Piperidine-mediated synthesis of thiazolyl chalcones and their derivatives as potent antimicrobial agents

Article abstract of DOI:10.1002/jhet.707

A series of new thiazolyl chalcones, 1-[2-amino-4-methyl-1, 3-thiazol-5-yl]-3-aryl-prop-2-en-1-one were prepared by piperidine mediated Claisen-Schmidt condensation of thiazolyl ketone with substituted aromatic aldehyde. These chalcones on cyclization gav

Full text of DOI:10.1002/jhet.707

September 2011
Piperidine-Mediated Synthesis of Thiazolyl Chalcones and Their
Derivatives as Potent Antimicrobial Agents
1181
P. Venkatesan,a* and T. Maruthavananb
aDepartment of Chemistry, Mahendra Institute of Technology, Namakkal-637 503, India
bDepartment of Chemistry, Sona College of Technology, Salem-636 005, India
*E-mail: venkatesanps@yahoo.co.in
Received August 9, 2010
DOI 10.1002/jhet.707
Published online 30 June 2011 in Wiley Online Library (wileyonlinelibrary.com).
A series of new thiazolyl chalcones, 1-[2-amino-4-methyl-1, 3-thiazol-5-yl]-3-aryl-prop-2-en-1-one were
prepared by piperidine mediated Claisen-Schmidt condensation of thiazolyl ketone with substituted aromatic
aldehyde. These chalcones on cyclization gave 2-amino-6-(2-amino-4-methyl-1,3-thiazol-5-yl)-4-aryl-4H-
pyridine-3-carbonitrile and 2-amino-6-(2-amino-4-methyl-1,3-thiazol-5-yl)-4-aryl-4H-pyran-3-carbonitrile.
The results showed that this skeletal framework exhibited marked potency as antimicrobial agents. The most
active antibacterial agent was 2-amino-6-(2-amino-4-methyl-1,3-thiazol-5-yl)-4-(4-chlorophenyl)-4H-pyran-
3-carbonitrile while 2-amino-6-(2-amino-4-methyl-1,3-thiazol-5-yl)-4-(4-methoyphenyl)-4H-pyran-3-carbo-
nitrile appeared to be the most active antifungal agent.
J. Heterocyclic Chem., 48, 1181 (2011).
INTRODUCTION
described in literature [12]. In the Claisen–Schmidt con-
densation of chalcone synthesis, strong alkali reduces
the yield of the target adduct and makes its purification
difficult, due to undesirable side reactions such as multi-
ple condensation, polymerization, and rearrangement
[13]. In this work, therefore, we used piperidine instead
of strong alkali for the synthesis of 1-[2-amino-4-
methyl-1,3-thiazol-5-yl]-3-aryl-prop-2-en-1-one (4a-e) as
shown in Scheme 1, which gives considerable yield.
The IR spectra of compounds 4a–e showed the
absorption band at 1620–1628 cmꢀ1 for C¼¼O group
and 1610–1612 cmꢀ1 for C¼¼C group indicating the
presence of a, b–unsaturated carbonyl group. The 1H
NMR spectra gave two doublets at d 7.60–7.64 ppm
and d 8.20–8.28 ppm with the coupling constant, J ¼
15.2 – 15.8 Hz. It evident that the olefinic protons at Ca
and Cb position of a, b–unsaturated carbonyl group are
arranged in trans configuration. Moreover, NAH asym-
metric stretching absorption band appeared around
3324–3354 cmꢀ1 and symmetric stretching absorption
band around 3402–3488 cmꢀ1 indicating the presence of
ANH2 group. The C¼¼N and CH¼¼CH ring stretching
absorption band appeared around 1596–1582 cmꢀ1 and
1498–1494 cmꢀ1, respectively, supporting the aromatic-
ity of thiazole ring. In addition, CAN stretching absorp-
The chalcone (1,3-diaryl-2-propen-1-one) derivative is
an important group of secondary metabolites found
ubiquitously in the plant kingdom. These are well-
known intermediates towards the synthesis of the variety
of heterocyclic compounds [1]. In addition, the chalcone
exhibits a various biological activities such as antibacte-
rial [2], antifungal [3], antiviral [4], anti-inflammatory
[5], antitumor [6], antioxidant [7], insect antifeedant [8],
and act as tyrosinase inhibitors [9]. The complex phar-
macological activities together with the easiest synthetic
method by Claisen-Schmidt condensation has solicited
considerable interest towards the synthesis of novel
chalcone as a potent microbial agents [10].
As thiazolidine moiety seems to be a potential phar-
macophore in various pharmacologically active agents
[11], we have synthesized chalcones with a thiazolidine
moiety and heterocyclized to cyanopyridine and cyano-
pyran derivatives as possible antimicrobial agents, which
could furnish better therapeutic results.
