Multitarget-directed resveratrol derivatives: Anti-cholinesterases, anti-β-amyloid aggregation and monoamine oxidase inhibition properties against Alzheimer's disease

Article abstract of DOI:10.1039/c3md00376k

Considering the complex pathogenesis factors of Alzheimer's disease (AD), the multitarget-directed ligand strategy is expected to provide superior effects to fight AD, instead of the classic one-drug-one-target strategy. Resveratrol, exhibiting important properties against AD, was suggested to be used as a starting compound for the treatment of AD. Based on these reasons, a series of resveratrol derivatives were designed, synthesized and biologically evaluated. Among them, compound 6r, exhibiting moderate cholinesterase inhibition activity (AChE, IC₅₀ = 6.55 μM; BuChE, IC₅₀ = 8.04 μM; SI = 1.23), significant inhibition of Aβ₄₂ aggregation (57.78%, at 20 μM) and acceptable inhibitory activity against monoamine oxidases (MAO-A, IC₅₀ = 17.58 μM; MAO-B, IC₅₀ = 12.19 μM), was a potential anti-Alzheimer agent with balanced activities. Consequently, this study provided useful information for further development of resveratrol derivatives as multitarget-directed agents for AD therapy. This journal is the Partner Organisations 2014.

Full text of DOI:10.1039/c3md00376k

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CONCISE ARTICLE
Multitarget-directed resveratrol derivatives: anti-
cholinesterases, anti-b-amyloid aggregation and
monoamine oxidase inhibition properties against
Alzheimer's disease†
Cite this: Med. Chem. Commun., 2014,
5, 609
*
Long-Fei Pan, Xiao-Bing Wang, Sai-Sai Xie, Su-Yi Li and Ling-Yi Kong
Considering the complex pathogenesis factors of Alzheimer's disease (AD), the multitarget-directed ligand
strategy is expected to provide superior effects to fight AD, instead of the classic one-drug-one-target
strategy. Resveratrol, exhibiting important properties against AD, was suggested to be used as a starting
compound for the treatment of AD. Based on these reasons, a series of resveratrol derivatives were
designed, synthesized and biologically evaluated. Among them, compound 6r, exhibiting moderate
cholinesterase inhibition activity (AChE, IC50 ¼ 6.55 mM; BuChE, IC50 ¼ 8.04 mM; SI ¼ 1.23), significant
inhibition of Ab42 aggregation (57.78%, at 20 mM) and acceptable inhibitory activity against monoamine
oxidases (MAO-A, IC50 ¼ 17.58 mM; MAO-B, IC50 ¼ 12.19 mM), was a potential anti-Alzheimer agent with
balanced activities. Consequently, this study provided useful information for further development of
resveratrol derivatives as multitarget-directed agents for AD therapy.
Received 7th December 2013
Accepted 14th February 2014
DOI: 10.1039/c3md00376k
www.rsc.org/medchemcomm
binding site acetylcholinesterase inhibitors (AChEIs) have
become more promising in AD treatment. In a normal brain,
Introduction
AChE is more active than BuChE. However, as AD progresses,
the activity of AChE gradually decreases, while that of BuChE is
unchanged or increased.12,13 Thus, BuChE becomes a modulator
to regulate ACh levels in cholinergic neurons. Due to the key
role of BuChE, inhibition of both AChE and BuChE are bene-
cial for AD treatment.
In contrast to the cholinergic hypothesis, the amyloid
hypothesis suggests that the aggregation of Ab leads to the
formation of amyloid plaques, resulting in neuronal dysfunc-
tion in AD patients.14–16 Ab is a 39- to 43-residue peptide
generated by the sequential cleaving of the amyloid precursor
protein (APP) by b- and g-secretases. Ab40 and Ab42 are the main
isoforms of Ab.17 Ab42 is the predominant form in amyloid
plaques, having lower solubility and stronger neuronal toxicity
than Ab40,18 therefore, the prevention of Ab42 formation or
aggregation is currently another potential method for the
treatment of AD.
