Design, synthesis and evaluation of new thiazole-piperazines as acetylcholinesterase inhibitors

Article abstract of DOI:10.3109/14756366.2012.709242

In this study, some new 2-(4-substituted piperazine-1-yl)-N-[4-(2- methylthiazol-4-yl)phenyl]acetamide derivatives were synthesized. The synthesized compounds were screened for their anticholinesterase activity on acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) enzymes by in vitro Ellman's method. The structural elucidation of the compounds was performed by using IR, ¹H-NMR, ¹³C-NMR and FAB⁺-MS spectral data and elemental analyses results. Biological assays revealed that at 0.1 μM concentration, the most active compounds against AChE were 5n, 5o and 5p that indicated 96.44, 99.83 and 89.70% inhibition rates, respectively. Besides, IC50 value of the compound 5o was determined as 0.011 μM, whereas IC50 value of standard drug donepezil was 0.054 μM. The synthesized compounds did not show any notable inhibitory activity against BChE.

Full text of DOI:10.3109/14756366.2012.709242

Journal of Enzyme Inhibition and Medicinal Chemistry, 2013; 28(5): 1040–1047
2013 Informa UK, Ltd.
©
ISSN 1475-6366 print/ISSN 1475-6374 online
DOI: 10.3109/14756366.2012.709242
ReseaRꢀh aRꢁIꢀle
Design, synthesis and evaluation of new thiazole-piperazines
as acetylcholinesterase inhibitors
1
1,2
1
Leyla Yurttaş , Zafer Asım Kaplancıklı , and Yusuf Özkay
1
Department of Pharmaceutical Chemistry, Faculty of Pharmacy, Anadolu University, Eskişehir, Turkey and
2
Department of Pharmaceutical Chemistry, Anadolu University, Graduate School of Health Sciences, Eskisehir, Turkey
abꢂtrꢃct
In this study, some new 2-(4-substituted piperazine-1-yl)-N-[4-(2-methylthiazol-4-yl)phenyl]acetamide
derivatives were synthesized. The synthesized compounds were screened for their anticholinesterase activity on
acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) enzymes by in vitro Ellman’s method. The structural
1
13
+
elucidation of the compounds was performed by using IR, H-NMR, C-NMR and FAB -MS spectral data and elemental
analyses results. Biological assays revealed that at 0.1 µM concentration, the most active compounds against AChE
were 5n, 5o and 5p that indicated 96.44, 99.83 and 89.70% inhibition rates, respectively. Besides, IC50 value of the
compound 5o was determined as 0.011 µM, whereas IC50 value of standard drug donepezil was 0.054 µM. The
synthesized compounds did not show any notable inhibitory activity against BChE.
Kꢄywordꢂ: Anticholinesterase activity, Elmann’s method, thiazole, piperazine
Introduction
or atrophy of the basal forebrain cholinergic neurons. e
loss of basal forebrain cholinergic cells results in an impor-
tant reduction in ACh level, which plays an important role
Acetylcholine (ACh) acts as an excitatory neurotransmit-
ter for voluntary muscles in the somatic nervous system
and as a preganglionic and a postganglionic transmitter
in the parasympathetic nervous system of vertebrates
and invertebrates . Acetylcholinesterase (AChE) is a
terminator enzyme of nerve impulse transmission at the
cholinergic synapses by quick hydrolysis of ACh to cho-
line and acetate. Inhibition of AChE evolves a strategy for
the treatment of several diseases as Alzheimer’s disease
7
in the cognitive impairment associated with AD .
Disruption of cholinergic transmission in AD was
1
,2
8,9
proved in many clinical and neuropathological studies .
As well as deficit of ACh, the loss of presynaptic M
2
0
1
muscarinic and nicotinic receptors has also been found .
ere are also evidences of an interaction between AChE
and Aβ, which is participated in plaques and plays an
essential role in AD pathophysiology. AChE constitutes a
stable complex with senile plaque components and may
even enhance the aggregation of Aβpeptides and amyloid
formation. e neurotoxicity of amyloid components
(AD), senile dementia, ataxia, myasthenia gravis and
3
Parkinson’s disease . AD is one form of senile dementia
which occurs due to various neuropathological conditions
such as senile plaques and neurofibrillary tangles. It is the
most common dementias that affects half of the popula-
1
1,12
may be risen up by the presence of AChE . In contrast
to the overall decrease of AChE in AD brains, at least in
its later stages, the local concentration of AChE around
4
,5
tion aged 85 years and seventh main cause of life lost
affecting 5.3 million people over the world. In AD, growing
numbers of nerve cells degenerate and die along with loss
in synapse through which information flows from and to
the brain. As a result cognitive impairment and dementia
1
3
the plaques increases as these lesions occur . In addition
to hydrolysing ACh, AChE may be also involved in other
functions such as cell proliferation, differentiation, and
responses to various damaging factors including stress
6
occur . e neuropathology of AD is generally character-
1
1,14
ized by the presence of numerous amyloid β-peptide (Aβ)
plaques, neurofibrillary tangles (NFT), and degeneration
and amyloid formation . Hence, for the most part,
inhibitors of AChE, enhancing the ACh concentration in
Address for Correspondence: Zafer Asım Kaplancıklı, Anadolu University, Faculty of Pharmacy, Department of Pharmaceutical Chemistry,
6470 Eskişehir, Turkey. Tel.: +90-222-3350580/3776; Fax: +90-222-3350750. E-mail: zakaplan@anadolu.edu.tr
Received 04 June 2012; revised 25 June 2012; accepted 25 June 2012)
2
(
1
040

New thiazole derivatives as acetylcholinesterase inhibitors 1041
2
0–22
23–25
the brain, have been introduced to the market for treating
mild-to-moderate AD.
activity of some thiazole
and piperazine
derivatives
was reported. As a result, we synthesized thiazole-piperazine
derivatives so as to investigate their cholinesterase inhibitory
potency, which will enable to study in vivo pharmacological
activity against AD on animal models.
