Synthesis and analgesic activity of some acetamide derivatives

Article abstract of DOI:10.3109/14756366.2011.587417

In the present study, some acetamide derivatives were synthesized and their potential analgesic activities were investigated. N-(benzothiazol-2-yl)-2-[(1- substituted-1H-tetrazol-5-yl)thio]acetamide derivatives were obtained by the nucleophilic substitution reaction of 2-chloro-N-(benzothiazole-2-yl)acetamides with appropriate tetrazol-5-thioles. The chemical structures of the compounds were elucidated by IR, ¹H-NMR, ¹³C-NMR and FAB ⁺-MS spectral data and elemental analyses. The prepared compounds were investigated for their potential analgesic properties against thermal, mechanical and chemical nociceptive stimuli using hot-plate, tail-clip and acetic acid-induced writhing tests, respectively. The assessment of motor coordination was carried out using Rota-Rod test. Tested compounds applied at 100mg/kg doses caused significant decrease in acetic acid-induced writhing responses and increase in hot-plate and tail-clip latencies. None of the compounds exhibited destructive effect on motor coordination of the mice in Rota-Rod performance.

Full text of DOI:10.3109/14756366.2011.587417

Journal of Enzyme Inhibition and Medicinal Chemistry, 2012; 27(2): 275–280
© 2012 Informa UK, Ltd.
ISSN 1475-6366 print/ISSN 1475-6374 online
DOI: 10.3109/14756366.2011.587417
RESEARCH ARTICLE
Synthesis and analgesic activity of some acetamide derivatives
Zafer Asim Kaplancikli1, Mehlika Dilek Altintop1, Gulhan Turan-Zitouni1, Ahmet Ozdemir1, and
Ozgur Devrim Can2
1Department of Pharmaceutical Chemistry, Faculty of Pharmacy, Anadolu University, Eskişehir, Turkey and
2Department of Pharmacology, Faculty of Pharmacy, Anadolu University, Eskişehir, Turkey
Abstract
In the present study, some acetamide derivatives were synthesized and their potential analgesic activities were
investigated. N-(benzothiazol-2-yl)-2-[(1-substituted-1H-tetrazol-5-yl)thio]acetamide derivatives were obtained by
the nucleophilic substitution reaction of 2-chloro-N-(benzothiazole-2-yl)acetamides with appropriate tetrazol-5-
thioles. The chemical structures of the compounds were elucidated by IR, 1H-NMR, 13C-NMR and FAB+-MS spectral data
and elemental analyses. The prepared compounds were investigated for their potential analgesic properties against
thermal, mechanical and chemical nociceptive stimuli using hot-plate, tail-clip and acetic acid-induced writhing
tests, respectively. The assessment of motor coordination was carried out using Rota-Rod test. Tested compounds
applied at 100mg/kg doses caused significant decrease in acetic acid-induced writhing responses and increase in
hot-plate and tail-clip latencies. None of the compounds exhibited destructive effect on motor coordination of the
mice in Rota-Rod performance.
Keywords: Acetamide, benzothiazole, tetrazole, hot-plate, writhing test, analgesic activity
Introduction
of COX-1. Although selective COX-2 inhibitors cause less
Pain, which is associated with a number of different
conditions, is the common symptom of many diseases.
Although there are many drugs currently available for
relieving pain, the treatment of pain is still a major prob-
lem due to the adverse effects accompanying the long-
GI adverse effects than nonselective NSAIDs, their use in
the treatment is also limited due to their serious cardio-
vascular effects1–5
.
From the above discussion, it is clear that the search
for new effective compounds has gained great impor-
tance. Acetamide derivatives have been found to pos-
sess analgesic activity. Paracetamol, which is one of the
world’s most widely used drugs, is an example of analge-
term use of these drugs1,2
.
Analgesics, which are most widely used drugs for the
treatment of pain, can be divided into two groups: mor-
phine and related drugs and nonsteroidal anti-inflamma-
tory drugs (NSAIDs). e fear of addiction and tolerance
associated with morphine and related drugs has led to
sic agents bearing acetamide group6–9
.
Medicinal chemists have carried out considerable
research for novel analgesic agents which possess carbox-
ylic acid moiety. e prominent compounds bearing car-
boxylic acid group are aspirin, ibuprofen and naproxen,
all of which are widely used as over-the-counter drugs
for the alleviation of pain. Many researchers have also
studied tetrazoles extensively due to the fact that new
effective compounds can be obtained by the bioisosteric
replacement of the carboxylic acid group with tetrazole
ring. Numerous studies have confirmed that tetrazole
the restriction and withdrawal of these drugs1–5
.
NSAIDs act primarily by inhibiting cyclooxygenase
(COX) enzymes, which catalyze the first step in the pros-
taglandin biosynthesis. e long-term use of NSAIDs
may also lead to severe gastrointestinal side effects,
which limit the use of these drugs. e adverse effects
accompanying the use of non-selective NSAIDs arise
from the reduction of the levels of protective prostaglan-
dins in the gastrointestinal (GI) tract due to the inhibition
derivatives possess analgesic activity2,10–15
.
Address for Correspondence: Dr. Zafer Asim Kaplancikli, Faculty of Pharmacy, Department of Pharmaceutical Chemistry, Anadolu
University, Eskisehir 26470, Turkey. Tel.: +90-222-3350580/3776; Fax: +90-222-3350750. E-mail: zakaplan@anadolu.edu.tr
(Received 07 April 2011; revised 09 May 2011; accepted 09 May 2011)
275

