Synthesis and antinociceptive behaviors of new methyl and hydroxyl derivatives of phencyclidine

Article abstract of DOI:10.2174/092986712798992057

Phencyclidine (I) and its derivatives show such pharmacological behaviors as analgesic, anticonsulvant, anti-anxiety and antidepressant, while interacting with central nervous system. In this study, new methyl and hydroxyl derivatives of PCP were synthesized and their antinociceptive behaviors in animals were examined by measuring the number of writhing in a writhing test of visceral pain and the pain scores in Formalin test. Compared to control and PCP groups, findings in experimental groups indicated the new synthesized analogues (compounds II, III and V, 10 mg/kg) of PCP were able to produce more analgesic effects in formalin and writhing tests, especially for compound V. It was concluded that the new synthesized derivatives of PCP could substantially and respectively diminish acute and chronic pains.

Full text of DOI:10.2174/092986712798992057

Current Medicinal Chemistry, 2012, 19, 763-769
763
Synthesis and Antinociceptive Behaviors of New Methyl and Hydroxyl Derivatives of
Phencyclidine
A. Ahmadi*,1, M. Kermani2, N. Naderi2, R. Hajikhani3, N.M. Rezaee1, M. Javadi1 and B.N. Niknafs4
1Department of Chemistry, Faculty of Science, Islamic Azad University, Karaj Branch, Karaj, Iran
2Neuroscience Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran
3Department of Physiology, Faculty of Science, Islamic Azad University, Karaj Branch- Karaj, Iran
4Islamic Azad University, Karaj Branch- Karaj, Iran
Abstract: Phencyclidine (I) and its derivatives show such pharmacological behaviors as analgesic, anticonsulvant, anti-anxiety and anti-
depressant, while interacting with central nervous system. In this study, new methyl and hydroxyl derivatives of PCP were synthesized
and their antinociceptive behaviors in animals were examined by measuring the number of writhing in a writhing test of visceral pain and
the pain scores in Formalin test. Compared to control and PCP groups, findings in experimental groups indicated the new synthesized
analogues (compounds II, III and V, 10 mg/kg) of PCP were able to produce more analgesic effects in formalin and writhing tests,
especially for compound V. It was concluded that the new synthesized derivatives of PCP could substantially and respectively diminish
acute and chronic pains.
Keywords: Antinociceptive behaviors, Formalin test, Phencyclidine, Writhing test.
writhing in writhing tests and measuring the pain scores in formalin
test.
1. INTRODUCTION
Phencyclidine (1-[1-phenylcyclohexyl] piperidine, PCP, I,
Scheme 1) is an aryl cyclohexyl amine compound that has received
much investigative attention due to the complex spectrum of
behaviors it induces and its complicated interaction with the central
nervous system (CNS). Phencyclidine administration may mimic
pharmacological properties similar to those of stimulants,
depressants, hallucinogens and analgesic agents depending upon the
dosage and species tested [1]. Also, experimental evidence suggests
that glutamate receptors are involved in the mechanisms controlling
the acquisition and expression of pain-related behaviors [2].
Majority of the PCP effects occurs in the central nervous system, at
least at recreational doses. Effects on other organ systems seem to
be significant only in overdose situations. It hardly appears to be a
specific PCP receptor in human brain as PCP seems to bind to the
N-methyl-D-aspartate (NMDA) receptor [3, 4]. Phencyclidine
analogues also bind to this site, while the binding efficiency tends
to correlate with the potency of the analog [5]. Glutamate is the
major excitatory neurotransmitter in the CNS involved in many
physiological and pathophysiological situations, including spinal
and supraspinal pain transmission. Therefore, the glutamate
receptor antagonists, particularly the NMDA receptor antagonists,
are amongst important agents in controlling various types of pain
[6]. Recently, several PCP derivatives (with substitution changes in
the molecule) have been synthesized and their pharmacological
activities have been tested [7-13]. Revealed in the previous works
[8-10, 12, 13] on this family of compounds, the incorporation of
methyl group to the aromatic ring of the molecule generates
pronounced effects on electron distribution and dipole moments
because of its high electron donating character [14]. In addition, the
hydroxyl group with high hydrophilic, polarity, and solubility
properties [15] may produce more analgesic effects on this family.