Consistent with reported studies, cholinesterase inhibi-
tors contain a basic centre, a core ring system and a linker
such as –O–, CH , CONH, CONH(CH ) etc. between core
2
2 n
15–17
ring and basic centres . For example, chemical struc-
tures of AChE inhibitors donepezil and BYYT-25 fit well to
such definition. ese agents contain an indan as a core
ring, methylene or oxygen as a linker and piperidine or
pyrrolydine cyclic amines as a basic centre. In the light of
above structural motif, we designed a new series of thia-
zole–piperazine derivatives (Figure 1). e reason for the
choice of thiazole and piperazine moieties was their AChE
inhibitory potency. Namely, thiazole based biomolecule
thiamine (vitamin B1) and its analogues were described
Mꢃtꢄriꢃꢅꢂ ꢃnd mꢄtꢆodꢂ
Chemistry
All chemicals were purchased from Sigma-Aldrich
Chemical Co. All melting points (m.p.) were determined
by Electrothermal 9100 digital melting point apparatus
and were uncorrected. Spectroscopic data were recorded
1
with the following instruments: H-NMR, Bruker 400
1
3
MHz spectrometer; C-NMR, Bruker 100 MHz spec-
trometer; MS-FAB, VG Quattro Mass spectrometer and
elemental analyses were performed on a Perkin Elmer
EAL 240 elemental analyser. Some characteristics of the
compounds are given in Table 1.
18
as AChE inhibitors . Acotiamide, new thiazole based drug
that enhances ACh release in the enteric nervous system via
muscarinic receptor antagonism and AChE inhibition was
19
discovered . Besides, in previous studies, cholinesterase
Figure 1. Structural motifs of AChE inhibitors BYYT-25, Donepezil, Acotiamide, and the synthesized compounds 5a–5p.
Table 1. Some physicochemical characteristics of the synthesized compounds.
Molecular
Compound
R
Yield (%)
70
M.p. (°C)
119
Molecular formula
C H N OS
weight
330
344
398
392
406
422
426.5
410
437
406
422
406
422
393
406
410
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
a
b
c
d
e
f
g
h
i
j
k
l
m
n
o
p
Methyl
1
7
22
4
Ethyl
72
90
C H N OS
18 24 4
Cyclohexyl
Phenyl
75
128
C H N OS
22 30 4
80
160
C H N OS
22 24 4
4-Methylphenyl
4-Methoxyphenyl
4-Chlorophenyl
4-Florophenyl
4-Nitrophenyl
3-Methylphenyl
3-Methoxyphenyl
2-Methylphenyl
2-Methoxyphenyl
2-Pyridyl
81
172–175
180
C H N OS
23 26 4
73
C H N O S
23 26 4 2
75
176
C H ClN OS
22 23 4
80
227
C H FN OS
22 23 4
76
283–286
190
C H N O S
22 23 5 3
72
C H N OS
23 26 4
74
143
C H N O S
23 26 4 2
75
142
C H N OS
23 26 4
70
168
C H N O S
23 26 4 2
71
167
C H N OS
21 23 5
Benzyl
82
140
C H N OS
23 26 4
2-Furoyl
76
146
C H N O S
21 22 4 3
©
2013 Informa UK, Ltd.

1
042 L. Yurttaş et al.
1
Synthesis of the compounds
N-[4-(2-Bromoacetyl)phenyl]acetamide (1)
H NMR (400 MHz, DMSO-d6): 2.14 (3H, s, N-CH ),
3
2.35-2.48 (8H, m, piperazine C-H), 2.67 (3H, s, C–CH ),
3
4
′-aminoacetophenone (0.05 mol, 6.75 g) and trieth-
3.09 (2H, s, CO–CH ), 7.66 (2H, d, J = 9.2 Hz, Ar-H), 7.77
2
ylamine (0.06 mol, 8.34 mL) were dissolved in THF
(1H, s, thiazole C -H), 7.84 (2H, d, J = 8.8 Hz, Ar-H), 9.74
5
(
(
100 mL) with a constant stirring at 0–5°C. Acetyl chloride
0.06 mol, 4.78 mL) was added dropwise to this solution
(1H, s, N–H).
1
3
C NMR (100 MHz, DMSO-d ): 19.59 (CH ), 46.43
6
3
gradually. e reaction mixture thus obtained was fur-
ther agitated for 1 h at room temperature. After evapora-
tion of solvent the residue was filtered and washed with
water and dried. en the obtained N-(4-acetylphenyl)
acetamide (0.04, 7.08 g mol) was brominated in 30 mL
acetic acid with the presence of 0.05 mol (2.58 mL) bro-
mine and 0.5 mL HBr to give N-[4-(2-bromoacetyl)phe-
nyl]acetamide (1) in 86% yield.
(CH ), 53.39 (2CH ), 55.23 (2CH ), 62.49 (CH ), 113.15
(CH), 120.13 (2CH), 127.01 (2CH), 130.15 (C), 138.92 (C),
154.27 (C), 166.02 (C), 168.98 (C).
3 2 2 2
For C H N OS calculated: 61.79% C, 6.71% H, 16.95%
1
7
22
4
N; found: 61.75% C, 6.70% H, 16.91% N.
+
MS (FAB) [M + 1] : m/z 331.
2-(4-Ethylpiperazine-1-yl)-N-[4-(2-methylthiazol-4-yl)pheny])
acetamide (5b)
−1
N-[4-(2-Methyl-4-thiazolyl)phenyl]acetamide (2)
IR (KBr) νmax(cm ): 3280 (amide N–H), 3054 (aromatic
C–H), 2940 (aliphatic C–H), 1680 (amide C=O), 1594-
1401 (C=C and C=N), 1280–1019 (C–N and C–O).
N-[4-(2-bromoacetyl)phenyl]acetamide
(0.03 mol,
7
.68 g) (1) and thioacetamide (0.03 mol, 2.25g) were
1
stirred in ethanol at room temperature for 48 h. e pre-
cipitated solid was filtered, dried and recrystallized from
ethanol to afford title compound in 78% yield.
H NMR (400 MHz, DMSO-d6): 0.99 (3H, t, J = 7.2, 7.2
Hz, CH –CH ), 2.32 (2H, q, J = 7.2, 14.2 Hz, CH –CH ), 2.42-
2
3
2
3
2.53 (8H, m, piperazine C-H), 2.71 (3H, s, C–CH ), 3.12 (2H,
3
s, CO–CH ), 7.69 (2H, d, J = 8.4 Hz, Ar–H), 7.81 (1H, s, thia-
2
4
-(2-Methyl-4-thiazolyl)aniline (3)
N-[4-(2-methyl-4-thiazolyl)phenyl]acetamide
0.025 mol, 5.8 g) (2) was refluxed in ethanol (15 mL) with
N HCl solution (10 mL). e reaction was monitored by
zole C -H), 7.86 (2H, d, J = 8.8 Hz, Ar–H), 9.76 (1H, s, N–H).
5
1
3
C NMR (100 MHz, DMSO-d ): 16.81 (CH ), 19.59
6
3
(
1
(CH ), 28.02 (CH ), 53.86 (2CH ), 55.47 (2CH ), 63.06
3 2 2 2
(CH ), 113.23 (CH), 120.47 (2CH), 127.08 (2CH), 130.76
2
TLC. When the reaction was completed, the mixture was
poured into ice water, neutralized with 10% NaOH solu-
tion and then filtered to give 4-(2-Methyl-4-thiazolyl)
aniline (3) in 92% yield.
