Synthesis, characterization, and antibacterial activities of some novel N,N'-disubstituted thiourea, 2-Amino thiazole, and imidazole-2-thione derivatives

Article abstract of DOI:10.1007/s00044-013-0883-y

In the search of bioactive molecules, a series of novel N-substituted thiourea derivatives 3(a-d) are prepared by reaction of the α-Amino pyridyl ketone hydrochloride (2a) with the corresponding aryl isothiocyanates. The synthesis of some new 2-Amino thiazoles 4(a-d) and imidazole-2-thiones 6(a-d) were attempted by intramolecular cyclization reaction of the N,N'-disubstituted thioureas 3(a-d) and their intermediate ketals 5(a-d) in diluted aqueous acidic and strong acidic mediums. The structure of all newly synthesized compounds was established by analytical and spectral data. The antibacterial studies to all of the synthesized compounds against Bacillus cereus, Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Enterococcus faecalis bacteria with Gram-positive and negative strains, as MIC values are reported. Some of these compounds such as 3a,b,d and 4b,d exhibited a good to significant antibacterial activity. Also, all of new synthesized compounds 3,4,6(a-d) were active against Gram-positive S. aureus bacterium. Thus, some of these compounds can emerge as a promising tool for further research work.

Full text of DOI:10.1007/s00044-013-0883-y

MEDICINAL
CHEMISTRY
RESEARCH
Med Chem Res
DOI 10.1007/s00044-013-0883-y
ORIGINAL RESEARCH
Synthesis, characterization, and antibacterial activities of some
novel N,N0-disubstituted thiourea, 2-amino thiazole,
and imidazole-2-thione derivatives
•
Mehdi Kalhor Mina Salehifar Iraj Nikokar
•
Received: 19 August 2013 / Accepted: 15 November 2013
Ó Springer Science+Business Media New York 2013
Abstract In the search of bioactive molecules, a series of
novel N-substituted thiourea derivatives 3(a–d) are prepared
by reaction of the a-amino pyridyl ketone hydrochloride (2a)
with the corresponding aryl isothiocyanates. The synthesis of
some new 2-amino thiazoles 4(a–d) and imidazole-2-thiones
6(a–d) were attempted by intramolecular cyclization reac-
tion of the N,N0-disubstituted thioureas 3(a–d) and their
intermediate ketals 5(a–d) in diluted aqueous acidic and
strong acidic mediums. The structure of all newly synthe-
sized compounds was established by analytical and spectral
data. The antibacterial studies to all of the synthesized
compounds against Bacillus cereus, Escherichia coli,
Pseudomonas aeruginosa, Staphylococcus aureus, and
Enterococcus faecalis bacteria with Gram-positive and
negative strains, as MIC values are reported. Some of these
compounds such as 3a,b,d and 4b,d exhibited a good to
significant antibacterial activity. Also, all of new synthesized
compounds 3,4,6(a–d) were active against Gram-positive S.
aureus bacterium. Thus, some of these compounds can
emerge as a promising tool for further research work.
Introduction
According to several recent researches, the continuous
application of drugs has resulted in the evolution of resis-
tant pathogenic microorganisms (Fluit et al., 2001;
National Nosocomial Infections Surveillance, 2004). One
of the strategies to overcome this serious problem is the
urgent synthetic development of drugs with new chemical
structures. For this purpose, we joined in one single
structure, two important biologically active scaffolds, the
thiazole or imidazole and pyridine rings from thiourea.
It is well known that N,N0-disubstituted thioureas are
important organic compounds because of their pharmaco-
logical activities (Tan et al., 2011; Schroeder, 1995;
Bhandari et al., 2008; French et al., 1970; Fanshewe and
Epstein, 1991). Specially, some of their derivatives have
been used in the anti-histamine drugs (Ganellin et al.,
1995). N,N0-(aroyl)thioureas are efficient ligands for the
separation and refinement of platinum group metals (Koch,
2001). These compounds are not only a segment of bio-
logically important but also a versatile intermediate for the
synthesis of heterocyclic compounds such as 1,3-thiazoles,
pyrimidines, 1,3-diazines, 1,3-quinazolines, and 1,2,4-tri-
azines (Dodson and Carroll King, 1945; Foster and Snyder,
1963; Winckelmann and Larsen, 1986; Gopalsamy and
Yang, 2000; Yang and Kaplan, 2001).