In this study, to produce the pronounced analgesic effects,
phencyclidine (I), 2-phenyl-2-piperidine-1-yl-cyclohexanol (IV)
and some of their new analogues (3-Methyl-4-(1-piperidin-1-yl-
cyclohexyl)-phenol (II), 1-[1-(4-Hydroxy-2-methyl-phenyl)-cyclo-
hexyl]-piperidin-4-ol (III) and 1-(2-hydroxy-1-p-tolyl-cyclohexyl)-
piperidine-4-ol (V)), were synthesized. Their antinociception
behaviors in animals were determined by counting the number of
OH
CH3
N
N
I
II
OH
CH3
OH
N
N
OH
III
IV
CH3
OH
N
OH
V
Scheme 1. Structural formulas of phencyclidine (I), (3-Methyl-4-(1-
piperidin-1-yl-cyclohexyl)-phenol (II), 1-[1-(4-Hydroxy-2-methyl-phenyl)-
cyclohexyl]-piperidin-4-ol (III), 2-phenyl-2-piperidine-1-yl-cyclohexanol
(IV), and 1-(2-hydroxy-1-p-tolyl-cyclohexyl)-piperidine-4-ol (V).
2. MATERIALS AND METHOD
2.1. General
In this study, cyclohexanone, piperidine, bromo benzene,
magnesium turning, diethyl ether, 4-hydroxy piperidine, 4-chloro-3-
methyl phenol, N-bromoacetamide (NBA), potassium t-butoxide
and all other chemicals were purchased from Merck Chemical Co.
(Darmstadt, Germany). Melting points (uncorrected) were
determined with a digital electrothermal melting point apparatus
(model 9100, Electrothermal Engineering Ltd., Essex, UK). 1H and
13C NMR spectra were recorded by Bruker 300 MHz (model AMX,
Karlsruhe, Germany) spectrometer (internal reference: TMS). IR
spectra were recorded by a Thermo Nicolet FT-IR (model Nexus-
*Address correspondence to this author at the Department of Chemistry, Faculty of
Science, Islamic Azad University, Karaj Branch, P.O.Box: 31485-313, Karaj, Iran; Tel:
0098-912-1879707; Fax: 0098-261-4418156;
E-mails: a-ahmadi@kiau.ac.ir, ahmadi3957@yahoo.com
0929-8673/12 $58.00+.00
© 2012 Bentham Science Publishers

764 Current Medicinal Chemistry, 2012 Vol. 19, No. 5
Ahmadi et al.
870, Nicolet Instrument Corp., Madison, Wisconsin, U.S.A.)
spectrometer. Mass spectra were recorded by an Agilent
Technology-5973 Mass Selective Detector (MSD) spectrometer
(Wilmington, USA). Elemental analyses were performed by using a
an oily compound (III, 2.82 g, 49% yield). The hydrochloride salt
of III (m.p. 177-178˚ C) was prepared with diethyl ether and HCl, It
was recrystallized from 2-propanol.
IR (KBr): 3369, 2927, 2857, 1581, 1479, 1294, 1163, 1053, 807
Heraeus
CHN-O-RAPID
elemental
analyzer.
Column
cm-1.
chromatographic separations were performed over Acros silica gel
(No.7631-86-9 particle size 35-70 micrometer, Geel, Belgium).
1H N.M.R. (CDCl3) (p.p.m.): 1.52-2.27 (19H, m),, 2.39 (3H, s),
3.5 (1H, m), 5.01 (1H, s), 6.05-6.47 (3H, m).
13C N.M.R. (CDCl3) (ppm): 12.4, 20.54, 20.94, 24.9, 28.3, 34.5,
43.3, 67.3, 71.3, 104.5, 111.04, 121.6, 139.6, 142.4, 158.8.
