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

Article abstract of DOI:10.1080/14786419.2010.536161

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 aromatic aldehyde. These chalcones on cyclisation gave 2-amino-6-

Full text of DOI:10.1080/14786419.2010.536161

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Piperidine-mediated synthesis
of thiazolyl chalcones and their
derivatives as potent antimicrobial
agents
P. Venkatesan a & T. Maruthavanan b
a Department of Chemistry , Mahendra Institute of Technology ,
Namakkal 637503 , India
b Department of Chemistry , Sona College of Technology , Salem
636005 , India
Published online: 11 Aug 2011.
To cite this article: P. Venkatesan & T. Maruthavanan (2012) Piperidine-mediated synthesis of
thiazolyl chalcones and their derivatives as potent antimicrobial agents, Natural Product Research:
Formerly Natural Product Letters, 26:3, 223-234, DOI: 10.1080/14786419.2010.536161
To link to this article: http://dx.doi.org/10.1080/14786419.2010.536161
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Natural Product Research
Vol. 26, No. 3, February 2012, 223–234
Piperidine-mediated synthesis of thiazolyl chalcones and their
derivatives as potent antimicrobial agents
a
P. Venkatesan and T. Maruthavanan
b
*
aDepartment of Chemistry, Mahendra Institute of Technology, Namakkal 637503, India;
bDepartment of Chemistry, Sona College of Technology, Salem 636005, India
(Received 21 August 2010; final version received 26 September 2010)
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 aromatic aldehyde.
These chalcones on cyclisation 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 result showed
that the compounds exhibited marked potency as antimicrobial agents.
Keywords: piperidine; chalcone; cyanopyridine; cyanopyran; antimicrobial
agent
1. Introduction
Chalcone (1,3-diaryl-2-propen-1-one) derivatives are 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
(Lokhande, Sakate, Taksande, & Navghare, 2005; Lorenz, Shahjahan Kabir, &
Cook, 2010) and also exhibit various biological activities such as antibacterial
(Venkatesan & Sumathi, 2010), antifungal (Lahtchev, Batovska, Parushev,
Ubiyvovk, & Sibirny, 2008), antiviral (Cheenpracha, Karalai, Ponglimanont,
Subhadhirasakul, & Tewtrakul, 2005), anti-inflammatory (Won et al., 2005),
antitumour (Rao et al., 2004), antioxidant (Vaya et al., 1997), and insect antifeedant
(Simmonds, Blaney, Delle Monache, & Marini Bettolo, 1990) and also act as
tyrosinase inhibitors (Khatib et al., 2005). The complex pharmacological activities
together with the easiest synthetic method by Claisen–Schmidt condensation have
attracted considerable interest towards the synthesis of novel chalcones as potent
microbial agents (Dimmock, Elias, Beazely, & Kandepu, 1999).
As thiazolidine moiety seems to be a potential pharmacophore in various
pharmacologically active agents (Nora de Souza & Almeida, 2003; Zia-ur-Rehman,
Choudary, & Ahmad, 2005), we have synthesised chalcones with a thiazolidine
moiety and heterocyclised to cyanopyridine and cyanopyran derivatives as possible
antimicrobial agents.
*Corresponding author. Email: venkatesanps@yahoo.co.in
ISSN 1478–6419 print/ISSN 1478–6427 online
ß 2012 Taylor & Francis
http://dx.doi.org/10.1080/14786419.2010.536161
http://www.tandfonline.com

224
P. Venkatesan and T. Maruthavanan
2. Results and discussion
2.1. Chemistry
In this study, 1-(2-amino-4-methyl-1,3-thiazol-5-yl)ethanone (2) was synthesised by
the cyclisation of 3-chloroacetylacetone (1) with thiourea in accordance with the
method described in the literature (Sayed, Raslan, Khalil, & Dawood, 1999). In the
Claisen–Schmidt condensation of chalcone synthesis, strong alkali reduces the yield
of the target adduct and makes its purification difficult due to undesirable side
reactions such as multiple condensation, polymerisation and rearrangement (Devitt,
Timoney, & Vickars, 1961). So, we used piperidine instead of a 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 a considerably better yield.
