Synthesis of some 2-[(benzazole-2-yl)thioacetylamino]thiazole derivatives and their antimicrobial activity and toxicity

Article abstract of DOI:10.1016/j.ejmech.2003.11.001

Some 2-[(benzazole-2-yl)thioacetylamino]thiazole derivatives (III) were synthesized by reacting 4-methyl-2-(chloroacetylamino)thiazole derivatives (I) with benzazol-2-thiole (II) in acetone in the presence of K₂CO ₃. The chemical structures of the compounds were elucidated by ¹H NMR and FAB⁺-MS spectral data. The prepared compounds were tested for antimicrobial activity and toxicity.

Full text of DOI:10.1016/j.ejmech.2003.11.001

European Journal of Medicinal Chemistry 39 (2003) 267–272
www.elsevier.com/locate/ejmech
Short communication
Synthesis of some 2-[(benzazole-2-yl)thioacetylamino]thiazole
derivatives and their antimicrobial activity and toxicity
a,
a
a
a
Gülhan Turan-Zitouni *, Sq eref Demirayak , Ahmet Özdemir , Zafer Asım Kaplancıklı ,
b
Mehmet TahaYıldız
a
Department of Pharmaceutical Chemistry, Faculty of Pharmacy, Anadolu University, 26470 Eski s¸ ehir, Turkey
b
Department of Biology, Faculty of Science, Osmangazi University, 26480 Eski s¸ ehir, Turkey
Received 21 March 2003; received in revised form 6 November 2003
Abstract
Some 2-[(benzazole-2-yl)thioacetylamino]thiazole derivatives (III) were synthesized by reacting 4-methyl-2-(chloroacetylamino)thiazole
derivatives (I) with benzazol-2-thiole (II) in acetone in the presence of K CO . The chemical structures of the compounds were elucidated by
2
3
1
+
H NMR and FAB -MS spectral data. The prepared compounds were tested for antimicrobial activity and toxicity.
2003 Elsevier SAS. All rights reserved.
©
Keywords: Thiazole; Benzothiazole; Benzimidazole; Benzoxazole; Antimicrobial activity
1
. Introduction
methylthiazole with chloroacetyl chloride in accordance
with the method described in the literature [17–19].
The benzothiazole ring is present in various marine or
Benzazol-2-thiole (II) derivatives used in the synthesis
were prepared according to the methods reported in the
literature [20].
terrestrial natural compounds, which have useful biological
activities [1–4]. Benzothiazole and its bioisosteres; benzox-
azole and benzimidazole, were studied for their antitumor,
antiviral and antimicrobial activities [5–9]. In the last few
years, it was reported that the 2 and 5-substituted benzothia-
zole, benzoxazole and benzimidazole derivatives had antimi-
crobial activities against some Gram-positive, Gram-
negative bacteria and the yeast Candida albicans, and these
compounds provided a wide variety of in vitro antimicrobial
effects especially against the enterobacter Pseudomonas
aeruginosa and the yeast C. albicans [10–16].
The reaction of 4-methyl-2-(chloroacetylamino)thiazole
(I), benzazol-2-thiole (II) and anhydrous potassium carbon-
ate in acetone gave the 2-[(benzazole-2-yl)thioacety-
lamino]thiazole derivatives (III a–s ) as shown in (Scheme
I).
Some characteristics of the synthesized compounds are
1
shown in Table 1. Analytical and spectral data (IR,
H NMR,
+
FAB -MS) confirmed the structures of the new compounds.
In view of these observations, some novel 2-[(benzazole-
2
-yl)thioacetylamino]thiazole derivatives have been synthe-
3
. Biology
sized in order to examine their in vitro antimicrobial activi-
ties against different Gram-positive, Gram-negative bacteria
and the yeast C. albicans in comparison with control drugs.