2.2. Preparations (Scheme 2-5)
2.2.1. 1-Piperidinocyclohexanecarbonitrile (1) and 4-hydroxy
piperidinocyclohexyl carbonitrile (2)
Anal. Calc. for: C18H27NO2; calc. (%): C 74.70, H 9.40, N 4.84;
found: C 74.77, H 9.45, N 4.79.
The compounds were prepared in an organic solvent based on a
published method from piperidine to 4-piperidinol, cyclohexanone
and KCN [16].
MS: m/z (regulatory intensity): 290 (20).
2.2.5. 1-phenylcyclohexanol (3) and 1-(p-tolyl) cyclohexanol (5)
2.2.2. 1-[1-phenylcyclohexyl] Piperidine (PCP) (I)
These compounds were prepared from phenyl magnesium
bromide or p-tolyl magnesium bromide and cyclohexanone based
on published methods [18, 19].
This compound was prepared based on a published method
from a solution of 1-piperidinocyclohexanecarbonitrile (1) in an
organic solvent to a refluxing solution of phenyl magnesium
bromide (prepared from 79g bromobenzene and 12.3g Mg in 200
ml of dry ether). The hydrochloride salt of I (m.p. 233-234˚ C) was
prepared with 2-propanol and HCl, before it was recrystallized from
2-propanol [17].
2.2.6. 1-phenylcyclohexene (4) and 1-(p-tolyl) cyclohexene (6)
Compounds were prepared from compounds 3 or 5 and mixture
of sulfuric and glacial acetic acid, based on a published method [18,
19].
2.2.7. 2-Bromo-1-phenyl-cyclohexanol (7) and 2-Bromo-1-p-tolyl-
cyclohexanol (9)
2.2.3. 1-[1-[3-hydroxy-5-methylphenyl] [cyclohexyl] piperidine
(II)
Compounds were prepared from addition of 0.0247mol of 4 or
in 70%dioxane (120ml) to 3.65g (0.0265mol) NBA in
50%dioxane, warmed in hot water for 2 minutes. Next, the mixture
was poured into ice-water, extracted with ether, dried and
concentrated. The concentrated oil compounds (4g and 4.1g) were
obtained (59% and 56%yields).
A solution, containing 3.9g (0.023mol) of nitrile compound (1)
in the mixture of dry diethyl ether and toluene (1:1) was added to a
refluxing solution of 4-hydroxy-2-methyl phenyl magnesium
chloride (Grignard reagent) which was prepared from 7.35g of 4-
chloro-3-methyl phenol and 1.23g Mg in 60ml dry ether. It was
refluxed for 14 additional days and left overnight at ambient
temperature (25˚C) before it was poured into ice-NH4Cl. The
organic layer was separated and the aqueous layer extracted with
diethyl ether. The combined organic layers water-washed, re-
extracted with 10% H2SO4, neutralized with 10% NaOH and re-
extracted with n-Hexane. The organic layer was successively water-
washed, dried over MgSO4 and evaporated under vacuum to obtain
an oily compound (II, 3.1 g, 56% yield). The hydrochloride salt of
II (m.p. 174-175˚C) was prepared with diethyl ether and HCl. It
was recrystallized from 2-propanol.
6
7:
IR (KBr): 3436, 2969, 2863, 1651, 1456, 1257, 1118, 871 cm-1.
1H N.M.R. (CDCl3) (ppm): 1.5-2.2 (9H, m), 3.9 (1H, m), 7.1-
7.3 (5H, m).
13C N.M.R. (CDCl3) (ppm): 18.2, 24.2, 26.8, 37, 52.1, 83.1,
125.6, 126.8, 128.2, 143.2.
MS: m/z (regulatory intensity): 254 (26).
9:
IR (KBr): 3450, 2938, 2800,2753, 1468, 1256, 1161, 1050, 874
cm-1.
IR (KBr): 3435, 2929, 2861, 1660, 1514, 1446, 809 cm-1.