276 Z. A. Kaplancikli et al.
Compounds bearing benzothiazole moiety have also
been reported to exhibit a wide spectrum of biological
N-(6-chlorobenzothiazol-2-yl)-2-[(1-methyl-1H-tetrazol-5-yl)
thio]acetamide (2g)
effects including analgesic activity16–20
.
IR (KBr) νmax (cm−1): 3230 (amide N-H), 1682 (amide
1
In this present study, we described the synthesis of
some acetamide derivatives, which possess two func-
tional moieties, namely benzothiazole and tetrazole and
focused on the potential analgesic properties of these
novel compounds.
C=O), 1627, 1542, 1392 (C=N, N=N and C=C). H NMR
(250 MHz, DMSO-d6): 3.90 (3H, s), 4.55 (2H, s), 7.20-7.91
(3H, m), 12.59 (1H, m). 13C NMR (100 MHz, DMSO-d6):
33.65 (CH3), 36.24 (CH2), 103.68 (CH), 115.25 (CH),
122.01 (CH), 132.67 (C), 142.22 (C), 152.09 (C), 154.69
(C), 158.17 (C), 166.81 (C). For C11H9ClN6OS2 calculated:
38.77% C, 2.66% H, 24.66% N; found: 38.80% C, 2.67% H,
24.70% N. MS (FAB) [M+1]+: m/z 341.
Methods
Chemistry
All reagents were used as purchased from commercial
supplierswithoutfurtherpurification.Meltingpointswere
determined using Electrothermal 9100 digital melting
point apparatus and were uncorrected (Electrothermal,
Essex, UK). e compounds were checked for purity
by TLC on silica gel 60 F254. Spectroscopic data were
recorded on the following instruments: IR, Shimadzu
435 IR spectrophotometer (Shimadzu, Tokyo, Japan); 1H
NMR, Bruker 250 MHz and 13C NMR, Bruker 100 MHz
NMR spectrometer (Bruker Bioscience, Billerica, MA)
in DMSO-d6 using TMS as internal standard; MS-FAB,
VG Quattro mass spectrometer (Fisons Instruments
Vertriebs GmbH, Mainz, Germany). Elemental analyses
were performed on a Perkin-Elmer EAL 240 elemental
analyser (Perkin-Elmer, Norwalk, CT).
Pharmacology
Animals
Swiss albino male mice, weighing 35–40 g, were housed
at room temperature of 24 1°C with 12/12-h light/dark
cycle. Twelve hours before each experiment, animals
received only water in order to avoid food interference
with substances absorption. e experimental protocols
have been approved by the Local Ethical Committee on
Animal Experimentation of Eskişehir Anadolu University,
Turkey.
Assessment of analgesic activity
Hot-plate test
Antinociceptive activities of the tested compounds
(2a–j) against thermal noxious stimuli were measured
by hot-plate test in mice as described previously22. Mice
were placed individually on a hot-plate analgesiameter
(Ugo Basile, Italy, No. 7280) which was set at 55 1.0°C
and the time of licking the forepaws or eventually
jumping were recorded as a parameter of nociception.
Maximum cut-off time was chosen as 30 s to avoid tis-
sue damage. Response latencies were measured 30 min
after the application of sunflower oil as control; mor-
phine sulphate (10 mg/kg) as reference drug and each
test compounds (100 mg/kg). e effects of the com-
pounds on nociception were determined by converting
the hot-plate latencies to percentage analgesic activity
according to the following equation:
General procedure for synthesis of the compounds
N-(benzothiazol-2-yl)-2-chloroacetamides (1a–e)
Chloroacetyl chloride (5 mmol) was added dropwise
with stirring to a mixture of 2-aminobenzothiazole (5
mmol) and triethylamine (2 mL) in toluene (50 mL) at
0−5°C. e solvent was evaporated under reduced pres-
sure. e residue was washed with water and crystallized
from ethanol20.
N-(benzothiazol-2-yl)-2-[(1-substituted-1H-tetrazol-5-yl)thio]
acetamide derivatives (2a–j)
A mixture of N-(benzothiazol-2-yl)-2-chloroacetamide
(1) (2 mmol) and tetrazol-5-thiole (2 mmol) in acetone
was stirred at room temperature for 8 h in the presence
of potassium carbonate and filtered. e residue was
washed with water and crystallized from ethanol21.
(postdrug latency
predrug latency)
predrug latency