3
.1. Antimicrobial activity
Antimicrobial activities of compounds were tested using
2
. Chemistry
microbroth dilution method [21–23]. Tested microorganism
strains were; Staphylococcus aureus (B-767), Escherichia
coli (B-3704), Bacillus subtilis (NRS-744), Streptococcus
faecium (B-3502), Staphylococcus epidermidis (B-4268) and
C. albicans (isolate obtained from Osmangazi Uni. Fac. of
Medicine).
In the present work, 4-methyl-2-(chloroacety-
lamino)thiazole (I) was prepared by reacting 2-amino-4-
*
Corresponding author.
E-mail address: gturan@anadolu.edu.tr (G. Turan-Zitouni).
©
2003 Elsevier SAS. All rights reserved.
doi:10.1016/j.ejmech.2003.11.001

268
G. Turan-Zitouni et al. / European Journal of Medicinal Chemistry 39 (2003) 267–272
4
. Result, discussion and conclusions
In the present work, 19 new compounds were synthesized.
The structures of the obtained compounds were elucidated by
spectral data. In the IR spectra, some significant stretching
bands due N–H, C=O, C=N and C=C were at 3225–
–
1
–1
–1
–1
3
220 cm , 1670–1665 cm , 1630 cm , 1580 cm , respec-
1
tively. In the H NMR spectra, the signal due to COCH
2
methylene protons, present in all compounds, appeared at
4
1
.2–4.4 ppm, as singlets. NHCO proton was observed at
2.3–13.1 ppm as broad.
The shrimp lethality assay is considered as a useful tool
for preliminary assessment of toxicity, and it has been used
for the detection of fungal toxins, plant extract toxicity,
heavy metals, cyanobacteria toxins, pesticides, and cytotox-
icity testing of dental materials [26], natural and synthetic
organic compounds [24]. It has also been shown that,
A. salina toxicity test results have a correlation with rodent
and human acute oral toxicity data. Generally, a good corre-
lation was obtained between A. salina toxicity test and the
rodent data. Likewise, the predictive screening potential of
the aquatic invertebrate tests for acute oral toxicity in man,
including A. salina toxicity test, was slightly better than the
rat test for test compounds [27].
Scheme 1. The general synthesis reactions.
Chloramphenicole and ketoconazole were used as control
drugs. The observed data on the antimicrobial activity of the
compounds and control drugs are given in Table 2.
In order to prevent the toxicity results from possible false
effects originated from solubility of compounds and DM-
SO’s possible toxicity effect, compounds were prepared by
dissolving in DMSO in the suggested DMSO volume ranges
3
.2. Toxicity
Bioactive compounds are often toxic to shrimp larvae.
[23].
Thus, in order to monitor these chemicals’in vivo lethality to
shrimp larvae (Artemia salina), Brine-Shrimp Lethality As-
say [24] was used. Results were analyzed with LC50 program
to determine LC50 values and 95% confidence intervals [25].
Results are given in Table 3.
MIC’s were recorded as the minimum concentration of
compound, which inhibits the growth of tested microorgan-
isms. All of the compounds tested were showed significant
antifungal activity against C. albicans, when compared with
Table 1
Some characteristics of the compounds
Compound
III-a
III-b
III-c
III-d
III-e
III-f
III-g
III-h
III-I
III-j
III-k
III-l
III-m
III-n
III-o
III-p
III-q
III-r
III-s
R
R′
X
m.p. (°C)
140
120
141
200
71
Yield (%)
78
Molecular formula
