Synthesis and biological evaluation of thiazolo and imidazo N-(4-nitrophenyl)-7-methyl-5-aryl-pyrimidine-6 carboxamide derivatives

Article abstract of DOI:10.1007/s11164-015-1922-8

Two new series of thiazolo and imidazo N-(4-nitrophenyl)-7-methyl-5-aryl-pyrimidine-6 carboxamide derivatives were synthesized. All the synthesized compounds were evaluated for their antimicrobial activity against Gram-positive bacteria: Staphylococcus aureus MTCC 3160, Bacillus subtilis MTCC 441, Gram-negative bacterium: Escherichia coli MTCC 443 and antifungal activity against Candida albicans MTCC 227 and Aspergillus Niger MTCC 281 and free radical scavenging activity. Compound 7e was found the most active antimicrobial comparable to standards taken. Compounds 7a, 7c, 9a, and 9d also showed significant antibacterial and antifungal activity. Further, compounds 7f, 9d, and 9h showed significant antioxidant activity with IC₅₀ comparable with the standard compound. The synthesized compounds were confirmed for their structure by means of various spectrometric techniques like IR, ¹H NMR, mass, and elemental analysis.

Full text of DOI:10.1007/s11164-015-1922-8

Res Chem Intermed
DOI 10.1007/s11164-015-1922-8
Synthesis and biological evaluation of thiazolo
and imidazo N-(4-nitrophenyl)-7-methyl-5-aryl-
pyrimidine-6 carboxamide derivatives
•
Priyanka Dhiman Neelam Malik
•
•
Prabhakar K. Verma Anurag Khatkar
Received: 4 September 2014 / Accepted: 8 January 2015
Ó Springer Science+Business Media Dordrecht 2015
Abstract Two new series of thiazolo and imidazo N-(4-nitrophenyl)-7-methyl-5-
aryl-pyrimidine-6 carboxamide derivatives were synthesized. All the synthesized
compounds were evaluated for their antimicrobial activity against Gram-positive
bacteria: Staphylococcus aureus MTCC 3160, Bacillus subtilis MTCC 441, Gram-
negative bacterium: Escherichia coli MTCC 443 and antifungal activity against
Candida albicans MTCC 227 and Aspergillus niger MTCC 281 and free radical
scavenging activity. Compound 7e was found the most active antimicrobial com-
parable to standards taken. Compounds 7a, 7c, 9a, and 9d also showed significant
antibacterial and antifungal activity. Further, compounds 7f, 9d, and 9h showed
significant antioxidant activity with IC50 comparable with the standard compound.
The synthesized compounds were confirmed for their structure by means of various
1
spectrometric techniques like IR, H NMR, mass, and elemental analysis.
Keywords Bigenelli-pyrimidine Á Dihydropyrimidine Á Antibacterial Á
Antifungal Á Antioxidant
Introduction
Over the past few years, there has been an increased use of antimicrobial drugs and
this has resulted in the development of resistance to these drugs. Different
mechanisms in microbes contribute to the development of resistance to antibiotics.
This leads to search for new heterocyclics as new antimicrobials with modified
action [1]. Scientific evidence suggests that free metals and radicals become more
harmful, which play an important role in the pathogenesis of many diseases [2].
P. Dhiman Á N. Malik Á P. K. Verma Á A. Khatkar (&)
Medicinal Chemistry Division, Faculty of Pharmaceutical Sciences, M.D. University,
Rohtak 124001, India
e-mail: anuragpharmacy@gmail.com
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P. Dhiman et al.
Generally, compounds having antioxidant activity have been proven to exhibit
anticancer [3], anti-hypertensive [4], anti-Alzheimer’s, anti-inflammatory, and
many other activities [5]. This fact attracted the special attention of researchers in
the identification and development of novel antioxidants that can prevent radical-
induced damages.
Pyrimidines with a vast literature and long history have been regarded as
important constituents of nucleic acids and many biological processes. Pyrimidine
moiety was also found to be embedded in a large number of alkaloids, drugs,
antibiotics, agrochemicals, and antimicrobial agents as parent component [6]. 1, 2,
3, 4-tetrahydro pyrimidine derivatives synthesis has recently came out of a growing
area of research to determine the most promising target molecules because of their
important medicinal and pharmacological properties such as antiviral [7], anti-
malarial [8], anticarcinogenic [9], hypoglycemic [10], and calcium channel
modulators [11]. Hence, keeping in view of the facts mentioned above and
continuing our research work on synthesis and biological evaluation of heterocy-
clic compounds [12–14] in our present work, we report the synthesis of two series
of thiazolo and imidazo N-(4-nitrophenyl)-7-methyl-5-aryl-pyrimidine-6 carbox-
amide derivatives, which can be synthesized by taking N-(4-nitrophenyl)-3-
oxobutamide (Biginelli reaction; a three-component cyclocondensation reaction is
one of the methods described to synthesize dihydropyrimidine derivatives) with
different aromatic aldehydes and thiourea, guanidine in the presence of concen-
trated HCl [15].
