Design, synthesis and evaluation of novel indandione derivatives as multifunctional agents with cholinesterase inhibition, anti-β-amyloid aggregation, antioxidant and neuroprotection properties against Alzheimer's disease

Article abstract of DOI:10.1016/j.bmc.2016.06.027

A series of novel 2-(4-(4-substituted piperazin-1-yl)benzylidene)-1H-indene-1,3(2H)-diones were designed, synthesized and appraised as multifunctional anti-Alzheimer agents. In vitro studies of compounds 27–38 showed that these compounds exhibit moderate

Full text of DOI:10.1016/j.bmc.2016.06.027

Accepted Manuscript
Design, Synthesis and Evaluation of Novel Indandione Derivatives as Multi-
functional Agents with Cholinesterase Inhibition, anti-β-amyloid Aggregation,
Antioxidant and Neuroprotection properties against Alzheimer’s Disease
Chandra Bhushan Mishra, Apra Manral, Shikha Kumari, Vikas Saini, Manisha
Tiwari
PII:
S0968-0896(16)30450-3
DOI:
http://dx.doi.org/10.1016/j.bmc.2016.06.027
BMC 13083
Reference:
Bioorganic & Medicinal Chemistry
To appear in:
Received Date:
Revised Date:
Accepted Date:
8 April 2016
11 June 2016
13 June 2016
Please cite this article as: Mishra, C.B., Manral, A., Kumari, S., Saini, V., Tiwari, M., Design, Synthesis and
Evaluation of Novel Indandione Derivatives as Multifunctional Agents with Cholinesterase Inhibition, anti-β-
amyloid Aggregation, Antioxidant and Neuroprotection properties against Alzheimer’s Disease, Bioorganic &
Medicinal Chemistry (2016), doi: http://dx.doi.org/10.1016/j.bmc.2016.06.027
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Design, Synthesis and Evaluation of Novel Indandione Derivatives as Multifunctional
Agents with Cholinesterase Inhibition, anti-β-amyloid Aggregation, Antioxidant and
Neuroprotection properties against Alzheimer's Disease
Chandra Bhushan Mishra1, Apra Manral1, Shikha Kumari1, Vikas Saini1, Manisha Tiwari*
Bio-Organic research laboratory, Dr. B. R. Ambedkar Centre for Biomedical Research,
University of Delhi, Delhi 110007, India
*Correspondence
Dr. Manisha Tiwari
Dr. B. R. Ambedkar Centre for Biomedical
Research, University of Delhi, Delhi 110007, India
E-mail: mtiwari07@gmail.com
1. These authors have contributed equally
1

Abstract
A series of novel 2-(4-(4-substituted piperazin-1-yl) benzylidene)-1H-indene-1,3(2H)-diones
were designed, synthesized and appraised as multifunctional anti-Alzheimer agents. In-vitro
studies of compounds 27-38 showed that these compounds exhibit moderate to excellent AChE,
BuChE and Aβ aggregation inhibitory activity. Notably, compounds 34 and 38 appeared as most
active multifunctional agents in the entire series and exhibited excellent inhibition against AChE
(IC50= 0.048 µM: 34; 0.036 µM: 38), Aβ aggregation (max %Inhibition 82.2%, IC50= 9.2 µM:
34; max % Inhibition 80.9%, IC50= 10.11 µM: 38) and displayed significant antioxidant potential
in ORAC-FL assay. Both compounds also successfully diminished H2O2 induced oxidative stress
in SH-SY5Y cells. Fascinatingly, compounds 34 and 38 showed admirable neuroprotective
effects against H2O2 and Aβ induced toxicity in SH-SY5Y cells. Additionally, both derivatives
showed no considerable toxicity in neuronal cell viability assay and represented drug likeness
properties in the primarily pharmacokinetics study. All these results together, propelled out that
compounds 34 and 38 might serve as promising multi-functional lead candidates for treatment of
AD in the future.
1. Introduction
Alzheimer's disease (AD) is a chronic neurodegenerative disorder that assaults the central
nervous system (CNS) by exerting progressive degeneration of its neurons.1 AD is well
characterized by dementia as well as cognitive impairments and currently affects over 48 million
people worldwide.2 Continuing for a long time, numerous investigations have focused on
deciphering the underlying mechanism of AD and it has come in light that multiple factors like
β-amyloid, acetylcholine (ACh), butyrylcholine and oxidative stress play a vital role in the
progression of AD.3 Nevertheless, upholding Ach levels through inhibition of
acetylcholineesterase (AChE) is continuously deliberated as the “gold standard” therapeutic
strategy for the management of AD. In support for this, four cholinesterase inhibitors (ChEls)
named tacrine, rivastigmine, donepezil and galantamine have entered in the market and yet
present in use (Figure 1).4 However, the use of tacrine has been limited now because of its
serious side effects such as hepatotoxicity, gastrointestinal disorders and hypotension. Other
2

drugs rivastigmine, donepezil and galantamine are effective, but they only target ACh rather
than, acting as multifunctional agent to treat AD.
O
NH2
O
O
N
N
Tacrine
Donepezil
O
O
O
H
N
H
N
N
O
OH
Rivastigmine
Galantamine
Fig 1. Chemical structures of well known Cholinesterase Inhibitors
It is well reported that accumulation of neurotoxic beta-amyloid (Aβ) peptide in the brain is a
major contributing factor which leads to the progression of AD and subsequently excessive Aβ
deposition exerts oxidative injury in the neuron.5 Additionally, several studies have shown that
reactive oxygen species (ROS) also play a crucial role in the development of AD because
oxidative cell injury manifested by nitration, lipid peroxidation as well as nucleic acid oxidation
is found in excessive levels in AD patients.6 Collectively, Aβ fragments and neurofibrils
deposition along with ROS overproduction are the main causes of neuroinflammation initiation
in AD. These neuroinflammatory paradigms alter production of chemokines, cytokines and
neurotoxins that precede neuronal degeneration in AD patients.7 For this reason, neuroprotection
approach is also highly beneficial and worthy strategy for AD treatment. Therefore, the
combination of ChEIs, Aβ disaggregation, neuroprotection and reduction of oxidative load may
produce a significant approach in AD management. By keeping this multi-factorial nature of AD
in mind, researchers today are concentrated on developing new Multi-target Directed Ligands
(MTLDs) to fight back against this disease.8-9 To solve this issue, single therapeutic agent with
multiple mechanism of action is inevitably required for the management of multifactorial disease
3

like AD. Designing of MTLDs heavily relies on the hybridization of two or more
pharmacophores. By exploiting this approach various hybrid molecules have been designed and
synthesized recently and fruitfully novel hybrids appeared as successful multifunctional agents to
treat AD.10-12
We are also actively engaged to develop potent MTLDs against AD and recently we have
developed piperazine/piperadine and diallyl disulfide analogs as multifunctional agent for the
treatment of AD.13-14 In this report, we have developed a novel series of 1,3 indandione
derivatives to study their multifunctional potential against AD. Indandiones and their derivatives
are an important class of bioactive molecules which possesses a broad spectrum biological
activities such as anticoagulants, anti-microbial, analgesic, anticancer as well as antiviral
activity.15-16 On the other hand the piperazine scaffold is widely used to develop numerous
biologically active agents such as antidepressants, anxiolytic, anticonvulsant, neuroprotective,
antioxidant and anti-Alzheimer’s.17 To proceed with our goal, we have rationally designed a
series of 2-(4-(4-substituted piperazin-1-yl)benzylidene)-1H-indene-1,3(2H)-diones which
consists of indanone moiety, curcumin fragment as well as piperazine moiety inside one frame as
shown in Figure 2.
4

