Synthesis and biological evaluation of some thiazole derivatives as new cholinesterase inhibitors

Article abstract of DOI:10.3109/14756366.2011.653355

In the present study, some thiazole derivatives were synthesized via the ring closure reaction of 1-[2-(2-oxobenzo[d]thiazol-3(2H)-yl)acetyl] thiosemicarbazide with various phenacyl bromides. The chemical structures of the compounds were elucidated by ¹H NMR, ¹³C NMR and mass spectral data and elemental analyses. Each derivative was evaluated for its ability to inhibit acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) using a modification of Ellman's spectrophotometric method. The compounds were also investigated for their cytotoxic properties using MTT assay. The most potent AChE inhibitor was found as compound 4e (IC50=25.5±2.12 g/mL) followed by compounds 4i (IC50=38.50±2.12 g/mL), 4c (IC50=58.42±3. 14 g/mL) and 4g (IC50=68±2.12 g/mL) when compared with eserine (IC50=0.025±0.01 g/mL). Effective compounds on AChE exhibited weak inhibition on BuChE (IC50 > 80 g/mL). MTT assay indicated that the cytotoxic dose (IC50=71.67±7.63 g/mL) of compound 4e was higher than its effective dose.

Full text of DOI:10.3109/14756366.2011.653355

Journal of Enzyme Inhibition and Medicinal Chemistry, 2013; 28(3): 509–514
© 2013 Informa UK, Ltd.
ISSN 1475-6366 print/ISSN 1475-6374 online
DOI: 10.3109/14756366.2011.653355
RESEARCH ARTICLE
Synthesis and biological evaluation of some thiazole
derivatives as new cholinesterase inhibitors
Gülhan Turan-Zitouni1, Ahmet Ozdemir1, Zafer Asim Kaplancikli1, Mehlika Dilek Altintop1,
Halide Edip Temel2, and Gülşen Akalın Çiftçi2
1Department of Pharmaceutical Chemistry, Anadolu University, Faculty of Pharmacy, Eskişehir, Turkey and
2Department of Biochemistry, Anadolu University, Faculty of Pharmacy, Eskişehir, Turkey
Abstract
In the present study, some thiazole derivatives were synthesized via the ring closure reaction of 1-[2-(2-oxobenzo[d]
thiazol-3(2H)-yl)acetyl]thiosemicarbazide with various phenacyl bromides.The chemical structures of the compounds
were elucidated by 1H NMR, 13C NMR and mass spectral data and elemental analyses. Each derivative was evaluated
for its ability to inhibit acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) using a modification of Ellman’s
spectrophotometric method. The compounds were also investigated for their cytotoxic properties using MTT assay.
The most potent AChE inhibitor was found as compound 4e (IC50 =25.5 2.12 µg/mL) followed by compounds 4i
(IC =38.50 2.12 µg/mL), 4c (IC50 =58.42 3.14 µg/mL) and 4g (IC50 =68 2.12 µg/mL) when compared with eserine
(IC5500 =0.025 0.01 µg/mL). Effective compounds on AChE exhibited weak inhibition on BuChE (IC50 > 80 µg/mL).
MTT assay indicated that the cytotoxic dose (IC50 =71.67 7.63 µg/mL) of compound 4e was higher than its effective
dose.
Keywords: Thiazole, hydrazide, anticholinesterase activity, cytotoxicity
Introduction
termination of cholinergic neurotransmission, but the
function of BuChE is not so clear1,4
.
Drug design through enzyme inhibition has gained great
importance as a promising approach for the rational
discovery of new drugs due to the increasing need to dis-
cover more selective and potent inhibitors in an effort to
Acetylcholinesterase inhibitors (AChEIs) exert their
therapeutic action by inhibiting AChE, which results in
the enhancement of cholinergic action2. In particular,
AChEIs play a leading role in the first-line treatment
for symptoms of Alzheimer’s disease, which is the most
increase the therapeutic benefit to patients1,2
.
Cholinesterase inhibitors (ChEIs) have attracted a
great deal of interest among researchers owing to their
importance in the treatment of myasthenia gravis, glau-
coma and Alzheimer’s disease1–3
Two cholinesterases are present in humans: acetyl-
cholinesterase (AChE), which selectively hydrolyses ace-
tylcholine, and butyrylcholinesterase (BuChE), which
is a non-specific cholinesterase. e main difference
between two types of cholinesterase is the respective
preferences for substrates: the former hydrolyses ace-
tylcholine more quickly; the latter hydrolyses butyryl-
choline more quickly. e main function of AChE is the
common age-related neurodegenerative disorder5–9
.