%Analgesic
activity
=
×100




N-(6-chlorobenzothiazol-2-yl)-2-[(1-phenyl-1H-tetrazol-5-yl)
thio]acetamide (2b)
IR (KBr) νmax (cm−1): 3262 (amide N-H), 1715 (amide C=O),
1675, 1552, 1385 (C=N, N=N and C=C). 1H NMR (250 MHz,
DMSO-d6): 4.54 (2H, s), 7.47 (1H, dd, J= 8.8, 2.2 Hz), 7.65-
7.75 (5H, m), 7.77 (1H, d, J= 8.7 Hz), 8.13 (1H, d, J= 2.2
Hz), 12.90 (1H, m). 13C NMR (100 MHz, DMSO-d6): 36.48
(CH2), 121.48 (CH), 121.90 (CH), 124.41 (2CH), 126.56
(CH), 127.79 (C), 130.09 (2CH), 130.72 (CH), 132.92 (C),
133.11 (C), 147.36 (C), 153.69 (C), 158.47 (C), 166.52 (C).
For C16H11ClN6OS2 calculated: 47.70% C, 2.75% H, 20.86%
N; found: 47.74% C, 2.75% H, 20.87% N. MS (FAB) [M+1]+:
m/z 403.
Tail-clip test
Antinociceptive activities of the tested compounds (2a–j)
against mechanical noxious stimuli were measured by
tail-clip test in mice as described previously23. A metal
artery clamp was applied to the tail of mouse and the
time spent before biting the clamp was recorded by a
stopwatch24. A sensitivity test was carried out before the
experimental session, and animals that did not respond
to the clamp within 10 s were discarded from the experi-
ments25. Maximum latency time (cut-off time) for the
Journal of Enzyme Inhibition and Medicinal Chemistry

Synthesis of some acetamide derivatives 277
tail-clip tests was chosen as 10 s to avoid possible tissue
damage26. Analgesia was expressed as a percentage of the
maximum possible effect (MPE %), according to the fol-
lowing equation27:
Statistical analysis
e data used in statistical analysis was obtained from six
animals for each of the groups. Experimental data from
behavioural tests were analysed by one-way analysis
of variance followed by Tukey’s test. Statistical evalua-
tion of the data was performed using GraphPad Prism
3.0 (GraphPad Software, San Diego, CA). Experimental
results were expressed as mean
between given sets of data were considered to be signifi-
cant when p value was less than 0.05.