Materials and methods
Melting points were determined in open glass capillaries on a Sonar melting point
apparatus and are uncorrected. The percentage yield was based upon the products
obtained after recrystallization. Reaction progress was monitored by thin-layer
chromatography (TLC) performed on silica gel G-coated plate in the solvent system
toluene: ethyl acetate (7.5:2.5), and the spots were located by iodine. Infrared (IR)
analysis was performed on a SHIMAZDU FT-IR instrument using KBr pellets and
was recorded in cm-1 1H NMR spectra were recorded on Bruker DRX-300
.
FTNMR spectrometer using DMSO-d6 solvent and are expressed in parts per
million (d, ppm) downfield from the internal standard TMS. Elemental analysis of
all the synthesized compounds was carried out on a Thermo Scientific Flash 2000
CHN analyzer. Mass spectra were taken on a Bruker Compass Data Analysis 4.0
mass spectrometer.
Procedure for synthesis of N-(4-nitrophenyl)-3-oxobutamide (3) [16]
A mixture of ethylacetoacetate (0.01 mol) and 4-nitro aniline (0.01 mol) in toluene
containing catalytic amount (0.05 ml, 40 %) of NaOH was refluxed on oil bath for
8 h. After completion of the reaction (TLC monitoring), the reaction mixture was
kept overnight; separated solid was filtered, washed with petroleum ether and
recrystallized from ethanol to obtain N-(4-nitrophenyl)-3-oxobutamide.
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Synthesis and biological evaluation
General procedure for synthesis of 5-(2-hydroxynaphthalen-1-yl)-7-methyl-N-
(4-nitrophenyl)-3,5-dihydro-2H-thiazolo/imidazo[3,2-a]pyrimidine-6-
carboxamide (7f, 9h) [16]
A mixture of N-(4-nitrophenyl)-3-oxobutamide (0.01 mol), 2-hydroxynaphthalde-
hyde (0.01 mol), guanidine/thiourea (0.01 mol), and ethanol (8 ml), containing
0.4 ml of concentrated HCl was heated under reflux for 6–8 h. The solution was
deep frozen overnight and precipitates were obtained. 1,2-dichloroethane (0.01 mol)
was added to a boiling solution of intermediate obtained above (0.01 mol) in
dimethyl formamide and then refluxed for 1 h. After completion of the reaction, the
contents were poured on crushed ice. The precipitates obtained were filtered, dried,
and recrystallized from ethanol.
General procedure for synthesis of substituted N-(4-nitrophenyl)-6-methyl-4-
phenyl-2-thioxo/imino-1,2,3,4-tetrahydropyrimidine-5-carboxamide derivatives
(6a–g)(8a–g) [16]
A mixture of N-(4-nitrophenyl)-3-oxobutamide (0.01 mol), different aromatic
aldehyde (0.01 mol), guanidine/thiourea (0.01 mol), and ethanol (8 ml), containing
0.4 ml of concentrated HCl was heated under reflux for 6–8 h. The solution was
deep frozen overnight and precipitates were obtained.
General procedure for synthesis of 5-substituted N-(4-nitrophenyl)-7-methyl-3,5-
dihydro-2H-imidazo/thiazolo [3,2-a]pyrimidine-6-carboxamide derivatives (7a–
g)(9a–g) [16]
1,2-dichloroethane (0.01 mol) was added to a boiling solution of substituted N-(4-
nitrophenyl)-6-methyl-4-phenyl-2-thioxo/imino-1,2,3,4-tetrahydropyrimidine-5-
carboxamide derivatives (0.01 mol) in dimethyl formamide and then refluxed for
1 h. After completion of the reaction, the contents were poured on crushed ice. The
precipitates obtained were filtered, dried, and recrystallized from ethanol.
Spectral data
Intermediate 4-(4-chlorophenyl)-6-methyl-N-(4-nitrophenyl)-2-thioxo-1,2,3,4 tetra-
hydropyrimidine-5-carboxamide 8d solid yellow; Anal. Calcd for C18H15ClN4O3S
C, 53.67; H, 3.75; N, 13.91 Found C, 53.58; H, 3.60; N, 13.92 IR (KBr pellets,
cm-1): 1,690 (C=O str., 20 amide), 3,343(N–H str., sec. amide), 1,581 (C=C str.,
skeletal vibration of phenyl nucleus), 860 (C–Cl), 1,211(C=S).
5-(2-hydroxyphenyl)-7-methyl-N-(4-nitrophenyl)-1,2,3,5-tetrahydroimidazo[1,2-
a]pyrimidine-6-carboxamide 7a solid brown (yield: 82 %), solid yellow; m.p.:
264–266 °C Rf 0.42; Anal. Calcd for C20H19N5O4 C, 61.06; H, 4.87; N, 17.80
Found C, 60.68; H, 4.56; N, 16.83; IR (KBr pellets, cm-1): 1,690 (C=O str., 20
amide), 3,046 (C=C–H asymmetrical str., aromatic), 3,156 (N–H str., sec. amide),
1,173 (C–N str., 30 aryl amine), 3,208 (OH str., phenyl), 1,583 (C=C str., skeletal
vibration of phenyl nucleus), 1,397 (C–NO2 str., C6H4NO2) 1H NMR, dppm
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(DMSO-d6) 7.25–7.76(m, 4H, Ar–H), 7.95–8.34(m, 3H, Ar–H), 6.91 (s, 1H, CH,
pyrimidine ring), 8.37(s, 1H, NH), 2.53–3.39(s, 2H, CH2), 5.47(1H, OH) m/e:
394.15 (M?1).