RESULT AND DISCUSSION
1-(2-Amino-4-methyl-1,3-thiazol-5-yl)ethanone (2)
was synthesized by cyclization of 3-chloroacetylacetone
.
tion band displayed around 1173–1176 cmꢀ1 13C NMR
spectra of compounds 4a–e exhibited chemical shifts at
(1) with thiourea in accordance with the method
C
V
2011 HeteroCorporation

1182
P. Venkatesan and T. Maruthavanan
Vol 48
Scheme 1
Scheme 3
3462–3474 cmꢀ1 and 3326–3356 cmꢀ1 and compounds
6a–e also gave the absorption band at 3456–3476 cmꢀ1
and 3342–3352 cmꢀ1 for the same. The stretching
absorption band about 2216–2232 cm–1 corresponding
to the ACBN group was observed for both the com-
pounds 5a–e and 6a–e. The 1H NMR spectra gave
additional broad singlet about d 5.67–5.84 ppm in com-
pounds 5a–e and broad singlet about d 5.67–5.84 ppm
in compounds 6a–e indicating formation of ANH2
group in both the compounds 5a–e and 6a–e. The sin-
glet around d 6.32–6.74 ppm was assigned to pyridine-
H of compounds 5a–e. Similarly, two doublets around
d 6.11–6.16 ppm and d 4.14–4.32 ppm with coupling
constant about J ¼ 3.04–3.09 Hz was assigned to py-
ran-H of compounds 6a–e. In the Mass spectral frag-
mentation of compounds 5a–e and 6a–e, loss of ACN
group was observed by lowering the m/z 26 from its
molecular ion peak (Mþ), which indicating the presence
of CN group in the heterocyclic ring of compounds
5a–e and 6a–e. The entire spectral data and elemental
analysis reports are consistent with the structure of
compounds 5a–e and 6a–e as expected, and they are
given in experimental part.
d 121.1–121.3 ppm (Ca), d 148.2–148.3 ppm (Cb), and
d 187.1–189.2 ppm (¼¼C¼¼O) indicating the presence of
a,b-unsaturated carbonyl groups of chalcone. The
methyl group on thiazole ring resonated at d 28.1–28.9
ppm. In addition, the signals at d 166.2–166.6 ppm, d
152.1–152.2 ppm, d 112.3–112.8 ppm were assigned to
C2, C3, and C5 of thiazole ring. The entire spectral data
and elemental analysis results are in agreement with the
proposed structure of chalcones 4a–e as expected, and
they are given in experimental part.
2-Amino-6-(2-amino-4-methyl-1,3-thiazol-5-yl)-4-aryl-
4H-pyridine-3-carbonitrile (5a–e) was prepared by hetero-
cyclization of thiazolyl chalcones (4a–e) with the etha-
nolic solution of malononitrile in presence of ammonium
acetate. Similarly, 2-amino-6-(2-amino-4-methyl-1,3-thia-
zol-5-yl)-4-aryl-4H-pyran-3-carbonitrile (6a–e) were pre-
pared by heterocyclization of thiazolyl chalcones (4a-e)
with the ethanolic solution of malononitrile in presence
of pyridine. The synthetic route of compounds 5a–e and
6a–e are in accordance with the method described in the
literature [14], and are outlined in Scheme 2 and Scheme
3, respectively.
Antimicrobial activities. The antimicrobial activity
of new synthesized compounds 4a–e, 5a–e, and 6a–e
was evaluated using the agar diffusion method [15]. The
in vitro antibacterial activity was evaluated against vari-
ous pathogenic bacteria (Gram-positive and Gram-
negative) viz., Staphylococcus aureus (S. aureus), Bacil-
lus subtilis (B. subtilis), Escherichia coli (E. coli), and
Salmonella typhi (S. typhi). Similarly, the in vitro anti-
fungal activity was evaluated against Aspergillus niger
(A. niger), Aspergillus flavus (A. flavus), Penicillium
chrysogenum (P. chrysogenum), and Fusarium monili-
forme (F. moniliforme). The results of antibacterial and
antifungal screening of the new synthesized compounds
are given in Table 1.
The signals for a, b–unsaturated carbonyl group was
not observed in the spectral data of compounds 5a–e
and 6a–e. It is evident that the formations of a new
heterocyclic ring in compounds 5a–e and 6a–e. IR
spectra of compounds 5a–e revealed the presence of
ANH2 stretching absorption bands in the region of
Scheme 2
The compound 2-amino-6-(2-amino-4-methyl-1,3-thia-
zol-5-yl)-4-(4-chlorophenyl)-4H-pyran-3-carbonitrile (6c)
was showed good activity (zone of inhibition up to 17–19
mM at the concentration of 12.5 lg/mL) against S. aureus
and S. typhi. The compounds, 1-(2-amino-4-methyl-1,3-
thiazol-5-yl)-3-(3-nitrophenyl)prop-2-en-1-one (4a) and
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September 2011 Piperidine-Mediated Synthesis of Thiazolyl Chalcones and Their Derivatives as Potent
Antimicrobial Agents
1183
1-(2-amino-4-methyl-1,3-thiazol-5-yl)-3-(4-methoxyphe-
nyl)prop-2-en-1-one (4e) were inactive against all test
bacterial strain. However, most of the compounds 5a–e
and 6a–e were showed moderate to good activity with
MIC value in the range of 6.25–25 lg/mL) in DMSO.
