New morpholine analogues of phencyclidine: Chemical synthesis and pain perception in rats

Article abstract of DOI:10.1016/j.pbb.2010.12.019

Phencyclidine (PCP, I) and most its derivatives have demonstrated some pharmacological effects. Accordingly, in this study, the new methoxy (III) and hydroxy-methyl (IV) morpholine PCP derivatives were synthesized. The acute and chronic pain activities of these drugs (III, IV) were investigated by tail immersion and formalin tests on rats and the results were compared with those in PCP, PCM (PCP-morpholine, II), and methyl-PCM (V). Findings indicated that III (6 mg/kg, i.p.) generates more analgesic effects in tail immersion test in comparison with I and II in 20, 40, 45 and 55 min post-injection. These effects were observed in 10, 20, 40, 45 and 50 min after the application of IV (at the same dosage). This analgesic effect was markedly seen in 20, 40, 45 and 50 min after compound IVs application in comparison with the drugs (I-V). In formalin test analysis, the acute chemical pain (Phase I) could not be affected by any drugs (I-V) while chronic formalin pain would be diminished by these new synthesized drugs (III and IV), especially in late Phase II, compared to I and II at the dosage of 6 mg/kg. It is, therefore, concluded that these new synthesized PCP derivates including methoxy-PCM (III) and hydroxy-methyl-PCM (IV) could substantially and respectively diminish acute thermal and chronic chemical pains.

Full text of DOI:10.1016/j.pbb.2010.12.019

Pharmacology, Biochemistry and Behavior 98 (2011) 227–233
Contents lists available at ScienceDirect
Pharmacology, Biochemistry and Behavior
journal homepage: www.elsevier.com/locate/pharmbiochembeh
New morpholine analogues of phencyclidine: Chemical synthesis and pain
perception in rats
b
c
a
Abbas Ahmadi a, , Mohsen Khalili , Ramin Hajikhani , Moslem Naserbakht
⁎
a
Department of Chemistry, Faculty of Science, Islamic Azad University, Karaj Branch- Karaj, Iran
Department of Physiology, Neuroscience and Herbal medicine research centers Shahed University, Tehran, Iran
Department of Physiology, Faculty of Science, Islamic Azad University, Karaj Branch- Karaj, Iran
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 4 August 2010
Received in revised form 14 December 2010
Accepted 19 December 2010
Available online 6 January 2011
Phencyclidine (PCP, I) and most its derivatives have demonstrated some pharmacological effects. Accordingly,
in this study, the new methoxy (III) and hydroxy-methyl (IV) morpholine PCP derivatives were synthesized.
The acute and chronic pain activities of these drugs (III, IV) were investigated by tail immersion and formalin
tests on rats and the results were compared with those in PCP, PCM (PCP-morpholine, II), and methyl-PCM
(V). Findings indicated that III (6 mg/kg, i.p.) generates more analgesic effects in tail immersion test in
comparison with I and II in 20, 40, 45 and 55 min post-injection. These effects were observed in 10, 20, 40, 45
and 50 min after the application of IV (at the same dosage). This analgesic effect was markedly seen in 20, 40,
45 and 50 min after compound IV's application in comparison with the drugs (I–V). In formalin test analysis,
the acute chemical pain (Phase I) could not be affected by any drugs (I–V) while chronic formalin pain would
be diminished by these new synthesized drugs (III and IV), especially in late Phase II, compared to I and II at the
dosage of 6 mg/kg. It is, therefore, concluded that these new synthesized PCP derivates including methoxy-
PCM (III) and hydroxy-methyl-PCM (IV) could substantially and respectively diminish acute thermal and
chronic chemical pains.
Keywords:
Phencyclidine
Methoxy-morpholine derivative
Hydroxyl-methyl derivative
Pain activities
Tail immersion test
Formalin test
© 2010 Elsevier Inc. All rights reserved.
1. Introduction
competitive, ‘open channel blockers’ of the NMDA receptor (Honey
et al., 1985). However, different receptors in the central nervous
1-(1-phenylcyclohexyl) piperidine (Phencyclidine, CAS 77-10-1,
PCP, I) is a synthetic drug with outstanding physiological properties.
It is initially synthesized in the early 1950 s as a potential surgical
anesthetic. PCP allows patients to enter into a trance-like state in
which the ‘perception’ of pain could be separated from the ‘sensation’
of pain, a state that has been termed ‘dissociative anesthesia’ (Erard
et al., 1980). It is also a non-competitive N-methyl-D-asparate (NMDA)
receptor antagonist, which has been demonstrated to produce
psychotomimetic effects on humans, but it is a widely abused drug
(Mori et al., 2001). Phencyclidine and its derivatives influence the
central nervous system and display analgesic, stimulant, depressant,
and hallucinogenic effects due to the existence of specific binding sites
in the brain (Al-deeb, 1994; Ahmadi and Mahmoudi, 2006).
