Synthesis, characterization and investigation of AChE and BuChE inhibitory activity of 1-alkyl-4-[(5,6-dimethoxy-1-indanone-2-yl)methylene]pyridinium halide derivatives

Article abstract of DOI:10.1007/s13738-019-01804-1

Abstract: The design, synthesis and characterization of a series of 1-alkyl-4-[(5,6-dimethoxy-1-indanone-2-yl)methylene]pyridinium halide derivatives as acetylcholinesterase and butyrylcholinesterase inhibitors for the treatment of Alzheimer’s disease were reported. The strategy for this synthesis was based on aldol condensation reaction between 4-pyridinecarboxaldehyde with 5,6-dimethoxy-1-indanone in the presence of NaOH in EtOH-H₂O solution as the first step and N-alkylation reaction of the produced 5,6-dimethoxy-2-[(pyridin-4-yl)methylene]-1-indanone with various alkyl halides (R–X) in the second step. This reaction was carried out under reflux temperature in polar aprotic solvents such as acetone or acetonitrile. ¹H and ¹³C NMR and FTIR spectroscopy along with CHN analysis were used to confirm the structure of our synthesized compounds. Biological activities including acetylcholinesterase and butyrylcholinesterase (BuChE) inhibitions for synthesized compounds were tested using the Ellman method. The results were compared with donepezil and galantamine, and among the synthesized compounds, the highest inhibitory activity with BuChE IC₅₀ = 0.55?μM was observed. Graphic abstract: [Figure not available: see fulltext.]

Full text of DOI:10.1007/s13738-019-01804-1

Journal of the Iranian Chemical Society
https://doi.org/10.1007/s13738-019-01804-1
ORIGINAL PAPER
Synthesis, characterization and investigation of AChE and BuChE
inhibitory activity of 1‑alkyl‑4‑[(5,6‑dimethoxy‑1‑indanone‑2‑yl)
methylene]pyridinium halide derivatives
Hanieh Farrokhi1 · Sakineh Mozafarnia1,2 · Keshvar Rahimpour1 · Mohammad Reza Rashidi2 ·
Reza Teimuri‑Mofrad1
Received: 12 July 2019 / Accepted: 20 October 2019
© Iranian Chemical Society 2019
Abstract
The design, synthesis and characterization of a series of 1-alkyl-4-[(5,6-dimethoxy-1-indanone-2-yl)methylene]pyridinium
halide derivatives as acetylcholinesterase and butyrylcholinesterase inhibitors for the treatment of Alzheimer’s disease were
reported. The strategy for this synthesis was based on aldol condensation reaction between 4-pyridinecarboxaldehyde with
5,6-dimethoxy-1-indanone in the presence of NaOH in EtOH-H2O solution as the frst step and N-alkylation reaction of the
produced 5,6-dimethoxy-2-[(pyridin-4-yl)methylene]-1-indanone with various alkyl halides (R–X) in the second step. This
reaction was carried out under refux temperature in polar aprotic solvents such as acetone or acetonitrile. 1H and 13C NMR
and FTIR spectroscopy along with CHN analysis were used to confrm the structure of our synthesized compounds. Biologi-
cal activities including acetylcholinesterase and butyrylcholinesterase (BuChE) inhibitions for synthesized compounds were
tested using the Ellman method. The results were compared with donepezil and galantamine, and among the synthesized
compounds, the highest inhibitory activity with BuChE IC50 =0.55 μM was observed.
Graphic abstract
Keywords 1-Indanone · Acetylcholinesterase (AChE) · Butyrylcholinesterase (BuChE) · Enzyme inhibitor
Extended author information available on the last page of the article
Vol.:(0123456789)
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Journal of the Iranian Chemical Society
Organic heterocyclic salts such as pyridinium, quinolin-
ium and N-methylimidazolium salts are an important class
of new compounds, which were used as nonlinear optics,
ionic liquids, key intermediate in organic reactions and bio-
logical applications. It is obvious that the compounds in
salt form were better dissolved in aqueous media; therefore,
most drugs are in the form of salt [16–21]. In this context, a
series of 1-alkyl-4-[(5,6-dimethoxy-1-indanone-2-yl)meth-
ylene]pyridinium halide derivatives were prepared from
5,6-dimethoxy-2-[(pyridin-4-yl)methylene]-1-indanone and
various alkyl halides. Biological activities including acetyl-
cholinesterase (AChE) and butyrylcholinesterase (BuChE)
inhibitions for synthesized compounds were assayed. The
results were compared with donepezil and galantamine.
Introduction
Alzheimer’s disease (AD) is the most common form of
dementia, which seems to be directly related to age [1].
The etiology of AD has not been fully understood yet; but
there are several reasons such as β-amyloid (Aβ) depos-
its, τ-protein aggregation, oxidative stress and low levels
of acetylcholine (Ach) have been considered as the main
causes of this disease [2, 3]. Acetylcholine (ACh), the
main neurotransmitter of the cholinergic pathway, plays
an important role in cognition impairment (e.g., Alzhei-
mer), and reducing the activity of this substance is one
of the main processes involved in AD development. Ser-
ine hydrolase enzymes include that acetylcholinesterase
(AChE) and butyrylcholinesterase (BuChE) are responsi-
ble for the hydrolysis of acetylcholine (ACh) [4]. AChE
inhibition has been known as a strategy to the AD treat-
ment through the ACh-level enhancement for years.