The IR spectra of compounds 4a–e showed the absorption band at 1620–
1628 cmꢀ1 for C¼O group and 1610–1612 cmꢀ1 for C¼C group, indicating the
presence of ꢀ, ꢁ-unsaturated carbonyl group. The 1H-NMR spectra gave two
doublets at ꢂ 7.60–7.64 ppm and ꢂ 8.20–8.28 ppm with the coupling constant,
J ¼ 15.2–15.8 Hz. It is evident that the olefinic protons at Cꢀ and Cꢁ positions of
ꢀ, ꢁ-unsaturated carbonyl group are arranged in trans configuration. Moreover,
N–H asymmetric stretching absorption band appeared around 3324–3354 cmꢀ1, and
symmetric stretching absorption band around 3402–3488 cmꢀ1 indicating the
presence of –NH2 group. The C¼N and CH¼CH ring stretching absorption
bands appeared around 1596–1582 cmꢀ1 and 1498–1494 cmꢀ1, respectively, support-
ing the aromaticity of thiazole ring. In addition, C–N stretching absorption band got
displayed at around 1173–1176 cmꢀ1 13C-NMR spectra of compounds 4a–e
.
exhibited chemical shifts at  ꢂ 121.1–121.3 ppm (Cꢀ), ꢂ 148.2–148.3 ppm (Cꢁ)
and ꢂ 187.1–189.2 ppm (4C¼O), indicating the presence of ꢀ, ꢁ-unsaturated
carbonyl groups of chalcone. The methyl group on thiazole ring resonated at
ꢂ 28.1–28.9 ppm. In addition, the signals at ꢂ 166.2–166.6 ppm, ꢂ 152.1–152.2 ppm
and ꢂ 112.3–112.8 ppm were assigned to C2, C3 and C5 of thiazole ring, respectively.
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 the
experimental part.
R1
R2
S
H
N
3a-e
H2N
H2N
NH2
O
O
O
S
C2H5OH / Et3N
Piperidine/EtOH
Cl
O
2
1
a: R1=NO2; R2=H
b: R1=H; R2=NO2
c: R1=H; R2=Cl
d: R1=H; R2=N(CH3)2
e: R1=H; R2=OCH3
R1
R2
N
S
H2N
O
4a-e
Scheme 1. Synthesis of 1-(2-amino-4-methyl-1,3-thiazol-5-yl)ethanone (2) and substituted
thiazolyl chalcone (4a–e).

Natural Product Research
225
2-amino-6-(2-amino-4-methyl-1,3-thiazol-5-yl)-4-aryl-4H-pyridine-3-carbonitrile
(5a–e) was prepared by heterocyclisation of thiazolyl chalcones (4a–e) with the
ethanolic solution of malononitrile in the presence of ammonium acetate. Similarly,
2-amino-6-(2-amino-4-methyl-1,3-thiazol-5-yl)-4-aryl-4H-pyran-3-carbonitrile (6a–
e) were prepared by the heterocyclisation of thiazolyl chalcones (4a–e) with the
ethanolic solution of malononitrile in the presence of pyridine. The synthetic route of
compounds 5a–e and 6a–e are in accordance with the method described in the
literature (Vyas et al., 2009), and are outlined in schemes 2 and 3, respectively. The
signals for ꢀ, ꢁ-unsaturated carbonyl group were not observed in the spectral data of
compounds 5a–e and 6a–e. The formations of a new heterocyclic ring in compounds
5a–e and 6a–e are evident. IR spectra of compounds 5a–e revealed the presence of –
NH2 stretching absorption bands in the region of 3462–3474 cmꢀ1 and 3326–
3356 cmꢀ1 and compounds 6a–e also gave absorption bands at 3456–3476 cmꢀ1 and
3342–3352 cmꢀ1 for the same. The stretching absorption band of about 2216–
2232 cmꢀ1 corresponding to the –CꢁN group was observed for both the compounds
1
5a–e and 6a–e. The H-NMR spectra gave an additional broad singlet at about
ꢂ 5.67–5.84 ppm, in compounds 5a–e and a broad singlet at about ꢂ 5.67–5.84 ppm in
compounds 6a–e, indicating the formation of –NH2 group in both the compounds
5a–e and 6a–e. The singlet around ꢂ 6.32–6.74 ppm was assigned to pyridine-H
of compounds 5a–e. Similarly, two doublets around ꢂ 6.11–6.16 ppm and
ꢂ 4.14–4.32 ppm with a coupling constant of about J ¼ 3.04–3.09 Hz was assigned
to pyran-H of compounds 6a–e. In the Mass spectral fragmentation of compounds
5a–e and 6a–e, loss of –CN group was observed by lowering the m/z 26 from its
molecular ion peak (Mþ), 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 the experimental part.
