Synthesis and Evaluation of Chroman-4-One Linked to N-Benzyl Pyridinium Derivatives as New Acetylcholinesterase Inhibitors

Article abstract of DOI:10.1002/ardp.201500149

A novel series of chroman-4-one derivatives containing the N-benzyl pyridinium moiety were designed, synthesized, and evaluated for their acetylcholinesterase (AChE) inhibitory activities. Among the various synthesized compounds, (E)-1-(2,3-dibromobenzyl)-4-((7-ethoxy-4-oxochroman-3-ylidene)methyl)pyridinium bromide (8l) depicted the most potent anti-AChE activity (IC₅₀=0.048μM). In addition, the molecular modeling study allowed us to detect possible binding modes that are in full compliance with the observed results through in vitro experiments. A novel series of chroman-4-one derivatives bearing N-benzyl pyridinium derivatives (8a-l) were synthesized and evaluated in vitro for their acetylcholinesterase inhibitory activities. The most promising compound, (E)-1-(2,3-dibromobenzyl)-4-((7-ethoxy-4-oxochroman-3-ylidene)methyl)pyridinium bromide 8l, showed an IC₅₀ value of 0.048μM.

Full text of DOI:10.1002/ardp.201500149

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Arch. Pharm. Chem. Life Sci. 2015, 348, 643–649
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Full Paper
Synthesis and Evaluation of Chroman-4-One Linked to N-Benzyl
Pyridinium Derivatives as New Acetylcholinesterase Inhibitors
Saman Arab1, Seyed-Esmail Sadat-Ebrahimi1, Maryam Mohammadi-Khanaposhtani1, Alireza Moradi2,
Hamid Nadri2, Mohammad Mahdavi1, Setareh Moghimi1, Mehdi Asadi1, Loghman Firoozpour3,
Morteza Pirali-Hamedani1, Abbas Shafiee1, and Alireza Foroumadi1,3
1
Department of Medicinal Chemistry, Faculty of Pharmacy and Pharmaceutical Sciences Research Center,
Tehran University of Medical Sciences, Tehran, Iran
Department of Medicinal Chemistry, Faculty of Pharmacy, Shahid Sadoughi University of Medical
2
Sciences, Yazd, Iran
3
Drug Design and Development Research Center, Tehran University of Medical Sciences, Tehran, Iran
A novel series of chroman-4-one derivatives containing the N-benzyl pyridinium moiety were
designed, synthesized, and evaluated for their acetylcholinesterase (AChE) inhibitory activities.
Among the various synthesized compounds, (E)-1-(2,3-dibromobenzyl)-4-((7-ethoxy-4-oxochroman-3-
ylidene)methyl)pyridinium bromide (8l) depicted the most potent anti-AChE activity (IC50 ¼ 0.048 mM).
In addition, the molecular modeling study allowed us to detect possible binding modes that are in
full compliance with the observed results through in vitro experiments.
Keywords: Acetylcholinesterase / Alzheimer’s disease / Chroman-4-one / Docking study / N-Benzyl
pyridinium
Received: April 24, 2015; Revised: June 17, 2015; Accepted: June 23, 2015
DOI 10.1002/ardp.201500149
Additional supporting information may be found in the online version of this article at the publisher’s web-site.
:
amyloid potency such as melatonin, rifampicin, benzofuran,
and acridinone derivatives which are in clinical trial [4].
Introduction
Alzheimer’s disease (AD) is an age-related disease leading to
progressive decline in cognition and memory [1]. There are
two main hypotheses in the pathogenesis of AD: reduced
levels of acetylcholine and the polymerization of the amyloid
b-peptide (Ab) in the brain [2]. Therefore, increasing the
synaptic level of acetylcholine by means of acetylcholinester-
ase inhibitors such as donepezil, rivastigmine, and galant-
amine could be beneficial to ameliorate the symptoms of AD
without any effect in the course of the disease [3]. The
suitable route to prevent the disease progression has been
reported by the assistance of various compounds with anti-
It is well known that AChE, in addition to the hydrolysis of
acetylcholine, interacts with Ab through peripheral anionic
site (PAS) and accelerates the polymerization of Ab pep-
tides [5–7]. Thus, applying dual binding site AChE inhibitors
which interact with both active site and PAS, would be a new
therapeutic approach for seeking new drug candidates
against AD [8, 9].
According to molecular and biological studies on donepezil
(Fig. 1A), the most popular approved therapies for AD, this
drug could be regarded as
a dual binding site AChE
inhibitor [10, 11]. Docking study evidences have also shown
that donepezil interacts with the catalytic site and PAS
through benzyl piperidine moiety and indanone ring,
respectively [12].
In recent years, our research group has reported the
synthesis of various new AChE inhibitors [13–16]. In this study,
we decided to design efficient dual AChE inhibitors based
on our previous reports on the potent donepezil analogs
(Fig. 1B and C) [17–19]. Accordingly, a novel series of N-benzyl-
Correspondence: Dr. Alireza Foroumadi, Department of Medici-
nal Chemistry, Faculty of Pharmacy and Pharmaceutical Sciences
Research Center, Tehran University of Medical Sciences, Tehran,
Iran.
E-mail: aforoumadi@yahoo.com
Fax: þ98-21-66461178
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Figure 1. Structures of donepezil hydrochloride (A), pyridinium containing AChE inhibitors (B, C), and designed compounds 8a–l (D).