Keywords N,N0-Disubstituted thiourea ꢀ Imidazole ꢀ
Thiazole ꢀ Microorganisms ꢀ Antibacterial activity
Thiazole and their derivatives have attracted continuing
interest over the years because of their varied biological
activities such as anti-bacterial (Tsuji and Ishikawa, 1994),
anti-fungal (Wilson et al., 2001), antitumor (Kumar et al.,
1993; Gouda et al., 2012), anticonvulsant (Ergenc and
Capan, 1994), antimalarial (Karade et al., 2008), herbi-
cidal, insecticidal, and anti-helminthic (Metzger, 1984).
The fused and pendent 1,3-thiazoles are a ubiquitous fea-
ture of many pharmaceutical products and can be found in
M. Kalhor (&) ꢀ M. Salehifar
Department of Chemistry, Payame Noor University,
PO Box 19395-369, Tehran, Iran
e-mail: mekalhor@gmail.com; mekalhor@pnu.ac.ir
I. Nikokar
Laboratory of Microbiology and Immunology of Infectious
Diseases, Guilan University of Medical Sciences,
PO Box 44715-1361, Guilan, Iran
123

Med Chem Res
Scheme 1 The synthetic pathways of compounds 3–6(a–d)
drugs that are useful in the treatment of hypertension (Patt
et al., 1992), schizophrenia (Jean et al., 1990), inflamma-
tion (Haviv et al., 1988; Clemence et al., 1988), allergies
(Hargrave et al., 1983), and HIV (Bell et al., 1995)
infections. Also, the aminothiazoles are known to be
ligands of estrogen receptors (Fink et al., 1999).
Results and discussion
Synthesis
The synthetic routes for the preparation of the target
compounds are outlined in Scheme 1. The required a-
amino pyridyl ketone 2a and acetal 2b were prepared via
reaction of 4-acetyl pyridine (1) with corresponding
reagents according to low improvement Neber rearrange-
ment (La Mattina, 1980; La Mattina and Suleske, 1985).
The preparation of the thiourea derivatives 3a–d was
achieved by the reaction of the corresponding arylisothio-
cyanate with a-amino pyridyl ketone 2a. Thiourea deriv-
atives 3a–d underwent an intramolecular cyclization under
concentrated acidic conditions to produce 2-amino-1,3-
thiazoles 4a–d in excellent yields as the new synthetic
pathway. Some of the major advantages of this practical
procedure are use of available and inexpensive material,
high yields, moderate temperature, easy workup and it can
be as an efficient synthetic pathway for preparation of the
2-amino-1,3-thiazole rings which the research is ongoing in
this regard.
Imidazoles are vastly distributed in nature and known
as biocatalyst and biological ligands. These compounds
play a vital role in life activities (Grimmett, 1984; Saeed
and Batool, 2007). Based on several literature surveys,
imidazole derivatives show a wide range of pharmaco-
logical activities (Shingalapur et al., 2009; Sharma et al.,
2009; Olender et al., 2009; Achar et al., 2010). Further-
more, imidazole-2-thiones have been used as light-sensi-
tive photographic materials (Saeki and Inagaki, 1985),
and rubber antioxidants (Horsey and Patel, 1993). Some
these derivatives, among methimazole, have been clini-
cally used for the treatment of several diseases (Kruse
et al., 1990).
In view of these points and as part of ongoing studies on
the synthesis and biological consideration of heterocycles
(Kalhor et al., 2011; Kalhor and Dadras, 2013; Mobinik-
haledi et al., 2010, 2012; Sharifzadeh et al., 2013), we wish
to report the synthesis of a new series of five-membered
heterocyclic titled compounds, bearing the pyridine ring
and their bactericidal activities.