(C), 139.02 (C), 154.47 (C), 166.16 (C), 169.00 (C).
For C H N OS calculated: 62.76% C, 7.02% H, 16.26%
1
8
24
4
N; found: 62.74% C, 7.01% H, 16.25% N.
+
MS (FAB) [M + 1] : m/z 345.
2
-Chloro-N-[4-(2-methyl-4-thiazolyl)phenyl]acetamide (4)
2-(4-Cyclohexylpiperazine-1-yl)-N-[4-(2-methylthiazol-4-yl)
Chloroacethyl chloride (0.025 mol, 2 mL) was added
dropwise over 15 min to a magnetically stirred solu-
tion of the 4-(2-Methyl-4-thiazolyl)aniline (0.022 mol,
pheny])acetamide (5c)
−1
IR (KBr) νmax(cm ): 3288 (amide N–H), 3056 (aromatic
C–H), 2991 (aliphatic C–H), 1675 (amide C=O), 1568–
1407 (C=C and C=N), 1311–1020 (C–N and C–O).
4
.18 g) (3) and triethylamine (0.025 mol, 3.48 mL) in dry
1
THF (15 mL). e reaction was monitored by TLC. After
the reaction was completed, the solvent was evaporated
under reduced pressure. Water was added to wash
the resulting solid, the mixture was filtered, dried and
recrystallized from ethanol to afford compound 4 in
H NMR (400 MHz, DMSO-d6): 1.16–1.24 (5H, m,
cyclohexyl C–H), 1.59–1.86 (5H, m, cyclohexyl C–H),
2.22–2.26 (1H, m, cyclohexyl C–H), 2.51–2.62 (8H, m,
piperazine C–H), 2.73 (3H, s, C–CH ), 3.09 (2H, s, CO–
3
CH ), 7.22 (1H, s, thiazole C -H), 7.59 (2H, d, J = 8.4 Hz,
2
5
8
3% yield.
Ar–H), 7.81 (2H, d, J = 8.8 Hz, Ar–H), 9.18 (1H, s, N–H).
1
3
C NMR (100 MHz, DMSO-d ): 19.52 (CH ), 26.04
6
3
General procedure for 2-(4-substituted piperazine-1-yl)-N-[4-
2-methylthiazol-4-yl)phenyl]acetamide derivatives (5a–5p)
(2CH ), 26.49 (CH ), 29.20 (2CH ), 49.33 (2CH ), 54.23
(2CH ), 62.24 (CH ), 63.62 (CH), 111.81 (CH), 119.72
2 2
2 2 2 2
(
A mixture of compound 4 (0.001 mol, 0.266 g), appro-
(2CH), 127.16 (2CH), 130.77 (C), 137.61 (C), 154.82 (C),
166.08 (C), 168.72 (C).
priate piperazine derivative (0.0011 mol) and K CO
2
3
(0.001 mol, 0.138 g) in acetone (15 mL) was refluxed
For C H N OS calculated: 66.30% C, 7.59% H, 14.06%
2
2
30
4
for 2 h. After cooling, the solvent was evaporated until
dryness. e residue was treated with 25mL of water.
Solidified product was filtered, washed with water and
recrystallized from ethanol to give the 5a–5p.
N; found: 66.32% C, 7.52% H, 14.02% N.
+
MS (FAB) [M + 1] : m/z 399.
2-(4-Phenylpiperazine-1-yl)-N-[4-(2-methylthiazol-4-yl)
phenyl]acetamide (5d)
−
1
2
-(4-Methylpiperazine-1-yl)-N-[4-(2-methylthiazol-4-yl)
IR (KBr) νmax(cm ): 3284 (amide N–H), 3053 (aromatic
C–H), 2958 (aliphatic C–H), 1676 (amide C=O), 1596–
1412 (C=C and C=N), 1302–1025 (C–N and C–O).
phenyl]acetamide (5a)
IR (KBr) νmax(cm ): 3282 (amide N–H), 3042 (aromatic
C–H), 2978 (aliphatic C–H), 1679 (amide C=O), 1584–
−1
1
H NMR (400 MHz, DMSO-d6): 2.67–2.69 (4H, m,
1
411 (C=C and C=N), 1309-1018 (C–N and C–O).
piperazine C–H), 2.71 (3H, s, C–CH ), 3.20–3.22 (6H, m,
3
Journal of Enzyme Inhibition and Medicinal Chemistry

New thiazole derivatives as acetylcholinesterase inhibitors 1043
1
piperazine C–H and CO–CH ), 6.78 (1H, t, J = 7.2, 7.2,
H NMR (400 MHz, DMSO-d6): 2.67 (4H, t, J = 4.4, 4.8
2
Ar–H), 6.94 (2H, d, J = 7.6 Hz, Ar–H), 7.21 (2H, t, J = 8, 8 Hz,
Ar–H), 7.71 (2H, d, J = 8.8 Hz, Ar–H), 7.81 (1H, s, thiazole
Hz, piperazine C–H), 2.71 (3H, s, C–CH ), 3.21 (4H, t, J =
3
4.4, 4.4 Hz, piperazine C–H), 3.35 (2H, s, CO–CH ), 6.95
2
C -H), 7.88 (2H, d, J = 8.8 Hz, Ar–H), 9.85 (1H, s, N–H).
(2H, d, J = 8.8 Hz, Ar–H), 7.23 (2H, d, J = 8.8 Hz, Ar–H),
5
1
3
C NMR (100 MHz, DMSO-d ): 19.60 (CH ), 53.52
7.72 (2H, t, J = 9.2 Hz, Ar–H), 7.81 (1H, s, thiazole C -H),
6
3
5
(
(
(
2CH ), 53.65 (2CH ), 62.48 (CH ), 113.18 (CH), 116.12
2CH), 119.02 (CH), 120.78 (2CH), 127.49 (2CH), 129.14
2CH), 130.15 (C), 138.92 (C), 151.28 (C), 154.27 (C),
7.88 (2H, d, J = 9.2 Hz, Ar–H), 9.85 (1H, s, N–H).
2
2
2
13
C NMR (100 MHz, DMSO-d ): 19.59 (CH ), 52.47 (2CH ),
6 3 2
54.88 (2CH ), 62.73 (CH ), 113.77 (CH), 120.14 (2CH), 121.58
2
2
1
66.22 (C), 167.95 (C).
(2CH), 127.56 (2CH), 128,49 (C), 130.23 (C), 132.69 (2CH),
138.86 (C), 152.63 (C), 154.16 (C), 166.45 (C), 168.89 (C).