4-((7-alkoxy-4-oxochroman-3-ylidene)methyl)pyridinium bro-
midederivatives8a–l(Fig. 1D)havebeendesigned,synthesized,
and evaluated as AChE inhibitors.
expressed as mean ꢀ SE of three independent experiments.
The anticholinesterase activities (mM) of two series 7-methoxy
and 7-ethoxy chroman-4-one derivatives (8a–f and 8g–l,
respectively) are shown in Table 1. Based on the enzyme
inhibition data, the target compounds showed significant
inhibitory activities toward acetylcholinesterase at concen-
trations less than 7.24 mM. Among 8l, 8k, 8h, 8a, 8f, and 8e
with satisfactory results, 8l from the second series of
compounds with IC50 value of 0.048 mM was found as the
most potent compound. Interestingly, 7-ethoxy derivatives
like 8l and 8k showed better effects with respect to their
corresponding 7-methoxy analogs (8f and 8e).
Results and discussion
Chemistry
The reaction of resorcinol 1 with 3-chloropropionic acid using
trifluoromethane sulfonic acid produced 3-chloro-1-(2,4-
dihydroxyphenyl)propan-1-one 2 which upon cyclization in
basic solution afforded 7-hydroxychroman-4-one 3 [20]. The
O-alkylation step by the action of alkyl halide in dry N,N-
dimethylformamide (DMF) produced 4 in good yield. Then,
In the first series of target compounds, 8f with two bromine
substituents at ortho- and meta-position of pendent benzyl
group revealed the most inhibitory effect against AChE
(IC50 ¼ 0.128 mM). In this category, un-substituted benzyl 8a
compound
4 was subjected to the condensation with
isonicotinic aldehyde 5 in the presence of p-toluenesulfonic
acid (PTSA) followed by N-alkylation using benzyl bromide
derivatives resulting in the formation of 8a–l in good yields
(Scheme 1).
(IC50 ¼ 0.194 mM) and 2-bromo benzyl derivative 8e (IC50
¼
0.502 mM) exhibited good inhibitory effects, respectively.
On the other hand, presence of fluorine or methyl group in
position 4 of pendent benzyl group (8b, 8d) led to the
reduction in anti-AChE activity (IC50 ¼ 3.814 and 7.242 mM,
respectively) compared to other compounds in this category.
In the second series (7-ethoxy derivatives, 8g–l), the
compound 8l with 2,3-dibromo substituents on pendent
Inhibitory activity against AChE
The in vitro activity of all compounds 8a–l for AChE inhibitory
activity was evaluated by Ellman’s method and compared
with donepezil as the standard drug [21]. All data were
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Scheme 1. Reagents and conditions: (a) 3-Chloropropionic acid, CF3SO3H, 80°C, 30 min; (b) 2.0 M NaOH, 5°C!r.t., 2 h; (c) alkyl halide,
K2CO3, DMF, 80°C, 3 h; (d) PTSA, toluene, reflux Dean–Stark, 6 h; (e) acetonitrile, reflux, 1–3 h.
benzyl group exhibited considerable inhibitory activity (IC50
¼ 0.046 mM) compared to donepezil (IC50 ¼ 0.022 mM). As well,
the presence of a bromine substituent in position 2 of
pendent benzyl group in 8k was found beneficial (IC50 ¼ 0.058
mM), while 8j with fluorine substituent in the same position
was the weakest halo-substituted compound in this series
(IC50 ¼ 0.463 mM). Moreover, the introduction of 4-chloro on
N-benzyl ring showed good anti-AChE potency as observed in
compound 8h (IC50 ¼ 0.091 mM). The presence of 4-nitro
substituent on the N-benzyl group instead of chlorine in 8i
led to the decreased inhibitory activity in comparison to the
compound 8h.
The results showed that inhibitory effects of designed
compounds 8a–l against AChE enzyme were dependent on
the type of alkoxy group in the position 7 of chroman-4-one as
well as type and the substitution pattern on the pendent
benzyl group of pyridinium ring. The presence of the ethoxy
group in second series imparted higher activity in comparison
Table 1. Acetylcholinesterase inhibition IC50 (nM) of compounds 8a–l.
Entry
R1
R2
R3
R4
IC50 (mM)a)
8a
8b
8c
8d
8e
8f
8g
8h
8i
8j
8k
8l
CH3
CH3
CH3
CH3
CH3
H
H
H
H
H
H
H
H
Br
H
H
H
H
H
Br
H
F
Br
CH3
H
H
H
Cl
NO2
H
H
H
0.194 ꢀ 0.43
3.81 ꢀ 0.003
N.d
7.24 ꢀ 0.02
0.502 ꢀ 0.031
0.128 ꢀ 0.001
N.d
0.091 ꢀ 0.012
2.713 ꢀ 0.34
0.463 ꢀ 0.017
0.058 ꢀ 0.23
0.048 ꢀ 0.052
0.022 ꢀ 0.00
H
Br
Br
H
H
H
F
Br
Br
CH3
CH2CH3
CH2CH3
CH2CH3
CH2CH3
CH2CH3
CH2CH3
Donepezil
hydrochloride
a) Values are the mean ꢀ SD. All experiments were performed at least three times.