Among the new synthesized chalcones, compound
1-(2-amino-4-methyl-1,3-thiazol-5-yl)-3-(4-nitrophenyl)-
prop-2-en-1-one (4b) was showed moderate activity
against A. flavus, and 1-(2-amino-4-methyl-1,3-thiazol-5-
yl)-3-(4-chlorophenyl)prop-2-en-1-one (4c) was showed
moderate activity against A. niger and P. chrysogenum
(zone of inhibition <10 mM at the concentration of 50
lg/mL). The chalcones 4a–e were inactive against most
of the fungal strain. However, the compounds 5a–e and
6a–e were showed remarkable antifungal activity. The
compound
2-amino-6-(2-amino-4-methyl-1,3-thiazol-5-
yl)-4-(4-methoyphenyl)-4H-pyran-3-carbonitrile (6e) was
showed good activity (zone of inhibition 16–18 mM at
concentration of 6.25–12.5 lg/mL) against A. niger, A.
flavus, and F. moniliforme. Similarly, 2-amino-6-(2-
amino-4-methyl-1,3-thiazol-5-yl)-4-(4-chlorophenyl)-4H-
pyran-3-carbonitrile (6c) showed good activity (zone of
inhibition up to 16 mM at the concentration of 12.5 lg/
mL) against A. niger and A. flavus but no activity against
F. moniliforme.
The mode of the antimicrobial action of chalcones
has long been believed, due to their reaction with impor-
tant thiol groups of essential enzymes via Michael addi-
tion at the ketovinyl double bond [16]. According to
Daniela Batovska et al. [17], p-electron withdrawing
group will increase the electrophilicity of C-b and thus
facilitate the nucleophilic attack of the cellular thiol
groups. Interesting, the antimicrobial activity was found
to be good in compounds 4b, 5b, and 6b rather than 4a,
5a, and 6a, which is due to p-NO2 substitution. How-
ever, nitro substitution has not shown significant antimi-
crobial activity against most of the test strains.
Compounds 5c and 6c, which carried p-Cl substituent,
exhibited moderate to good antibacterial and antifungal
activity against most of the test strains. Similarly, com-
pound 6e showed almost good activities due to the pres-
ence of p-OCH3 substitution. In general, on heterocycli-
zation of thiazolyl chalcones (4a–e) to cyanopyridine
(5a–e) and cyanopyran (6a–e) derivatives, both antibac-
terial and antifungal activities were increased remark-
ably. As nitrogen containing heterocyclic compound is
generally known to possess antimicrobial activity due to
the formation of hydrogen bonding with the active site
of an enzyme [18], it is believed that the ANH2 group
and ACN group of cyanopyridine/cyanopyran ring sys-
tems may act as the active center.
It can be concluded that the cyanopyridine and cyanopyr-
ane derivatives meet stereochemical and electronic require-
ments of the target in a better way than chalcone, and hence
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1184
P. Venkatesan and T. Maruthavanan
Vol 48
Anal. Calcd for C13H11N3O3S (289.31): C, 53.97; H, 3.83; N,
14.52%, Found: C, 53.94; H, 3.81; N, 14.54%.
exhibited good antibacterial and antifungal activity. Pre-
dominantly, cyanopyrane derivatives showed excellent anti-
microbial activities. In addition, 2-amino-6-(2-amino-4-
methyl-1,3-thiazol-5-yl)ꢀ4-(4-chlorophenyl)-4H-pyran-3-
carbonitrile (6c) acts as the most active antibacterial agent
and 2-amino-6-(2-amino-4-methyl-1,3-thiazol-5-yl)-4-(4-
methoy-phenyl)-4H-pyran-3-carbonitrile (6e) appeared to
be the most active antifungal agent.
1-(2-Amino-4-methyl-1,3-thiazol-5-yl)-3-(4-nitrophenyl)prop-2-
en-1-one (4b). Pale Yellow solid, yield 1.88 g (65%), mp 146–
148ꢁC; UV (CHCl3): 286, 348 nm; ir: 3488 and 3324 (NH2),
3168 (ArCH), 1620 (C¼¼O), 1494 (CH¼¼CH), 1552 and 1424
(ArNO2), 1592 (C¼¼N), 1174 cmꢀ1 (CAN str); 1H NMR
(CDCl3): d 2.51 (3H, s, CH3 thiazole, 8.86 (2H, br s, NH2 thi-
azole), 7.36–8.24 ppm (6H, m, ArH þ CH¼¼CH); 13C NMR
(CDCl3): d 187.9, 166.6, 155.3, 152.1, 148.3, 128.4, 125.1,
122.2, 121.1, 112.6, 28.2 ppm; ms: m/z 290 (Mþ þ 1); Anal.
Calcd for C13H11N3O3S (289.31): C, 53.97; H, 3.83; N,
14.52%, Found: C, 54.01; H, 3.82; N, 14.54%.