PCP binds into the N-methyl-D-asparate (NMDA) receptor complex
and blocks NMDA-mediated gating of the calcium channel conduc-
tance (Kapur and Seeman, 2002; Olney et al., 1991). They are classified
with many behavioral effects in common with other phencyclidine-
like drugs including anaesthetics, antinociceptives, psychotomimetics,
anticonvulsants, neuroprotectives and amnesic drugs concern to non-
system are involved in the modulation of behavioral effect of PCP and
its analogues.
Many PCP derivatives (with changes in substitution on the
molecule) have been synthesized and their pharmacological activities
have been tested in recent years (Al-deeb, 1996; Ogunbadeniyi and
Adejare, 2002; Ahmadi and Mahmoudi, 2005). 1-[1-[2-methoxyphenyl]
[cyclohexyl] morpholine (methoxy-PCM, III) and 1-[1-[4-hydroxy-2-
methylphenyl] [cyclohexyl] morpholine, (hydroxy-methyl-PCM, IV) as
new analogues of I, have been synthesized in this study. Methoxy and
hydroxyl-methyl groups were added to the aromatic ring and morpho-
line group instead of the piperidine ring of the molecule to examine
analgesic effects on rats using the tail immersion (as a model of acute
thermal pain) and the formalin (as a model of acute chemical and
chronic pain) tests. The results were compared with PCP and PCM (1-[1-
phenylcyclohexyl] morpholine, CAS 2201-40-3, PCP-morpholine, II)
and methyl-PCM (1-[1-[4-methylphenyl][cyclohexyl] morpholine, V)
(Ahmadi et al., 2010; Ahmadi et al., 2011).
As it was revealed in previous works (Ahmadi et al., 2009; Ahmadi
et al., 2010) with this family of compounds, the incorporation of
methyl and methoxy groups to the aromatic ring of the molecule
would generate pronounced effects on electron distribution and dipole
moments because of their high electron donating characters (Johnson
et al., 1981). The same have been applied to the incorporation of
⁎
Corresponding author. Department of Chemistry, Faculty of Science, Islamic Azad
University, Karaj Branch, P.O. Box: 31485-313, Karaj, Iran.
E-mail address: abbas_ahmady_3957@yahoo.com (A. Ahmadi).
0091-3057/$ – see front matter © 2010 Elsevier Inc. All rights reserved.
doi:10.1016/j.pbb.2010.12.019

228
A. Ahmadi et al. / Pharmacology, Biochemistry and Behavior 98 (2011) 227–233
morpholine, with many pharmacological behaviors (Beckett and
Kourounakis, 1976; Chen et al., 2003), and analgesic properties
(Beckett and Kourounakis, 1976). In addition, the hydroxyl group
with high hydrophilic, polarity, and solubility properties (Shebley
et al., 2006) may produce more analgesic effects in this family. Also,
to increase the low potency (Soine, 1986; Budd, 1981) of PCM,
compared to PCP, these changes are applied to the PCM molecule in
anticipation of producing the pronounced effects on the activity of
the new synthesized drugs (III and IV) in the current study.
2. Materials and method
2.1. General
Cyclohexanone, piperidine, bromo benzene, magnesium turning,
diethyl ether, 4-bromo toluene, morpholine, 2-bromo anisole, 4-
chloro-3-methyl phenol and all other chemicals were purchased from
Merck Chemical Co. (Darmstadt, Germany). Later, the melting points
(uncorrected) were determined using a digital Electrothermal melting
point apparatus (model 9100, Electrothermal Engineering Ltd., Essex,
UK). 1H and 13C NMR spectra were recorded on Bruker 300 MHz
(model AMX, Karlsruhe, Germany) spectrometer (internal reference:
TMS). IR spectra were recorded on a Thermo Nicolet FT-IR (model
Nexus-870, Nicolet Instrument Corp., Madison, Wisconsin, USA)
spectrometer. Mass spectra were recorded on an Agilent Technology-
5973 Mass Selective Detector (MSD) spectrometer (Wilmington, USA).
Column chromatographic separations were performed over Acros silica
gel (No. 7631-86-9 particle size 35–70 micrometer, Geel, Belgium).
Adult female rats (at Pasteur's Institute, Tehran, Iran), weighing 250–
300 g were used for the pharmacological testing.
Scheme 1. Structure formulas of PCP (I), PCM (II), methoxy-PCM (III), hydroxy-
methyl-PCM (IV), methyl-PCM (V) and carbonitrile intermediates 1 and 2.
2.2. Preparations (Schemes 1–3)
2.2.1. 1-Piperidinocyclohexanecarbonitrile, PCC (1)
1-morpholinocyclohexanecarbonitrile (2) in an organic solvent to a
refluxing solution of 4-tolyl magnesium bromide (prepared from
8.55 g 4-bromotoluene and 1.22 g of Mg in 20 ml of dry ether). The
hydrochloride salt of I (m.p. 183–184 °C) was prepared using diethyl
ether and HCl, and it was recrystallized from 2-propanol.