Fig 2. Designing strategy of indandione-piperazine hybrid molecules
Studies have supported that indanone moiety plays an important role in AChEs inhibition.18 In
addition to this, curcumin appeared as a potential Aβ aggregation inhibitor with potent
antioxidant activity19 and the piperazine scaffold is also used extensively to develop AChE
inhibitors, neuroprotective as well as antioxidant molecules.17 Thus, our designed molecules are
endowed with necessary pharmacophoric features required for AChEs inhibition, Aβ aggregation
inhibition, neuroprotective and antioxidant activity, which may warrant their multifunctional
activity for AD.
2. Results and discussion
2.1. Chemistry
The synthesis of target compounds 2-(4-(4-substituted piperazin-1-yl)benzylidene)-1H-indene-
1,3(2H)-dione (27-38) was carried out according to Scheme 1. Briefly, a mixture of substituted
piperazine, 4-fluorobenzaldehyde and K2CO3 were heated at 1300C in DMF for 15-24h.
Thereafter, the reaction mixture was poured into ice cold water and the appeared precipitate was
filtered and dried to achieve formyl derivatives 14-25. Finally, obtained formyl derivatives 14-25
were coupled with 1,3 indandione 26 by employing Knoevenagel condensation reaction in the
presence of piperidine to yield final products 27-38. Obtained final products were purified by
column chromatography using chloroform and methanol (98:2) as an eluent and fully
characterized by 1HNMR, 13CNMR, mass spectroscopy as well as elemental analysis.
5

R= 1, 14, 27: Phenyl
R= 7, 20, 33: Benzoyl
= 8, 21, 34: Furoyl
= 2, 15, 28: p-fluorophenyl
= 3, 16, 29: p-trifluoromethylphenyl
= 4, 17, 30: p-chlorophenyl
= 5, 18, 31: p-methylphenyl
= 6, 19, 32: o, p- dimethylphenyl
= 9, 22, 35: Diphenylmethyl
= 10, 23, 36: Piperonyl
= 11, 24, 37: 2-pyridyl
=12, 25, 38: 2-pyrimidyl
Scheme. 1. Reagents and conditions. A; DMF, K2CO3, reflux; 15-24h; B. Ethanol, piperidine, reflux, 2-
4h.
2.2. Cholinesterase inhibition activity and structure activity relationship (SAR)
The target compounds (27-38) were tested for their potential to inhibit AChE and
butyrylcholinesterase (BuChE) enzymes. The IC50 values and selectivity index obtained for each
tested compound including the reference drug donepezil, are summarized in Table 1. All tested
compounds exhibits moderate to excellent inhibitory activity for both ChEls with IC50 values
ranging from sub-micromolar to nanomolar and on the basis of these results the following
structure activity relationship (SAR) was obtained. Within phenyl substituted derivatives, it was
observed that the inhibitory activity against AChE was substantially improved as electron
withdrawing properties of substitutent was increased and in result compound 29 (IC50 =
6

Table1. In vitro inhibition of AChE, BuChE, Aβ1-42 aggregation and oxygen radical absorbance
capacity (ORAC, Trolox equivalents) of compounds 27-38
O
O
N
N
R
where
‘R’
IC50 S.D (µM)
SIc
(BuChE/
AChE)
Aβ1-42 aggregation
Compound
27
inhibition (%)d
ORACe
eeAChEa
eqBuChEb
1.9
29.6
15.1
4.8
57.3 0.34
61.8 0.42
74.9 0.72
60.8 0.56
0.55 0.04
2.439 0.08
0.173 0.09
0.141 0.06
0.231 0.04
0.251 0.02
4.660 0.02
28
29
30
31
32
1.03 0.02
0.72 0.05
0.82 0.03
2.30 0.14
2.39 0.08
5.134 0.03
2.137 0.04
1.109 0.07
0.392 0.06
1.5
62.4 0.67
1.39
0.298 0.01
14.21 0.16
69.9 0.42
53.9 0.66
0.415 0.01
33
34
0.9
2.45 0.04
3.52 0.23
13.37 0.13
2.605 0.05
54.2
82.2 1.13
(9.2 0.15)f
0.048 0.002
0.061 0.007
35
54.9
1.89 0.07
80.6 1.08
3.352 0.11
(11.75 0.10)f
7

36
33.8
3.46 0.15
0.131 0.02
0.112 0.04
4.249 0.08
71.8 0.78
70.9 0.82
N
N
37
38
7.8
2.19 0.12
2.84 0.11
0.88 0.002
2.778 0.04
77.1
80.9 0.94
0.036 0.003
(10.11 0.06)f
N
Donepezil
Curcumin
-
86.1
-
n.t
n.t
n.t
0.039 0.002
-
3.36 0.2
-
-
53.8 0.63
(21.81 0.16)f
a 50% inhibitory concentration (means SD of three experiments) of AChE from electric eel.
b 50% inhibitory concentration (means SD of three experiments) of BuChE from equine serum.
cSI selectivity index for AChE; IC50eeBuChE/eqIC50 AChE.
d
Inhibition of self-induced Aβ1–42 aggregation (25µM) by tested inhibitors at 25µM by
thioflavin-T based fluorescence method (means S.D of three experiments)
eData are expressed as µmol of trolox equivalent/µmol of tested compound.
fIC50 value was determined from dose-response curves. Data are expressed as means S.D of
three independent experiments; n.t. -not tested.
0.141µM) consist of the trifluoromethyl substituent at phenyl ring appeared as most potent
among them. In contrast to this, compounds 31 (IC50 = 0.251µM) and 32 (IC50 = 0.298µM)
containing electron-donating groups such as p-methyl and di-methyl, in the terminal phenyl ring
showed quite better activity than those compounds which comprises of un-substituted phenyl
ring (compound 27, IC50 = 2.439µM). Hence, in this sub-series, the trend obtained in inhibitory
potency against AChE is follow as: p-CF3> p-F> p-Cl> p-Methyl> 2,4-dimethyl>H.
Furthermore, the replacement of phenyl group with other heterocyclic moieties leads to
significant improvement in ChEls inhibitory potencies as well as selectivity of the compounds.
For instance, compound 34 having furoyl group at terminal position and compound 35 with
diphenyl ring exhibited 2.9 and 2.3 fold rise in inhibitory potency, respectively. Moreover, 34
and 35 showed better selectivity for AChE over BuChE, as compared to most active compound
29 of the phenyl substituted sub-series. The overall results of this study undoubtedly indicated
that compound 38 comprising a terminal pyrimidine ring attached to piperazine linker, showed
excellent AChE inhibitory activity among the entire series with an IC50 = 0.036µM and is
8

slightly higher than Donepezil (IC50 = 0.039µM). Moreover, its high selectivity index, i.e., 77.1
fold is indicative of its favorable binding affinity for AChE over the BuChE. Almost all the
tested compounds exhibited a comparatively lower inhibitory potency against BuChE, with IC50
values ranging from 0.392 to 13.37µM indicating their preferable selectivity towards AChE.
However, compounds 34 and 38 showed comparatively better selectivity for AChE than other
tested derivatives. This selectivity profile may prove to be beneficial to diminish peripheral
cholinergic side effects and would surely bestow lower toxicity.
2.3. Kinetic study of AChE inhibition
To gain further insight into the mechanism of action of compound 38, Lineweaver-Burk double
reciprocal plots for AChE inhibition were generated and are shown in Figure 3. The interception
of the lines in the Lineweaver-Burk plot above the x-axis with both increased slope (decreased
Vmax) and intercepts (higher Km) at increasing concentrations of the inhibitor, indicated a
mixed-type inhibition, which verifies that compound 38 might be able to interact with both the
catalytic active site (CAS) and peripheral anionic site (PAS) of AChE.
Fig 3. Lineweaver-Burk plot for the Inhibition of AChE by compound 38
9