EXPERIMENTAL
1-(2-Amino-4-methyl-1,3-thiazol-5-yl)-3-(4-chlorophenyl)prop-
2-en-1-one (4c). Colorless solid, yield 2 g (72%), mp 146–
148ꢁC; UV (CHCl3): 262, 366 nm; ir: 3402 and 3336 (NH2),
3164 (ArCH), 1626 (C¼¼O), 1494 (CH¼¼CH), 1584 (C¼¼N),
General. All the common chemicals, 3-chloroacetylacetone
(1) and substituted aryl aldehyde (3a–e) were obtained from
Sigma-Aldrich chemicals (India). Melting points of synthesized
compounds were determined in open glass capillaries and were
uncorrected. UV spectra were recorded using Perkin-Elmer
402 UV–vis spectrophotometer. IR spectra were recorded on
1
1176 (CAN str), 724 cmꢀ1 (ArCl); H NMR (CDCl3): d 2.51
(3H, s, CH3 thiazole, 8.68 (2H, br s, NH2 thiazole), 7.28–8.42
ppm (6H, m, ArH þ CH¼¼CH); 13C NMR (CDCl3): d 188.2,
166.4, 156.2, 152.2, 148.2, 126.8, 124.4, 122.2, 121.3, 112.8,
1
Perkin-Elmer 577 IR spectrophotometer using KBr pellets. H
28.6 ppm; ms: m/z 280 (Mþ
C13H11ClN2OS (278.75): C, 56.01; H, 3.96; N, 10.05%,
Found: C, 56.06; H, 3.97; N, 10.02%.
þ
1); Anal. Calcd for
NMR and 13C NMR spectra were recorded on Brucker 300
MHz NMR Spectrometer in CDCl3 with tetramethylsilane as
the internal standard and the chemical shifts were reported in
ppm scale. Mass spectra were studied using Finnigan MAT
8230 mass spectrometer. Elemental analysis was done on
Vario EL-III elemental analyzer and analyzed reports were
within 6 0.4% of the theoretical values. The purity of the
compounds was checked by thin layer chromatography on
silica gel 60 F254 (Merck, India) and spots were developed
using iodine vapour or ultraviolet light.
1-(2-Amino-4-methyl-1,3-thiazol-5-yl)-3-(4-dimethylamino-
phenyl)prop-2-en-1-one (4d). Pale yellow solid, yield 1.67 g
(58%), mp 128–130ꢁC; UV (CHCl3): 272, 382 nm; ir (KBr,
cmꢀ1): 3486 and 3324 (NH2), 3168 (ArCH), 1620 (C¼¼O),
1498 (CH¼¼CH), 1582 (C¼¼N), 1173 cmꢀ1 (CAN str); 1H
NMR (300 MHz, CDCl3): d 2.51 (3H, s, CH3 thiazole, 8.84
(2H, br s, NH2 thiazole), 7.12–8.36 (6H, m, ArH þ CH¼¼CH),
2.84 ppm (6H, s, N(CH3)2); 13C NMR (300 MHz, CDCl3): d
189.2, 166.6, 158.3, 152.1, 148.3, 128.6, 125.2, 122.2, 121.1,
112.6, 44.6, 28.1 ppm; ms: m/z 288 (Mþ þ 1); Anal. Calcd for
C15H17N3OS (287.38): C, 62.73; H, 5.95; N, 14.66%, Found:
C, 62.69; H, 5.96; N, 14.62%.
1-(2-Amino-4-methyl-1,3-thiazol-5-yl)-3-(4-methoxyphenyl)-
prop-2-en-1-one (4e). Colorless solid, yield 1.81 g (66%), mp
136–138ꢁC; UV (CHCl3): 286, 386 nm; ir: 3448 and 3326 (NH2),
3186 (ArCH), 1628 (C¼¼O), 1498 (CH¼¼CH), 1596 (C¼¼N), 1232
and 1028 (CAO str), 1174 cmꢀ1 (CAN str); 1H NMR (CDCl3): d
2.52 (3H, s, CH3 thiazole, 8.68 (2H, br s, NH2 thiazole), 7.21-
8.32 (6H, m, ArH þ CH¼¼CH), 3.81 ppm (3H, s, ArOCH3); 13C
NMR (CDCl3): d 188.6, 166.2, 157.9, 152.1, 148.2, 127.4, 124.8,
122.2, 121.2, 112.8, 53.8, 28.5 ppm; ms: m/z 275 (Mþ þ 1);
Anal. Calcd for C14H14N2O2S (274.34): C, 61.32; H, 5.12; N,
10.24%, Found: C, 61.29; H, 5.14; N, 10.21%.
General procedure for synthesis of 2-amino-6-(2-amino-
4-methyl-1,3-thiazol-5-yl)-4-aryl-4H-pyridine-3-carbonitrile
derivatives (5a-e). The thiazolyl chalcone, 4a–e (0.01 mol),
malononitrile (0.66 g, 0.01 mol) and ammonium acetate (6.16 g,
0.08 mol) in ethanol (95%, 25 mL) were refluxed on a water
bath for 4–10 h. The progress of reaction was monitored by TLC
at the appropriate time intervals. The solution was poured on to
crushed ice and kept aside. The precipitate thus separated was
collected by filtration and crystallized from ethanol.