C13H11N OS Cl
H
Cl
NH
NH
NH
NH
NH
NH
NH
NH
O
4
2
H
NO2
H
75
C13H11N O S
5 3
2
CH3
CH3
72
C14H14N OS
4 2
CH3
H
76
C15H16N O S
4 3
2
COOC H5
69
C16H16N O S
4 3
2
2
COOC H5
Cl
172
167
152
180
139
102
155
144
169
164
185
208
85
79
C16H15N O S Cl
2
4
3
2
2
2
COOC H5
CH3
NO2
Cl
71
C17H18N O S
4 3
2
COOC H5
70
C16H15N O S
5 3
2
H
69
C13H10N O S Cl
3
2
2
2
2
H
NO2
H
O
77
C13H10N O S
4 4
CH3
CH3
CH3
CH3
O
75
C14H13N O S
3 2
Cl
O
80
C14H12N O S Cl
3
2
2
2
2
2
CH3
NO2
H
O
81
C15H15N O S
3 2
O
78
C14H12N O S
4 4
COOC H5
O
74
C16H15N O S
3 4
2
COOC H5
Cl
O
77
C16H14N O S Cl
2
3
3
2
COOC H5
NO2
H
O
79
C16H14N O S
4 6
2
2
CH3
S
72
C14H13N OS
3 3
COOC H5
H
S
156
74
C16H15N O S
3 3
2
3

G. Turan-Zitouni et al. / European Journal of Medicinal Chemistry 39 (2003) 267–272
269
Table 2
MIC values of the compounds as µg/ml
Compound S. aureus E. coli
B. subtilis
62.5
62.5
62.5
7.81
62.5
62.5
62.5
62.5
15.62
31.25
15.62
62.5
62.5
62.5
62.5
62.5
62.5
31.25
–
S. faecium
31.25
31.25
3.90
S. epidermidis
3.90
C. albicans
III-a
III-b
III-c
III-d
III-e
III-f
III-g
III-h
III-j
III-l
III-m
III-n
III-o
III-p
III-q
III-r
III-s
A
31.25
15.62
7.81
62.5
62.5
62.5
62.5
62.5
62.5
62.5
125
4
7.81
8
15.62
15.62
15.62
15.62
15.62
31.25
7.81
8
62.5
7.81
16
4
31.25
31.25
15.62
62.5
62.5
62.5
8
15.62
62.5
8
16
4
31.25
62.5
62.5
62.5
62.5
62.5
62.5
62.5
62.5
62.5
62.5
62.5
–
1.95
62.5
15.62
15.62
15.62
15.62
62.5
4
15.62
31.25
62.5
3.90
8
31.25
62.5
16
8
31.25
31.25
3.90
62.5
8
62.5
31.25
7.81
4
31.25
31.25
31.25
–
4
31.25
7.81
62.5
16
–
1.95
B
–
–
8
Control compounds: A, chloramphenicole; B, ketoconazole.
ketoconazole. It was also observed that these compounds
have antimicrobial activity against all tested bacteria when
compared with chloramphenicole.
amino-4-methylthiazole (0.01 mol) in anhydrous benzene
and the mixture was treated as described in literature.
In consideration of these data, it has been seen that; espe-
cially 2- and 5-substituted benzazole derivatives have shown
antimicrobial activities against some Gram-positive, E. coli
and the yeast C. albicans.
5.1.1.2. 2-[(Benzazole-2-yl)thioacetylamino]thiazole de-
rivatives (III a–s): A mixture of 5-substituted-4-methyl-2-
(chloroacetylamino)thiazole (I) (0.01 mol), benzazol-2-
thiole II (0.01 mol) and K CO (0.01 mol) in acetone (50 ml)
2
3
The only non-toxic compound III-j is the one of the most
effective compound against C. albicans and other bacteria at
the same time.
was refluxed for 8 h. After cooling, the solution was evapo-
rated until dryness. The residue was washed with water and
recrystallized from ethanol.
–
1
In comparison of the results of toxicity and antimicrobial
activity tests, it is seen that the antimicrobial activity of the
compounds are not due to their general toxicity effect, how-
ever their antimicrobial activity can be possibly because of
their selective antimicrobial effect.
III a–e, g, h: IR (KBr, cm ): 3225 (NH), 1665 (C=O),
1
630 (C=N), 1580 (C=C).
1
III-a: H NMR (DMSO-d ): d (ppm): 2.70 (3H, s, CH ),
6
3
4
.20 (2H, s, COCH ), 7.10 (1H, s, thiazole C ), 7.60 (1H,
2 5
d [J = 8.31 Hz], benzimidazole C ), 7.80 (1H, s, benzimi-
6
dazole C ), 7.85 (1H, d [J = 8.40 Hz], benzimidazole C ),
4
7
5. Experimental
10.50 (1H, s, benzimidazole N–H), 12.70 (1H, br.,
NHCO). MS (FAB) [M+1]: m/z 339.8.
