Synthesis, biologicalevaluation, and molecular modeling of (E)-2-aryl-5-styryl-1,3,4-oxadiazolederivatives as acetylcholine esterase inhibitors

Article abstract of DOI:10.1007/s00044-013-0786-y

A library of 2,5-disubstituted 1,3,4-oxadiazole derivatives of (E)-2-aryl-5-(3,4,5-trimethoxystyryl)-1,3,4-oxadiazoles 4(a-o) and (E)-2-aryl-5-(2-benzo[d][1,3]dioxol-5-yl)vinyl)-1,3,4-oxadiazoles 5(a-q) were synthesized and evaluated for their in vitro acetylcholinesterase (AChE) inhibitory activity. All the synthesized compounds exhibited moderate to good inhibitory activity toward the AChE enzyme. Among the oxadiazole derivatives examined, compounds 4a, 4g, 5c, and 5m (IC₅₀ values of 24.89, 13.72, 37.65, and 19.63 μM, respectively) were found to be promising inhibitors of AChE. Molecular protein-ligand docking studies were examined for these compounds using GOLD docking software and their binding conformations were determined and the simultaneous interactions mode was also established for the potent derivatives. Springer Science+Business Media 2013.

Full text of DOI:10.1007/s00044-013-0786-y

MEDICINAL
CHEMISTRY
RESEARCH
Med Chem Res (2014) 23:2080–2092
DOI 10.1007/s00044-013-0786-y
ORIGINAL RESEARCH
Synthesis, biological evaluation, and molecular modeling of (E)-2-
aryl-5-styryl-1,3,4-oxadiazole derivatives as acetylcholine esterase
inhibitors
•
Ahmed Kamal Anver Basha Shaik G. Narender Reddy
•
•
•
C. Ganesh Kumar Joveeta Joseph G. Bharath Kumar
•
•
•
Uppula Purushotham G. Narahari Sastry
Received: 21 February 2013 / Accepted: 10 September 2013 / Published online: 6 October 2013
Ó Springer Science+Business Media New York 2013
Abstract A library of 2,5-disubstituted 1,3,4-oxadiazole
derivatives of (E)-2-aryl-5-(3,4,5-trimethoxystyryl)-1,3,4-
oxadiazoles 4(a–o) and (E)-2-aryl-5-(2-benzo[d][1,3]diox-
ol-5-yl)vinyl)-1,3,4-oxadiazoles 5(a–q) were synthesized
and evaluated for their in vitro acetylcholinesterase
(AChE) inhibitory activity. All the synthesized compounds
exhibited moderate to good inhibitory activity toward the
AChE enzyme. Among the oxadiazole derivatives exam-
ined, compounds 4a, 4g, 5c, and 5m (IC50 values of 24.89,
13.72, 37.65, and 19.63 lM, respectively) were found to be
promising inhibitors of AChE. Molecular protein–ligand
docking studies were examined for these compounds using
GOLD docking software and their binding conformations
were determined and the simultaneous interactions mode
was also established for the potent derivatives.
deficiency in choline acetyltransferase (ChAT) activity in the
hippocampus and cerebral cortex. A significant correlation has
been found between a decrease in cortical cholinergic activity
and the deterioration of mental test scores in patients suffering
from AD. Therefore, potentiation of central cholinergic
activity has been proposed as a possible therapeutic approach
to improve cognitive function in AD patients (Bartus et al.,
1982). Among the most promising strategies is the elevation of
the brain concentration of neurotransmitter acetylcholine
(ACh) by centrally acting acetylcholinesterase (AChE, EC
3.1.1.7) inhibitors. During the past decade, several cholinergic
drugshave been launchedin themarket, includingthe synthetic
compounds, Tacrine (Davis and Powchik, 1995), Galantha-
mine (Rainer, 1997), Donepezil (Kawakami et al., 1996), and
Rivastigmine (Prous et al., 1996). It has been reported that use
of these drugs produced significant cognitive improvement
(Wagstaff and McTavish, 1994; Bartus et al., 1982; Johansson
et al., 1996). However, a major drawback on their widespread
use as a general therapy exhibited undesirable side effects such
as hepatotoxicity which impose severe dose limits.
Keywords 2-Aryl-5-styryl-1,3,4-oxadiazoles ꢀ
Derivatives ꢀ Acetylcholine esterase inhibitors ꢀ
Molecular modeling
ThecomprehensivestudyoftheAChEinhibitorcomplexes
by X-ray crystallography indicated that AChE possessed a
narrow gorge with two separate ligand binding sites, an
acylation site (active site) and a peripheral site which is also
called peripheral anionic site. Simultaneous binding to the
catalytic anionic subsite and the peripheral anionic site is
responsible for the enhanced binding of gorge-spanning
ligands, such as galanthamine (Fig. 1a) and donepezil
(Fig. 1b). Recent biochemical studies have shown that the
peripheral anionic site is also implicated in promoting
aggregation of the beta-amyloid (Ab) peptide responsible for
the neurodegenerative process in AD (Alvarez et al., 1997,
1998; De Ferrari et al., 2001). Thus, the design of inhibitors
interacting with the peripheral anionic site is of potential
interest for the treatment of AD (Andreani et al., 2001).
Introduction
Alzheimer’s disease (AD), the most common neurodegenera-
tive disorder associated with aging, is accompanied by severe
A. Kamal (&) ꢀ A. B. Shaik ꢀ G. N. Reddy ꢀ
C. G. Kumar ꢀ J. Joseph ꢀ G. B. Kumar
Chemical Biology Laboratory, Medicinal Chemistry and
Pharmacology Division, CSIR-Indian Institute of Chemical
Technology, Hyderabad 500007, India
e-mail: ahmedkamal@iict.res.in
U. Purushotham ꢀ G. N. Sastry
Molecular Modeling Group, CSIR-Indian Institute of Chemical
Technology, Hyderabad 500007, India
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Med Chem Res (2014) 23:2080–2092
2081
Fig. 1 Chemical structures of
galanthamine, donepezil, (E)-2-
(2-furan-2-yl)-5-(3,4,5-
H
3CO
N
trimethoxystyryl)-1,3,4-
O
O
N
oxadiazole (4g), and (E)-2-(2-
benzo[d][1,3]dioxol-5-yl)vinyl)-
5-(2-chloro-4-fluorophenyl)-
1,3,4-oxadiazole (5m)
H
H
H
3CO
3CO
H
O
Galanthamine
Donepezil
N
N
N
N
l
C
H
H
3CO
O
O
O
O
O
3CO
F
H
OC
3
5m
4g
Heterocyclic compounds containing the five-membered
oxadiazole nucleus possess a diversity of useful biological
effects. Differently 2,5-disubstituted oxadiazole moieties
have also been reported to have other interesting activities
such as analgesic (Narayana et al., 2005; Alam et al., 2011),
antimicrobial (Gaonkar et al., 2006), anticonvulsant (Zarghi
et al., 2005), and anti-hepatitis B viral activities (Tan et al.,
2006). In particular, oxadiazole derivatives bearing the
1,3,4-oxadiazole nucleus are known to have unique anti-
edema and anti-inflammatory activities (Narayana et al.,
2005; Alam et al., 2011) and also exhibit AChE inhibitory
activity (Al-Kazzaz et al., 2011) and central nervous system
depressant activity (Singh et al., 2012). However, docking
studies have not been reported for these aforementioned
derivatives. Considering these facts, we have synthesized
(E)-2-aryl-5-styryl-1,3,4-oxadiazole derivatives 4(a–o) and
5(a–q), which are hybrids containing both the styryl and
oxadiazole moieties, that contain trimethoxy phenyl and 3,4-
(methylenedioxy) phenyl groups (Fig. 1—4g, 5m) by facile
procedures described previously (Shi et al., 2001; Lee et al.,
2010; Bhattacharya et al., 2010; Jha et al., 2010). Addi-
tionally, their effect on AChE inhibition was investigated
and docking simulations were also carried out on the three-
dimensional structures of AChE, to understand the structural
requirements for the recognition between the AChE and the
ligands.
Spectrochem Pvt. Ltd, Mumbai, India and were used
without further purification. Reactions were monitored by
TLC, performed on silica gel glass plates containing 60
GF-254, and visualization on TLC was achieved by UV
light or iodine indicator. Column chromatography was
performed with Merck 60–120 mesh silica gel. The NMR
spectra were recorded on Gemini Varian-VXR-Unity
(200 MHz) or Bruker UXNMR/XWIN-NMR (300 MHz)
instruments. Chemical shifts (d) are reported in ppm rela-
tive to the peak for tetramethylsilane (TMS) as an internal
standard, and coupling constants are reported in Hertz
(Hz). IR spectra are recorded on Perkin-Elmer model 683
or 1310 spectrometer with sodium chloride optics. ESI
spectra were recorded on Micro mass, Quattro LC using
ESI? software with capillary voltage of 3.98 kV and ESI
mode positive ion trap detector. Melting points were
determined with an Electro thermal melting point apparatus
and are uncorrected.
General procedure for the synthesis of carboxylic acid
ester 7(a–q)
To 10 ml of ethanol, (1.0 mol) of carboxylic acid 6(a–
q) was added in a 100-ml round-bottomed flask. To this,
catalytic amount of concentrated H2SO4 was added at room
temperature and was heated under reflux with continuous
stirring for 3–4 h at 85 °C. After 3 h, the reaction was
monitored by TLC using ethyl acetate and hexane (3:7)
system. Stirring was continued until TLC indicated the
completion of reaction. Then the reaction mixture was
allowed to reach the room temperature. Ethanol was dis-
tilled off under reduced pressure and the residue was dis-
solved in water and then extracted twice with ethyl acetate.