2.2. Pharmacology
The antimicrobial activity of the new synthesised compounds 4a–e, 5a–e and 6a–e
was evaluated using the agar diffusion method (Shrinivasan, Nathan, Suresh, &
Lakshmana Perumalsamy, 2001). The in vitro antibacterial activity was evaluated
against various pathogenic bacteria viz., Staphylococcus aureus (S. aureus), Bacillus
subtilis (B. subtilis), Escherichia coli (E. coli) and Salmonella typhi (S. typhi).
Similarly, the in vitro antifungal activity was evaluated against Aspergillus niger
R1
R2
N
H2N
CH2(CN)2
S
4a-e
N
CH3COONH4
N
NH2
5a-e
Scheme 2. Synthesis of cyanopyridine (5a–e).

226
P. Venkatesan and T. Maruthavanan
R1
R2
N
H2N
CH2(CN)2
Pyridine
S
4a-e
O
N
NH2
6a-e
Scheme 3. Synthesis of cyanopyran (6a–e).
Table 1. Antibacterial activity of compounds 4a–e, 5a–e and 6a–e.
Diameters of zone inhibition in mm (MIC value, mg mLꢀ1
)
Compounds
S. aureus
B. subtilis
E. coli
S. typhi
4a
4b
4c
4d
4e
–
510 (50)
–
510 (50)
–
–
–
–
–
–
–
–
–
–
11 ꢂ 0.8 (6.25)
13 ꢂ 1.2 (12.5)
–
–
–
–
5a
5b
5c
5d
5e
6a
6b
6c
–
510 (50)
–
510 (50)
12 ꢂ 1.1 (12.5)
510 (50)
16 ꢂ 1.2 (25)
–
–
13 ꢂ 1.4 (12.5)
–
–
–
12 ꢂ 1.3 (6.25)
–
–
–
–
–
–
14 ꢂ 1.2 (6.25)
510 (50)
510 (50)
18 ꢂ 0.9 (12.5)
–
–
510 (50)
14 ꢂ 1.2 (25)
18 ꢂ 1.0 (12.5)
14 ꢂ 1.2 (6.25)
15 ꢂ 0.7 (12.5)
25–28 (6.25)
16 ꢂ 0.8 (25)
14 ꢂ 1.3 (12.5)
–
–
–
–
6d
6e
16 ꢂ 1.1 (25)
12 ꢂ 1.2 (25)
510 (50)
19–22 (6.25)
aCip
19–23 (6.25)
23–29 (6.25)
a
Note: Cip, Ciprofloxacin.
(A. niger), Aspergillus flavus (A. flavus), Penicillium chrysogenum (P. chrysogenum)
and Fusarium moniliforme (F. moniliforme). The results of antibacterial and
antifungal screening of the newly synthesised compounds are given in Tables 1
and 2, respectively. Among the newly synthesised chalcones, the compound 6c
showed good activity (zone of inhibition up to 17–19 mM at the concentration of
12.5 mg mLꢀ1) against S. aureus and S. typhi and the compound 6e showed good
activity (zone of inhibition 16–18 mM at concentration of 6.25–12.5 mg mLꢀ1) against
A. niger, A. flavus and F. moniliforme. Also, the compound 4b showed moderate
activity against A. flavus, and 4c showed moderate activity against A. niger and P.
chrysogenum (zone of inhibition 5 10 mM at the concentration of 50 mg mLꢀ1). The
chalcones 4a–e were inactive against most of the fungal strains. However, the
compounds 5a–e and 6a–e showed remarkable antifungal activity. Similarly, 6c
showed good activity (zone of inhibition up to 16 mM at the concentration of
12.5 mg mLꢀ1) against A. niger and A. flavus but no activity against F. moniliforme.

Natural Product Research
Table 2. Antifungal activity of compounds 4a–e, 5a–e and 6a–e.