2-Amino-6-(2-amino-4-methyl-1,3-thiazol-5-yl)-4-(3-nitro-
phenyl)-4H-pyridine-3-carbonitrile (5a). Yellow solid, (0.94
g (25.5%), mp 216–218ꢁC; UV (CHCl3): 262, 374 nm; ir:
3462 and 3342 (NH2), 3182 (ArCH), 2216 (CBN), 1581
(C¼¼N), 1512 (CH¼¼CH), 1546 and 1374 cmꢀ1 (ArNO2); 1H
NMR (CDCl3): d 2.51 (3H, s, CH3 thiazole), 8.42 (2H, br s,
NH2 thiazole), 6.74 (1H, s, H Pyridine), 5.67 (2H, br s, NH2
General procedure for synthesis of 1-[2-amino-4-methyl-
1,3-thiazol-5-yl]ethanone (2). To a stirred solution of thiourea
(15.2 g, 0.2 mol) in absolute ethanol (75 mL) containing a cat-
alytic amount of triethylamine, a solution of 3-chloroacetylace-
tone (26.9 g, 0.2 mol) in 10 mL of absolute ethanol was added
drop wise. After complete addition, the mixture was stirred at
room temperature for 30 min and then refluxed for 5 h. The
reaction mixture was cooled, a solid filtered off, washed with
cold ethanol, dried, and finally recrystallized from DMF to get
the compound 2 with 65 % yield. mp 275ꢁC [lit mp 274–
1
276ꢁC], H NMR (300 MHz, CDCl3): d 2.78 (s, 3H, CH3 thia-
zole), 2.35 (s, 3H, CH3 acetyl), 8.48 (br s, 2H, NH2 thiazole).
General procedure for synthesis of 1-(2-amino-4-methyl-
1, 3-thiazol-5-yl)-3-aryl-prop-2-en-1-one (4a-e). To a mixture
of 1-[2-amino-4-methyl-1,3-thiazol-5-yl]ethanone (0.01 mol)
and arylaldehyde (0.01 mol) in ethanol (50 mL), piperidine (1
mL) was added and refluxed. After the completion of reaction,
which was monitored by TLC, ethanol was distilled off and
residue was poured on ice water (100 mL). It was kept over-
night in the refrigerator. The resulting solid was collected by
filtration, washed with distilled water, and recrystallized from
methanol to give corresponding thiazolyl chalcone 4a–e.
1-(2-Amino-4-methyl-1,3-thiazol-5-yl)-3-(3-nitrophenyl)prop-
2-en-1-one (4a). Pale yellow solid, yield 1.62 g (56%), mp.
148–150ꢁC; UV (CHCl3): 268, 322 nm; ir: 3468 and 3354
(NH2), 3184 (ArCH), 1620 (C¼¼O), 1497 (CH¼¼CH), 1596
(C¼¼N), 1546 and 1424 (ArNO2), 1175 cmꢀ1 (CAN str); 1H
NMR (CDCl3): d 2.48 (3H, s, CH3 thiazole), 8.82 (2H, br s,
NH2 thiazole), 7.41–8.12 ppm (6H, m, ArH þ CH¼¼CH); 13C
NMR (CDCl3): d 187.1, 166.2, 152.1, 144.2, 148.2, 129.3,
124.7, 122.2, 121.1, 112.3, 28.9 ppm; ms: m/z 290 (Mþ þ 1);
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September 2011 Piperidine-Mediated Synthesis of Thiazolyl Chalcones and Their Derivatives as Potent
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1185
Pyridine), 7.43–8.06 ppm (4H, m, ArH); ms: m/z 353 (Mþ
1); Anal. Calcd for C16H12N6O2S (352.37): C, 54.52; H, 3.44;
N, 23.86%, Found: C, 54.54; H, 3.43; N, 23.85%.
þ
2-Amino-6-(2-amino-4-methyl-1,3-thiazol-5-yl)-4-(4-nitrophenyl)-
4H-pyran-3-carbonitrile (6b). Yellow solid, yield 0.99
g
(26.7%), mp 192–194ꢁC; UV (CHCl3): 266, 384 nm; ir (KBr,
cmꢀ1): 3458 and 3348 (NH2), 3174 (ArCH), 2218 (CBN),
1582 (C¼¼N), 1516 (CH¼¼CH), 1532 and 1366 cmꢀ1 (ArNO2);
1H NMR (CDCl3): d 2.22 (3H, s, CH3 thiazole), 8.98 (2H, br
s, NH2 thiazole), 6.16 (1H, d, J ¼ 3.09 Hz, H Pyran), 4.32
(1H, d, J ¼ 3.09 Hz, H Pyran), 5.96 (2H, br s, NH2 Pyran),
7.18-7.92 ppm (4H, m, ArH); ms: m/z 356 (Mþ þ 1); Anal.
Calcd for C16H13N5O3S (355.37): C, 54.08; H, 3.69; N,
19.71%, Found: C, 54.04; H, 3.67; N, 19.74%.
2-Amino-6-(2-amino-4-methyl-1,3-thiazol-5-yl)-4-(4-nitro-
phenyl)-4H-pyridine-3-carbonitrile (5b). Yellow solid, yield
0.96 g (26.1%), mp 172–174ꢁC; UV (CHCl3): 282, 386 nm;
ir: 3468 and 3338 (NH2), 3188 (ArCH), 2224 (CBN), 1579
(C¼¼N), 1514 (CH¼¼CH), 1552 and 1354 cmꢀ1 (ArNO2); 1H
NMR (CDCl3): d 2.50 (3H, s, CH3 thiazole), 8.62 (2H, br s,
NH2 thiazole), 6.68 (1H, s, H Pyridine), 5.72 (2H, br s, NH2
Pyridine), 7.24-8.08 ppm (4H, m, ArH); ms: m/z 353 (Mþ
1); Anal. Calcd for C16H12N6O2S (352.37): C, 54.54; H, 3.43;
N, 23.85%, Found: C, 54.58; H, 3.44; N, 23.79%.