1
5.1. Chemistry
III-b: H NMR (DMSO-d ): d (ppm): 2.70 (3H, s, CH ),
6
3
4
.30 (2H, s, COCH ), 7.10 (1H, s, thiazole C ), 7.65 (1H,
2 5
All melting points (m.p.) were determined in open capil-
d [J = 8.61 Hz], benzimidazole C ), 7.80 (1H, s, benzimi-
6
laries on a Gallenkamp apparatus and are uncorrected. The
purity of the compounds was routinely checked by thin layer
chromatography (TLC) using silica gel 60G (Merck). Spec-
troscopic data were recorded by the following instruments.
dazole C ), 7.90 (1H, d [J = 8.61 Hz], benzimidazole C ),
4
7
1
0.50 (1H, s, benzimidazole N–H), 12.70 (1H, br.,
NHCO).
1
1
III-c: H NMR (250 MHz, DMSO-d , d ppm): 2.15 and
6
IR, Shimadzu IR-435 spectrophotometer; H NMR, Bruker
2
.25 (6H, two s, thiazole C and C –CH ), 4.40 (2H, s,
250 MHz spectrometer.
4 5 3
COCH ), 7.10–7.60 (4H, m, aromatic protons), 10.60
2
5.1.1. General procedure for synthesis of the compounds
(1H, s, benzimidazole N–H), 12.30 (1H, br, NHCO).
1
III-d: H NMR (250 MHz, DMSO-d , d ppm): 2.10 and
6
5.1.1.1. 5-Substituted-4-methyl-2-(chloroacetylamino)thiaz-
2.20 (6H, two s, thiazole C and C –CH ), 2.40 (3H, s,
4
5
3
ole (I): Chloroacetyl chloride (0.01 mol) and triethylamine
0.01 mol) were added to a solution of 5-substituted-2-
benzimidazole C –CH ), 4.30 (2H, s, COCH ), 6.90–7.60
(3H, m, aromatic protons), 10.80 (1H, s, benzimidazole
5 3 2
(

270
G. Turan-Zitouni et al. / European Journal of Medicinal Chemistry 39 (2003) 267–272
Table 3
Toxicity assay
a
Chemical
Cons. (µg/ml)
10
Mortality
Toxicity
Harmful
LC50
Upper 95% lim.
357.26
Lower 95% lim
111.43
III-a
0
199.53
1
1
00
2
000
10
0
III-b
III-c
III-d
III-e
III-f
III-g
III-h
III-j
III-l
III-m
III-n
III-o
III-p
III-q
III-r
III-s
a
10
Harmful
Harmful
Harmful
Toxic
316.23
681.29
100.00
21.54
628.26
159.17
–
1
1
00
000
2
8
10
0
–
1
1
00
000
0
6
10
4
8385.68
9.87
–
1.19
47.01
–
1
1
00
000
5
6
10
3
1
1
00
000
9
10
5
10
Very toxic
Toxic
10.00
1
1
00
000
8
10
4
10
14.68
–
–
1
1
00
000
10
10
4
10
Toxic
17.78
71.13
4.45
1
1
00
000
8
10
0
10
Non-toxic
Harmful
Harmful
Very toxic
Very toxic
Toxic
1000.00
398.11
251.19
10.00
1
1
00
000
0
5
10
0
1005.52
388.81
–
157.62
162.28
–
1
1
00
000
2
7
10
0
1
1
00
000
1
10
5
10
1
1
00
000
10
10
5
10
10.00
–
–
1
1
00
000
9
10
4
10
15.85
50.29
71.13
–
4.99
4.45
–
1
1
00
000
9
10
4
10
Toxic
17.78
1
1
00
000
8
10
5
10
Very toxic
Harmful
10.00
1
1
00
000
9
10
2
10
100.00
403.21
24.80
1
1
00
000
5
8
Ten organisms (A. salina) tested for each concentration.
