Synthesis and pharmacological evaluation of 1,3,4-oxadiazole bearing bis(heterocycle) derivatives as anti-inflammatory and analgesic agents

Article abstract of DOI:10.1016/j.ejmech.2009.04.006

A series of novel ether-linked bis(heterocycle)s have been synthesized via [3 + 2]-cycloaddition reaction of nitrile oxide with allyl alcohol followed by intramolecular 1,3-diploar cycloaddition reaction of nitrile imine with carbonyl group. All the newly

Full text of DOI:10.1016/j.ejmech.2009.04.006

European Journal of Medicinal Chemistry 44 (2009) 3898–3902
Contents lists available at ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Original article
Synthesis and pharmacological evaluation of 1,3,4-oxadiazole bearing
bis(heterocycle) derivatives as anti-inflammatory and analgesic agents
,
a
b
b
B. Jayashankar a , K.M. Lokanath Rai , N. Baskaran , H.S. Sathish
*
a Department of Studies in Chemistry, University of Mysore, Manasagangotri, Mysore 570006, India
b Department of Biochemistry, Justice K.S. Hegde Medical Academy, Mangalore 574160, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of novel ether-linked bis(heterocycle)s have been synthesized via [3 þ 2]-cycloaddition reaction
of nitrile oxide with allyl alcohol followed by intramolecular 1,3-diploar cycloaddition reaction of nitrile
imine with carbonyl group. All the newly synthesized compounds were screened for their anti-inflam-
matory and analgesic activities. Among the list of compounds (7a–k) studied, 7d, 7g, 7j, and 7k exhibited
excellent activity comparable to ibuprofen and aspirin at the similar dosages.
Received 14 August 2008
Received in revised form
30 March 2009
Accepted 2 April 2009
Available online 14 April 2009
Ó 2009 Elsevier Masson SAS. All rights reserved.
Keywords:
Bis(heterocycle)
Anti-inflammatory
Analgesic
1,3,4-Oxadiazole
Chloramine-T
1. Introduction
synthetic interest, since the product isoxazolines obtained are the
versatile intermediates for the synthesis of bifuctional compounds
The wide occurrence of the heterocycles in bioactive natural
products and pharmaceuticals has made them as important
synthetic targets. Isoxazoline and 1,3,4-oxadiazoles represent
a class of heterocyclic compounds of great importance in biological
chemistry. For instance, compounds possessing 1,3,4-oxadiazole
moiety show anticancer [1] and tyrosinase inhibitory activity [2].
Substituted 1,3,4-oxadiazoles have revealed antibacterial [3], anti-
mycobacterial [4], antifungal [5], anti-inflammatory [6], analgesic
[7], anticonvulsant [8], antihypoglycemic [9] and insecticidal
properties [10]. Isoxazoline possesses biological activities like [11]
(insecticidal, antibacterial, antibiotic, antitumour, antifungal, etc).
In fact, Valdecoxib an isoxazoline derivative, is now widely used in
the market as anti-inflammatory drug [12]. Literature studies
reveal that 2,5-disubstituted-1,3,4-oxadiazoles have been synthe-
sized either by microwave irradiation of the hydrazide and
carboxylic acid mixture [13] or by thermal/acid catalyzed cycliza-
tion of 1,2-diacylhydrazines [14]. 2,5-Disubstituted-1,3,4-oxadia-
zoles have also been synthesized by oxidative cyclization of
semicarbazone/hydrazone using chloramine-T as an oxidant [15].
1,3-Dipolar cycloaddition reactions are useful tools for con-
structing isoxazoline [16] and nitrile oxides serve as excellent 1,3-
dipoles. Cycloaddition of nitrile oxide to olefinic compounds is of
[17]. Although various bis(heterocycle)s have been synthesized our
attention was directed to the recent work of Padmavathi et al., who
synthesized isoxazoline bearing bis(heterocycle) by the reaction of
bischalcones [18] and bissulfones [19] as dipolarophiles with nitrile
oxide as 1,3-dipole.
In our laboratory Rai and Hassner extensively used chloramine-
T for the generation of nitrile oxide and nitrile imine from aldoxime
and aldehyde hydrazone respectively [20]. For instance, we have
recently reported the synthesis of ether-linked bis(isoxazoline) via
1,3-dipolar cycloaddition reactions of nitrile oxides with allyl
alcohol and allyl ethers [21]. With this background, it is considered
worthwhile to prepare bis(heterocycle) bearing both isoxazoline
and 1,3,4-oxadiazole moieties starting from simple aromatic
aldoxime and screen them for anti-inflammatory and analgesic
activities. The present communication deals with the synthesis and
pharmacological evaluation of hitherto unknown ether-linked
bis(heterocycle) bearing 1,3,4-oxadiazole and an isoxazoline unit.