þ
2-Amino-6-(2-amino-4-methyl-1,3-thiazol-5-yl)-4-(4-chloro-
phenyl)-4H-pyran-3-carbonitrile (6c). Yellow solid, yield 1.02
g (28.3%), mp 162–164ꢁC; UV (CHCl3): 272, 386 nm; ir
(KBr, cmꢀ1): 3464 and 3352 (NH2), 3182 (ArCH), 2224
(CBN), 1588 (C¼¼N), 1514 (CH¼¼CH), 728 cmꢀ1 (ArCl); 1H
NMR (CDCl3): d 2.23 (3H, s, CH3 thiazole), 8.92 (2H, br s,
NH2 thiazole), 6.11 (1H, d, J ¼ 3.08 Hz, H Pyran), 4.28 (1H,
d, J ¼ 3.08 Hz, H Pyran), 5.92 (2H, br s, NH2 Pyran), 7.18–
7.98 ppm (4H, m, ArH); ms: m/z 346 (Mþ þ 1); Anal. Calcd
for C16H13ClN4OS (344.82): C, 55.73; H, 3.8; N, 16.25%,
Found: C, 55.75; H, 3.81; N, 16.27%.
2-Amino-6-(2-amino-4-methyl-1,3-thiazol-5-yl)-4-(4-chloro-
phenyl)-4H-pyridine-3-carbonitrile (5c). Yellow solid, yield
0.94 g (26.3%), mp 158–160ꢁC; UV (CHCl3): 274, 378 nm; ir: 3474
and 3326 (NH2), 3154 (ArCH), 2218 (CBN), 1582 (C¼¼N), 1518
1
(CH¼¼CH), 726 cmꢀ1 (ArCl); H NMR (CDCl3): d d 2.55 (3H, s,
CH3 thiazole), 8.64 (2H, br s, NH2 thiazole), 6.72 (1H, s, H Pyri-
dine), 5.84 (2H, br s, NH2 Pyridine), 7.28–8.01 ppm (4H, m, ArH);
ms: m/z 343 (Mþ þ 1); Anal. Calcd for C16H12ClN5S (341.82): C,
56.22; H, 3.54; N, 20.49%, Found: C, 56.28; H, 3.53; N, 20.42%.
2-Amino-6-(2-amino-4-methyl-1,3-thiazol-5-yl)-4-(4-dimethy-
laminophenyl)-4H-pyridine-3-carbonitrile (5d). Yellow solid,
yield 0.99 g (27.1%), mp 234–236ꢁC; UV (CHCl3): 276, 384
nm; ir: 3462 and 3356 (NH2), 3176 (ArCH), 2224 (CBN),
1581 (C¼¼N), 1512 cmꢀ1 (CH¼¼CH); 1H NMR (CDCl3): d
2.42 (3H, s, CH3 thiazole), 8.68 (2H, br s, NH2 thiazole), 6.32
(1H, s, H Pyridine), 5.82 (2H, br s, NH2 Pyridine), 7.23–8.23
2-Amino-6-(2-amino-4-methyl-1,3-thiazol-5-yl)-4-(4-dimethyla-
minophenyl)-4H-pyran-3-carbonitrile (6d). Yellow solid, yield
1.02 g (27.6%), mp 138–140ꢁC; UV (CHCl3): 276, 382 nm;
ir: 3456 and 3342 (NH2), 3164 (ArCH), 2226 (CBN), 1588
1
(C¼¼N), 1512 cmꢀ1 (CH¼¼CH); H NMR (CDCl3): d 2.23 (3H,
s, CH3 thiazole), 8.96 (2H, br s, NH2 thiazole), 6.12 (1H, d, J
¼ 3.08 Hz, H Pyran), 4.14 (1H, d, J ¼ 3.08 Hz, H Pyran),
5.88 (2H, br s, NH2 Pyran), 7.12–7.92 (4H, m, ArH), 2.83
ppm (6H, s, ArCH3); ms: m/z 354 (Mþ þ 1); Anal. Calcd for
C18H19N5OS (353.44): C, 61.17; H, 5.42; N, 19.81%, Found:
C, 61.19; H, 5.43; N, 19.79%.
(4H, m, ArH), 2.84 ppm (6H, s, ArCH3); ms: m/z 351 (Mþ
1); Anal. Calcd for C18H18N6S (350.44): C, 61.69; H, 5.18; N,
23.98%, Found: C, 61.65; H, 5.19; N, 23.96%.
þ
2-Amino-6-(2-amino-4-methyl-1,3-thiazol-5-yl)-4-(4-methoxy-
phenyl)-4H-pyridine-3-carbonitrile (5e). Yellow solid, yield
0.91 g (27.1%), mp 196–198ꢁC; UV (CHCl3): 282, 394 nm;
ir: 3474 and 3336 (NH2), 3176 (ArCH), 2216 (CBN), 1578
2-Amino-6-(2-amino-4-methyl-1,3-thiazol-5-yl)-4-(4-methoy-
phenyl)-4H-pyran-3-carbonitrile (6e). Yellow solid, yield 0.93
g (27.3%), mp 158–160ꢁC; UV (CHCl3): 284, 374 nm; ir:
3464 and 3348 (NH2), 3178 (ArCH), 2224 (CBN), 1583
1
(C¼¼N), 1514 cmꢀ1 (CH¼¼CH); H NMR (CDCl3): d 2.39 (3H,
s, CH3 thiazole), 8.68 (2H, br s, NH2 thiazole), 6.41 (1H, s, H
Pyridine), 5.78 (2H, br s, NH2 Pyridine), 7.48–8.12 (4H, m,
ArH), 3.81 ppm (3H, s, ArOCH3); ms: m/z 338 (Mþ þ 1);
Anal. Calcd for C17H15N5OS (337.4): C, 60.52; H, 4.48; N,
20.76%, Found: C, 60.48; H, 4.47; N, 20.71%.
