Molecular properties prediction and synthesis of new oxadiazole derivatives possessing 3-fluoro-4-methoxyphenyl moiety as potent anti-inflammatory and analgesic agents

Article abstract of DOI:10.1007/s00706-015-1528-2

A new series of 1,2,4- and 1,3,4-oxadiazole derivatives possessing 3-fluoro-4-methoxyphenyl moiety were efficiently synthesized and characterized by spectroscopic methods and elemental analysis. All the compounds were evaluated in vivo for their anti-infl

Full text of DOI:10.1007/s00706-015-1528-2

Monatsh Chem
DOI 10.1007/s00706-015-1528-2
ORIGINAL PAPER
Molecular properties prediction and synthesis of new oxadiazole
derivatives possessing 3-fluoro-4-methoxyphenyl moiety as potent
anti-inflammatory and analgesic agents
1
1
2
1
Dinesha
•
Shivapura Viveka
•
Prasanna S. Khandige
•
Gundibasappa K. Nagaraja
Received: 26 March 2015 / Accepted: 29 June 2015
Ó Springer-Verlag Wien 2015
Abstract A new series of 1,2,4- and 1,3,4-oxadiazole
derivatives possessing 3-fluoro-4-methoxyphenyl moiety
were efficiently synthesized and characterized by spectro-
scopic methods and elemental analysis. All the compounds
were evaluated in vivo for their anti-inflammatory and
analgesic properties, and were found to be low lethal as
ascertained by the LD50 test. The present study suggests
that three compounds were found to have good anti-in-
flammatory activity in the carrageenan-induced rat paw
edema test, while a fair number of compounds showed
significant analgesic activity in the tail flick test. In silico
ADME properties of synthesized compounds were also
analysed and showed potential to develop as good oral drug
candidates.
Keywords Synthesis Á Oxadiazoles Á
Anti-inflammatory activity Á Analgesic activity Á
Molecular properties prediction
Introduction
Nonsteroidal anti-inflammatory drugs (NSAIDs) are the
most widely prescribed therapeutics for the treatment of
inflammation and related conditions [1]. The major
mechanism by which the NSAIDs elicit their therapeutic
effects is by blocking the formation of prostanoids, lipidic
mediators derived from fatty acid metabolism, by inhibit-
ing cyclooxygenase (COX) enzymes [2, 3]. But most of the
NSAIDs are generally associated with several side effects,
especially gastric ulceration [4]. Therefore, the challenge
still exists to develop effective NSAIDs with enhanced
safety profile.
Graphical abstract
O
N
N
O
N
N
O
O
Oxadiazoles are making a huge impact on multiple drug
discovery programmes across a variety of disease areas,
including anti-tubercular, antibacterial, antiviral, anti-in-
flammatory, antifungal, and insecticidal activities [5–13].
Moreover, oxadiazoles are very good bioisosteres for car-
boxylic acids, esters, and carboxamides, which contribute
substantially to increasing pharmacological activity by
participating in hydrogen bonding interactions with the
receptors [14, 15]. The fluorinated compounds also possess
promising pharmacological activities, which originate from
their uniquely high thermal stabilities and lipophilicity.
The survey of literature reveals that many fluorinated
analogues are also available as NSAIDs; examples are
diflunisal (Dolobid), flurbiprofen (Froben), deracoxib,
lumiracoxib, and flufenamic acid [16, 17]. Thus, the evo-
lution of alternatives to NSAIDs is being attempted all over
the world.
R1
R2
F
F
Electronic supplementary material The online version of this
article (doi:10.1007/s00706-015-1528-2) contains supplementary
material, which is available to authorized users.
&
Gundibasappa K. Nagaraja
nagarajagk@gmail.com
1
2
Department of Studies in Chemistry, Mangalore University,
Mangalagangotri 574199, Karnataka, India
Department of Pharmacology, NGSM Institute of
Pharmaceutical Sciences, Paneer, Deralakatte, Mangalore
5
74160, Karnataka, India
123

Dinesha et al.
The escalating cost of drug discovery and development is
challenging and the chances of success are incredibly low,
particularly in recent years [18]. Problems with the drug
candidate’s absorption, distribution, metabolism, and excre-
tion (ADME), however, have already been identified as
important reasons for its failure in the late stages of the drug
development process. Therefore, it is important to accurately
predict these qualities earlier in the investigation of the lead
candidates [19, 20]. Computational methods have emerged as
a robust strategy for reducing the number of experimental
studies necessary for compound selection and development
and for improving the success rate. In this context, in silico
approaches are being used today in drug discovery to assess
the ADME properties of compounds in the early stages of
discovery/development [21]. The first assessment of ADME
properties will help pharmaceutical scientists to select the
most effective candidates for development, in addition to
rejecting individuals with a low likelihood of success. These
advantages prompted us to predict the molecular properties
that influence many ADME properties.
of hydrazide (4) with appropriate aromatic acids in phos-
phorous
oxychloride
afforded
2-(3-fluoro-4-
5a–5f.
methoxyphenyl)-5-substituted-1,3,4-oxadiazoles
The purity of synthesized compounds was checked by TLC,
column chromatography, and elemental analysis.
The structures of the synthesized compounds 1a–1f, 3a–
3f, and 5a–5f were established on the basis of their single-
1
crystal X-ray diffraction method and spectral data (IR, H
1
3
NMR, C NMR, and LC–MS). The structure of O-acyla-
tion of amidoxime 1c was confirmed by single-crystal
X-ray diffraction analysis (Fig. 1). The compound was
crystallized in orthorhombic Pna2 space group [24].
1
The IR spectrum of compound 3e showed absorption
-
1
bands at 2985, 1625, 1504, 1288, and 1095 cm for its Ar
C–H, C=N, C=C, C–O, and C–F groups, respectively. The
1
H NMR spectrum of 3e, which showed multiplet in the
region 7.40–8.08 ppm was due to the aromatic protons.