Diameter of zone inhibition in mm (MIC value, mg mLꢀ1
227
)
Compounds
A. niger
A. flavus
P. chrysogenum
F. moneliforme
4a
4b
4c
4d
4e
5a
5b
5c
5d
5e
6a
6b
6c
6d
6e
aFlu
–
–
–
–
–
–
–
–
–
–
510 (50)
510 (50)
–
–
–
–
510 (50)
–
–
–
–
–
–
–
–
510 (50)
12 ꢂ 1.2 (25)
510 (50)
–
–
13 ꢂ 1.1 (12.5)
–
510 (50)
–
14 ꢂ 1.2 (25)
510 (50)
–
14 ꢂ 1.1 (6.25)
510 (50)
13 ꢂ 1.2 (25)
510 (50)
14 ꢂ 1.2 (25)
16 ꢂ 0.9 (12.5)
19–24 (6.25)
15 ꢂ 1.0 (6.25)
510 (50)
–
12 ꢂ 0.9 (6.25)
15 ꢂ 0.8 (12.5)
16 ꢂ 1.1 (12.5)
–
–
14 ꢂ 1.2 (25)
16 ꢂ 1.1 (12.5)
–
–
12 ꢂ 1.2 (25)
510 (50)
14 ꢂ 1.3 (25)
20–25 (6.25)
17 ꢂ 1.2 (6.25)
16 ꢂ 1.3 (12.5)
20–23 (6.25)
19–24 (6.25)
a
Note: Flu, Fluconazole.
The mode of the antimicrobial action of chalcones has long been believed to be
due to their reaction with important thiol groups of essential enzymes via Michael
addition at the ketovinyl double bond (Opletalova, Ricicarova, Sedivy, Meltrova, &
Krivakova, 2000). Also, p-electron withdrawing group will increase the electrophi-
licity of C-ꢁ and thus facilitate the nucleophilic attack of the cellular thiol groups
(Batovska et al., 2009). Interestingly, 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. Compounds 5c and 6c, which are carrying p-Cl substituent, exhibited
moderate to good antibacterial and antifungal activity against most of the test
strains. Similarly, compound 6e showed almost good activities due to the presence of
p-OCH3 substitution. In general, microbial activities were increased remarkably on
heterocyclisation of thiazolyl chalcones (4a–e) to cyanopyridine (5a–e) and
cyanopyran (6a–e) derivatives. 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 (Li et al., 1995), it is believed that the –NH2
group and –CN group of cyanopyridine/cyanopyran ring systems may act as the
active centre.
3. Experimental
3.1. General
All the common chemicals, 3-chloroacetylacetone (1) and substituted aryl
aldehyde (3a–e), were obtained from Sigma–Aldrich chemicals. The melting
points of the synthesised compounds were determined in open glass capillaries

228
P. Venkatesan and T. Maruthavanan
and were uncorrected. UV spectra were recorded using Perkin Elmer 402 UV-Vis
spectrophotometer. IR spectra were recorded on Perkin Elmer 577 IR spectro-
1
photometer using KBr pellets. H-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 analyser and the analysed reports were with-
in ꢂ 0.4% of the theoretical values. The purity of the compounds was checked by
thin layer chromatography on silica gel 60 F254 (Merck) and spots were developed
using iodine vapour or ultraviolet light.
3.2. 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 catalytic amount of triethylamine, a solution of 3-chloroacetylacetone
(26.9 g, 0.2 mol) in 10 mL of absolute ethanol was added dropwise. After complete
addition, the mixture was stirred at room temperature for 30 min and then refluxed
for 5 h. The reaction mixture was cooled, and a solid was filtered off, washed with
cold ethanol, dried and finally recrystallised from DMF to get the compound 2 with
65% yield. m.p. 275ꢃC (lit m.p. 274–276ꢃC) (Sayed et al., 1999), 1H-NMR (300 MHz,
CDCl3): ꢂ 2.78 (s, 3H, CH3 thiazole), 2.35 (s, 3H, CH3 acetyl) and 8.48 (br s, 2H,
NH2 thiazole).
3.3. 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 overnight
in the refrigerator. The resulting solid was collected by filtration, washed with
distilled water and recrystallised from methanol to get the corresponding thiazolyl
chalcone (4a–e).
3.3.1. 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%), m.p. 148–150ꢃC, ꢃmax (CHCl3, nm): 268, 322.
IR (KBr, cmꢀ1): 3468 and 3354 (NH2), 3184 (ArCH), 1620 (C¼O), 1497 (CH¼CH),
1
1596 (C¼N), 1546 and 1424 (ArNO2) and 1175 (C–N str). H-NMR (300 MHz,
CDCl3): ꢂ 2.48 (3H, s, CH3 thiazole), 8.82 (2H, br s, NH2 thiazole) and 7.41–8.12
(6H, m, ArH þ CH¼CH). 13C-NMR (300 MHz, CDCl3): ꢂ 187.1, 166.2, 152.1, 144.2,
148.2, 129.3, 124.7, 122.2, 121.1, 112.3 and 28.9. m/z: 290 (Mþ þ 1). Anal. Calcd for
C13H11N3O3S (289.31): C, 53.97%; H, 3.83%; and N, 14.52%, Found: C, 53.94%;
H, 3.81%; and N, 14.54%.