In the last few decades, the chemistry of thiazoles and
their fused heterocyclic derivatives has received con-
siderable attention due to their synthetic and biological
importance. Compounds bearing thiazole moiety have
been reported to exhibit a wide spectrum of biological
.
effects including anticholinesterase activity10–16
.
Acotiamide hydrochloride (acotiamide; N-[2-
[bis(1-methylethyl)amino]ethyl]-2-[(2-hydroxy-4,
5-dimethoxybenzoyl)amino]thiazole-4-carboxamide
monohydrochloride trihydrate, Z-338) has been reported
Address for Correspondence: Dr. Zafer Asim Kaplancikli, Department of Pharmaceutical Chemistry, Anadolu University, Faculty of
Pharmacy, 26470 Eskişehir, Turkey. Tel: +90-222-3350580/3776. Fax: +90-222-3350750. E-mail: zakaplan@anadolu.edu.tr
(Received 21 November 2011; revised 22 December 2011; accepted 22 December 2011)
509

510 G. Turan-Zitouni et al.
to be a new selective AChEI for the treatment of func-
tional dyspepsia in clinical studies15.
collected by filtration, washed with water, dried, and
recrystallized from ethanol.
In a previous work, the inhibition of AChE by thia-
mine and its derivatives was investigated and structure-
activity relationship study was also carried out to identify
structural features that are associated with the inhibitory
potency of these compounds16.
Some researchers also carried out considerable
research for novel cholinesterase inhibitors bearing
amide and hydrazide moieties previously17.
2-(2-Oxobenzo[d]thiazol-3(2H)-yl)-N′-(4-phenylthiazol-2-yl)
acetohydrazide derivatives (4a–j)
A mixture of 1-[2-(2-oxobenzo[d]thiazol-3(2H)-yl)acetyl]
thiosemicarbazide (3) (0.001 mol) and appropriate phen-
acyl bromide (0.001 mol) was refluxed in ethanol (15 mL)
for 3 h. After cooling, the resulting solid was collected by
filtration, dried, and recrystallized from ethanol.
On the basis of these findings, we became interested
in biological evaluation of thiazoles as anticholinesterase
agents. Herein, we described the synthesis of novel thi-
azole derivatives bearing hydrazide moiety and focused
on their anticholinesterase effects on AChE and BuChE.
e compounds were also investigated for their cytotoxic
properties.
N′-(4-phenylthiazol-2-yl)-2-(2-oxobenzo[d]thiazol-3(2H)-yl)
acetohydrazide (4a)
1H NMR (400 MHz, DMSO-d6): δ 4.77 (2H, s), 7.10–7.45
(6H, m), 7.68 (2H, m), 7.84 (2H, m), 9.64 (1H, brs), 10.75
(1H, s).
13C NMR (100 MHz, DMSO-d6): δ 43.22 (CH2), 103.4
(CH), 111.3 (CH), 121.2 (C), 122.8 (CH), 123.3 (CH), 125.6
(2CH), 126.5 (CH), 127.5 (CH), 128.5 (2CH), 134.5 (C),
137.0 (C), 150.4 (C), 166.3 (C), 169.1 (C), 171.5 (C).
For C18H14N4O2S2, calculated: C, 56.53; H, 3.69; N, 14.65;
found: C, 56.52; H, 3.71; N, 14.61.
Methods
Chemistry
All reagents were purchased from commercial sup-
pliers and used without further purification. Melting
points (m.p.) were determined on a Electrothermal
9100 melting point apparatus (Weiss-Gallenkamp,
Loughborough, UK) and are uncorrected. Proton
nuclear magnetic resonance (1H NMR) spectra were
recorded on Bruker 400 MHz spectrometer (Bruker,
Billerica, MA, USA). Carbon nuclear magnetic reso-
nance (13C NMR) spectra were recorded on Bruker
100 MHz spectrometer (Bruker, Billerica, MA, USA).
Chemical shifts were expressed in parts per million
(ppm) and tetramethylsilane was used as an inter-
nal standard. Mass spectra were recorded on a VG
Quattro Mass spectrometer (Agilent, Minnesota, USA).