Similarly, the three protons of methoxy group appeared as
a singlet at 3.96 ppm. The structure of 3e was confirmed by
the appearance of peaks at 169.4 and 174.8 ppm due to
1
3
An appreciation of these findings has driven us to syn-
thesize some new series of oxadiazole derivatives, wherein
potent 1,2,4- and 1,3,4-oxadiazole moiety is linked to
oxadiazole C-3 and C-5, respectively, in the C NMR
spectrum. The LC–mass spectra of compound 3e showed a
?
molecular ion peak at m/z = 305 ([M?H] , 96 %) and
?
corresponding isotopic peak at m/z = 307 (([M?H] ? 2) ,
3
-fluoro-4-methoxyphenyl moiety at the C-5 position to see
the additive effect of these rings towards the anti-inflam-
matory and analgesic activities with higher selectivity and
less toxicity.
32 %), which was in agreement with the molecular formula
C H ClFN O . In the IR spectrum, the absence of
1
5
10
2 2
absorption bands, NH–NH2 in the region of
-
448–3437 cm and C=O in the region of 1690 cm ,
1
-1
3
indicated the formation of compound 5f from the corre-
sponding acid hydrazide 4. The absorption bands at 3020,
Results and discussion
Chemistry
-
610, 1506, 1276 and 1018 cm are characteristic of the
1
1
Ar C–H, C=N, C=C, C–O, and C–F groups, respectively.
1
The H NMR spectrum of 5f, which showed multiplet in
Readily available starting materials and simple synthetic
procedures are very attractive and convenient for the syn-
thesis of numerous oxadiazoles. The synthetic route used to
prepare starting materials and the title compounds is out-
lined in Scheme 1. The key intermediates, aryl amidoximes
the region 6.70–7.90 ppm was due to the aromatic protons.
Two singlets, which appeared in the region 3.90 and
2.98 ppm were due to the three protons of the methoxy
1
3
group and six protons of the N,N-dimethyl group. The
C
NMR spectra of 5f revealed two signals at 152.1 and
153.4 ppm corresponding to oxadiazole C-2 and C-5,
respectively. Further confirmation of the structure was
given by LC–mass spectra, which showed a molecular ion
1
a–1f and 3-fluoro-4-methoxybenzohydrazide (4), are
required as starting material for the synthesis of the title
compounds 3a–3f and 5a–5f. The aryl amidoximes 1a–1f
were synthesized through the condensation of the corre-
sponding aryl nitriles with aqueous hydroxylamine
hydrochloride in basic medium by an earlier reported
method [23]. Then, it involves the coupling of aryl ami-
doximes with 3-fluoro-4-methoxybenzoic acid in the
presence of HATU (1-[bis(dimethylamino)methylene]-1H-
?
peak at m/z = 314 ([M?H] , 97 %). In the same way, the
structures of all the final compounds were confirmed by
their characterization data, physical data, and the same is
summarized in the Experimental section.
Anti-inflammatory activity
[
1,2,3]-triazolo[4,5-b]pyridinium-3-oxide hexafluorophos-
phate) and excess of N-methylmorpholine (NMM) [24]
Anti-inflammatory activity of all the synthesized com-
pounds was evaluated by carrageenan-induced rat paw
edema model (Table 1). The results revealed that the
compounds exhibited moderate to excellent anti-inflam-
matory activity ranging from 39 to 73 % inhibition and the
followed by in situ thermal cyclization afforded 3-(3-fluoro-
4
-methoxyphenyl)-5-substituted-1,2,4-oxadiazoles 3a–3f.
-Fluoro-4-methoxybenzohydrazide (4) was synthesized
3
according to an earlier reported method [22]. The treatment
1
23

Molecular properties prediction and synthesis of new oxadiazole derivatives possessing…
Scheme 1
O
O
F
NH2
N
NH
2
O
N
a
N
1
b
O
R -CN
OH
HO
R1
O
R1
F
N
R1
O
O
F
1
a-1f
2
3a-3f
O
F
O
O
N
H
N
c
N
R2
HO
OH
O
H N
F
2
R2
O
O
O
F
2
4
5a-5f
(
a) aq. NH
2
OH.HCl, NaHCO
3
, EtOH, reflux, 6 h; (b) HATU, DMF, NMM, reflux, 3 h; (c) POCl
3
, reflux, 5 h
3a
3
b
3c
5c
3d
5d
3e
5e
3f
Compound
R1
F
Br
Cl
Cl
N
N
Cl
5
a
5b
5f
Compound
R2
O
Cl
OH
OCF3
Cl
N
inhibition values. The compounds 5f, 3c, and 3e also
showed moderate anti-inflammatory activity with 58, 56,
and 51 %, respectively. Compounds 5e (39 %) and 5b
(41 %) had the lowest effect and were poor inhibitors;
presumably as a result of unfavourable electronic character
and polarity. However, halogens can consequently increase
the polarity and can also serve to block metabolism at
particularly reactive sites and reduce metabolism of the
aromatic group, by decreasing its electron density [30].
Fig. 1 Molecular structure of O-acylation of amidoxime 1c with the
atom numbering scheme. Thermal ellipsoids for non-hydrogen atoms
are drawn at the 30 % probability level
Analgesic activity
The results of the analgesic activity indicated that the test
compounds exhibited moderate analgesic activity at 30 min
of reaction time; the activity increased at 60 min, further, it
reached peak level at 90 min, while decline in activity was
observed at 120 min (Table 2). Particularly, samples 3a
(7.54 ± 0.12), 3f (7.10 ± 0.06), and 5a (7.32 ± 0.18)
displayed excellent activity in 90 min duration and their
results were comparable with standard drug pentazocine.
Compounds 5f, 3c, 5e, and 3e showed moderate activity
with rapid onset of action when compared with the standard.