Natural Product Research
229
3.3.2. 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%), m.p. 146–148ꢃC, ꢃmax (CHCl3, nm): 286, 348.
IR (KBr, cmꢀ1): 3488 and 3324 (NH2), 3168 (ArCH), 1620 (C¼O), 1494 (CH¼CH),
1
1552 and 1424 (ArNO2), 1592 (C¼N) and 1174 (C–N str). H-NMR (300 MHz,
CDCl3): ꢂ 2.51 (3H, s, CH3 thiazole, 8.86 (2H, br s, NH2 thiazole) and 7.36–8.24 (6H,
m, ArH þ CH¼CH). 13C-NMR (300 MHz, CDCl3): ꢂ 187.9, 166.6, 155.3, 152.1,
148.3, 128.4, 125.1, 122.2, 121.1, 112.6 and 28.2. m/z: 290 (Mþ þ 1). Anal. Calcd for
C13H11N3O3S (289.31): C, 53.97%; H, 3.83%; and N, 14.52%, Found: C, 54.01%;
H, 3.82%; and N, 14.54%.
3.3.3. 1-(2-amino-4-methyl-1,3-thiazol-5-yl)-3-(4-chlorophenyl)
prop-2-en-1-one (4c)
Colourless solid, yield 2 g (72%), m.p. 146–148ꢃC, ꢃmax (CHCl3, nm): 262, 366. IR
(KBr, cmꢀ1): 3402 and 3336 (NH2), 3164 (ArCH), 1626 (C¼O), 1494 (CH¼CH),
1
1584 (C¼N), 1176 (C–N str) and 724 (ArCl). H-NMR (300 MHz, CDCl3): ꢂ 2.51
(3H, s, CH3 thiazole, 8.68 (2H, br s, NH2 thiazole), 7.28–8.42 (6H, m,
ArH þ CH¼CH). 13C-NMR (300 MHz, CDCl3): ꢂ 188.2, 166.4, 156.2, 152.2, 148.2,
126.8, 124.4, 122.2, 121.3, 112.8 and 28.6. m/z: 280 (Mþ þ 1). Anal. Calcd for
C13H11ClN2OS (278.75): C, 56.01%; H, 3.96%; and N, 10.05%, Found: C, 56.06%;
H, 3.97%; and N, 10.02%.
3.3.4. 1-(2-amino-4-methyl-1,3-thiazol-5-yl)-3-(4-dimethylaminophenyl)
prop-2-en-1-one (4d)
Pale yellow solid, yield 1.67 g (58%), m.p. 128–130ꢃC, ꢃmax (CHCl3, nm): 272, 382.
IR (KBr, cmꢀ1): 3486 and 3324 (NH2), 3168 (ArCH), 1620 (C¼O), 1498 (CH¼CH),
1
1582 (C¼N) and 1173 (C–N str). H-NMR (300 MHz, CDCl3): ꢂ 2.51 (3H, s, CH3
thiazole, 8.84 (2H, br s, NH2 thiazole), 7.12–8.36 (6H, m, ArH þ CH¼CH) and 2.84
(6H, s, N(CH3)2). 13C-NMR (300 MHz, CDCl3): ꢂ 189.2, 166.6, 158.3, 152.1, 148.3,
128.6, 125.2, 122.2, 121.1, 112.6, 44.6 and 28.1. m/z: 288 (Mþ þ 1). Anal. Calcd for
C15H17N3OS (287.38): C, 62.73%; H, 5.95%; and N, 14.66%, Found: C, 62.69%; H,
5.96%; and N, 14.62%.