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Conclusion
In this study, we found some new derivatives of the
chroman-4-one linked to benzyl pyridinium group as new
acetylcholinesterase inhibitors with moderate to high
effects. According to the available biological data, anti-
AChE activity of these compounds was sensitive to the type
of alkoxy group in position 7 of chroman-4-one as well as the
type and pattern of substitution on the pendent benzyl
group of pyridinium ring. Structure–affinity relationships
of synthesized compounds were explained by docking
simulations.
Experimental
Figure 2. Superposed structure of 8l (cyan) and donepezil (pink)
inside the active site of AChE.
Chemistry
Melting points were determined with a Kofler hot stage
apparatus and are uncorrected. 1H and 13C NMR spectra were
recorded with a Bruker FT-500, using TMS as an internal
standard. IR spectra were recorded on a Nicolet Magna FTIR
550 spectrophotometer using KBr disks. Mass spectra were
obtained with an Agilent Technology (HP) mass spectrometer
operating at an ionization potential of 70 eV. Elemental
analysis for C, H, and N was determined with an Elementar
Analysensysteme GmbH VarioEL CHNS mode.
to methoxy analogs. On the other hand, it seems that the
bromine substituent had a positive effect on anti-AChE
activity of these compounds.
Docking studies
To gain a perspective on the interaction of the target
compounds with the active site of the AChE enzyme, docking
studies were performed by Autodock Tools (1.5.6) and
Discovery Studio 4.0 Client. In this study, among several
available crystal structures of the acetylcholine esterase
enzyme in the RCSB protein data bank (http://www.rcsb.
org/pdb/home/home.do), PDB structure of 1EVE complexed
with donepezil was retrieved for docking purpose. Among
the synthesized compounds, compound 8l as the most potent
compound was subjected to docking studies. Figure 2 shows a
superposition of the best pose of 8l and the co-crystallized
donepezil in the active site of AChE.
General procedure for the synthesis of 7-alkoxychroman-
4-one (4)
To
a mixture of 7-hydroxychroman-4-one 3 (1 mmol)
and potassium carbonate (1.5 mmol) in DMF (5 mL), alkyl
halide (1 mmol) was added and the mixture was stirred
for 4 h at 80°C. After cooling, water (20 mL) was added
and the residue was extracted with ethyl acetate
(3 ꢁ 30 mL). The combined organic layers were dried with
Na2SO4 and the solvent was removed under reduced
pressure to afford 4.
The possible interactions of 8l with amino acid residues
in the active site of enzyme obtained from molecular
modeling are depicted in Fig. 3. Trp84, Phe330, and
Tyr334 are responsible for the interactions of 8l with CAS.
The p–p stacking interactions between the pendant benzyl
group and pyridinium ring with aromatic moieties of Trp84
and Phe330, respectively, and p-cation interaction of the
positively charged nitrogen with Tyr334 are considered as
important interactions in CAS. Hydrogen bonding between
carbonyl moiety of chroman-4-one and hydroxyl group
of Tyr121 accompanied by the hydrophobic interaction
between 7-ethoxy group of chroman-4-one and Trp279
was detected in the PAS [22]. Compounds 8l and 8f
with 2,3-dibromo substituents on pendent benzyl group
showed the best effect in each series. According to Fig. 3, it is
clear that 3-bromine substituent in 8l shows
a weak
interaction with carbonyl group of active site which is in
accordance with the obtained results through in vitro
experiments [23].
Figure 3. Docking of 8l in the active site of AChE. The
interactions are shown by dashed line.
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0
0
0
0
General procedure for the synthesis of 7-alkoxy-3-(pyridin-
4-ylmethylene)chroman-4-one (6)
J ¼ 5.2 Hz, 2H, H2 , H6 ), 8.36 (d, J ¼ 5.2 Hz, 2H, H3 , H5 ), 8.03 (s,
00
1H, CH), 7.81 (d, J ¼ 7.6 Hz, 1H, H5), 7.77 (d, J ¼ 8.3 Hz, 2H, H3
,
00
00
00
7-Alkoxychroman-4-one 4 (1 mmol), isonicotinaldehyde 5
(1.4 mmol), and PTSA (1.5 mmol) were suspended in toluene
(25 mL) and heated to reflux using water separator for 3 h. The
resulting mixture was cooled to 25–40°C and the solid was
filtered. The wet solid was suspended in aqueous solution of
sodium hydrogen carbonate (50 mL, 10%) and stirred for 30–
60 min at room temperature. The resulting solid was filtered,
washed with water (50 mL), and dried. The crude solid was
purified by crystallization from acetonitrile.
H5 ), 7.34 (d, J ¼ 8.3 Hz, 2H, H2 , H6 ), 7.28 (d, J ¼ 3.3 Hz, 1H, H8),
7.25 (d, J ¼ 7.6 Hz, 1H, H6), 5.78 (s, 2H, N-CH2), 4.45 (s, 2H,
O-CH2), 3.86 (s, 3H, OCH3); 13C NMR (125 MHz, DMSO-d6):
194.3, 158.2, 155.1, 148.7, 139.1, 136.6, 134.3, 131.6, 130.6,
129.4, 128.9, 128.3, 127.4, 126.9, 119.2, 111.9, 58.5, 55.3, 51.4;
Anal. elem. calcd.: C: 53.41, H: 3.70, N: 2.71. Found: 53.72,
H: 3.25, N: 3.06.