This suggests that electron diminishing and electron
releasing groups are responsible for the activity. Moreover,
compounds which showed best anti-inflammatory activity
also exhibited significant analgesic activity.
standard drug diclofenac Na showed 75 % inhibition at 3 h
post-drug administration. Compounds 3a, 3f, and 5a turned
out to be the most active with significant paw edema
inhibition. Interestingly, most of the new compounds
showed remarkable activity in the first 1 h of administra-
tion ([50 % inhibition), particularly compounds 3a and 3f
exhibited higher inhibition than that of diclofenac Na in the
initial 1 h. Compound 3a demonstrated a high degree of
activity with (73 %) inhibition followed by 3f (71 %) and
5a (69 %). Compounds 3a and 3f with a halogen group at
C-2 and compound 5a having an electron donating group at
C-3 of the phenyl ring were correlated with higher
123

Dinesha et al.
Table 1 Anti-inflammatory activity of oxadiazole derivatives 3a–3f and 5a–5f by the carrageenan-induced rat paw edema assay
a
3
b
Treatments
Mean paw volume/cm – SEM
% Inhibition of edema
1
/h 2/h
3/h
1/h
2/h
3/h
Control
1.13 ± 0.01
1.45 ± 0.001
1.42 ± 0.001
–
–
–
Diclofenac Na
0.42 ± 0.02***
0.40 ± 0.05***
0.51 ± 0.01*
0.46 ± 0.04**
0.52 ± 0.02*
0.48 ± 0.06**
0.38 ± 0.01***
0.43 ± 0.04***
0.57 ± 0.03*
0.54 ± 0.05*
0.49 ± 0.06
0.39 ± 0.001***
0.43 ± 0.003***
0.70 ± 0.004**
0.57 ± 0.005*
0.72 ± 0.006*
0.67 ± 0.005**
0.45 ± 0.006***
0.48 ± 0.005***
0.76 ± 0.003
0.36 ± 0.01***
0.39 ± 0.002***
0.78 ± 0.006
63
65
55
59
54
58
66
62
50
52
57
49
60
73
70
52
61
50
54
69
67
48
53
52
62
63
75
73
45
56
43
51
71
69
41
47
44
39
58
3
3
3
3
3
3
5
5
5
5
5
5
a
a
b
c
d
e
f
0.63 ± 0.001**
0.81 ± 0.003
0.70 ± 0.006**
0.41 ± 0.004**
0.44 ± 0.002***
0.84 ± 0.004
a
b
c
d
e
f
0.68 ± 0.002*
0.70 ± 0.004
0.75 ± 0.002*
0.79 ± 0.003
0.58 ± 0.02*
0.45 ± 0.03***
0.56 ± 0.003
0.87 ± 0.001*
0.60 ± 0.002**
0.54 ± 0.002**
Dose levels: test compounds (50 mg/kg b.w.), diclofenac Na (10 mg/kg b.w.)
b
SEM standard error mean; n = 6, ANOVA followed by Dunnett’s test, * P B 0.05, ** P B 0.01, *** P B 0.001 significant from control
Table 2 Analgesic activity of oxadiazole derivatives 3a–3f and 5a–5f by the tail flick method
a
b
Treatments
Tail flick latency/s (mean ± SEM)
/min 30/min
0
60/min
90/min
120/min
Control
2.50 ± 0.58
2.60 ± 0.50
2.00 ± 0.11
2.50 ± 0.02
2.38 ± 0.08
2.11 ± 0.24
2.42 ± 0.20
2.11 ± 0.01
2.50 ± 0.10
2.24 ± 0.22
2.10 ± 0.02
2.60 ± 0.30
2.35 ± 0.04
2.43 ± 0.07
2.63 ± 0.17
2.58 ± 0.26
2.56 ± 0.30
2.52 ± 0.24
Pentazocine
6.67 ± 0.35***
5.75 ± 0.26***
3.90 ± 0.19
7.35 ± 0.24***
7.00 ± 0.14**
5.31 ± 0.11*
6.24 ± 0.33**
5.22 ± 0.18*
5.92 ± 0.32*
6.53 ± 0.11**
6.77 ± 0.16**
5.50 ± 0.12*
4.88 ± 0.08*
4.30 ± 0.09
7.79 ± 0.18***
7.54 ± 0.12***
4.87 ± 0.08*
6.75 ± 0.05**
5.42 ± 0.30*
6.24 ± 0.11**
7.10 ± 0.06***
7.32 ± 0.18***
5.42 ± 0.33**
5.36 ± 0.22
7.66 ± 0.16***
6.92 ± 0.16**
4.45 ± 0.10
3
3
3
3
3
3
5
5
5
5
5
5
a
a
b
c
d
e
f
6.08 ± 0.35*
4.80 ± 0.12
6.32 ± 0.14**
5.11 ± 0.24*
5.83 ± 0.23*
6.86 ± 0.17**
6.81 ± 0.22**
5.10 ± 0.16
5.50 ± 0.15*
5.45 ± 0.16**
5.83 ± 0.26***
5.31 ± 0.18*
4.04 ± 0.04*
3.60 ± 0.06
a
b
c
d
e
f
4.72 ± 0.02
5.50 ± 0.15*
6.86 ± 0.08*
6.60 ± 0.24**
4.80 ± 0.12
5.42 ± 0.10**
6.00 ± 0.18***
6.43 ± 0.15***
6.86 ± 0.06**
2.30 ± 0.11**
6.40 ± 0.12*
Dose levels: test compounds (50 mg/kg b.w.), pentazocine (10 mg/kg b.w.)