The combined organic solutions were washed with satu-
rated NaHCO3 solution, finally washed with water and
Materials and methods
Synthesis and structural characterization
All chemicals were purchased from different companies
like Sigma-Aldrich, St. Louis, MO, USA, Alfa Aesar,
Johnson Matthey Company, Ward Hill, MA, USA, and
123

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Med Chem Res (2014) 23:2080–2092
dried over anhydrous Na2SO4. The solvent was removed
under vacuum to get carboxylic acid ester, which is an oily
liquid. The ester obtained was taken as such in the next step
of synthesis.
ppm; IR (KBr) (mmax/cm-1): m = 3449, 2925, 2833, 1641,
1583, 1526, 1502, 1452, 1418, 1331, 1245, 1128 cm-1; MS
(ESI): m/z 339[M?1]; HR-MS (ESI) for C19H19N2O4 cal-
culated m/z: 339.1344, found m/z: 339.1332.
General procedure for the synthesis of acid hydrazides
(E)-2-p-tolyl-5-(3,4,5-trimethoxystyryl)-1,3,4-oxadiazole
8(a–q)
(4b)
To the carboxylic acid ester (1.0 mol) obtained in step I,
10 ml of ethanol was added in a 100-ml round-bottomed
flask. To this, hydrazine hydrate (4.0 mol) was added at
room temperature and then heated under reflux conditions
with continuous stirring for 3–4 h at 85 °C. After 3 h, the
reaction was monitored by TLC using ethyl acetate and
hexane (1:1) system. Stirring was continued until TLC
indicated the completion of reaction. The reaction was
allowed to reach the room temperature. Ethanol was dis-
tilled off under reduced pressure. The residue was dis-
solved in water and extracted twice with ethyl acetate,
dried over anhydrous Na2SO4 and the solvent was removed
under reduced pressure to afford the compound 8(a–q) as
crystalline solid. The hydrazide obtained was taken as such
in the next step of synthesis.
Pale yellow-colored solid; (yield 550 mg, 79.8 %): Rf = 0.4
(50 % ethyl acetate/hexane); mp: 134–136 °C; 1H NMR
(400 MHz, CDCl3); d 2.45 (s, 3H, –CH3), 3.86 (s, 3H, –OCH3),
3.91 (s, 6H, –OCH3), 6.76 (s, 2H, ArH), 6.98 (d, 1H,
J = 16.4 Hz, trans-CH=CH), 7.29 (d, 2H, J = 8.1 Hz,
ArH), 7.48 (d, 1H, J = 16.4 Hz, trans-CH=CH), 7.98 (d,
2H, J = 8.1 Hz, ArH); 13C NMR (75 MHz, CDCl3): d
21.6(CH3), 56.1(OCH3), 61.0 (OCH3), 104.5, 109.4 (Ar–
C), 121.0, 126.8 (Ar–C), 129.7 (HC=CH), 138.5 (HC=CH),
142.3(C–OCH3), 153.5(C–OCH3), 164.0 (C=N) ppm; IR
(KBr) (mmax/cm-1): m = 3423, 3046, 2936, 1633, 1579,
1498, 1331, 1243, 1126 cm-1; MS (ESI): m/z 353 [M?1];
HR-MS (ESI) m/z for C20H18N2O4 calculated m/z:
353.1518, found m/z: 353.1512.
(E)-2-(2,4-dichlorophenyl)l-5-(3,4,5-trimethoxystyryl)-
General procedure for the synthesis of (E)-2-aryl-5-
styryl-1,3,4-oxadiazoles 4(a–o) and 5(a–q)
1,3,4-oxadiazole (4c)
Yellow-colored solid; (yield 690 mg, 80.7 %): Rf = 0.5 (50 %
ethyl acetate/hexane); mp: 154–156 °C; 1H NMR (300 MHz,
CDCl3); d 3.86 (s, 3H, –OCH3), 3.91 (s, 6H, –OCH3), 6.76 (s,
2H, ArH), 6.98 (d, 1H, J = 16.4 Hz, trans-CH=CH), 7.39–7.42
(m, 1H, ArH), 7.49 (d, 1H, J = 16.4 Hz, trans-CH=CH), 7.99
To an equimolar mixture, (0.002 mol) of 3,4,5-trimeth-
oxycinnamic acid or 3,4-(methyledioxy)cinnamic acid, an
appropriate acid hydrazide in 7–8 ml of phosphorus oxy-
chloride was added and the reaction mixture was refluxed
at 110 °C for 5–6 h. After completion of reaction, the
mixture was poured onto crushed ice (40 g) and neutralized
with saturated NaHCO3 solution. The product so obtained
was extracted twice with ethyl acetate and dried on anhy-
drous Na2SO4. The solvent was removed under reduced
pressure to get the crude product. This residue was further
purified by column chromatography by using ethyl acetate
and hexane to yield pure solid (E)-2-aryl-5-styryl-1,3,4-
oxadiazoles 4(a–o) and 5(a–q).
(d, 1H, J = 1.8 Hz, ArH), 8.07 (d, 1H, J = 8.4 Hz, ArH); 13
C
NMR (75 MHz, CDCl3): d 56.1 (OCH3), 60.9 (OCH3),
104.6(Ar–C), 108.8(Ar–C), 121.5(Ar–C), 127.5(HC=CH),
130.0, 131.1, 131.7(Ar–C), 133.6 (HC=CH), 138.0(Ar–C),
139.5(C–OCH3), 153.4(C–OCH3), 161.6(C=N), 164.1(C=N)
ppm; IR (KBr) (mmax/cm-1): m = 3385, 2925, 1635, 1584,
1507, 1454, 1413, 1334, 1241 cm-1; MS (ESI): m/z 407
[M?1]; HR-MS (ESI) m/z for C19H17N2O4Cl2 calculated m/z:
407.0565, found m/z: 407.0556.
(E)-2-phenyl-5-(3,4,5-trimethoxystyryl)-1,3,4-oxadiazole
(E)-2-(2-chloropyridin-3-yl)-5-(3,4,5-trimethoxystyryl)-
(4a)
1,3,4-oxadiazole (4d)
Pale yellow solid; (yield 620 mg, 87.3 %): Rf = 0.6 (50 %
ethyl acetate/hexane); mp: 150–153 °C; 1H NMR
(300 MHz, CDCl3); d 3.89 (s, 3H, –OCH3), 3.92 (s, 6H,
–OCH3), 6.79 (s, 2H, ArH), 7.00 (d, 1H, J = 15.8 Hz, trans-
CH=CH), 7.48–7.56 (m, 4H, Hz, ArH, J = 15.8 Hz, trans-
CH=CH), 8.09–8.15 (m, 2H, ArH); 13C NMR (75 MHz,
CDCl3): d 56.0 (OCH3), 60.9 (OCH3), 104.6 (Ar–C), 109.2
(Ar–C), 123.7 (HC=CH), 126.8, 128.9, 130.2(Ar–C), 131.6
(HC=CH), 138.7 (C–OCH3), 153.4 (C–OCH3), 164.1(C=N),
Yellow-colored solid; (yield 410 mg, 52.2 %): Rf = 0.4
1
(50 % ethyl acetate/hexane); mp: 141–143 °C; H NMR
(200 MHz, CDCl3); d 3.87 (s, 3H, –OCH3), 3.92 (s, 6H,
–OCH3), 6.76 (d, 2H, J = 7.5 Hz, ArH), 6.98 (d, 1H,
J = 15.8 Hz, trans-CH=CH), 7.40–7.45 (m, 1H, ArH),
7.55 (d, 1H, J = 15.8 Hz, trans-CH=CH), 8.46–8.57 (m,
2H, ArH); 13C NMR (75 MHz, CDCl3): d 56.1 (OCH3),
60.9 (OCH3), 104.8, 105.4, 108.6, 120.3 (Ar–C), 122.4
(HC=CH), 130.3 (HC=CH), 139.7(C–OCH3), 139.9, 140.1,
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Med Chem Res (2014) 23:2080–2092
2083
148.9 (Ar–C), 151.7 (Ar–C–Cl), 153.4 (Ar–C), 153.5 (C–
J = 16.0 Hz, trans-CH=CH), 6.96–7.00 (s, 1H, ArH), 7.46
(d, 1H, J = 16.4 Hz, trans-CH=CH), 7.55 (s, 1H, ArH), 8.12
(s, 1H, ArH); 13C NMR (75 MHz, CDCl3 ? DMSO-d6): d
56.0 (OCH3), 60.9 (OCH3), 104.5 (Ar–C), 108.4, 109.0,
111.6 (Ar–C), 130.2 (HC=CH), 139.7 (C–O), 138.6 (C–
OCH3), 143.4 (Ar–C), 144.4 (C–O), 153.4 (C–OCH3), 159.0
(C=N), 163.5 (C=N) ppm; IR (KBr) (mmax/cm-1): m = 3442,
3033, 2945, 2834, 1653, 1582, 1419, 1240, 1162, 1126,
975 cm-1; MS (ESI) m/z 329; HR-MS (ESI) m/z for
C17H17N2O5 calculated m/z: 329.1137, found m/z: 329.1127.
OCH3), 160.8 (C=N), 165.2 (C=N) ppm; IR (KBr) (mmax
/
cm-1): m = 3424, 3060, 2930, 1740, 1642, 1583, 1462,
1239, 1134, 962 cm-1; MS (ESI) m/z 374; HR-MS (ESI)
m/z for C18H17N3O4Cl calculated m/z: 374.0907, found
m/z: 374.0908.