2. Results and discussion
2.1. Chemistry
The desired starting materials 1a–e were prepared by the
condensation of hydroxyl amine with corresponding aromatic
* Corresponding author. Tel.: þ91 821 2419667.
E-mail address: bjshankar@yahoo.com (B. Jayashankar).
0223-5234/$ – see front matter Ó 2009 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2009.04.006

B. Jayashankar et al. / European Journal of Medicinal Chemistry 44 (2009) 3898–3902
3899
aldehydes by employing well known method available in the
literature [21]. Aromatic aldoximes 1a–e were subjected to oxida-
tive dehydrogenation using chloramine-T afforded expected nitrile
oxides, which were intercept in situ by ethanolic solution of allyl
alcohol. The reaction was carried under reflux conditions to obtain
the pale yellow oils of (4,5-dihydro-3-arylisoxazol-5-yl)methanol
2a–e.
indomethacin caused gastric ulcers in 7 of the 8 treated rats (7/8) at
10 mg/kg os dose [22].
3. Experimental section
3.1. Chemistry
The (4,5-dihydro-3-arylisoxazol-5-yl)methanol 2a–e were
further treated with ethyl chloroacetate in the presence of phase
transfer catalyst such as tetrabutylammonium bromide and
potassium hydroxide to get the etherialester of 4,5-dihydro-3-aryl-
isoxazole 3a–e as yellow oils. The esters 3a–e were refluxed with
hydrazine hydrate in ethanol to obtain the hydrazides 4a–e, which
were further condensed with aromatic aldehydes 5a–g to yield the
respective hydrazones 6a–k. The oxidation of hydrazones 6a–k
with chloramine-T to generate nitrile imines followed by intra-
molecular cyclization with adjacent carbonyl group yielded the pale
yellow solid, identified by NMR spectroscopy as 2-(((4,5-dihydro-3-
aryl-isoxazol-5-yl)methoxy)methyl)-5-aryl-1,3,4-oxadiazole 7a–k
(Scheme 1).
Melting points were determined on Thomas Hoover melting
point apparatus and are uncorrected. 1H NMR spectra were recor-
ded on a Bruker AM 300 MHz spectrometer using CDCl3 as solvent
and tetramethylsilane as internal standard. 13C NMR spectra were
measured on Jeol 400 (100 MHz) instrument. The chemical shifts
are expressed in
d and following abbreviations were used.
s ¼ singlet, d ¼ doublet, t ¼ triplet and m ¼ multiplet. Infrared (IR)
spectra were recorded on Shimadzu 8300 IR spectrometer.
Elemental analyses were obtained on a Vario-EL instrument. Thin
layer chromatography was carried out with BDH silica gel G on
glass slides.
3.1.1. Procedure for the synthesis of (4,5-dihydro-3-arylisoxazol-5-yl)
methanol 2(a–e) [21]
1H NMR spectra of compound 7a showed multiplet at
d 3.88–
3.98 ppm and doublet of doublet at 4.29 ppm (J ¼ 8.2, 2.2 Hz)
An equimolar mixture of 1(a–e) (7.40 mmol) and chloramine-T
trihydrate (7.41 mmol) in ethanol (20 mL) was stirred for 5 min at
room temperature. To this mixture, allyl alcohol (7.41 mmol) in
ethanol (5 mL) was added and warmed on a water bath for 3 h.
After completion of the reaction (monitored by TLC), it was cooled
to room temperature. Sodium chloride formed in the reaction
mixture was filtered off and washed with ethanol (1 ꢁ15 mL). The
combined filtrate and washings were evaporated in vacuum. The
residual part was extracted into ether (25 mL), washed successively
with water (2 ꢁ15 mL), 5% NaOH (2 ꢁ 15 mL) and saturated brine
solution (1 ꢁ10 mL). The organic layer was dried over anhydrous
sodium sulphate. The solvent was evaporated and the remaining
residue was subjected to the column chromatography using the
chloroform–acetone (9:1) as eluent to get the 2(a–e) as yellow oil.
The same procedure was used for all.
correspond to OCH2 group attached to the isoxazoline and 1,3,4-
oxadiazole respectively. Another multiplet (m) at
to the methine proton, doublet of doublet at
d
5.10 corresponds
d
3.37 ppm (J ¼ 8.0,
2.4 Hz) corresponds to the methylene proton of the isoxazoline ring.
Aromatic protons and other substituents are at the expected region.