b
SEM standard error mean; n = 6, ANOVA followed by Dunnett’s test, * P B 0.05, ** P B 0.01, *** P B 0.001 significant from control
ADME profiling
prediction method and is presented in Table 3. The number
of rotatable bonds (n-ROTB) and Lipinski’s rule of five
were calculated [32]. The rule states that most molecules
with good membrane permeability have a molecular weight
B500, a log P B 5, hydrogen bond donor sites B5, and
hydrogen bond acceptor sites (N and O atoms) B10. This
approach has been widely used as a filter for substances
that were likely to be further developed in drug design
From the varieties of pharmacological activities of the
oxadiazole scaffold, it is important to explore the drug-like
properties of this series of compounds. The computational
study of synthesized compounds was assessed using
ADME (absorption, distribution, metabolism, and elimi-
nation; http://www.molinspiration.com/cgi-bin/properties)
1
23

Molecular properties prediction and synthesis of new oxadiazole derivatives possessing…
Table 3 Pharmacokinetic parameters important for good oral bioavailability of oxadiazole derivatives 3a–3f and 5a–5f
3
2
˚
Volume/A
˚
TPSA/A
Compound
%ABS
NROTB
HBA
HBD
Log P
MW
Lipinski’s violations
3
3
3
3
3
3
5
5
5
5
5
5
a
b
c
d
e
f
92
88
92
88
92
92
89
85
89
92
92
91
253.41
226.43
260.93
226.43
244.13
244.13
256.14
238.61
270.87
247.39
257.66
276.50
48.16
61.05
48.16
61.05
48.16
48.16
57.39
68.39
57.39
48.16
48.16
51.40
3
3
4
3
3
3
4
3
5
4
3
4
4
5
4
5
4
4
5
5
5
4
4
5
0
0
0
0
0
0
0
1
0
0
0
0
4.75
2.58
4.48
2.80
4.55
4.50
3.91
3.39
4.84
3.47
5.16
3.98
367.14
271.25
318.73
271.25
304.70
304.70
300.29
286.26
354.26
284.29
339.15
313.33
0
0
0
0
0
0
0
0
0
0
1
0
a
b
c
d
e
f
%ABS percentage of absorption, TPSA topological polar surface area, NROTB number of rotatable bonds, MW molecular weight, log P logarithm
of compound partition coefficient between n-octanol and water, HBA number of hydrogen bond donors, HBD number of hydrogen bond
acceptors
programmes. In addition, the topological polar surface area
TPSA) was calculated, since it is a very useful parameter
X-ray diffraction method and elemental analysis. These
oxadiazole hybrids were tested for their in vivo anti-in-
flammatory and analgesic potential. Some of the
compounds, exclusively 3a, 3f, and 5a revealed potent anti-
inflammatory and analgesic activities. The presence of the
electron donor, acceptor or halo-substituted groups in the
phenyl ring at positions C-2 and C-3, in addition, to the
3-fluoro-4-methoxyphenyl ring at position C-5 of the
oxadiazole ring, causes a significant escalation in the
activities. In silico ADME prediction of the synthesized
compounds indicated that they had potential to develop as
good oral drug candidates. These results prompted us to
establish structure–activity relationships in the listing of
synthesized compounds. These results further confirmed
that suitable incorporation of different structural elements
into a new single chemical entity enables achievement of
higher inhibitory potency and selectivity. Besides, the
active compounds in the present study make for interesting
compounds when compared to the current therapeutic
agents.
(
for the prediction of transport properties of drugs in the
intestines and blood–brain barrier crossing [33]. TPSA is a
sum of the surfaces of polar atoms (usually oxygen,
nitrogen, and attached hydrogen) in a molecule. TPSA and
volume are inversely proportional to %ABS. TPSA was
used to calculate the percentage of absorption (%ABS)
according to the equation: %ABS = 109 ± 0.345 9
TPSA. Molecules violating more than one of these rules
may have problems with bioavailability [34, 35].
The synthesized compounds in general possess sufficient
number of rotatable bonds (3-5) and, therefore, exhibit
good conformational flexibility. From all ADME parame-
ters, it can be observed that all the synthesized compounds
exhibited excellent %ABS (85–92 %). The most active
compounds showed 3a (92 %), 3f (92 %), and 5a (89 %)
absorption, respectively. Furthermore, none of the com-
pounds violated Lipinski’s rule of five, except 5e, which
violated only one rule of five as represented by the log
P value. Thus, the results showed the most possible utility
of the series for developing compounds with good drug-
like properties. Theoretically, these compounds should
present good passive oral absorption and differences in
their bioactivity cannot be attributed to this property.
Experimental
All solvents and reagents were purchased from Sigma-
Aldrich Chemicals Pvt. Ltd. (Bangalore, India). Melting
point was taken in an open capillary tube. The purity of the
compound was confirmed by thin-layer chromatography
using Merck silica gel 60 F254-coated aluminium plates. IR
spectrum was recorded on Shimadzu-FTIR Infrared spec-
Conclusion
To summarize, two new sets of oxadiazole hybrids having
1
13
3
-fluoro-4-methoxyphenyl group were successfully syn-
trometer in KBr. H NMR and C NMR spectra were
recorded on 400 MHz and 100 MHz Bruker AMX-400 and
Agilent-NMR spectrometers, with 5-mm PABBO BB-1H
TUBES with TMS as internal standard in DMSO-d6/
thesized. The structures of the new derivatives were
1
confirmed by numerous spectral studies such as IR, H
1
NMR, C NMR, and LC–MS followed by single-crystal
3
123

Dinesha et al.
CDCl . LC–MS was obtained using Agilent 1200 series LC
3
4-[5-(3-Fluoro-4-methoxyphenyl)-1,2,4-oxadiazol-3-
yl]pyridine (3b, C14
White solid; yield 91 %; m.p.: 135–137 °C; H NMR
(400 MHz, DMSO-d ): d = 3.95 (s, 3H, OCH ), 7.42–8.82
m, 7H, Ar–H) ppm; C NMR (100 MHz, CDCl3):
and Micromass zQ spectrometer. Elemental analysis was
carried out using VARIO EL-III (Elementar Analysensys-
teme GmbH).