1H N.M.R. (CDCl3) (ppm): 1.08-2.22 (20H, m), 2.27 (3H, s),
5.01 (1H, m), 6.05-6.47 (3H, m).
1H N.M.R. (CDCl3) (ppm): 1.5-2.2 (9H, m), 2.37 (3H, s), 3.9
(1H, m), 7.1-7.3 (5H, m).
13C N.M.R. (CDCl3) (ppm): 12.4, 20.54, 24.32, 28.04, 32.58,
49.32, 111.04, 121.6, 139.6, 142.4, 135.7, 158.8.
13C N.M.R. (CDCl3) (ppm): 18.2, 20.3, 24.2, 26.8, 37, 52.1,
83.1, 125.6, 126.8, 128.2, 143.2.
Anal. Calc. for: C18H27NO; calc. (%): C 79.07, H 9.95, N 5.12;
found: C 79.11, H 9.90, N 5.15.
MS: m/z (regulatory intensity): 268 (30).
2.2.8. 1-Phenyl-7-oxa-bicyclo [4.1.0] heptane (8) and 1- p-tolyl-7-
oxa-bicyclo [4.1.0] heptane (10)
MS: m/z (regulatory intensity): 273 (24).
2.2.4. 1-[1-[3-hydroxy-5-methylphenyl] [cyclohexyl]-4-piperidinol
(III)
Potassium t-butoxide (2.2g, 0.0196mol) was added to the
solutions of 7 or 9 in benzene (120ml) and stirred for one hour.
Then Potassium t-butoxide (2.2g, 0.0196mol) was re-added and
stirred for 3 more hours. Then water was added, extracted with
benzene, dried and concentrated. The concentrated oil compounds
(1.5 and 1 g) were obtained (68% and 56% yields).
A solution, containing 4.16 g (0.023mol) of nitrile compound
(2) in the mixture of dry diethyl ether and toluene (1:1) was added
to a refluxing solution of 4-hydroxy-2-methylphenyl magnesium
chloride (Grignard reagent) which was prepared from 7.35 g of 4-
chloro-3-methyl phenol and 1.23g Mg in 100ml dry ether. It was
refluxed for 20 additional days and left overnight at ambient
temperature (25˚C) before it was poured into ice-NH4Cl. The
organic layer was separated and the aqueous layer extracted with
diethyl ether. The combined organic layers washed with water, re-
extracted with 10% H2SO4, neutralized with 10% NaOH and re-
extracted with n-Hexane. The organic layer was successively water-
washed, dried over MgSO4 and evaporated under vacuum to obtain
8:
IR (KBr): 2934, 2858, 1600, 1494, 1445, 742, 759, 696 cm-1.
1H N.M.R. (CDCl3) (ppm): 1.5-1.9 (8H, m), 3.3 (1H, m), 7.1-
7.3 (5H, m).
13C N.M.R. (CDCl3) (ppm): 19.3, 24.2, 25.6, 34.1, 67.2, 71.9,
125.8, 126.8, 128.2, 144.2.
MS: m/z (regulatory intensity): 174 (25).

Phencyclidines Antinociceptive Behaviors
Current Medicinal Chemistry, 2012 Vol. 19, No. 5
765
was poured into ice-water and extracted by ether. The organic layer
was separated and the aqueous layer extracted with diethyl ether.
The combined organic layers water-washed, re-extracted with 10%
H2SO4, neutralized with 10% NaOH and re-extracted with diethyl
ether. The organic layer was successively water-washed, dried over
MgSO4 and evaporated under vacuum to obtain the oily compound
(mixture of two isomers) which was passed from silica gel column
chromatography to afford 1.9 g (50% yield) of V.
O
H
N
N
C
N
NaHSO3
KCN
+
+
(1)
OH
O
H
N
N
C
N
IR (KBr): 3422, 2930, 2854, 1595, 1446, 1260, 1074, 740, 699
cm-1.
NaHSO3
KCN
1H N.M.R. (CDCl3) (ppm): 1.49-2.26 (18H, m),, 2.37 (3H, s),
3.5-3.74 (2H, m), 6.85-7.1 (4H, m).