(E)-2-(2-bromophenyl)-5-(3,4,5-trimethoxystyryl)-1,3,4-
oxadiazole (4e)
Yellow-colored solid; (yield 535 mg, 161.1 %): Rf = 0.5
1
(50 % ethyl acetate/hexane); mp: 122–125 °C; H NMR
(E)-2-(4-nitrophenyl)-5-(3,4,5-trimethoxystyryl)-1,3,4-
(300 MHz, CDCl3); d 3.86 (s, 3H, –OCH3), 3.91 (s, 6H,
–OCH3), 6.89 (d, 1H, J = 8.3 Hz, ArH), 6.93 (s, 1H, ArH),
7.41–7.55 (m, 4H, J = 7.0 Hz, ArH, J = 15.8 Hz, trans-
CH=CH), 8.01–8.12 (m, 2H, ArH); 13C NMR (75 MHz,
CDCl3): d 56.0 (OCH3), 60.8 (OCH3), 104.5, 109.0, 109.1,
121.3(Ar–C), 125.0 (HC=CH), 126.8, 127.5, 128.9, 130.1,
131.4, 131.6, 132.3(Ar–C), 134.5(HC=CH), 138.7(C–
OCH3), 139.2(Ar–C–Br), 153.4(C–OCH3), 161.8(C=N),
164.3(C=N) ppm; IR (KBr) (mmax/cm-1): m = 3455, 3051,
2989, 2832, 1973, 1740, 1704, 1636, 1584, 1524, 1460,
1417, 1329, 1244, 1181, 1131 cm-1; MS (ESI) m/z 417;
HR-MS (ESI) m/z for C19H18N2O4Br calculated m/z:
417.0449, found m/z: 417.0452.
oxadiazole (4h)
Yellow-colored solid; (yield 425 mg, 52.84 %): Rf = 0.4
1
(50 % ethyl acetate/hexane); mp: 183–185 °C; H NMR
(400 MHz, CDCl3); d 3.87 (s, 3H, –OCH3), 3.92 (s, 6H,
–OCH3), 6.78 (s, 2H, ArH), 6.97 (d, 1H, J = 16.4 Hz, trans-
CH=CH–), 7.56 (d, 1H, J = 16.4 Hz, trans-CH=CH), 8.29
(d, 2H, J = 8.6 Hz, ArH), 8.38 (d, 2H, J = 7.5 Hz, ArH);
13C NMR (75 MHz, CDCl3 ? DMSO-d6): d 56.1 (OCH3),
60.9 (OCH3), 104.7, 108.4, 121.5(Ar–C), 125.4 (HC=CH),
126.0, 129.9, 130.3 (Ar–C), 132.4 (HC=CH), 139.9 (C–
OCH3), 148.5 (C–NO2), 153.5 (C–OCH3), 161.9 (C=N),
164.8 (C=N) ppm; IR (KBr) (mmax/cm-1): m = 3426, 2926,
1633, 1584, 1555, 1529, 1456, 1413, 1332, 1243, 1156,
1123 cm-1; MS (ESI) m/z: 384; HR-MS (ESI) m/z for
C19H18N3O6 calculated m/z: 384.1195, found m/z: 384.1185.
(E)-2-(2-benzofuran-2-yl)-5-(3,4,5-trimethoxystyryl)-1,3,4-
oxadiazole (4f)
Yellow-colored solid; (yield 715 mg, 90.05 %): Rf = 0.4 (50 %
1
ethyl acetate/hexane); mp: 189–190 °C; H NMR (200 MHz,
(E)-2-(3,4,5-trimethoxyphenyl)-5-(3,4,5-trimethoxystyryl)-
1,3,4-oxadiazole (4i)
CDCl3); d 3.87 (s, 3H, –OCH3), 3.92 (s, 6H, –OCH3), 6.79
(s, 1H, ArH), 6.98 (d, 1H, J = 16.0 Hz, trans-CH=CH),
7.28–7.36 (m, 2H, J = 8.8 Hz, ArH), 7.40–7.46 (m, 1H,
J = 7.7 Hz, ArH), 7.56–7.65 (m, 3H, J = 7.7 Hz ArH,
J = 16.0 Hz trans-CH=CH), 7.69 (d, 1H, J = 7.5 Hz,
ArH); 13C NMR (75 MHz, CDCl3): d 56.1 (OCH3), 60.9
(OCH3), 104.7 (Ar–C),108.5 (Ar–C), 110.1, 111.9, 122.2
(Ar–C), 124.0 (HC=CH), 127.2(Ar–C), 130.0 (HC=CH),
140.5 (C–O), 139.6 (C–OCH3), 153.5 (C–OCH3), 155.6
Light yellow-colored solid; (yield 310 mg, 61.19 %):
Rf = 0.4 (50 % ethyl acetate/hexane); mp: 153–155 °C; 1H
NMR (300 MHz, CDCl3 ? DMSO-d6); d 3.86 (s, 3H,
–OCH3), 3.90 (s, 3H, –OCH3), 3.91 (s, 6H, –OCH3), 3.97
(s, 6H, –OCH3), 6.77 (s, 2H, ArH), 6.95 (d, 1H,
J = 16.6 Hz, trans-CH=CH–), 7.29 (d, 2H, J = 3.7 Hz,
ArH), 7.49 (d, 1H, J = 16.6 Hz, trans-CH=CH–); 13C
NMR (75 MHz; CDCl3 ? DMSO-d6): d 56.1 (OCH3),
60.9 (OCH3), 104.2, 104.6, 109.1 (Ar–C), 118.8 (HC=CH),
130.2 (HC=CH), 138.6, 138.7(C–OCH3), 139.8, 141.2 (Ar–
C), 153.4, 153.6 (C–OCH3), 163.6 (C=N), 163.8 (C=N) ppm;
IR (KBr) (mmax/cm-1): m = 3419, 2928, 2835, 1641, 1584,
1497, 1458, 1417, 1328, 1238, 1180, 1124 cm-1; MS (ESI)
m/z: 428; HR-MS (ESI) m/z for C22H24N2O7Na calculated
m/z:451.1481, found m/z: 451.1494.
(C–O), 157.1(C=N), 164.1(C=N) ppm; IR (KBr) (mmax
/
cm-1): m = 3423, 3050, 2928, 2834, 1638, 1583, 1453,
1420, 1247, 1132, 972 cm-1; MS (ESI) m/z: 379; HR-MS
(ESI) m/z for C21H19N2O5 calculated m/z: 379.1293, found
m/z: 379.1281.
(E)-2-(2-furan-2-yl)-5-(3,4,5-trimethoxystyryl)-1,3,4-
oxadiazole (4g)
(E)-2-(3-nitrophenyl)-5-(3,4,5-trimethoxystyryl)-1,3,4-
Light yellow-colored solid; (yield 410 mg, 87.1 %):
Rf = 0.5 (50 % ethyl acetate/hexane); mp: 154–157 °C; 1H
NMR (300 MHz, CDCl3 ? DMSO-d6); d 3.86 (s, 3H,
–OCH3), 3.91 (s, 6H, –OCH3), 6.75 (s, 2H, ArH), 6.93 (d, 1H,
oxadiazole (4j)
Yellow-colored solid; (yield 410 mg, 50.97 %): Rf = 0.4
1
(50 % ethyl acetate/hexane); mp: 156–158 °C; H NMR
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Med Chem Res (2014) 23:2080–2092
(E)-2-(5-bromopyridin-3-yl)-5-(3,4,5-trimethoxystyryl)-
(300 MHz, CDCl3); d 3.89 (s, 3H, –OCH3), 3.92 (s, 6H,
–OCH3), 6.82 (s, 2H, ArH), 6.99 (d, 1H, J = 16.4 Hz,
trans-CH=CH), 7.61 (d, 1H, J = 16.4 Hz, trans-CH=CH),
7.74 (t, 1H, J = 7.9 Hz, ArH), 8.39–8.43 (m, 1H, ArH),
8.51 (d, 1H, J = 7.7 Hz, ArH), 8.89 (s, 1H, ArH); 13C
NMR (75 MHz, CDCl3): d 56.1 (OCH3), 60.9 (OCH3),
104.7, 108.4, 121.5 (Ar–C), 125.4 (HC=CH), 126.0, 129.9,
130.3(Ar–C), 132.4 (HC=CH), 139.9 (C–OCH3), 148.5
(C–NO2), 153.5 (C–OCH3), 161.9 (C=N), 164.8 (C=N)
ppm; IR (KBr) (mmax/cm-1); m = 3423, 2925, 1733, 1638,
1584, 1523, 1461, 1419, 1339, 1244, 1127 cm-1; MS (ESI)
m/z: 384; HR-MS (ESI) m/z for C19H18N3O6 calculated
m/z: 384.1195, found m/z: 384.1185.
1,3,4-oxadiazole (4m)
Yellow-colored crystals; (yield 256 mg, 29.23 %):
Rf = 0.4 (50 % ethyl acetate/hexane); mp: 156–159 °C;
1H NMR (300 MHz, CDCl3); d 3.91 (s, 3H, –OCH3), 3.91
(s, 6H, –OCH3), 6.83 (s, 2H, ArH), 7.03 (d, 1H,
J = 15.8 Hz, trans-CH=CH–), 7.60 (d, 1H, J = 15.8 Hz,
trans-CH=CH–), 8.55 (s, 1H, ArH), 8.87 (s, 1H, ArH), 9.27
(s, 1H, ArH); 13C NMR (75 MHz; CDCl3): d 56.1 (OCH3),
60.1 (OCH3), 104.7, 108.4 (Ar–C), 129.8 (HC=CH), 136.1
(HC=CH), 140.0 (C–OCH3), 145.6, 153.2 (ArC–N), 153.4
(C–OCH3), 160.5 (C=N), 164.9 (C=N) ppm; IR (KBr)
(mmax/cm-1): m = 3422, 3042, 2928, 1734, 1638, 1579,
1518, 1455, 1415, 1330, 1243, 1186, 1125 cm-1; MS (ESI)
m/z: 418 [M?], 420 [M2?]; HR-MS (ESI) m/z for
C18H19N3O4Br calculated m/z: 418.0378, found m/z:
418.0386.