Absence of amide NH frequency in the region 3400–3200 cmꢀ1
confirms the formation of the product. The 13C NMR and elemental
analysis data further confirm the structures of 7a–k.
2.2. Pharmacology
All the compounds were tested for anti-inflammatory activity in
carrageenen-induced edema assay in rats at a dosage of 100 mg/kg
po (Table 1). Four compounds (7d, 7g, 7j, and 7k) showed signifi-
cant activity. Among these compounds, the two dichlorophenyl
derivatives, 7g and 7j revealed more than 50% activity. However at
all of the doses they were less active than ibuprofen. Further, all of
these compounds were tested for analgesic activity at 100 mg/kg in
acetic acid-induced assay in mice (Table 2). Five compounds had
significant activity and the compound 7g exhibited the highest
activity in the series. The compounds of statistical significance were
also evaluated for their acute gastrolesivity in rats (at 200 mg/kg os
dose): for all the compounds tested no acute gastrolesivity effect
was detected in each of the eight treated rats (0/8), whereas
3.1.2. Procedure for the synthesis of ethyl 2-((4,5-dihydro-3-
phenylisoxazol-5-yl)methoxy)acetate 3(a–e)
A
mixture of 2(a–e) (5.23 mmol) and ethyl chloroacetate
(5.24 mmol) was stirred overnight in the presence of tetrabuty-
lammonium bromide (0.52 mmol) and powdered KOH (5.34 mmol)
in THF (20 mL). After completion of the reaction, the mixture was
diluted with (25 mL) water and product was extracted with the ethyl
acetate(25 mL). Theextractwaswashedwithwater(10 mL)andthen
dried (Na2SO4). The solvent was evaporated and the remaining pale
ClCH2COOEt
OH
O
NHNH2
O
OEt
NH2NH2.H2O
EtOH
O
(Bu)4 N Br
KOH
O
O
OH
N
N
N
H
C
Chloramine-T
EtOH
O
O
OH
4a-e
R
N
THF
3a-e
R
R
R
R'CHO
2a-e
1a-e
EtOH
O
5a-g
R,R'
a
4-MeC6H4
4-OMeC6H4
3,4,5-(OMe)3C6H2
3-O2NC6H4
H
N
b
c
d
e
f
O
N
O
O
N
N
Chloramine-T
EtOH
O
N
N
O
R'
4-O2NC6H4
4-ClC6H4
6a-k
R
R
7a-k
R'
g
2,4-Cl2C6H3
Scheme 1.

3900
B. Jayashankar et al. / European Journal of Medicinal Chemistry 44 (2009) 3898–3902
Table 1
After completion of the reaction, the mass was cooled and the solid
formed was filtered to give acetohydrazone 6(a–k), which was used
directly for next reaction.
Anti-inflammatory activity and acute gastrolesivity of compounds 7a–k.
Compound
Edema volumeb (mL)
ꢃ SD
Edema inhibitionc
(%)
Acute gastrolesivity
in ratg
7a
7b
7c
7d
7e
7f
7g
7h
0.27 ꢃ 0.04d
0.31 ꢃ 0.07e
0.32 ꢃ 0.08d
0.25 þ 0.05d
0.36 ꢃ 0.07f
0.32 ꢃ 0.05e
0.22 ꢃ 0.04e
0.27 ꢃ 0.08d
0.30 ꢃ 0.05d
0.25 ꢃ 0.06e
0.27 ꢃ 0.08e
0.17 ꢃ 0.06f
42.5
40.3
32.0
46.8a
37.9
–
–
–
0/8
–
3.1.5. Synthesis of 2-(((4,5-dihydro-3-arylisoxazol-5-yl)
methoxy)methyl)-5-aryl-1,3,4-oxadiazoles: 7(a–k)
3.1.5.1. Synthesis of 2-(((4,5-dihydro-3-p-tolylisoxazol-5-yl)methox-
y)methyl)-5-(3,4,5-trimethoxy phenyl)-1,3,4-oxadiazole: typical
procedure (7a). A mixture of 6a (1.0 g, 2.26 mmol) and chloramine-
T trihydrate (0.64 g, 2.27 mmol) in ethanol (20 mL) was refluxed
under stirring for 3 h. It was then concentrated under reduced
pressure and the residue was extracted with diethyl ether (25 mL).