2.4. Inhibition of self mediated Aβ1-42 aggregation
Targeting self-induced Aβ1-42 aggregation represents an emerging approach for discovering drug
candidates for AD. Aβ1-42 has a high tendency to form fibrils and aggregates and its oligomers are
neurotoxic that cause membrane disruption in neuronal cells.20 To scrutinize the capability of target
compounds (27-38) to inhibit the self-mediated Aβ1-42 aggregation, the Thioflavin T (ThT)
21
fluorescence assay was implemented. Curcumin was taken as positive control because it is best
known anti-amyloidogenic agent. Most of test compounds showed better inhibitory activity against
Aβ1–42 aggregation (1-1.5 folds) at 25µM when compared to the curcumin (Table 1). It was observed
that the introduction of an electron rich substituent as in compounds 31 (62.4%) and 32 (69.9%)
exhibited significant improvement towards inhibition of Aβ1–42 aggregation. Furthermore, other
derivatives (34-38), which consist of different heterocyclic rings at their terminal end offered a
noticeable improvement in inhibition of Aβ1–42 aggregation. The most profound inhibition was
distinguished in compound 34, 35 and 38 having furoyl, diphenyl and pyrimidine moieties,
respectively inhibited more than 80% of Aβ1–42 aggregation which was nearly 1.5 folds greater than
inhibition by curcumin. All the three derivatives, achieved IC50 values much lower than that of
curcumin (IC50= 21.8 µM) as shown in Table 1. The combined result of β-amyloid and AChE
inhibition studies suggests that these derivatives act as dual AChE inhibitors. This kind of inhibitors is
often gifted with Aβ anti-aggregating properties, which arises either from the blockade of the AChE
peripheral anionic site (PAS) or from a direct interaction with Aβ (blockade of spontaneous Aβ
aggregation), and in the latter case it is likely due to the presence of curcumin fragment in the
designed inhibitors.
2.5. Inhibition of Aβ1-42 aggregation observed by Transmission Electron Microscopy (TEM)
Additionally, Aβ1-42 aggregation potential of the most potent derivatives 34 and 38 was also evaluated
by TEM study. After incubation at 37°C for 72 h, Aβ1-42 alone aggregated into mature, denser and
bulkier aggregates (Figure 4b), as compared to disaggregated Aβ1-42 alone (Figure 4a) kept at 0°C.
However, disaggregation effects were clearly visible upon treatment of compounds 34 and 38 for 72h
(25µM each) and few Aβ fibrils were observed (Figure 4d, 4f), as compared to standard curcumin
(Figure 4c).
10

c
a
b
0.2 µm
0.5 µm
0.5 µm
d
f
0.2 µm
0.2 µm
Fig 4. TEM images for Aβ-induced aggregation and test compound induced Aβ disaggregation: (a)
25µM Aβ1–42 alone at 0 h (b) 25µM Aβ1–42 alone at 24 h, 37°C (c) 25µM Aβ1–42 and 25µM curcumin (d)
25µM Aβ1–42 and 25µM compound 34 (f) 25µM Aβ1–42 and 25µM compound 38
Thus, the results of TEM are consistent with ThT binding assay where compounds 34 and 38
potentially inhibit Aβ aggregation noticeably through direct interaction or by blocking PAS site of
AChE.
2.6. Molecular docking study with AChE and BuChE
In order to study the binding mode and selectivity of most active compounds 34 and 38 with two
cholinesterases, TcAChE (PDB code: 1EVE) and HuBuChE (PDB code: 4TPK), molecular docking
was carried out using the docking program DS Client v 4.0 package. The active site of TcAChE
enzyme consists of the catalytic anionic site (CAS) containing Trp84 and Phe330 residues and the
peripheral anionic site (PAS) comprising mainly of Tyr70, Asp72, Tyr121, Tyr334, and Trp279
residues. Compound 38, with strong inhibitory activity and high selectivity to AChE, exhibited
multiple binding modes with AChE. The 1,3-indandione moiety adopted an appropriate orientation
for its interaction with CAS near the bottom of the gorge, via the σ–π interaction with indole ring of
Trp84 residue. The binding affinity can also be attributed to the π -π stacking interaction between the
terminal pyrimidine ring and Trp279 residue of PAS site. Moreover, phenyl ring, present between
11

piperazine linker and indandione moiety, engage in π –π stacking interaction with Phe331 residue
(Figure 5a, 5b).
5a
5b
Fig 5. Docking simulation of compound 38 with TcAChE: (a) Stereoviews looking down the gorge of TcAChE
binding with compound 38. (b) 2D schematic diagram of docking model of compound 38 with TcAChE.
Hydrogen-bond interactions as blue dashed line, π-π and cationic- π interactions are represented by an orange
line with symbols indicating the interaction
In compound 34–TcAChE complex, both phenyl ring and indole ring of 1,3-indandione moeity
simultaneously stacked against the indole ring of Trp279 residue via π-π stacking. Furthermore,
binding affinity was also contributed by furan ring present at terminal end establishes σ-π interaction
with Trp84 residue of CAS (Figure 6a, 6b). The binding mode of compounds 34 and 38 with BuChE
revealed that they also occupy the large catalytic cavity of BuChE and establishes π-π stacking
interactions between aromatic Tyr332 residue and phenyl ring of the compound. However, there were
no other significant interactions found in compound 34–BuChE/ 38–BuChE complex (Figure 7a, 7b).
Meanwhile, the calculated binding free energy of compounds 34 and 38 with AChE is lower than that
with BuChE.
12

6b
6a
Fig 6. Molecular docking studies of compound 34 with TcAChE: (a) Stereoviews TcAChE binding with
compound 34, showing hydrogen bond donors and acceptors residues around compound. (b)2D schematic
diagram of docking model of compound 34 with TcAChE. Residues involved in hydrogen-bonding, charge or
polar interactions are represented by magenta-coloured circles. Van der Waals interactions are represented by
green circles. The solvent accessible surface of an atom is represented by a blue halo around the atom.
Hydrogen-bond interactions as blue dashed line, π-π and cationic- π interactions are represented by an orange
line with symbols indicating the interaction
7b
7a
13

Fig 7 (a) 2D schematic diagram of docking model of compound 34 with HuBuChE. Residues involved in
hydrogen-bonding, charge or polar interactions are represented by magenta-colored circles. Van der Waals
interactions are represented by green circles. The solvent accessible surface of an atom is represented by a blue
halo around the atom. Hydrogen-bond interactions as blue dashed line (b) 2D schematic diagram of docking
model of compound 38 with HuBuChE. Residues involved in hydrogen-bonding, charge or polar interactions
are represented by magenta-colored circles. Van der Waals interactions are represented by green circles. The
solvent accessible surface of an atom is represented by a blue halo around the atom. Hydrogen-bond
interactions as blue dashed line.
Thus, these compounds exhibited satisfactory selectivity for the inhibition of AChE over BuChE and
exhibited a dual binding mode of action, i.e. they can simultaneously interact with CAS and PAS site
of AChE enzyme.22
2.8 Antioxidant activity by ORAC-FL method
Oxidative stress plays a pivotal role in the progression of AD and antioxidant therapy may contribute
significant role in the treatment of AD.6 In this regard, antioxidant activities of synthesized
compounds (27-38) were assessed by the well-established ORAC-FL method.23 Results shown that
these all compounds proved moderate to good antioxidant capacities ranging from 0.55 to 3.52 times
the Trolox value (Table 1). As consistent with AChE and ThT results, compounds having furoyl (34),
piperonyl (36) and pyrimidyl (38) ring in their molecular frame possessed admirable antioxidant
activity in the entire series. The ORAC-FL values were recorded 3.52, 3.46 and 2.84 trolox
equivalents for compounds 34, 36 and 38, respectively. The antioxidant potential of compounds 34,
36 and 38, advocated their multifunctional endeavors to defend against AD.
2.9. Intracellular antioxidant activity
The intracellular antioxidant activity of compounds 34 and 38 (5, 10 and 20µM) against H2O2-
induced ROS in SH-SY5Y cells were assessed by DCFH-DA fluorescent assay. Exposure of SH-
SY5Y cells to H2O2 (200µM) increased the intracellular ROS accumulation by about 1.58 fold, p <
0.001, in 24h. Treatment with compound 34, fashioned a dose dependent inhibitory effect (5µM, p <
0.05; 10µM, p < 0.01 and 20µM, p < 0.001) on ROS formation without affecting basal levels of ROS.
On the other hand, compound 38 also exerted a considerable inhibitory effect at the dose of 10µM and
20µM (Figure 8a). These results visibly suggested that compounds 34 and 38 have immense potential
14