(E)-4-((7-Methoxy-4-oxochroman-3-ylidene)methyl)-1-(4-
methylbenzyl)pyridinium bromide (8d)
–
–
General procedure for the synthesis of (E)-1-benzyl-4-((7-
alkoxy-4-oxochroman-3-ylidene)methyl)pyridin-1-ium
bromide (8)
Yellow solid; yield: 79%; mp > 250°C; IR (KBr): 1703 (C O),
ꢂ1
–
–
1646 (C C alkene) cm
;
1H NMR (500 MHz, DMSO-d6): 8.79
0
0
(d, J ¼ 5.4 Hz, 2H, H2 , H6 ), 8.09 (s, 1H, CH), 7.98 (d, J ¼ 5.4 Hz,
0
0
To the stirred solution of 7-alkoxy-3-(pyridin-4-ylmethylene)-
chroman-4-one 6 (1 mmol) in dry acetonitrile (7 mL) under
reflux, benzyl bromide derivatives 7 (1.2 mmol) were added
and the reaction was continued for 2–3 h. Upon completion,
the solvent was removed and n-hexane (15 mL) was added to
the residue. The precipitated crystals were separated by
filtration, washed with n-hexane, and purified if needed by
flash chromatography using chloroform/methanol (99:1) as
the mobile phase to afford compounds 8a–l.
2H, H3 , H5 ), 7.92 (d, J ¼ 8.9 Hz, 1H, H5), 7.49 (d, J ¼ 7.9 Hz, 2H,
0
0
0
0
0
0
0
0
H3 , H5 ), 7.10–7.17 (m, 3H, H2 , H6 , H6), 7.07 (d, J ¼ 3.3 Hz, 1H,
H8), 5.76 (s, 2H, N–CH2), 4.58 (s, 2H, O–CH2), 3.89 (s, 3H,
OCH3), 2.31 (s, 3H, CH3); 13C NMR (125 MHz, DMSO-d6): 193.1,
158.4, 155.1, 148.7, 138.2, 136.6, 134.2, 131.5, 130.5, 129.4,
128.9, 128.3, 126.2, 119.2, 111.7, 58.0, 55.2, 52.7, 21.3; Anal.
elem. calcd.: C: 63.73. H: 4.90. N: 3.10. Found: 63.67, H: 4.52,
N: 2.94.
(E)-1-(2-Bromobenzyl)-4-((7-methoxy-4-oxochroman-3-
(E)-1-Benzyl-4-((7-methoxy-4-oxochroman-3-ylidene)-
methyl)pyridinium bromide (8a)
ylidene)methyl)pyridinium bromide (8e)
–
–
Yellow solid; yield: 73%; mp > 250°C; IR (KBr): 1704 (C O),
1637 (C C alkene) cmꢂ1; 1H NMR (500 MHz, DMSO-d6): 9.10 (d,
–
–
–
Yellow solid; yield: 76%; mp > 250°C; IR (KBr): 1708 (C O),
–
1635 (C C alkene) cmꢂ1; 1H NMR (500 MHz, DMSO-d6) 9.18 (d,
J ¼ 6.5 Hz, 2H, H2 , H6 ), 8.21 (d, J ¼ 6.4 Hz, H3 , H5 ), 8.05 (s, 1H,
–
–
0
0
0
0
0
0
0
00
J ¼ 6.4 Hz, 2H, H2 , H6 ), 8.19 (s, 1H, CH), 8.09 (d, J ¼ 6.4 Hz, H3 ,
CH), 8.03 (d, J ¼ 8.5 Hz, 1H, H5), 7.72 (d, J ¼ 7.8 Hz, H3 ), 7.35 (t,
00
0
00
00
00
H5 ), 7.88 (d, J ¼ 7.8 Hz, 1H, H5), 7.56 (m, 2H, H2 , H6 ), 7.41 (m,
J ¼ 7.5 Hz, 1H, H5 ), 7.32 (t, J ¼ 7.8 Hz, H4 ), 7.26 (d, J ¼ 7.6 Hz,
00
00
00
00
3H, H3 , H4 , H5 ) 7.17 (t, J ¼ 7.8 Hz, 1H, H6), 7.05 (d, J ¼ 2.6 Hz,
1H, H8), 5.85 (s, 2H, N–CH2), 4.47 (s, 2H, O–CH2), 3.89 (s, 3H,
OCH3); 13C NMR (125 MHz, DMSO-d6) 194.8, 158.4, 155.8,
151.4, 144.5, 134.9, 129.7, 129.6, 129.3, 128.3, 126.8, 125.9,
120.2, 117.4, 115.4, 111.2, 62.7, 56.6, 51.5; Anal. elem. calcd.:
C: 63.02, H: 4.60, N: 3.20. Found: C: 63.22, H: 4.34, N: 3.08.