According to several reports, various derivatives of
1-indanone moiety have important role in biological activ-
ities such as antiproliferative activity, acetylcholinester-
ase inhibition in donepezil (Aricept) for the treatment of
Alzheimer’s disease, and etc. [5–8]. Tacrine, donepezil,
rivastigmine and galantamine include the acetylcholine
esterase inhibitors (AChE) for the treatment of Alzhei-
mer’s disease [8–12]. Donepezil hydrochloride is the sec-
ond drug approved by the US FDA for the treatment of
AD [13, 14]. At frst glance, donepezil is divided into four
parts that are shown in Fig. 1; part 1: 1-indanone moiety,
part 2: linkage moiety, part 3: piperidine moiety and part
4: benzyl moiety. Choosing the best moiety to replace with
other analogous to improve the inhibition activity is one
of the most challenging debates among the scientists [15].
According to diferent results that were mentioned in
researches on compounds having high acetylcholinesterase
inhibitions, 5,6-dimethoxy-1-indanone was chosen as part
1, carbon with double-bond form as linker, pyridine as part
3 and pyridinium cation form of various alkyls as part 4
for increasing solubility in water of acetylcholinesterase
and butyrylcholinesterase inhibitors.
Experimental
Materials and instruments
All materials used in synthesis were purchased from
Merck and Sigma-Aldrich. All reactions were carried out
under argon atmosphere. Column chromatography was
performed using SiO2 (60 Å, 230–400 mesh, particle size
0.040–0.063 mm) at 25 °C. Melting points were determined
on a MEL-TEMP model 1202D and are uncorrected. FTIR
spectra were recorded on a Bruker Tensor 27 spectrometer
1
as KBr disks. The H NMR and 13C NMR spectra were
recorded on a Bruker Spectrospin Avance 400 and 100 MHz
spectrometer, respectively, used solvents was CDCl3 and
DMSO-d6. 13C NMR spectra were determined on the same
instrument at 100 MHz. All chemical shifts were reported
as δ (ppm), and coupling constants (J) were given in Hz.
The elemental analyses were carried out with an Elementor
Vario EL. III instrument.
Synthesis
Synthesis of 5,6‑dimethoxy‑2‑[(pyridin‑4‑yl)
methylene]‑1‑indanone (3)
To a solution of 1 mmol of 4-pyridinecarboxaldehyde and
1 mmol of 5,6-dimethoxy-1-indanone in 10 ml EtOH,
aqueous solution of NaOH (10%) was added dropwise.
The reaction mixture was stirred overnight at room tem-
perature. The obtained solid was fltered and recrystallized
from EtOH to give 3 as an of-white solid [22]; yield 67%;
mp: 118–120 °C; FTIR (KBr) ν 3008, 2937, 1691, 1600,
1465, 1315, 1268, 1029 cm−1; 1H NMR (400 MHz, CDCl3):
3.82 (3H, s, OCH3), 3.91 (3H, s, OCH3), 4.03 (2H, s, CH2),
7.17 (1H, s, Ar), 7.22 (1H, s, Ar), 7.42 (1H, s, =CH), 7.67
(2H, d, 3JH–H =5.36, pyridine-H), 8.64 (2H, d, 3JH–H =5.46,
pyridine-H).
O
O
H2
C
H2
C
N
O
3
1
2
4
Fig. 1 Donepezil molecular structure
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Journal of the Iranian Chemical Society
General procedure for the synthesis of compounds (5a–o)
131.61, 130.01, 128.61, 124.96, 123.42, 108.41, 105.30,
62.41, 57.17, 56.31, 32.01; Anal. Calc. for C24H21Br2NO3:
C, 54.26; H, 3.98; N, 2.64%. Found: C, 54.29; H, 3.97; N,
2.63%.
5,6-Dimethoxy-2-[(pyridin-4-yl)methylene)-1-indanone
(0.35 mmol) was dissolved in 4 cc acetone (for synthesis of
5a) or acetonitrile (for synthesis of 5b–o) under refux tem-
perature, and then 1.05 mmol of appropriate alkyl halides
was added. The reaction mixture was stirred for 48 h under
refux condition. The precipitate was fltered and washed
with appropriate solvent. The obtained solid was dried under
reduced pressure to aford related compounds.