Elemental analyses were performed on a Perkin-Elmer
EAL 240 elemental analyser (Perkin-Elmer, Norwalk,
CT, USA).
MS (ES): [M + 1]+: 383
N′-(4-p-tolylthiazol-2-yl)-2-(2-oxobenzo[d]thiazol-3(2H)-yl)
acetohydrazide (4b)
1H NMR (400 MHz, DMSO-d6): δ 2.32 (3H, s), 4.77 (2H, s),
7.10–7.40 (5H, m), 7.68 (2H, m), 7.72 (2H, m), 9.60 (1H,
brs), 10.73 (1H, s).
13C NMR (100 MHz, DMSO-d6): δ 20.77 (CH3), 43.21
(CH2), 102.5 (CH), 111.4 (CH), 121.2 (C), 122.9 (CH),
123.3 (CH), 125.5 (2CH), 126.5 (CH), 129.1 (2CH), 131.9
(C), 136.8 (C), 137.0 (C), 150.5 (C), 166.3 (C), 169.1 (C),
171.5 (C).
For C19H16N4O2S2, calculated: C, 57.56; H, 4.07; N, 14.13;
found: C, 57.55; H, 4.05; N, 14.15.
MS (ES): [M + 1]+: 397
N′-(4-(4-chlorophenyl)thiazol-2-yl)-2-(2-oxobenzo[d]thiazol-
3(2H)-yl)acetohydrazide (4c)
General procedure for the synthesis of the compounds
Ethyl 2-(2-oxobenzo[d]thiazol-3(2H)-yl)acetate (1)
1H NMR (400 MHz, DMSO-d6): δ 4.78 (2H, s), 7.15–7.40
(3H, m), 7.46 (2H, m), 7.68 (2H, m), 7.85 (2H, m), 9.68
(1H, brs), 10.76 (1H, s).
A
mixture of benzo[d]thiazol-2(3H)-one (0.1 mol)
and ethyl chloroacetate (0.1 mol) in the presence of
potassium carbonate (0.1 mol) in acetone (50 mL) was
refluxed for 10 h. e reaction mixture was poured into
100 mL of ice–water mixture, filtered and washed with
water18.
13C NMR (100 MHz, DMSO-d6): δ 43.22 (CH2), 104.2
(CH), 111.3 (CH), 121.2 (C), 122.9 (CH), 123.3 (CH), 126.5
(CH), 127.2 (2CH), 128.6 (2CH), 131.9 (C), 133.4 (C), 137.0
(C), 149.2 (C), 166.3 (C), 169.1 (C), 171.7 (C).
For C18H13ClN4O2S2, calculated: C, 51.86; H, 3.14; N,
13.44; found: C, 51.85; H, 3.15; N, 13.40.
2-(2-Oxobenzo[d]thiazol-3(2H)-yl)acetohydrazide (2)
A mixture of the ester (1) (0.09 mol) and hydrazine
hydrate (0.18 mol) in ethanol (50 mL) was stirred at room
temperature for 3 h and then filtered18.
MS (ES): [M + 1]+: 418
N′-(4-(4-bromophenyl)thiazol-2-yl)-2-(2-oxobenzo[d]thiazol-
3(2H)-yl)acetohydrazide (4d)
1-[2-(2-Oxobenzo[d]thiazol-3(2H)-yl)acetyl]
thiosemicarbazide (3)
A mixture of the hydrazide (2) (0.05mol), potassium
thiocyanate (0.1 mol), conc. HCl (20 mL) in water (40 mL)
was refluxed for 3 h. After cooling, the resulting solid was
1H NMR (400 MHz, DMSO-d6): δ 4.77 (2H, s), 7.15–7.30
(3H, m), 7.36 (2H, m), 7.55–7.70 (2H, m), 7.78 (2H, m),
9.66 (1H, brs), 10.74 (1H, s).
13C NMR (100 MHz, DMSO-d6): δ 43.22 (CH2), 104.3
(CH), 111.3 (CH), 120.5 (C), 121.2 (C), 122.9 (CH), 123.3
Journal of Enzyme Inhibition and Medicinal Chemistry

Some thiazole derivatives as new cholinesterase inhibitors 511
(CH), 126.5 (CH), 127.6 (2CH), 131.5 (2CH), 133.7 (C),
137.0 (C), 149.3 (C), 166.3 (C), 169.2 (C), 171.7 (C).