Alzheimer's disease (AD), a progressive, chronic and fatal
neurodegenerative disorder characterized by memory loss,
cognitive impairment and decline in language, affects older
people all over the world.1 The pathology of AD includes
cholinergic system dysfunction,2 aggregated b-amyloid (Ab)
protein deposits,3 metal dyshomeostasis,4 s-protein hyper-
phosphorylation,5 oxidative stress,6 neural loss and so on.7
These factors provide the bases for some hypotheses such as
cholinergic hypothesis, one of the most classical hypotheses of
AD, which suggests that the cognitive and memory deteriora-
tions associated with AD are caused by the decline of acetyl-
choline (ACh). ACh can be degraded by two types of
cholinesterases (ChEs), namely acetylcholinesterase (AChE) and
butyrylcholinesterase (BuChE).8 The X-ray crystallographic
structure of AChE reveals that it contains two binding sites: the
catalytic active site (CAS) and the peripheral anionic site (PAS)
connected by a deep, hydrophobic gorge.9,10 Generally, inhibi-
tors that bind to either one of these sites can inhibit AChE.
Current studies indicate that the PAS of AChE not only facili-
tates cholinergic transmission but also accelerates deposition
and aggregation of Ab.11 In consideration of these reasons, dual
It has been reported that monoamine oxidase (MAO), playing
an important role in dopaminergic and serotoninergic neuro-
transmitter systems, is
a target for some multifactorial
diseases.19 MAO is a avoenzyme that catalyzes the deamination
of amines and is responsible for the regulation and metabolism
of major monoamine neurotransmitters. It has two isoforms
named MAO-A and MAO-B.20 MAO-A is involved in psychiatric
conditions and depression, while MAO-B accelerates the
oxidative deamination of neurotransmitters, resulting in
enhanced production of free radicals thus causing oxidative
State Key Laboratory of Natural Medicines, Department of Natural Medicinal
Chemistry, China Pharmaceutical University, 24 Tong Jia Xiang, Nanjing 210009,
People's Republic of China. E-mail: cpu_lykong@126.com; Fax: +86-25-8327-1405;
Tel: +86-25-8327-1405
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c3md00376k
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stress.21 As a result, selective inhibitors of MAO-A have been
shown to be effective antidepressants, whereas MAO-B inhibi-
tors are useful in neurodegenerative disorders such as AD.22 AD
patients commonly have depressive symptoms which have been
considered as risk factors for the development of AD. Therefore,
dual inhibition of MAO-A and MAO-B, rather than only MAO-B,
should contribute to AD therapy.23
Results and discussion
Chemistry
The synthetic routes of resveratrol derivatives are shown in
Scheme 1. The commercially available 3,5-dimethox-
ybenzylalcohol was reacted with phosphorus tribromide in the
presence of pyridine to give compound 2, which was further
reuxed in triethyl phosphate to provide compound 3 in 95%
yield. 4-Hydroxybenzaldehyde reacted with different a,u-dibro-
moalkanes in acetonitrile produced compounds 4a–g in 72–88%
yields, and these compounds were then treated with N-methyl-
benzylamine and other amines in the presence of potassium
carbonate to afford the key intermediates 5a–v in 73–84% yields.
Finally, the target products 6a–v were obtained by the reaction of
3 with 5a–v through Wittig–Horner reaction in 40–54% yields.
The pioneering strategy for treating AD aimed at a single
target, such as ChEs, Ab, transition metal ions or MAO. However,
due to the complexity of AD, molecules that modulate the activity
of a single target might not be sufficient to alter the progression
of this disease. Thus, an efficient therapy is more likely to be
achieved by drugs that incorporate several pharmacological
effects into a single molecular entity.24 This approach has been
explored by many research groups and different multitarget-
directed compounds have been reported in recent literature.25–27
In the light of this point, we are devoted to the study of multi-
functional agents that not only merely inhibit ChEs, but also
decrease Ab aggregation and inhibit MAOs as well.