H10FN O )
3 2
1
6
3
1
3
(
General procedure for the synthesis of aryl
amidoximes 1a–1f
d = 56.3, 111.3, 115.5, 115.7, 116.0, 117.2, 119.6, 121.8,
142.5, 162.7, 164.9, 172.3 ppm; IR (KBr): vꢀ = 2958 (Ar
C–H), 1614 (C=N), 1522 (C=C), 1270 (C–O), 1072 (C–F)
-
1
?
Sodium bicarbonate (5.88 g, 70 mmol) was added in por-
cm ; LC–MS: m/z (%) = 272 ([M ? H] , 68).
-(3-Chlorobenzyl)-5-(3-fluoro-4-methoxyphenyl)-1,2,4-
oxadiazole (3c, C H ClFN O )
tions to a solution of 4.79 g hydroxylamine hydrochloride
3
70 mmol) in 20 cm of water. A solution of aryl nitriles
3
(
3
35 mmol) in 50 cm of ethanol was then added, and the
16 12
2 2
(
1
Pale yellow solid; yield 85 %; m.p.: 140–142 °C; H NMR
400 MHz, DMSO-d ): d = 3.65 (s, 2H, CH ), 3.95 (s, 3H,
mixture stirred under reflux for 6 h. The precipitate formed
was filtered off and purified by crystallization from ethanol.
Melting points of compounds 1b–1f were in agreement
with the literature values [23, 25–28].
(
6
2
1
3
OCH ), 7.22–7.85 (m, 7H, Ar–H) ppm;
3
C NMR
(
100 MHz, DMSO-d ): d = 32.0, 56.3, 119.0, 123.4,
6
127.2, 127.5, 128.6, 131.0, 133.6, 139.5, 139.7, 140.7,
3
-Bromo-2-fluorobenzamidoxime (1a, C H BrFN O)
7
147.6, 149.2, 162.6, 167.8 ppm; IR (KBr): vꢀ = 2941 (Ar
C–H), 1631 (C=N), 1535 (C=C), 1290 (C–O), 1105 (C–F)
6
2
1
Pale brown solid; yield 72 %; m.p.: 145–147 °C; H NMR
-
cm ; LC–MS: m/z (%) = 319 ([M?H] , 95), 321
1
?
(
400 MHz, CDCl ): d = 4.82 (s, 2H, NH ), 7.20–8.05 (m,
3
2
1
H, Ar–H), 10.20 (s, 1H, OH) ppm; C NMR (100 MHz,
3
?
(([M?H] ? 2) , 32).
3
CDCl ): d = 110.5, 122.3, 127.2, 127.4, 136.1, 158.4,
3
3
-[5-(3-Fluoro-4-methoxyphenyl)-1,2,4-oxadiazol-3-
1
65.2 ppm; IR (KBr): vꢀ = 3445, 3358 (NH ), 3190 (OH),
2
yl]pyridine (3d, C H FN O )
14 10
-
061 (Ar C–H), 1665 (C=N), 962 (N–O) cm ; LC–MS:
1
3 2
3
1
White solid; yield 86 %; m.p.: 151–153 °C; H NMR
?
m/z (%) = 233 ([M?H] , 98), 235 (([M?H] ? 2) , 86).
?
(
400 MHz, DMSO-d ): d = 3.96 (s, 3H, OCH ), 7.90–8.92
6
3
1
m, 7H, Ar–H) ppm; C NMR (100 MHz, CDCl3):
3
(
General procedure for the synthesis of 3,5-
disubstituted 1,2,4-oxadiazoles 3a–3f
d = 56.4, 110.7, 114.1, 114.3, 116.2, 119.7, 120.5, 122.6,
42.5, 156.7, 162.7, 169.0 ppm; IR (KBr): vꢀ = 2972 (Ar
C–H), 1610 (C=N), 1515 (C=C), 1282 (C–O), 1065 (C–F)
1
To a solution of 0.51 g 3-fluoro-4-methoxybenzoic acid (2,
3
-1
?
cm ; LC–MS: m/z (%) = 272 ([M?H] , 72).
-(4-Chlorophenyl)-5-(3-fluoro-4-methoxyphenyl)-1,2,4-
oxadiazole (3e, C H ClFN O )
3
mmol) in 10 cm of DMF 1.15 g 1-[bis(dimethy-
3
lamino)methylene]-1H-[1,2,3]-triazolo[4,5-b]pyridinium-
-oxide hexafluorophosphate (HATU, 3 mmol) was added
3
15 10
2 2
1
3
White solid; yield 82 %; m.p.: 123–125 °C; H NMR
followed by 1 cm N-methylmorpholine (9 mmol) and
lastly substituted aryl amidoximes 1a–1f in DMF. The
reaction mixture was stirred and refluxed for 3 h. After
removal of solvent under vacuum, the reaction mixture was
purified on a silica gel column eluting with 1–5 %
methanol in dichloromethane. The desired 3,5-disubstituted
(
400 MHz, DMSO-d ): d = 3.96 (s, 3H, OCH ), 7.40–8.08
6
3
1
3
(m, 7H, Ar–H) ppm;
C NMR (100 MHz, CDCl3):
d = 56.3, 113.4, 116.1, 116.8, 117.0, 127.2, 127.4, 129.1,
29.9, 137.4, 150.9, 151.5, 153.4, 169.4, 174.8 ppm; IR
KBr): vꢀ = 2985 (Ar C–H), 1624 (C=N), 1504 (C=C),
1
(
-
1
1
288 (C–O), 1095 (C–F) cm ; LC–MS: m/z (%) = 305
1
,2,4-oxadiazoles were isolated and crystallized from
?
?
(
[M?H] , 96), 307 (([M?H] ? 2) , 32).
-(2-Chlorophenyl)-5-(3-fluoro-4-methoxyphenyl)-1,2,4-
oxadiazole (3f, C H ClFN O )
ethanol.