For C18H13BrN4O2S2, calculated: C, 46.86; H, 2.84; N,
12.14; found: C, 46.85; H, 2.80; N, 12.15.
For C18H12Cl2N4O2S2, calculated: C, 47.90; H, 2.68; N,
12.41; found: C, 47.92; H, 2.70; N, 12.38.
MS (ES): [M + 1]+: 452
MS (ES): [M + 1]+: 462
N′-(4-(2,4-dichlorophenyl)thiazol-2-yl)-2-(2-oxobenzo[d]
thiazol-3(2H)-yl)acetohydrazide (4i)
1H NMR (400 MHz, DMSO-d6): δ 4.77 (2H, s), 7.05–7.35
(3H, m), 7.37 (1H, s), 7.48 (1H, dd, J= 8.5, 2.2 Hz), 7.63–
7.70 (2H, m), 7.88 (1H, d, J= 8.5 Hz), 9.68 (1H, brs), 10.75
(1H, s).
13C NMR (100 MHz, DMSO-d6): δ 43.22 (CH2), 109.0
(CH), 111.3 (CH), 121.2 (C), 122.8 (CH), 123.3 (CH), 126.5
(CH), 127.4 (CH), 129.7 (CH), 131.4 (C), 131.9 (C), 132.3
(CH), 132.4 (C), 137.0 (C), 145.7 (C), 166.3 (C), 169.1 (C),
170.7 (C).
N′-(4-(4-nitrophenyl)thiazol-2-yl)-2-(2-oxobenzo[d]thiazol-
3(2H)-yl)acetohydrazide (4e)
1H NMR (400 MHz, DMSO-d6): δ 4.78 (2H, s), 7.15–7.40
(3H, m), 7.66 (2H, s), 8.10 (2H, m), 8.27 (2H, m), 9.80 (1H,
brs), 10.81 (1H, s).
13C NMR (100 MHz, DMSO-d6): δ 43.22 (CH2), 108.3
(CH), 111.3 (CH), 121.2 (C), 122.9 (CH), 123.3 (CH), 124.0
(2CH), 126.4 (2CH), 126.5 (CH), 137.0 (C), 140.5 (C), 146.2
(C), 148.4 (C), 166.4 (C), 169.2 (C), 172.0 (C).
For C18H13N5O4S2, calculated: C, 50.58; H, 3.07; N, 16.38;
found: C, 50.55; H, 3.10; N, 16.35.
For C18H12Cl2N4O2S2, calculated: C, 47.90; H, 2.68; N,
12.41; found: C, 47.89; H, 2.71; N, 12.39.
MS (ES): [M + 1]+: 428
MS (ES): [M + 1]+: 452
N′-(4-(3-chlorophenyl)thiazol-2-yl)-2-(2-oxobenzo[d]thiazol-
3(2H)-yl)acetohydrazide (4f)
N′-(4-(2,5-dichlorophenyl)thiazol-2-yl)-2-(2-oxobenzo[d]
thiazol-3(2H)-yl)acetohydrazide (4j)
1H NMR (400 MHz, DMSO-d6): δ 4.77 (2H, s), 7.15–7.32
(3H, m), 7.40 (1H, dd, J= 8.6, 2.7 Hz), 7.47 (1H, s), 7.55
(1H, d, J= 8.6 Hz), 7.66 (1H, dd, J= 7.8, 1.2 Hz), 7.92 (1H,
d, J= 2.7 Hz), 9.71 (1H, brs), 10.76 (1H, s).
1H NMR (400 MHz, DMSO-d6): δ 4.77 (2H, s), 7.0–8.0 (9H,
m), 9.69 (1H, s), 10.75 (1H, s).
13C NMR (100 MHz, DMSO-d6): δ 43.21 (CH2), 105.0
(CH), 111.3 (CH), 121.2 (C), 122.9 (CH), 123.3 (CH), 124.1
(CH), 125.2 (CH), 126.5 (CH), 127.2 (CH), 130.5 (CH),
133.4 (C), 136.5 (C), 137.0 (C), 148.8 (C), 166.3 (C), 169.2
(C), 171.6 (C).