For C H ClN OS calculated: 61.89% C, 5.43% H,
For C H N OS calculated: 67.32% C, 6.16% H, 14.27%
2
2
24
4
N; found: 67.30% C, 6.14% H, 14.26% N.
2
2
23
4
+
MS (FAB) [M + 1] : m/z 393.
13.12% N; found: 61.84% C, 5.41% H, 13.00% N.
+
MS (FAB) [M + 1] : m/z 427.5.
2
4
-[4-(4-Methylphenyl)piperazine-1-yl]-N-[4-(2-methylthiazol-
-yl)phenyl]acetamide (5e)
2-[4-(4-Florophenyl)piperazine-1-yl]-4-[4-(2-methylthiazol-
4-yl)phenyl]acetamide (5h)
−
1
IR (KBr) νmax(cm ): 3285 (amide N–H), 3012 (aromatic
C–H), 2963 (aliphatic C–H), 1678 (amide C=O), 1595–
1
−1
IR (KBr) νmax(cm ): 3277 (amide N–H), 3044 (aromatic
C–H), 2973 (aliphatic C–H), 1680 (amide C=O), 1589–
1410 (C=C and C=N), 1296–1012 (C–N and C–O).
413 (C=C and C=N), 1294–1026 (C–N and C–O).
1
H NMR (400 MHz, DMSO-d6): 2.18 (3H, s, C–CH ),
3
1
2
3
6
7
7
.64–2.66 (4H, m, piperazine C–H), 2.69 (3H, s, C–CH ),
H NMR (400 MHz, DMSO-d6): 2.68 (4H, t, J = 4.4, 4.8 Hz,
3
.12–3.14 (4H, m, piperazine C–H), 3.18 (2H, s, CO–CH ),
piperazine C–H), 2.71 (3H, s, C–CH ), 3.16 (4H, t, J = 4.4, 4.4
2
3
.83 (2H, d, J = 8.8 Hz, Ar–H), 7.00 (2H, d, J = 8 Hz, Ar–H),
Hz, piperazine C–H), 3.21 (2H, s, CO–CH ), 6.92–7.07 (4H,
2
.69 (2H, d, J = 8, 4 Hz, Ar–H), 7.80 (1H, s, thiazole C -H),
m, Ar–H), 7.71 (2H, d, J = 9.2 Hz, Ar–H), 7.82 (1H, s, thiazole
5
.86 (2H, d, J = 8.8 Hz, Ar–H), 9.82 (1H, s, N–H).
C -H), 7.88 (2H, d, J = 8.8 Hz, Ar–H), 9.85 (1H, s, N–H).
5
1
3
13
C NMR (100 MHz, DMSO-d ): 19.60 (CH ), 21.33
C NMR (100 MHz, DMSO-d ): 19.54 (CH ), 52.47
6
3
6
3
(
(
(
CH ), 53.47 (2CH ), 55.84 (2CH ), 62.73 (CH ), 113.39
CH), 120.56 (2CH), 121.56 (2CH), 127.73 (2CH), 130.73
C), 132.48 (2CH), 138.92 (C), 139.46 (C), 141.63 (C),
(2CH ), 54.49 (2CH ), 62.79 (CH ), 113.25 (CH), 115.62
3
2
2
2
2 2 2
(2CH), 117.83 (2CH), 120.88 (2CH), 127.83 (2CH), 130.45
(C), 138.86 (C), 147.80 (C), 154.16 (C), 158.32 (C), 166.45
(C), 168.89 (C).
1
54.54 (C), 166.79 (C), 168.78 (C).
For C H N OS calculated: 67.95% C, 6.45% H, 13.78%
For C H FN OS calculated: 64.37% C, 5.65% H,
2
3
26
4
22 23
4
N; found: 67.93% C, 6.47% H, 13.74% N.
13.65% N; found: 64.40% C, 5.61% H, 13.62% N.
+
+
MS (FAB) [M + 1] : m/z 407.
MS (FAB) [M + 1] : m/z 411.
2
-[4-(4-Methoxyphenyl)piperazine-1-yl]-N-[4-(2-
2-[4-(4-Nitrophenyl)piperazine-1-yl]-N-[4-(2-methylthiazol-
methylthiazol-4-yl)phenyl]acetamide (5f)
IR (KBr) νmax(cm ): 3282 (amide N–H), 3050 (aromatic
4-yl)pheny]acetamide (5i)
IR (KBr) νmax(cm ): 3278 (amide N–H), 3020 (aromatic
−
1
−1
C–H), 2943 (aliphatic C–H), 1679 (amide C=O), 1585–
C–H), 2943 (aliphatic C–H), 1677 (amide C=O), 1598–
1
414 (C=C and C=N), 1305–1018 (C–N and C–O).
H NMR (400 MHz, DMSO-d6): 2.76 (3H, s, C–CH ), 2.80
1477 (C=C and C=N), 1311–1045 (C–N and C–O).
1
1
H NMR (400 MHz, DMSO-d6): 2.68 (4H, t, J = 4.4, 4.8
3
(4H, t, J = 4.8, 4.8 Hz, piperazine C–H), 3.17 (4H, t, J = 4.8,
Hz, piperazine C–H), 2.71 (3H, s, C–CH ), 3.34 (2H, s,
3
4
.8 Hz, piperazine C–H), 3.21 (2H, s, CO–CH ), 3.78 (3H,
CO–CH ), 3.55 (4H, t, J = 5.2, 4.4 Hz, piperazine C–H), 7.04
2
2
s, O–CH ), 6.86 (2H, d, J = 8.4 Hz, Ar–H), 6.92 (2H, d, J = 8.8
(2H, d, J = 8.8 Hz, Ar–H), 7.71 (2H, d, J = 8.8 Hz, Ar–H),
3
Hz, Ar–H), 7.25 (1H, s, thiazole C -H), 7.64 (2H, d, J = 8, 8
7.81 (1H, s, thiazole C -H), 7.88 (2H, d, J = 8.4 Hz, Ar–H),
5
5
Hz, Ar–H), 7.85 (2H, d, J = 8.4 Hz, Ar–H), 9.20 (1H, s, N–H).
8.06 (2H, d, J = 9.2 Hz, Ar–H), 9.88 (1H, s, N–H).
1
3
13
C NMR (100 MHz, DMSO-d ): 19.32 (CH ), 50.91
C NMR (100 MHz, DMSO-d ): 19.61 (CH ), 53.96
6
3
6
3
(
(
(
(
2CH ), 53.66 (2CH ), 55.56 (CH ), 62.02 (CH ), 111.61
(2CH ), 55.88 (2CH ), 62.49 (CH ), 112.14 (2CH), 113.29
2
2
3
2
2 2 2
CH), 114.51 (2CH), 118.35 (2CH), 119.48 (2CH), 126.98
2CH), 130.67 (C), 137.32 (C), 145 (C), 154.08 (C), 154.60
C), 165.85 (C), 168.14 (C).
(CH), 120.83 (2CH), 127.25 (2CH), 127.93 (2CH), 130.89
(C), 138.92 (C), 139.52 (C), 154.21 (C), 156.19 (C), 166.56
(C), 168.78 (C).
For C H N O S calculated: 65.38% C, 6.20% H, 13.26%
For C H N O S calculated: 60.39% C, 5.30% H, 16.01%
2
3
26
4
2
22 23
5
3
N; found: 65.34% C, 6.23% H, 13.24% N.
N; found: 60.36% C, 5.32% H, 16.03% N.
+
+
MS (FAB) [M + 1] : m/z 423.
MS (FAB) [M + 1] : m/z 438.
2
4
-[4-(4-Chlorophenyl) piperazine-1-yl]-N-[4-(2-methylthiazol-
2-[4-(3-Methylphenyl)piperazine-1-yl]-N-[4-(2-methylthiazol-
-yl)phenyl]acetamide (5g)
4-yl)phenyl]acetamide (5j)
−
1
−1
IR (KBr) νmax(cm ): 3279 (amide N–H), 3052 (aromatic
IR (KBr) νmax(cm ): 3282 (amide N–H), 3041 (aromatic
C–H), 2947 (aliphatic C–H), 1673 (amide C=O), 1579–
C–H), 2963 (aliphatic C–H), 1683 (amide C=O), 1589–
1
445 (C=C and C=N), 1289–1030 (C–N and C–O).
1427 (C=C and C=N), 1311–1040 (C–N and C–O).
©
2013 Informa UK, Ltd.

1
044 L. Yurttaş et al.
1
H NMR (400 MHz, DMSO-d6): 2.33 (3H, s, C–CH ),
2-[4-(2-Methoxyphenyl)piperazine-1-yl]-N-[4-(2-
3
2
.76 (3H, s, C–CH ), 2.80 (4H, t, J = 4.8, 4.8 Hz, pipera-
methylthiazol-4-yl)phenyl]acetamide (5m)
3
−1
zine C–H), 3.21 (2H, s, CO–CH ), 3.26 (4H, t, J = 4.8, 4.8
Hz, piperazine C–H), 6.71–6.77 (3H, m, Ar–H), 7.17 (1H,
t, J = 7.6, 7.6 Hz, Ar–H), 7.25 (1H, s, thiazole C -H), 7.63
IR (KBr) νmax(cm ): 3281 (amide N–H), 3054 (aromatic
C–H), 2976 (aliphatic C–H), 1680 (amide C=O), 1596–
1414 (C=C and C=N), 1301–1019 (C–N and C–O).
2
5
1
(
9
2H, t, J = 9.2 Hz, Ar–H), 7.85 (2H, d, J = 8.4 Hz, Ar–H),
.20 (1H, s, N–H).
H NMR (400 MHz, DMSO-d6): 2.66–2.70 (4H, m,
piperazine C–H), 2.71 (3H, s, C–CH ), 3.04 (4H, brs,
3
1
3
C NMR (100 MHz, DMSO-d ): 19.33 (CH ), 21.77
piperazine C–H), 3.32 (2H, s, CO–CH ), 3.77 (3H, s, O–
6
3
2
(
(
(
(
CH ), 49.59 (2CH ), 53.58 (2CH ), 62.04 (CH ), 111.65
CH ), 6.85–6.95 (4H, m, Ar–H), 7.72 (2H, d, J = 8.4 Hz,
3
2
2
2
3
CH), 113.40 (CH), 117.13 (CH), 119.47 (2CH), 121.09
CH), 127.01 (2CH), 129.04 (C), 130.69 (C), 137.29
CH) 138.92 (C), 151.05 (C), 154.60 (C), 165.85 (C),
Ar-H), 7.86 (1H, s, thiazole C -H), 7.88 (2H, d, J = 8 Hz,
5
Ar–H), 9.85 (1H, s, N–H).
1
3
C NMR (100 MHz, DMSO-d ): 19.66 (CH ), 53.79
6
3
1
68.10 (C).
(2CH ), 55.90 (2CH ), 56.45 (CH ), 62.02 (CH ), 112.54
2 2 3 2
For C H N OS calculated: 67.95% C, 6.45% H, 13.78%
(CH), 113.56 (CH), 118.75 (CH), 120.79 (2CH), 122.64
(CH), 124.86 (CH), 127.89 (2CH), 130.79 (C), 139.52 (C),
142.14 (C), 151.46 (C), 154.17 (C), 166.52 (C), 168.99 (C).
For C H N O S calculated: 65.38% C, 6.20% H, 13.26%
2
3
26
4
N; found: 67.91% C, 6.48% H, 13.72% N.
+
MS (FAB) [M + 1] : m/z 407.
2
3
26
4
2
2
-[4-(3-Methoxyphenyl)piperazine-1-yl]-N-[4-(2-
N; found: 65.36% C, 6.21% H, 13.26% N.
+
methylthiazol-4-yl)phenyl]acetamide (5k)
IR (KBr) νmax(cm ): 3281 (amide N–H), 3043 (aromatic
MS (FAB) [M + 1] : m/z 423.
−1
C–H), 2967 (aliphatic C–H), 1681 (amide C=O), 1578-
2-[4-(2-Pyridyl)piperazine-1-yl]-N-[4-(2-methylthiazol-4-yl)
1
419 (C=C and C=N), 1289–1013 (C–N and C–O).
H NMR (400 MHz, DMSO-d6): 2.66 (4H, t, J = 4.8, 4.8,
phenyl]acetamide (5n)
IR (KBr) νmax(cm ): 3278 (amide N–H), 3044 (aromatic
1
−1
piperazine C–H), 2.71 (3H, s, C–CH ), 3.20–3.22 (4H, m,
C–H), 2978 (aliphatic C–H), 1678 (amide C=O), 1595–
3
piperazine C–H), 3.32 (2H, s, CO–CH ), 3.71 (3H, s, O–
1407 (C=C and C=N), 1307–1005 (C–N and C–O).