3
3
1
-(3-Bromo-2-fluorophenyl)-5-(3-fluoro-4-methoxyphenyl)-
,2,4-oxadiazole (3a, C H BrF N O )
1
15 10
2 2
5
9
2 2 2
1
1
White solid; yield 77 %; m.p.: 163–165 °C; H NMR
(
Pale yellow solid; yield 80 %; m.p.: 178–180 °C; H NMR
400 MHz, DMSO-d ): d = 3.93 (s, 3H, OCH ), 7.20–8.00
(
400 MHz, CDCl ): d = 3.91 (s, 3H, OCH ), 7.00–8.02
6
3
3
3
1
3
1
m, 6H, Ar–H) ppm; C NMR (100 MHz, CDCl3):
3
(m, 7H, Ar–H) ppm;
C NMR (100 MHz, CDCl3):
(
d = 56.4, 112.8, 115.9, 117.2, 119.7, 121.1, 124.4, 128.7,
31.0, 139.7, 147.6, 149.4, 157.7, 167.9, 172.8 ppm; IR
KBr): vꢀ = 3030 (Ar C–H), 1620 (C=N), 1520 (C=C),
d = 56.3, 110.7, 113.4, 115.8, 116.0, 116.5, 116.6, 117.0,
50.9, 151.7, 153.5, 155.8, 158.3, 165.1, 174.4 ppm; IR
KBr): vꢀ = 3078 (Ar C-H), 1622 (C=N), 1514 (C=C), 1280
1
1
(
(
(
(
-
1
-
1
1275 (C–O), 1080 (C–F) cm ; LC–MS: m/z (%) = 305
C–O), 1128 (C–F) cm ; LC–MS: m/z (%) = 367
?
([M?H] , 92), 307 (([M?H] ? 2) , 35).
?
?
[M?H] , 95), 369 (([M?H] ? 2) , 99).
?
1
23

Molecular properties prediction and synthesis of new oxadiazole derivatives possessing…
-
1517 (C=C), 1282 (C–O), 1018 (C–F) cm ; LC–MS: m/
1
General procedure for the synthesis of 2,5-
disubstituted 1,3,4-oxadiazoles 5a–5f
?
z (%) = 285 ([M?H] , 99).
2
1
-(2,4-Dichlorophenyl)-5-(3-fluoro-4-methoxyphenyl)-
A mixture of 0.92 g 3-fluoro-4-methoxybenzohydrazide (4,
5
,3,4-oxadiazole (5e, C H Cl FN O )
1
5
9
2
2 2
mmol) with different aromatic carboxylic acid (5 mmol)
1
White solid; yield 72 %; m.p.: 116–118 °C; H NMR
3
was refluxed with 10 cm phosphorous oxychloride for 5 h.
Reaction mixture was concentrated through rotovap, the
residue was quenched with ice water and the solid sepa-
rated was filtered off, washed with water, and purified by
crystallization from ethanol to afford 2,5-disubstituted
(
400 MHz, DMSO-d ): d = 3.95 (s, 3H, OCH ), 7.39–8.19
6
3
1
m, 6H, Ar–H) ppm; C NMR (100 MHz, DMSO-d6):
3
(
d = 56.3, 110.7, 117.4, 118.2, 118.6, 125.5, 125.6, 127.2,
27.4, 128.6, 136.1, 139.7, 147.6, 153.2, 155.6 ppm; IR
KBr): vꢀ = 3025 (Ar C–H), 1608 (C=N), 1542 (C=C),
1
(
1
,3,4-oxadiazoles.
-
1
1
241 (C–O), 1030 (C–F) cm ; LC–MS: m/z (%) = 339
?
([M?H] , 94), 341 (([M?H] ? 2) , 65), 343
?
2
-(3-Fluoro-4-methoxyphenyl)-5-(3-methoxyphenyl)-1,3,4-
?
(([M?H] ? 4) , 10).
oxadiazole (5a, C H FN O )
1
6
13
2 3
1
Pale brown solid; yield 70 %; m.p.: 154–156 °C; H NMR
4
-[5-(3-Fluoro-4-methoxyphenyl)-1,3,4-oxadiazol-2-yl]-
(
400 MHz, DMSO-d ): d = 3.81 (s, 3H, OCH ), 3.94 (s,
6
3
1
N,N-dimethylaniline (5f, C H FN O )
17 16
3
3 2
3
H, OCH ), 6.70–7.98 (m, 7H, Ar–H) ppm; C NMR
3
1
Cream solid; yield 80 %; m.p.: 160–162 °C; H NMR
400 MHz, CDCl ): d = 2.98 (s, 6H, 2 CH ), 3.90 (s, 3H,
(
100 MHz, DMSO-d ): d = 56.6, 59.1, 110.6, 114.9,
6
(
3
3
1
21.1, 127.2, 127.3, 128.6, 130.8, 132.3, 139.7, 139.9,
1
3
OCH ), 6.70–7.90 (m, 7H, Ar–H) ppm;
3
C NMR
1
47.6, 149.3, 153.6, 155.0 ppm; IR (KBr): vꢀ = 3055 (Ar
C–H), 1614 (C=N), 1535 (C=C), 1262 (C–O), 1089 (C–F)
(100 MHz, CDCl ): d = 40.2, 56.3, 111.2, 111.3, 113.4,
3
1
1
14.6, 117.2, 123.3, 128.3, 150.2, 150.3, 151.0, 152.1,
-
1
?
cm ; LC–MS: m/z (%) = 301 ([M ? H] , 95).
-[5-(3-Fluoro-4-methoxyphenyl)-1,3,4-oxadiazol-2-
yl]phenol (5b, C H FN O )
53.4 ppm; IR (KBr): vꢀ = 3020 (Ar C–H), 1610 (C=N),
-
1
4
1506 (C=C), 1276 (C–O), 1018 (C–F) cm ; LC–MS: m/z
?