Cholinesterase inhibitory activity
Inhibitory activities of the target compounds against AChE
(from an electric eel) and BuChE (from equine serum) were
tested by the spectrophotometric method of Ellman et al. with
tacrine and galantamine as reference standards.35,36 The IC50
values for AChE and BuChE inhibitions are summarized in
Table 1. Most of the synthesized compounds showed higher
inhibitory potency against ChEs than resveratrol, indicating
that the introduction of amino group side chains could indeed
increase the inhibitory capacity of the target compounds. To get
the optimal linker length, compounds 6a–g were designed and
Resveratrol (trans-3,40,5-trihydroxystilbene) is
a natural
phenolic compound, present in many plants. In vitro and in vivo
studies show that resveratrol has a number of biological activi-
ties including anti-inammatory and antioxidant properties.28,29
Recently, many researchers have focused on its effects against
AD, and demonstrated that resveratrol can inhibit Ab self-
aggregation, attenuate Ab-induced toxicity, promote Ab clear-
ance and reduce senile plaques.30,31 Some studies also show that
it has inhibitory effects on MAO activities.32,33 It could be
concluded that resveratrol might be used as
a starting
synthesized. As shown in Fig. 2, compound 6e (AChE, IC50
¼
compound in the design of multitargeted drugs for the treat-
ment of AD. Hence, a series of resveratrol analogues, a 3,5-
dimethoxy-trans-stilbene fragment linked with different amines
by a 2- to 8-carbon spacer, were designed. Amino groups,
protonated at physiological pH, could bind to the CAS of AChE.34
The stilbene moiety could interact with the PAS via aromatic
stacking interactions, meanwhile, inhibit Ab self-aggregation
and MAOs. Variable carbon spacers were designed to make the
designed compounds t the gorge and interact with both sites of
AChE (Fig. 1). Herein, we report the design, synthesis, evaluation
and molecular modeling of resveratrol derivatives as multi-
targeted compounds with anti-ChEs, anti-Ab aggregation and
MAO inhibition properties for the treatment of AD.
11.70 mM; BuChE, IC50 ¼ 26.38 mM) was the best inhibitor
against AChE and BuChE, revealing that a six-carbon linker
between the trans-stilbene moiety and amino group was the
suitable length for ChE inhibition.
With the optimal length of the linker in hand, different
terminal amines were introduced to explore the structure–
activity relationship. It is worth noting that 6h (AChE, IC50
¼
1.56 mM) was almost 8-fold more potent than 6e. It could be
concluded that increased lipophilicity could lead to a rise in
AChE inhibitory potency.37,38 In comparison with compounds 6e
and 6h, inhibitory activities of 6i–n toward AChE were strongly
decreased, revealing that the N-benzyl-N-ethyl group could
completely ll the bottom of the AChE gorge and most of the
Fig. 1 Design strategy for resveratrol derivatives.
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Scheme 1 Synthesis of resveratrol derivatives. Reagents and conditions: (i) PBr3, pyridine, CH2Cl2, 0 ꢀC to r.t., 4 h; (ii) triethyl phosphate, 160 ꢀC,
4 h; (iii) a,u-dibromoalkanes, K2CO3, acetonitrile, 40 ꢀC, 4 h; (iv) NHR1, K2CO3, acetonitrile, reflux, 8 h; (v) 3, CH3ONa, DMF, 0 ꢀC, 0.5 h to r.t. 8 h.
changes on this part of the molecule were not allowed. With the Interestingly, the inhibitory activity of compound 6q was less
exception of 6i (IC50 ¼ 2.27 mM), compounds 6j–n behaved than those of 6o and 6p, which might be attributed to the steric
similarly in the inhibition to BuChE, indicating that the hindrance of the dipropylamine group. It also could be seen that
o-methoxy group could stabilize the charged amino group compounds 6t and 6u, possessing oxygen atoms in the cyclic
through inductive and resonance effects.39
amino groups, exhibited weaker activities towards ChEs than
Next, a phenyl ring was deleted from the amino group side those of 6r–t. The result suggested that the electron-withdrawing
chains with the aim to explore the differences between aliphatic effects of oxygen atoms might reduce the electronic density of
amines (6o–q) and aromatic amines (6e and 6h) against ChEs. amines and further impact on its protonation, thereby dimin-
The results showed that this modication did not remarkably ishing the interaction between the terminal nitrogen and ChEs.