13C N.M.R. (CDCl3) (ppm): 20.5, 21.4, 27.6, 31.7, 34, 42.6,
65.8, 67.8, 79, 126.7, 128.9, 135.1, 141.8.
(2)
OH
Scheme 2. Synthesis of intermediates 1 and 2.
Anal. Calc. for: C18H27NO2; calc. (%): C 74.70, H 9.40, N 4.84;
found: C 74.66, H 9.44, N 4.80.
10:
IR (KBr): 2926, 1578, 1489, 1246, 1034, 821, 673 cm-1.
MS: m/z (regulatory intensity): 284 (15).
1H N.M.R. (CDCl3) (ppm): 1.5-1.9 (8H, m), 2.36 (3H,s), 3.3
(1H, m), 7.1-7.3 (5H, m).
2.3. Pharmacological Methods
13C N.M.R. (CDCl3) (ppm): 19.2, 20.6, 24.2, 25.6, 34.1, 67.2,
71.9, 125.8, 126.8, 128.2, 144.2.
2.3.1. Subjects
Fifty-eight adult male Wistar rats (250-300g) and male NMRI
mice (25-30g) (Pasteur’s Institute, Tehran) were experimented with
Formalin and Writhing tests, respectively. Animals were kept under
standard laboratory conditions, with tap water and regular rat chow
ad libitum. They were housed in groups of five animals in each
cage in a temperature (22±2˚C) and humidity controlled room on 12
hours light/dark cycles. All experiments were conducted in
accordance with the Guide for the Care and Use of Laboratory
Animals (National Institute of Health Publication No. 80-23,
revised 1996) and were approved by the Research and Ethics
Committee of Shahid Beheshti University of Medical Sciences,
Tehran-Iran.
MS: m/z (regulatory intensity): 188 (23).
2.2.9. 2-phenyl-2-piperidine-1-yl-cyclohexanol (IV)
The compound was prepared based on a published method with
some modifications [20, 21]. Compound 8 (2.26 g, 0.013 mol),
ethylene glycol (50 ml) and piperidine (11.9 g, 0.14 mol) were
refluxed for 16 hours. The mixture was poured into ice-water and
extracted by ether. The organic layer was separated and the aqueous
layer extracted with diethyl ether. The combined organic layers
water-washed, re-extracted with 10% H2SO4, neutralized with 10%
NaOH and re-extracted with diethyl ether. The organic layer was
successively water-washed, dried over MgSO4 and evaporated
under vacuum to obtain an oily compound (mixture of two isomers)
which was passed from silica gel column chromatography to afford
white solid compound (IV, 2 g, 54% yield) (m.p. 135 ˚C).
2.3.2. Behavioral studies
2.3.2.1. Formalin-Induced Nociceptive Behavior
Formalin test was carried out to evaluate the antinociceptive
effects of PCP and its new derivatives against inflammatory pain
[22]. Fifty-eight male Wistar albino rats, weighing 250 to 300g,
were placed individually in an open Plexiglas chamber
(35ꢀ35ꢀ35cm3) with a mirror angled at 45º below position to allow
2.2.10. 1-(2-hydroxy-1-p-tolyl-cyclohexyl)-piperidine-4-ol (V)
A mixture of 2.444g (0.014mol) of 10 and 14.4g (0.14mol) 4-
piperidinol in ethylene glycol (50ml) was refluxed for 16 hours. It
MgBr
MgCl
OH
Br
Cl
N
(1)
Mg, Ether
I2
Ether, Tuloene
(I)
OH
CH3
CH3
CH3
(1)
Mg, Ether
I2
Ether,Tuloene
N
OH
(II)
OH
CH3
OH
N
(2)
Ether,Tuloene
(III)
Scheme 3. Synthesis of compounds I-III.