(postdrug latency
predrug latency)
(cut-off time
% MPE =
×100
SEM. Differences
predrug latency)
Writhing test
Results
Antinociceptive activities of the tested compounds
(2a–j) against chemical noxious stimuli were measured
by acetic acid-induced writhing test in mice as described
previously22. Mice were pre-treated with sunflower oil,
morphine sulphate or test compounds (100 mg/kg, i.p.)
30 min prior to intraperitoneal injection of 0.6% acetic
acid (Merck, Brazil) at a dose of 10 mL/kg. Five minutes
after the injection of acetic acid, the number of abdominal
contractions and stretches during the following 10 min
was recorded. e percentage protection of writhing was
calculated according to the following formula:
Initially,
2-chloro-N-(benzothiazol-2-yl)acetamides
(1a–e) were obtained by reacting 2-aminobenzothiazoles
with chloroacetyl chloride in the presence of triethylam-
ine, which was responsible for the removal of hydrogen
chloride from the reaction mixture.
e desired compounds (2a–j) were prepared by
reacting
with appropriate tetrazol-5-thioles. is nucleophilic
substitution reaction was carried out in the presence of
potassium carbonate. ese reactions are summarized in
Scheme 1.
2-chloro-N-(benzothiazol-2-yl)acetamides
(control mean






e structures of the compounds (2a–j) were con-
firmed by IR, H-NMR, 13C-NMR and FAB+-MS spectral
1
treated mean)
% Protection =
×100
data and elemental analyses.
In the IR spectra, all derivatives have a strong char-
acteristic band in the region 1715–1650 cm−1 due to the
 (control mean) 




1
amide C=O stretching vibration. In the H-NMR spectra
of all compounds (2a–j), the signal due to the amide
proton appears at 12–13 ppm. In their 13C-NMR spec-
tra, the signal due to the amide carbon is observed at
166–167 ppm. In the mass spectra of all compounds, the
M+1 peak is observed. All compounds gave satisfactory
elemental analysis.
All of the test compounds at 100mg/kg doses caused
significant increases in the reaction times of mice against
thermal noxious stimulus in hot-plate tests. Compounds
2b, 2e, 2g, and 2j exhibited the highest antinociceptive
actions (Figure 1).
Assessment of motor coordination via Rota-Rod test
For evaluating any non-specific muscle-relaxant or motor
coordination impairing effects of the tested compounds
(2a–j), mice were submitted to the Rota-Rod task as
described previously22. Before the experimental session,
three trials were given for three consecutive days on the
Rota-Rod apparatus (Ugo Basile 7560, Milano, Italy) set at
a rate of 16 revolutions per minute. Mice that were able to
remain on the rod longer than 180 s were selected for the
test. Each mouse was tested in the Rota-Rod and latency
to fall from the rotating mill was recorded.
Scheme 1. e synthetic protocol of the compounds (2a–j).
© 2012 Informa UK, Ltd.