The extract was washed with water (15 mL), 1 N NaOH (2 ꢁ10 mL)
and then dried (Na2SO4). The solvent was evaporated and the
remaining residue was subjected to the column chromatography
using chloroform–acetone (9:1) as eluent. Compound 7a obtained
as yellow solid (0.82 g, 72%), m.p. 168–170 ꢂC. The same procedure
was used for all. 1H NMR CDCl3: 2.30 (s, 3H, CH3), 3.37 (dd, 2H,
J ¼ 8 Hz, 2.4 Hz CH2), 3.83 (s, 6H, OCH3), 3.86 (s, 3H, OCH3), 3.88–
3.98 (m, 2H, OCH2), 4.29 (dd, 2H, J ¼ 8.2 Hz, 2.2 Hz, OCH2), 5.10 (m,
1H, CH), 6.80 (s, 2H, ArH), 7.11–7.50 (m, 4H, ArH). 13C NMR CDCl3:
24.9 (C), 37.5 (C), 56.7 (2C), 57.1 (C), 71.1 (C), 75.6 (C), 78.2 (C), 104.7
(2C), 120.6 (C), 129.1 (2C), 129.3 (2C), 131.1 (C), 139.2 (C), 140.2 (C),
38.4
53.1a
42.5
41.2
–
0/8
0/8
–
0/8
0/8
–
7i
7j
51.9a
48.0a
70.7a
7k
Ibuprofen
a
Statistically significant.
At 100 mg/kg po, edema volume measured 3 h after carrageenen injection, and
b
expressed as mean ꢃ standard deviations (n ¼ 4).
c
Percentage of edema inhibition calculated by comparing with the vehicle-
treated control animals.
d
Control edema volume ¼ 0.47 ꢃ 0.04.
e
Control edema volume ¼ 0.52 ꢃ 0.03.
f
Control edema volume ¼ 0.58 ꢃ 0.05.
g
Number of rats showing gastric lesions. For indomethacin gastrolesivity see
Ref. [22].
151.2 (2C), 156 (C), 160 (C), 164.5 (C). IR (KBr pellets cmꢀ1
) n 3104,
2944, 1688, 1672, 1668, 1390, 1288, 1265. Anal. Calcd for
C23H25N3O6; C, 62.86; H, 5.73; N, 9.56; Found C, 62.95; H, 5.77; N,
9.53%.
yellow oily substance 3(a–e) was purified by column chromatog-
raphy (chloroform–acetone 9:1) and used for next step.
3.1.3. Procedure for the synthesis of 2-((4,5-dihydro-3-
phenylisoxazol-5-yl)methoxy)acetohydrazide 4(a–e)
3.1.5.2. (((4,5-Dihydro-3-p-tolylisoxazol-5-yl)methoxy)methyl)-5-
(4-chlorophenyl)-1,3,4-oxadiazole (7b). Obtained from 6b (1.0 g,
2.6 mmol) and chloramine-T trihydrate (0.73 g, 2.6 mmol) as
yellow solid (0.69 g, 69%), m.p. 157–159 ꢂC. 1H NMR CDCl3: 2.33 (s,
3H, CH3), 3.37 (dd, 2H, J ¼ 8.0 Hz, 2.4 Hz, CH2), 3.86–3.96 (m, 2H,
OCH2), 4.32 (dd, 2H, J ¼ 8.2 Hz, 2.4 Hz, OCH2), 5.13 (m, 1H, CH), 7.13–
7.52 (m, 8H, ArH), 13C NMR CDCl3: 24.2 (C), 37.4 (C), 70.4 (C), 75.4
(C), 78.1 (C), 124.6 (C), 128.9 (2C), 129.1 (2C), 129.3 (2C), 129.5 (2C),
131.1 (C), 134.5 (C), 140.9 (C), 156.6 (C), 161.1 (C), 164.5 (C). IR (KBr
The esters 3(a–e) (3.61 mmol) were added drop wise to the 98%
hydrazine hydrate (3 mL) with stirring and refluxed for 15 min.
After that ethanol (15 mL) was added and refluxed for another 2 h.
After completion of the reaction (TLC chloroform–acetone 9:1), the
reaction mixture was cooled and extracted into ethyl acetate
(25 mL), washed with water (2 ꢁ 15 mL) and dried (Na2SO4).
Solvent was evaporated to yield 4(a–e).
pellets cmꢀ1
) n 3071, 2924, 1681, 1666, 1648, 1382, 1283, 1260. Anal.
3.1.4. Procedure for the synthesis 2-((4,5-dihydro-3-phenylisoxazol-
5-yl)methoxy)-N0-benzylideneacetohydrazides 6(a–k)
An equimolar mixture of 4(a–e) (3.80 mmol) and 5(a–g)
(3.82 mmol) was refluxed in ethanol for 3 h. The progress of the
reaction was monitored by the TLC (chloroform–acetone 9.5:0.5).