766 Current Medicinal Chemistry, 2012 Vol. 19, No. 5
Ahmadi et al.
pretreated with phencyclidine and its various derivatives and i.p.
injection of the compounds. Thirty minutes later, acetic acid (0.6%
v/v, 10 mg/kg) was i.p. injected before the mice were placed in an
observation box. The intensity of nociceptive behaviors was
quantified by counting the total number of writhes between 0 and
30 min after acid acetic injection. The writhing responses consisted
of contraction of the abdominal muscles.
O
MgBr
H2SO4
Ether
+
OH
CH3COOH
(3)
CH3
(4)
2.3.2.3. Statistical Analysis
CH3
Nociception in animals was determined by counting the number
of writhings in Writhing test and the pain scores in Formalin test. In
Formalin test, the overall change sin pain score were evaluated by
obtaining the area-under-the-curve (AUC) of pain scores. To
compare the pain scores changes in control and treated rats in
Formalin test, a two-way analysis of variance (ANOVA) was
conducted. For comparing AUCs of pain scores in Formalin test
and fluctuation in the number of writhing in Writhing test, one-way
ANOVA followed by Tukey’s test of multiple comparisons were
applied. Statistical analysis was performed using Graph Pad Prism
5 (Graph Pad Software Inc.) under the level of p<0.05 statistical
significance.
O
MgBr
CH3
H2SO4
Ether
+
OH
CH3COOH
(5)
Scheme 4. Synthesis of intermediates 3-6.
(6)
an unobstructed view of the paws by the researchers. The animals
were habituated to the observation chamber for 30 minutes prior to
the experimental sessions. Formalin solutions were prepared at
2.5% in saline from a formalin stock (Sigma, St. Louis, USA) and
injected intradermally (i.d.) to right hind paw of rat in a volume of
50 ꢀl with a 27-gauge needle (the formalin stock corresponds to a
37% formaldehyde solution). Observations to determine
nociceptive responses began upon placing the rats into the box and
continued for the following 60 minutes. A nociceptive score was
determined for every 5-minute block by measuring the amount of
time spent in every four behavioral categories (0=the position and
posture of the injected hind paw was indistinguishable from the
contra lateral paw; 1=the injected paw had little or no weight placed
on it; 2=the injected paw was elevated with no contact with any
surface; 3=the injected paw was licked, bitten or shaken). Then, a
weighted nociceptive score, ranging from 0 to 3, was calculated by
multiplying the time spent in every category by the category
weight, summed and divided by the total time spent (300seconds)
for every 5-minute block. Separate groups of rats (n=7-8 rats per
group) received various derivatives of Phencyclidine (10mg/kg) or
saline, 30 min prior to formalin injection.
3. RESULTS
3.1. Chemistry
Phencyclidine (I), 2-phenyl-2-piperidine-1-yl-cyclohexanol
(IV) and some of their new analogues (3-methyl-4-(1-piperidin-1-
yl-cyclohexyl)-phenol (II), 1-[1-(4-hydroxy-2-methyl-phenyl)-
cyclohexyl]-piperidin-4-ol (III) and 1-(2-hydroxy-1-p-tolyl-
cyclohexyl)-piperidine-4-ol (V)) were synthesized by the reaction
of substituted Grignard reagent with carbonitrile compounds, or by
addition of NBA to arylalkenes to produce aryl bromohydrin
cyclohexanes compounds and potassium t-butoxide to produce aryl-
1,2-epoxycyclohexanes [24]. Addition of piperidine or 4-
piperidinol to the phenyl or p-tolyl-1,2-epoxycyclohexanes (8 and
10) yielded the desired compounds (IV and V) [16-21].
Demonstrated in literature on this family of compounds [8-10,
12, 13], the incorporation of methyl group to the aromatic ring of
the molecule generates some pronounced effects on electron
distribution and dipole moments due to its high electron donating
character [14]. In addition, the hydroxyl group with high
hydrophilic, polarity, and solubility properties [15] produces more
analgesic effects on this family [8, 10, 13]. Therefore, as it was
anticipated, compounds II, III, and V showed more antinociception
effects, relative to control and phencyclidine groups.