(%) = 314 ([M?H] , 97).
1
5
11
2 3
1
Pale red solid; yield 59 %; m.p.: 120–122 °C; H NMR
(
(
(
400 MHz, DMSO-d ): d = 3.97 (s, 3H, OCH ), 6.82–7.89
Animals
6
3
1
3
m, 7H, Ar–H), 9.38 (s, 1H, OH) ppm; C NMR
100 MHz, DMSO-d ): d = 57.3, 116.1, 116.2, 121.3,
Healthy male Wistar rats (150–200 g) and male Swiss
albino mice (Mus musculus) were used for pharmacologi-
cal screenings. The animals were procured from
Venkateshwara Enterprises, Bangalore, India, (245/
CPCSEA) and housed individually in polypropylene cages,
maintained under standard conditions of alternating 12-h
light and dark cycles at a constant temperature (25 ± 2 °C
and 35–60 % relative humidity). The pharmacological
evaluations were conducted after obtaining ethical clear-
ance from the Institutional Animal Ethical Committee of
K.S. Hegde Medical Academy, Deralakatte, Mangalore
6
1
1
1
28.1, 128.7, 128.9, 129.7, 146.3, 149.7, 150.5, 153.7,
57.0 ppm; IR (KBr): vꢀ = 3366 (OH), 3063 (Ar C–H),
-
1
616 (C=N), 1526 (C=C), 1270 (C–O), 1050 (C–F) cm
;
?
LC–MS: m/z (%) = 287 ([M?H] , 70).
-(3-Fluoro-4-methoxyphenyl)-5-[4-(trifluo-
romethoxy)phenyl]-1,3,4-oxadiazole
5c, C H F N O )
2
(
1
6 10 4 2 3
1
White solid; yield 55 %; m.p.: 145–147 °C; H NMR
(
400 MHz, DMSO-d ): d = 3.90 (s, 3H, OCH ), 6.94–8.05
6
3
1
m, 7H, Ar–H) ppm; C NMR (100 MHz, DMSO-d6):
3
(
(India), Reg. no. 115/1999/CPCSER. The animals were fed
d = 56.4, 110.7, 119.6, 121.0, 122.2, 127.2, 127.4, 128.6,
39.6, 144.1, 147.6, 149.3, 152.7, 157.6 ppm; IR (KBr):
vꢀ = 3032 (Ar C–H), 1621 (C=N), 1538 (C=C), 1259 (C–
standard mice and rat pellets procured from Hindustan
Lever Ltd., Mumbai, India, and water ad libitum.
1
-
1
?
O), 1025 (C–F) cm ; LC–MS: m/z (%) = 355 ([M?H] ,
Acute toxicity
8
6).
2
-Benzyl-5-(3-fluoro-4-methoxyphenyl)-1,3,4-oxadiazole
The test compounds used in the pharmacological study
were evaluated for their acute toxicity in mice. Symptoms
of intoxications were not observed in the animals (disori-
entation, hyperactivity, piloerection, and hyperventilation).
(
5d, C H FN O )
16 13 2 2
1
Light cream solid; yield 84 %; m.p.: 172–174 °C; H NMR
(
400 MHz, DMSO-d ): d = 3.90 (s, 3H, OCH ), 4.32 (s,
6
3
1
3
H, CH ), 7.28–7.75 (m, 8H, Ar–H) ppm; C NMR
2
Median lethal dose (LD ) in male Swiss albino mice (Mus
50
2
(
100 MHz, CDCl ): d = 31.9, 56.3, 113.4, 114.8, 116.6,
16.7, 123.5, 123.8, 127.6, 128.8, 129.0, 150.5, 150.9,
musculus) was determined by employing the standard
methods [36, 37]. From the experiment, oral LD50 of test
compounds were found to be 500 mg/kg body weight at
3
1
1
53.4 ppm; IR (KBr): vꢀ = 3016 (Ar C–H), 1622 (C=N),
123

Dinesha et al.
4
8 h duration. Hence, 50 mg/kg, i.e., 1/10 of cutoff value
Acknowledgments The authors are thankful to The Head, NMR
Centre, IISc Bangalore and The Principal, NGSM Institute of Phar-
maceutical Sciences, Paneer, Deralakatte, Mangalore for providing
the facility for spectral analysis, pharmacological evaluation and also
to UGC-BSR for the financial assistance provided to one of the
authors, Dinesha.
was taken as the screening dose for the evaluation of anti-
inflammatory and analgesic activities.
Anti-inflammatory activity
The in vivo anti-inflammatory activity was evaluated using
the carrageenan-induced rat paw edema assay model [29].