The imidazole-2-thiones 6a–d were afforded by reflux-
ing a mixture corresponding aryl isothiocyanate and am-
inoacetal 2b in ethanol to form an acetal-thiourea
derivative as intermediate 5a–d which was isolated and
123

Med Chem Res
Table 1 Antibacterialactivities of chemical compounds3–6(a–d) (zone
of inhibition in mm)
Table 2 Minimum inhibitory concentration (MIC) of the selected
compounds against microbial strains (lg/ml)
Compound B.
cereus
E. coli P.
aeruginosa
S.
aureus
E.
faecalis
Compound B. cereus E. coli P. aeruginosa S. aureus E. faecalis
a
3a
3b
3d
4b
4c
4d
6a
6b
6c
6d
–
512
–
128
256
–
32
256
128
32
128
64
–
3a
3b
3c
3d
4a
4b
4c
4d
6a
6b
6c
6d
8
10
8
15
25
18
8
10
18
8
64
256
64
–
a
14
10
14
6
–
8
8
–
8
–
256
–
8
–
128
–
15
10
–
18
10
29
20
31
16
18
16
20
22
10
10
17
12
10
–
–
–
128
16
512
–
–
128
–
512
–
20
8
–
256
256
256
128
–
128
–
–
–
–
10
–
–
18
–
–
–
–
8
–
512
–
–
18
–
7
–
–
Disc diffusion method used to determine the MICs (Wayne, 2011;
Chand et al., 1994). DMSO only, control for compounds
9
–
–
–
–
–
a
Not tested
Gentamicinb 26
23
24
25
Dimethyl sulfoxide (DMSO) only, control for compounds and
references
other protons and carbons appeared in the expected region
of spectrums.
a
Not active
b
Reference compound
Antibacterial activities
immediately heated in aqueous 10 %HCl via modified
method of Marckwald (Matsuda et al., 1997).
Applying the agar plate diffusion technique (Wayne, 2011;
Chand et al., 1994), all of newly synthesized compounds
were screened in vitro for antimicrobial activities against
five pathogenic bacteria. The results of the bioassay are
given in Table 1. A cursory view of the data indicates that
some of the compounds 3a,b,d and 4b,d exhibit a moderate
to high activity against four bacteria with Gram-positive
and -negative strain. Also, all compounds are active against
Staphylococcus aureus microbe. It is considerable that
compounds 3a, 4b, and 4d were found to be more active
against S. aureus as Gram-positive bacterium than genta-
micin, which is a known antimicrobial drug. Therefore,
these compounds can have the potential to be good anti-
bacterial candidate that the research is ongoing in this
regard. We can also compare the inhibitory effects of
compounds 3b–d with their products, thiazoles 4b–d, after
cyclization. For instance, after cyclization of 3b and 3d, the
inhibitory effect of the resulting thiazoles 4b and 4d are
strikingly increased.
The structure of synthesized compounds was established
1
by means of their IR, H NMR, 13C NMR spectra, and
elemental analyses. The IR spectra of thiourea derivatives
3a–d showed characteristic absorptions at 1202–1342,
1592–1653, and 3260–3474 cm-1 for the C=S, C=O, and
1
NH stretching vibrations, respectively. H NMR spectra of
3a–d showed broad peaks at 5.63–11.64 ppm due to the
resonance of CH2–NH–CS and NH–CS protons, which
disappeared upon D2O addition. The 13C NMR spectrum of
compound 3a showed ten signals, including a signal at
49 ppm for CH2, a signal at 180 ppm for the C=S, and a
signal at 188 ppm for the carbonyl carbon atoms.
The IR spectra of 2-amino thiazoles 4a–c showed
absorption bands at 3,241–3,467 cm-1 characteristic for
1
the NH group. Also in the H NMR spectra of all 1,3-
thiazoles, the disappearance of CH2NH signals of 4a–d, the
appearance of the NH broad signal at 10.65–10.92 ppm,
and singlet signal at 8.04–8.15 ppm for aromatic hydrogen
(C–H) the ring, confirm the formation of thiazole ring.