to overcome oxidative load in SH-SY5Y cells, which make them capable to save cell against
oxidative damage.
2.10. Neuroprotection activity against H2O2 induced neurotoxicity
AD is a deadly progressive neurodegenerative disorder and ongoing neuron degeneration is the result
of excessive ROS production as well Aβ accumulation.24 Therefore, neuroprotective strategy
considered as permanent therapy for AD besides other symptomatic relief strategy. To achieve this
approach, the neuroprotective potential of the compounds 34 and 38 against H2O2-induced
neurotoxicity in SH-SY5Y cells were assessed by cell viability assay at three different concentrations
(5, 10 and 20 µM). Treatment of cells with H2O2 (200µM) for 24 h, resulted in a marked decrease in
cell viability (46%, p < 0.001) as compared to untreated control. The co-treatment of cells with
compounds 34 and 38 ameliorated H2O2-induced neurotoxicity in a concentration dependent manner
(Figure 8b). Compound 34 exhibited the highest protective capability at 10µM (p < 0.01) while
compound 38 showed similar protective ability at 20µM (p < 0.01). To validate these results, phase
contrast microscopy was employed to visualize the neuroprotective effect of the compound against
H2O2 induced neurotoxicity (Figure 8c).
8a
8b
15

ii
i
iii
iv
8c
Fig.8. Compounds 34 and 38 significantly reduced oxidative stress and exhibited the neuroprotective
effect on SH-SY5Y cells: (a) effect of compounds 34 and 38 on diminution of oxidative stress in DCF
florescence assay. (b) Phase-contrast micrographs showing H2O2-induced neurotoxicity and
neuroprotection of compound 34 and compound 38 in SH-SY5Y cells. (i) Cells without treatment (ii)
H2O2 alone (200μM) (iii) Compound 34 (20μM) was given for 24 h with H2O2 (200μM) at 37° C. (iv)
Compound 38 (20μM) was given for 24 h with H2O2 (200μM) at 37°C. All data were expressed as mean
S.D of three experiments and each included triplicate sets. #p < 0.05, ##p < 0.01, ###p < 0.001 vs control;
*p < 0.05, **p < 0.01, ***p < 0.001 vs H2O2 alone. Statistical analysis was performed using one way
ANOVA followed by Bonferroni test.
Microscopic observations showed that a large number of H2O2-treated cells became rounded,
vacuolated and floated, which clearly indicated apoptosis or necrosis in SH-SY5Y cells. However, the
treatment with compounds 34 and 38 (20µM) shielded these morphological changes and significantly
prevented the cell death induced by H2O2 toxicity in these cells. These results educe that compounds
34 and 38 successfully reduced H2O2 induced neurotoxicity in SH-SY5Y cells.
2.11. Neuroprotective activity against Aβ induced neurotoxicity
To elucidate extensive neuroprotective potential of compounds 34 and 38, they were also tested
against Aβ1–42 induced neurotoxicity in SH-SY5Y neuroblastoma cells. Results showed that co-
treatment of cells with both compounds for 24h ameliorated Aβ induced neurotoxicity in a
concentration dependent manner and exhibited neuroprotective effects at concentration ranging from
5 to 20µM (Figure 9a). The similar neuroprotective ability of compounds 34 and 38 were also
16

visualized by microscopic imaging where both compounds restored apoptosis associated
morphological changes in SH-SY5Y cells (Figure 9b).
i
ii
ii
i
9b
9a
Fig 9. Neuroprotection against Aβ-induced toxicity: (a) Compounds 34 and 38 were tested for
neuroprotective activity against Aβ toxicity in SH-SY5Y cell. Results are expressed as percent viability
compared to untreated control. All data were expressed as mean S.D of three experiments and each
included triplicate sets. #p < 0.05, ##p < 0.01, ###p < 0.001 vs control; *p < 0.05, **p < 0.01, ***p < 0.001
vs Aβ1–42 alone. Statistical analysis was performed using one way ANOVA followed by Bonferroni test.
(b) Phase-contrast micrographs showing Aβ-induced neurotoxicity and neuroprotection of 34 and 38 in
SH-SY5Y cells. (i) Cells without treatment. (ii) Aβ alone (25μM). (iii) Compound 34 (20μM) was given
for 24 h with Aβ (25μM) at 37° C. (iv) Compound 38 (20μM) was given for 24 h with Aβ (25μM) at 37°
C
These results suggested that these novel compounds exerted marked neuroprotection against Aβ-
induced neurotoxicity. The neuroprotective nature of these compounds confirms their potential as
multifunctional agent which not just able to maintain choline levels, but they likewise possess the
capacity to block progression of nerve cell degeneration.
2.12. Cytotoxicity study on normal neuronal cells
Additionally, toxicity of compounds 34 and 38 were assessed in SH-SY5Y neuronal cell line with
different concentrations ranging from 1-100 µM. After exposing the cells to these compounds for 48
h, the cell viability was evaluated by 3-(4, 5-dimethylthiazol-2-yl) -2, 5-diphenyltetrazolium (MTT)
17

assay. The results showed a dose-dependent effect of the tested compounds 34 (1µM: 98.1 3.6%;
5µM: 96.4 3.2%; 10µM: 95.3 4.6%; 25µM: 93.9 2.7%; 50µM: 89.6 3.1%; 75µM: 86.3 2.6%
and 100µM: 82.3 3.5%) and 38 (1µM: 98.1 3.6%; 5µM: 96.4 3.2%; 10µM: 95.3 4.6%; 25µM:
93.9 2.7%; 50µM: 89.6 3.1%; 75µM: 86.3 2.6% and 100µM: 82.3 3.5%) on the viability of
SH-SY5Y cells at different concentrations in the range from 1µM to 100µM. Interestingly, both
compounds did not produce a significant cytotoxic effect on the cells up to 100 µM concentration
after 24 h treatment (Figure 10).
110
34
38
100
90
80
70
concentration (µM)
Fig 10. Effect of compounds 34 and 38 on the viability of SH-SY5Y cells. The cells were incubated with the
indicated concentrations of the tested compounds for 48 h. The cell viability was assessed by MTT assay.
Percentages of the cell viability are presented as mean SEM from 3 independent experiments
Thus, the results indicate that these new compounds did not exhibit cytotoxicity.
2.13. In-silico physicochemical and pharmacokinetic study
Primarily pharmacokinetic properties of most active compounds 34 and 38 were evaluated by
Molinspiration and Biovia discovery studio software (Table 2, Figure 11).
18

Table 2 Physicochemical and Pharmacokinetic properties of most active compound 34 and 38
Comp. No Mol. Wt. AlogP98 HBAb HBDa NRBa Volume PSAa
BBB Absorption Hepatotoxicity
Level Level Level
412
396
3.67
3.77
6
6
0
0
3
3
363 71.16
355 63.82
2
1
0
0
0
0
34
38
a HBA: H-bond acceptor, HBA: H-bond donor, NRB: number of rotatable bonds
Fig 11. Discovery Studio 2.1 (Accelrys, San Diego, CA) ADMET Descriptors, 2D polar surface area (PSA 2D) in
A02 for compounds 34 and 38 are plotted against their corresponding calculated partition coefficient (ALogP98).
The area cover by the ellipses is a prediction of good intestinal absorption absorption and BBB with no violation of
ADMET properties.
,Results showed that both compounds obey Lipinski rule25 of 5 [molecular weight (Mol. Wt.) ≤ 500,
HBD ≤ 5, HBA ≤ 10, log P ≤ 5.0 and <10 number of rotatable bonds]. The polar surface area (PSA) is
an important descriptor to predict oral bioavailability and blood brain barrier (BBB) penetration
ability of any new molecule. Here, both compounds positively showed acceptable PSA, which
indicates their good oral bioavailability and BBB penetration when administered in-vivo. Moreover,
due to presence of appropriate number of rotatable bonds compounds 34 and 38 are likely to provide
optimal flexibility at the targeted site in the brain to exert desired biological activity. It was also
examined that compounds 34 and 38 displayed an absorption level ‘0’ which support their excellent
human intestinal absorption (HIA) property.26 Hepatotoxicity always remains a major concern for any
19