1
(C¼¼N), 1512 cmꢀ1 (CH¼¼CH); H NMR (CDCl3): d 2.22 (3H,
s, CH3 thiazole), 8.89 (2H, br s, NH2 thiazole), 6.11 (1H, d, J
¼ 3.08 Hz, H Pyran), 4.22 (1H, d, J ¼ 3.08 Hz, H Pyran),
5.82 (2H, br s, NH2 Pyran), 7.38–7.52 (4H, m, ArH), 3.61
ppm (3H, s, ArOCH3); ms: m/z 341 (Mþ þ 1); Anal. Calcd
for C17H16N4O2S (340.4): C, 59.98; H, 4.74; N, 16.46%,
Found: C, 59.92; H, 4.75; N, 16.48%.
General procedure for synthesis of 2-amino-6-(2-amino-4-
methyl-1,3-thiazol-5-yl)-4-aryl-4H-pyran-3-carbonitrile deriv-
atives (6a-e). The thiazolyl chalcone, 4a–e (0.01 mol) and
malononitrile (0.66 g, 0.01 mol) dissolved in dry pyridine (15
mL) were refluxed on a water bath for 4–10 h. The progress
of reaction was monitored by TLC at appropriate time interval.
The solution was poured on to crushed ice, neutralized with
dil. HCl and kept aside. The precipitate thus separated was
collected by filtration and crystallized from ethanol.
Procedure for antimicrobial activity. The antimicrobial ac-
tivity of newly synthesized compounds was evaluated using the
agar diffusion method. Briefly, a 24/48 h-old culture of selected
bacteria/fungi was mixed with sterile physiological saline (0.85%),
and the turbidity was adjusted to the standard inoculum of Mac-
Farland scale 0.5 [~106 colony forming units (CFU) per milliliter].
Petri plates containing 20 mL of Mueller Hinton Agar (MHA;
Hi-Media) were used for all the bacteria tested. Fungi were cul-
tured in Sabouraud’s dextrose agar (SDA)/potato dextrose agar
(PDA; Hi-Media, India) and were purified by single spore isolation
technique. The inoculum was spread on the surface of the solidified
media and Whatman no. 1 filter paper discs (6 mm in diameter)
impregnated with the test compound (20 lL/disc) were placed on
the plates. Ciprofloxacin (5 lg/disc, Hi-Media) was used as posi-
tive control for bacteria. Fluconazole (10 lg/disc, Hi-Media), was
used as positive control for fungi. A paper disc impregnated with
dimethylsulfoxide (DMSO) was used as negative control. Plates
inoculated with the bacteria were incubated for 24 h at 37ꢁC and
2-Amino-6-(2-amino-4-methyl-1,3-thiazol-5-yl)-4-(3-nitrophenyl)-
4H-pyran-3-carbonitrile (6a). Yellow solid, yield 1.01
g
(27.2%), mp 164–166ꢁC; UV (CHCl3): 290, 376 nm; ir (KBr,
cmꢀ1): 3476 and 3351 (NH2), 3166 (ArCH), 2232 (CBN),
1586 (C¼¼N), 1514 (CH¼¼CH), 1532 and 1328 cmꢀ1 (ArNO2);
1H NMR (CDCl3): d 2.23 (3H, s, CH3 thiazole), 8.96 (2H, br
s, NH2 thiazole), 6.12 (1H, d, J ¼ 3.04 Hz, H Pyran), 4.28
(1H, d, J ¼ 3.04 Hz, H Pyran), 5.92 (2H, br s, NH2 Pyran),
7.38–7.86 ppm (4H, m, ArH); ms: m/z 356 (Mþ þ 1); Anal.
Calcd for C16H13N5O3S (355.37): C, 54.08; H, 3.69; N,
19.71%, Found: C, 54.06; H, 3.68; N, 19.69%.
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

1186
P. Venkatesan and T. Maruthavanan
Vol 48
the fungal culture was incubated for 72 h at 25ꢁC. The inhibition
zone diameters were measured in millimeters. All the tests were
performed in triplicate and the average was taken as final reading.
Determination of MIC. Solutions of the test compounds,
ciprofloxacin and fluconazole were prepared in DMSO at a
concentration of 100 lg/mL. From the stock solution, serial
dilutions of the compounds (50, 25, . . . 3.12 lg/mL) were
prepared to determine the MIC. All determinations were
done in triplicates and the average was taken as final reading.
The standard antibiotic, ciprofloxacin (100 lg/mL) for bacte-
ria and fluconazole (100 lg/mL) for fungi were used as posi-
tive controls and 100 mL of DMSO used as a negative con-
trol. At the end of the incubation period, the MIC values
were determined.