(E)-2-(2-chlorophenyl)-5-(3,4,5-trimethoxystyryl)-1,3,4-
oxadiazole (4k)
Yellow-colored solid; (yield 516 mg, 52.0 %): Rf = 0.5
1
(50 % ethyl acetate/hexane); mp: 144–146 °C; H NMR
(E)-2-(4-methoxyphenyl)-5-(3,4,5-trimethoxystyryl)-1,3,4-
(200 MHz, CDCl3); d 3.89 (s, 3H, –OCH3), 3.93 (s, 6H,
–OCH3), 6.79 (s, 2H, ArH), 6.98 (d, 1H, J = 16.8 Hz,
trans-CH=CH–), 7.41–7.58 (m, 4H, ArH, J = 16.8 Hz,
trans-CH=CH–), 8.09 (d, 1H, J = 7.9 Hz, ArH) 13C NMR
(75 MHz, CDCl3 ? DMSO-d6): d 56.1 (OCH3), 60.9
(OCH3), 104.6, 109.0 (Ar–C), 127.0 (HC=CH), 130.1,
131.0, 131.2 (Ar–C), 132.3 (HC=CH), 132.9 (ArC–Cl),
139.2 (Ar–C), 139.8 (C–OCH3), 153.4 (C–OCH3), 162.2
(C=N), 164.5 (C=N) ppm; IR (KBr) (mmax/cm-1):
m = 3429, 2689, 2927, 2834, 2365, 1741, 1636, 1585,
1525, 1447, 1416, 1330, 1244, 1132 cm-1; MS (ESI) m/z
472; HR-MS (ESI) m/z for C19H18N2O4Cl calculated m/z:
373.0955, found m/z: 373.0946.
oxadiazole (4n)
Light yellow-colored solid; (yield 526 mg, 68.06 %):
Rf = 0.6 (50 % ethyl acetate/hexane); mp: 150–152 °C; 1H
NMR (300 MHz, CDCl3); d 3.91 (s, 3H, –OCH3), 3.88 (s,
3H, –OCH3), 3.91 (s, 6H, –OCH3), 6.76 (s, 2H, ArH), 6.95
(d, 1H, J = 16.8 Hz, trans-CH=CH–), 6.99 (d, 2H,
J = 8.9 Hz, ArH), 7.46 (d, 1H, J = 16.8 Hz, trans-
CH=CH–), 8.01 (d, 1H, J = 8.9 Hz, ArH); 13C NMR
(75 MHz; CDCl3):
d 55.4 (OCH3), 56.0 (OCH3),
60.9(OCH3), 104.4, 109.3, 114.4 (Ar–C), 130.3 (HC=CH),
128.6 (HC=CH), 138.1(C–OCH3), 153.4 (C–OCH3), 160.7
(C=N), 162.2 (C=N) ppm; IR (KBr) (mmax/cm-1):
m = 3427, 2919, 2844, 1615, 1531, 1499, 1458, 1420,
1334, 1306, 1252, 1131, 1167 cm-1; MS (ESI) m/z: 369
[M?]; HR-MS (ESI) m/z for C18H19N3O4Br calculated m/z:
369.1450 found m/z: 369.1446.
(E)-2-(2-chloro-4-fluorophenyl)-5-(3,4,5-trimethoxystyryl)-
1,3,4-oxadiazole (4l)
Light yellow-colored solid; (yield 328 mg, 50.0 %):
Rf = 0.5 (50 % ethyl acetate/hexane); mp: 160–162 °C; 1H
NMR (300 MHz, CDCl3 ? DMSO-d6); d 3.86 (s, 3H,
–OCH3), 3.92 (s, 6H, –OCH3), 6.76 (s, 2H, ArH), 6.98 (d,
1H, J = 16.4 Hz, trans-CH=CH–), 7.12–7.19 (m, 1H,
ArH), 7.30–7.34 (m, 1H, ArH), 7.48 (d, 1H, J = 16.4 Hz
trans-CH=CH), 8.11–8.17 (m, 1H, ArH); 13C NMR
(75 MHz, CDCl3 ? DMSO-d6): d 56.1 (OCH3), 60.9
(OCH3), 104.6, 108.9, 114.7, 115.0, 118.6, 118.9, 119.5
(Ar–C), 130.1 (HC=CH), 132.6 (HC=CH), 132.7 (ArC–
Cl), 139.3 (C–OCH3), 153.4 (C–OCH3), 161.6 (C=N),
164.6(C=N), 165.5(ArC–F) ppm; IR (KBr) (mmax/cm-1):
m = 3421, 3067, 2924, 1733, 1637, 1585, 1503, 1464,
1416, 1333, 1244, 1200, 1126 cm-1; MS (ESI) m/z 391;
HR-MS (ESI) m/z for C19H17N2O4FCl calculated m/z:
391.0860, found m/z: 391.0849.
(E)-2-(pyridin-3-yl)-5-(3,4,5-trimethoxystyryl)-1,3,4-
oxadiazole (4o)
Yellow-colored crystals; (yield 426 mg, 59.6 %): Rf = 0.5
1
(50 % ethyl acetate/hexane); mp: 136–139 °C; H NMR
(300 MHz, CDCl3); d 3.89 (s, 3H, –OCH3), 3.93 (s, 6H,
–OCH3), 6.79 (s, 2H, ArH), 7.02 (d, 1H, J = 15.4 Hz,
trans-CH=CH–), 7.39–7.42 (m, 1H, J = 3.6 Hz, ArH),
7.51 (d, 1H, J = 15.4 Hz, trans-CH=CH–), 8.38 (d, 1H,
J = 7.2 Hz, ArH), 8.72 (d, 1H, J = 4.5 Hz, ArH) 9.34 (s,
2H, ArH); 13C NMR (75 MHz, CDCl3): d 56.1 (OCH3),
60.1 (OCH3), 104.7, 108.4 (Ar–C), 124.2 (HC=CH), 129.4
(Ar–C–N), 133.4 (HC=CH), 138.1(C–OCH3), 147.6 (Ar–
C–N), 151.4 (C–OCH3), 161.5 (C=N), 164.9 (C=N) ppm;
IR (KBr) (mmax/cm-1): m = 3418, 2923, 2849, 1711, 1621,
123

Med Chem Res (2014) 23:2080–2092
2085
1584, 1508, 1465, 1420, 1340, 1317, 1247, 1191,
1120 cm-1; MS (ESI) m/z: 339 [M?], HR-MS (ESI) m/z
for C18H17N3O4 calculated m/z: 339.1208, found m/z:
339.1218.
trans-CH=CH), 8.17 (t, 1H, J = 8.8 Hz, ArH), 8.29 (d, 1H,
J = 7.7 Hz, ArH), 8.36 (d, 2H, J = 9.0 Hz, ArH), 8.44 (t,
1H, J = 9.0 Hz, ArH); 13C NMR (75 MHz, CDCl3 ?
DMSO-d6): d 101.2 (O–CH2–O), 111.6, 114.9, 118.9,
123.8 (Ar–C), 124.2 (HC=CH), 127.7, 128.0, 132.1 (Ar–
C), 133.6 (HC=CH), 146.6 (Ar–C–O), 147.8 (Ar–C–O),
148.9 (Ar–C–NO2), 161.8 (C=N), 163.5 (C=N) ppm; IR
(KBr) (mmax/cm-1): m = 3024, 2926, 1752, 1695, 1630,
1544, 1502, 1492, 1482, 1292, 1266, 1202, 1154 cm-1; MS
(ESI) m/z: 337 [M?], HR-MS (ESI) m/z for C17H12N3O5
calculated m/z: 339.0716, found m/z: 339.0720.
(E)-2-(2-benzo[d][1,3]dioxol-5-yl)vinyl)-5-(3-nitrophenyl)-
1,3,4-oxadiazole (5a)
Yellow-colored crystals; (yield 406 mg, 46.3 %): Rf = 0.4
1
(40 % ethyl acetate/hexane); mp: 152–155 °C; H NMR
(300 MHz, CDCl3 ? DMSO-d6); d 6.02 (s, 2H, OCH2O),
6.79–6.96 (m, 2H, ArH, J = 17.1 Hz, trans-CH=CH–),
7.01–7.17 (m, 2H, ArH), 7.58–7.65 (m, 1H, J = 16.2 Hz,
trans-CH=CH–), 7.69–7.85 (m, 1H, ArH), 8.36–8.58 (m,
2H, J = ArH), 8.90 (d, 1H, J = 8.7 Hz ArH); 13C NMR
(75 MHz, CDCl3): d 101.6 (O–CH2–O), 110.2, 113.7,
117.3, 121.1 (Ar–C), 125.2 (HC=CH), 127.1, 130.1, 132.6
(Ar–C), 134.1 (HC=CH), 138.2 (Ar–C), 141.4 (Ar–C–
NO2), 149.0 (Ar–C–O), 149.6 (Ar–C–O), 161.0 (C=N),
163.8 (C=N) ppm; IR (KBr) (mmax/cm-1): m = 3376, 2924,
2853, 1741, 1705, 1632, 1554, 1523, 1496, 1450, 1345,
1262, 1174, 1103 cm-1; MS (ESI) m/z: 337 [M?], HR-MS
(ESI) m/z for C17H12N3O5 calculated m/z: 339.0716, found
m/z: 339.0720.
(E)-2-(2-benzo[d][1,3]dioxol-5-yl)vinyl)-5-(3,4,5-
trimethoxyphenyl)-1,3,4-oxadiazole (5d)
Light yellow-colored solid; (yield 615 mg, 61.9 %):
Rf = 0.4 (40 % ethyl acetate/hexane); mp: 149–152 °C; 1H
NMR (300 MHz, CDCl3); d 3.89 (s, 3H, OCH2O), 3.96 (s,
6H, OCH3), 6.02 (s, 2H, OCH2O), 6.83 (d, 1H, J = 7.9 Hz,
ArH), 6.87 (d, 1H, J = 15.8 Hz, trans-CH=CH), 7.03 (d,
1H, J = 7.9 Hz, ArH), 7.07–7.14 (m, 1H, ArH), 7.30 (d,
2H, J = 9.8 Hz, ArH), 7.50 (d, 1H, J = 17.8 Hz, trans-
CH=CH); 13C NMR (75 MHz, CDCl3): d 56.1 (OCH3),
60.2 (OCH3), 101.5 (O–CH2–O), 103.9, 104.2, 106.0,
107.8, 108.4, 118.5 (Ar–C), 124.3(HC=CH), 129.1 (Ar–C),
138.8 (HC=CH), 148.8 (Ar–C–O), 148.0 (Ar–C–O), 153.4
(C–OCH3), 162.9 (C=N), 164.1 (C=N) ppm; IR (KBr)
(mmax/cm-1): m = 3423, 3050, 2928, 2834, 1638, 1583,
1453, 1420, 1247, 1132, 972 cm-1; MS (ESI) m/z: 383
[M?], HR-MS (ESI) m/z for C20H19N2O6 calculated m/z:
383.1206, found m/z: 383.1209.