new drug development program and compounds 34 and 38 were found non-hepatotoxic. This study
evidently indicates the suitability of compounds 34 and 38 as drug like candidates for future.
3. Conclusion
In conclusion, herein we have successfully designed and synthesized a novel series of 2-(4-(4-
substituted piperazin-1-yl)benzylidene)-1H-indene-1,3(2H)-diones derivatives as potent multitarget
agents for the treatment of AD. Synthesized derivatives 27-38 pointedly inhibited AChE and Aβ
aggregation. Compounds 34 and 38 were found most active inhibitor among entire series and
inhibited AChE selectively over BuChE and also excellently inhibited Aβ aggregation as compared to
standard drug Donepezil. In-silico docking studies of compounds 34 and 38 further confirmed their
preferable binding with AChE over BuChE and also displayed interaction with key amino acids of
Aβ. Moreover, 34 and 38 acted as potent antioxidant agents in ORAC-FL assay and significantly
abridged H2O2 induced oxidative stress concentration dependently in DCF-fluorescence assay in SH-
SY5Y cells. Furthermore, compounds 34 and 38 exhibited potential neuroprotective effects in H2O2
and Aβ induced neurodegeneration in SH-SY5Y cells. In addition to this, both derivatives did not
exert toxicity against normal neuronal SH-SY5Y cells up to 100µM concentration and displayed
favorable drug like properties in primarily pharmacokinetic studies. Thus, novel indandione
derivatives 34 and 38 emerged as potent and safe multifunctional agents against AD and may develop
as suitable multifunctional agents for the management of AD in the future.
4. Experimental section
4.1. Chemistry
All the chemicals and reagents were obtained from Sigma Aldrich (St. Louis, MO, USA), Alfa
Aesar (Massachusetts), S.D Fine Chemicals (India) and Merck (Darmstadt, Germany) and
solvents for reaction medium were dried by standard methods. Melting points were taken in open
capillaries using model KSPII, KRUSS, (Germany). The nuclear magnetic resonance (NMR)
spectra were recorded on high resolution Jeol-400MHz NMR spectrophotometer (USA). Mass
20

spectra were recorded on an Agilent 6310 Ion trap LC/MS and elemental analysis (C, H and N)
was carried on Elementaranalysensysteme.
4.2. General procedure for synthesis of 4-(4-substituted piperazin-1-yl) benzaldehyde (14-
25)
A mixture of substituted piperazine (10 mmole), 4-fluorobenzaldehyde (10 mmole) and K2CO3
(2 mmole) were refluxed at 1300C in DMF for 15-24h. Thereafter, the reaction mixture was
poured into ice cold water and the precipitate that appeared was filtered and dried to accomplish
formyl derivatives (14-25) in a yield of 80-90%.
4.2.1. 4-(4-phenylpiperazin-1-yl) benzaldehyde (14)
White solid; yield 85% ; mp: 125-1270C ;1H NMR (CDCl3,400 MHz): δ3.35 (t, 4H, piperazine,
J= 4.9Hz), 3.57 (t, 4H, piperazine, J= 5.3 Hz), 6.91-6.98 (m, 5H, Ar-H), 7.28-7.32 (m, 2H, Ar-H,
J= 8.4 Hz), 7.78 (d, 2H, Ar-H, J= 8.4 Hz), 9.80 (s, 1H, CH); LC–MS: m/e 267 (M+1).
4.2.2. 4-(4-(4-fluorophenyl)piperazin-1-yl)benzaldehyde (15)
1
White solid; yield 80% ; mp: 130-1320C ; H NMR(CDCl3,400 MHz): δ3.25 (t, 4H, piperazine,
J= 4.9 Hz), 3.55 (t, 4H, piperazine, J= 4.9 Hz), 6.90-7.02 (m, 6H, Ar-H), 7.78 (d, 2H, Ar-H, J=
9.1 Hz), 9.80 (s, 1H, CH); LC–MS: m/e 285 (M+1).
4.2.3.4 -(4-(trifluoromethyl) piperazin-1-yl) benzaldehyde (16)
1
White solid; yield 87% ; mp: 185-1870C ; H NMR(CDCl3,400 MHz): δ3.47 (t, 4H, piperazine,
J= 4.9 Hz), 3.60 (t, 4H, piperazine, J= 4.9 Hz), 6.96 (dd, 4H, Ar-H, J= 8.7 Hz), 7.52 (d, 2H, Ar-
H, J= 9.1 Hz), 7.80 (d, 2H, Ar-H, J= 9.1 Hz), 9.81 (s, 1H, CH); LC–MS: m/e 335(M+1).
4.2.4. 4-(4-(4-chlorophenyl) piperazin-1-yl) benzaldehyde (17)
White solid; yield 85% ; mp: 147-1490C ; 1H NMR(CDCl3,400 MHz): δ3.31 (t, 4H, piperazine,
J= 4.6 Hz), 3.56 (t, 4H, piperazine, J= 4.9 Hz), 6.86 (d, 2H, Ar-H, J= 9.1 Hz), 6.96 (d, 2H, Ar-H,
J= 8.4 Hz), 7.22 (d, 2H, Ar-H, J= 8.0 Hz), 7.79 (d, 2H, Ar-H, J= 9.1 Hz), 9.80 (s, 1H, CH); LC–
MS: m/e 301 (M+1).
4.2.5. 4-(4-(p-tolyl)piperazin-1-yl)benzaldehyde (18)
21

White solid; yield 88% ; mp: 145-1470C ; 1H NMR(CDCl3,400 MHz): δ2.29 (s, 3H, CH3), 3.28
(t, 4H, piperazine, J= 4.9 Hz), 3.55 (t, 4H, piperazine, J= 5.3 Hz), 6.89 (d, 2H, Ar-H, J= 8.3 Hz),
6.97 ( d, 2H, Ar-H, J= 9.1 Hz), 7.11 (d, 2H, Ar-H, J= 8.4 Hz), 7.78 ( d, 2H, Ar-H, J= 9.1 Hz),
9.79 (s, 1H, CH); LC–MS: m/e 281(M+1).
4.2.6. 4-(4-(2,4-dimethylphenyl)piperazin-1-yl)benzaldehyde (19)
White solid; yield 78% ; mp: 155-1570C ; 1H NMR(CDCl3,400 MHz): δ2.28 (s, 3H, CH3), 2.31
(s, 3H, CH3), 3.02 (t, 4H, piperazine, J= 4.9 Hz), 3.55 (t, 4H, piperazine, J= 4.9 Hz), 6.93-7.03
(m, 5H, Ar-H), 7.77 ( d, 2H, Ar-H, J= 9.1 Hz), 9.79 (s, 1H, CH); LC–MS: m/e 295(M+1)
4.2.7. 4-(4-benzoylpiperazin-1-yl)benzaldehyde (20)
1
White solid; yield 78%; mp:101-1030C; H NMR(CDCl3,400 MHz):δ3.30-3.84 (m, 8H,
piperazine), 6.85 (d, 2H, Ar-H, J= 9.1 Hz), 7.32-7.37 (m, 5H, Ar-H), 7.70 (d, 2H, Ar-H, J=9.1
Hz), 9.72 (s, 1H, CH), LC–MS: m/e 295 (M+1).
4.2.8. 4-(4-(furan-3-carbonyl)piperazin-1-yl)benzaldehyde (21)
White solid; yield 86% ; mp: 98-1000C ; 1H NMR(CDCl3,400 MHz):δ3.51 (t, 4H, piperazine, J=
5.3Hz), 4.01 (s, 4H, piperazine), 6.52 (dd, 1H, Ar-H, J= 3.4 Hz), 6.95 (d, 2H, Ar-H, J= 9.1 Hz),
7.08 (d, 1H, Ar-H, J= 3.8 Hz), 7.52 (s, 1H, Ar-H), 7.77 (d, 2H, Ar-H, J= 9.1 Hz), 9.81 (s. 1H,
CH); LC–MS: m/e 285(M+1).
4.2.9. 4-(4-benzhydrylpiperazin-1-yl)benzaldehyde (22)
1
White solid; yield 82% ; mp: 122-1240C ; H NMR(CDCl3,400 MHz): δ2.54 (t, 4H, piperazine,
J= 4.9Hz), 3.39 (t, 4H, piperazine, J= 4.9 Hz), 4.26 (s, 1H, CH), 6.87 (d, 2H, Ar-H, J= 8.4 Hz),
7.18-7.31 (m, 6H, Ar-H), 7.44 (d, 4H, Ar-H, J= 7.6 Hz), 7.71 (d, 2H, Ar-H, J= 9.1 Hz), 9.76 (s,
1H, CH); LC–MS: m/e 357(M+1).
4.2.10. 4-(4-(benzo[d][1,3]dioxol-5-ylmethyl)piperazin-1-yl)benzaldehyde (23)
White solid; yield 78%; mp:115-1170C; 1H NMR(CDCl3,400 MHz): δ2.57 (t, 4H, piperazine, J=
4.9Hz), 3.40 (t, 4H, piperazine, J= 4.9 Hz), 3.47 (s, 2H, CH2), 5.95 (s, 2H, CH2), 6.76 (s, 2H, Ar-
H), 6.88-6.91 (m, 3H, Ar-H), 7.74 (d, 2H, Ar-H, J= 8.4 Hz), 9.77 (s, 1H, CH); LC–MS: m/e 325
(M+1).
22