3.3.5. 1-(2-amino-4-methyl-1,3-thiazol-5-yl)-3-(4-methoxyphenyl)
prop-2-en-1-one (4e)
Colourless solid, yield 1.81 g (66%), m.p. 136–138ꢃC, ꢃmax (CHCl3, nm): 286, 386. IR
(KBr, cmꢀ1): 3448 and 3326 (NH2), 3186 (ArCH), 1628 (C¼O), 1498 (CH¼CH),
1596 (C¼N), 1232 and 1028 (C–O str), 1174 (C–N str). 1H-NMR (300 MHz, CDCl3):
ꢂ 2.52 (3H, s, CH3 thiazole, 8.68 (2H, br s, NH2 thiazole), 7.21–8.32 (6H, m,
ArH þ CH¼CH) and 3.81 (3H, s, ArOCH3). 13C-NMR (300 MHz, CDCl3): ꢂ 188.6,
166.2, 157.9, 152.1, 148.2, 127.4, 124.8, 122.2, 121.2, 112.8, 53.8 and 28.5. m/z: 275
(Mþ þ 1). Anal. Calcd for C14H14N2O2S (274.34): C, 61.32%; H, 5.12%; and N,
10.24%, Found: C, 61.29%; H, 5.14%; and N, 10.21%.

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3.4. 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 crystallised from
ethanol.
3.4.1. 2-amino-6-(2-amino-4-methyl-1,3-thiazol-5-yl)-4-(3-nitrophenyl)-4H-pyri-
dine-3-carbonitrile (5a)
Yellow solid, (0.94 g (25.5%), m.p. 216–218ꢃC, ꢃmax (CHCl3, nm): 262, 374. IR (KBr,
cmꢀ1): 3462 and 3342 (NH2), 3182 (ArCH), 2216 (CꢁN), 1581 (C¼N), 1512
(CH¼CH), and 1546 and 1374 (ArNO2). 1H-NMR (300 MHz, CDCl3): ꢂ 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 pyridine) and 7.43–8.06 (4H, m, ArH). m/z: 353 (Mþ þ 1). Anal. Calcd for
C16H12N6O2S (352.37): C, 54.52%; H, 3.44%; and N, 23.86%, Found: C, 54.54%;
H, 3.43%; and N, 23.85%.
3.4.2. 2-amino-6-(2-amino-4-methyl-1,3-thiazol-5-yl)-4-(4-nitrophenyl)-4H-pyri-
dine-3-carbonitrile (5b)
Yellow solid, yield 0.96 g (26.1%), m.p. 172–174ꢃC, ꢃmax (CHCl3, nm): 282, 386. IR
(KBr, cmꢀ1): 3468 and 3338 (NH2), 3188 (ArCH), 2224 (CꢁN), 1579 (C¼N), 1514
(CH¼CH) and 1552 and 1354 (ArNO2). 1H-NMR (300 MHz, CDCl3): ꢂ 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) and 7.24–8.08 (4H, m, ArH). m/z: 353 (Mþ þ 1). Anal. Calcd for
C16H12N6O2S (352.37): C, 54.54%; H, 3.43%; and N, 23.85%, Found: C, 54.58%;
H, 3.44%; and N, 23.79%.
3.4.3. 2-amino-6-(2-amino-4-methyl-1,3-thiazol-5-yl)-4-(4-chlorophenyl)-4H-pyri-
dine-3-carbonitrile (5c)
Yellow solid, yield 0.94 g (26.3%), m.p. 158–160ꢃC, ꢃmax (CHCl3, nm): 274, 378. IR
(KBr, cmꢀ1): 3474 and 3326 (NH2), 3154 (ArCH), 2218 (CꢁN), 1582 (C¼N), 1518
(CH¼CH), and 726 (ArCl). 1H-NMR (300 MHz, CDCl3): ꢂ 2.55 (3H, s, CH3
thiazole), 8.64 (2H, br s, NH2 thiazole), 6.72 (1H, s, H pyridine), 5.84 (2H, br s, NH2
pyridine), and 7.28–8.01 (4H, m, ArH). m/z: 343 (Mþ þ 1). Anal. Calcd for
C16H12ClN5S (341.82): C, 56.22%; H, 3.54%; and N, 20.49%, Found: C, 56.28%; H,
3.53%; and N, 20.42%.