5-(4-(dimethylamino)phenyl)-7-methyl-N-(4-nitrophenyl)-1,2,3,5-tetrahydroimi-
dazo[1,2-a]pyrimidine-6-carboxamide 7b solid red; Anal. Calcd for C22H24N6O3 C,
62.84; H, 5.75; N, 19.99 Found C, 61.74; H, 5.95; N, 18.90; IR (KBr pellets, cm-1):
1,687 (C=O str., 20 amide), 3,075 (C=C–H Asymmetrical str., aromatic), 3,170 (N–
H str., sec, amide), 1,645 (C=N str., pyrimidine ring), 1,279 (C–N str., 30 aryl
amine), 1,317 (C–N str., aryl 30 amine), 1,017 (C–O str., OCH3), 1,573 (C=C str.,
skeletal vibration of phenyl nucleus), 1,514 (C–NO2 str., C6H4NO2) 1H NMR, dppm
(DMSO-d6)7.47–7.56 (m, 4H, Ar–H), 7.53–7.65(m, 3H, Ar–H), 6.91 (s, 1H, CH,
pyrimidine ring), 8.05(s, 1H, NH), 2.67–3.91 (s, 2H, CH2) m/e: 422.20 (M?2).
5-(4-hydroxyphenyl)-7-methyl-N-(4-nitrophenyl)-1,2,3,5-tetrahydroimidazo[1,2-
a]pyrimidine-6-carboxamide (7c) solid yellow; Anal. Calcd for C20H19N5O4 C,
61.06; H, 4.87; N, 17.80 Found C, 60.98; H, 4.77; N, 17.84; IR (KBr pellets, cm-1):
1,688 (C=O str., 20 amide), 3,077 (C=C–H Asymmetrical str., aromatic), 3,108 (N–
H str., sec. amide), 1,073 (C–N str., 30 aryl amine), 1,290 (C–O str., OCH3), 3,216
(OH str., phenyl), 1,584 (C=C str., skeletal vibration of phenyl nucleus), 1,502 (C–
NO2 str., C6H4NO2) 1H NMR, dppm (DMSO-d6) 7.14–7.74(m, 4H, Ar–H),
7.81–8.83(m, 3H, Ar–H), 6.91 (s, 1H, CH, pyrimidine ring), 8.76 (s, 1H, NH),
2.91–3.86 (s, 2H, CH2), 5.03(1H, OH) m/e: 395.15 (M?2).
5-(4-formylphenyl)-7-methyl-N-(4-nitrophenyl)-1,2,3,5-tetrahydroimidazo[1,2-
a]pyrimidine-6-carboxamide (7d) solid dark brown; Anal. Calcd for C21H19N5O4 C,
62.22; H, 4.72; N, 17.27 Found C, 61.98; H, 4.78; N, 17.29; IR (KBr pellets, cm-1):
1,683 (C=O str., 20 amide), 3,072 (C=C–H asymmetrical str., aromatic), 3,212 (N–H
str., sec. amide), 1,646 (C=N str., pyrimidine ring), 1,124 (C–N str., 30 aryl amine),
1,301 (C–O str., OCH3), 1,725 (C=O str., aldehyde), 1,581 (C=C str., skeletal
vibration of phenyl nucleus), 1,480 (C–NO2 str., C6H4NO2) 1H NMR, dppm (DMSO-
d6) 7.28–7.79(m, 4H, Ar–H), 7.95–8.35(m, 3H, Ar–H), 6.81 (s, 1H, CH, pyrimidine
ring), 8.39(s, 1H, NH), 2.45–3.49(s, 2H, CH2), 5.49(1H, OH) m/e: 406.15 (M?1).
7-methyl-5-(2-nitrophenyl)-N-(4-nitrophenyl)-1,2,3,5-tetrahydroimidazo[1,2-
a]pyrimidine-6-carboxamide (7e) solid white; Anal. Calcd for C20H18N6O5 C,
56.87; H, 4.30; N, 19.90 Found C, 55.78; H, 4.36; N, 19.99; IR (KBr pellets, cm-1):
1,684 (C=O str., 20 amide), 3,076 (C=C–H Asymmetrical str., aromatic), 3,171 (N–
H str., sec. amide), 1,645 (C=N str., pyrimidine ring), 1,106 (C–N str., 30 aryl
amine), 1,247 (C–O str., OCH3), 1,572 (C=C str., skeletal vibration of phenyl
nucleus), 1,440 (C–NO2 str., C6H4NO2) 1H NMR, dppm (DMSO-d6) 7.45–7.77 (m,
4H, Ar–H), 7.93–8.35 (m, 3H, Ar–H), 6.97 (s, 1H, CH, pyrimidine ring), 8.38 (s,
1H, NH), 2.57–3.35(s, 2H, CH2), 5.87(1H, OH) m/e: 423.14 (M?1).