[5] (a) Won, S. J.; Liu, C. T.; Tsao, L. T.; Weng, J. R.; Ko,
H. H.; Wang, J. P.; Lin, C. N. Eur J Med Chem 2005, 40, 103; (b).
Babu, M. A.; Shakya, N.; Prathipati, P.; Kaskhedikar, S. G.; Saxena,
A. K. Bioorg Med Chem 2002, 10, 4035.
[6] (a) Robinson, T. P.; Hubbard, R. B.; Ehlers, T. J.; Arbiser,
J. L.; Goldsmith, D. J.; Bowen, J. P. Bioorg Med Chem 2005, 13,
4007; (b). Rao, Y. K.; Fang, S. H.; Tzeng, Y. M. Bioorg Med Chem
2004, 12, 2679.
[7] Vaya, J.; Belinky, P. A.; Aviram, M. Free Radic Biol Med
1997, 23, 302.
[8] Simmonds, M. S. J.; Blaney, W. M.; Monacho, F. D.; Mar-
niBettolo, G. B. J Chem Ecol 1990, 16, 365.
[9] Khatib, S.; Nerya, O.; Musa, R.; Shmuel, M.; Tamir, S.;
Vaya, J. Bioorg Med Chem 2005, 13, 433.
[10]
(a) Dimmock, J. R.; Elias, D. W.; Beazely, M. A.; Kan-
depu, N. M. Curr Med Chem 1999, 6, 1125; (b) Ni, L.; Meng, C. Q.;
Sikorski, J. A. Expert Opin Ther Pat 2004, 14, 1669.
Acknowledgments. The authors are thankful to Prof. R. Gandhi-
dasan, School of the Chemistry, Madurai Kamaraj University,
India, for his valuable suggestions.
[11]
(a) Milne, G. W. A. Handbook of Antineoplastic Agents;
Gower: London, 2000; (b) De Souza, M. V. N.; De Almeida, M. V.
Quim Nova 2003, 26, 366; (c) Rehman, M. Z.; Anwar, C. J.; Ahmad,
S. Bull Korean Chem Soc 2005, 26, 1771; (d) Gupta, R. R.; Kumar,
M.; Gupta, V. Heterocyclic Chemistry of Five membered Hetero-
cycles; Springer-Verlag: New York, 1999; p 416.
REFERENCES AND NOTES
[1] (a) Lorenz, M.; Shahjahan Kabir, M.; Cook, J. M. Tetrahe-
dron Lett 2010, 51, 1095; (b) Menezes, M. J.; Manjrekar, S.; Pai, V.;
Patre, R. E.; Tilve, S. G. Indian J Chem 2009, 48B, 1311; (c).
Lokhande, P. D.; Sakate, S. S.; Taksande, K. N.; Navghare, B. Tetra-
hedron Lett 2005, 46, 1573.
[12] Sayed, S. M.; Raslan, M. A.; Khalil, M. A.; Dawood, K. M.
Heteroatom Chem 1999, 10, 385.
[13] Devitt, P. F.; Timoney, A.; Vickars, M. A. J Org Chem
1961, 26, 4941.
[14] Vyas, D. H.; Tala, S. D.; Akbari, J. D.; Dhaduk, M. F.;
Joshi, K. A.; Joshi, H. S. Indian J Chem 2009, 48B, 833
[15] Shrinivasan, D.; Sangeetha, N.; Suresh, T.; Lakshmanaperu-
malsamy, P. J Ethnopharmacol 2001, 74, 217.
[2] (a) Venkatesan, P.; Sumathi, S. J Heterocycl Chem 2010, 47,
81; (b). Nielsen, S. F.; Bosen, T.; Larsen, M.; Schonning, K.; Kromann,
H. Bioorg Med Chem 2004, 12, 3047; (c). Nielsen, S. F.; Larsen, M.;
Bosen, T.; Schonning, K.; Kromann, H. J Med Chem 2005, 48, 2667.
[16] Opletalova, V.; Ricicarova, P.; Sedivy, D.; Meltrova, D.;
Krivakova, J. Folia Pharm Univ Carol 2000, 25, 21.
[3]
(a) Lahtchev, K. L.; Batovsha, D. L.; Parushev, St. P.;
Ubiyvovk, V. M.; Sibirny, A. A. Eur J Med Chem 2008, 43, 2220;
(b) Nowakowska, Z.; Edzia, B. K.; Schroeder, G. Eur J Med Chem
2008, 43, 707.
[17] Batovska, D.; Parushev, S.; Stamboliyska, B.; Tsvetkova, I.;
Ninova, M.; Najdenski, H. Eur J Med Chem 2009, 44, 2211.
[18] Li, R.; Kenyon, G. L.; Cohen, F. E.; Chen, X.; Gong, B.;
Dominguez, D. E.; Kurzban, G.; Miller, R. E.; Nuzum, E. O.; Rosen-
thal, P. J.; McKerrow, J. H. J Med Chem 1995, 38, 5031.
[4] Cheenpracha, S.; Karalai, C.; Ponglimanont, C.; Subhadhir-
asakul, S.; Tewtrakal, S. Bioorg Med Chem 2005, 14, 1710.
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet