Design and discovery of Novel Thiazole acetamide derivatives as anticholinesterase agent for possible role in the management of Alzheimer's

Article abstract of DOI:10.1016/j.bmcl.2016.01.001

A novel series of thiazole acetamides was synthesized in excellent yields and characterized with the aid of various spectroscopic and elemental analysis. These compounds were evaluated for in vitro acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) inhibitory activities for possible benefit in Alzheimers disease (AD). Among the synthesized compound, 6d was identified as the most potent compound of AChE (IC₅₀= 3.14 ± 0.16 μM) with a selectivity index (SI) of 2.94 against BuChE. These compounds were further tested for inhibition of Aβ aggregation and β-secretase, where it showed potent inhibition which confirmed its multifactorial benefits in AD. The toxicity and docking study were also carried out to exemplify the pharmacological profile of compound 6d as prospective lead molecule against AD.

Full text of DOI:10.1016/j.bmcl.2016.01.001

Bioorganic & Medicinal Chemistry Letters xxx (2016) xxx–xxx
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Design and discovery of Novel Thiazole acetamide derivatives as
anticholinesterase agent for possible role in the management of
Alzheimer’s
⇑
Zhi-Qing Sun, Li-Xiang Tu, Feng-Juan Zhuo, Song-Xia Liu
Department of Internal Neurology, Linyi People’s Hospital, No. 27, Jiefang Road, Linyi, Shandong 276000, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel series of thiazole acetamides was synthesized in excellent yields and characterized with the aid
of various spectroscopic and elemental analysis. These compounds were evaluated for in vitro acetyl-
cholinesterase (AChE) and butyrylcholinesterase (BChE) inhibitory activities for possible benefit in
Alzheimers disease (AD). Among the synthesized compound, 6d was identified as the most potent
Received 21 September 2015
Revised 16 December 2015
Accepted 4 January 2016
Available online xxxx
compound of AChE (IC50 = 3.14 ± 0.16 lM) with a selectivity index (SI) of 2.94 against BuChE. These
compounds were further tested for inhibition of Ab aggregation and b-secretase, where it showed potent
inhibition which confirmed its multifactorial benefits in AD. The toxicity and docking study were also
carried out to exemplify the pharmacological profile of compound 6d as prospective lead molecule
against AD.
Keywords:
Synthesis
Thiazole acetamides
Acetylcholinesterase
Docking
Ó 2016 Published by Elsevier Ltd.
Across a globe, the greater number of elder population was
affected by progressive, never-ending, neurodegenerative disorder
known as Alzheimers disease (AD).1 It is characterized by a loss
of memory and cognitive abilities affecting about 6% of the popu-
lation worldwide aged over 65. Studies suggest that, the loss of
cholinergic neurons in the hippocampus and the cerebral cortex
of the central nervous system (CNS) are the ultimate cause of cog-
Therefore, on the basis of above, we are encouraged to design
and develop Novel Thiazole acetamides as anticholinesterase inhi-
bitors for potential benefit in AD.
The development of target analogues 6 (a–j) were realised in an
efficient synthetic manner as depicted in Scheme 1. The substi-
tuted benzaldehyde (1) was allowed to react with thiourea to
afford phenyl thiazole (3) in efficient yield via cyclo-condensation
reaction. This reaction was carried out in the presence of Bromine
–3
4
–6
nitive and behavioral abnormalities that characterize AD.
There-
fore, early therapeutic approaches to treat AD were aimed at
escalating the availability of the cholinergic neurotransmitter
acetylcholine (ACh). The levels of ACh could be maintained by
two types of agents, viz., drugs directly acting on cholinergic recep-
tor or drugs preventing its degradation via inhibiting the activity of
acetylcholinesterase (AChE) enzyme. The latter class of drug, that
is, AChE inhibitors (AChEIs) is considered superior over directly
acting ACh ligands for the symptomatic relief of AD by enhancing
which leads to the formation of a-haloketones and reaction gener-
ally referred as Hantzsch thiazole synthesis. Moreover, in a second
step, the chloro acetyl chloride was used to replace the free amine
of the above synthesized thiazole to afford compound 4. This
resultant compound was then reacted with distinguished anilines
5 (a–j) to furnish target analogues 6 (a–j). Here, various electron
donating and withdrawing substituent were introduced on the R1
positions to determine its potential effect as anti-choline esterase.
The structure of various title derivatives 6 (a–j) was ascertained
7
,8
the cholinergic action.
Thiazoles are an important class of heterocyclic molecules
exhibiting numerous pharmacological activities, for instance,
by spectral analysis. The FT-IR peaks of title compounds showed at
À1
3368–3385 cm
(strong, broad) show characteristic of amide
9
10
11
antimicrobial , anticancer
and antimalarial
including anti-
hydrogen (ACONHA). All compounds exhibits stretching vibration
choline esterase activity.12 More recently, acotiamide hydrochlo-
ride, a thiazole based selective AChEI for the treatment of
functional dyspepsia has been identified and now being in
advanced stages of clinical studies.13
between 1658 to 1678 cm which attributable to C@O group. All
À1
compounds displayed characteristic carbon, carbon double bonds
À1
(C@C) peak at 1559–1571 cm in its expected region. Further-
1
13
more, the H NMR C NMR and MS signals of the title compounds
were also observed in their expected region.
The bioactivities of the organic medicinal agents (OMAs) have
been greatly dependent upon physicochemical properties.
⇑
Corresponding author. Tel./fax: +86 539 8226999.
E-mail address: liusongxia@hotmail.com (S.-X. Liu).
http://dx.doi.org/10.1016/j.bmcl.2016.01.001
960-894X/Ó 2016 Published by Elsevier Ltd.
0
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Z.-Q. Sun et al. / Bioorg. Med. Chem. Lett. xxx (2016) xxx–xxx
2 3 2 3
Scheme 1. Synthesis of Thiazole acetamides derivative. Reagents and conditions: (a) Br , Reflux; (b) DCM, Et N, 0 °C – rt, 4 h; (c) ACN, K CO , Reflux 4–8 h.
Therefore, the developed thiazole acetamides analogues were rig-
orously analyzed by Molinspiration, a web based software. It was
used to predict parameter such as MiLogP, TPSA and
able to cross the cell membrane which is a key parameter for trans-
portation across and in turn is needed for the generation of bioac-
tivity. Moreover, it will be suitable for drug absorption owing to
1
4
16
druglikeness.
the acceptable TPSA value.
The MiLogP (octanol/water partition coefficient) is able to
envisage the ability of the molecule to cross the cell membrane.
This methodology is based on the sum of fragment based contribu-
tions and correction factors for the compounds analyzed. Molecu-
lar Polar Surface Area or Total Polar Surface Area (TPSA) is
calculated as a sum of fragment based contributions in which sur-
face areas correspond to polar fragments centered to N- and O- and
by hydrogen atoms attached to them are to be considered.1 It has
been deemed as a very efficient descriptor illustrating the drug
absorption (including intestinal absorption, bioavailability, Caco-
BuChE was found in elevated concentration in AD and responsi-
ble for hydrolyzing the acetyl choline, thus, inhibition of BuChE
was also considered as a fruitful target for symptomatic relief in
ADs. Consequently, the inhibitory effect of target analogues was
analyzed for both AChE and BuChE using Ellman method. Rivastig-
mine was used as standard in this comparison test. The inhibitory
potency (IC50) of tested compounds along with selectivity index
has been outlined in Table 2. According to the results, the entire
set of the synthesized compound showed considerable inhibition
of both the enzymes. It has been found that, compound 6a, bearing
no substituent showed least activity against the tested enzymes.
Whereas, on the introduction of the methyl as a substitutent (6b)
render compound much more active in regard of inhibitory
potency and SI. On changing the substitution pattern, from para
to ortho, the activity was decreased marginally. The highest inhibi-
tory potency was reported by the compound 6d having p-methoxy
against the tested enzymes along with high SI. Whereas, it’s iso-
meric counterpart, compound 6e exhibit less pronounced activity
than the parent. The activity was significantly abolished in the
presence of an electron withdrawing group. Particularly, in the
case of compound 6f and 6g, marked reduction in activity was
observed with minimal difference. On replacing the nitro with
chloro, the activity was declined more than twofold with a mild
reduction in SI. No significant difference was observed in the case
of compound 6j against both the tested enzymes with less selectiv-
ity for AChE. It is surprising to note that, none of the synthesized
compound exhibited activity similar or better than Rivastigime.
However, the structure activity relationship (SAR) suggests that,
presence of electron donating group seemed to be suitable for
5
2
permeability) and blood brain barrier permeability. This method
is based on contribution of group obtained by comparing the sum
of fragment contributions to ‘‘real” 3D volume for a training set of
about 12,000 drug-like molecules. Moreover, the semiempirical
AM1 method was used for the optimization of the 3D molecular
geometries for a training set.
The ability of a molecule to iterate for adopting the best possi-
ble conformation in binding pocket was determined by the Num-
ber of Rotatable Bonds. It has been directly related with an oral
bioavailability of drugs and defined as any single bond except
the aromatic, bonded to non-terminal non-hydrogen atom. Due
to high rotational energy barrier, amide CAN bonds are not consid-
1
6
ered. The results of the rigorous analysis of compounds 6 (a–j) in
terms of molecular properties which depicts pharmacokinetics tol-
erability on the basis of above discussed parameters has been
shown in Table 1. It was found that, the entire set of molecules
obeyed Lipinski rule of five recommendations suggesting to have
good bioavailability necessary for new chemical entities (Nviola-
tion = 0). As shown by MilogP value, these molecules were also
Table 1
Molecular properties of compounds 6 (a–j)
Compound
miLogP
TPSA
Natoms
MW
nON
nOHNH
nviolations
nrotb
Volume
6
6
6
6
6
6
6
6
6
6
a
b
c
d
e
f
g
h
i
3.65
4.10
4.05
3.70
3.66
3.61
3.56
4.33
4.28
3.81
41.99
41.99
41.99
51.22
51.22
87.81
87.81
41.99
41.99
41.99
21
22
22
23
23
24
24
22
22
22
294.38
308.41
308.41
324.40
324.40
339.38
339.38
328.82
328.82
312.37
3
3
3
4
4
6
6
3
3
3
1
1
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
0
0
4
4
4
5
5
5
5
4
4
4
261.60
278.17
278.17
287.15
287.15
284.94
284.94
275.14
275.14
266.54
j
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Z.-Q. Sun et al. / Bioorg. Med. Chem. Lett. xxx (2016) xxx–xxx
3
Table 2
Table 3
In vitro inhibition of AChE and BuChE of compound 6 (a–j)
Inhibitory effects of compounds 6d against Ab aggregation and b-secretase
Compound
R
AChE Inhibition
IC50 M)
BuChE Inhibition
(IC50 M)
Selectivity
index
Compound IC50
, lM
a
(
,
l
,
l
Ab aggregation
b-secretase
6
6
6
6
6
6
6
6
6
6
a
b
c
d
e
f
g
h
i
H
4-CH
2-CH
4-OCH
2-OCH
4-NO
2-NO
4-Cl
2-Cl
4-F
32.45 ± 0.24
6.18 ± 0.61
7.71 ± 0.54
3.14 ± 0.16
5.23 ± 0.42
8.21 ± 0.25
8.25 ± 0.37
22.43 ± 0.34
23.12 ± 0.26
26.63 ± 0.14
12.65 ± 0.22
30.67 ± 0.55
9.43 ± 0.42
8.11 ± 0.35
9.24 ± 0.32
10.83 ± 0.37
6.32 ± 0.39
11.28 ± 0.25
25.27 ± 0.28
26.42 ± 0.18
26.33 ± 0.33
1.12 ± 0.45
0.94
1.52
1.05
2.94
2.07
0.76
1.36
1.12
1.14
0.98
0.08
6
d
10.6 ± 1.2
11.3 ± 0.3
13.2 ± 0.4
6.1 ± 0.8
3
3
Curcumin
3
3
2
2
j
Rivastigmine
a
Selectivity of inhibitor potency BChE/AChE.
Figure 1. Structure activity realationship (SAR) study of compound 6 (a-j) against
AChE inhibition.
Figure 2. Percentage of viability of HeLa cells in the presence of compound 6d at
various concentrations.
activity, while electron withdrawing group lessen the activity. The
position of the group also has marked influence on the activity,
such as, para is found much more active than meta substituted
derivatives. The observation of SAR has been elucidated in Figure 1.
Current drug discovery approaches to treat AD were aimed at
development of multi-target directed ligands concentrated to
attack on distinct AD-relevant goals.17,18 Consequently, according
to the amyloid hypothesis, accumulation of Ab peptide produced
after cleavage of amyloid precursor protein by b-secretase in pro-
tein triggers numerous pathophysiological changes that eventually
lead to cognitive dysfunction, particularly in AD.19 Therefore, inhi-
bition of b-secretase and Ab aggregation by selective inhibitors
offers great interest in the discovery for agents modifying the dis-
ease condition. Thus, the inhibitory activity of compound 6d was
determined against Ab aggregation and b-secretase, using cur-
cumin as reference control showed in Table 3. The inhibitory abil-
aggregation and b-secretase by fluorometric assay. It has been
found that, compound 6d (IC50 = 10.6 ± 1.2 lM) exhibit better
activity than curcumin against the Ab aggregation. Where, it has
been found a nearly twofold less active than standard against b-
secretase.
Toxicity is a much critical factor to be considered during the
drug development process. Thus, after confirmation of the high
bioactivity and mechanism of action of most active compound
6d, it is worthwhile to perform its toxicity study. The human cer-
vical carcinoma cell line (HeLa 229) was used for cytotoxicity
assessment using the MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-
diphenyl-2H-tetrazolium bromide] assay. As shown in Figure 2, it
was revealed that compound 6d did not exhibit significant toxicity
within 2 h of administration, but viability has been reduced in the
ity was evaluated at a single concentration (100 lM) against Ab
Figure 3. Docked orientation of compound 6d in the catalytic site of acetyl choline esterase.
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Z.-Q. Sun et al. / Bioorg. Med. Chem. Lett. xxx (2016) xxx–xxx
2
4 h study period. Thus, it was corroborated that it did not appre-
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Supplementary data
Supplementary data associated with this article can be found, in
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Please cite this article in press as: Sun, Z.-Q.; et al. Bioorg. Med. Chem. Lett. (2016), http://dx.doi.org/10.1016/j.bmcl.2016.01.001