5-(2-hydroxynaphthalen-1-yl)-7-methyl-N-(4-nitrophenyl)-1,2,3,5-tetrahydroimi-
dazo[1,2-a]pyrimidine-6-carboxamide (7f) solid red; Anal. Calcd for C24H21N5O4
C, 65.00; H, 4.77; N, 15.79 Found C, 65.98; H, 4.79; N, 14.91; IR (KBr pellets,
cm-1): 1,685 (C=O str., 20 amide), 3,075 (C=C–H Asymmetrical str., aromatic),
3,168 (N–H str., sec. amide), 1,645 (C=N str., pyrimidine ring), 1,106 (C–N str., 30
aryl amine), 1,217 (C–O str., OCH3), 1,571 (C=C str., skeletal vibration of phenyl
nucleus), 1,440 (C–NO2 str., C6H4NO2) 1H NMR dppm (DMSO-d6) 7.55–7.73 (m,
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Synthesis and biological evaluation
4H, Ar–H), 7.94–8.34 (m, 3H, Ar–H), 6.96 (s, 1H, CH, pyrimidine ring), 8.38 (s,
1H, NH), 2.57–3.33(s, 2H, CH2), 5.82(1H, OH) m/e: 444.16 (M?1).
5-(3,4-dimethoxyphenyl)-7-methyl-N-(4-nitrophenyl)-1,2,3,5-tetrahydroimi-
dazo[1,2-a]pyrimidine-6-carboxamide (7g) solid brown; Anal. Calcd for
C22H23N5O5 C, 60.40; H, 5.30; N, 16.01Found C, 60.87; H, 5.74; N, 16.56; IR
(KBr pellets, cm-1): 1,688 (C=O str., 20 amide), 3,025 (C=C–H Asymmetric str.,
aromatic), 3,168 (N–H str., sec. amide), 1,645 (C=N str., pyrimidine ring), 1,166 (C–
N str., 30 aryl amine), 1,278 (C–O str., OCH3), 1,575 (C=C str., skeletal vibration of
phenyl nucleus), 1,440 (C–NO2 str., C6H4NO2) 1H NMR dppm (DMSO-d6)
7.55–7.78 (m, 4H, Ar–H), 7.83–8.34 (m, 3H, Ar–H), 6.98 (s, 1H, CH, pyrimidine
ring), 8.35 (s, 1H, NH), 2.67–3.36 (s, 2H, CH2), 5.86 (1H, OH) m/e: 438.17 (M?1).
5-(4-hydroxy-3-methoxyphenyl)-7-methyl-N-(4-nitrophenyl)-1,2,3,5-tetrahydro-
imidazo[1,2-a]pyrimidine-6-carboxamide (7h °) solid yellow; Anal. Calcd for
C21H21N5O5 C, 59.57; H, 5.00; N, 16.54 Found C, 57.92; H, 5.67; N, 16.76; IR (KBr
pellets, cm-1): 1,687 (C=O str., 20 amide), 3,077 (C=C–H Asymmetric str.,
aromatic), 3,108 (N–H str., sec. amide), 1,109 (C–N str., 30 aryl amine), 1,290 (C–O
str., OCH3), 1,584 (C=C str., skeletal vibration of phenyl nucleus), 3,216 (OH str.,
1
phenyl), 1,467 (C–NO2 str., C6H4NO2) H NMR dppm (DMSO-d6) 7.55–7.78 (m,
4H, Ar–H), 7.94–8.37 (m, 3H, Ar–H), 6.98 (s, 1H, CH, pyrimidine ring), 8.37 (s,
1H, NH), 2.67–3.37 (s, 2H, CH2), 5.77 (1H, OH) m/e: 424.16 (M?1).
5-(4-hydroxyphenyl)-7-methyl-N-(4-nitrophenyl)-3,5-dihydro-2H-thiazolo[3,2-
a]pyrimidine-6-carboxamide (9a) solid green; Anal. Calcd for C20H18N4O4S C,
58.53; H, 4.42; N, 13.65 Found C, 57.94; H, 4.49; N, 13.87; IR (KBr pellets, cm-1):
1,690 (C=O str., 20 amide), 2,981 (C=C–H asymmetrical str., aromatic), 3o72 (N–H
str., sec. amide), 1,082 (C–N str., 30 aryl amine), 3,209 (OH str., phenyl), 678 (C–S–
C str., Thiazole ring), 1,577 (C=C str., skeletal vibration of phenyl nucleus), 1,465
1
(C–NO2 str., C6H4NO2) H NMR, dppm (DMSO-d6) 7.05–7.45 (m, 4H, Ar–H),
7.70–7.86 (m, 3H, Ar–H), 6.89(s, 1H, CH, pyrimidine ring), 8.01 (s, 1H, NH),
2.66–3.92(s, 2H, CH2), 5.50 (1H, OH) m/e: 411.11(M?1).