affect the inhibitory potency. In addition, compared to 6o–q with
alkyl amine groups, compounds 6r–t bearing cyclic amine groups
demonstrated slightly better inhibitory activities against AChE,
Kinetic study of AChE inhibition
but no clear trend was observed for BuChE. As the lipophilicity In order to gain insight into the mechanism of action of these
increased, the activities against AChE of 6r–t became stronger. derivatives on AChE, compound 6h was selected for kinetic
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Table 1 Inhibition of AChE, BuChE and self-induced Ab42 aggregation activities of the synthesized compounds
IC50a (mM)
Compounds
R1
n
AChE
BuChE
Selectivity indexb
Ab42 aggregation inhibitionc (%)
6a
6b
6c
6d
6e
6f
2
3
4
5
6
7
8
79.30 ꢁ 2.81
58.06 ꢁ 2.21
60.89 ꢁ 2.44
39.16 ꢁ 1.06
11.70 ꢁ 0.34
23.40 ꢁ 0.86
26.50 ꢁ 0.94
89.56 ꢁ 3.54
77.31 ꢁ 2.76
40.58 ꢁ 1.63
43.67 ꢁ 2.01
26.38 ꢁ 1.28
41.67 ꢁ 1.89
46.85 ꢁ 2.07
1.13
1.33
0.67
1.13
2.25
1.78
1.77
26.14 ꢁ 3.45
46.40 ꢁ 3.15
44.72 ꢁ 1.29
36.40 ꢁ 1.28
49.79 ꢁ 2.18
43.57 ꢁ 3.01
47.20 ꢁ 2.78
6g
6h
6i
6
1.56 ꢁ 0.08
3.64 ꢁ 0.06
1.69
53.49 ꢁ 2.13
6
54.93 ꢁ 2.38
2.27 ꢁ 0.09
0.04
64.53 ꢁ 2.18
6j
6
6
71.53 ꢁ 2.95
89.73 ꢁ 4.12
>100
>100
>1.40
>1.11
55.17 ꢁ 2.34
53.25 ꢁ 1.09
6k
6l
6
6
86.61 ꢁ 3.55
77.85 ꢁ 3.01
53.03 ꢁ 2.18
51.98 ꢁ 1.89
0.61
0.67
29.55 ꢁ 2.05
28.25 ꢁ 3.21
6m
6n
6o
6p
6
6
6
92.30 ꢁ 4.31
4.15 ꢁ 0.11
8.19 ꢁ 0.20
85.38 ꢁ 3.42
13.19 ꢁ 0.62
10.35 ꢁ 0.49
0.93
3.18
1.26
37.28 ꢁ 1.24
40.33 ꢁ 1.09
42.85 ꢁ 2.98
6q
6
12.09 ꢁ 0.34
7.49 ꢁ 0.12
0.61
41.45 ꢁ 2.56
6r
6s
6
6
6.55 ꢁ 0.16
5.02 ꢁ 0.13
8.04 ꢁ 0.22
1.23
2.14
57.78 ꢁ 2.36
54.00 ꢁ 1.87
10.68 ꢁ 0.19
6t
6
4.07 ꢁ 0.10
10.10 ꢁ 0.32
2.48
52.10 ꢁ 2.22
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Table 1 (Contd.)
IC50a (mM)
Compounds
R1
n
AChE
BuChE
Selectivity indexb
1.34
Ab42 aggregation inhibitionc (%)
42.55 ꢁ 1.87
6u
6
17.20 ꢁ 0.43
24.35 ꢁ 1.08
23.13 ꢁ 0.90
6v
6
34.32 ꢁ 1.18
1.41
42.16 ꢁ 3.54
Tacrine
0.205 ꢁ 0.02
2.77 ꢁ 0.15
165.24 ꢁ 48
n.t.d
0.052 ꢁ 0.001
13.61 ꢁ 0.28
752.46 ꢁ 87
n.t.d
0.25
4.91
4.55
n.t.d
Galantamine
Resveratrol
Curcumin
n.t.d
68.51 ꢁ 2.46
>1.26
52.21 ꢁ 1.30
a
b
c
IC50: 50% inhibitory concentration (mean ꢁ SEM of three experiments). Selectivity index ¼ IC50(BuChE)/IC50(AChE). Inhibition of self-
mediated Ab42 aggregation and the measurements were carried out in the presence of 20 mM compounds (mean ꢁ SEM of three experiments).
d
n.t. ¼ not tested.
Fig. 2 Effects of alkyl chain lengths on anti-ChEs activities.
measurements because it showed the highest inhibitory activity
against AChE. The graphical presentation of the steady-state
inhibition data of 6h for AChE is shown in Fig. 3. The results
indicated that both slopes and intercepts were increased at
Fig. 3 Lineweaver–Burk plot for the inhibition of AChE by compound 6h.
increasing concentration of the inhibitor. This pattern indi-
cated that compound 6h was a mixed-type inhibitor, which
AChE, and stacked against the phenyl ring of Phe 330 and Trp 84
could bind to the CAS as well as the PAS of AChE, demonstrating
the rationality of our molecular design.
˚
with the ring-to-ring distance of 3.75 and 3.73 A, respectively. The
docking results indicated that the 6h was a mixed-type inhibitor
of AChE, which were consistent with our kinetic analysis result.
Although there is little difference between compounds 6h
and 6i–n, 6i–n showed an obviously reduced anti-AChE activity
compared with 6h. Compounds 6i and 6l were selected as
representative compounds to further explore the binding
modes. From Fig. 4, it could be seen that both of them could
bind to the CAS via the cation–p interaction with the indole ring
of Trp 84, but no p–p stacking interactions were observed at the
CAS and the PAS. These results might lead to the lower inhibi-
tory capacity of 6i–n.