Calcd for C20H18ClN3O3; C, 62.58; H, 4.73; N, 10.95; Found C, 62.63;
H, 4.77; N, 10.92%.
3.1.5.3. 2-(((4,5-Dihydro-3-p-tolylisoxazol-5-yl)methoxy)methyl)-5-
(4-nitrophenyl)-1,3,4-oxadiazole (7c). Obtained from 6c (1.0 g,
2.52 mmol) and chloramine-T trihydrate (0.70 g, 2.52 mmol) as
yellow solid (0.76 g, 76%), m.p. 163–165 ꢂC. 1H NMR CDCl3: 2.36 (s,
3H, CH3), 3.36 (dd, 2H, J ¼ 8.0 Hz, 2.4 Hz, CH2), 3.83–3.93 (m, 2H,
OCH2), 4.30 (dd, 2H, J ¼ 8.2 Hz, 2.3 Hz, OCH2), 5.05 (m, 1H, CH), 7.13
(d, 2H, ArH), 7.51 (d, 2H, ArH), 7.71 (d, 2H, ArH), 8.23 (d, 2H, ArH).
13C NMR CDCl3: 24.7 (C), 37.6 (C), 70.8 (C), 75.2 (C), 78.1 (C), 121.6
(2C), 128.5 (2C), 129.2 (2C), 129.4 (2C), 131.1 (C), 132.2 (C), 140.9 (C),
Table 2
Analgesic activity of compounds 7a–k.
Compound
No. of writhes in
% Reduction
15 min ꢃ SDa
from controlb
7a
7b
7c
7d
7e
7f
7g
7h
7i
7j
7k
Aspirin
42 ꢃ 11c
43 ꢃ 08d
38 ꢃ 07d
31 þ 12e
44 ꢃ 06c
38 ꢃ 08e
30 ꢃ 14e
36 ꢃ 12d
40 ꢃ 07c
35 ꢃ 10c
40 ꢃ 06d
29 ꢃ 06d
41.6
36.8
44.1
50.8f
38.8
39.7
52.3f
47.0f
44.4
51.4f
48.5f
57.3f
148.5 (C), 156.2 (C), 160.8 (C), 164.5 (C). IR (KBr pellets cmꢀ1
) n 3092,
2949,1688,1670,1661,1383,1278,1261. Anal. Calcd for C20H18N4O5;
C, 60.91; H, 4.60; N, 14.21; Found C, 60.95; H, 4.67; N, 14.19%.
3.1.5.4. 2-(((4,5-Dihydro-3-p-tolylisoxazol-5-yl)methoxy)methyl)-5-
(2,4-dichlorophenyl)-1,3,4-oxadiazole (7d). Obtained from 6d (1.0 g,
2.38 mmol) and chloramine-T trihydrate (0.68 g, 2.42 mmol) as
yellow solid (0.66 g, 67%), m.p. 151–153 ꢂC. 1H NMR CDCl3: 2.34 (s,
3H, CH3), 3.39 (dd, 2H, J ¼ 8.3 Hz, 2.2 Hz, CH2), 3.86–3.96 (m, 2H,
OCH2), 4.30 (dd, 2H, J ¼ 8.3 Hz, 2.2 Hz, OCH2), 5.12 (m, 1H, CH), 7.12
(d, 2H, ArH), 7.51 (d, 2H, ArH), 7.28 (d, 2H, ArH), 7.63 (s, 1H, ArH). 13C
NMR CDCl3: 24.5 (C), 37.3 (C), 70.7 (C), 75.3 (C), 78.0 (C), 127.6 (C),
129.0 (2C), 129.3 (2C), 130.3 (C), 130.9 (C), 131.0 (C), 133.9 (C), 135.2
(C), 135.9 (C), 140.6 (C), 156.5 (C), 161.1 (C), 164.5 (C). IR (KBr pellets
a
At 100 mg/kg po, number of writhes in 15 min beginning 5 min after acetic acid
injection, expressed mean ꢃ standard deviation (n ¼ 6).
b
Percentage of writhing inhibition calculated by comparing with vehicle-treated
control animals.
c
Control number of writhes ¼ 72 ꢃ 11.
d
Control number of writhes ¼ 68 ꢃ 7.
e
Control number of writhes ¼ 63 ꢃ 7.
f
cmꢀ1
) n 3101, 2962, 1683, 1677, 1670, 1392, 1282, 1262. Anal. Calcd
Statistically significant.