5-(2-formylphenyl)-7-methyl-N-(4-nitrophenyl)-3,5-dihydro-2H-thiazolo[3,2-
a]pyrimidine-6-carboxamide (9b) solid yellow; Anal. Calcd for C21H18N4O4S C,
59.70; H, 4.29; N, 13.26 Found C, 59.76; H, 4.34; N, 13.67; IR (KBr pellets, cm-1):
1,690 (C=O str., 20 amide), 3,076 (C=C–H asymmetrical str., aromatic), 3,120 (N–H
str., sec. amide), 1,138 (C–N str., 30 aryl amine), 1,736 (C=O str., aldehyde), 1,232 (C–
O str., OCH3), 667 (C–S–C str., Thiazole ring), 1,537 (C=C str., skeletal vibration of
phenyl nucleus), 1,414 (C–NO2 str., C6H4NO2) 1H NMR, dppm (DMSO-d6)7.27–7.75
(m, 4H, Ar–H), 7.79–8.17(m, 3H, Ar–H), 6.92 (s, 1H, CH, pyrimidine ring), 8.78 (s, 1H,
NH), 2.64–3.64 (s, 2H, CH2), 9.89 (m, 1H, CHO) m/e: 423.11 (M?1).
5-(4-formylphenyl)-7-methyl-N-(4-nitrophenyl)-3,5-dihydro-2H-thiazolo[3,2-
a]pyrimidine-6-carboxamide (9c) solid brown; Anal. Calcd for C21H18N4O4S C,
59.70; H, 4.29; N, 13.26 Found C, 59.87; H, 4.33; N, 13.35; IR (KBr pellets, cm-1):
1,689 (C=O str., 20 amide), 3,068 (C=C–H asymmetrical str., aromatic), 3,280 (N–H
str., sec. amide), 1,092 (C–N str., 30 aryl amine), 1,601 (C=N str., pyrimidine ring),
1,727 (C=O str., aldehyde), 1,260 (C–O str., OCH3), 640 (C–S–C str., Thiazole
ring), 1,506 (C=C str., skeletal vibration of phenyl nucleus), 1,384 (C–NO2 str.,
1
C6H4NO2) H NMR, dppm (DMSO-d6) 7.42–7.87(m, 4H, Ar–H), 7.87–7.98 (m,
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3H, Ar–H), 6.91 (s, 1H, CH, pyrimidine ring), 8.21 (s, 1H, NH), 2.49–3.84(s, 2H,
CH2), 10.48 (s, 1H, CHO) m/e: 423.11 (M?1).
5-(4-chlorophenyl)-7-methyl-N-(4-nitrophenyl)-3,5-dihydro-2H-thiazolo[3,2-
a]pyrimidine-6-carboxamide (9d) solid red; Anal. Calcd for C20H17ClN4O3S C,
56.01; H, 4.00; N, 13.06 Found C, 55.57; H, 4.67; N, 13.12; IR (KBr pellets, cm-1):
1,690 (C=O str., 20 amide), 3,024 (C=C–H Asymmetric str., aromatic), 3,165 (N–H
str., sec. amide), 1,645 (C=N str., pyrimidine ring), 1,166 (C–N str., 30 aryl amine),
1,217 (C–O str., OCH3), 1,570 (C=C str., skeletal vibration of phenyl nucleus), 760
(C–CI str., phenyl), 1,439 (C–NO2 str., C6H4NO2) 636 (C–S–C str., Thiazole ring),
1H NMR dppm (DMSO-d6) 7.45–7.79 (m, 4H, Ar–H), 7.73–8.55 (m, 3H, Ar–H),
6.98 (s, 1H, CH, pyrimidine ring), 8.37 (s, 1H, NH), 2.67–3.55(s, 2H, CH2),
5.97(1H, OH) m/e: 430.07 (M?2).
5-(4-(dimethylamino)phenyl)-7-methyl-N-(4-nitrophenyl)-3,5-dihydro-2H-thiaz-
olo[3,2-a]pyrimidine-6-carboxamide (9e) solid yellow; Anal. Calcd for C22H23N5-
O3S C, 60.39; H, 5.30; N, 16.01 Found C, 60.40; H, 5.36; N, 16.23; IR (KBr pellets,
cm-1): 1,688 (C=O str., 20 amide), 3,024 (C=C–H asymmetric str., aromatic), 3,168
(N–H str., sec. amide), 1,645 (C=N str., pyrimidine ring), 1,167 (C–N str., 30 aryl
amine), 1,279 (C–O str., OCH3), 1,572 (C=C str., skeletal vibration of phenyl
nucleus), 1,341 (C–N str., 30 aryl amine), 637 (C–S–C str., Thiazole ring), 1,440
(C–NO2 str., C6H4NO12H NMR dppm (DMSO-d6) 7.45–7.77 (m, 4H, Ar–H),
7.93–8.35 (m, 3H, Ar–H), 6.97 (s, 1H, CH, pyrimidine ring), 8.38 (s, 1H, NH),
2.57–3.35 (s, 2H, CH2), 5.89 (1H, OH) m/e: 438.16 (M?1).