Male Wistar rats (150–200 g) were fasted with free access
to water at least 12 h prior to the experiments and were
divided randomly into 14 groups of six each. The control
References
1
. Kharbanda C, Alam MS, Hamid H, Javed K, Bano S, Dhulap A,
Ali Y, Syed N, Haider S (2014) Bioorg Med Chem 22:5804
2. Kujubu DA, Fletcher BS, Varnum BC, Lim RW, Herschman HR
1991) J Biol Chem 266:12866
3
(
. Vane JR (1971) Nature. New Biol 231:232
. Hawkey CJ (2000) Gastroenterology 119:521
. Joshi SD, Vagdevi HM, Vaidya VP, Gadaginamath GS (2008)
Eur J Med Chem 43:1989
group received 1 cm of 0.5 % sodium CMC, while the
3
4
5
standard group received 10 mg/kg b.w. of diclofenac Na
and test groups received 50 mg/kg b.w. of synthesized
compounds 3a–3f and 5a–5f. The rats were dosed orally,
1
3
h later a subplantar injection of 0.05 cm of 1 % solution
6
7
. Mullican MD, Wilson MW, Connor DT, Kostlan CR, Schrier DJ,
Dyer RD (1993) J Med Chem 36:1090
. Boschelli DH, Connor DT, Bornemeier DA, Dyer RD, Kennedy
JA, Kuipers PJ, Okonkwo GC, Schrier DJ, Wright CD (1993) J
Med Chem 36:1802
of carrageenan in sterile distilled water was administered to
the left hind footpad of each animal. The paw edema
volume was measured with a digital plethysmometer at 1,
8
9
. Raman K, Singh KH, Salzman SK, Parmar SS (1993) J Pharm Sci
8
. S¸ ahin G, Palaska E, Kelicen P, Demirdamar R, Altınok G (2001)
Arzneim Forsch 51:478
2
, and 3 h after the carrageenan injection. The paw edema
2:167
volume was compared with the vehicle control group and
the percentage inhibition of edema was calculated using the
formula:
10. Gaonkar SL, Rai KML, Prabhuswamy B (2006) Eur J Med Chem
1:841
1. El-Emam AA, Al-Deeb OA, Al-Omar MA, Lehmann J (2004)
Bioorg Med Chem 12:5107
2. Bakht MA, Shahar Yar M, Abdel-Hamid SG, Al Qasoumi SI,
Samad A (2010) Eur J Med Chem 45:5862
3. Shi W, Qian X, Zhang R, Song G (2001) J Agric Food Chem
9:124
4. Guimaraes CR, Boger DL, Jorgensen WL (2005) J Am Chem Soc
27:17377
5. Bostr o¨ m J, Hogner A, Llin a` s A, Wellner E, Plowright AT (2012)
J Med Chem 55:1817
6. Manjunatha K, Poojary B, Lobo PL, Fernandes J, Kumari NS
2010) Eur J Med Chem 45:5225
7. Akhter M, Husain A, Azad B, Ajmal M (2009) Eur J Med Chem
4:2372
18. Narayanan R, Gunturi SB (2005) Bioorg Med Chem 13:3017
4
%
Inhibition ¼ ð1 À Vt=VcÞ Â 100
where V is the mean paw volume of the test drug-treated
1
1
1
1
1
1
1
t
rats and V is the mean paw volume of the control group.
c
4
Analgesic activity
1
The analgesic activity was determined by the tail flick
method [31]. Male Wistar rats (150–200 g) in groups of six
animals each were selected by the random sampling tech-
nique. Pentazocine at a dose level of 10 mg/kg was
administered as a reference drug for comparison. The test
compounds, at dose level of 50 mg/kg, were administered
orally using the intragastric tube. The animals were held in
position by a suitable restrain with the tail extending out
and the tail (up to 5 cm) was then dipped in a beaker of
water maintained at 55 ± 1 °C. The time taken to with-
draw the tail clear out of water was taken as the reaction
time and recorded in seconds. The readings were recorded
at 0, 30, 60, 90, and 120 min after administration of
compounds. A cutoff point of 10 s was observed to prevent
tail damage.
(
4
1
9. Moda TL, Montanari CA, Andricopulo AD (2007) Bioorg Med
Chem 15:7738
2
2
0. Norinder U, Bergstr o¨ m CAS (2006) Chem Med Chem 1:920
1. RajaSekhar KK, Shankarananth V, Nithya K, Lakshmi Sravanthi
B, Praveen Naik M, Ratnam NV (2012) J Pharm Res 5:232
2. Dinesha, Viveka S, Chandra S, Nagaraja GK (2015) Monatsh
Chem 146:207
3. Prabhuswamy M, Dinesha, Pampa KJ, Madan Kumar S, Nagaraja
GK, Lokanath NK (2014) Mol Cryst Liq Cryst 593:243
24. Dinesha, Prabhuswamy M, Viveka S, Lokanath NK, Nagaraja
GK (2014) J Single Mol Res 2:27
2
2
2
5. Prabhuswamy M, Dinesha, Abdoh MMM, Pampa KJ, Madan
Kumar S, Nagaraja GK, Lokanath NK (2015) Mol Cryst Liq
Cryst 606:189
Statistical analysis
2
2
2
6. Wang PL, Li HL, Zeng HS, Kang SS, Wang HB (2007) Acta
Cryst E63:o4236
7. Kang SS, Zeng HS, Li HL, Wang HB, Wang PL (2007) Acta
Cryst E63:o4698
8. (a) Stephenson L, Warburton W, Wilson M (1969) J Chem Soc C
6:861; (b) Cottrell DM, Capers J, Salem MM, DeLuca-Fradley K,
Croft SL, Werbovetz KA (2004) Bioorg Med Chem 12:2815
In the present study, data values were expressed as
mean ± SEM, by one-way ANOVA with Dunnett’s t test
to compare the difference between the groups. P \ 0.05
was considered as significant difference.
1
23

Molecular properties prediction and synthesis of new oxadiazole derivatives possessing…
2
3
9. Winter CA, Risley EA, Nuss GN (1962) Proc Soc Exp Biol Med
11:544
0. Rose TE, Morisseau C, Liu JY, Inceoglu B, Jones PD, Sanborn
JR, Hammock BD (2010) J Med Chem 53:7067
1. Kar DM, Sahu SK, Misro PK (2003) Indian Drugs 40:261
2. Lipinski CA, Lombardo F, Dominy BW, Feeney PJ (2001) Adv
Drug Deliv Rev 46:3
34. Ertl A, Rohde B, Selzer P (2000) J Med Chem 43:3714
35. Wang RX, Fu Y, Lai LH (1997) J Chem Inf Comput Sci 37:615
36. Lorke D (1983) Arch Toxicol 54:275
37. Akhila JS, Shyamjith M, Deepa B, Alwar MC (2007) Cur Sci
93:917
1
3
3
3
3. Zhao Y, Abraham MH, Lee J, Hersey A, Luscombe NC, Beck G,
Sherborne B, Cooper I (2002) Pharm Res 19:1446
123