This compound was prepared in an organic solvent based on a
published method (Geneste et al., 1980) from 4-piperidinol, cyclohex-
anone and KCN with a yield of 77% (m.p: 113–114 °C), IR: 2222 cm1−
,
C`N, str.
2.2.2. 1-Morpholinocyclohexanecarbonitrile, MCC (2)
2.2.6. 1-[1-[2-methoxylphenyl][cyclohexyl] morpholine (methoxy-PCM)
(III)
This compound was prepared according to a published method
(Abdol-Rahman et al., 1975; Geneste et al., 1980) from morpholine,
cyclohexanone and KCN with a yield of 81.5% (m.p: 41–43 °C), IR:
A solution, containing 3.84 g (0.02 mol) of nitrile compound (MCC,
2) in the mixture of dry diethyl ether and THF (1:1), was added to a
refluxing solution of 2-anisol magnesium bromide (Grignard
reagent), which was prepared from 9.35 g of 2-bromo anisole and
1.22 g of Mg in 20 ml of dry ether. It was refluxed for 10 additional
hours and was left overnight at ambient temperature (25 °C) and was
subsequently poured into ice-NH4Cl. The organic layer was separated
and washed with water and the base was neutralized with 10% of
2220 cm1− C`N, str.
,
2.2.3. 1-[1-phenylcyclohexyl] piperidine (PCP) (I)
This compound was prepared in a 58% yield based on a published
method (Maddox et al., 1965) from adding a solution of 1-
piperidinocyclohexanecarbonitrile (1) in an organic solvent to a
refluxing solution of phenyl magnesium bromide (prepared from 79 g
bromobenzene and 12.3 g of Mg in 200 ml of dry ether). The
hydrochloridesalt of I (m.p. 233–234 °C)wasprepared using 2-propanol
and HCl, and it was recrystallized from 2-propanol.
2.2.4. 1-[1-phenylcyclohexyl] morpholine (PCM) (II)
This compound was prepared in a 70.6% yield based on a published
method (Maddox et al., 1965) from adding a solution of 1-
morpholinocyclohexanecarbonitrile (2) in an organic solvent to a
refluxing solution of phenyl magnesium bromide (prepared from
7.85 bromobenzene and 1.22 g of Mg in 20 ml of dry ether). The
hydrochloride salt of II (m.p. 187–188 °C) was prepared using diethyl
ether and HCl, and it was recrystallized from 2-propanol.
2.2.5. 1-[1-[4-methylphenyl][cyclohexyl] Morpholine (V)
This compound was prepared in a 68.7% yield based on a
published method (Ahmadi et al., 2010) from adding a solution of
Scheme 2. Synthesis of intermediates 1 and 2.

A. Ahmadi et al. / Pharmacology, Biochemistry and Behavior 98 (2011) 227–233
229
Scheme 3. Synthesis of target compounds I–V.
H2SO4, washed with 20% of NaOH, reextracted with n-hexane, and it
was dried and concentrated. The pale solid compound was obtained,
which was passed through a silica gel column using ethyl acetate-
hexane (95:5) as the eluent to afford 3.9 g of III (41% yield).
The hydrochloride salt of III (m.p. 167–169 °C) was prepared using
diethyl ether and HCl, and it was recrystallized from 2-propanol.
layer was separated and washed with water and the base was
neutralized with 10% of H2SO4, washed with 20% of NaOH, reextracted
with n-hexane, and it was dried and concentrated. The pale solid
compound was obtained, which was passed through a silica gel
column using ethyl acetate-hexane (95:5) as the eluent to afford 1.3 g
(38% yield) of IV (m.p. 38-39.3).
IR (KBr): 2932, 2852, 1596, 1491, 1455, 1263, 1240, 1118, 804 cm-1
.
The hydrochloride salt of IV (m.p. 181–182 °C) was prepared using
diethyl ether and HCl, and it was recrystallized from 2-propanol.
IR (KBr): 3377, 2937, 2861,2823, 1580, 1455, 1276, 1119, 1034, 802
1H N.M.R. (CDCl3) (p.p.m.): 1.2–1.92 (10 H, m), 2.33–2.6 (4 H, m),
3.62–3.65 (4 H, m),3.79 (3 H, s), 6.8–7.4 (4 H, m).
13C N.M.R. (CDCl3) (p.p.m.): 25.7, 26, 32.6, 51.3, 56.1, 67.3, 75.4, 112,
120.7, 126.9, 127.5, 134.5, 161.2.
cm-1
.
1H N.M.R. (CDCl3) (p.p.m.): 1.2–1.98 (10 H, m), 2.1–2.5 (4 H, m), 2.6
(3 H, s), 3.70–3.73 (4 H, m), 5.78 (1 H, s), 6.9–7.66 (4 H, m).