3.4.4. 2-amino-6-(2-amino-4-methyl-1,3-thiazol-5-yl)-4-(4-dimethylaminophenyl)-
4H-pyridine-3-carbonitrile (5d)
Yellow solid, yield 0.99 g (27.1%), m.p. 234–236ꢃC, ꢃmax (CHCl3, nm): 276, 384. IR
(KBr, cmꢀ1): 3462 and 3356 (NH2), 3176 (ArCH), 2224 (CꢁN), 1581 (C¼N) and
1
1512 (CH¼CH). H-NMR (300 MHz, CDCl3): ꢂ 2.42 (3H, s, CH3 thiazole), 8.68

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(2H, br s, NH2 thiazole), 6.32 (1H, s, H pyridine), 5.82 (2H, br s, NH2 pyridine),
7.23–8.23 (4H, m, ArH) and 2.84 (6H, s, ArCH3). m/z: 351 (Mþ þ 1). Anal. Calcd for
C18H18N6S (350.44): C, 61.69%; H, 5.18%; and N, 23.98%, Found: C, 61.65%;
H, 5.19%; and N, 23.96%.
3.4.5. 2-amino-6-(2-amino-4-methyl-1,3-thiazol-5-yl)-4-(4-methoxyphenyl)-4H-
pyridine-3-carbonitrile (5e)
Yellow solid, yield 0.91 g (27.1%), m.p. 196–198ꢃC, ꢃmax (CHCl3, nm): 282, 394. IR
(KBr, cmꢀ1): 3474 and 3336 (NH2), 3176 (ArCH), 2216 (CꢁN), 1578 (C¼N), and
1
1514 (CH¼CH). H-NMR (300 MHz, CDCl3): ꢂ 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), and 3.81 (3H, s, ArOCH3). m/z: 338 (Mþ þ 1). Anal. Calcd
for C17H15N5OS (337.4): C, 60.52%; H, 4.48%; and N, 20.76%, Found: C, 60.48%;
H, 4.47%; and N, 20.71%.
3.5. General procedure for synthesis of 2-amino-6-(2-amino-4-methyl-1,3-thiazol-5-
yl)-4-aryl-4H-pyran-3-carbonitrile derivatives (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 for 4–10 h. The progress of reaction
was monitored by TLC at appropriate time intervals. The solution was poured on to
crushed ice, neutralised with diluted HCl and kept aside. The precipitate thus
separated was collected by filtration and crystallised from ethanol.
3.5.1. 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%), m.p. 164–166ꢃC, ꢃmax (CHCl3, nm): 290, 376. IR
(KBr, cmꢀ1): 3476 and 3351 (NH2), 3166 (ArCH), 2232 (CꢁN), 1586 (C¼N), 1514
(CH¼CH) and 1532 and 1328 (ArNO2). 1H-NMR (300 MHz, CDCl3): ꢂ 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) and 7.38–7.86 (4H, m,
ArH). m/z: 356 (Mþ þ 1). Anal. Calcd for C16H13N5O3S (355.37): C, 54.08%; H,
3.69%; and N, 19.71%, Found: C, 54.06%; H, 3.68%; and N, 19.69%.
3.5.2. 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%), m.p. 192–194ꢃC, ꢃmax (CHCl3, nm): 266, 384. IR
(KBr, cmꢀ1): 3458 and 3348 (NH2), 3174 (ArCH), 2218 (CꢁN), 1582 (C¼N), 1516
1
(CH¼CH), 1532 and 1366 (ArNO2). H-NMR (300 MHz, CDCl3): ꢂ 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), and 7.18–7.92 (4H, m,
ArH). m/z: 356 (Mþ þ 1). Anal. Calcd for C16H13N5O3S (355.37): C, 54.08%; H,
3.69%; and N, 19.71%, Found: C, 54.04%; H, 3.67%; and N, 19.74%. Anal. Calcd
for C16H13N5O3S (355.37): C, 54.08%; H, 3.69%; and N, 19.71%, Found: C,
54.04%; H, 3.67%; and N, 19.74%.

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3.5.3. 2-amino-6-(2-amino-4-methyl-1,3-thiazol-5-yl)-4-(4-chlorophenyl)-4H-
pyran-3-carbonitrile (6c)
Yellow solid, yield 1.02 g (28.3%), m.p. 162–164ꢃC, ꢃmax (CHCl3, nm): 272, 386. IR
(KBr, cmꢀ1): 3464 and 3352 (NH2), 3182 (ArCH), 2224 (CꢁN), 1588 (C¼N), 1514
1
(CH¼CH), 728 (ArCl). H-NMR (300 MHz, CDCl3): ꢂ 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), and 7.18–7.98 (4H, m, ArH). m/z:
346 (Mþ þ 1). Anal. Calcd for C16H13ClN4OS (344.82): C, 55.73%; H, 3.8%; and N,
16.25%, Found: C, 55.75%; H, 3.81%; and N, 16.27%.