1H, H6 ), 7.19 (d, J ¼ 8.5 Hz, 1H, H6), 7.11 (d, J ¼ 2.3 Hz, 1H, H8),
5.67 (s, 2H, N–CH2), 4.52 (s, 2H, O–CH2), 3.97 (s, 3H, OCH3);
13C NMR (125 MHz, DMSO-d6): 195.0, 158.1, 155.9, 151.2,
148.7, 139.0, 136.6, 134.2, 131.6, 130.5, 129.4, 128.9, 128.3,
127.4, 126.9, 126.2, 119.2, 117.9, 116.4, 111.3, 57.3, 55.9, 52.9;
MS m/z (%) 439 ([Mþþ2], 8), 437 (Mþ, 8), 241 (12), 228 (11),
169 (15), 161 (25), 83 (39), 69 (19), 55 (97), 41 (100); Anal.
elem. calcd.: C: 53.41, H: 3.70, N: 2.71. Found: 53.26, H: 3.48,
N: 2.83.
(E)-1-(4-Fluorobenzyl)-4-((7-methoxy-4-oxochroman-3-
ylidene)methyl)pyridinium bromide (8b)
–
–
Yellow solid; yield: 73%; mp > 250°C; IR (KBr): 1693 (C O),
1640 (C C alkene) cmꢂ1; 1H NMR (500 MHz, DMSO-d6): 8.97 (d,
(E)-1-(2,3-Dibromobenzyl)-4-((7-methoxy-4-oxochroman-
–
–
0
0
0
0
J ¼ 5.6 Hz, 2H, H2 , H6 ), 7.23 (d, J ¼ 5.6 Hz, 2H, H3 , H5 ), 8.06 (s,
3-ylidene)methyl)pyridinium bromide (8f)
–
–
00
00
1H, CH), 7.94 (d, J ¼ 7.9 Hz, 2H, H3 , H5 ), 7.91 (d, J ¼ 8.9 Hz, 1H,
Yellow solid; yield: 74%; mp > 250°C; IR (KBr): 1705 (C O),
H5), 7.48 (d, J ¼ 7.9 Hz, 2H, H2 , H6 ), 7.18 (d, J ¼ 1.5 Hz, 1H, H8),
7.11 (d, J ¼ 8.9 Hz, 1H, H6), 5.87 (s, 2H, N–CH2), 4.61 (s, 2H,
O–CH2), 3.98 (s, 3H, OCH3); 13C NMR (125 MHz, DMSO-d6):
193.1, 163.0, 158.9, 155.2, 151.6, 149.0, 142.6, 131.8, 131.0,
129.9, 128.1, 126.9, 125.9, 119.2, 114.6, 110.5, 60.0, 55.5, 52.0;
Anal. elem. calcd.: C: 60.54, H: 4.20, N: 3.07. Found: C: 60.14, H:
4.38, N: 3.24.
1640 (C C alkene) cmꢂ1; 1H NMR (500 MHz, DMSO-d6): 9.15 (d,
–
–
00
00
0
0
0
0
J ¼ 5.7 Hz, 2H, H2 , H6 ), 8.28 (d, J ¼ 5.7 Hz, H3 , H5 ), 8.25 (s, 1H,
00
CH), 8.04 (d, J ¼ 7.7 Hz, 1H, H5), 7.84 (t, J ¼ 9.0 Hz, 1H, H5 ), 7.76
00
00
(d, J ¼ 9.0 Hz, 1H, H4 ), 7.73 (d, J ¼ 9.0 Hz, 1H, H6 ), 7.30 (d,
J ¼ 7.7 Hz, 1H, H6), 7.14 (d, J ¼ 3.5 Hz, 1H, H8), 5.70 (s, 2H,
N–CH2), 4.60 (s, 2H, O–CH2), 3.88 (s, 3H, OCH3); 13C NMR
(125 MHz, DMSO-d6): 193.4, 157.5, 155.5, 149.4, 138.0, 131.8,
131.5, 130.9, 129.5, 128.3, 128.1, 127.9, 127.6, 125.7, 119.1,
114.5, 114.2, 111.3, 58.9, 55.4, 52.4; MS m/z (%) 517 ([Mþþ2],
6), 515 (Mþ., 6), 268 (28), 267 (100), 266 (93), 250 (30), 151 (77),
117 (22), 79 (23), 63 (38), 51 (28); Anal. elem. calcd.: C: 46.34, H:
3.04, N: 2.35. Found: 46.64, H: 2.86, N: 2.62.
(E)-1-(4-Bromobenzyl)-4-((7-methoxy-4-oxochroman-3-
ylidene)methyl)pyridinium bromide (8c)
–
–
Yellow solid; yield: 72%; mp > 250°C; IR (KBr): 1700 (C O),
1633 (C C alkene) cmꢂ1; 1H NMR (500 MHz, DMSO-d6): 9.04 (d,
–
–
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(E)-1-Benzyl-4-((7-ethoxy-4-oxochroman-3-ylidene)-
methyl)pyridinium bromide (8g)
114.8, 111.1, 58.8, 56.8, 51.5, 17.8; Anal. elem. calcd.: C: 61.29,
H: 4.50, N: 2.98. Found: C: 61.51, H: 4.74, N: 3.25.
