120(20), 105(10), 95(20). Anal. Calcd for C14H11Cl2N3OS : C, 49.37; H,
3.23; N, 12.34; Found: C, 49.34; H, 3.20; N, 12.31%.
4-Substituted- 2-(3-methyl-7-substituted
quinoxaline-2-one-1-yl)-1,3-thiazoles (8a-i)—
General Procedure
An equimolar mixture of 7a-c (10 mmol) and amine (10 mmol) was
refluxed in methylisobutylketone (MIBK, 20 ml) for 3–4 hours, in the
presence of sodium hydroxide. The product was then poured into chilled
water. The organic layer was separated, washed with water, dried over
anhydrous sodium sulfate and finally evaporated to dryness under re-
duced pressure and the solid obtained was recrystallized from chloro-
form.
8a. MS (m/z, %): 355(M+1, 40), 354(M+, 20), 277(10), 235(10),
1
207(20), 179(20), 120(20), 105(10), 95(5). H-NMR (CDCl3) δ: 7.53 (s,
1H, thiazole), 7.23 (s, 1H, CH), 6.93–6.95 (d, 1H, CH, J = 8.88 Hz), 6.61–
6.64 (d, 1H, CH, J = 8.88 Hz), 5.04 (s, 2H, CH2), 3.55 (s, 2H, -N-CH2),
3.25 (t, 4H, -CH2-O-CH2-, morpholine protons), 2.82–2.87 (t, 4H, -CH2-
N-CH2-, morpholine protons), 2.55 (s, 3H, CH3), 2.48(s, 3H, CH3).13C
NMR (DMSO): 20.71, 21.85, 44.26, 50.80, 53.49, 66.85, 118.64, 123.44,
124.36, 131.80, 133.16, 137.06, 137.67, 139.92, 141.98, 159.00, 166.02.
8e. MS (m/z, %): 354(M+1, 100), 353(M+, 30), 277(10), 207(30),
120(20), 105(20), 95(15). 1H-NMR (CDCl3) δ: 7.92 (d, 1H, CH, J =
7.67 Hz), 7.55 (s, 1H, thiazole), 7.27–7.33 (m, 2H, 2-CH), 6.69 (d,1H,
CH, J = 7.50 Hz), 4.98 (s, 2H, CH2), 3.56 (s, 2H, -N-CH2), 2.46–2.49(m,
8H), 2.41(s, 3H, CH3), 2.26(s, 3H, N-CH3).13C NMR (DMSO): 20.72,
44.26, 45.70, 50.19, 52.44, 53.67, 116.89, 123.59, 128.34, 129.77, 133.99,
135.34, 138.51, 139.92, 141.98, 141.98, 159.08, 165.79.
8i. MS (m/z, %): 359(M+1, 80), 358(M+, 30), 277(10), 235 (20),
207(30), 120(20), 105(20), 95(15). 1H-NMR (CDCl3) δ: 7.50 (s, 1H), 7.45
(s, 1H, thiazole), 7.30–7.32 (d, 1H, CH, J = 8.50 Hz), 7.08–7.11 (d, 1H,
CH, J = 8.50 Hz), 5.06 (s, 2H, CH2), 3.53 (s, 2H, -N-CH2), 2.59–2.67(m,
4H), 2.44(s, 3H, CH3), 1.72–1.76 (m, 4H, pyrrolidine protons).13C NMR
(DMSO): 20.64, 23.65, 44.26, 49.68, 53.96, 115.91, 123.09, 126.37,
126.76, 132.72, 134.51, 137.27, 139.92, 141.98, 159.12, 165.97.
BIOLOGICAL ACTIVITY
Antibacterial Studies
The newly synthesized compounds were screened for their antibac-
terial activity against Escherichia coli [ATTC-25922], Staphylococcus

1298
S. Wagle et al.
aureus [ATTC-25923], Pseudomonas aeruginosa [ATTC-27853], and
Klebsiella pneumoniae [Recultered] bacterial strains by serial plate di-
lution method. Serial dilutions of the drug in Muller-Hilton broth were
taken in tubes and their pH was adjusted to 5.0 using phosphate buffer.
A standardized suspension of the test bacterium was inoculated and
incubated for 16–18 h at 37◦C. The minimum inhibitory concentration
(MIC) was noted by seeing the lowest concentration of the drug at which
there was no visible growth.
A number of antimicrobial discs are placed on the agar for the sole
purpose of producing zones of inhibition in the bacterial lawn. Twenty
milliliters of agar media was poured into each petri dish. Excess of sus-
pension was decanted and plates were dried by placing in incubator
at 37◦C for an hour. Using an agar punch, wells were made on these
seeded agar plates and minimum inhibitory concentrations of the test
compounds in dimethylsulfoxide (DMSO) were added into each well. A
control was also prepared for the plates in the same way using solvent
DMSO. The petri dishes were prepared in triplicate and maintained at
37◦C for 3–4 days. Antibacterial activity was determined by measuring
the diameter of inhibition zone. Activity of each compound was com-
pared with Ciprofloxacin as standard.18,19 The results of antibacterial
activity are summarized in Table III.
Antifungal Studies
The newly synthesized compounds were screened for their antifun-
gal activity against Aspergilus flavus (NICM No.524), Aspergilus fu-
migatus (NICM No.902), Candida albicans (NICM No.300), Penicillium
marneferei (Recultered) and Trichophyton mentagrophytes (Recultered)
in DMSO by serial plate dilution method.20,21 Subourands agar media
was prepared by dissolving peptone (1 g), D-glucose (4 g), and agar (2 g)
in distilled water (100 ml) and adjusting the pH to 5.7. Normal saline
was used to make a suspension of spore of fungal strains for lawning. A
loopful of particular fungal strain was transferred to 3 ml saline to get
a suspension of corresponding species. Twenty millimeter of agar me-
dia was poured into each petri dish. Excess of suspension was decanted
and the plates were dried by placing in an incubator at 37◦C for 1 hour.
Using an agar punch, wells were made and each well is labeled, and
minimum inhibitory concentrations of the test compounds in DMSO
were added into each well. A control was also prepared for the plates in
the same way using solvent DMSO. The petri dishes were prepared in
triplicate and maintained at 37◦C for 3–4 days. Antifungal activity was
determined by measuring the diameter of the inhibition zone. Activity

Novel 2,4-Disubstituted Thiazole
1299
of each compound was compared with Ciclopirixolamine as standard.
The results of antifungal activity are given in the Table IV.
CONCLUSIONS
A new series of thiazole derivatives containing 3-methyl-7-substituted
quinoxaline-2-one moiety in position 2 and substituted aryl/alkyl
groups in position 4 were synthesized and screened for their antimi-
crobial activities. The testing results indicated that out of thirty com-
pounds tested, six compounds showed good antimicrobial activity, which
is almost comparable with the standard. We noticed that, the observed
antimicrobial activity is due to the presence of pharmacologically active
substituents like salicylamide, p-methyl benzene and N-methyl mor-
pholine substituents in the thiazoles and methyl group in quinoxalines
moiety.
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