The 1H NMR spectra of imidazoles 4a–d showed singlet
peaks at 10.85–11.62 ppm attributed to the resonance of
the SH or NH protons, which disappeared upon D2O
addition. In the 13C NMR spectra of compounds 6a–d, the
appearance of signals at the region between 166.3 and
167.9 ppm attributed to the carbon resonance of the C=N
or C=S group in imidazole rings is in support of the
expected thiol or thione structures. The resonance of all
In addition, investigation of the minimum inhibitory
concentration (MIC) values of the potent derivatives
against five microorganisms was performed and the
results are presented in Table 2. The compound 4d
indicates the highest bactericidal activity (16 lg/ml)
against S. aureus bacterium. Also compounds 3a,b and
4b have a high activity (32–64 lg/ml) against three
microorganisms. Just as was predicated, the compounds
6a–d are not shown considerable bactericidal activity
(Table 2).
123

Med Chem Res
Experimental
(KBr) mmax 3351, 3260 (N–H), 2939 (C–H), 1607(C=O),
1531, 1489, 1407 (C=N, C=C), 1342 (C=S), 1090 (C–Cl),
1
Melting points were determined using an electrothermal
digital apparatus and are uncorrected. FT-IR spectra were
obtained with a SHIMADZU-IR Prestige-21 spectrometer
using KBr discs. The NMR spectra were recorded on a
Bruker (500 MHz) spectrometer. Chemical shifts (ppm)
are referenced to tetramethylsilane (TMS) as internal
standard. Elemental analyses were performed with as ele-
mental analyzer (Elemental, Vario EL III) at Arak Uni-
versity. Reactions were monitored by thin layer
chromatography (TLC). The a-amino pyridyl ketone
dihydrochloride 2a and a-amino pyridyl acetal 2b were
prepared with low improvement following the previously
reported procedure (La Mattina, 1980; La Mattina and
Suleske, 1985).
825 cm-1; H-NMR (500 MHz, DMSO-d6): d = 4.03 (s,
2H, CH2), 7.30 (d, 2H, J = 8.65 Hz, H–Ar), 7.43–7.46 (m,
4H, H-Aryl and H-Pyr), 8.61 (d, 2H, J = 8.65 Hz, H-Pyr),
9.70 (br, 1H, NH), 11.16 (br, 1H, NH) ppm; the NH protons
disappeared on D2O addition; 13C-NMR (125 MHz,
DMSO–d6): d = 49.3 (CH2, C-5), 122.5 (CH, C-8,10),
124.6 (CH, C-16,18), 128.3 (CH, C-15,19), 128.6 (C,
C-17), 138.5 (C, C-14), 147.9 (C, C-9), 149.9 (CH,
C-7,11), 181.2 (C=S), 186.1 (C=O) ppm; Anal. Calcd. for
C14H12ClN3OS: C, 54.99; H, 3.96; N, 13.74; S, 10.49;
found: C, 55.12; H, 3.98; N, 13.69; S, 10.55 %.
1-(2-Oxo-2-(pyridin-4-yl)ethyl)-3-(p-tolyl)thiourea (3c)
Yellowish needles (EtOH); this compound was prepared by
refluxing for 9 h in 84 % yield; mp 185–186 °C; FT-IR
(KBr) mmax 3383 (N–H), 2941 (C–H), 1592 (C=O), 1537,
1401, 1370 (C=N, C=C), 1307 (C=S), 1061, 643,
General procedure for synthesis of the N,N0-
disubstituted thioureas 3a–d (Scheme 1)
1
A solution of a-amino pyridyl ketone 2a (2 mmol) and
sodium carbonate (1 mmol) in ethanol (15 ml) was stirred
at room temperature for 10 min. To the reaction mixture,
corresponding isothiocyanate was added, followed by re-
fluxing for 9–10 h and monitored by TLC. After completing
the reaction, 1 ml water was added and to reflux was con-
tinued for 1 h. The result was concentrated and cooled to
room temperature to give the solid product 3a–d, which was
filtered, air dried, and recrystallized from ethanol.