–
–
Yellow solid; yield: 76%; mp > 250°C; IR (KBr): 1705 (C O),
1642 (C C alkene) cmꢂ1; 1H NMR (500 MHz, DMSO-d6): 9.21 (d,
(E)-1-(2-Bromobenzyl)-4-((7-ethoxy-4-oxochroman-3-
–
–
0
0
0
J ¼ 5.8 Hz, 2H, H2 , H6 ), 8.26 (s, 1H, CH), 8.19 (d, J ¼ 5.8 Hz, H3 ,
ylidene)methyl)pyridinium bromide (8k)
–
–
0
00
00
H5 ), 7.88 (d, J ¼ 8.9 Hz, 1H, H5), 7.71 (m, 2H, H2 , H6 ), 7.16 (m,
Yellow solid; yield: 75%; mp > 250°C; IR (KBr): 1697 (C O),
3H, H3 , H4 , H5 ) 7.10–7.12 (m, 2H, H6, H8), 5.79 (s, 2H, N–CH2),
4.63 (s, 2H, O–CH2), 3.91 (q, J ¼ 9.45 Hz, 2H, O–CH2–CH3), 1.21
(t, J ¼ 9.85 Hz, 3H, O–CH2–CH3); 13C NMR (125 MHz, DMSO-d6):
193.7, 158.7, 155.3, 148.7, 138.8, 136.8, 134.4, 131.9, 130.6,
129.4, 129.2, 128.8, 126.3, 123.6, 119.6, 119.3, 113.2, 111.5;
Anal. elem. calcd.: C: 63.73, H: 4.90, N: 3.10. Found: 63.92, H:
5.11, N: 3.67.
1643 (C C alkene) cmꢂ1; 1H NMR (500 MHz, DMSO-d6): 8.96 (d,
–
–
00
00
00
0
0
0
J ¼ 5.1 Hz, 2H, H2 , H6 ), 8.23 (s, 1H, CH), 8.11 (d, J ¼ 6.4 Hz, H3 ,
0
00
H5 ), 7.88 (d, J ¼ 7.6 Hz, 1H, H5), 7.75 (dd, J ¼ 6.8, 1.9 Hz, H3 ),
00
00
7.50 (t, J ¼ 7.0 Hz, 1H, H5 ), 7.42 (t, J ¼ 6.8 Hz, 1H, H4 ), 7.36 (dd,
00
J ¼ 7.0, 1.5 Hz, H6 ), 7.16 (d, J ¼ 1.8 Hz, 1H, H8), 7.01 (dd, J ¼ 7.6,
2.2 Hz, 1H, H6), 5.92 (s, 2H, N–CH2), 4.61 (s, 2H, O–CH2), 4.18 (q,
J ¼ 9.4 Hz, 2H, O–CH2–CH3), 1.37 (t, J ¼ 9.4 Hz, 3H, O–CH2–CH3);
13C NMR (125 MHz, DMSO-d6): 192.4, 158.3, 156.3, 149.2,
148.4, 136.3, 133.6, 132.2, 131.5, 131.3, 129.9, 129.7, 129.2,
128.1, 126.6, 124.5, 113.1, 111.1, 58.2, 55.0, 50.1, 19.2; Anal.
elem. calcd.: C: 54.26, H: 3.98, N: 2.64. Found: C: 54.58, H: 4.32,
N: 2.87.
(E)-1-(4-Chlorobenzyl)-4-((7-ethoxy-4-oxochroman-3-
ylidene)methyl)pyridinium bromide (8h)
–
–
Yellow solid; yield: 78%; mp > 250°C; IR (KBr): 1706 (C O),
1644 (C C alkene) cmꢂ1; 1H NMR (500 MHz, DMSO-d6): 9.14 (d,
–
–
0
0
J ¼ 4.8 Hz, 2H, H2 , H6 ), 8.20 (s, 1H, CH), 8.10 (d, J ¼ 4.8 Hz, 2H,
0
0
00
H3 , H5 ), 7.86 (d, J ¼ 7.5 Hz, 1H, H5), 7.57 (d, J ¼ 8.1 Hz, 2H, H3
,
(E)-1-(2,3-Dibromobenzyl)-4-((7-ethoxy-4-oxochroman-3-
00
00
00
H5 ), 7.40 (d, J ¼ 8.1 Hz, 2H, H2 , H6 ), 7.14 (d, J ¼ 2.4 Hz, 1H, H8),
7.04 (dd, J ¼ 7.5, 2.5 Hz, 1H, H6), 5.83 (s, 2H, N–CH2), 4.58 (s, 2H,
O–CH2), 4.16 (q, J ¼ 9.8 Hz, 2H, O–CH2–CH3), 1.36 (t, J ¼ 9.8 Hz,
3H, O–CH2–CH3); 13C NMR (125 MHz, DMSO-d6): 194.4, 159.0,
155.3, 152.7, 144.7, 138.5, 136.5, 133.9, 133.1, 130.7, 128.4,
126.5, 124.2, 123.1, 116.5, 111.7, 58.6, 55.8, 51.5, 17.7; Anal.
elem. calcd.: C: 59.22, H: 4.35, N: 2.88. Found: C: 59.43, H: 4.66,
N: 3.16.