4.2.11.4-(4-(pyridin-2-yl)piperazin-1-yl)benzaldehyde (24)
White solid; yield 82%; mp: 140-1420C ; 1H NMR(CDCl3,400 MHz): δ2.39 (s, 4H, piperazine),
3.36 (s, 4H, piperazine), 6.83 (d, 2H, Ar-H, J= 9.9 Hz), 7.24 (s, 2H, Ar-H), 7.75 (q, 4H, Ar-H, J=
9.1 Hz), 10.0 (s, 1H, CH); LC–MS: m/e 268(M+1).
4.2.12.4-(4-(pyrimidin-2-yl)piperazin-1-yl)benzaldehyde (25)
1
White solid; yield 79% ; mp: 138-1400C ; H NMR(CDCl3,400 MHz): δ3.51 (t, 4H, piperazine,
J= 5.3 Hz), 4.00 (t, 4H, piperazine, J= 5.3 Hz), 6.55 (t, 1H, Ar-H, J= 4.4 Hz), 6.95 (d, 2H, Ar-H,
J= 9.1 Hz), 7.78 (d, 2H, Ar-H, J= 8.4 Hz), 8.33 (d, 2H, J= 4.5 Hz), 9.79 (s, 1H, CH); LC–MS:
m/e 269 (M+1).
4.3. General procedure for synthesis of 2-(4-(4-substituted piperazin-1-yl)benzylidene)-1H-
indene-1,3(2H)-dione (27-38)
Piperidine (2mL) was added to a solution of formyl derivatives 14-25 (4 mmole) and 1,3-
indandione (4 mmol) in 20mL of anhydrous ethanol. The reaction mixture was stirred for 3-6h
and the precipitate that appeared was filtered and dried. The acquired crude products were
purified by column chromatography using chloroform:methanol (98:02) as eluent.
4.3.1.2-(4-(4-phenylpiperazin-1-yl) benzylidene)-1H-indene-1,3(2H)-dione(27)
1
Yellow solid; yield 85%; mp: 210-2120C; HNMR (CDCl3, 400 MHz): δ3.37(t, 4H, 2xCH2, J=
6.0 Hz), 3.66(t, 4H, 2xCH2, J= 5.7 Hz), 6.90-6.98 (m, 5H, Ar), 7.31(t, 2H, Ar, J= 7.8Hz), 7.74-
13
7.76(m, 2H, Ar), 7.80(s, 1H, CH), 7.92-7.97(m, 2H, Ar), 8.55(d, 2H, Ar, J= 9.1 Hz); C NMR
(CDCl3, 100 MHz): δ 46.6, 48.8, 113.2, 116.2, 120.3, 122.6, 123.5, 124.2, 129.2, 134.3, 134.6,
137.6, 139.8, 142.3, 146.9, 150.8, 153.9, 189.9, 191.3; LC-MS: m/z, 395 (M+1); Anal. Calcd for
C26H22N2O2: C, 79.16; H, 5.62; N, 7.10Found: C, 79.47; H, 5.41; N, 7.35.
4.3.2. 2-(4-(4-(4-fluorophenyl) piperazin-1-yl)benzylidene)-1H-indene-1,3(2H)-dione (28)
1
Yellow solid; yield 76%; mp: 210-2120C; HNMR (CDCl3, 400 MHz): δ 3.20(t, 4H, 2xCH2, J=
5.3 Hz), 3.58 (t, 4H, 2XCH2, J= 5.3 Hz), 6.84-6.96 (m, 6H, Ar), 7.67-7.69(m, 2H, Ar), 7.73(s,
1H, CH), 7.86-7.90(m, 2H, Ar), 8.87(d, 2H, Ar, J= 8.4Hz);LC-MS: m/z, 413 (M+1); Anal. Calcd
for C26H21FN2O2: C, 75.71; H, 5.13; F, 4.61; N, 6.79Found: C, 75.46; H, 5.34; N, 7.09.
23

4.3.3.2-(4-(4-(4-(trifluoromethyl)phenyl)piperazin-1-yl)benzylidene)-1H-indene-1,3(2H)-
dione (29)
Yellow solid; yield 74%; mp: 240-2420C; 1HNMR (CDCl3, 400 MHz): δ 3.49(t, 4H, 2X CH2, J=
4.9), 3.68(t, 4H, 2XCH2, J= 5.3 Hz), 6.93-6.97(m, 4H, Ar), 7.52(d, 2H, Ar, J= 8.4 Hz), 7.74-
7.76(m, 2H, Ar), 7.80(s, 1H, CH), 7.93-7.97(m, 2H, Ar), 8.55(d, 2H, Ar, J= 9.1Hz);LC-MS: m/z,
463 (M+1);Anal. Calcd for C27H21F3N2O2: C, 70.12; H, 4.58; N, 6.06Found:C, 69.80; H, 4.87; N,
6.47
4.3.4. 2-(4-(4-(4-chlorophenyl)piperazin-1-yl)benzylidene)-1H-indene-1,3(2H)-dione (30)
Yellow solid; yield 65%; mp: 222-2250C; 1HNMR (CDCl3, 400 MHz): δ 3.32(t, 4H, 2XCH2, J=
5.7 Hz), 3.65(t, 4H, 2XCH2, J= 5.3 Hz), 6.87(d, 2H, Ar, J= 9.1 Hz), 6.96(d, 2H, Ar, J= 9.1 Hz),
7.22-7.23(m, 2H, Ar), 7.72-7.77(m, 2H, Ar), 7.80(s, 1H, CH), 7.93-7.97(m, 2H, Ar), 8.54(d, 2H,
Ar, J= 9.1 Hz); ); LC-MS: m/z, 429 (M+1);Anal. Calcd for C26H21ClN2O2: C, 72.81; H, 4.94; N,
6.53 Found:73.19; H, 5.23; N, 6.21.
4.3.5. 2-(4-(4-(p-tolyl) piperazin-1-yl)benzylidene)-1H-indene-1,3(2H)-dione (31)
1
Yellow solid; yield 68%; mp: 198-2000C; HNMR (CDCl3, 400 MHz): δ 2.29(s, 3H, CH3),
3.29(t, 4H, 2XCH2, J= 4.9 Hz), 3.64(t, 4H, 2X CH2, J= 4.9 Hz), 6.88(d, 2H, Ar, J= 7.6 Hz),
6.96(d, 2H, Ar, J= 8.4 Hz), 7.11(d, 2H, Ar, J= 7.6 Hz), 7.34-7.75(m, 2H, Ar), 7.79(s, 1H, CH),
13
7.92-7.95(m, 2H, Ar), 8.53(d, 2H, Ar, J= 8.4 Hz); C NMR (CDCl3, 100 MHz): δ 20.4, 46.6,
113.1, 116.6, 122.6, 123.5, 124.2, 129.7, 129.9, 134.3, 134.5, 137.6, 139.8, 142.2, 146.9, 148.6,
148.9, 153.9, 187.7, 191.3; LC-MS: m/z, 409 (M+1);Anal. Calcd for C27H24N2O2: C, 79.39; H,
5.92; N, 6.86Found: C, 79.69; H, 5.79; N, 6.57
4.3.6. 2-(4-(4-(2,4-dimethylphenyl)piperazin-1-yl)benzylidene)-1H-indene-1,3(2H)-dione (32)
1
Yellow solid; yield 90%; mp: 170-1720C; HNMR (CDCl3, 400 MHz): δ 2.29(s, 3H, CH3),
2.32(s, 3H, CH3), 3.03(t, 4H, 2XCH2, J= 4.9 Hz), 3.62(t, 4H, 2XCH2, J= 4.8Hz), 6.92-7.04(m,
5H, Ar), 7.73-7.76(m, 2H, Ar), 7.77(s, 1H, CH), 7.92-7.96(m, 2H, Ar), 8.34(d, 2H, Ar, J= 9.0
Hz);13C NMR (CDCl3, 100 MHz): δ 17.7, 20.7, 47.3, 51.6, 113.0, 113.2, 119.0, 122.6, 123.4,
124.1, 127.1, 131.7, 132.0, 132.5, 133.2, 134.3, 134.5, 137.5, 137.7, 139.8, 142.2, 146.9, 148.3,
24