504 cm-1; H-NMR (500 MHz, CDCl3): d = 2.39 (s, 3H,
CH3), 4.03 (s, 2H, CH2), 5.63 (br, 1H, NH), 6.83 (d, 2H,
J = 8.15 Hz, H–Ar), 7.16 (d, 2H, J = 8.10 Hz, H–Ar),
7.25–7.27 (m, 2H, H-Pyr), 7.65 (br, 1H, NH), 8.57 (d, 2H,
J = 8.69, H-Pyr); 13C-NMR (125 MHz, CDCl3): d = 21.0
(CH3, C-20), 49.4 (CH2, C-5), 100.6 (CH, C-8,10), 121.9
(CH, C-15,19), 125.2 (CH, C-16,18), 130.5(C, C-14), 132.8
(C, C-17), 137.6 (C, C-9), 149.5 (CH, C-7,11), 180.6
(C=S), 185.6 (C=O) ppm; Anal. Calcd. for C15H15N3OS:
C, 63.13; H, 5.30; N, 14.73; S, 11.24; found: C, 62.83; H,
5.31; N, 14.81; S, 11.10 %.
1-(4-Nitrophenyl)-3-(2-oxo-2-(pyridin-4-yl)ethyl)thiourea
(3a)
1-(2-Oxo-2-(pyridin-4-yl)ethyl)-3-phenylthiourea (3d)
Yellowish needles (EtOH); this compound was prepared by
refluxing for 10 h in 89 % yield; mp 200–201 °C; FT-IR
(KBr) mmax 3289 (N–H), 1653 (C=O), 1600, 1547 (C=N,
Yellowish needles (EtOH); this compound was prepared by
refluxing for 9 h in 86 % yield; mp 187–188 °C; FT-IR (KBr)
C=C), 1506, 1328 (NO2), 1202 (C=S), 1033, 844 cm-1
;
mmax 3474, 3181 (N–H), 3013, 2948(C–H), 1593 (C=O), 1535,
1H-NMR (500 MHz, DMSO–d6): d = 4.05 (s, 2H, CH2),
7.47 (d, 2H, J = 6.00 Hz, H–Ar), 7.82 (m, 2H, H–Ar),
8.13–8.24 (m, 2H, H–Ar), 8.62 (d, 2H, J = 8.50 Hz, H–
Ar), 10.23 (s, 1H, NH), 11.64 (s, 1H, NH) ppm; 13C-NMR
(125 MHz, DMSO–d6): d = 49.4 (CH2, C-5), 120.6 (CH,
C-8,10), 121.5 (CH, C-16,18), 122.5 (CH, C-15,19), 124.8
(C, C-9), 146.4 (C, C-17), 147.6 (C, C-14), 150.1 (CH,
C-7,11), 180.5 (C=S), 188.1 (C=O) ppm; Anal. Calcd. for
C14H12N4O3S: C, 53.16; H, 3.82; N, 17.71; S, 10.14;
found: C, 53.37; H, 3.79; N, 17.68; S, 10.22 %.
1445, 1369 (C=N, C=C), 1207 (C=S), 684, 601 cm-1; H-
NMR (500 MHz, CDCl3): d = 4.04 (s, 2H, CH2), 5.78 (br, 1H,
NH), 6.97 (d, 2H, J = 7.50 Hz, H–Ar), 7.26–7.37 (m, 5H, H–
Ar and H-Pyr), 8.25 (br, 1H, NH), 8.56 (d, 2H, J = 8.62 Hz,
H-Pyr); 13C-NMR (125 MHz, CDCl3): d = 49.4 (CH2, C-5),
121.9 (CH, C-8,10), 124.7 (CH, C-15,19), 127.3 (C, C-17),
129.9 (CH, C-16,18), 135.7 (C, C-14), 148.2 (C, C-9), 149.7
(CH, C-7,11), 180.4(C=S), 188.4(C=O)ppm; Anal. Calcd.for
C14H13N3OS: C, 61.97; H, 4.83; N, 15.49; S, 11.82: found: C,
61.69; H, 4.86; N, 15.56; S, 11.73 %.
1
1-(4-Chlorophenyl)-3-(2-oxo-2-(pyridin-4-yl)ethyl)thiourea
General procedure for synthesis of the 2-amino-thiazols
(3b)
4a–d
Yellowish needles (EtOH); this compound was prepared by
The N-thioureas 3a–d (0.9 mmol) were added slowly to
concentrated sulfuric acid (5–10 ml), which was stirred and
refluxing for 10 h in 83 % yield; mp 191–192 °C; FT-IR
123

Med Chem Res
kept at 0 °C. The reaction mixture was stirred at room
temperature for 4 h. It was then poured into ice-water
(25 g) and neutralized with concentrated aqueous ammo-
nia. The precipitate was filtered, washed with water
(15 ml), dried, and recrystallized from DMF/H2O to give
pure 4a–d.