278 Z. A. Kaplancikli et al.
Table 1. Protection percentage values of morphine and test
compounds (2a–j) in acetic acid-induced writhing test.
Treatment
Protection %
Morphine sulphate (10mg/kg)
Compound 2a (100mg/kg)
Compound 2b (100mg/kg)
Compound 2c (100mg/kg)
Compound 2d (100mg/kg)
Compound 2e (100mg/kg)
Compound 2f (100mg/kg)
Compound 2g (100mg/kg)
Compound 2h (100mg/kg)
Compound 2i (100mg/kg)
Compound 2j (100mg/kg)
84.7
74.1
81.2
55.9
44.7
25.3
72.9
79.4
61.2
46.5
28.2
e test compounds also increased the reaction times
of mice in tail-clip tests against mechanical noxious stim-
uli. Compounds 2b, 2e, 2g, and 2j were again the most
effective in the tail-clip tests (Figure 1).
In writhing tests, all test compounds prevent the ani-
mals from acetic acid-induced abdominal contractions
and stretches. Chloride derivative compounds 2b and 2g
and non-substituted derivatives 2a and 2f were the most
active compounds among the test compounds (Figure 1).
Percentage protection values induced by each of the
compounds were shown in Table 1.
No significant change was observed in the falling
latencies of animals in Rota-Rod tests (data not shown).
Discussion
e results of this present study exhibited the significant
antinociceptive activities for all of the test compounds
(2a–j). Antinociceptive activities observed in all hot-plate,
tail-clip and acetic acid-induced writhing tests clearly
showed the pharmacological effects of these compounds
on thermal, mechanical and chemical nociceptive
pathways.
Hot-plate and tail-clip tests have been reported
as a measure of centrally mediated transient pain. As
reported previously, the hot-plate test predominantly
measures responses organized supraspinally, whereas
the tail-clip test mainly measures spinal reflexes27,28
.
As test compounds showed significant analgesic
activities in both hot-plate and tail-clip tests, it may
be suggested that analgesic activities observed in the
present study are related to both supraspinal and spi-
nal mechanisms.
Compounds 2e and 2j carrying ethoxy group as
well as 2b and 2g carrying chloride group on their
benzothiazole rings exhibited the highest antinocice-
ptive actions in both hot-plate and tail-clip tests. On
the other hand, unsubstituted compounds 2a and
2f exhibited relatively lower antinociceptive actions
in both tests. Observed results can be depended on
the lipophilic character of the compounds since the
ethoxy and chloro substitutions increase the lipophi-
licity of the structure when compared with the other
Figure1. Antinociceptiveeffectsofmorphineandtestcompounds.
(A) Hot-plate test. (B) Tail-clip test. (C) Acetic acid induced
writhing test. Values are given as mean SEM. Significancy against
control values *p< 0.05, **p< 0.01, ***p< 0.001. One-way ANOVA,
post-hoc Tukey’s test, n = 6.
substituents. Depending on this respect, it may be
declared that ethoxy and chloro substituents distin-
guish an optimum lipophilicity, which is a key property
that influences the ability of a drug to reach the target
by transmembrane diffusion and to have a major effect
on the biological activity.
Journal of Enzyme Inhibition and Medicinal Chemistry