1‑(3‑Bromobenzyl)‑4‑[(5,6‑dimethoxy‑1‑indanone‑2‑yl)
methylene]pyridinium bromide (5d) From 0.26 g of 3-bro-
mobenzylbromide, 0.11 g (0.22 mmol) of white solid was
obtained in 63% yield; mp: 232–234 °C; FTIR (KBr) ν
3004, 2939, 1690, 1600, 1467, 1312, 1268, 1038, 699, 785,
1
845 cm−1; H NMR (400 MHz, DMSO): δ 3.69 (3H, s,
1‑Methyl‑4‑[(5,6‑dimethoxy‑1‑indanone‑2‑yl)methylene]
pyridinium iodide (5a) From 0.14 g of methyliodide, 0.11 g
(0.8 mmol) of cloudy white solid was obtained in 80% yield;
mp: 222–224 °C; FTIR (KBr) ν 3008, 2934, 1685, 1640,
1462, 1317, 1273, 1026 cm−1; 1H NMR (400 MHz, DMSO):
δ 3.84 (3H, s, OCH3), 3.92 (3H, s, OCH3), 4.17 (2H, s, CH2),
4.28 (3H, s, CH3), 7.12 (1H, s, Ar–H), 7.28 (1H, s, Ar–H),
OCH3), 3.91 (2H, s, OCH3), 4.16 (2H, s, CH2), 5.78 (2H, s,
CH2),7.19 (1H, s, Ar–H), 7.26 (1H, s, Ar–H), 7.44 (1H, m,
Ar–H), 7.58 (1H, s, =CH), 7.68–7.59 (2H, m, Ar–H), 7.89
(1H, s, Ar–H), 8.42 (2H, d, 3JH–H =6.16, pyridine-H), 9.16
3
(2H, d, JH–H =6.14, pyridine-H); 13C NMR (100 MHz,
DMSO): 191.18, 156.81, 151.78, 150.20, 146.90, 46.31,
144.98, 137.21, 132.80, 132.22, 132.01, 129.80, 128.35,
128.50, 124.93, 122.71, 108.40, 105.32, 61.99, 56.77,
56.30, 32.08; Anal. Calc. for C24H21Br2NO3: C, 54.26; H,
3.98; N, 2.64%. Found: C, 54.28; H, 3.97; N, 2.65%.
3
7.55 (1H, s, =CH), 8.18 (2H, d, JH–H =5.90, pyridine-H),
9.15 (2H, d, 3JH–H =5.70, pyridine-H); 13CNMR (100 MHz,
DMSO): 32.24, 55.46, 56.23, 61.24, 123.07, 128.44, 129.31,
138.02, 138.55, 139.12, 145.62, 146.24, 150.01, 155.62,
156.16, 192.04; Anal. Calc. for C18H18INO3: C, 51.08; H,
4.29; N, 3.31%. Found: C, 51.11; H, 4.27; N, 3.32%.
1‑(2‑Bromobenzyl)‑4‑[(5,6‑dimethoxy‑1‑indanone‑2‑yl)
methylene]pyridinium bromide (5e) From 0.26 g of 2-bro-
mobenzylbromide, 0.12 g (0.23 mmol) of of-white solid
was obtained in 66% yield; mp: 212–214 °C; FTIR (KBr)
ν 2932, 1689, 1590, 1464, 1309, 1027, 847, 752, 539 cm−1;
1HNMR (400 MHz, DMSO): δ 3.76 (3H, s, OCH3), 3.92
(3H, s, OCH3), 4.18 (2H, s, CH2), 5.86 (2H, s, CH2), 7.20
1‑Benzyl‑4‑[(5,6‑dimethoxy‑1‑indanone‑2‑yl)methylene]
pyridinium chloride (5b) From 0.13 g of benzylchloride,
0.12 g (0.31 mmol) of white solid was obtained in 90%
yield; mp: 226–228 °C; FTIR (KBr) ν 3008, 2833, 1683,
1
3
1600, 1462, 1317, 1272,1071 cm−1; H NMR (400 MHz,
(1H, s, Ar), 7.28 (1H, s, Ar), 7.37 (1H, dd, JH–H =7.6 Hz,
DMSO): δ 3.92 (3H, s, OCH3), 3.85 (3H, s, OCH3), 4.18
(2H, s, CH2), 5.76 (2H, s, CH2), 7.18 (1H, s, Ar–H),7.27
(1H, s, Ar–H), 6.47–7.58 (3H, m, Ar–H, =CH), 7.61–7.72
(3H, m, Ar–H), 8.15 (2H, d, 3JH–H =6.20, pyridine-H), 9.13
Ar), 7.44 (1H, m, Ar), 7.51 (1H, s, =CH), 7.60 (1H, s, Ar),
7.79 (1H, dd, 3JH–H =7.9, Hz, Ar), 8.48 (2H, d, 3JH–H =6.55,
3
pyridine-H), 9.15 (2H, d, JH–H =6.55, pyridine-H); 13C
NMR (100 MHz, DMSO): 191.33, 156.11, 152.30, 150.17,
147.22, 146.30, 145.71, 133.90, 133.68,131.92, 131.60,
129.79, 129.22, 128.50, 125.31, 123.76, 108.40, 105.28,
63.30, 56.70, 56.28, 31.90; Anal. Calc. For C24H21Br2NO3:
C, 54.26; H, 3.98; N, 2.64%. Found: C, 54.23; H, 3.97; N,
2.63%.
3
(2H, d, JH–H =6.20, pyridine-H); 13C NMR (100 MHz,
DMSO): 191.20, 157.18, 151.71, 150.12, 147.02, 146.30,
145.11,134.18, 130.02, 129.71, 129.70, 129.21, 128.52,
125.25, 108.31, 105.20, 63.12, 56.71, 55.92, 31.19; Anal.
Calc. for C24H22ClNO3: C, 70.67; H, 5.44; N, 3.43%. Found:
C, 70.63; H, 5.45; N, 3.42%.
1‑(2‑Chlorobenzyl)‑4‑[(5,6‑dimethoxy‑1‑indanone‑2‑yl)
1‑(4‑Bromobenzyl)‑4‑[(5,6‑dimethoxy‑1‑indanone‑2‑yl)
methylene]pyridinium bromide (5c) From 0.26 g of 4-bro-
mobenzylbromide, 0.12 g (0.23 mmol) of white solid was
obtained in 66% yield; mp: 228–229 °C; FTIR (KBr) ν 3048,
2834, 1682, 1600, 1464, 1320, 1272, 1020, 803, 533 cm−1;
1H NMR (400 MHz, DMSO): δ 3.84 (3H, s, OCH3), 3.91
(3H, s, OCH3), 4.13 (2H, s, CH2), 5.70 (2H, s, CH2), 7.18
(1H, s, Ar–H), 7.29 (1H, s, Ar–H), 7.56–7.61 (3H, m, Ar–H,
=CH), 7.66–7.72 (2H, d, 3JH–H =8.37, Ar–H), 8.39 (2H, d,
methylene]pyridinium chloride (5f) From 0.17 g of
1-chloro-2-(chloromethyl)benzene, 0.09 g (0.21 mmol) of
white solid was obtained in 60% yield; mp: 222–224 °C;
FTIR (KBr) ν 3004, 2944, 1691, 1600, 1640, 1464, 1317,
1
1272, 1024, 757, 855, 525 cm−1; H NMR (400 MHz,
DMSO): δ 3.76 (3H, s, OCH3), 3.92 (3H, s, OCH3), 4.17 (2H,
s, CH2), 5.92 (2H, s, CH2), 7.36 (1H, s, Ar), 7.45 (1H, s, Ar),
3
7.52 (1H, dd, JH–H =7.5 Hz, Ar), 7.58 (1H, m, Ar), 7.49
3
(1H, s, =CH), 7.63 (1H, s, Ar), 7.80 (1H, dd, JH–H =7.5,
3
3
3JH–H =6.50, pyridine-H), 9.21 (2H, d, JH–H =6.50, pyri-
Hz, Ar), 8.79 (2H, d, JH–H =6.50, pyridine-H), 9.14 (2H,
dine-H); 13C NMR (100 MHz, DMSO): 190.99, 156.81,
152.03, 150.21, 146.99, 146.31, 145.20, 134.32, 132.60,
d, 3JH–H =6.50, pyridine-H); 13C NMR (100 MHz, DMSO):
191.36, 156.11, 152.30, 150.17, 147.22, 146.30, 145.71,
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Journal of the Iranian Chemical Society
133.90, 133.67,131.92, 138.60, 129.81, 129.23, 128.50,
125.33, 123.76, 108.40, 105.27, 63.32, 55.93, 56.25, 31.89;
Anal. Calc. for C24H21Cl2NO3: C, 65.17; H, 4.79; N, 3.17%.
Found: C, 65.21; H, 4.80; N, 3.16%.
1‑(2‑Hydroxyethyl)‑4‑[(5,6‑dimethoxy‑1‑indanone‑2‑yl)
methylene]pyridinium chloride (5j) From 0.08 g of 2-chlo-
roethanol, 0.07 g (0.19 mmol) of white solid was obtained
in 54% yield; mp: 229–232 °C; FTIR (KBr) ν 3400,
1
2935, 1692, 1591, 1463, 1316, 1032, 853 cm−1; H NMR
1‑Hexyl‑4‑[(5,6‑dimethoxy‑1‑indanone‑2‑yl)methylene]
pyridinium bromide (5g) From 0.17 g of 1-bromohexane,
0.08 g (0.19 mmol) of white solid was obtained in 54% yield;
mp: 228–231 °C; FTIR (KBr) ν 2931, 1686, 1642, 1591,
(400 MHz, DMSO): δ 3.63–3.66 (2H, m, CH2-OH), 3.75
(3H, s, OCH3), 3.92 (3H, s, OCH3), 4.17 (2H, s, CH2),
4.69 (2H, t, CH2), 7.34 (1H, s, Ar–H), 7.38 (1H, s, =CH),
3
7.63 (1H, s, Ar–H), 8.46 (2H, d, JH–H =6.55, pyridine-H),
1
3
1466, 1312, 1271, 1121, 845 cm−1; H NMR (400 MHz,
9.14 (2H, d, JH–H =6.56, pyridine-H), –OH not detected;
DMSO): δ 0.80 (3H, s, CH3), 1.05–1.15 (6H, m, CH2),
1.91–1.94 (2H, m, CH2), 3.73 (3H, s, OCH3), 3.84 (3H, s,
OCH3), 4.11 (2H, m, CH2), 4.93 (2H, t, CH2), 7.40 (1H, s,
Ar–H), 7.43 (1H, s, =CH), 7.56 (1H, s, Ar–H), 8.75 (2H, d,
13C NMR (100 MHz, DMSO): 32.45, 55.19, 55.26, 56.24,
60.52, 116.06, 120.72, 133.61, 138.51, 139.32, 139.79,
142.51, 145.01, 147.33, 150.17, 155.44, 191.82; Anal. Calc.
for C19H20ClNO4: C, 63.07; H, 5.57; N, 3.87%. Found: C,
63.09; H, 5.58; N, 3.86%.
3
3JH–H =6.71, pyridine-H), 9.09 (2H, d, JH–H =6.71, pyri-
dine-H); 13C NMR (100 MHz, DMSO): 14.25, 22.73, 27.21,
31.52, 32.28, 52.06, 55.47, 56.26, 60.96, 122.93, 128.42,
129.33, 137.99, 138.56, 139.14, 145.61, 146.22, 150.13,
155.54, 156.14, 191.84; Anal. Calc. for C23H28BrNO3: C,
61.89; H, 6.32; N, 3.14%. Found: C, 61.87; H, 6.31; N,
3.15%.
1‑(Acetic acid)‑4‑[(5,6‑dimethoxy‑1‑indanone‑2‑yl)methyl‑
ene]pyridinium chloride (5k) From 0.10 g of 2-chloroacetic
acid, 0.09 g (0.25 mmol) of white solid was obtained in 71%
yield; mp: 231–236 °C; FTIR (KBr) ν 3426, 2943, 1688,
1
1503, 1314, 1272, 1029, 848 cm−1; H NMR (400 MHz,
DMSO): δ 3.76 (3H, s, OCH3), 3.94 (3H, s, OCH3), 4.15
(4H, s, CH2), 4.98 (1H, m, CH2), 7.35 (1H, d, Ar–H), 7.42
(1H, s, =CH), 7.66 (1H, s, Ar–H), 8.12 (2H, d, 3JH–H =5.70,
1‑(2‑Propenyl)‑4‑[(5,6‑dimethoxy‑1‑indaanone‑2‑yl)meth‑
ylene]pyridinium chloride (5h) From 0.08 g of 3-chloro-
prop-1-ene, 0.07 g (0.26 mmol) of white solid was obtained
in 74% yield; mp: 225–230 °C; FTIR (KBr) ν 2937, 1688,
3
pyridine-H), 9.18 (2H, d, JH–H =5.68, pyridine-H), –OH
not detected; 13C NMR (100 MHz, DMSO): 33.06, 56.18,
56.33, 58.86, 115.6, 120.71, 133.58, 138.50, 138.96, 139.31,
142.50, 144.51, 147.32, 150.16, 155.52, 178.99, 192.15;
Anal. Calc. for C19H18ClNO5: C, 60.73; H, 4.38; N, 3.73%.
Found: C, 60.75; H, 4.37; N, 3.74%.
1
1505, 1316, 1269, 1028, 830 cm−1; H NMR (400 MHz,
DMSO): δ 3.75 (3H, s, OCH3), 3.94 (3H, s, OCH3), 4.15
(2H, s, CH2), 5.28 (2H, m, CH2), 5.24–5.31 (2H, m, =CH2),
6.12 (1H, m, =CH), 7.35 (1H, s, Ar–H), 7.42 (1H, s,
3
=CH), 7.60 (1H, s, Ar–H), 8.70 (2H, d, JH–H =5.25, pyr-
3
idine-H), 9.12 (2H, d, JH–H =5.48, pyridine-H); 13C NMR
1‑(Propionic acid)‑4‑[(5,6‑dimethoxy‑1‑indanone‑2‑yl)meth‑
ylene]pyridinium chloride (5l) From 0.11 g of 3-chloropro-
panoic acid, 0.11 g (0.28 mmol) of white solid was obtained
in 80% yield; mp: 241–243 °C; FTIR (KBr) ν 3532, 3052,
2836, 1689, 1730, 1641, 1568, 1466, 1317, 1271, 1025,
846 cm−1; 1H NMR (400 MHz, DMSO): δ 3.02 (2H, m, CH2
–COOH), 3.75 (3H, s, OCH3), 3.94 (3H, s, OCH3), 4.16 (2H,
s, CH2), 4.72 (2H, m, –CH2–N), 7.33 (1H, s, Ar–H), 7.41
(1H, s, =CH), 7.65 (1H, s, Ar–H), 8.13 (2H, d, 3JH–H =6.10,
pyridine-H), 9.11 (2H, d, 3JH–H =6.00, pyridine-H), –OH not
detected; 13C NMR (100 MHz, DMSO): 32.95, 34.92, 48.32,
56.14, 56.25, 115.6, 120.71, 133.56, 138.52, 138.84, 139.29,
142.51, 144.53, 147.32, 151.01, 155.52, 176.91, 192.18;
Anal. Calc. for C20H20ClNO5: C, 61.62; H, 5.17; N, 3.59%.
Found: C, 61.64; H, 5.18; N, 3.60%.
(100 MHz, DMSO): 52.06, 55.47, 56.32, 58.28, 117.2,
122.94, 128.41, 129.32, 132.90, 138.01, 138.56, 139.14,
145.56, 146.25, 151.05, 155.56, 156.12, 192.03; Anal. Calc.
for C20H20ClNO3: C, 67.13; H, 5.63; N, 3.91%. Found: C,
67.15; H, 5.62; N, 3.90%.
1‑[2‑(Pyrrolidin‑1‑yl)ethyl]‑4‑[(5,6‑dimethoxy‑1‑in‑
danone‑2‑yl)methylene]pyridinium bromide (5i) From
0.18 g of 1-(2-bromoethyl)pyrrolidine, 0.08 g (0.17 mmol)
of white solid was obtained in 49% yield; mp: 230–236 °C;
FTIR (KBr) ν 2929, 2861, 1687, 1463, 1316, 1268, 1031,
1
870 cm−1; H NMR (400 MHz, DMSO): δ 1.83–1.90 (4H,
m, CH2), 2.46–2.59 (6H, m, CH2–N), 3.74 (3H, s, CH3), 3.96
(3H, s, OCH3), 4.16 (2H, m, CH2), 5.03 (2H, t, CH2), 7.28
(1H, s, Ar–H), 7.45 (1H, s, =CH), 7.63 (1H, s, Ar–H), 8.92
(2H, d, 3JH–H =6.00, pyridine-H), 9.08 (2H, d, 3JH–H =5.93,
pyridine-H); 13C NMR (100 MHz, DMSO): 23.67, 32.41,
48.94, 55.24, 56.16, 56.24, 57.05, 115.6, 120.71, 133.58,
138.5, 139.33, 139.82, 142.50, 144.51, 147.32, 150.16,
155.52, 191.64; Anal. Calc. for C23H27BrN2O3: C, 60.14; H,
5.92; N, 6.10%. Found: C, 60.15; H, 5.93; N, 6.09%.
1‑(Butyric acid)‑4‑[(5,6‑dimethoxy‑1‑indanone‑2‑yl)methyl‑
ene]pyridinium chloride (5m) From 0.13 g of 4-chlorobu-
tanoic acid, 0.11 g (0.30 mmol) of white solid was obtained
in 86% yield; mp: 232–236 °C; FTIR (KBr) ν 3392, 2937,
1
1691, 1593, 1499, 1315, 1263, 1026, 823 cm−1; H NMR
(400 MHz, DMSO): δ 2.98 (2H, t, CH2 –COOH), 2.36 (2H,
1 3

Journal of the Iranian Chemical Society
m, CH2), 3.75 (3H, s, OCH3), 3.95 (3H, s, OCH3), 4.17 (2H,
s, CH2), 4.68 (2H, m, –CH2–N), 7.34 (1H, s, Ar–H), 7.40
(1H, s, =CH), 7.68 (1H, s, Ar–H), 8.12 (2H, d, 3JH–H =6.10,
pyridine-H), 9.11 (2H, d, 3JH–H =6.00, pyridine-H), –OH not
detected; 13C NMR (100 MHz, DMSO): 24.86, 32.54, 34.92,
48.32, 53.21, 56.14, 56.25, 115.6, 120.71, 133.55, 137.94,
138.81, 138.97, 142.51, 144.53, 147.32, 151.05, 155.52,
178.43, 192.18; Anal. Calc. for C21H22ClNO5: C, 62.46; H,
5.49; N, 3.47%. Found: C, 62.44; H, 5.50; N, 3.46%.
were produced from fresh blood [24]. 5,5′-Dithiobis
(2-nitrobenzoic acid) (Ellman’s reagent, DTNB), phosphate
bufer (PB), acetylthiocholine (ATC) and butylthiocholine
(BTC) were purchased from Sigma-Aldrich, Praque. Quartz
cuvettes were used for measuring purposes. All of the syn-
thesized compounds were solved in DMSO. The Na2HPO4
bufers (0.1 M) with pH = 7 and 8 were used to prepare
5,5′-dithiobis (2-nitrobenzoic acid) (DTNB, 3.5 mM) and
acetylthiocholine (ATC, 7 mM) or butylthiocholine (BTC,
7 mM) solutions, respectively. All tests were carried out in
0.1 M of Na2HPO4 bufer, pH=8. The assay medium (1 mL)
consists of 550 μL of phosphate bufer (pH 8), 150 μL of
DTNB, and 150 μL of substrate, 150 μL of inhibitor (10−4 to
10−10 M) in test cuvettes and 700 μL of phosphate bufer (pH
8), 150 μL of DTNB, and 150 μL of inhibitor solutin (10−4
to 10−10 M) in control cuvettes were incubation for 5 min in
37 °C. The reaction was initiated by an immediate addition
of 50 μL of enzyme. The activity was determined by measur-
ing the increase in absorbance at 412 nm at 5-min interval
using a spectrophotometer Helios Zeta (Thermospectronic,
Cambridge, UK). Each experiment was carried out twice.
BuChE study was conducted in a similar situation that is
described above. Nonlinear and linear regressions were used
to estimate the drug concentration inducing 50% inhibition
of the AChE or BuChE activity.
1‑(4‑Oxopentyl)‑4‑[(5,6‑dimethoxy‑1‑indanone‑2‑yl)meth‑
ylene]pyridinium chloride (5n) From 0.12 g of 5-chlo-
ropentan-2-one, 0.07 g (0.19 mmol) of white solid was
obtained in 54% yield; mp: 228–234 °C; FTIR (KBr) ν
1
2834, 1689, 1593, 1316, 1265, 1026, 824 cm−1; H NMR
(400 MHz, DMSO): δ 2.10 (3H, s, CH3), 2.15 (2H, t,
CH2), 2.40 (2H, t, CH2-CO), 3.75 (3H, s, OCH3), 3.94 (3H,
s,OCH3), 4.18 (2H, s, CH2), 4.68 (2H, s, CH2–N), 7.35 (1H,
s, Ar–H), 7.43 (1H, s, =CH), 7.68 (1H, s, Ar–H), 8.16 (2H,
d, 3JH–H =5.38, pyridine-H), 9.13 (2H, d, 3JH–H =5.36, pyri-
dine-H); 13C NMR (100 MHz, DMSO): 22.93, 29.81, 32.26,
42.71, 53.31, 55.61, 56.25, 122.93, 128.42, 129.33, 138.01,
138.54, 139.17, 145.62, 146.22, 150.13, 155.54, 156.14,
192.13, 207.71; Anal. Calc. for C22H24ClNO4: C, 65.75; H,
6.02; N, 3.49%. Found: C, 65.77; H, 6.01; N, 3.48%.
1‑[(5‑Hydroxy‑4H‑pyran‑4‑one‑2‑yl)methyl]‑4‑[(5,6‑dimeth‑
oxy‑1‑indanone‑2‑yl)methylene]
pyridinium
chloride
Results and discussion
(5o) From 0.17 g of 5-(chloromethyl)-2-hydroxy-4H-pyran-
4-one, 0.11 g (0.26 mmol) of light brown solid was obtained
in 74% yield; mp: 254–256 °C; FTIR (KBr) ν 3395, 3051,
2835, 1688, 1644, 1596, 1467, 1317, 1272, 1052, 855 cm−1;
1H NMR (400 MHz, DMSO): δ 3.75 (3H, s, OCH3), 3.95
(3H, s,OCH3), 4.16 (2H, s, CH2), 4.40 (2H, s, CH2–N), 6.68
(1H, s, =CH2 pyran), 6.82 (1H, s =CH2 pyran), 7.34 (1H,
s, Ar–H), 7.44 (1H, s, =CH), 7.67 (1H, s, Ar–H), 8.15(2H,
Chemistry
4-Pyridinecarboxaldehyde (1) is one of the well-known
aromatic aldehydes used in organic synthesis. Synthesis of
5,6-dimethoxy-2-[(pyridin-4-yl)methylene)-1-indanone (3)
was reported in the literature as an aldol condensation reac-
tion between 5,6-dimethoxy-1-indanone (2) and 4-pyridi-
necarboxaldehyde (1) under alkaline or acidic conditions
[22]. This compound was prepared in the presence of NaOH
10% in ethanol. In continuation, the 1-alkyl-4-[(5,6-dimeth-
oxy-1-indanone-2-yl)methylene]pyridinium halide deriva-
tives (4a-p) were synthesized via N-alkylation reaction of
5,6-dimethoxy-2-[(pyridin-4-yl)methylene]-1-indanone (3)
with various alkyl halides (R–X). This reaction was carried
out under refux temperature in acetone or acetonitrile as
solvent (Scheme 1).
3
3
d, JH–H =5.46, pyridine-H), 9.13 (2H, d, JH–H =5.42, pyr-
idine-H), –OH not detected; 13C NMR (100 MHz, DMSO):
32.44, 55.46, 56.18, 64.41, 113.31, 122.91, 128.01, 128.42,
129.33, 137.99, 138.56, 139.12, 145.63, 146.28, 150.13,
155.54, 156.14, 163.54, 172.71, 181.32, 191.91; Anal. Calc.
for C23H20ClNO6: C, 62.52; H, 4.56; N, 3.17%. Found: C,
62.54; H, 4.55; N, 3.18%.
Biochemical studies: cholinesterase inhibitory
activities
According to the results previously reported, polar
aprotic solvents such as acetone, acetonitrile and DMSO
are the suitable solvents for this type of reactions [6].
According to the results obtained from experiments in the
case of iodide alkyl halides, the reaction was completed in
mild temperature. Acetone was chosen as solvent, because
the iodide is good leaving groups. In the case of chlo-
ride and bromide alkyl halides, higher temperature was
Cholinesterase activity of the new synthesized compounds
was measured using the Ellman method [23], and acetylthio-
choline or butyrylthiocoline was used as substrate for AChE
or BuChE, respectively. The 50% inhibitory concentration
was measured and expressed as IC50. Human erythrocytes
AChE (hAChE) and human plasmatic BuChE (hBuChE)
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Journal of the Iranian Chemical Society
Compound
-R
5a
5b
5c
5d
5e
Br
H
C
H
H
H
H
-CH3
C
C
Br
C
H
H
Br
H
X
I
Cl
5g
Br
5h
Br
5i
Br
5j
Compound
5f
H
H2
C
C
C
C
OH
-R
H2
C
H2
H2
N
H
Cl
X
Cl
Br
5l
Cl
Br
5n
Cl
Compound
5k
5m
5o
O
H2
C
O
O
H2
C
OH
OH
C
-R
X
H2
C
OH
C
O
H2
H2
O
O
OH
Cl
Cl
Cl
Cl
Cl
Scheme 1 Synthesis of pyridinium halide derivatives (i) EtaOH, NaOH 10% (ii) acetone or acetonitrile, refux
required for completion of reaction and acetonitrile was
used as solvent for these compounds.
indanone:alkylhalide ratio, time and temperature. Among
diferent times, the optimal results were obtained in 48 h and
for refux temperature (80 °C for CH3CN). By increasing the
indanone:alkylhalide ratio until 1:3, the yield was increased
up to 90%, but there was no change in yield afterward.