3.5.4. 2-amino-6-(2-amino-4-methyl-1,3-thiazol-5-yl)-4-(4-(dimethylamino-
phenyl)-4H-pyran-3-carbonitrile (6d)
Yellow solid, yield 1.02 g (27.6%), m.p. 138–140ꢃC, ꢃmax (CHCl3, nm): 276, 382. IR
(KBr, cmꢀ1): 3456 and 3342 (NH2), 3164 (ArCH), 2226 (CꢁN), 1588 (C¼N) and
1
1512 (CH¼CH). H-NMR (300 MHz, CDCl3): ꢂ 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) and 2.83 (6H, s,
ArCH3). m/z: 354 (Mþ þ 1). Anal. Calcd for C18H19N5OS (353.44): C, 61.17%; H,
5.42%; and N, 19.81%, Found: C, 61.19%; H, 5.43%; and N, 19.79%.
3.5.5. 2-amino-6-(2-amino-4-methyl-1,3-thiazol-5-yl)-4-(4-methoyphenyl)-4H-
pyran-3-carbonitrile (6e)
Yellow solid, yield 0.93 g (27.3%), m.p. 158–160ꢃC, ꢃmax (CHCl3, nm): 284, 374. IR
(KBr, cmꢀ1): 3464 and 3348 (NH2), 3178 (ArCH), 2224 (CꢁN), 1583 (C¼N) and
1
1512 (CH¼CH). H-NMR (300 MHz, CDCl3): ꢂ 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) and 3.61 (3H, s,
ArOCH3). 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%; and N, 16.48%.
3.6. Procedure for antimicrobial activity
3.6.1. Disc diffusion method
The antimicrobial activity of newly synthesised 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 [ꢄ106 colony-forming units (CFU) per
millilitre]. Petri plates containing 20 mL of Mueller Hinton agar (MHA, Hi-Media)
were used for all the bacteria tested. Fungi was cultured in Sabouraud’s dextrose
agar (SDA)/potato dextrose agar (PDA) (Hi-Media) and were purified by single-
spore isolation technique. The inoculum was spread on the surface of the solidified
media and Whatman number 1 filter paper discs (6 mm in diameter) impregnated
with the test compound (20 mL/disc) were placed on the plates. Ciprofloxacin (5 mg/
disc, Hi-Media) was used as positive control for bacteria. Fluconazole (10 mg/disc,
Hi-Media) was used as positive control for fungi. A paper disc impregnated with

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dimethyl sulfoxide (DMSO) was used as negative control. Plates inoculated with the
bacteria were incubated for 24 h at 37ꢃC and the fungal culture was incubated for
72 h at 25ꢃC. The inhibition zone diameters were measured in millimeters. All the
tests were performed in triplicate and the average was taken as the final reading.
3.6.2. Determination of MIC
Solutions of the test compounds ciprofloxacin and fluconazole were prepared in
DMSO at a concentration of 100 mg mLꢀ1. From the stock solution, serial dilutions
of the compounds (50, 25, . . . , 3.12 mg mLꢀ1) were prepared to determine the
minimum inhibitory concentration (MIC). All determinations were done in
triplicates and the average was taken as final reading. The standard antibiotics,
ciprofloxacin (100 mg mLꢀ1) for bacteria and fluconazole (100 mg mLꢀ1) for fungi,
were used as positive controls and 100 mL of DMSO used as a negative control. At
the end of the incubation period, the MIC values were determined.
4. Conclusion
A series of thiazolyl chalcones were synthesised by piperidine-mediated Claisen–
Schemidt condensation. From these, a series of cyanopyridine and cyanopyran
derivatives were prepared and they showed better antibacterial and antifungal activity
than that of thiazolyl chalcone. Predominantly, cyanopyrane derivatives showed
excellent antimicrobial activities. In addition, 2-amino-6-(2-amino-4-methyl-
1,3-thiazol-5-yl)-4-(4-chlorophenyl)-4H-pyran-3-carbonitrile (6c) and 2-amino-6-(2-
amino-4-methyl-1,3-thiazol-5-yl)-4-(4-methoy-phenyl)-4H-pyran-3-carbonitrile (6e)
were found to be the most active antibacterial agent and antifungal agent, respectively.
Acknowledgements
The authors thank Professor R. Gandhidasan, School of the Chemistry, Madurai Kamaraj
University, India, for his valuable suggestions.
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