13C N.M.R. (CDCl3) (p.p.m.): 19.7, 25.7, 26, 32.6, 51.3, 67.3, 78.8,
112.6, 117.2, 127.8, 131.7, 135.7, 154.1.
MS: m/z (regulatory intensity): 275 (80).
2.2.7. 1-[1-[4-Hydroxy-2-methylphenyl][cyclohexyl] morpholine
(hydroxy-methyl –PCM) (IV)
MS: m/z (regulatory intensity): 275 (11).
A solution, containing 3.84 g (0.02 mol) of nitrile compound (MCC,
2) in the mixture of dry diethyl ether and THF (1:1), was added to a
refluxing solution of 4-hydroxy-2-methylphenyl magnesium chloride
(Grignard reagent) which was prepared from 10.70 g of 4-chloro-3-
methyl phenol and 1.22 g of Mg in 20 ml of dry ether and it was
refluxed for 15 additional hours. It was left overnight at ambient
temperature (25 °C) and was then poured into ice-NH4Cl. The organic
2.3. Pharmacological methods
Adult female rats (at Pasteur's Institute, Tehran), weighing 250–
300 g at the beginning of the experiment were randomly housed.
There were three to four of them per cage in a temperature-controlled
colony room under light/dark cycles. The animals were given free

230
A. Ahmadi et al. / Pharmacology, Biochemistry and Behavior 98 (2011) 227–233
access to water and standard laboratory rat chow (supplied by Pars
Company, Tehran, Iran). All behavioral experiments were carried
out between 11 a.m. and 4 p.m. under normal room light and at the
25 °C temperature. All animals were injected by an investigator and
were evaluated by another. The study was carried out in accordance
with the guidelines set forth in the Guide for the ‘Care and Use of
Laboratory Animals’ (NIH) and those of the ‘Research Council of
Shahed University of Medical Sciences’ (Tehran, Iran).
the desired compounds. The reaction between Grignard reagents and
carbonitriles was slow and incomplete. Therefore, to overcome this
limitation, molar ratio of Grignard reagents to carbonitriles was
increased. This higher ratio could also help the reaction between Mg
and hydroxyl substituted phenyl (IV) to form the Grignard reagent,
without protecting hydroxyl group by trimethylchlorosilane, which
has been applied previously (Itzhak et al., 1981). Even then, still
significant quantities of unreacted carbonitrile were present in the
reaction products and the yield was low. Long reaction times were then
resorted, but these alternatives caused problems such as the formation
of side products. The mechanism of the reaction seems to explain the
formation copious amounts of side products. Nitrile, which is an efficient
leaving group, could be easily removed from the quaternary carbon of
the carbonitrile, particularly given the effects of neighboring nitrogen on
stabilizing resulting tertiary carbocation. The SN1 attack of the Grignard
reagent on the carbocation is complicated by the neighboring piperidine
and morpholine, which can form an enamine or imine. The reactivity
of these groups could contribute significantly to the formation of side
products observed (Ahmadi et al., 2009).
2.3.1. Tail immersion test
The acute thermal pain was modeled by the tail immersion test
(Ramabadran et al., 1989; Molina et al., 1994). Thirty minutes after an
i.p. injection of drugs, (PCP, PCM, methyl-PCM, methoxy-PCM and
hydroxy-methy-PCM, 6 mg/kg; dissolved in saline), the rats (n=12 in
each group) were housed in an animal restrainer (in control group
saline as vehicle were applied). Then, the terminal 5 cm of their tails
were first submerged into the water temperature room (22~24 °C) to
check the aversion to water and were then immersed into the 54 °C
water. The reaction time between immersing the tail and its removal
from heated water was measured. Cut-off latency in 15 s was
employed to avoid damaging the tail (Hamura et al., 2000).
Spectroscopic data (IR, 1H and 13C NMR, mass) confirmed the
structure of the compound III and IV. The melting points of the known
compounds also confirmed their identity. The purity of each compound
was checked by TLC using ethyl acetate-hexane as the eluent.
2.3.2. Formalin test
The formalin test has been introduced by (Dubuisson and Dennis
(1977). In this test, the formaldehyde solution (50 μl, 2.5%) was
injected subcutaneously into the plantar surface of the hind paw.
Then, the animal was placed in a Plexiglas chamber (30×30×30 cm3),
with a mirror placed at the 45° angle underneath for accurate
observation. In the treatment groups, the drugs (PCP, PCM, methyl-
PCM, methoxy-PCM and hydroxy-methy-PCM, 6 mg/kg; dissolved
in saline) were administered intraperitoneally 30 min prior to the
formaldehyde injection (in control group saline as vehicle were
applied). Before the experiment, all animals were brought to the test
chamber five times at 5-min intervals in order for them to be adapted
to the environment. The behavioral pain reactions, due to formalin
injection, were detected and recorded for 1 h. The first 15 min after
formalin injection is known as the early (I) or acute chemical phase,
and the period between 15 and 60 min is known as the second (II) or
the chronic phase. However, the chronic phase can be divided into the
initial (15–40 min) and the late (40–60 min) periods.