J = 8.70 Hz, H-Pyr), 10.65 (s, 1H, NH) ppm; 13C-NMR
(125 MHz, DMSO–d6): d = 20.7 (CH3, C-19), 118.2 (CH,
C-8,10), 119.9 (CH, C-14,18), 123.6 (C, C-5), 128.1 (CH,
C-15,17), 129.9 (C, C-16), 130.9 (C, C-13), 134.2 (CH,
C-4), 141.1 (C, C-9), 148.8 (CH, C-7,11), 165.2 (C-2,
N=C–S thiazole) ppm; Anal. Calcd. for C15H13N3S: C,
67.39; H, 4.90; N, 15.72; S, 11.99: found: C, 67.68; H,
4.91; N, 15.67; S, 11.88 %.
N-(4-Nitrophenyl)-5-(pyridin-4-yl)thiazol-2-amine (4a)
Yellowish needles (DMF/H2O); this compound was pre-
pared by refluxing for 4 h in 100 % yield; mp 370–371 °C;
FT-IR (KBr) mmax 3281 (N–H), 1596, 1549, 1413 (C=N,
N-Phenyl-5-(pyridin-4-yl)thiazol-2-amine (4d)
Yellowish needles (DMF/H2O); this compound was pre-
pared by refluxing for 4 h in 85 % yield; mp 340–343 °C;
FT-IR (KBr) mmax 3467 (N–H), 3001, 2837 (C–H), 1631,
C=C), 1501, 1330 (NO2), 1103, 611 cm-1 1H-NMR
;
(500 MHz, DMSO–d6): d = 7.57 (d, 2H, J = 6.20 Hz, H–
Ar), 7.88 (d, 2H, J = 8.52 Hz, H-Pyr), 8.15 (s, 1H,
H-thiazole), 8.24 (d, 2H, J = 8.1 Hz, H–Ar), 8.55 (d, 2H,
J = 6.00, H-Pyr), 10.90 (s, 1H, NH) ppm; 13C-NMR
(125 MHz, DMSO–d6): d = 117.1 (CH, C-8,10), 120.0
(CH, C-14,18), 121.9 (C, C-5), 125.9 (CH, C-15,17), 138.8
(CH, C-4), 139.2 (C, C-16), 141.1 (C, C-9), 146.8 (C,
C-13), 150.6 (CH, C-7,11), 163.3 (N=C–S thiazole) ppm;
Anal. Calcd. for C14H10N4O2S: C, 56.37; H, 3.38; N,
18.78; S, 10.75: found: C, 56.07; H, 3.40; N, 18.65; S,
10.82 %.
1503, 1463 (C=N, C=C), 1206, 1150, 1020 cm-1 1H-
;
NMR (500 MHz, DMSO–d6): d = 7.07–7.41 (m, 5H, H–
Ar), 7.59 (d, 2H, J = 7.50 Hz, H-Pyr), 8.23 (s, 1H,
H-thiazole), 8.57 (d, 2H, J = 8.50 Hz, H-Pyr) 10.92 (br,
1H, NH) ppm. EIMS (m/z, %): 253 (M?, 25), 149 (10), 109
(10), 97 (20), 91 (10), 83 (25), 69 (80), 57 (100); Anal.
Calcd. for C14H11N3S: C, 66.38; H, 4.38; N, 16.59; S,
12.66: found: C, 66.08; H, 4.41; N, 16.60; S, 12.76 %.
General procedure for synthesis of the imidazole
2-thiones 6a–d
N-(4-Chlorophenyl)-5-(pyridin-4-yl)thiazol-2-amine (4b)
A mixture of the appropriate aryl isothiocyanate (3 mmol)
and pyridine amino acetal 2b (3 mmol) in ethanol (10 ml)
was refluxed for 4 h. After evaporating the solvent,
intermediate compounds 5(a–d) were formed which were
dissolved in 10 % HCl (10 ml) and heating to reflux for
22–29 h. After completion of the reaction (monitoring by
TLC plate), the mixture was cooled and neutralized with
a solution of 10 % NaOH. The precipitate was filtered
and washed thoroughly with water (5 ml), dried, and re-
crystallized from EtOH/H2O to give the pure products
6a–d.