5-(4-methoxyphenyl)-7-methyl-N-(4-nitrophenyl)-3,5-dihydro-2H-thiazolo[3,2-
a]pyrimidine-6-carboxamide (9f) solid red; Anal. Calcd for C21H20N4O4S C, 59.42;
H, 4.75; N, 13.20 Found C, 60.55; H, 4.79; N, 13.26; IR (KBr pellets, cm-1): 1,688
(C=O str., 20 amide), 3,026 (C=C–H asymmetric str., aromatic), 3,171 (N–H str.,
sec. amide), 1,640 (C=N str., pyrimidine ring), 1,161 (C–N str., 30 aryl amine),
1,218 (C–O str., OCH3), 1,556 (C=C str., skeletal vibration of phenyl nucleus),
1
1,466 (C–NO2 str., C6H4NO2) H NMR dppm (DMSO-d6) 7.45–7.87 (m, 4H, Ar–
H), 7.83–8.45 (m, 3H, Ar–H), 6.98 (s, 1H, CH, pyrimidine ring), 8.48 (s, 1H, NH),
2.57–3.37 (s, 2H, CH2), 5.88(1H, OH) m/e: 426.12 (M?2).
5-(3,4-dimethoxyphenyl)-7-methyl-N-(4-nitrophenyl)-3,5-dihydro-2H-thiazol-
o[3,2-a]pyrimidine-6-carboxamide (9g) solid white; Anal. Calcd for C22H22N4O5S
C, 58.14; H, 4.88; N, 12.33 Found C, 59.19; H, 4.85; N, 12.34; IR (KBr pellets,
cm-1): 1,687 (C=O str., 20 amide), 3,015 (C=C–H asymmetric str., aromatic), 3,155
(N–H str., sec. amide), 1,160 (C–N str., 30 aryl amine), 1,245 (C–O str., OCH3),
1,597 (C=C str., skeletal vibration of phenyl nucleus), 686 (C–S–C str., Thiazole
ring), 1,459 (C–NO2 str., C6H4NO2) 1H NMR dppm (DMSO-d6) 7.35–7.78 (m, 4H,
Ar–H), 7.94–8.36 (m, 3H, Ar–H), 6.87 (s, 1H, CH, pyrimidine ring), 8.37 (s, 1H,
NH), 2.47–3.38 (s, 2H, CH2), 5.88 (1H, OH) m/e: 455.13 (M?1).
5-(2-hydroxynaphthalen-1-yl)-7-methyl-N-(4-nitrophenyl)-3,5-dihydro-2H-thiaz-
olo[3,2-a]pyrimidine-6-carboxamide (9h) solid red; Anal. Calcd for C24H20N4O4S
C, 62.60; H, 4.38; N, 12.17 Found C, 62.76; H, 4.42; N, 12.76; IR (KBr pellets,
cm-1): 1,688 (C=O str., 20 amide), 3,047 (C=C–H asymmetric str., aromatic), 3,154
(N–H str., sec. amide), 1,169 (C–N str., 30 aryl amine), 1,208 (C–O str., OCH3),
1,589 (C=C str., skeletal vibration of phenyl nucleus), 627 (C–S–C str., Thiazole
123

Synthesis and biological evaluation
ring), 3,254 (OH str., phenyl), 1,484 (C–NO2 str., C6H4NO2) 1H NMR dppm
(DMSO-d6) 7.43–7.78 (m, 4H, Ar–H), 7.97–8.45 (m, 3H, Ar–H), 6.96 (s, 1H, CH,
pyrimidine ring), 8.37 (s, 1H, NH), 2.53–3.37 (s, 2H, CH2), 5.87 (1H, OH) m/e:
461.12 (M?1) (Tables 1, 2).
Biological screening of synthesized pyrimidine derivatives
Evaluation of antimicrobial activity
Determination of minimum inhibitory concentration (MIC) in-vitro antimicrobial
activity of synthesized compounds was performed against Gram-positive bacteria:
Staphylococcus aureus MTCC 3,160, Bacillus subtilis MTCC 441, Gram-negative
bacterium: Escherichia coli MTCC 443 and fungal strains: Candida albicans
MTCC 227 and Aspergillus niger MTCC 281 using tube dilution method using
ciprofloxacin and fluconazole as standard drugs for antibacterial and antifungal
activity, respectively [17]. Dilutions of test and standard compounds were prepared
in double-strength nutrient broth—I.P. (bacteria) or Sabouraud dextrose broth I.P.
(fungi) [18]. The inoculated tubes were incubated at 37 1 °C for 24 h (bacteria),
at 25 1 °C for 7 d (A. niger) and at 37 1 °C for 48 h (C. albicans),
respectively, and the results were recorded in terms of MIC (the lowest
Table 1 Arrangement of
substituents used for targeted
compounds
Compound
R1
R2
R3
R4
X
7a
7b
7c
7d
7e
7f
OH
H
H
H
H
H
H
H
H
H
H
H
H
N
N
N
N
N
N
N(CH3)2
OH
H
H
CHO
H
NO2
HO
O
7g
7h
9a
9b
9c
9d
9e
9f
H
OCH3
OCH3
H
OCH3
OH
H
H
H
H
H
H
H
H
H
N
N
S
S
S
S
S
S
S
S
H
H
OH
CHO
H
H
H
H
CHO
Cl
H
H
H
H
N(CH3)2
OCH3
OCH3
H
H
9g
9h
H
OCH3
HO
O
123