(E)-2-(2-benzo[d][1,3]dioxol-5-yl)vinyl)-5-(2-chlorophenyl)-
1,3,4-oxadiazole (5b)
Yellow-colored crystals; (yield 537 mg, 63.3 %): Rf = 0.5
1
(40 % ethyl acetate/hexane); mp: 144–146 °C; H NMR
(300 MHz, CDCl3); d 6.02 (s, 2H, OCH2O), 6.82 (d, 1H,
J = 8.3 Hz, ArH), 6.93 (d, 1H, J = 15.4 Hz, trans-
CH=CH–), 7.03 (d, 1H, J = 6.0 Hz, ArH), 7.08 (s, 1H,
ArH), 7.42 (d, 1H, J = 15.8 Hz, trans-CH=CH–), 7.39-
7.98 (m, 3H, ArH), 8.08 (d, 1H, J = 7.5 Hz, ArH); 13C
NMR (75 MHz, CDCl3): d 101.3 (O–CH2–O), 109.6,
111.4, 121.2 (Ar–C), 124.1 (HC=CH), 126.6, 127.5, 129.7
(Ar–C), 132.5 (Ar–C–Cl), 131.1 (Ar–C), 134.5 (HC=CH),
139.2, 140.3 (Ar–C), 149.7 (Ar–C–O), 148.4 (Ar–C–O),
162.1 (C=N), 164.9 (C=N), ppm; IR (KBr) (mmax/cm-1):
m = 3445, 3070, 2918, 1634, 1598, 1522, 1495, 1446,
1353, 1256, 1101 cm-1; MS (ESI) m/z: 327 [M?], HR-MS
(ESI) m/z for C18H17N3O4 calculated m/z: 327.0536, found
m/z: 327.0544.
(E)-2-(2-(benzo[d][1,3]dioxol-5-yl)vinyl)-5-(3,4-
dimethoxyphenyl)-1,3,4-oxadiazole (5e)
Light yellow-colored solid; (yield 655 mg, 71.5 %):
Rf = 0.5 (40 % ethyl acetate/hexane); mp: 143–145 °C; 1H
NMR (300 MHz, CDCl3 ? DMSO-d6); d 3.95 (s, 3H,
OCH3), 3.98 (s, 3H, OCH3), 6.01 (s, 2H, OCH2O), 6.82 (d,
1H, J = 8.5 Hz, ArH), 6.89 (d, 1H, J = 17.0 Hz, trans-
CH=CH), 6.95 (d, 1H, J = 8.5 Hz, ArH), 7.03 (d, 1H,
J = 8.5 Hz, ArH), 7.07 (s, 1H, ArH), 7.50 (d, 1H,
J = 17.0 Hz, trans-CH=CH), 7.61–7.67 (m, 2H,
J = 8.5 Hz, ArH); 13C NMR (75 MHz, CDCl3 ? DMSO-
d6): d 55.3(OCH3), 60.91 (OCH3), 104.4 (O–CH2–O),
109.5, 114.4, 116.2 (Ar–C), 128.6 (HC=CH), 130.3
(HC=CH), 138.1(C–OCH3), 139.6 (Ar–C–O), 150.1 (Ar–
C–O), 153.4 (C–OCH3), 162.2 (C=N), 163.7 (C=N) ppm;
IR (KBr) (mmax/cm-1): m = 3418, 2922, 2852, 1736, 1638,
1601, 1507, 1449, 1326, 1255, 1183, 1142, 1108 ppm; MS
(ESI) m/z: 353 [M?], HR-MS (ESI) m/z for C19H16N2O5
calculated m/z: 353.1176, found m/z: 353.1178.
(E)-2-(2-benzo[d][1,3]dioxol-5-yl)vinyl)-5-(4-nitrophenyl)-
1,3,4-oxadiazole (5c)
Yellow-colored solid; (yield 400 mg, 45.6 %): Rf = 0.4
1
(40 % ethyl acetate/hexane); mp: 152–154 °C; H NMR
(300 MHz, CDCl3 ? DMSO-d6); d 6.04 (s, 2H, OCH2O),
6.77–6.93 (m, 1H, J = 16.4 Hz, trans-CH=CH), 7.02–7.11
(m, 1H, ArH), 7.25 (s, 1H, ArH), 7.55 (d, 1H, J = 16.2 Hz,
123

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Med Chem Res (2014) 23:2080–2092
(E)-2-(2-benzo[d][1,3]dioxol-5-yl)vinyl)-5-(2,4-
(HC=CH), 128.5 (Ar–C), 134.5 (HC=CH), 146.6 (Ar–C–
N), 148.1 (Ar–C–O), 148.6 (Ar–C–O), 162.2 (C=N), 164.5
(C=N) ppm; IR (KBr) (mmax/cm-1); m = 3418, 3028, 2921,
2853, 1709, 1609, 1500, 1443, 1365, 1311, 1260, 1211,
1155, 1100, 1040 cm-1; MS (ESI) m/z: 373 [M?], HR-MS
(ESI) m/z for C17H10N3O3Br calculated m/z: 373.9910,
found m/z: 373.9920.
dichlorophenyl)-1,3,4-oxadiazole (5h)
Yellow-colored solid; (yield 494 mg, 52.48 %): Rf = 0.5
1
(40 % ethyl acetate/hexane); mp: 162–164 °C; H NMR
(400 MHz, CDCl3); d 6.09 (s, 2H, OCH2O), 6.90 (d, 1H,
J = 7.6 Hz, ArH), 6.93–6.98 (m, 1H, J = 16.1 Hz, trans-
CH=CH), 7.09(d, 1H, J = 7.6 Hz, ArH), 7.11 (s, 1H, ArH),
7.41–7.50 (m, 1H, J = 7.6 Hz, ArH), 7.56–7.66 (m, 2H,
J = 16.2 Hz, trans-CH=CH), 8.10 (d, 1H, J = 8.5 Hz
ArH); 13C NMR (75 MHz, CDCl3): d 101.4 (O–CH2–O),
110.8, 113.6, 118.3 (Ar–C), 125.7 (HC=CH), 126.9, 129.0,
131.1 (Ar–C), 132.6 (Ar–C–Cl), 134.9 (HC=CH), 139.6
(Ar–C–Cl), 148.0 (Ar–C–O), 148.0 (Ar–C–O), 162.4(C=N),
164.4 (C=N) ppm; IR (KBr) (mmax/cm-1): m = 3780, 3693,
3409, 3075, 2920, 2852, 1732, 1635, 1595, 1523, 1493, 1450,
1408, 1356, 1261, 1103 cm-1; MS (ESI) m/z: 361 [M?], HR-
MS (ESI) m/z for C17H11N3O3Cl2 calculated m/z: 361.0146,
found m/z: 361.0156.
(E)-2-(2-benzo[d][1,3]dioxol-5-yl)vinyl)-5-phenyl-1,3,4-
oxadiazole (5k)
Yellow-colored solid; (yield 244 mg, 32.1 %): Rf = 0.4
1
(40 % ethyl acetate/hexane); mp: 150–151 °C; H NMR
(200 MHz, CDCl3); d 6.02 (s, 2H, OCH2O), 6.81 (d, 1H,
J = 8.3 Hz, ArH), 6.88 (d, 1H, J = 15.8 Hz, trans-
CH=CH), 7.02 (d, 1H, J = 1.5 Hz, ArH), 7.07 (s, 1H,
ArH), 7.47–7.55 (m, 4H, ArH, J = 15.8 Hz, trans-
CH=CH), 8.06–8.12 (m, 2H, ArH); 13C NMR (75 MHz,
CDCl3): d 101.3 (O–CH2–O), 112.5, 116.2, 119.7 (Ar–C),
124.7 (HC=CH), 127.1, 127.8, 128.6, 130.4, 131.1 (Ar–C),
135.4 (HC=CH), 148.7 (Ar–C–O), 148.2 (Ar–C–O), 162.0
(C=N), 164.5 (C=N) ppm; IR (KBr) (mmax/cm-1);
m = 3423, 3080, 2919, 1733, 1641, 1603, 1493, 1447,
1358, 1260, 1099, 1030 cm-1; MS (ESI) m/z: 293 [M?],
HR-MS (ESI) m/z for C17H13N3O3 calculated m/z:
293.0926, found m/z: 293.0914.
(E)-2-(2-benzo[d][1,3]dioxol-5-yl)vinyl)-5-(3-chloro-4-
fluorophenyl)-1,3,4-oxadiazole (5i)
Light yellow-colored solid; (yield 680 mg, 76.0 %):
Rf = 0.5 (40 % ethyl acetate/hexane); mp: 172–175 °C; 1H
NMR (200 MHz, CDCl3); d 6.02 (s, 2H, OCH2O),
6.77–6.92 (m, 2H, ArH, J = 16.6 Hz, trans-CH=CH),
7.00–7.08 (m, 2H, ArH), 7.23–7.35 (m, 1H, ArH),
7.42–7.64 (m, 1H, J = 15.8 Hz, trans-CH=CH), 7.97–8.04
(m, 1H, ArH), 8.06–8.17 (m, 1H, ArH); 13C NMR
(75 MHz, CDCl3): d 101.4 (O–CH2–O), 110.9, 116.6,
119.8 (Ar–C), 121.2 (Ar–C–Cl), 122.4 (Ar–C), 124.7
(HC=CH), 128.4, 129.4 (Ar–C), 131.6 (HC=CH), 148.2
(Ar–C–O), 149.7 (Ar–C–O), 161.4 (C=N), 162.1 (C=N),
164.8 (Ar–C–F) ppm; IR (KBr) (mmax/cm-1); m = 3418,
2922, 2853, 1714, 1636, 1603, 1492, 1447, 1358,
1259 cm-1; MS(ESI) m/z: 345 [M?], HR-MS(ESI) m/z for
C17H11N2O3ClF calculated m/z: 345.0421, found m/z:
345.0424.