Yellowish needles (DMF/H2O); this compound was pre-
pared by refluxing for 4 h in 92 % yield; mp 364–366 °C;
FT-IR (KBr) mmax 3241 (N–H), 3047 (C–H), 1629, 1599,
1546, 1494 (C=N, C=C), 1211, 1037 (C–S), 815 (C–
1
Cl) cm-1; H-NMR (500 MHz, DMSO–d6): d = 7.38 (d,
2H, J = 8.50 Hz, H–Ar), 7.51 (d, 2H, J = 6.00 Hz, H–
Ar), 7.69 (d, 2H, J = 8.50 Hz, H-pry), 8.04 (s, 1H,
H-thiazole), 8.51 (d, 2H, J = 8.00 Hz, H-Pyr), 10.70 (br,
1H, NH) ppm; the NH proton disappeared on D2O addi-
tion; 13C-NMR (125 MHz, DMSO–d6): d = 119.4 (CH,
C-8,10), 119.8 (CH, C-14,18), 124.5 (C, C-5), 125.8 (C,
C-16), 129.3 (CH, C-15,17), 139.2 (CH, C-4), 139.4 (C,
C-13), 139.7 (C, C-9), 150.4 (CH, C-7,11), 164.6 (N=C–S
thiazole) ppm; Anal. Calcd. for C14H10ClN3S: C, 58.43; H,
3.50; N, 14.60; S, 11.14: found: C, 58.62; H, 3.56; N,
14.81; S, 11.22 %.
1-(4-Nitrophenyl)-5-(pyridin-4-yl)-1H-imidazole-2(3H)-
thione (6a)
White needles (EtOH/H2O); this compound was prepared
by refluxing for 22 h in 76 % yield; mp 177–180 °C; FT-
IR (KBr) mmax 3288 (N–H), 3075 (C–H), 1602, 1553 (C=N,
C=C), 1505, 1335 (NO2), 1200 (C=S), 1103, 1033,
5-(Pyridin-4-yl)-N-(p-tolyl)thiazol-2-amine (4c)
1
839 cm-1; H-NMR (500 MHz, CDCl3): d = 6.98 (d, 2H,
Yellowish needles (DMF/H2O); this compound was pre-
pared by refluxing for 4 h in 98 % yield; mp 355–356 °C;
FT-IR (KBr) mmax 3234 (N–H), 3081 (C–H), 1608, 1541,
J = 8.85 Hz, H–Ar), 7.46–7.55 (m, 2H, H–Ar), 8.18–8.24
(m, 4H, H–Ar), 8.29 (s, 1H, H–Ar), 11.62 (br, 1H, NH),
ppm; 13C-NMR (125 MHz, DMSO–d6): d = 119.4 (CH,
C-3), 121.5 (CH, C-8,10), 125.1 (C, C-4), 128.3 (CH,
C-15,17), 129.1 (CH, C-14,18), 138.5 (C, C-13), 143.3 (C,
C-16), 144.4 (C, C-9), 150.4 (CH, C-7,11), 167.9 (C=S)
ppm; Anal. Calcd. for C14H10N4O2S: C, 56.37; H, 3.38; N,
1500 (C=N, C=C), 1210, 808, 619 cm-1
;
1H-NMR
(500 MHz, DMSO–d6): d = 2.28 (s, 3H, CH3), 7.14–7.22
(m, 2H, H-Aryl), 7.49–7.54 (m, 3H, H–Ar), 8.01 (t, 1H,
J = 6.45 Hz, H-Pyr), 8.07 (s, 1H, H-thiazole), 8.51 (d, 2H,
123

Med Chem Res
18.78; S, 10.75: found: C, 56.77; H, 3.41; N, 18.62; S,
10.61 %.