13C NMR (100MHz, DMSO-d6): δ43.21 (CH2), 109.8 (CH),
111.3 (CH), 121.2 (C), 122.8 (CH), 123.3 (CH), 126.4 (CH),
128.5 (CH), 129.1 (C), 130.3 (CH), 131.8 (C), 132.1 (CH), 134.3
(C), 137.0 (C), 145.3 (C), 166.3 (C), 169.1 (C), 170.7 (C).
For C18H12Cl2N4O2S2, calculated: C, 47.90; H, 2.68; N,
12.41; found: C, 47.88; H, 2.70; N, 12.38.
For C18H13ClN4O2S2, calculated: C, 51.86; H, 3.14; N,
13.44; found: C, 51.85; H, 3.16; N, 13.42.
MS (ES): [M + 1]+: 418
MS (ES): [M + 1]+: 452
N′-(4-(3-nitrophenyl)thiazol-2-yl)-2-(2-oxobenzo[d]thiazol-
3(2H)-yl)acetohydrazide (4g)
AChE and BuChE inhibitory activity
1H NMR (400 MHz, DMSO-d6): δ 4.78 (2H, s), 7.05–7.40
(3H, m), 7.61 (1H, s), 7.70 (2H, m), 8.14 (1H, dd, J= 8.1,
2.3 Hz), 8.27 (1H, d, J= 7.9 Hz), 8.64 (1H, t, J= 2.0 Hz), 9.78
(1H, brs), 10.80 (1H, s).
AChE and BuChE inhibitory activity was determined
by Ellman’s method with minor modifications (Electric
eel AChE enzyme was used instead of bovine AChE
enzyme and buffer was added 2.4 mL instead of 3 mL)19.
Compounds 4a–j were dissolved in DMSO and tested
at final concentration range 5–80 µg/mL. Twenty micro
litre of enzyme (AChE or BuChE, 1 U/mL), 10 µL sample
added to 2.4 mL buffer, the mixture was incubated at
37°C for 15 min. After 15 min incubation, 50 µL of 0.01 M
5,5′-dithio-bis(2-nitrobenzoic acid) and 20 µL of 75mM
acetylthiocholine iodide or 25 mM butyrylthiocholine
iodide were added, and the final mixture was incubated
at room temperature for 30 min. Blank was prepared
using 10 µL of DMSO instead of the test sample with all
other procedures similar to those used in the case of the
sample mixture. Absorbances were measured at 412 nm
and 37°C using polystyrol cuvets with spectrophotometer
(Shimadzu, UV-1700). Experiment was done in triplicate.
Data are expressed as mean standard deviation (SD).
e inhibition (percent) of AChE or BuChE was calcu-
lated using the following equation:
13C NMR (100 MHz, DMSO-d6): δ 43.21 (CH2), 106.2
(CH), 111.3 (CH), 119.9 (CH), 121.2 (C), 122.1 (CH), 122.9
(CH), 123.3 (CH), 126.5 (CH), 130.2 (CH), 131.6 (CH),
136.0 (C), 137.0 (C), 148.1 (C), 148.3 (C), 166.4 (C), 169.1
(C), 172.1 (C).
For C18H13N5O4S2, calculated: C, 50.58; H, 3.07; N, 16.38;
found: C, 50.59; H, 3.09; N, 16.34.
MS (ES): [M + 1]+: 428
N′-(4-(3,4-dichlorophenyl)thiazol-2-yl)-2-(2-oxobenzo[d]
thiazol-3(2H)-yl)acetohydrazide (4h)
1H NMR (400 MHz, DMSO-d6): δ 4.77 (2H, s), 7.0–7.4
(3H, m), 7.49 (1H, s), 7.62–7.67 (2H, m), 7.80 (1H, dd,
J = 8.5, 2.0 Hz), 8.06 (1H, d, J = 2.0 Hz), 9.70 (1H, brs),
10.75 (1H, s).
13C NMR (100 MHz, DMSO-d6): δ 43.23 (CH2), 105.7
(CH), 111.3 (CH), 121.2 (C), 122.9 (CH), 123.3 (CH), 125.6
(CH), 126.5 (CH), 127.1 (CH), 129.7 (C), 130.8 (CH), 131.4
(C), 135.0 (C), 137.0 (C), 147.8 (C), 166.3 (C), 169.1 (C),
171.7 (C).