P. Dhiman et al.
Table 2 Physicochemical
properties of synthesized
pyrimidine derivatives
Compound
M. wt.
m. p.(C0)
Rf value*
Yield (%)
7a
7b
7c
7d
7e
7f
393.4
420.4
393.4
405.4
422.3
443.4
437.4
423.4
410.4
422.4
422.4
428.5
437.5
424.4
454.5
460.5
240–247
275–279
234–247
216–219
231–235
251–256
220–228
274–276
234–238
135–137
234–238
175–177
188–192
234–236
264–267
255–260
0.32
0.47
0.49
0.40
0.46
0.45
0.35
0.37
0.35
0.39
0.30
0.43
0.76
0.38
0.41
0.43
78.81
66.25
65.44
67.17
68.53
47.40
68.32
79.27
58.48
78.63
48.72
55.11
73.84
83.25
87.57
76.68
7g
7h
9a
9b
9c
9d
9e
9f
*S.D = Standard Deviation
(Average of three
determinations)
9g
9h
concentration of test substance which inhibited the growth of microorganisms)
given in Table 3.
Free radical scavenging activity
Free radical scavenging activity of synthesized compounds against stable free
radical 2,2-diphenyl-2-picrylhydrazyl hydrate (DPPH) was determined spectropho-
tometrically. When DPPH reacts with an antioxidant compound, which can donate
hydrogen, it is reduced. Following the reduction, its deep violet color in methanol
bleaches to yellow, and shows a significant absorption decrease at 517 nm. Fifty
milliliters of various concentrations (25, 50, 75, and 100) lg/ml of the compounds
dissolved in methanol was added to 5 ml of a 0.004 % methanol solution of DPPH.
After a 30-min incubation period at room temperature, the absorbance was read
against a blank at 517 nm. Tests were carried out in triplicate, and ascorbic acid was
used as a positive control. IC50 values were calculated (Table 4). Scavenging of
DPPH free radical was calculated as: DPPH scavenging activity (%) = [(Ac–At)/
Ac] 9 100 where, Ac is the absorbance of the control reaction At is the absorbance
of the test compound.
Results and discussion
Chemistry
The synthesis of two series of pyrimidine (7a–h) and (9a–h) derivatives was carried
out as outlined in the Scheme 1. All the compounds were obtained in appreciable
123

Synthesis and biological evaluation
Table 3 Minimum inhibitory concentration for the antimicrobial activity of newly synthesized pyrim-
idine derivatives
Compound
Minimum inhibitory concentration (lM)
B. subtilis
S. aureus
E. coli
C. albicans
A. niger
7a
7b
7c
7d
7e
7f
11.53
27.38
11.17
32.07
10.46
28.17
23.47
32.76
13.32
17.23
21.32
11.78
31.19
21.08
22.67
23.32
8.71a
11.24
17.19
12.17
17.04
09.27
15.37
22.75
33.78
12.67
18.25
21.33
09.76
26.38
21.06
22.35
23.67
8.71a
10.34
24.27
11.36
32.04
10.46
28.18
24.47
32.78
13.34
17.27
12.26
11.64
26.38
26.07
24.67
22.32
8.71a
11.27
16.18
11.32
31.07
09.27
29.15
22.44
31.76
12.32
24.63
20.37
11.78
26.38
27.07
22.34
28.67
10.09b
10.53
16.18
12.15
17.07
10.46
15.37
22.75
27.38
12.67
23.63
23.27
12.38
24.38
21.04
22.69
28.67
10.09b
7g
7h
9a
9b
9c
9d
9e
9f
9g
9h
Std.
a
Ciprofloxacin
b
Fluconazole
Table 4 Percentage inhibition and IC50 value for free radical scavenging activity of the synthesized
pyrimidine derivatives
Compound
IC50 (mean S.D.)* (lg/ml)
Compound
IC50 (mean SD)* (lg/ml)
7a
52.43 0.152
47.2 0.563
55.2 0.162
47.5 0.244
52.9 0.087
42.8 0.788
62.2 0.124
57.8 0.387
9a
75.4 0.170
51.7 0.068
64.2 0.117
41.6 0.382
58.8 0.346
52.3 0.571
60.2 0.542
42.3 0.087
7b
9b
7c
9c
7d
9d
7e
9e
7f
9f
7g
9g
7h
9h
Ascorbic acid
41.9 0.089
*S.D = Standard Deviation (Average of three determinations)
yield and their physicochemical characteristics are presented in Table 2. The
structures of the synthesized compounds were established on the basis of their
consistent IR, NMR, and mass spectral characteristics in addition to elemental
analysis (C, H, N), which were in full agreement with the assigned molecular
structures and the data. IR spectrum showed a definite absorption at 1,690 cm-1 due
123