Biological screening
The antibacterial activity of synthesized compounds were
screened at a concentration of 10 mg/ml against five ref-
erence strains of bacteria including Bacillus cereus ATCC
11778 (Gram-positive), S. aureus ATCC 25923 (Gram-
positive), Escherichia coli ATCC 25922 (Gram-negative),
Pseudomonas aeruginosa ATCC 27853 (Gram-negative),
and Enterococcus faecalis ATCC 29212 (Gram-positive).
Tested compounds were dissolved in dimethyl sulfoxide
(DMSO) for the preparation of stock solution. The solvent
control was included, although no antibacterial activity has
been noted. All samples were tested in triplicate and the
average results were recorded. Microbial susceptibility
testing of all compounds was carried out by diffusion agar
and minimal inhibitory concentration (MIC) methods
according to Clinical and Laboratory Standards Institute
(CLSI) guideline (Wayne, 2011; Chand et al., 1994). The
suspension of bacteria was adjusted to 0.5 MacFarland
Standard (106 c.f.u/ml) and spread over Muller-Hinton
agar. The tested compounds are placed in random well
position on the plate, after overnight incubation at 37 °C
the zone of inhibition determinate. The results of the bio-
assay are given in Tables 1 and 2.
1-(4-Chlorophenyl)-5-(pyridin-4-yl)-1H-imidazole-2(3H)-
thione (6b)
White needles (EtOH/H2O); this compound was prepared
by refluxing for 24 h in 73 % yield; mp 102–103 °C; FT-
IR (KBr) mmax 3238 (N–H), 3050 (C–H), 1599, 1544, 1484,
1429, 1388 (C=N, C=C), 1322 (C=S), 1035, 815 (C–Cl),
718 cm-1 1H-NMR (500 MHz, CDCl3): d = 7.23–7.27
;
(m, 5H, H–Ar), 7.30 (d, 2H, J = 7.50 Hz, H–Ar), 8.62 (d,
2H, J = 8.50 Hz, H-Pyr), 11.62 (s, 1H, NH or SH) ppm;
the NH or SH proton disappeared on D2O addition; 13C-
NMR (125 MHz, CDCl3): d = 119.4 (CH, C-3), 122.7
(CH, C-8,10), 129.0 (C, C-4), 130.5 (CH, C-15,17), 134.7
(C, C-13), 135.6 (C, C-16), 138.0 (CH, C-14,18), 142.6 (C,
C-9), 150.5 (CH, C-7,11), 162.8 (C=S) ppm; Anal. Calcd.
for C14H10ClN3S: C, 58.43; H, 3.50; Cl, 12.32; N, 14.60; S,
11.14: found: C, 58.93; H, 3.55; N, 14.70; S, 11.04 %.
5-(Pyridin-4-yl)-1-(p-tolyl)-1H-imidazole-2(3H)-thione
(6c)
White needles (EtOH/H2O); this compound was prepared
by refluxing for 27 h in 55 % yield; mp 86–88 °C; FT-IR
(KBr) mmax 3224 (N–H), 3039, 2987 (C–H), 1598, 1540,
Acknowledgments We are indebted to the Chemistry Department
of Payame Noor University and the Medical Sciences of Guilan
University for the evaluating of biological activities.
1408 (C=N, C=C), 1323 (C=S), 1211, 1035 cm-1 1H-
;
NMR (500 MHz, CDCl3): d = 2.34 (s, 3H, CH3),
7.14–7.22 (m, 5H, H–Ar), 7.42 (br s, 2H, H-Pyr), 8.37 (d,
2H, J = 7.50 Hz, H-Pyr), 10.85 (br, 1H, NH or SH) ppm;
13C-NMR (125 MHz, CDCl3): d = 20.9 (CH3), 117.1 (CH,
C-3), 119.9 (CH, C-8,10), 121.5 (C, C-4), 123.8 (CH,
C-15,17), 129.5 (C, C-13), 135.1 (CH, C-14,18), 138.5 (C,
C-16), 148.5 (C, C-9), 148.9 (CH, C-7,11), 166.3 (C=S)
ppm; Anal. Calcd. for C15H13N3S: C, 67.39; H, 4.90; N,
15.72; S, 11.99: found: C, 67.09; H, 4.93; N, 15.52; S,
11.80 %.
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