3.2. Pharmacology
3.2.1. General consideration
Mortality (number of death), morbidity (defined as any abnormal
condition or behavior due to a disorder), irritability (a condition of
aggressiveness or increased response on handling) and other related
abnormal states have not been observed in the experimental animals.
However, the motor coordination index (measured by Rota-rod
apparatus, Harvard, UK) did not indicate any significant difference
among the treated rats.
3.2.2. The analgesic activity of PCP (I), PCM (II), methoxy-pcm (III),
hydroxy-methyl-PCM (IV) and methyl-PCM (V) hydrochloride with tail
immersion test
The intraperitoneal injection of PCP (I), PCM (II), methoxy-PCM
(III), hydroxy-methyl-PCM (IV) and methyl-PCM (V) with the dosage
of 6 mg/kg generated analgesic effects in the tail immersion test. The
results indicated that III can generate more analgesic effects in the
tail immersion test (as a model of acute thermal pain) in comparison
with PCP and PCM, especially in 20, 40, 45 and 55 min after the
drug injection (Fig. 1). These effects were seen 10, 20, 40, 45 and
50 min after the application of hydroxy-methyl-PCM (IV, with the
3. Results
3.1. Chemistry
Phencyclidine, 1-[1-phenylcyclohexyl] morpholine, 1-[1-[2-
methoxylphenyl] [cyclohexyl] morpholine, 1-[1-[4-hydroxy-2-
methylphenyl][cyclohexyl] morpholine, and 1-[1-[4-methylphenyl]
[cyclohexyl] morpholine (I–V) were synthesized by the reaction of
substituted Grignard reagent and carbonitrile compounds. The addition
of methyl and methoxy groups to the aromatic ring (having high
electron donating, electron distribution, and dipole moments charac-
ters) and hydroxyl group (with strong hydrophilic, polarity, and
solubility properties) introduced more analgesic effects to this
family (Johnson et al., 1981; Al-deeb, 1994; Ahmadi et al., 2009). In
addition, the incorporation of morpholine group, with substantial
pharmacologicaland analgesic properties (Rekka et al., 1990; Chen et al.,
2003) of its derivatives, is induced to have pronounced effects on our
new synthesized [III and IV] drugs' activity. The known procedures with
appropriate modifications were applied in thesynthesis of compounds I,
II, V, 1, and 2 (Maddox et al., 1965; Abdol-Rahman et al., 1975; Geneste
et al., 1980).
PCP
PCM
MethoxyPCM
Saline
8
7
6
5
4
3
2
1
0
2
5
10 15 20 25 30 35 40 45 50 55
Time (Min)
Bromobenzene and its methoxy (III), hydroxyl-methyl (IV), and
methyl (V) derivatives were reacted with magnesium to form Grignard
reagents whichwerethen reacted with piperinocyclohexanecarbonitrile
(PCC, 1) and morpholinocyclohexanecarbonitrile (MCC, 2) to form
Fig. 1. Mean tail immersion test (s) in animals receiving PCP (I), PCM (II) and Methoxy-
PCM (III) hydrochloride. The bars in each line represent mean SEM of tail withdrawal
latency (s) in 12 animals.

A. Ahmadi et al. / Pharmacology, Biochemistry and Behavior 98 (2011) 227–233
231
3
10
9
8
7
6
5
4
3
2
1
0
PCP
Saline
PCP
PCM
MethoxyPCM
PCM
*
HydroxyPCM
Saline
*
2.5
2
*
*$
1.5
1
0.5
0
2
5
10 15 20 25 30 35 40 45 50 55
Phase I
Initial phase II
Late phase II
Time (Min)
Fig. 4. Comparison of the acute chemical and chronic formalin pain in PCP (I), PCM (II)
and methoxy-PCM (III) hydrochloride animal groups. Bars show the mean SEM of
pain score. As indicated, administration of the III had no effect in acute chemical pain
(phase I) in comparison with I and II, but the initial and late phases of chronic pain
could be significantly reduced by following the administration of PCM and especially
compound III in late phase. n=12 in each experimental group. * and $ (pb0.05) show
the difference between control (saline) and PCM groups, respectively.
Fig. 2. Mean tail immersion test (s) in animals receiving PCP (I), PCM (II) and hydroxy-
methyl-pCM (IV) hydrochloride. The bars in each line represent mean SEM of tail
withdrawal latency (s) in 12 animals.
same dosage) (Fig. 2). Meanwhile, this analgesic effect was markedly
observed in 20, 40, 45 and 50 min after the compound IV application
in comparison with drugs (I–V) (Fig. 3). Therefore, it seems that the
strong electron donating property of the methoxy and methyl groups;
the hydrophilic, polarity, and solubility properties of hydroxyl group
on phenyl ring; and also morpholine instead of piperidine rings
(Beckett and Kourounakis, 1976; Shebley et al., 2006), facilitated more
binding to the NMDA receptor complex and could increase the tail
immersion latencies in comparison with other drugs, as anticipated.