(E)-2-(2-(benzo[d][1,3]dioxol-5-yl)vinyl)-5-(2-bromophenyl)-
1,3,4-oxadiazole (5l)
Light yellow-colored solid; (yield 459 mg, 47.7 %):
Rf = 0.5 (40 % ethyl acetate/hexane); mp: 139–142 °C; 1H
NMR (300 MHz, CDCl3); d 6.02 (s, 2H, OCH2O), 6.80 (d,
1H, J = 7.9 Hz, ArH), 6.89 (d, 1H, J = 16.4 Hz, trans-
CH=CH), 7.05 (d, 1H, J = 8.1 Hz, ArH), 7.08 (s, 1H,
ArH), 7.34–7.41 (m, 4H, J = 7.7 Hz, ArH), 7.42–7.54 (m,
2H, ArH, J = 16.4 Hz, trans-CH=CH), 7.74 (d, 1H,
J = 7.9 Hz, ArH), 8.03–8.12 (m, 1H, ArH); 13C NMR
(75 MHz, CDCl3): d 101.5 (O–CH2–O), 108.6, 105.9,
107.7, 121.4 (Ar–C), 123.7 (HC=CH), 127.5 (Ar–C–Br),
126.8, 129.0, 132.3, 131.55, 134.5 (HC=CH), 138.5, 139.1,
149.3 (Ar–C–O), 148.4 (Ar–C–O), 162.6 (C=N), 164.8
(C=N) ppm; IR (KBr) (mmax/cm-1); m = 3430, 2911, 1640,
1602, 1523, 1495, 1445, 1357, 1260, 1290, 1198, 1104,
1038 cm-1; MS (ESI) m/z: 371 [M?], HR-MS (ESI) m/z
for C17H12N2O3Br calculated m/z: 371.0031, found m/z:
371.0040.
(E)-2-(2-benzo[d][1,3]dioxol-5-yl)vinyl)-5-(5-bromopyridin-
3-yl)-1,3,4-oxadiazole (5j)
Yellow-colored solid; (yield 298 mg, 30.0 %): Rf = 0.4
1
(40 % ethyl acetate/hexane); mp: 140–142 °C; H NMR
(300 MHz, CDCl3 ? DMSO-d6); d 6.03 (s, 2H, OCH2O),
6.80 (d, 1H, J = 8.3 Hz, ArH), 6.94 (d, 1H, J = 15.8 Hz,
trans-CH=CH), 7.01–7.05 (m, 1H, J = 6.7 Hz, ArH), 7.08
(s, 1H, ArH), 7.25 (s, 2H, ArH), 7.50 (d, 1H, J = 15.8 Hz,
trans-CH=CH), 8.46–8.49 (m, 1H, ArH), 8.75–8.81 (m,
1H, ArH), 9.18–9.22 (m, 1H, ArH); 13C NMR (75 MHz,
CDCl3 ? DMSO-d63): d 101.2 (O–CH2–O), 111.5, 112.3,
114.6, 118.7, 121.6 (Ar–C), 122.4(Ar–C–Br), 126.1
(E)-2-(2-benzo[d][1,3]dioxol-5-yl)vinyl)-5-(2-chloro-4-
fluorophenyl)-1,3,4-oxadiazole (5m)
Light yellow-colored solid; (yield 396 mg, 57.0 %):
Rf = 0.5 (40 % ethyl acetate/hexane); mp: 165–167 °C; 1H
123

Med Chem Res (2014) 23:2080–2092
2087
(E)-2-(2-benzo[d][1,3]dioxol-5-yl)vinyl)-5-(pyridin-3yl)-
NMR (300 MHz, CDCl3 ? DMSO-d6); d 6.05 (s, 2H,
OCH2O), 6.84 (d, 1H, J = 8.5 Hz, ArH), 6.91–6.97 (m,
1H, J = 17.0 Hz trans-CH=CH), 7.06 (d, 1H, J = 6.8 Hz,
ArH), 7.12 (s, 1H, ArH), 7.16–7.26 (m, 1H, ArH),
7.33–7.37 (m, 1H, ArH), 7.56 (d, 1H, J = 17.0 Hz, trans-
CH=CH); 13C NMR (75 MHz, CDCl3 ? DMSO-d6): d
101.4 (O–CH2–O), 110.9, 116.6, 119.8, 121.2, 122.4 (Ar–
C), 124.1 (HC=CH), 128.2, 129.4 (Ar–C–Cl), 131.6
(HC=CH), 148.2(Ar–C–O), 149.7 (Ar–C–O), 161.4 (C=N),
162.1 (C=N), 164.8 (Ar–C–F) ppm; IR (KBr) (mmax/cm-1);
m = 3417, 2917, 1734, 1638, 1606, 1495, 1456, 1413,
1361, 1301, 1260, 1201, 1097 cm-1; MS (ESI) m/z: 345
[M?], HR-MS (ESI) m/z for C17H11N2O3ClF calculated
m/z: 345.0421, found m/z: 345.0424.
1,3,4-oxadiazole (5p)
Yellow-colored crystals; (yield 358 mg, 46.8 %): Rf = 0.5
1
(40 % ethyl acetate/hexane); mp: 126–128 °C; H NMR
(200 MHz, CDCl3); d 6.02 (s, 2H, OCH2O), 6.82 (d, 1H,
J = 8.1 Hz, ArH), 6.94 (d, 1H, J = 15.3 Hz, trans-
CH=CH), 7.03 (d, 1H, J = 8.1 Hz, ArH), 7.09 (s, 1H,
ArH), 7.38–7.41 (m, 1H, ArH), 7.50 (d, 1H, J = 15.8 Hz,
trans-CH=CH), 8.36 (d, 2H, J = 8.1 Hz, ArH), 8.72(d, 1H,
J = 4.7 Hz, ArH), 9.32(s, 1H, ArH); 13C NMR (75 MHz,
CDCl3): d 101.2 (O–CH2–O), 110.6, 114.2, 120.0 (Ar–C),
124.3(HC=CH), 125.0, 127.9 (Ar–C), 133.2 (Ar–C–N),
134.9 (HC=CH), 148.2 (Ar–C–O), 149.8 (Ar–C–O), 162.5
(C=N), 164.3 (C=N) ppm; IR (KBr) (mmax/cm-1);
m = 3419, 2921, 2853, 1613, 1596, 1500, 1450, 1417,
1363, 1317, 1265, 1207, 1182, 1105, 1033 cm-1; MS (ESI)
m/z:294 [M?], HR-MS (ESI) m/z for C18H15N2O3 calcu-
lated m/z: 294.0806, found m/z: 294.0820.
(E)-2-(2-benzo[d][1,3]dioxol-5-yl)vinyl)-5-(2-
chloropyridin-3yl)-1,3,4-oxadiazole (5n)
Yellow-colored solid; (yield 470 mg, 55.0 %): Rf = 0.5
1
(40 % ethyl acetate/hexane); mp: 137–139 °C; H NMR
(E)-2-(2-benzo[d][1,3]dioxol-5-yl)vinyl)-5-(4-
(400 MHz, CDCl3); d 6.05 (s, 2H, OCH2O), 6.80 (d, 1H,
J = 8.3 Hz, ArH), 6.91–6.97 (m, 1H, J = 16.2 Hz, trans-
CH=CH), 7.03 (d, 1H, J = 6.8 Hz, ArH), 7.08 (s, 1H,
ArH), 7.16 (s, 2H, ArH), 7.50 (d, 1H, J = 16.2 Hz, trans-
CH=CH); 13C NMR (75 MHz, CDCl3): d 101.2 (O–CH2–
O), 111.5, 112.3, 117.8, 118.0, 121.6 (Ar–C), 123.4
(HC=CH), 126.1, 128.5 (Ar–C), 134.5 (HC=CH), 146.6
(Ar–C–N), 148.1 (Ar–C–O), 148.5 (Ar–C–O), 162.2
(C=N), 164.5 (Ar–C–Cl) ppm; IR (KBr) (mmax/cm-1);
m = 3419, 3081, 2918, 1699, 1606, 1496, 1450, 1384,
1347, 1258, 1172, 1125, 1039 cm-1; MS (ESI) m/z: 329
[M?], HR-MS (ESI) m/z for C16H11N3O3Cl calculated m/z:
329.0406, found m/z: 329.0416.
methoxyphenyl)-1,3,4-oxadiazole (5q)
Yellow-colored crystals; (yield 341 mg, 40.7 %): Rf = 0.5
1
(40 % ethyl acetate/hexane); mp: 145–147 °C; H NMR
(300 MHz, CDCl3); d 3.89 (s, 3H, OCH3), 6.03 (s, 2H,
OCH2O), 7.02–7.09 (m, 4H, ArH), 7.50 (d, 1H,
J = 15.8 Hz, trans-CH=CH), 7.94 (d, 1H, J = 9.0 Hz,
ArH), 8.02–8.08 (m, 3H, ArH, J = 15.8 Hz, trans-
CH=CH); 13C NMR (75 MHz, CDCl3): d 56.0, 102.0 (O–
CH2–O), 111.6, 114.8, 115.7, 118.7, 119.0(Ar–C), 123.6
(HC=CH), 129.0, 129.7, 128.3 (Ar–C), 133.4 (HC=CH),
148.6 (Ar–C–O), 148.0 (Ar–C–O), 159.8 (Ar–C–OCH3),
162.3 (C=N), 164.6 (C=N) ppm; IR (KBr) (mmax/cm-1);
m = 3422, 2925, 2856, 1735, 1622, 1450, 1257, 1170,
1031 cm-1; MS (ESI) m/z: 283 [M?], HR-MS (ESI) m/z
for C19H13N2O4 calculated m/z: 283.1109, found m/z:
283.1107.