I (%) = 100 − (ODsample/ODcontrol ) × 100
© 2013 Informa UK, Ltd.

512 G. Turan-Zitouni et al.
each well and after a few minutes at room temperature
to ensure that all crystals were dissolved, absorbance
was read at 540 nm with a microtitre plate spectropho-
tometer (Bio-Tek plate reader). Each concentration was
repeated in three wells and IC50 values were defined as
the drug concentrations that reduced absorbance to
50% of control values.
Toxicity
e level of cellular MTT (3-(4,5-dimethylthiazol-2-yl)-
2,5-diphenyltetrazolium bromide) (Sigma) reduction
was quantified as previously described in the litera-
ture with small modifications as represented below in
detail20,21
.
Cell culture and drug treatment
NIH/3T3 cells were obtained from the American Type
Culture Collection (ATCC, USA). e cells were incu-
bated in Dulbecco’s modified Eagle’s medium supple-
mented with 10% fetal calf serum (Life Technologies,
UK), 100 IU/mL penicillin (Gibco, Paisley, Scotland)
and 100 mg/mL streptomycin (Gibco) at 37°C in
a humidified atmosphere of 95% air and 5% CO2.
Exponentially growing cells were plated at 2 × 104 cells/
mL into 96-well microtiter tissue culture plates (Nunc,
Denmark) and incubated for 24 h before the addition
of the drugs (the optimum cell number for cytotoxicity
assays was determined in preliminary experiments).
Stock solutions of compounds were prepared in DMSO
(Sigma-Aldrich, Poole, UK) and further dilutions were
made with fresh culture medium (the concentration of
DMSO in the final culture medium was <0.1% which
had no effect on the cell viability).
Results and discussion
Initially,ethyl2-(2-oxobenzo[d]thiazol-3(2H)-yl)acetate
(1) was synthesized via the reaction of benzo[d]thiazol-
2(3H)-one with ethyl chloroacetate in the presence of
potassium carbonate. en, this ester (1) was converted
to the corresponding hydrazide derivative (2).
1-[2-(2-Oxobenzo[d]thiazol-3(2H)-yl)acetyl]thi-
osemicarbazide (3) was obtained by the reaction of the
hydrazide derivative (2) with potassium thiocyanate
and conc. HCl. e ring closure of compound 3 with
phenacyl bromides gave the target compounds (4a–j).
ese reactions are summarized in Scheme 1 and some
properties of the compounds are given in Table 1. e
structures of these compounds (4a–j) were confirmed
1
by H NMR, 13C NMR and mass spectral data and ele-
mental analyses.
e anticholinesterase effects of the compounds
(4a–j) on AChE and BuChE were determined by a
modification of Ellman’s spectrophotometric method
(Table 2).
MTT assay for cytotoxicity of the compounds
e MTT assay is widely used as a measure of cyto-
toxicity. After 24 h of preincubation, the tested com-
pounds were added to give final concentration in the
range 0.5–500 µg/mL and the cells were incubated for
24 h. At the end of this period, MTT was dissolved in
phosphate buffered saline at 5 mg/mL and filtered to
sterilize. At the time indicated above, stock MTT solu-
tion (20 μL/200 μL medium) was added to all wells of
assay, and the plates were incubated for 4 h at 37°C.
After the medium was removed, the formazan crystals
formed by MTT metabolism were solubilized by addi-
tion of 200 μL DMSO (instead of acid-isopropanol) to
Among these compounds (4a–j), compound 4e can
be identified as the most promising anticholinesterase
agent due to its inhibitory effect on AChE with an IC50
value of 25.5 2.12 µg/mL when compared with eserine
(IC50 =0.025 0.01 µg/mL). In our previous study, we also
reportedthatgalantamineexhibiteditsinhibitoryeffecton
AChE with an IC50 value of 0.28 0.04 µg/mL22. Compound
4e also showed the highest AChE inhibitory effect when
compared with galantamine. Although compounds 4e
and 4g possess nitro substituent on phenyl ring, they
show different levels of anticholinesterase activity. e
Scheme 1. e synthetic protocol of the title compounds (4a–j).
Journal of Enzyme Inhibition and Medicinal Chemistry

Some thiazole derivatives as new cholinesterase inhibitors 513
Table 1. Some properties of the synthesized compounds (4a–j).
Table 3. In vitro cytotoxicity of the compounds (4a–j).