B. Jayashankar et al. / European Journal of Medicinal Chemistry 44 (2009) 3898–3902
3901
for C20H17C12N3O3; C, 57.43; H, 4.10; N, 10.05; Found C, 57.45; H,
4.17; N, 10.02%.
(C), 124.7 (C), 128.8 (2C), 129.8 (2C), 129.9 (C), 134.4 (C), 134.9 (C),
135.2 (C), 148.2 (C), 156.8 (C), 160.1 (C), 164.4 (C). IR (KBr pellets
cmꢀ1
) n 3109, 2941, 1689, 1676, 1670, 1393, 1282, 1265. Anal. Calcd
3.1.5.5. 2-(((4,5-Dihydro-3-(4-methoxyphenyl)isoxazol-5-yl)methox-
y)methyl)-5-p-tolyl-1,3,4-oxadiazole (7e). Obtained from 6e (1.0 g,
2.67 mmol) and chloramine-T trihydrate (0.75 g, 2.67 mmol) as
yellow oil (0.72 g, 73%).1H NMR CDCl3: 2.33 (s, 3H, CH3), 3.28 (dd, 2H,
J ¼ 8.2 Hz, 2.2 Hz, CH2), 3.76 (s, 3H, OCH3), 3.79–3.89 (m, 2H, OCH2),
4.21 (dd, 2H, J ¼ 8.2 Hz, 2.2 Hz, OCH2), 4.98 (m, 1H, CH), 6.90 (d, 2H,
ArH), 7.11 (d, 2H, ArH), 7.22 (s, 2H, ArH), 7.53 (d, 2H, ArH). 13C NMR
CDCl3: 24.6 (C), 37.2 (C), 56.1 (C), 70.8 (C), 75.4 (C), 78.0 (C),114.7 (2C),
123.4 (C), 126.4 (C), 127.1 (2C), 129.3 (2C), 130.5 (2C), 138.5 (C), 156.2
for C19H15ClN4O5; C, 55.02; H, 3.64; N, 13.51; Found C, 55.05; H,
3.62; N, 13.53%.
3.1.5.10. 2-(((4,5-Dihydro-3-(4-nitrophenyl)isoxazol-5-yl)methoxy)
methyl)-5-(2,4-dichlorophenyl)-1,3,4-oxadiazole (7j). Obtained from
6j (1.0 g, 2.21 mmol) and chloramine-T trihydrate (0.63 g,
2.24 mmol) as yellow solid (0.67 g, 68%), m.p. 177–179 ꢂC. 1H NMR
CDCl3: 3.33 (dd, 2H, J ¼ 7.8 Hz, 2.0 Hz, CH2), 3.86–3.97 (m, 2H,
OCH2), 4.30 (dd, 2H, J ¼ 8.4 Hz, 2.2 Hz, OCH2), 5.13 (m, 1H, CH), 7.31
(d, 2H, ArH), 7.40 (s, 1H, ArH), 7.61 (d, 2H, ArH), 8.11 (d, 2H, ArH), 13C
NMR CDCl3: 37.9 (C), 71.5 (C), 75.6 (C), 78.2 (C), 121.7 (2C), 127.2 (C),
130.0 (2C), 130.4 (C), 130.9 (C), 133.8 (C), 135.2 (C), 135.8 (C), 140.2
(C), 158.9 (C), 163.1 (C), 164.6 (C). IR (KBr pellets cmꢀ1
) n 3036, 2932,
1678, 1662, 1648, 1387, 1283, 1260. Anal. Calcd for C21H21N3O4; C,
66.48; H, 5.58; N, 11.08; Found C, 66.45; H, 5.57; N, 11.05%.
(C), 150.8 (C), 156.8 (C), 164.7 (C). IR (KBr pellets cmꢀ1
) n 3112, 2950,
3.1.5.6. 2-(((4,5-Dihydro-3-(4-methoxyphenyl)isoxazol-5-yl)methox-
y)methyl)-5-(4-nitrophenyl)-1,3,4-oxadiazole (7f). Obtained from 6f
(1.0 g, 2.43 mmol) and chloramine-T trihydrate (0.7 g, 2.49 mmol)
1693, 1677, 1665, 1393,1290,1269. Anal. Calcd for C19H14C12N4O5; C,
50.80; H, 3.14; N, 12.47; Found C, 50.82; H, 3.12; N, 12.49%.