N–H), 12.30 (1H, br., NHCO). MS (FAB) [M+1]: m/z
65.4.
aromatic protons), 12.50 (1H, s, benzimidazole N–H),
13.10 (1H, br., NHCO).
3
1
1
III-e: H NMR (250 MHz, DMSO-d , d ppm): 1.30 (3H, t,
III-g: H NMR (250 MHz, DMSO-d , d ppm): 1.20 (3H, t,
6
6
COOCH –CH ), 2.55 (3H, s, thiazole C –CH ), 4.30 (2H,
COOCH –CH ), 2.30 (3H, s, benzimidazole C –CH ),
2
3
4
3
2
3
5
3
q, COOCH ), 4.40 (2H, s, COCH ), 7.15–7.55 (4H, m,
2.40 (3H, s, thiazole C –CH ), 4.20 (2H, q, COOCH ),
4 3 2
2
2

G. Turan-Zitouni et al. / European Journal of Medicinal Chemistry 39 (2003) 267–272
271
4
.30 (2H, s, COCH ), 6.90 (1H, d, J = 8.30 Hz, benzimi-
5.2.2. Toxicity
2
dazole C ), 7.20 (1H, s, benzimidazole C ), 7.30 (1H, d
6
4
Brine-shrimp toxicity assay was used to determine cyto-
toxicity levels of the compounds. The compounds prepared
by dissolving in DMSO in the suggested DMSO volume
ranges [24]. Artificial seawater is prepared by dissolving
3.8 g sea salt per liter of sterile water. The eggs of the
brine-shrimp A. salina, readily available as a fish food in pet
shops, placed in artificial seawater and allowed 48 h at room
temperature to hatch and mature. After brine-shrimp larvae
have matured (after 2 days), 10 of them placed into each vial
contains; 10, 100 and 1000 µg/ml concentrations of the
compounds which were prepared by dissolving in DMSO
and then added to 5 ml of artificial seawater. After 24 h have
elapsed, number of surviving shrimps counted and recorded
with the aid of 3× magnifying glasses. Larvae were consid-
ered dead, if they did not exhibit any internal or external
movement during several seconds of observation. Results
were analyzed with the LC50 program to determine LC50
values and 95% confidence intervals.
[
J = 8.13 Hz], benzimidazole C ), 12.50 (1H, s, benzimi-
7
dazole N–H), 12.70 (1H, br., NHCO). MS (FAB) [M+1]:
m/z 391.4.
1
III-h: H NMR (250 MHz, DMSO-d , d ppm): 1.30 (3H, t,
6
COOCH –CH ), 2.50 (3H, s, thiazole C –CH ), 4.20 (2H,
2
3
4
3
q, COOCH ), 4.30 (2H, s, COCH ), 7.50 (1H, d
2
2
[
[
[
J = 8.85 Hz], benzimidazole C ), 8.00 (1H, dd
7
J = 6.54 Hz], benzimidazole C ), 8.20 (1H, d
6
J = 2.31 Hz], benzimidazole C ), 12.10 (1H, s, benzimi-
4
dazole N–H), 12.30 (1H, br, NHCO).
–1
III k, l, n–p: IR (KBr, cm ): 3220 (NH), 1667 (C=O),
1
630 (C=N), 1580 (C=C).
1
III-k: H NMR (250 MHz, DMSO-d , d ppm): 2.10 and
6
2
.20 (6H, two s, thiazole C and C –CH , 4.40 (2H, s,
4 5 3)
COCH ), 7.20–7.70 (4H, m, aromatic protons), 12.30
2
(
1H, br, NHCO). MS (FAB) [M+1]: m/z 320.4.
1
III-l: H NMR (250 MHz, DMSO-d , d ppm): 2.15 and
6
2
.25 (6H, two s, thiazole C and C –CH ), 4.45 (2H, s,
4 5 3
References
COCH ), 7.40–7.80 (3H, m, aromatic protons), 12.40
2
(
1H, br, NHCO).