Molecular modeling studies
To further investigate the binding mode of the inhibitors, a
molecular docking study was performed with the most active
compound 6h using Molecular Operating Environment (MOE)
soware package. The X-ray crystal structure of the AChE
complex with bis(7)-tacrine (PDB code: 2CKM) was obtained from
the Protein Data Bank. By analyzing as shown in Fig. 4(A) and (B),
compound 6h could perfectly t into the gorge of AChE and
simultaneously interact with the CAS and PAS of AChE. The
phenyl ring substituted with methoxy groups was observed to
bind to the PAS via p–p stacking interactions with the indole ring
Inhibition of Ab42 self-induced aggregation
˚
of Trp 279 with the distance of 4.16 A. In the bottom of the gorge,
the charged nitrogen of N-benzylethanamine could establish a The inhibition of self-induced Ab42 aggregation of these resvera-
˚
cation–p interaction (4.63 A) with the indole ring of Trp 84. The trol derivatives was evaluated using a thioavin-T based uoro-
phenyl ring of N-benzylethanamine was bound to the CAS of metric assay.40 Inhibition activities are listed in Table 1 as
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Fig. 4 Docking models of compounds 6h (A and B), 6i (C) and 6l (D) with AChE generated with MOE.
inhibition ratios at a test concentration of 20 mM. Compared with MAO-A inhibition was very weak and no apparent structure–
the reference compounds, resveratrol (68.51%, at 20 mM) and activity relationship existed, while the MAO-B inhibitory activity
curcumin (52.21%, at 20 mM), compounds 6h–k and 6r–t gave was relatively potent and related to the length of the alkyl chain.
equal or better results, with inhibition ratios from 52.10% to Among 6a–h with the number of methylene varying from two to
64.53%. Compound 6i (64.53%, at 20 mM) was the strongest eight, compound 6b with a 3-carbon spacer gave the best inhi-
inhibitor among all these compounds. From the inhibition values bition for MAO-B (IC50 ¼ 5.01 mM). Shortening or extending the
of 6r–v and 6o–q, it was observed that compounds with cyclic chain length could not improve the activity and it decreased as
monoamine groups had better inhibitory activities than those the number of carbon atoms varied from four to eight. On the
with chain monoamine groups. Compounds 6i–k exhibited higher other hand, it can be seen from the IC50 values that 6e (IC50
levels of inhibitory potency than compounds 6l–n, revealing that 40.29 mM) was more potent than 6h–n, and a similar trend was
electron-withdrawing substituents on the N-benzyl group might be observed for 6o–q. Compounds bearing small amine groups
¼
benecial to their activities against Ab42 aggregation.
exhibited a good MAO-B inhibitory potency, which revealed that
steric hindrance of the substituted amino groups seemed to
play a key role in the modulation of MAO-B inhibitory activity.
Among the synthesized compounds, 6r displayed good inhibi-
Inhibition of MAO activity
To conrm the multipotent biological prole of all compounds, tion towards both MAO-A and MAO-B (MAO-A, IC50 ¼ 17.58 mM;
the activities of inhibiting the MAO-A and MAO-B were deter- MAO-B, IC50 ¼ 12.19 mM; SI ¼ 0.70). Surprisingly, 6h, the best
mined. The inhibitory activities were investigated by measuring ChE inhibitor, did not display potent inhibitions against MAOs
the effects of each derivative on the production of hydrogen (MAO-A, IC50 ¼ 89.65 mM; MAO-B, IC50 ¼ 58.31 mM). Compound
peroxide from p-tyramine, using the Amplex Red MAO assay, 6r, exhibiting remarkable MAO inhibitory activities, moderate
with iproniazid as the reference.41 Based on the screening data inhibition of ChEs and signicant inhibition of Ab42 aggrega-
(Table 2), most of the compounds displayed slightly better tion, showed a balanced biological prole against all tested
inhibitory activities towards MAO-B than towards MAO-A. targets and was chosen for further evaluation.
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Table 2 MAO inhibitory activities of the synthesized compounds
6h exhibited the best AChE (IC50 ¼ 1.56 mM) inhibitory activi-
ties, good inhibition of Ab42 aggregation (53.49%, at 20 mM), but
displayed poor anti-MAOs activities. In contrast, compound 6r,
exhibiting signicant inhibition of Ab42 aggregation, acceptable
MAO inhibitory activities and moderate inhibition of ChEs, was
a balanced inhibitor towards all tested targets for treating AD.