2.3.2.2. Acetic Acid-Induced writhing in Mice
Visceral chemical antinociception was evaluated with Writhing
test [23]. Separate groups of mice (9-10 mice per group) were
NBA
OH
Pyridine
O
OH
Br
(4)
(7)
(8)
CH3
(IV)
CH3
CH3
OH
H3C
NBA
OH
4-Piperidinol
O
OH
Br
(9)
(6)
(10)
(V)
Scheme 5. Synthesis of intermediates 7-10 and compounds IV and V.

Phencyclidines Antinociceptive Behaviors
Current Medicinal Chemistry, 2012 Vol. 19, No. 5
767
A
B
2.5
2.5
2.0
1.5
1.0
0.5
0.0
2.0
1.5
1.0
0.5
0.0
0
0
0
5
5
5
10 15 20 25 30 35 40 45 50 55 60
Time (min)
0
5
10 15 20 25 30 35 40 45 50 55 60
Time (min)
C
D
2.5
2.0
1.5
1.0
0.5
0.0
2.5
2.0
1.5
1.0
0.5
0.0
0
5
10 15 20 25 30 35 40 45 50 55 60
Time (min)
10 15 20 25 30 35 40 45 50 55 60
Time (min)
E
2.5
2.0
1.5
1.0
0.5
0.0
10 15 20 25 30 35 40 45 50 55 60
Time (min)
Fig. (1). Compared changes in pain scores during 60 min after i.d. injection of phencyclidine and its various derivatives (10 mg/kg) consisted of compound IV
(A), compound V (B), compound II (C), compound I (D), and compound III (E) with control group that received vehicle (saline). Every data point represents
mean±S.E.M. of 7-8 rats.
Spectroscopic data (IR, 1H and 13C NMR, Mass) confirmed the
structure of the compounds 7-10, II, III and V. The melting points
of the known compounds also confirmed their identity. The purity
of every compound was checked by TLC with ethyl acetate-hexane
as the eluent.
revealed a significant decrease in AUC of pain scores in rats treated
with V (p<0.001), II (p<0.05), and III (p<0.001) compared to
control group. No significant variations in AUC of pain score were
observed in rats pretreated with drug no.4 (I) (phencyclidine)
compared to control group (Fig. 2). In addition, V also showed
significant decrease in AUC of pain scores compared to I in
pretreated group (p<0.01).
3.2. Pharmacology
3.2.1. General Consideration
100
Mortality (number of death), morbidity (abnormal condition or
behavior due to a disorder), irritability (aggressiveness or increased
response on handling) and other related abnormal states were not
observed in the experimental animals. However, the motor
coordination index (measured by Rota-rod apparatus, Harvard, UK)
did not indicate any significant differences among the treated rats or
mice (data not shown).
*
80
60
40
20
0
++
***
***
3.2.2. Effect of Phencyclidine and its Derivatives on Pain Related
Behavior of Rats in Formalin Test
Intradermal injection of formalin into dorsal surface of hind
paw produced a biphasic pain related behavior in rats (Fig. 1). Two-
way ANOVA revealed a significant effects of treatment for V [F
(1,144) =53.45, p<0.0001; Fig. 1B], II [F(1,144)=8.788, p=0.0118;
Fig. 1C], and III [F(1,144)=23.37, p=0.0004; Fig. 1E]. Moreover,
one-way ANOVA revealed a significant difference in the AUC of
pain scores for various compounds [F (5,42) = 8.445, p<0.0001;
Fig. 2]. Further analysis with Tukey’s multiple comparison test,
Control
I
II
III
IV
V
Fig. (2). Changes in the AUC of pain scores in Formalin test. Rats were
pretreated with vehicle (control group), phencyclidine (I, 10 mg/kg), or
phencyclidine derivatives (II-V; 10 mg/kg) 30 min before Formalin test.
Bars represent mean+S.E.M of 7-8 rats. * p<0.05, ** p<0.01, *** p<0.001
significant difference compared to control group. ++ p<0.01, significant
differences compared to phencyclidine (I) treated group.