Yield m.p. Molecular
(%) (°C) formula
Molecular
weight
Compound
IC50 (µg/mL)a
52.67 23.69
18.50 1.32
46.67 2.88
75.00 21.79
71.67 7.63
42.67 6.43
4.93 0.11
Compound
R
4a
4b
4c
4d
4e
4f
4g
4h
4i
4a
4b
4c
4d
4e
4f
H
64
67
75
69
89
68
87
72
71
70
227 C18H14N4O2S2
224 C19H16N4O2S2
239 C18H13ClN4O2S2
255 C18H13BrN4O2S2
252 C18H13N5O4S2
229 C18H13ClN4O2S2
256 C18H13N5O4S2
240 C18H12Cl2N4O2S2
231 C18H12Cl2N4O2S2
235 C18H12Cl2N4O2S2
382.46
396.49
416.90
461.36
427.46
416.90
427.46
451.35
451.35
451.35
p-CH3
p-Cl
p-Br
p-NO2
m-Cl
m-NO2
3,4-Cl
2,4-Cl
2,5-Cl
28.33 5.77
52.33 7.50
103.33 20.81
4g
4h
4i
4j
aCytotoxicity of compounds to mouse fibroblast (NIH/3T3) cell
line. Incubation for 24h. IC50 is the drug concentration required
to inhibit 50% of the cell growth. e values represent mean
standard deviation of triplicate determinations.
4j
m.p., melting point.
Table 2. e anticholinesterase activities of the compounds
(4a–j) as IC50 values (µg/mL).
study indicated that compound 4g possessed the highest
cytotoxicity, whereas compound 4j exhibited the lowest
cytotoxicity against mouse fibroblast (NIH/3T3) cell line
among the title compounds.
AChE
80 µg/mL
BuChE
80 µg/mL
(%
inhibition) µg/mL
(%
IC50
µg/mL
IC50
inhibition)
Compound
4a
4b
NA
NA
NA
NA
32.95 1.78
20.51 0.77
>80
>80
Conclusion
4c
4d
4e
4f
4g
4h
4i
4j
67.02 2.52 58.42 3.14 6.04 3.17
4.74 0.84 >80 NA
93.30 2.30 25.5 2.12 24.78 3.75
>80
In the present paper, we synthesized a series of thiazole
derivatives and evaluated their anticholinesterase effects
and cytotoxicity.
e biological results indicate that functional groups
on the phenyl ring have a considerable influence on
anticholinesterase activity and toxicity. In particular,
compound 4e is the most promising AChEI due to its
inhibitory effect on AChE with an IC50 value of 25.5 2.12
µg/mL. In addition, the cytotoxic dose (IC50 = 71.67 7.63
µg/mL) of compound 4e is higher than its effective dose.
NA
>80
6.38 1.49
59.12 3.54
20.93 2.09
>80
68 2.12
>80
12.60 1.62
5.85 0.53
14.04 3.15
>80
>80
>80
84.90 2.67 38.50 2.12 18.75 3.58
>80
10.53 2.16
–
>80
NA
NA
Eserine
0.025 0.01
0.05 0.02
NA, not active.
former bearing p-nitro group exhibits the inhibitory effect
on AChE with an IC50 value of 25.5 2.12 µg/mL, whereas
the latter bearing m-nitro group exhibits the inhibitory
effect on AChE with an IC50 value of 68 2.12 µg/mL.
Compounds 4e and 4g also exhibit different levels of
cytotoxicity with IC50 values of 71.67 7.63 and 4.93 0.11
µg/mL, respectively. ese observations indicate that the
position of nitro substituent on phenyl ring has a crucial
influence on anticholinesterase activity and cytotoxicity.
It is apparent that there is a positive correlation between
anticholinesterase activity and p-nitro group. Compound
4i carrying 2,4-dichloro group on phenyl ring exhibits the
inhibitory effect on AChE with an IC50 value of 38.50 2.12
µg/mL, whilst compound 4c bearing p-chloro group on
phenyl ring exhibits the inhibitory effect on AChE with
an IC50 value of 58.42 3.14 µg/mL. Compounds 4d, 4f,
4h, 4j exhibit weak inhibition on AChE (IC50 > 80 µg/mL),
whereas compounds 4a and 4b are inactive.
Declaration of interest
e authors report no conflicts of interest.
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