(E)-2-(2-benzo[d][1,3]dioxol-5-yl)vinyl)-5-p-tolyl-1,3,4-
oxadiazole (5o)
Light yellow-colored solid; (yield 504 mg, 63.3 %):
Rf = 0.4 (40 % ethyl acetate/hexane); mp: 158–160 °C; 1H
NMR (200 MHz, CDCl3); d 2.44 (s, 3H, –CH3), 6.02 (s,
2H, OCH2O), 6.82 (d, 1H, J = 8.3 Hz, ArH), 6.87(d, 1H,
J = 15.8 Hz, trans-CH=CH), 7.02 (d, 1H, J = 7.5 Hz,
ArH), 7.06 (s, 1H, ArH), 7.28 (d, 2H, J = 7.5 Hz, ArH),
7.50 (d, 1H, J = 16.2 Hz, trans-CH=CH), 7.96(d, 2H,
J = 8.3 Hz, ArH); 13C NMR (75 MHz, CDCl3): d 26.3
(–CH3), 101.3 (O–CH2–O), 110.5, 114.3, 119.7, 122.2 (Ar–
C), 125.0 (HC=CH), 126.9, 127.4, 128.5, 129.7, 130.8 (Ar–
C), 134.5 (HC=CH), 139.6 (Ar–C), 147.9 (Ar–C–O), 148.4
(Ar–C–O), 162.1 (C=N), 164.5 (C=N) ppm; IR (KBr)
(mmax/cm-1); m = 3782, 3692, 3631, 3428, 2919, 1731,
1631, 1604, 1492, 1524, 1444, 1355, 1312, 1254 cm-1; MS
(ESI) m/z: 307 [M?], HR-MS (ESI) m/z for C18H15N2O3
calculated m/z: 307.1082, found m/z: 307.1095.
In vitro acetylcholinesterase (AChE) assay
AChE inhibitory assay was performed in 96-well microtiter
plates based on the modified method of Ellman et al.
(1961). The enzyme hydrolyzed the substrate acetylthi-
ocholine resulting in the product thiocholine which reacts
with Ellman’s reagent (5,50-dithio-bis-2-nitrobenzoic acid,
DTNB) in situ and gives the yellow-colored chromophore
of 5-thio-2-nitrobenzoic acid (TNB) which can be detected
at 405 nm. The absorption intensity of TNB adduct
(405 nm) is proportional to the formation of thiocholine;
therefore, the AChE activity. In each well of the 96-well
microtiter plate, 5 ll of compound and 10 ll of
0.01 U ml-1 of AChE (Electrophorus electricus AChE
123

2088
Med Chem Res (2014) 23:2080–2092
Type VI-S, EC 3.1.1.7, Sigma) were incubated at 4 °C for
20 min before the addition of 10 ll of 1.5 mM ATCI in
phosphate buffer (pH 7.5), 60 ll of 3 mM DTNB in
phosphate buffer (pH 7.5), and 60 ll of 0.1 M phosphate
buffer (pH 7.5) and absorbance was measured at 405 nm
every 30 s for 4 min 9 8 times on a TRIAD multimode
reader (Dynex Technologies, Inc., Chantilly, VA, USA).
The rate of reactions was calculated using the Manager
software of the multimode reader. Percentage of inhibition
was calculated by comparing the rates for each sample with
respect to the blank (10 % DMSO in buffer). Galantha-
mine hydrobromide (0.1 lM ml-1) as well as donepezil
(0.1 lM ml-1), both in DMSO solvent were used as
positive controls. Each assay was performed in triplicate
and the AChE inhibitory values are the average of three
independent experiments.
active site residue Trp84 was defined as the center of grid,
and the grid was made up of the grid points 70(X), 80(Y),
˚
and 126(Z) with grid spacing of 0.375 A. The number of
generations, energy evaluations, and individuals in the
population are set to 27000, 5 9 106, and 150, respec-
tively. The 50°/step was used for quaternion and torsion,
˚
while 2 A/step was used for the translation during the
docking run. The Lamarckian genetic algorithm was
adopted for sampling ligand conformations. The default
parameters of free energy scoring function were used for
the docking studies (Srivastava et al., 2011).
Results and discussion
The synthesis of (E)-2-aryl-5-styryl-1,3,4-oxadiazole deriv-
atives 4(a–o) and 5(a–q) described in the study are outlined
in Scheme 1 and the structural data are presented in Table 1.
Different aryl esters 7(a–q) were synthesized by esterifica-
tion of substituted aryl carboxylic acids 6(a–q) in the pre-
sence of H2SO4 (catalyst) in ethanol. The esters were
washed with saturated NaHCO3 solution to afford pure
carboxylic acid esters. In the next step, these synthesized
esters were converted to their corresponding hydrazides 8(a–
q) on refluxing with hydrazine hydrate in ethanol. These
hydrazides were cyclized with 3,4,5-trimethoxycinnamic
acid or 3,4-(methylenedioxy)cinnamic acid in the presence
of phosphorus oxychloride on refluxing for 5–6 h to afford
the desired (E)-2-aryl-5-styryl-1,3,4-oxadiazole derivatives
4(a–o) and 5(a–q), respectively, in good yields. The purity
of all the synthesized compounds was examined by TLC and
AChE inhibitor galanthamine (a reversible cholinester-
ase inhibitor) was used in the concentration range of
0.1–100 lM to inhibit AChE of electric eel. The stock
solutions of the (E)-2-aryl-5-styryl-1,3,4-oxadiazole deriv-
atives were prepared based on the molecular weight of the
individual compounds being dissolved in DMSO and to get
the concentration of the original stock solution equivalent
to 1000 lM in DMSO. This stock solution was further
diluted to get the compound dilutions from 0.1, 1.0, 10, 50,
and 100 lM per 5 ll of DMSO. Inhibition by (E)-2-aryl-5-
styryl-1,3,4-oxadiazole derivatives was studied in the pre-
sence of different concentrations of compounds and the
percentage inhibition of enzyme activity was calculated.
The inhibition of AChE by 4(a–o) and (5a–q) derivatives
was analyzed in terms of IC50 values in lM obtained in
comparison to that of galanthamine.
1
their corresponding spectral data were recorded for H and
13C NMR, FT-IR, and HR-MS which confirmed the pro-
Molecular docking studies
posed structures.
The effect on AChE inhibition of these compounds with
various substituents in the aryl ring is shown in Table 1.
Among the 30 synthesized compounds, four compounds
such as 4a, 4g, 5c, and 5m showed promising inhibitory
activity with the IC50 values 24.89, 13.72, 37.65, and
19.63 lM, respectively. The compounds 5c, 5d, 5e, 5l, 5g,
5b, 5a, 5h, 5k, 5j, 5p, 5n, and 4h exhibited moderate
inhibitory activity, while the remaining synthesized com-
pounds showed less to moderate inhibitory activity. The
inhibition of enzyme activity increased proportionately
with an increase in concentration for the two most prom-
ising compounds of each group (4a, 4g and 5c, 5m). The
presence of five-membered heterocyclic moiety (4g) at
position C2 of oxadiazole ring showed more inhibition than
the phenyl group (4a). The compound having 2-chloro-4-
fluorophenyl at position C2 and 3,4-(methylenedioxy)styryl
group at position C5 of oxadiazole (5m) showed significant
inhibition when compared to other compounds in the same
series. The compounds 5m and 5c were more active than
Molecular docking studies were performed using GOLD
(version 3.2) program protocol on the 1,3,4-oxadiazole
derivatives with well-known complex acetylcholinesterase
complexed with donepezil ligand which is marketed as
Aricept (PDBID: 1EVE) which is downloaded from the
RCSB protein data bank (Kryger et al., 1999; Badrinarayan
et al., 2011; Badrinarayan and Sastry, 2011). The Accelrys
Discovery studio protein preparation wizard was used to
prepare the protein with default settings. The ligands were
subjected to energy minimization at AM1 level of theory.
The default parameters in GOLD 3.2, such as number of
islands 5, population size 100, number of operations
100,000, niche size 2, selection pressure 1, the van der
Waals and hydrogen bonding set to 4.0 and 2.5, respec-
tively, were used to perform GOLD docking calculations
(Ravindra et al., 2008; Srivastava et al., 2011). The binding
site in AutoDock is defined by the grid of interaction
points. The atom number 1280, the hydrogen atom of the
123

Med Chem Res (2014) 23:2080–2092
2089
N
N
R1
H3CO
H3CO
O
OCH3
(iii)
4(a-o)
O
O
O
(ii)
(i)
NH2
R
OH
R
O
R
N
H
6(a-q)
(iv)
7(a-q)
8(a-q)
8(a-q)
N
N
R2
O
O
6(a-q)
7(a-q)
a
R=Ph
O
b R=(4-CH3)Ph
5(a-q)
5(a-q)
R2=(3-NO2)Ph
b R2=(2-Cl)Ph
R2=(4-NO2)Ph
R2=3,4,5(OCH3)3Ph
c
R=2,4-(Cl)2Ph
4(a-o)
R1=Ph
b R1=(4-CH3)Ph
d
e
f
R=(2-Cl)Py
R=(2-Br)Ph
R=2-BenFur
a
a
c
c
R1=2,4-(Cl)2Ph
g
R=2-Fur
d
e
d
e
f
R1=(2-Cl)Py
R1=(2-Br)Ph
R1=2-BenFur
h
i
j
R=(4-NO3)Ph
R2=3,4(OCH3)2Ph
h R2=2,4-(Cl)2Ph
i R2=(3-Cl,4-F)Ph
R=3,4,5(OCH3)3Ph
R=(3-NO2)Ph
R=(2-Cl)Ph
g
R1=2-Fur
k
j
k
h
i
j
R1=(4-NO2)Ph
R1=3,4,5(OCH3)3Ph
R1=(3-NO2)Ph
R1=(2-Cl)Ph
l R1=(2-Cl,4-F)Ph
R1=(5-Br)Py
R2=(5-Br)Py
R =Ph
2
l R=(2-Cl,4-F)Ph
m
R=(5-Br)Py
l R2=(2-Br)Ph
m R2=(3-Cl,4-F)Ph
n R2=(2-Cl)Py
o R2=(4-CH3)Ph
R2=Py
p R2=(4-OCH3)Ph
n
o
q
R=(4-OCH3)Ph
k
R=Py
R=3,4(OCH3)2Ph
R=(3-Cl,4-F)Ph
p
m
n
o
q
R1=(4-OCH3)Ph
R1=Py
Scheme 1 Synthesis of (E)-2-aryl-5-styryl-1,3,4-oxadiazole 4(a–
o) and 5(a–q): reagents and conditions: (i) H2SO4 (catalyst)/EtOH,
3–4 h, reflux, (80–90 %); (ii) NH2–NH2ꢀH2O/EtOH, 3–4 h, reflux,
(72–79 %); (iii) POCl3, 5–6 h, 110 °C, (51–70 %); 3,4,5-trimethoxy-
cinnamic acid or 3,4-(methylenedioxy)cinnamic acid. Note: Ph
phenyl, Py pyridyl, Fur furyl, BenFur benzofuryl
compound 4a which is due to the presence of electron-
withdrawing groups like (NO2) and (Cl and F) in 5c and
5m, respectively. The compounds with the presence of
high electronegative groups like chlorine and fluorine at
positions C2 and C4 in the phenyl ring (5m) were more
active as compared to positions C3 and C4 in the phenyl
ring (5i). Overall, the synthesized compounds showed good
to moderate inhibitory activity with IC50 values ranging
from 13 to 65 lM. The compounds in the series 5(a–q) that
contained the 3,4-(methylenedioxy) group at position C5
showed better activity than the compounds in the series
4(a–q) that contained 3,4,5-trimethoxystyryl group (except
compounds 4a and 4g). The two most promising com-
pounds of each group (4a, 4g and 5c, 5m) were further
subjected to molecular docking studies to investigate their
inhibition pattern.