The difference between the tail immersion latencies was evaluated
utilizing the analysis of variance method (ANOVA).
4. Discussion
Phencyclidine is well absorbed by all routes of administration. The
intravenous administration results, in a very rapid (in seconds) onset
of action with peak effect, were reached after 10 min (Mozayani,
2003).Interestingly; studies on a single bolus of PCP in rats have
shown that the peak PCP concentration in the brain occurs in 30 s. This
apparent contradiction with the onset of peak effects is probably
due to the fact that the serum level decreases 30 times faster than the
brain concentration. Thus, the drug reaches a peak at 30 s, but it tends
to remain in the brain for a longer duration of time than the blood
levels would indicate.
Various animal models of nociception have been used to charac-
terize the specific pain conditions in human beings. For example, tail
immersion, tail flick, and hot plate experiments evaluated analgesic
effects on acute coetaneous thermal pain; and intraplantar injections
of formalin, Zymosan, and carrageenan are also the models of chemical
acute and chronic pain (Dougherty and Staats, 1999).
3.2.3. The analgesic activity of PCP (I), PCM (II), methoxy-PCM (III),
hydroxy-methyl-PCM (IV) and methyl-PCM (V) hydrochloride with
formalin test
The drugs (I–V) were administered intraperitoneally with the
dosage of 6 mg/kg, 30 min before the formaldehyde injection. The
results showed that III and IV were not effective for acute formalin
chemical pain similar to other drugs (Figs. 4 and 5). However, the
chronic formalin pain (phase II) could significantly be attenuated
using IV and III compared to PCP and PCM, and the later derivative
(III) was more effective in the late phase of the chronic pain compared
to other drugs (Fig. 6). The difference in the pain scores was evaluated
using the analysis of variance method (ANOVA).
The analgesic activities of new synthesized analogues of PCP
(III, IV) with the changes in substitution on its phenyl (with methoxy
and hydroxyl-methyl groups) and replacing of piperidine with morpho-
line rings were evaluated by tail immersion and formalin tests in this
paper.
3
2.5
2
Saline
PCP
PCM
HydroxyPCM
PCP
PCM
MethoxyPCM
MethylPCM
HydroxyPCM
Saline
*
10
9
8
7
6
5
4
3
2
1
0
*
*
1.5
1
0.5
0
Phase I
Initial phase II
Late phase II
Fig. 5. Comparison of the acute chemical and chronic formalin pain in PCP (I), PCM (II)
and hydroxy-methyl-PCM (IV) hydrochloride animal groups. Bars show the mean SEM
of pain score. As indicated, administration of the IV had no effect in acute chemical
pain (phase I) in comparison with I and II, but the initial and late phases of chronic pain
could be significantly reduced by following the administration of PCM and especially
compound IV in late phase. n=12 in each experimental group. * and $ (pb0.05) show
the difference between control (saline) and PCM groups, respectively.
2
5
10 15 20 25 30 35 40 45 50 55
Time (Min)
Fig. 3. Mean tail immersion test (s) in animals receiving PCP (I), PCM (II), methoxy-
PCM (III), hydroxy-methyl-PCM (IV) and methyl-PCM (V) hydrochloride. The bars in
each line represent mean SEM of tail withdrawal latency (s) in 12 animals.

232
A. Ahmadi et al. / Pharmacology, Biochemistry and Behavior 98 (2011) 227–233
3.5
3
Saline
In addition, no patent has been applied nor any commercial right
has been given to any company and/or institution, and it will not be
done later either.
PCP
PCM
Methoxy-PCM
Methyl-PCM
Hydroxy-PCM
*
*$
2.5
2
*
*
Acknowledgements
*$
*$
1.5
1
This work was done as a research project at Islamic Azad
University, Karaj branch by financial support of INFS (Iranian National
Foundation Support) and we are indebted them.
The authors would also like to express their appreciation to Mojdeh
Javadi and Fariba Ansari for their assistance in the chemical experiments
and pharmacological tests. Our sincere thanks go to Ahmad Jahan Latibari
and Navid Rahmani for their attempts in editing this paper, as well as
Natasha Qale, the CamTESOL International editor, for her final revision.
0.5
0
Phase I
Initial phase II
Late phase II
Fig. 6. Comparison of the acute chemical and chronic formalin pain in PCP (I), PCM (II),
methoxy-PCM (III) and hydroxy-methyl-PCM (IV) hydrochloride animal groups.
Bars show the mean SEM of pain score. As indicated, the administration of the
new drugs (III and IV) had no effects in acute chemical pain (phase I), but the initial
and late phases of the chronic pain could be significantly reduced by following
the administration of PCM and especially compound III in late phase. n=12 in each
experimental group. * and $ (pb0.05) show the difference between control (saline) and
PCM groups, respectively.