2
1
CH ), 6.35–6.54 (3H, m, Ar–H), 7.11 (1H, t, J = 8, 8.2 Hz)
H NMR (400 MHz, DMSO-d6): 2.73–2.75 (4H, m,
3
7
7
.71 (2H, d, J = 9.2 Hz, Ar–H), 7.81 (1H, s, thiazole C -H),
piperazine C–H), 2.76 (3H, s, C–CH ), 3.21 (2H, s, CO–
5
3
.87 (2H, d, J = 8.8 Hz, Ar–H), 9.84 (1H, s, N–H).
CH ), 3.63 (4H, t, J = 5.2, 4.8 Hz piperazine C–H), 6.65–
2
1
3
C NMR (100 MHz, DMSO-d ): 19.53 (CH ), 53.42
6.68 (2H, m, Ar–H), 7.26 (1H, s, thiazole C -H), 7.50 (1H,
6
3
5
(
(
(
2CH ), 55.64 (2CH ), 55.90 (CH ), 62.88 (CH ), 103.50
CH), 106.12 (CH), 109.45 (CH), 113.79 (CH), 120.46
2CH), 127.09 (2CH), 130.14 (CH), 130.18 (C), 138.89 (C),
t, J = 7.6, 4.8 Hz, Ar–H), 7.63 (2H, d, J = 8.4 Hz, Ar–H), 7.85
(2H, d, J = 8.8 Hz, Ar–H), 8.21 (1H, d, J = 5.2 Hz, Ar–H),
9.85 (1H, s, N–H).
2
2
3
2
13
1
50.11 (C), 154.17 (C), 160.15 (C), 166.78 (C), 168.49 (C).
For C H N O S calculated: 65.38% C, 6.20% H, 13.26%
C NMR (100 MHz, DMSO-d ): 19.32 (CH ), 45.52 (2CH ),
6 3 2
53.34 (2CH ), 62.13 (CH ), 107.26 (CH), 111.62 (CH), 113.81
2
3
26
4
2
2
2
N; found: 65.37% C, 6.21% H, 13.25% N.
(CH), 127.01 (2CH), 130.71 (C), 137.28 (CH), 137.57 (C),
148.01 (CH), 154.59 (C), 159.32 (C), 165.85 (C), 168.98 (C).
For C H N OS calculated: 64.10% C, 5.89% H, 17.80%
+
MS (FAB) [M + 1] : m/z 423.
2
1
23
5
2
4
-[4-(2-Methylphenyl)piperazine-1-yl]-N-[4-(2-methylthiazol-
N; found: 64.14% C, 5.87% H, 17.83% N.
+
-yl)pheny]acetamide (5l)
MS (FAB) [M + 1] : m/z 394.
−
1
IR (KBr) νmax(cm ): 3280 (amide N–H), 3046 (aromatic
C–H), 2974 (aliphatic C–H), 1679 (amide C=O), 1599–
2-[4-(2-Benzyl)piperazine-1-yl]-N-[4-(2-methylthiazol-4-yl)
1
402 (C=C and C=N), 1299–1004 (C–N and C–O).
phenyl]acetamide (5o)
IR (KBr) νmax(cm ): 3276 (amide N–H), 3023 (aromatic
1
−1
H NMR (400 MHz, DMSO-d6): 2.31 (3H, s, C–CH ),
3
2
.76 (3H, s, C–CH ), 2.80 (4H, t, J = 4.8, 4.8 Hz, pipera-
C–H), 2986 (aliphatic C–H), 1676 (amide C=O), 1598–
3
zine C–H), 3.01 (4H, t, J = 4.4, 4 Hz, piperazine C–H),
.23 (2H, s, CO–CH ), 6.99-7.07 (2H, m, Ar–H), 7.19
1421 (C=C and C=N), 1301–1027 (C–N and C–O).
1
3
H NMR (400 MHz, DMSO-d6): 2.50–2.65 (8H, brs,
2
(
2H, t, J = 6, 6 Hz, Ar–H), 7.25 (1H, s, thiazole C -H),
piperazine C–H), 2.77 (3H, s, C–CH ), 3.14 (2H, s, CO–
5
3
7
9
.65 (2H, d, J = 8 Hz, Ar–H), 7.86 (2H, d, J = 8 Hz, Ar–H),
CH ), 3.55 (2H, s, N–CH –C), 7.25–7.34 (6H, m, thiazole
2
2
.26 (1H, s, N–H).
C -H and Ar–H), 7.62 (2H, d, J = 9.2 Hz, Ar–H), 7.85 (2H,
5
1
3
C NMR (100 MHz, DMSO-d ): 18.08 (CH ), 19.54
d, J = 9.2 Hz, Ar–H), 9.21 (1H, s, N–H).
6
3
1
3
(
(
(
(
CH ), 52.20 (2CH ), 54.30 (2CH ), 62.34 (CH ), 111.87
C NMR (100 MHz, DMSO-d ): 19.59 (CH ), 53.48
3
2
2
2
6
3
CH), 119.258 (2CH), 119.78 (CH), 123.72 (CH), 126.84
CH), 127.24 (2CH), 130.89 (C), 131.41 (CH), 132.94
C), 137.50 (CH), 151.27 (C), 154.83 (C), 166.14 (C),
(2CH ), 53.80 (2CH ), 62.22 (CH ), 63.17 (CH ), 111.82
2 2 2 2
(CH), 119.72 (2CH), 127.21 (2CH), 127.43 (CH), 128.54
(2CH), 129.37 2CH), 130.81 (C), 137.59 (CH), 138.14 (C),
154.86 (C), 166.11 (C), 168.67 (C).
1
68.61 (C).
For C H N OS calculated: 67.95% C, 6.45% H, 13.78%
For C H N OS calculated: 67.95% C, 6.45% H, 13.78%
2
3
26
4
23 26
4
N; found: 67.94% C, 6.49% H, 13.72% N.
N; found: 67.93% C, 6.41% H, 13.74% N.
+
+
MS (FAB) [M + 1] : m/z 407.
MS (FAB) [M + 1] : m/z 407.
Journal of Enzyme Inhibition and Medicinal Chemistry

New thiazole derivatives as acetylcholinesterase inhibitors 1045
2
-[4-(2-Furoyl)piperazine-1-yl]-N-[4-(2-methylthiazol-4-yl)
DTNB and 10 μL substrate. All processes were assayed in
triplicate. e inhibition rate (%) was calculated by the
following equation:
phenyl]acetamide (5p)
IR (KBr) νmax(cm ): 3288 (amide N–H), 3056 (aromatic
−
1
C–H), 2969 (aliphatic C–H), 1679 (amide C=O), 1599–
Inhibition % =
(
A _ AI
)
/ A × 100
1
427 (C=C and C=N), 1280–1020 (C–N and C–O).