With the precursor 3 in hand, the focus was on the opti-
mization of reaction condition for compound 5b as repre-
sentative of the fnal products. As can be seen in Table 1,
the N-alkylation reaction was surveyed in the variety of
Table 1 Obtained yield in %
Temperature (°C)
Indanone:alkylhalide 1:1 1:1.5
r.t 40 80 r.t 40 80 r.t 40 80 r.t 40 80 r.t 40 80 r.t 40 80
10 12 10 14 13 18 10 15 25 10 20 60 10 20 60
for compound 5b in diferent
indanone:alkylhalide ratio, time
and temperature
1:2
1:2.5
1:3
1:3.5
Time
24 h
48 h
72 h
0
0
7
10 13 20 10 20 27 10 18 48 12 20 56 25 38 90 25 38 90
10 13 20 10 20 27 10 18 48 12 20 56 25 38 90 25 38 90
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Journal of the Iranian Chemical Society
Table 2 In vitro hAChE and
hBuChE inhibitory activity and
selectivity index of indanone
derivatives
Compound
Yield (%)
AChE IC50 (μM)
BuChE IC50 (μM)
AChE IC50/
BuChEIC50
Donepezil
–
0.04
14.4
0.003
Galantamine
3
–
3
31.6
0.095
–
–
23.958
2.430
22.192
1.971
40.182
0.177
–
–
–
–
67
81
90
66
64
48
60
57
59
50
56
71
81
84
56
77
16.2%
108
46
17.3
48.6
10.8
22.1
4.6
9.94%
2.06%
1.92
7.12
2.19
5.48
0.55
26.03
4.13%a
12.97%a
9.71%a
0.5%a
221.94
1.54%a
0
5a
5b
5c
5d
5e
5f
5g
5h
5i
5j
5k
5l
5m
5n
5o
24.25%a
4.85%a
11.13%a
22.95%a
34
0.153
21.35%a
18.16%a
22.60%
–
–
–
13.12%
aPercent inhibition at a concentration of 100 μM
All molecular structures of the synthesized compounds
were confrmed by 1H NMR, 13C NMR and FTIR spectros-
copy and elemental analysis.
results in Table 1 indicated that bromine atom in ortho posi-
tion shows a better inhibition for hAChE (compound 5e);
meanwhile, a better inhibition of hBuChE was obtained when
the bromine set in meta position (compound 5d).
Inhibition of human AChE and BuChE
The extent of inhibition was expressed as the chemical con-
centration at which 50% of enzyme activity was inhibited
(IC50). The IC50 values of compounds 3 and 5a–o were
determined against human erythrocyte AChE and human
plasmatic butyrylcholinesterase using the method of Ell-
man et al. [23]. The IC50 values and selectivity index (SI)
of synthesized pyridinium halide derivatives and the control
compounds, donepezil and galantamine are summarized in
Table 2. These synthesized derivatives demonstrated inhibi-
tory activity against both hAChE and hBuChE with IC50 val-
ues ranging from micro-molar to submicromolar concentra-
tions. The IC50 values of the synthesized compounds suggest
strong BuChE inhibition in comparison with AChE for these
derivatives. Among these compounds, the highest inhibition
of hAChE was recorded for 5g (IC50: 4.6 μM, weaker than
donepezil and galantamine). The most potent inhibitor of
hBuChE is 5f which showed IC50: 0.55 μM, while this value
is approximately 26.18 times higher than donepezil and 57.45
times higher than galantamine; but in the case of hAChE,
this compound showed IC50: 22.1 μM that is weaker than
donepezil and galantamine. It is notable that the compounds
with chlorine and bromine atoms substitution on phenyl ring
show better inhibition compared with the others. Summarized
Conclusion
In summary, a series of 1-alkyl-4-[(5,6-dimethoxy-1-in-
danone-2-yl)methylene]pyridinium halide were designed
and synthesized with acceptable yield using N-alkylation
reaction of 5,6-dimethoxy-2-[(pyridin-4-yl)methylene)1-
indanone. Anti-AChE and anti-BuChE efects of all syn-
thesized compounds were tested, 1-hexyl-4-[(5,6-dimeth-
oxy-1-indanone-2-yl)methylene]pyridinium bromide (5g)
displayed excellent inhibition of hAChE, and the most potent
inhibitor of hBuChE was 1-(2-chlorobenzyl)-4-[(5,6-dimeth-
oxy-1-indanone-2-yl)methylene]pyridinium chloride (5f).
Acknowledgements This project was fnancially supported by a grant
from Deputy for Research and Technology of Iranian Ministry of
Health and Medical Education. The authors would like to acknowledge
the fnancial support from Tabriz University of medical sciences and
the University of Tabriz.
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Afliations
Hanieh Farrokhi1 · Sakineh Mozafarnia1,2 · Keshvar Rahimpour1 · Mohammad Reza Rashidi2 ·
Reza Teimuri‑Mofrad1
1
* Mohammad Reza Rashidi
Department of Organic and Biochemistry, Faculty
rashidi@tbzmed.ac.ir
of Chemistry, University of Tabriz, Tabriz, Iran
2
* Reza Teimuri-Mofrad
Research Center for Pharmaceutical Nanotechnology, Tabriz
University of Medical Sciences, Tabriz, Iran
teymouri@tabrizu.ac.ir
1 3