P. Dhiman et al.
O
O
NO2
+
OEt
1
NH2
2
toluene
NaOH
O
O2N
NH2
NH2
+
NH2
NH2
S
NH
+
HN
H3C
O
Thiourea
Guanidine
N-(4-nitrophenyl)-3-oxobutamide
4
5
3
R2
R2
Ethanol
R1
R3
R4
R1
R3
R4
(conc.HCL)
reflux 8-10 h
O
O
Ethanol
(conc.HCL)
reflux 8-10 h
OH
Ethanol
(conc.HCL)
reflux 8-10 h
O
R3
R4
O
R2
R1
NH
R3
O2N
R4
R2
R1
O2N
NH
O
O2N
OH
O
NH
NH
NH
H3C
8a-g
N
H
S
N
H
NH
H3C
N
H
H3C
N
H
X
6a-e-g-h
Dimethyl
formamide
ClCH2CH2Cl
X=S, NH
6f, 8h
Dimethyl
R3
R2
ClCH2CH2Cl
R4
formamide
Dimethyl
ClCH2CH2Cl
R4
formamide
O2N
R1
N
R3
R2
O
NH
O2N
O2N
R1
N
OH
N
O
O
H3C
N
S
NH
N
H
9a-g
H3C
N
H3C
N
X
N
H
7a-e-g-h
7f, 9h
Scheme 1 Synthesis of methyl 5-substituted N-(4-nitrophenyl)-7-methyl-3, 5-dihydro-2H-thiazolo/
imidazo[3,2-a]pyrimidine-6-carboxamide derivatives
to carboxamide group. The formation of compound 9d was further supported by
disappearance of the IR band at 1,211 cm-1 (8d) due to the C=S group and
appearance of a new band at 636 cm-1 due to the C–S–C bond. The strong
absorption bands appeared between 3,141 and 3,189 cm-1 in the IR spectra of
compounds (7a–h) corresponding to secondary amine (N–H) group present in
1
pyrimidine ring. The H NMR data of compounds revealed signals between 6.84
123

Synthesis and biological evaluation
and 6.97 dppm for CH of pyrimidine ring. The 1H NMR data of compounds
revealed signals between 8.07 and 8.19 dppm NH of pyrimidine ring.
Biological evaluation
Antimicrobial activity
All the synthesized compounds were screened for their antimicrobial activity and
the results showed that p-chloro substituted pyrimidine derivative 7-methyl-5-(2-
nitrophenyl)-N-(4-nitrophenyl)-1,2,3,5-tetrahydroimidazo[1,2-a]pyrimidine-6-car-
boxamide 7e was found to be the most active antimicrobial comparable to standards
taken. Compounds 7a, 7c, 9a and 9d also showed significant antibacterial and
antifungal activity. This may be due to the presence of electron-withdrawing group
present on the aromatic ring attached to pyrimidine moiety. The role of the electron-
withdrawing group in increasing the antimicrobial activity is supported by the
results of Mostafa et al. [19].
Free radical scavenging activity
Compounds concentration providing 50 % inhibition (IC50) was calculated as per
the method described by Bondet et al. [20]. Tests were carried out in triplicate, and
ascorbic acid was used as a positive control. Standard curve was plotted for different
concentrations of ascorbic acid. The results of antioxidant activity showed that few
synthesized compounds exhibit considerable antioxidant activity. Chloro substitu-
tion 9d at the para position of phenyl ring increases the antioxidant activity, which
is also supported by Kumar et al. [21]. Substitution of bulky group like naphthol (9h
and 7f) also increases the activity, which is also favored by Bhalghat et al. [22].
p-nitro group increases the overall antimicrobial activity.
NO2
Electron withdrawing group on aromatic ring increases
antimicrobial activity
NH
H3C
N
O
N
Bulky group increase the antioxidant activity
X
R
Substitution with electron withdrawing group
inceases antioxidant activity
Fig. 1 Structure–activity relationship of the synthesized derivatives
123

P. Dhiman et al.
Structure–activity relationship (SAR)
From the results of the antimicrobial and antioxidant activities of the synthesized
substituted pyrimidine 6-carboxamide derivatives, the following structure–activity
relationships can be derived (Fig. 1):
1. The results of antibacterial activity indicated that compound 7-methyl-5-(2-
nitrophenyl)-N-(4-nitrophenyl)-1,2,3,5-tetrahydroimidazo[1,2-a]pyrimidine-6-
carboxamide 7e was found to be most potent among all the synthesized
compounds. This may be due to the presence of the electron-withdrawing nitro
group.
2. p-nitro group at N-substituted phenyl ring of all synthesized pyrimidine
derivatives increases the overall antimicrobial activity.
3. Substitution of chloro group in compound 9d at phenyl ring attached to
pyrimidine ring increases the antioxidant activity.
4. Presence of bulky group in compound (9h and 7f) also found to increase the
antioxidant activity.
Conclusions
Two series of new thiazolo and imidazo pyrimidine derivatives were synthesized
and their antimicrobial and antioxidant activities have been evaluated. Compound 7-
methyl-5-(2-nitrophenyl)-N-(4-nitrophenyl)-1,2,3,5-tetrahydroimidazo[1,2-a]pyrim-
idine-6-carboxamide 7e was found to be the most active antimicrobial comparable
to standards taken. Compounds 7a, 7c, 9a, and 9d also have shown significant
antibacterial and antifungal activity. Compounds 7f, 9d, and 9h have shown
promising antioxidant activity with IC50 comparable with standard compound.
Hence, this research represents a class of wide-spectrum antimicrobial agents and
potential antioxidant agents, which can further be explored for future research.
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