as yellow oil (0.77 g, 78%). 1H NMR CDCl3:
d
3.27 (dd, 2H, J ¼ 8.2 Hz,
3.1.5.11. 2-(((4,5-Dihydro-3-(4-nitrophenyl)isoxazol-5-yl)methoxy)
methyl)-5-(3,4,5-trimethoxyphenyl)-1,3,4-oxadiazole (7k). Obtained
from 6k (1.0 g, 2.11 mmol) and chloramine-T trihydrate (0.6 g,
2.13 mmol) as yellow solid (0.81 g, 81%), m.p. 186–188 ꢂC. 1H NMR
CDCl3: 3.31 (dd, 2H, J ¼ 7.8 Hz, 2.4 Hz, CH2), 3.81 (s, 6H, OCH3), 3.85
(s, 3H, OCH3), 3.76–3.86 (m, 2H, OCH2), 4.20–4.41 (dd, 2H,
J ¼ 8.2 Hz, 2.3 Hz, OCH2), 5.14 (m, 1H, CH), 6.56 (s, 2H, ArH), 7.60 (d,
2H, ArH), 8.10 (d, 2H, ArH), 13C NMR CDCl3: 37.8 (C), 56.3 (2C), 56.6
(C), 71.6 (C), 75.7 (C), 78.3 (C), 104.8 (2C), 120.4 (C), 121.6 (2C), 130.2
(2C), 139.7 (C), 140.2 (C), 150.8 (C), 151.5 (2C), 156.7 (C), 161.1 (C),
2.2 Hz, CH2), 3.76 (s, 3H, OCH3), 3.83–3.93 (m, 2H, OCH2), 4.28 (dd,
2H, J ¼ 8.4 Hz, 2.5 Hz, OCH2), 5.07 (m, 1H, CH), 6.88 (d, 2H, ArH),
7.33 (d, 2H, ArH), 7.75 (d, 2H), 8.26 (d, 2H). 13C NMR CDCl3:
d 37.5
(C), 56.2 (C), 70.8 (C), 75.5 (C), 78.3 (C), 114.7 (2C), 121.6 (2C), 126.4
(C), 128.3 (2C), 130.1 (2C), 132.2 (C), 148.2 (C), 156.7 (C), 160.0 (C),
163.1 (C), 164.5 (C). IR (KBr pellets cmꢀ1
) n 3087, 2964, 1694, 1682,
1667, 1391, 1281, 1270. Anal. Calcd for C20H18N4O6; C, 58.53; H, 4.42;
N, 13.65; Found C, 58.55; H 4.47; N, 13.59%.
3.1.5.7. 2-(((4,5-Dihydro-3-(3,4,5-trimethoxyphenyl)isoxazol-5-yl)met-
hoxy)methyl)-5-(2,4-dichlorophenyl)-1,3,4-oxadiazole (7g). Obtained
from 6g (1.0 g, 2.02 mmol) and chloramine-T trihydrate (0.58 g,
2.06 mmol) as yellow solid (0.65 g, 64%), m.p. 168–170 ꢂC. 1H NMR
CDCl3: 3.22 (dd, 2H, J ¼ 8.0 Hz, 2.0 Hz, CH2), 3.88 (s, 6H, OCH3), 3.83
(s, 3H, OCH3), 3.81–3.91 (m, 2H, OCH2), 4.29 (dd, 2H, J ¼ 8.2 Hz,
2.3 Hz, OCH2), 5.01 (m, 1H, CH), 6.8 (s, 2H, ArH), 7.33 (s, 2H, ArH),
7.43 (s,1H, ArH). 13C NMR CDCl3: 37.4 (C), 56.4 (2C), 56.8 (C), 70.8 (C),
75.3 (C), 78.1 (C), 106.7 (2C), 127.6 (C), 128.1 (C), 130.4 (C), 130.9 (C),
133.6 (C), 135.1 (C), 135.8 (C), 141.5 (C), 151.1 (2C), 156.5 (C), 159.8 (C),
164.5 (C). IR (KBr pellets cmꢀ1
) n 3114, 2948, 1691, 1677, 1670, 1389,
1290, 1267. Anal. Calcd for C22H22N4O8; C, 56.17; H, 4.71; N, 11.91;
Found C, 56.18; H, 4.72; N, 11.89%.
3.2. Pharmacology
Albino rats of either sex (150–180 g) and albino mice of either
sex (8–25 g) were used. The compounds were administered po
using a feeding tube as homogenized suspensions in 0.5% sodium
carboxymethyl cellulose; 0.5% sodium carboxymethyl cellulose was
administered as the vehicle control.