H NMR (400 MHz, DMSO-d6): 2.71 (4H, t, J = 4.4, 4.8
C
C
1
where A is the absorbance in the presence of the inhibi-
tor, A is the absorbance of the control and A is the
absorbance of blank reading. Both of the values were
corrected with blank-reading value. SPSS for Windows
5.0 was used for statistical analysis. Data was expressed
I
Hz, piperazine C–H), 2.77 (3H, s, C–CH ), 3.21 (2H, s, CO–
3
C
B
CH ), 3.92 (4H, brs, piperazine C–H), 6.49–6.50 (1H, m,
2
furan C -H), 7.05 (1H, d, J = 3.6 Hz, furan C -H), 7.27 (1H,
4
3
s, thiazole C -H), 7.49 (1H, s, furan C -H), 7.63 (2H, d, J =
5
5
1
8
.4 Hz, Ar–H), 7.87 (2H, d, J = 8.8 Hz, Ar–H), 9.06 (1H, s,
as Mean ± SD.
N–H).
1
3
C NMR (100 MHz, DMSO-d ): 19.56 (CH ), 53.83
6
3
(
(
(
2CH ), 55.31 (2CH ), 62.30 (CH ), 113.66 (CH), 111.93
CH), 117.13 (CH), 119.81 (2CH), 127.27 (2CH), 131.09
C), 137.34 (C), 144.05 (CH), 148.01 (C), 154.27 (C),
Rꢄꢂuꢅtꢂ ꢃnd diꢂcuꢂꢂion
2
2
2
Chemistry
In the present study, some 2-(4-substituted piperazin-
1
59.34 (C), 166.02 (C), 168.98 (C).
1
-yl)-N-[4-(2-methylthiazol-4-yl)phenyl]acetamide
For C H N O S calculated: 61.44% C, 5.40% H, 13.65%
2
1
22
4
3
derivatives (5a–5p) were synthesized. Target com-
pounds were obtained at five steps. Initially, 4-ami-
noacetophenone was acetylated with acetyl chloride
to obtain N-(4-acetylphenyl)acetamide. Thus, amine
group was protected in further ring closure step. N-(4-
acetylphenyl)acetamide was brominated to afford
N-[4-(2-bromoacetyl)phenyl]acetamide (1). Reaction
of compound 1 with thioacetamide gave the N-[4-
N; found: 61.40% C, 5.43% H, 13.68% N.
+
MS (FAB) [M + 1] : m/z 411.
AChE/BChE Inhibition
All compounds were subjected to a slightly modified
26
method of Ellman’s test in order to evaluate their
potency to inhibit AChE and BuChE. e spectrophoto-
metric method is based on the reaction of released thio-
choline to give a coloured product with a chromogenic
reagent 5,5-dithio-bis(2-nitrobenzoic)acid (DTNB).
AChE, (E.C.3.1.1.7 from Electric Eel, 500 units), BChE,
(
2-methyl-4-thiazolyl)phenyl]acetamide (2) , which
was deacetylated in 10% HCl solution to 4-(2-Methyl-
4
2
-thiazolyl)aniline (3) in the next reaction step.
-Chloro-N-[4-(2-methyl-4-thiazolyl)phenyl]acet-
(
E.C. 3.1.1.8, from horse serum, 1000 units) and done-
pezil hydrochloride were purchased from Sigma–Aldrich
Steinheim, Germany). Potassium dihydrogen phos-
amide (4) was obtained via acetylation of compound
with chloroacetyl chloride. At the final reaction
3
(
step, corresponding N-substituted piperazines were
reacted with compound 4 to achieve 2-(4-substituted
piperazine-1-yl)-N-[4-(2-methylthiazol-4-yl)phenyl]
acetamide derivatives (5a–5p). Synthetic protocol for
the compounds is outlined in Scheme 1. Some charac-
teristics of the synthesized compounds are presented
in Table 1.
phate, DTNB, potassium hydroxide, sodium hydrogen
carbonate, gelatine, acetylthiocholine iodide (ATC) and
butrylthiocholine iodide (BTC) were obtained from
Fluka (Buchs, Switzerland). Spectrophotometric mea-
surements were performed on a 1700 Shimadzu UV-1700
UV–Vis spectrophotometer.
Cholinesterase activity of the compounds (5a–5p) was
measured in 100 mM phosphate buffer (pH 8.0) at 25°C,
using ATC and BTC (75 mM) as substrates. In both cases,
DTNB (10 mM) was used in order to observe absorbance
changes at 412 nm. Donepezil hydrochloride was used as
2
7
a positive control .
Enzymatic assay
Enzyme solutions were prepared in gelatine solution
(1%), at a concentration of 2.5 units/mL. AChE or BChE
solution (50 µL) and compound solution (50 µL), which
−1
is prepared in 2% DMSO at a concentration range of 10 –
−6
1
0
mM, were added to 3.0 mL phosphate buffer (pH
8
± 0.1) and incubated at 25°C for 5 min. e reaction was
started by adding (DTNB) (50 µL) and ATC (10 µL) to the
enzyme-inhibitor mixture. e production of the yellow
anion was recorded for 10 min at 412 nm. As a control,
an identical solution of the enzyme without the inhibitor
was processed following the same protocol. e blank
reading contained 3.0 mL buffer, 50 μL 2% DMSO, 50 μL
Scheme 1. Synthesis of the compounds (5a–5p). Reagents: (i)
acetyl chloride, TEA, THF, 0–5°C; (ii) Br , AcOH; (iii) thioacetamide,
2
EtOH, r.t.; (iv) 1 N HCl, EtOH, reflux; (v) chloroacetyl chloride, TEA,
THF, r.t.; (vi) appropriate 4-substituted piperazine, K CO , acetone,
2
3
reflux.
©
2013 Informa UK, Ltd.

1
046 L. Yurttaş et al.
Structure elucidations of the final compounds were
values of the compounds 5d–5i, 5k, and 5l could not be
calculated due to their poor inhibition potency, which
did not exceed the 50% even at the highest concentra-
tion (100 µM). However, the compounds 5a–5c, and 5m
showed IC values in the range of 6.34–8.42 µM. Besides,
1
performed with IR, H NMR and FAB-MS spectroscopic
methods and elemental analysis. Characteristic stretch-
ing absorption of C=O groups were observed at 1683–
−1
1
1
673 cm . e stretching absorption at about 3288–3276,
5
0
−
1
599–1402 and 1311–1004 cm were recorded for N–H
the compounds 5n, 5o, and 5p indicated significant
AChE inhibitory activity, which is comparable with that
of donepezil. e compound 5n, containing 2-pyridyl
bonds, C=C and C=N double bonds, and C–O and C–N
1
bonds, respectively. In the H NMR spectra, all of the
th
aromatic and aliphatic protons were observed at esti-
mated areas. N–H and CH protons of the acetamide moi-
ety gave peaks at about δ 9.88–9.06 and 3.35–3.09 ppm
moiety at 4 position of piperazine ring, displayed similar
inhibitory potency with the reference drug. Furthermore,
IC50 (0.11 µM) of 4-benzylpiperazine fragment bearing
compound 5o was five-fold lower than that of donepezil.