768 Current Medicinal Chemistry, 2012 Vol. 19, No. 5
Ahmadi et al.
3.2.3. Effect of Phencyclidine and its Derivatives on Pain Related
Behavior of Rats in Writhing Test
aromatic rings of I, these new drugs (II, III and V) have a
noticeable lipophilic-hydrophilic ratio which helps to produce more
analgesic effects, compared to control and PCP groups especially
for compound V. In comparison, it seems incorporation of
hydrophilic group (OH) on cyclohexane ring of I (compound IV)
alone is an inefficient factor in producing better pain relief
properties. Adding this group to piperidine and phenyl rings in
As shown in Fig. (3), One-way ANOVA revealed a significant
change in the number of writhings for experimental groups
[F(6,49)=12.19, p<0.0001]. Further analysis with Dunnett’s
multiple comparison test revealed a significant decrease in number
of writhings for the mice pretreated with IV (P<0.01), V (p<0.001),
II (p<0.001), and III (p<0.01) compared to the control group. No
significant change in the number of writhing was observed in rats
pretreated with drug no. 4 (I) (phencyclidine), with the same dosage
of the other compounds (Fig. 3).
addition
of
methyl
group
on
aromatic
moiety
(compound III), similar to compound II (with only these groups in
phenyl ring together), could produce more analgesic effects
compare to compound IV. Also for compound V, a strong position
of the groups (methyl group on aromatic ring with good lipophilic
effects and two hydroxyl groups on every cyclohexane and
piperidine rings) was traced with no steric hindrance, which could
cause to producing a new drug with an excellent receptor
antagonistic property for decreasing pain.
100
80
+
**
In addition, because it was reported that NMDA receptors,
especially NR2B-containing receptor subtypes, had a key role in
reliving pain [29, 30], it demonstrated a central mechanism(s) for
the mentioned effects via antagonizing the NMDA receptors on
pain modulatory center periaqueductal gray. Therefore it was
concluded the newly synthetic drugs (compounds II, III and V)
could yield more antinociception effects and they could act through
central and peripheral analgesic mechanism(s), respectively.
++
***
**
60
40
20
0
+++
***
5. CONCLUSION
Control
I
II
III
IV
V
It was concluded that these new synthesized derivatives (II, III
and V) of PCP, produced more analgesic effects in Formalin and
Writhing tests compared to control and phencyclidine groups,
especially for compound V with higher electron donating, lipophilic
and hydrophilic properties which could substantially and
respectively diminish inflammatory and visceral pains.
Fig. (3). Compared number of writhings after i.p. administration of acetic
acid in mice in experimental groups. Animals in every group was pretreated
with vehicle (control group), phencyclidine (I, 10 mg/kg), or phencyclidine
derivatives (II-V; 10 mg/kg) 30 min before writhing test. Bars represent
mean+S.E.M. of 9-10 mice.
** p<0.01, *** p<0.001 significant difference compared to control group. +
p<0.05, ++ p<0.01, +++ p<0.001 significant differences compared to
phencyclidine (I) treated group.
ACKNOWLEDGEMENTS
The authors would like to appreciate Dr. Natasha Q. Pourdana,
the CamTESOL certified editor, for her attempts in proofreading
the initial drafts of this article. We are also indebted to the Islamic
Azad University, Karaj Branch-Iran for its financial supports to
accomplish this research project.
4. DISCUSSION
Phencyclidine was originally developed to be used in humans
as an anesthetic in 1959, but soon it was restricted due its
psychotomimetic effects which included prolonged thoughts and
visual disturbances and agitation [25]. Consequently, the focus of
research on PCP shifted from its application as an anesthetic
compound toward potential application as a neuropharmaceuticals
[26]. Furthermore, the search on noncompetitive NMDA
antagonists was substantially assisted through the development of a
reliable binding assay. To date, a considerable number of PCP
derivatives has been synthesized and assayed as substrates for the
PCP binding site [27, 28].
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Received: October 25, 2011
Revised: December 07, 2011
Accepted: December 09, 2011