derivatives and AChE enzyme using GOLD (version 3.2)
docking software. The docking studies have been per-
formed on four promising molecules 4a, 4g, 5c, and 5m
with well-known acetylcholinesterase with donepezil
which is marketed as Aricept (PDBID: 1EVE). The protein
crystal structure has been retrieved from RCSB protein
data bank. The AChE protein structure is available from
two different sources of organisms, namely Electrophorus
electricus and Torpedo californica, in the protein data
bank. However, there is no ligand–enzyme complex
reported for Electrophorus electricus AChE (Ee AChE).
Hence, the Torpedo californica AChE (Tc AChE) ligand–
enzyme complex 1EVE has been used for the molecular
docking studies. The characteristic difference between
these two enzymes is the replacement of Phe330 in Tc
AChE with Tyr337 in Ee AChE. The active site radius was
˚
set to 10 A from the atom number 1280, the hydrogen atom
The molecular docking studies have been carried out to
evaluate the binding affinity between 1,3,4-oxadiazole
of the active site residue Trp84, which forms hydrophobic
123

2090
Med Chem Res (2014) 23:2080–2092
Table 1 Structures of compounds 4(a–o) and 5(a–q) and their in vitro AChE inhibitory activities
N
N
N
N
H
H
3CO
R1
O
O
O
R2
O
3CO
H
OC
3
4(a-o)
5(a-q)
Compound
R1
IC50 value (lM, mean SE)
Compound
R2
IC50 value (lM, mean SE)
4a
4b
4c
4d
4e
4f
Ph
24.89 0.03
60.21 0.03
62.22 0.01
61.21 0.04
64.92 0.06
60.43 0.02
13.72 0.01
49.01 0.07
61.50 0.03
65.79 0.03
58.07 0.02
60.23 0.03
62.75 0.02
61.21 0.02
65.01 0.03
4.420 0.06
5a
5b
5c
5d
5e
5h
5i
(3-NO2)Ph
(2-Cl)Ph
49.36 0.01
47.42 0.03
37.62 0.02
48.56 0.05
40.52 0.03
50.28 0.03
49.64 0.03
52.53 0.08
50.10 0.03
40.18 0.03
19.63 0.01
54.33 0.06
45.31 0.01
48.52 0.04
42.76 0.02
(4-CH3)Ph
2,4-(Cl)2Ph
(2-Cl)Py
(2-Br)Ph
2-BenFur
2-Fur
(4-NO2)Ph
3,4,5(OCH3)2Ph
3,4(OCH3)3Ph
2,4-(Cl)2Ph
(3-Cl,4-F)Ph
(5-Br)Py
4g
4h
4i
(4-NO2)Ph
5j
3,4,5(OCH3)3Ph
(3-NO2)Ph
(2-Cl)Ph
5k
5l
Ph
4j
(2-Br)Ph
4k
4l
5m
5n
5o
5p
5q
(2-Cl,4-F)Ph
(2-Cl)Py
(2-Cl,4-F)Ph
(5-Br)Py
4m
4n
4o
(4-CH3)Ph
Py
(4-OCH3)Ph
Py
(4-OCH3)Ph
Galanthamine (control)
Ph phenyl, Py pyridyl, Fur furyl, BenFur benzofuryl
p–p interactions with donepezil. The default parameters
were used for docking in the GOLD software. The cross-
validation of the GOLD docking results has been carried
out using another docking protocol AutoDock. Results of
both the docking methods followed same trends (Table 2).
Thus, we have used GOLD results for the discussion in this
manuscript. From the GOLD software results, it is obvious
that these ligands showed very close docking scores when
compared with donepezil ligand (58.16). The GOLD
docking results (Table 3) depicted 4g as the best active
compound among the four ligands, which showed excellent
biological activity with IC50 value of 13 lM among all
compounds. The interactions of ligands in the binding site
have been depicted in Fig. 2. In active site the best ranking
compound 4g (GOLD score 55.09) showed hydrophobic
CH–p and p–p interactions with TRP84 and HIS440 resi-
dues, respectively. The diazole ring showed a strong cat-
ion–p type interaction with TYR334 residue (Fig. 2),
which is absent in the remaining ligands. The hydrophobic
p–p, CH–p, hydrogen bonding, and electrostatic interac-
tions in active site made 4g ligand as the most active
compound. The ligand 5m (GOLD score 54.08) depicted
Table 2 The docking results of (E)-2-aryl-5-styryl-1,3,5-oxadiazole
derivatives using acetylcholinesterase enzyme (PDBID: 1EVE) with
GOLD and AutoDock softwares
Ligand name
GOLD
AutoDock
4g
55.09
51.19
54.08
51.99
58.16
596.08
452.90
551.37
470.31
642.75
4a
5m
5c
Donepezil
Table 3 The GOLD docking results of (E)-2-aryl-5-styryl-1,3,5-
oxadiazole derivatives using acetylcholinesterase enzyme (PDBID:
1EVE)
Ligand name Fitness Fitness rank Hb_ext vdw_ext Int
4g
55.09
51.19
54.08
51.99
58.16
1
4
2
3
1
6.00
6.00
1.97
2.00
0.08
31.70
34.49
42.18
45.15
50.03
-8.36
-6.14
-3.3
4a
5m
5c
-5.41
-10.72
Donepezil
123

Med Chem Res (2014) 23:2080–2092
2091
Fig. 2 The docked poses of the compounds in the active site of acetylcholinesterase enzyme (PDBID: 1EVE) and score in the parenthesis using
GOLD protocol. Various non-covalent interactions and hydrogen bonding interactions showed in dotted lines
strong hydrophobic interactions with PHE331, HIS440,
and TRP84 residues in the active site. Beside these inter-
actions, the 5m ligand showed CH–p and CH–O interac-
tions with TYR334 and PHE290 residues, respectively
(Fig. 2). The electrostatic (cation–p) type of interaction
between the diazole and TYR334 residue (ligand 4g) was
absent in case of ligand 5m. The compounds 4a and 5c also
showed similar type of interactions; however, these ligands
had less interactions when compared to the above two
compounds (Fig. 2). The lack of hydrophobic and hydro-
gen bonding interactions made these ligands lesser active
than other ligands. All the above-mentioned interactions
conventional hydrogen bonds at the bottom of the gorge
were observed. These types of interactions were already
known for other crystallized inhibitors of AChE (e.g., do-
nepezil and galanthamine) and, therefore, the docking
results were likely to be meaningful for the tested ligands.
Moreover, all compounds were potentially able to bind
inside the active side.
Conclusion
In our study, we have described for the first time the syn-
thesis, biological evaluation, and molecular modeling of
(E)-2-aryl-5-styryl-1,3,4-oxadiazole derivatives as AChE
inhibitors. All the compounds showed good to moderate
AChE inhibitory activity with IC50 values in the range of
13–65 lM. Based on molecular modeling results it was
observed that the compounds 4a, 4g, 5c, and 5m bind to the
AChE enzyme in a similar manner as donepezil. The strong
hydrophobic interactions between the ligand and aromatic
˚
are in the range \4.0 A distance between ligand and
binding site residues. Similar to the donepezil, the 1,3,4-
oxadiazole derivatives showed a strong interaction with
one face of the benzyl ring and displayed a classic parallel
p–p stacking with the six-membered ring of the TRP84
indole. In conclusion, the docking results included hydro-
phobic and electrostatic interactions with binding site
(TRP84, HIS440, and TYR334) amino acid residues and
123

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pounds similar to donepezil ligand interactions. This
investigation provided an insight for the future direction in
the development of conjugates such as potential AChE
inhibitors.
Jha KK, Samad A, Kumar Y, Shaharyar M, Khosla RL, Jain J, Kumar V,
Singh P (2010) Design, synthesis and biological evaluation of 1,3,4-
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Acknowledgments The authors A. B. S. and G. N. R are thankful to
CSIR, New Delhi, for the award of research fellowships.
¨
Johansson M, Hellstrom-Lindahl E, Nordberg A (1996) Steady-state
Conflict of interest None.
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