ylidene)methyl)pyridinium bromide (8l)
–
–
Yellow solid; yield: 68%; mp > 250°C; IR (KBr): 1704 (C O),
1645 (C C alkene) cmꢂ1; 1H NMR (500 MHz, DMSO-d6): 9.16 (d,
–
–
0
0
0
0
J ¼ 5.1 Hz, 2H, H2 , H6 ), 8.10 (d, J ¼ 5.1 Hz, H3 , H5 ), 8.01 (s, 1H,
00
CH), 7.89 (d, J ¼ 8.4 Hz, 1H, H5), 7.66 (d, J ¼ 7.1 Hz, H4 ), 7.28 (t,
00
00
J ¼ 7.1 Hz, 1H, H5 ), 7.26 (d, J ¼ 7.1 Hz, 1H, H6 ), 7.13 (d,
J ¼ 2.5 Hz, 1H, H8), 7.02 (dd, J¼ 8.5, 2.8 Hz, 1H, H6), 5.82 (s, 2H,
N–CH2), 4.66 (s, 2H, O–CH2), 4.17 (q, J ¼ 9.4 Hz, 2H,
O–CH2–CH3), 1.21 (t, J ¼ 9.4 Hz, 3H, O–CH2–CH3); 13C NMR
(125 MHz, DMSO-d6): 194.2, 158.9, 155.3, 152.8, 144.8, 143.1,
136.5, 133.1, 130.9, 129.5, 128.3, 126.7, 124.2, 123.0, 116.5,
111.2, 59.8, 55.8, 51.8; Anal. elem. calcd.: C: 47.24, H: 3.30, N:
2.30. Found: C: 47.69, H: 3.51, N: 2.07.
(E)-4-((7-Ethoxy-4-oxochroman-3-ylidene)methyl)-1-(4-
nitrobenzyl)pyridinium bromide (8i)
–
–
Yellow solid; yield: 69%; mp > 250°C; IR (KBr): 1708 (C O),
1642 (C C alkene), 1370–1546 (NO ) cmꢂ1; 1H NMR (500 MHz,
–
–
2
0
0
DMSO-d6): 9.11 (d, J ¼ 4.8 Hz, 2H, H2 , H6 ), 8.30 (d, J ¼ 4.8 Hz,
0
0
00
00
AChE inhibition assay
2H, H3 , H5 ), 8.23 (s, 1H, CH), 8.12 (d, J ¼ 7.6 Hz, 2H, H3 , H5 ),
00
00
7.88 (d, J ¼ 8 Hz, 1H, H5), 7.88 (d, J ¼ 7.6 Hz, 2H, H2 , H6 ), 7.16
(d, J ¼ 1.8 Hz, 1H, H8), 7.05 (dd, J¼ 8.0, 1.9 Hz, 1H, H6), 5.97 (s,
2H, N–CH2), 4.52 (s, 2H, O–CH2), 4.17 (q, J ¼ 9.4 Hz, 2H,
O–CH2–CH3), 1.37 (t, J ¼ 9.4 Hz, 3H, O–CH2–CH3); 13C NMR
(125 MHz, DMSO-d6): 194.3, 158.6, 155.2, 150.0, 144.6, 144.1,
138.4, 134.1, 130.7, 129.8, 126.4, 125.4, 113.2, 112.8, 111.9,
59.2, 55.0, 52.8, 17.8; Anal. elem. calcd.: C: 57.96, H: 4.26, N:
5.63. Found: C: 58.21, H: 4.57, N: 5.39.
Colorimetric Ellman’s method was used to evaluate the
inhibitory potency of target compounds toward AChE [20].
Acetylcholinesterase (AChE, E.C. 3.1.1.7, Type V-S, lyophilized
powder, from electric eel, 1000 unit) was obtained from
Sigma–Aldrich. 5,50-Dithiobis-(2-nitrobenzoic acid) (DTNB),
potassium dihydrogen phosphate, dipotassium hydrogen
phosphate, potassium hydroxide, sodium hydrogen carbon-
ate, and acetylthiocholine iodide were purchased from Fluka.
Donepezil hydrochloride was obtained from Merck, Darm-
stadt, Germany. In short, to determine IC50 values, 50 mL of the
five different concentrations of the test compounds that
produced inhibition in the range of 20–80% was added to the
mixture of 3 mL phosphate buffer 0.1 M, pH ¼ 8.0, and 100 mL
of DTNB solution (0.1 M) and 50 mL AChE. Ten microliters
solution of acetylthiocholine iodide (0.15 M) as substrate was
added following 10 min incubation at 25°C. The progress
curve was plotted by measuring the absorbance at 412 nm for
6 min. The IC50 values were determined graphically from
inhibition curves (inhibitor concentration vs. percent of
inhibition). UNICO double beam spectrophotometer 2100
was used for colorimetric measurements.