Synthesis of some acetamide derivatives 279
e acetic acid-induced abdominal construction is a
visceral pain model employed as a test tool for the assess-
ment of antinociceptive activities of new analgesic com-
pounds29. It has been suggested that acetic acid injection
into peritoneal cavity leads to an increased level of COX
and lipooxygenase products in peritoneal fluids and the
release of various inflammatory mediators such as brady-
kinin, substance P, TNF-α, IL-1β, IL-8, which eventually
excites the primary afferent nociceptors entering dorsal
horn of the central nervous system30. erefore, inhibition
ofaceticacid-inducedwrithingbehaviouraftertheadmin-
istration of test compounds suggests that the mechanisms
of the compounds may at least partly be related to the
inhibition of COX and/or LOX and other inflammatory
mediators in peripheral tissues, thereby interfering with
the mechanism of signal transduction in primary afferent
nociceptors. Chloride derivative compounds 2b and 2g
and non-substituted derivatives 2a and 2f were the most
active compounds among the test compounds. On the
other hand, compounds 2e and 2j carrying ethoxy group,
which were quite active in hot-plate and tail-clip tests,
exhibited relatively lower antinociceptive actions in the
writhing test. Greater analgesic activity of the compounds
2b, 2g, 2a and 2f with respect to 2e and 2j may be related
with electronic features of the molecules. Compounds 2b
and 2g carry an electron withdrawing chloro substituent
and 2a and 2f are in non-substituted forms. However,
less active compounds 2c, 2h, 2d, 2i, 2e and 2j bear elec-
tron donating substituents such as methyl, methoxy and
ethoxy, which increase the electron density of the com-
pounds. erefore, it may be suggested that substitution
with electron donating groups decreases, whereas elec-
tron withdrawing chloro group increases the peripheral
analgesic activity of the compounds.
activities and support the previous papers reporting the
antinociceptive activities of various benzothiazole, tetra-
zole or acetamide derivatives6–20
.
Declaration of interest
e authors report no conflicts of interest. e authors
alone are responsible for the content and writing of the
paper.
References
1. Moore ND. In search of an ideal analgesic for common acute pain.
Acute Pain 2009;11:129–137.
2. Buschmann H, Christoph T, Friderichs E, Maul C, Sundermann
B. Analgesics: From chemistry and pharmacology to clinical
application. Weinheim: Wiley-VCH Germany, 2002: pp. 1–264.
3. Turunen JH, Mäntyselkä PT, Kumpusalo EA, Ahonen RS. Frequent
analgesic use at population level: Prevalence and patterns of use.
Pain 2005;115:374–381.
4. Simmons DL, Botting RM, Hla T. Cyclooxygenase isozymes: e
biology of prostaglandin synthesis and inhibition. Pharmacol Rev
2004;56:387–437.
5. Dannhardt G, Laufer S. Structural approaches to explain the
selectivityofCOX-2inhibitors:Isthereacommonpharmacophore?
Curr Med Chem 2000;7:1101–1112.
6. Moore A, Collins S, Carroll D, McQuay H. Paracetamol with and
without codeine in acute pain: A quantitative systematic review.
Pain 1997;70:193–201.
7. Onkol T, Dogruer DS, Ito S, Sahin MF. Synthesis and antinociceptive
activity
of
(5-chloro-2-benzothiazolinon-3-yl)acetamide
derivatives. Arch Pharm (Weinheim) 2000;333:337–340.
8. Pilli HG, Ozkanli F, Safak C, Erdogan H, Unlü S, Gümüsel B et al.
2-(6-Acyl-2-benzoxazolinone-3-yl)acetamide and acetonitrile
derivatives with analgesic activities. Pharmazie 1994;49:63–64.
9. Dogruer DS, Unlü S, Yesilada E, Fethi Sahin M. N-(2-pyridinyl)-2-
[2(3H)-benzazolone-3-yl]acetamides: Synthesis, antinociceptive
and anti-inflammatory activity. Farmaco 1997;52:745–750.
10. JubyPF,HudymaTW,BrownM.Preparationandantininflammatory
properties of some 5-(2-anilinophenyl)tetrazoles. j Med Chem
1968;11:111–117.
11. Bachar SC, Lahiri SC. Synthesis of chloro and bromo substituted
5-(indan-1’-yl)tetrazoles and 5-(indan-1’-yl)methyltetrazoles as
possible analgesic agents. Pharmazie 2004;59:435–438.
12. Ciapetti P, Giethlen B. Molecular variations based on isosteric
replacements. In: Wermuth CM (ed.). The Practice of Medicinal
Chemistry, Burlington: Academic Press USA, 2008: pp.
290–342.
As benzothiazole ring, tetrazole ring was also substi-
tuted in the present study. However, the substitution of tet-
razole ring with methyl or phenyl group did not cause any
significant differences in the pharmacological activity.
Tested compounds did not impair the motor perfor-
mance in Rota-Rod test, indicating that the observed
antinociception unlikely occurred due to motor
abnormalities.
13. Rajasekaran A, ampi PP. Synthesis and analgesic evaluation of
some 5-[β-(10-phenothiazinyl)ethyl]-1-(acyl)-1,2,3,4-tetrazoles.
Eur j Med Chem 2004;39:273–279.
Conclusion
14. Vicini P, Amoretti L, Barocelli E, Chiavarini M, Impicciatore M.
Synthesis and anti-inflammatory, antipyretic and analgesics
properties of 5-(1,2-benzisothiazolyl)tetrazoles. Farmaco Sci
1986;41:111–118.
15. Shanmugapandiyan P, Ramesh A. Synthesis and biological
applications of certain 1-acetamido-(benzothiazol-2’-yl)-5-
aryltetrazole and benzothiazol-2’-yl-1-ethylamine-5-aryltetrazoles.
J Pharm Chem 2008;2:169–173.
16. Paramashivappa R, Phani Kumar P, Subba Rao PV, Srinivasa Rao
A. Design, synthesis and biological evaluation of benzimidazole/
benzothiazole and benzoxazole derivatives as cyclooxygenase
inhibitors. Bioorg Med Chem Lett 2003;13:657–660.
17. Yous S, Poupaert JH, Chavatte P, Espiard JG, Caignard DH,
Lesieur D. Synthesis and pharmacological evaluation of analgesic
6-substituted 2(3H)-benzothiazolones. Drug Des Discov
2001;17:331–336.
e antinociceptive evaluations of some acetamide
derivatives were demonstrated in the present study.
e compounds (2a–j) exhibited statistically significant
antinociceptive activities against thermal, mechani-
cal, and chemical noxious stimuli in hot-plate, tail-clip
and acetic acid-induced writhing tests, respectively.
Based on these findings, it can be concluded that all the
compounds (2a–j) act on all thermal, mechanical, and
chemical nociceptive pathways and effect supraspinal,
spinal and peripheral nociceptive mechanisms.
e findings of this present investigation prove the
hypothesis that acetamide derivatives carrying ben-
zothiazole and tetrazole rings possess antinociceptive
© 2012 Informa UK, Ltd.