In the cell toxicity assay, 6r showed non-toxicity towards the SH-
SY5Y cell at 1–50 mM. Altogether, the multifunctional effects of
these resveratrol derivatives qualied them as potential anti-AD
drug candidates, and 6r could be a promising lead compound
for further research.
a
IC50 (mM)
Compounds
MAO-A
MAO-B
Selectivity indexb
6a
6b
6c
6d
6e
6f
6g
>100
>100
>100
97.38 ꢁ 8.6
90.35 ꢁ 6.02
>100
89.04 ꢁ 3.51
5.01 ꢁ 0.12
34.61 ꢁ 0.97
16.19 ꢁ 0.69
40.29 ꢁ 1.77
63.77 ꢁ 3.25
>100
<0.89
<0.50
<0.35
0.16
0.45
<0.64
—
>100
6h
6i
89.65 ꢁ 5.39
58.31 ꢁ 0.41
0.65
—
>100
>100
6j
6k
>100
>100
>100
>100
—
—
Abbreviations
6l
>100
>100
—
6m
6n
6o
6p
6q
6r
6s
6t
>100
>100
97.51 ꢁ 6.03
<0.97
—
AD
Alzheimer's disease
Cholinesterases
Acetylcholinesterase
Butyrylcholinesterase
b-Amyloid
Catalytic anionic site
Peripheral anionic site
Acetylcholinesterase inhibitors
Amyloid precursor protein
Monoamine oxidase
Molecular operating environment
Selectivity index
>100
ChEs
AChE
BuChE
Ab
CAS
PAS
AChEIs
APP
MAO
MOE
SI
33.09 ꢁ 1.01
37.46 ꢁ 1.74
89.43 ꢁ 7.58
17.58 ꢁ 0.76
29.83 ꢁ 0.87
24.27 ꢁ 0.91
>100
10.09 ꢁ 0.43
7.52 ꢁ 0.19
92.43 ꢁ 5.39
12.19 ꢁ 0.40
14.21 ꢁ 0.57
16.29 ꢁ 0.73
14.60 ꢁ 0.64
>100
0.31
0.20
1.03
0.70
0.48
0.67
<0.14
—
6u
6v
>100
Resveratrol
Iproniazid
17.41 ꢁ 0.51
29.37 ꢁ 0.68
1.68
1.19
6.58 ꢁ 0.69
7.82 ꢁ 0.41
a
IC50
:
50% inhibitory concentration (mean
ꢁ
SEM of three
experiments). b Selectivity index ¼ IC50 (MAO-B)/IC50 (MAO-A).
Acknowledgements
We acknowledge the nancial support from the Program for
Changjiang Scholars and Innovative Research Team in Univer-
sity (IRT1193), a Project Funded by the Priority Academic
Program Development of Jiangsu Higher Education Institutions
(PAPD).
SH-SY5Y neuroblastoma cell toxicity
On basis of the results above, the most potent compound 6r was
selected to further examine the potential toxicity effect on the
human neuroblastoma cell line SH-SY5Y.22,42 Aer exposing the
cells to this compound for 24 h, the cell viability was evaluated
by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium
(MTT) assay. The result indicated that 6r did not show any
signicant effect on cell viability at 1–50 mM (1 mM: 97.0 ꢁ
14.2%; 5 mM: 95.6 ꢁ 13.4%; 10 mM: 94.4 ꢁ 13.6%; 25 mM: 93.2 ꢁ
10.5%; 50 mM: 90.8 ꢁ 6.9%). This suggested that 6r was nontoxic
to SH-SY5Y cells and might be a suitable inhibitor for
treating AD.
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In conclusion, a series of resveratrol derivatives were designed,
synthesized and evaluated as multitarget-directed anti-Alz-
heimer agents for their inhibitory activities on ChEs, Ab42
aggregation and MAOs. Most of those compounds could effec-
tively inhibit ChEs than resveratrol. Enzyme kinetics and the
molecular modeling studies revealed that the compounds could
bind simultaneously to the CAS and the PAS of AChE.
Compounds 6h–k and 6r–t exhibited inhibitory percentages
similar to the reference compounds resveratrol and curcumin
in inhibition of Ab42 aggregation assay. For MAO, most of the
compounds showed slightly better inhibitory activities towards
MAO-B than MAO-A. Among the tested compounds, compound
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