References
Abdol-Rahman MO, Aboul-Eneim MN, Tammom GH. Action of Grignard reagents
aryllithium on 1, 1-disubstituted cyclohexane derivatives. Egypt J Chem 1975;18(3):
581–6.
Ahmadi A, Mahmoudi A. Synthesis and biological properties of 2- hydroxy-1- (1-
phenyltetralin) piperidine and some of its intermediates as derivatives of
phencyclidine. Arzneimittelforschung 2005;55(9):528–32.
Ahmadi A, Mahmoudi A. Synthesis with improved yield and study on analgesic effect of
2-methoxyphencyclidine. Arzneimittelforschung 2006;56(5):346–50.
Ahmadi A, Khalili M, Abbassi S, Javadi M, Mahmoudi A, Hajikhani R. Synthesis and
study on analgesic effects of 1-[1-[4-methylphenyl][cyclohexyl]-4-piperidinol and
1-[1-[4-methoxyphenyl][cyclohexyl]]-4-piperidinol as two new phencyclidine
derivatives. Arzneimittelforschung 2009;59(4):202–6.
Ahmadi A, Khalili M, Mihandoust F, Barghi L. Synthesis and determination of acute and
chronic pain activities of 1-[1-[3-methyphenyl][tetralyl]] piperidine as a new deriva-
tive of phencyclidine via tail immersion and formalin tests. Arzneimittelforschung
2010;60(1):30–5.
Ahmadi A, Khalili M, Hajikhani R, Naserbakht M. Synthesis and determination of acute
and chronic pain activities of 1-[1-[4-methylphenyl][cyclohexyl] morpholine as a
new phencyclidine derivative in Rats. Arzneimittelforschung 2011;61:1-11.
Al-deeb OAA. Synthesis and analgesic activity of new phencyclidine derivatives.
Arzneimittelforschung 1994;44(II):1141–4.
The results indicated that III and IV produce more analgesic effects
in the tail immersion test compared with PCP and PCM. In addition,
this analgesic effect was remarkably seen after the compound IV's
application in comparison with all drugs (I–V). It was reported that
NMDA receptors, especially NR2B-containing receptor subtypes,
have a key role as a pain killer (Chizh et al., 2001; Jacquet, 1988) and
it has shown the central mechanism(s) for the mentioned effects
via antagonizing the NMDA receptors on pain modulatory center
periaqueductal gray. As a result, the new synthetic drugs (compound
III and IV) in this study would release more anti-nociception than
other drugs. In the formalin test analysis, the acute chemical pain
(phase I) could not be affected by any drugs (I–V) and chronic formalin
pain could be diminished by these newly synthesized drugs (III
and IV), especially in late phase II compared to PCP and PCM. However,
biphasic analgesic effects of these new drugs in acute thermal pain
could be justified by their potent pharmacokinetic/pharmacodynamic
ratio (i.e., rapid and high serum level concentration of drugs due to i.p.
injection) in rats (Proksch et al., 2000). In addition, high tissue storage
of the drugs, their redistribution to the serum, and the production of
potent drugs which are active metabolites in the liver or other organs,
could explain the analgesic effects of these drugs in late chronic formalin
and second acute (40–45 min) thermal pain (Deleuze-Masquefa et al.,
1997; Proksch et al., 2000).
Al-deeb OAA. New analgesic derived from the phencyclidine analogue hiencyclidine.
Arzneimittelforschung 1996;46(I):505–8.
Beckett AH, Kourounakis P. The relationship between chemical structure and basicity in
some morpholine compounds. Arzneimittelforschung 1976;26:1810–1.
Budd RD. Phencyclidine (PCP)-structure versus reactivity. Clin Toxicol 1981;18(9):1033–41.
Chen DM, Chen K, Wang H. Antithrombotic effects of morpholine and piperazine ring
derivatives and their molecular mechanism. Yao Xue Xue Bao 2003;38(9):641–5.
Chizh BA, Headley PM, Tzschentke TM. NMDA receptor antagonists as analgesics: focus
on the NR2B subtype. Trends Pharmacol Sci 2001;22:636–42.
Deleuze-Masquefa C, Michaud M, Vignon J, Kamenka JM. 1-[1-2-Benzo [b] thiopheneyl)
cyclohexyl]piperidine hydrochloride (BTCP) yields two active primary metabolites
in vitro: synthesis, identification from rat liver microsome extracts, and affinity for
the neuronal dopamine transporter. J Med Chem 1997;40(25):4019–25.
Dougherty PM, Staats PS. Intrathecal drug therapy for chronic pain from basic science
to clinical practice. Anesthesiology 1999;91:1891–918.
Dubuisson D, Dennis SG. The formalin test: a quantitative study of the analgesic effects of
morphine, meperidine, and brain stem stimulation in rats and cats. Pain 1977;4(2):
161–74.