280 Z. A. Kaplancikli et al.
18. Gökce M, Cakir B, Erol K, Sahin MF. Synthesis and
antinociceptive activity of [(2-oxobenzothiazolin-3-yl)methyl]-
4-alkyl/aryl-1,2,4-triazoline-5-thiones. Arch Pharm (Weinheim)
2001;334:279–283.
19. Bahekar SS, Shinde DB. Synthesis and anti-inflammatory activity
of [2-(benzothiazol-2-ylimino)-4-oxo-3-phenylthiazolidin-5-yl]-
acetic acid derivatives. J Korean Chem Soc 2003;47:237–240.
20. Bhargava PN, Ram P. Synthesis of local anesthetics. Bull Chem Soc
Japan 1965;38:339–341.
21. Connell RD, Lease TG, Ladouceur GH, Osterhout MH. α-Alkoxy-
and α-thioalkoxyamide neuropeptide Y NPY5 receptor antagonists
and therapeutic methods using them. US Patent 1999;5939462A
19990817.
25. Adeyemi OO, Okpo SO, Okpaka O. e analgesic effect of the
methanolic extract of Acanthus montanus. J Ethnopharmacol
2004;90:45–48.
26. Oztürk N, Baser KH, Aydin S, Oztürk Y, Calis I. Effects of Gentiana
lutea ssp. symphyandra on the central nervous system in mice.
Phytother Res 2002;16:627–631.
27. Gabra BH, Sirois P. Beneficial effect of chronic treatment with the
selective bradykinin B1 receptor antagonists, R-715 and R-954, in
attenuating streptozotocin-diabetic thermal hyperalgesia in mice.
Peptides 2003;24:1131–1139.
28. Wong CH, Dey P, Yarmush J, Wu WH, Zbuzek VK. Nifedipine-
induced analgesia after epidural injection in rats. Anesth Analg
1994;79:303–306.
22. Kaplancikli ZA, Turan-Zitouni G, Ozdemir A, Can O, Chevallet
P. Synthesis and antinociceptive activities of some pyrazoline
derivatives. Eur J Med Chem 2009;44:2606–2610.
23. Can OD, Ozkay UD, Oztürk N, Oztürk Y. Effects of hawthorn seed
and pulp extracts on the central nervous system. Pharm Biol
2010;48:924–931.
29. De Souza MM, Pereira MA, Ardenghi JV, Mora TC, Bresciani LF,
Yunes RA et al. Filicene obtained from Adiantum cuneatum
interacts with the cholinergic, dopaminergic, glutamatergic,
GABAergic, and tachykinergic systems to exert antinociceptive
effect in mice. Pharmacol Biochem Behav 2009;93:40–46.
30. Ikeda Y, Ueno A, Naraba H, Oh-ishi S. Involvement of vanilloid
receptor VR1 and prostanoids in the acid-induced writhing
responses of mice. Life Sci 2001;69:2911–2919.
24. D’Amour FE, Smith DL. A method for determining loss of pain
sensation. J Pharmacol Exp er 1941;72:74–79.
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