154.2, 189.8, 191.4; LC-MS: m/z, 423 (M+1);Anal. Calcd for C28H26N2O2: C, 79.59; H, 6.20; N,
6.63Found: C,79.90; H, 6.01; N, 6.31
4.3.7.2-(4-(4-benzoylpiperazin-1-yl)benzylidene)-1H-indene-1,3(2H)-dione (33)
1
Yellow solid; yield 88%; mp: 260-2620C; HNMR (CDCl3, 400 MHz): δ 3.48-3.95(m, 8H,
4XCH2), 6.92(d, 2H, Ar, J= 8.4 Hz), 7.45(s, 5H, Ar), 7.74-7.76(m, 2H, Ar), 7.79(s, 1H, CH),
7.93-7.95(m, 2H, Ar), 8.52(d, 2H, Ar, J= 8.4 Hz);13C NMR (CDCl3, 100 MHz): δ 46.9, 113.4,
113.6, 122.7, 124.1, 124.9, 127.0, 127.2, 128.6, 130.1, 134.5, 134.7, 135.1, 137.3, 137.5, 139.8,
142.2, 146.7, 153.6, 189.7, 191.3;LC-MS: m/z, 423 (M+1);Anal. Calcd for C27H22N2O3: C, 76.76;
H, 5.25; N, 6.63Found: C, 77.01, H, 5.45; N, 6.36.
4.3.8. 2-(4-(4-(furan-2-carbonyl) piperazin-1-yl)benzylidene)-1H-indene-1,3(2H)-dione (34)
1
Yellow solid; yield 78%; mp: 250-2520C; HNMR (CDCl3, 400 MHz): δ 3.53(t, 4H, 2 X CH2),
3.95(s, 4H, 2 XCH2), 6.45-6.46(m, 1H, Ar), 6.86(d, 2H, Ar, J= 9.1Hz), 7.03(d, 1H, Ar, J=
3.0Hz), 7.45(s, 1H, Ar), 7.67-7.70(m, 2H, Ar), 7.73(s, 1H, CH), 7.87-7.90(m, 2H, Ar), 8.47(d,
2H, Ar, J= 9.1 Hz); 13C NMR (CDCl3, 100 MHz): δ 29.5, 46.5, 111.5, 113.2, 117.2, 122.7, 123.7,
124.6, 134.5, 134.7, 137.5, 139.8, 142.1, 144.0, 146.8, 147.6, 153.5, 159.1, 189.8, 191.3; LC-MS:
m/z, 413 (M+1);Anal. Calcd for C25H20N2O4: C, 72.80; H, 4.89; N, 6.79 Found: C, 72. 49; H, 5.11;
N, 6.44.
4.3.9. 2-(4-(4-benzhydrylpiperazin-1-yl)benzylidene)-1H-indene-1,3(2H)-dione (35)
Yellow solid; yield 85%; mp: 228-2300C; 1HNMR (CDCl3, 400 MHz): δ 2.55(t, 4H, 2 X CH2, J=
4.9 Hz), 3.48(t, 4H, 2 X CH2, J= 4.9 Hz), 4.26(s, 1H, CH), 6.87(d, 2H, Ar, J= 8.4 Hz), 7.19-
7.22(m, 2H, Ar), 7.28-7.32(m, 4H, Ar), 7.45(d, 4H, Ar), 7.72-7.74(m, 2H, Ar), 7.77(s, 1H, CH),
13
7.91-7.94(m, 2H, Ar), 8.50(d, 2H, Ar, J= 9.1 Hz); C NMR (CDCl3, 100 MHz): δ 46.7, 52.4,
76.6, 112.9, 122.6, 123.2, 123.9, 127.1, 127.8, 128.6, 134.3, 134.5, 137.6, 139.9, 142.2, 147.0,
154.1, 190.0, 191.5; LC-MS: m/z, 485 (M+1);Anal. Calcd for C33H28N2O2: C, 81.79; H, 5.82; N,
5.78Found: C, 81. 45; H, 5.64; N, 6.06
4.3.10. 2-(4-(4-(benzo[d][1,3]dioxol-5-ylmethyl)piperazin-1-yl)benzylidene)-1H-indene-
1,3(2H)-dione (36)
25

Yellow solid; yield 90%; mp: 170-1720C; 1HNMR (CDCl3, 400 MHz): δ 2.57(t, 4H, 2X CH2, J=
4.9 Hz), 3.47-3.50(m, 6H, 3X CH2), 5.95(s, 2H, CH2), 6.76(s, 2H, Ar), 6.88-6.91(m, 3H, Ar),
13
7.72-7.74(m, 2H, Ar), 7.77(s, 1H, CH), 7.92-7.95(m, 2H, Ar), 8.50(d, 2H, Ar, J= 8.3 Hz); C
NMR (CDCl3, 100 MHz): δ 46.6, 52.4, 62.5, 100.9, 107.9, 109.3, 113.0, 122.1, 122.6, 123.2, 124.0,
131.4, 134.2, 134.5, 137.6, 139.8, 142.2, 146.7, 147.0, 147.7, 154.1, 189.8, 191.4; LC-MS: m/z,
453 (M+1);Anal. Calcd for C28H24N2O4: C, 74.32; H, 5.35; N, 6.19Found: C, 74.53, H, 5.11; N,
5.94
4.3.11. 2-(4-(4-(pyridin-2-yl)piperazin-1-yl)benzylidene)-1H-indene-1,3(2H)-dione (37)
1
Yellow solid; yield 89%; mp: 178-1800C; HNMR (CDCl3, 400 MHz): δ 3.64-3.67(m, 4H, 2 X
CH2), 3.75-3.77(m, 4H, 2 X CH2), 6.66-6.69(m, 2H, Ar), 6.94(d, 2H, Ar, J= 8.4 Hz), 7.51-
7.55(m, 1H, Ar), 7.73-7.75(m, 2H, Ar), 7.79(s, 1H, CH), 7.92-7.96(m, 2H, Ar), 8.21-8.22(m, 1H,
13
Ar), 8.54(d, 2H, Ar, J= 9.1 Hz); C NMR (CDCl3, 100 MHz): δ 44.4, 46.1, 106.9, 112.9, 113.7,
122.6, 123.4, 124.2, 134.3, 134.5, 137.6, 139.8, 142.2, 146.9, 147.9, 153.8, 158.8, 189.8, 191.4;
LC-MS: m/z, 396 (M+1);Anal. Calcd for C25H21N3O2: C, 75.93; H, 5.35; N, 10.63Found: C, 75.
61; H, 5.54; N, 10.99.
4.3.12. 2-(4-(4-(pyrimidin-2-yl) piperazin-1-yl)benzylidene)-1H-indene-1,3(2H)-dione (38)
Yellow solid; yield 91%; mp: 210-2120C; 1HNMR (CDCl3, 400 MHz): δ 3.61(t, 4H, 2 X CH2, J=
5.3 Hz), 4.01(t, 4H, 2 X CH2, J= 5.3 Hz), 6.56(t, 1H, Ar, J= 4.5 Hz), 6.95(d, 2H, Ar, J= 9.1 Hz),
7.73-7.76(m, 2H, Ar), 7.79(s, 1H, CH), 7.93-7.96(m, 2H, Ar), 8.34(d, 2H, Ar, J= 4.6 Hz), 8.55(d,
2H, Ar, J= 9.1 Hz); 13C NMR (CDCl3, 100 MHz): δ 43.0, 46.3, 110.4, 113.0, 122.6, 123.5, 124.2,
134.3, 134.6, 137.6, 139.8, 142.2, 147.0, 153.9, 157.8, 161.3, 189.8, 191.4; LC-MS: m/z, 397
(M+1);Anal. Calcd for C24H20N4O2: C, 72.71; H, 5.08; N, 14.13Found:C, 72. 98; H, 5.29, N,
13.92.
4.4. Biological Evaluations
4.4.1. Inhibition of AChE and BuChE
AChE and BuChE inhibitory activities of the test compounds (27-38) were determined by the
modified Ellman’s method.27 Briefly, stock solutions of tested compounds (10 mM) were prepared in
26