164.7 (C). IR (KBr pellets cmꢀ1
) n 3058, 2934, 1678, 1665, 1656, 1380,
1278, 1256. Anal. Calcd for C22H21Cl2N3O6: C, 53.45; H, 4.28; N, 8.50;
Found C, 53.46; H, 4.27; N, 8.53%.
3.1.5.8. 2-(((4,5-Dihydro-3-(3-nitrophenyl)isoxazol-5-yl)methoxy)
methyl)-5-(3,4,5-trimethoxyphenyl)-1,3,4-oxadiazole (7h). Obtained
from 6h (1.0 g, 2.11 mmol) and chloramine-T trihydrate (0.6 g,
2.13 mmol) as yellow solid (0.80 g, 79%), m.p. 177–179 ꢂC. 1H NMR
CDCl3: 3.34 (dd, 2H, J ¼ 8.3 Hz, 2.0 Hz, CH2), 3.86 (s, 6H, OCH3), 3.80
(s, 3H, OCH3), 3.79–3.89 (m, 2H, OCH2), 4.26 (dd, 2H, J ¼ 8.2 Hz,
2.0 Hz, OCH2), 5.14 (m, 1H, CH), 6.48 (s, 2H, ArH), 7.89 (d, 2H, ArH),
8.26 (d, 2H, ArH), 13C NMR CDCl3: 37.7 (C), 56.3 (2C), 56.6 (C), 71.4
(C), 75.5 (C), 78.0 (C), 104.7 (2C), 120.7 (C), 123.3 (C), 124.2 (C), 130.2
(C), 134.9 (C), 135.3 (C), 139.2 (C), 148.2 (C), 151.4 (2C), 156.8 (C),
3.2.1. Carrageenen-induced edema
Groups of four rats were dosed at 100 mg/kg po with the test
compounds, 1 h before 0.05 mL of a 1% suspension of Type IV
Lambda (Sigma) carrageenen was injected into the subplantar
region at the right hind paw; additional groups of four rats were
similarly pretreated with 100 mg/kg ibuprofen (positive control) or
10 mL/kg 0.5% sodium carboxymethyl cellulose (vehicle controls)
[23]. Paw volumes were measured by water displacement in
a plethysmograph immediately after carrageenen injection and
again 3 h later. Edema volumes for test-compound-treated and
positive-control rats were compared statistically with those for the
vehicle-treated control rats; data are reported as percentage edema
inhibition.
160.7 (C), 164.4 (C). IR (KBr pellets cmꢀ1
) n 3104, 2945, 1688, 1675,
1662, 1387, 1281, 1260. Anal. Calcd for C22H22N4O8; C, 56.17; H, 4.71;
N, 11.91; Found C, 56.15; H, 4.74; N, 11.90%.
3.1.5.9. 2-(((4,5-Dihydro-3-(3-nitrophenyl)isoxazol-5-yl)methox-
y)methyl)-5-(4-chlorophenyl)-1,3,4-oxadiazole (7i). Obtained from
6i (1.0 g, 2.40 mmol) and chloramine-T trihydrate (0.68 g,
2.41 mmol) as yellow solid (0.80 g, 79%), m.p. 168–170 ꢂC. 1H NMR
CDCl3: 3.36 (dd, 2H, J ¼ 8.4 Hz, 2.2 Hz, CH2), 3.84–3.96 (m, 2H,
OCH2), 4.27 (dd, 2H, J ¼ 8.0 Hz, 2.2 Hz, OCH2), 5.12 (m, 1H, CH), 7.31
(d, 2H, ArH), 7.42 (d, 2H, ArH), 7.60 (d, 2H, ArH), 8.32 (d, 2H, ArH),
13C NMR CDCl3: 37.7 (C), 71.2 (C), 75.6 (C), 78.0 (C), 123.7 (C), 124.2
3.2.2. Gastrolesivity
The acute gastrolesivity of the test compounds was evaluated by
examining the stomachs excised 5 h after oral administration of the
drugs in rats. The stomachs fixed in 2% formalin, were opened and
examined with a stereomicroscope by an observer unaware of the
treatment the rats received. Acute gastrolesivity was expressed as
the number of animals with gastric damage over the number of
treated animals.

3902
B. Jayashankar et al. / European Journal of Medicinal Chemistry 44 (2009) 3898–3902
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5 min after the acetic acid injection and the total number of writhes
recorded. The mean value of writhes for each group was calculated
and compared statistically with that for the vehicle-treated control
group (n ¼ 6); datawere reported as percent inhibition of the number
of writhes. The test was repeated on additional groups of six mice,
treated with compounds for which the reduction inwrithes had been
calculated to be >10%; these results are shown in Table 2.
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