[1] G.P. Gunawardana, S. Kohmoto, S.P. Gunesakara, O.J. McConnel,
F.E. Koehn, J. Am. Chem. Soc. 110 (1988) 4856–4858.
1
III-n: H NMR (250 MHz, DMSO-d , d ppm): 2.10 and
2
COCH ), 7.85 (1H, d [J = 8.82 Hz], benzoxazole C ), 8.20
6
[
[
[
2] G.P. Gunawardana, S. Kohmoto, N.S. Burres, Tetrahedron Lett. 30
1989) 4359–4362.
.20 (6H, two s, thiazole C and C –CH , 4.45 (2H, s,
4 5 3)
(
2
6
3] G.P. Gunawardana, F.E. Koehn, A.Y. Lee, J. Clardy, H.Y. He,
J.D. Faulkner, J. Org. Chem. 57 (1992) 1523–1526.
(1H, d [J = 8.91 Hz], benzoxazole C ), 8.45 (1H, s,
7
benzoxazole C ), 12.30 (1H, br, NHCO).
4
4] A.R. Carroll, P.J. Scheuer, J. Org. Chem. 55 (1990) 4426–4431.
1
III-o: H NMR (250 MHz, DMSO-d , d ppm): 1.20 (3H, t,
COOCH –CH ), 2.50 (3H, s, thiazole C –CH ), 4.20 (2H,
6
[5] J.S. Kim, Q. Sun, B. Gatto, C. Yu, A. Liu, L.F. Liu, E.J. La Voie,
Bioorg. Med. Chem. 4 (1996) 621–630.
2
3
4
3
q, COOCH ), 4.40 (2H, s, COCH ), 7.30–7.65 (4H, m,
aromatic protons), 12.60 (1H, br, NHCO). MS (FAB)
[6] L. Perrin, A. Rakik, S. Yearly, C. Baumberger, S. Kinloch-de Loies,
M. Pechiere, B. Hirschei, AIDS 10 (1996) 1233–1237.
2
2
[
M+1]: m/z 378.4.
[7] S. Staszewski, F.E. Massari, A. Kober, R. Göhler, S.K. Durr,
W. Anderson, C.L. Schneider, J.A. Waterburry, K.K. Bakshi, V.J. Tay-
lor, J. Infect. Dis. 171 (1995) 1159–1165.
1
III-p: H NMR (250 MHz, DMSO-d , d ppm): 1.20 (3H, t,
COOCH –CH ), 2.45 (3H, s, thiazole C –CH ), 4.20 (2H,
q, COOCH ), 4.40 (2H, s, COCH ), 7.30–7.75 (3H, m,
6
2
3
4
3
[
8] D.B. Olsen, S.S. Carroll, J.C. Culberson, J.A. Shafer, L.C. Kuo,
Nucleic Acids Res. 22 (1994) 1437–1443.
2
2
aromatic protons), 12.30 (1H, br, NHCO).
˙
[
9] I. Yalçın, E. Sq ener, T. Özden, A. Akin, Eur. J. Med. Chem. 25 (1990)
–1
7
05–708.
III-r: IR (KBr, cm ): 3223 (NH), 1670 (C=O), 1630
˙
[10] E. Sq ener, I. Yalçın, E. Sungur, Quant. Struc. Act. Rolat. 10 (1991)
(
C=N), 1580 (C=C).
2
23–228.
1
III-r: H NMR (250 MHz, DMSO-d , d ppm): 2.10 and
6
˙
˙
[
11] I. Yalçın, I. Ören, E. Sq ener, A. Akın, N. Uçartürk, Eur. J. Med. Chem.
2
.20 (6H, two s, thiazole C and C –CH ) 4.40 (2H, s,
4 5 3
2
7 (1992) 401–406.
COCH ), 7.20–7.95 (4H, m, aromatic protons), 12.30
2
˙
[
[
12] I. Yalçın, E. Sq ener, Int. J. Pharm. 98 (1993) 1–8.
(1H, br, NHCO). MS (FAB) [M+1]: m/z 336.4.
˙
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