Observed results prompted us to explore a relationship
between AChE inhibitory activity and chemical struc-
tures of the compounds. e compounds 5d–5m, which
carry N-(substituted-phenyl)piperazines as variable side
groups showed poorest AChE inhibitory potency in the
series. In these compounds, substitution of phenyl ring
on different positions with methyl, methoxy, chloro or
nitro groups did not influence the enzymatic activity.
e reason of ineffectiveness of the compounds 5d–5m
may be related with electron withdrawing character of
the phenyl ring, which decreases electron density on the
piperazine moiety. In a previous study, electron donat-
ing effect was reported as the most important factor on
the benzyl benzene ring, suggesting a role in regulating
the protonation equilibrium at the benzylic nitrogen of
the piperazine skeleton [24]. is report may be useful
for explanation of inhibition potency differences of the
compounds (5a-5p) against AChE. Contrary the phenyl
as singlet, respectively. e C -H proton of the thiazole
5
was observed as a singlet at δ 7.86–7.22. Methyl protons
on the thiazole ring gave a singlet at δ 2.77–2.18 ppm.
Protons of piperazine ring were resonated at δ 3.92–2.35
largely as two different triplets. Two doublets belonging
to aromatic protons of 1,4-disubstituted phenyl ring were
13
observed at δ 7.88–7.59 ppm. In the C NMR spectra,
the signal of characteristic carbonyl carbon was seen at
about δ 166 ppm. Methylene (CH ) carbon, which was
2
bonded to carbonyl was seen at about δ 62.02–63.06
ppm. Methyl carbon on the thiazole ring was appeared at
about δ 19.32–19.66 ppm. e carbons of the piperazine
were seen at δ 45.52-55.84 ppm as two different peaks.
M + 1 peaks in MS spectra were in agreement with the
calculated molecular weight of the target compounds.
Elemental analysis results for C, H and N elements
were satisfactory within ± 0.4 % calculated values of the
compounds.
th
Enzymatic activity
substituent, aliphatic side groups at 4 position of piper-
Synthesized compounds were assayed by Ellman’s
method so as to investigate their inhibitory activity
against AChE and BChE. Results are given in Table 2. Test
compounds were found to be inactive on BChE. On the
other hand, they inhibited AChE to different extents. IC50
azine as methyl, ethyl, cyclohexyl and benzyl enhance
the AChE inhibitory activity to different extents. In addi-
tion, N-substitution of piperazine with heteroaryls as
2-pridyl or 2-furoyl also increases the biological activ-
ity. However, similar to phenyl ring, heteroaryl moieties
Table 2. Percentage AChE and BChE inhibition of the compounds and IC values.
5
0
AChE Inhibition (%)
1 µM
BChE Inhibition (%)
1 µM
Comp.
100 µM
0.01 µM
8.52 ± 0.18
14.65 ± 1.26
10.23 ± 0.96
6.17 ± 1.11
6.31 ± 1.34
9.67 ± 0.72
8.29 ± 2.07
5.23 ± 0.49
6.41 ± 1.34
13.96 ± 2.16
4.89 ± 1.44
5.47 ± 0.28
13.28 ± 1.55
41.13 ± 3.47
49.22 ± 4.57
29.16 ± 1.84
36.26 ± 4.28
IC (µM)
100 µM
IC (µM)
5
0
50
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
a
b
c
d
e
f
g
h
i
j
k
l
m
n
o
p
69.42 ± 5.09
58.79 ± 6.44
72.13 ± 9.26
38.17 ± 4.21
21.49 ± 3.22
43.15 ± 5.89
39.71 ± 5.27
42.63 ± 2.64
30.48 ± 4.25
58.36 ± 7.34
34.24 ± 2.51
28.53 ± 4.81
63.21 ± 7.26
96.44 ± 5.21
99.83 ± 4.42
89.70 ± 6.37
96.82 ± 5.09
41.26 ± 2.14
38.24 ± 4.04
40.29 ± 3.49
19.24 ± 2.61
16.42 ± 1.28
22.70 ± 0.89
18.47 ± 1.67
19.06 ± 2.16
14.28 ± 1.81
27.42 ± 2.28
11.74 ± 4.16
12.24 ± 3.91
39.53 ± 4.21
84.96 ± 7.63
87.70 ± 6.75
63.61 ± 4.19
78.16 ± 5.43
7.12 ± 0.64
29.32 ± 3.41
14.22 ± 2.16
25.54 ± 4.32
18.36 ± 0.87
13.21 ± 1.63
18.37 ± 1.44
21.51 ± 2.96
16.23 ± 1.84
9.29 ± 2.45
6.13 ± 1.53
4.81 ± 0.94
8.75 ± 2.62
4.43 ± 0.82
8.62 ± 1.43
3.56 ± 0.45
6.31 ± 0.97
7.14 ± 0.68
2.24 ± 1.24
7.24 ± 1.16
5.41 ± 0.82
8.03 ± 1.84
13.07 ± 0.56
18.89 ± 2.61
21.12 ± 1.15
14.69 ± 0.76
42.83 ± 3.23
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
7.18 ± 0.67
11.74 ± 1.43
6.34 ± 1.31
>100
>100
>100
>100
>100
>100
88.35 ± 6.88
>100
16.33 ± 1.47
12.81 ± 1.61
27.67 ± 2.12
31.48 ± 4.93
42.09 ± 5.16
46.35 ± 5.08
39.27 ± 1.19
71.56 ± 6.14
>100
8.42 ± 1.23
0.051 ± 0.002
0.011 ± 0.001
0.27 ± 0.001
0.054 ± 0.002
Donepezil
Journal of Enzyme Inhibition and Medicinal Chemistry

New thiazole derivatives as acetylcholinesterase inhibitors 1047
decrease the electron density of piperazine ring, but
there is a significant difference between the inhibitory
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contain N-phenyl substituted piperazine derivatives and
N-heteroaryl substituted piperazine derivatives, respec-
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withdrawing characteristics of substituents need to be
sought. In this case, polarizability and hydrogen bond-
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groups may be suggested for the reason of enzymatic
activity differences. Due to increasing polarizability and
hydrogen bonding capability, interaction between AChE
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containing compounds 5n and 5p than the N-phenyl
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