(E)-4-((7-Ethoxy-4-oxochroman-3-ylidene)methyl)-1-(2-
fluorobenzyl)pyridinium bromide (8j)
–
–
Yellow solid; yield; 72%; mp > 250°C; IR (KBr): 1709 (C O),
1633 (C C alkene) cmꢂ1; 1H NMR (500 MHz, DMSO-d6): 9.15 (d,
–
–
0
0
0
J ¼ 4.8 Hz, 2H, H2 , H6 ), 8.25 (s, 1H, CH), 8.10 (d, J ¼ 6.4 Hz, H3 ,
0
00
00
H5 ), 7.87 (d, J ¼ 7.8 Hz, 1H, H5), 7.50 (d, J ¼ 7.8 Hz, H3 , H4 ),
00
00
7.42 (d, J ¼ 8.9 Hz, 1H, H6 ), 7.26 (t, J ¼ 8.9 Hz, 1H, H5 ), 7.14 (d,
J ¼ 2.3 Hz, 1H, H8), 7.04 (dd, J¼ 8.0, 2.9 Hz, 1H, H6), 5.85 (s, 2H,
N–CH2), 4.55 (s, 2H, O–CH2), 4.16 (q, J ¼ 9.1 Hz, 2H,
O–CH2–CH3), 1.36 (t, J ¼ 9.1 Hz, 3H, O–CH2–CH3); 13C NMR
(125 MHz, DMSO-d6): 194.5, 162.9, 158.7, 152.9, 147.9, 145.1,
143.7, 141.0, 136.7, 133.1, 130.2, 128.5, 124.1, 123.2, 116.5,
ß 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.archpharm.com
648

RCHH HARM
A P
Arch. Pharm. Chem. Life Sci. 2015, 348, 643–649
Chroman-4-one Linked to N-Benzyl Pyridinium Derivatives
Archiv der Pharmazie
Molecular docking study
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M. Bartolini, V. Andrisano, P. Valenti, M. J. Recanatini,
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Docking studies were performed using the AUTODOCK 4.2
program. For this purpose, the crystal structure of acetylcho-
linesterase enzyme (pdb code: 1EVE) was taken from the
Brookhaven protein database (http://www.rcsb.org) as a
complexboundwithinhibitorE2020(donepezil).Subsequently,
the water molecules and the original inhibitors were removed
from the protein structure. The 3D structure of the compound
8l was provided using Marvine Sketch 5.8.3, 2012, ChemAxon
(http: //www. chemaxon.com) and converted to pdbqt
coordinate by AUTODOCK 4.2 program. Also, the autodock
format of protein was provided using the same software. Polar
hydrogen atoms were added to amino acid residues using
Autodock Tools (ADT; version 1.5.6), Koullman charges were
assigned to all atoms of the enzyme, and the obtained enzyme
structure was used as an input for the AUTOGRID program.
AUTOGRID performed a pre-calculated atomic affinity grid
maps for each atom type in the ligand, plus an electrostatics
map, anda separatedesolation mappresentedin thesubstrate
ꢀ
Z. Radic, P. Taylor, O. Lockridge, B. P. Doctor, Eur. J.
Biochem. 2003, 270, 4447–4458.
[12] H. Dong, C. M. Yuede, C. A. Coughlan, K. M. Murphy,
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[13] M. M. Khanaposhtani, M. Saeedi, M. Mahdavi, N. S.
Zafarghandi, R. Sabourian, E. K. Razkenari, H. Alinezhad,
M. Khanavi, A. Foroumadi, A. Shafiee, T. Akbarzadeh,
Eur. J. Med. Chem. 2015, 92, 799–806.
̊
molecule. All maps were calculated with 0.375 A spacing
between grid points. The center of the grid box was placed at
the center of donepezil with coordinates x ¼ 1.75, y ¼ 63.1,
z ¼ 67.11. The dimensions of the active site box were set at
36 ꢁ 34 ꢁ 56thatcoveredallbindingsitesoccurredinactivesite
of the enzyme. Flexible ligand docking was accomplished for
the compound 8l. Each docked system was carried out by 100
runs of the AUTODOCK search by the Lamarckian genetic
algorithm (LGA). Other than the above-mentioned param-
eters, the other parameters were accepted as default. The
lowest energy conformation of ligand–enzyme complex was
considered for analyzing the interactions between AChE and
the inhibitor. The results were visualized using Discovery
Studio 4.0 Client.
[14] M. Khoobi, F. Ghanoni, H. Nadri, A. Moradi, M. P.
Hamedani, F. H. Moghadam, S. Emami, M. Vosooghi,
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2015, 89, 296–303.
[15] H. Akrami, B. F. Mirjalili, M. Khoobi, H. Nadri, A. Moradi,
A. Sakhteman, S. Emami, A. Foroumadi, A. Shafiee,
Eur. J. Med. Chem. 2014, 84, 375–381.
[16] M. Alipour, M. Khoobi, A. Moradi, H. Nadri, F. H.
Moghadam, S. Emami, Z. Hasanpour, A. Foroumadi,
A. Shafiee, Eur. J. Med. Chem. 2014, 82, 536–544.
[17] H. Nadri, M. Pirali-Hamedani, M. Shekarchi, M. Abdollahi,
V. Sheibani, M. Amanlou, A. Shafiee, A. Foroumadi,
Bioorg. Med. Chem. 2010, 18, 6360–6366.
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A. Moradi, A. Sakhteman, M. Ghandi, A. Shafiee, Bioorg.
Med. Chem. 2012, 20, 7214–7222.
This study was part of the PhD thesis of Saman Arab and
supported by Tehran University of Medical Sciences.
[19] S. Noushini, E. Alipour, S. Emami, M. Safavi, S. K.
Ardestani, A. R. Gohari, A. Shafiee, A. Foroumadi, Daru J.
Pharm. Sci. 2013, 21, 31–37.
The authors have declared no conflicts of interest.
[20] A. Foroumadi, A. Samzadeh-Kermani, S. Emami,
G. Dehghan, M. Sorkhi, F. Arabsorkhi, M. R. Heidari,
M. Abdollahi, A. Shafiee, Bioorg. Med. Chem. Lett. 2007,
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Stone, Biochem. Pharmacol. 1961, 7, 88–95.
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ß 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.archpharm.com
649