ethanol and diluted using 0.1 M KH2PO4/K2HPO4 buffer (pH 8.0) to afford a final concentration range
between (1-100 µM). Enzyme solutions were prepared by dissolving lyophilized powder in double-
distilled water. The assay solution consisted of 1mL of 0.1 M phosphate buffer KH2PO4/K2HPO4,
25µL of AChE (0.22 U/mL, E.C. 3.1.1.7, from electric eel) or 25µL of BuChE (0.06 U/mL, E.C.
3.1.1.8, from equine serum) and 100 µL of various concentrations of test compounds which was
allowed to stand for 5 min before 100 µL of 0.01 M DTNB were added. A positive control of
donepezil was used in the same range of concentrations. The reaction was started by addition of 20µL
of the 0.075 M substrate solution (acetylthiocholine/ butyrylthiocholine) and exactly 2 min after
substrate addition the absorption was measured at 25°C at 412 nm. The non-enzymatic hydrolysis of
acetylthiocholine/ butyrylthiocholine iodide was also measured in enzyme-free assay systems, and the
results were employed as blank. In control experiments, inhibitor-free assay systems were utilized to
measure the full activity. The percent inhibition was calculated by the following expression: (1-
Ai/Ac) x 100, where Ai and Ac are the absorbances obtained for AChE in the presence and absence of
the inhibitors, respectively, after subtracting the respective background. Each experiment was
performed in triplicate, and the mean standard deviation was calculated. Data from concentration-
inhibition experiments of the inhibitors were calculated by nonlinear regression analysis, using the
Graph Pad Prism 5 program.
4.4.2. Kinetic study of AChE
Kinetic study of AChE was performed by using a previously reported method.27 Test compound was
added into the assay solution and pre-incubated with the enzyme at 37°C for 15 min, followed by the
addition of substrate. Kinetic characterization of the hydrolysis of ATC catalyzed by AChE was
carried out spectrometrically at 412 nm. A parallel control was made with the assay solution of no
inhibitor for each time. The plots were assessed by a weighted least square analysis that assumed the
variance of V to be a constant percentage of V for the entire data set. Slopes of these reciprocal plots
were then plotted against the concentration of the inhibitors in a weighted analysis and Ki was
determined as the ratio of the plot intercept to the plot slope.
4.4.3. Thioflavin T (ThT) assay
27

Commercially available peptides were first treated with hexafluoroisopropanol (HFIP) at 5mg/ml to
avoid self-aggregation. The clear solution containing the dissolved peptide was then aliquoted in
micro centrifuge tube. The HFIP was allowed to evaporate under a stream of nitrogen until a clear
film remained in the test tube. The pre-treated Aβ1-42 samples were then dissolved in DMSO in order
to have a stable stock solution (Aβ = 1mM). For the inhibition of self-mediated Aβ1–42 aggregation
experiment, the Aβ stock solution was diluted with 50mM phosphate buffer (pH 7.4) to 25µM before
use. A mixture of the peptide (10µL, 25µM, final concentration) with or without the tested compound
(25µM) was incubated at 37°C for 48 h. To quantify amyloid fibril formation, the thioflavin-T
fluorescence method was used.28 Blanks containing 50 mM phosphate buffer (pH 7.4) instead of Aβ
with or without inhibitors were also carried out. After incubation, samples were diluted to a final
volume of 200µL with 50mM glycine–NaOH buffer (pH 8.0) containing thioflavin-T (5µM). Then,
the fluorescence intensities were recorded five minutes later (excitation, 450 nm; emission, 485 nm).
The percent inhibition of aggregation was calculated by the expression (1-IFi/IFc) × 100% in which
IFi and IFc are the fluorescence intensities obtained for Aβ in the presence and absence of inhibitors
after subtracting the background, respectively. Each measurement was run in triplicate.
4.4.4. Oxygen radical absorbance capacity (ORAC-FL) assay
The reaction was carried out in 75mM phosphate buffer (pH 7.4), and the final reaction mixture was
200µL. Antioxidant (20µL) and FL (120µL; 70mM, final concentration) solutions were placed in a
black 96-well microplate (96F untreated, Nunc). The mixture was preincubated for 15 min at 37°C,
and then AAPH solution (60µL, 12mM, final concentration) was added rapidly using a multichannel
pipette. The microplate was immediately placed in the reader and the fluorescence recorded every
minute for 80 min (excitation, 485 nm; emission, 520 nm). Samples were measured at different
concentrations (1-25µM). A blank (FL + AAPH) using phosphate buffer instead of the tested
compound and eight calibration solutions using Trolox (1-25µM), final concentration) as antioxidant
were also carried out in each assay. A blank using phosphate buffer instead of the tested compound
was also carried out. All of the reaction mixtures were prepared in triplicate, and at least three
independent runs were performed for each sample. The antioxidant curves (fluorescence versus time)
were normalized to the curve of the blank. The area under the fluorescence decay curve (AUC) was
calculated using the following equation:
28

i = 80
AUC = 1 + Σ (fi/f0)
i = 1
Where f0 is the initial fluorescence reading at 0 min and fi is the fluorescence reading at time i. The
net AUC was calculated by the following equation: AUCsample - AUCblank. The regression equations
between the net AUC and the Trolox concentrations were calculated. The ORAC-FL value for each
sample was calculated using the standard curve, and the ORAC-FL value of each tested compound is
thus expressed as Trolox equivalents.
4.4.5. ROS measurements under H2O2 -induced cellular stress
ROS assay was performed in living cells as previously described by Wang and Zhu.29 SH-SY5Y
cells were seeded at 2 x104 cells per well in 96-well plates for neuroprotection activity assay.
Briefly, intracellular ROS production was measured from SH-SY5Y cells by treating them with
fluorescent probe 2′,7′-dichlorofluorescein diacetate (DCFH-DA) for 20 min after 24h of H2O2
(200µM) treatment in the presence or absence of compounds 34 and 38 (5, 10 and 20µM). As a
nonpolar compound, DCFH-DA crosses cell membrane and cellular esterases cleaved diacetate
groups of DCFH-DA to form non-fluorescent 2′,7′-dichlorofluorescein (DCFH). In the presence
of intracellular ROS, DCFH is oxidized very quickly to highly fluorescent DCFH. The total
fluorescence was measured using an ELISA plate reader (Tecan infinity 20) at an emission
wavelength of 488 nm and an excitation wavelength of 524 nm.
4.4.6. TEM assay
Aβ1–42peptide (Sigma) stock was diluted with 20mM phosphate buffer (pH 7.4) at 4°C to 40 mM
before use. For the inhibition of Aβ1–42aggregation experiment, Aβ1–42was incubated within the
presence and absence of compounds 34, 38 and curcumin at 37°C for 48h. The final
concentration of Aβ1–42 and compounds were 50µM and 25µM respectively. Aliquots (10µL) of
the samples were placed on a carbon coated copper/rhodium grid for 2 min at room temperature.
Each grid was stained with uranyl acetate (1%) for 2 min. The excess staining solution was
removed and the specimen was transferred for imaging with transmission electron microscopy
(JEOL JEM-1400).
29