Erard R, Luisada R, Peele R. The PCP psychosis prolonged intoxication or drug-
precipitated functional illness? J Psychoact Drugs 1980;12:235.
Geneste P, Kamenka JM, Dessapt P. Method for stereoselective production of
substituted cyclohexylcyanhydrines. Bull Soc Chim Fr 1980;2:187–91.
Hamura H, Yoshida M, Shimizu K, Matsukura T, Suzuki H, Narita M, et al.
Antinociceptive effect of the combination of pentazocine with morphine in the
tail-immersion and scald-pain tests in rats. Jpn J Pharmacol 2000;83(4):286–92.
Honey CR, Miljkovic Z, Macdonald JF. Ketamine and phencyclidine cause a voltage-
dependent block of responses to L aspartic acid. Neurosci Lett 1985;61:135–9.
Hunskaar S, Hole K. The formalin test in mice: dissociation between inflammatory and
non-inflammatory pain. Pain 1987;30:103–14.
Finally, with respect to marked acute analgesic effects of III and IV
and chronic anti-nociceptive effects of IV, it could be concluded that
III and IV act through central and peripheral analgesic mechanism(s),
respectively. Because it was revealed that formalin acute pain was
mediated through central mechanism(s) and peripheral modulatory
substances like inflammatory mediators (prostaglandins, interlukins,
potassium and substance p) were considered as responsible for
chronic formalin pain (Hunskaar and Hole, 1987; Shibata et al., 1989).
5. Conclusion
Itzhak Y, Kalir A, Weissman BA, Cohen S. New analgesic drugs derived from
phencyclidine. J Med Chem 1981;24:496–9.
Jacquet Y. The NMDA receptor: central role in pain inhibition in rat periaqueductal
gray. Eur J Pharmacol 1988;154:271–6.
Johnson PY, Pan R, Quan Wen J, Halfman CJ. Synthesis of amine derivatives of
phencyclidine. J Org Chem 1981;46:2049–54.
Kapur S, Seeman P. NMDA receptor antagonists ketamine and PCP have direct effects
on the dopamine D2 and serotonin 5-HT2 receptors—implications for models of
schizophrenia. Mol Psychiatry 2002;7:837–44.
It is concluded that these new synthesized derivates of PCP
including methoxy-PCM (III) and hydroxy-methyl-PCM (IV) could
substantially and respectively diminish acute thermal and chronic
chemical pains.
6. Conflict of interest
Maddox VH, Godefroi EF, Parcell RF. The synthesis of phencyclidine and other 1-
arylcyclohexylamines. J Med Chem 1965;8:230–5.
Molina N, Bedran-de-Castro MT, Bedran-de-Castro JC. Sex-related differences in the
analgesic response to the rat tail immersion test. Braz J Med Biol Res 1994;27(7):
1669–72.
This research is not a part of our normal lecturing, employment,
consultation, and involvement; and no institution will require any
rights from this work.

A. Ahmadi et al. / Pharmacology, Biochemistry and Behavior 98 (2011) 227–233
233
Mori A, Noda Y, Mamiya T, Miyamoto Y, Nakajima A, Furukawa H, et al. Phencyclidine-
induced discriminative stimulus is mediated via phencyclidine binding sites on
the N-methyl-D-aspartate receptor-ion channel complex, not via sigma receptors.
Behav Brain Res 2001;119:33–40.
Mozayani A. Phencyclidine—effects on human performance and behavior. Forensic
Sci Rev 2003;15(1):62–74.
Ramabadran K, Bansinath M, Turndorf H, Puig MM. Tail immersion test for the evaluation
of a nociceptive reaction in mice. Methodological considerations. J Pharmacol Methods
1989;21(1):21–31.
Rekka E, Retsas S, Demopoulos VJ, Kourounakis PN. Lipophilicity of some substituted
morpholine derivatives synthesized as potential antinociceptive agents. Arch
Pharm (Weinheim) 1990;323(1):53–6.
Ogunbadeniyi AM, Adejare A. Syntheses of fluorinated phencyclidine analogs. J Fluorine
Chem 2002;114:39–42.
Shebley M, Jushchyshyn MI, Hollenberg F. Selective pathways for the metabolism of
phencyclidine by cytochrome P450 2B enzymes: identification of electrophilic
methabolites, glutathione and N-acetyl cysteine adducts. Drug Metab Dispos
2006;34(3):375–83.
Shibata M, Ohkubo T, Takahashi H, Inoki R. Modified formalin test: characteristic
biphasic pain response. Pain 1989;38:347–52.
Olney JW, Labruyere J, Wang G, Wozniak DF, Price MT, Sesma MA. NMDA antagonist
neurotoxicity: mechanism and prevention. Science 1991;254:1515–8.
Proksch JW, Gentry WB, Owens SM. The effect of rate of drug administration on the
extent and time course of phencyclidine distribution in rat brain, testis, and serum.
Drug Metab Dispos 2000;28(7):742–7.
Soine WH. Clandestine drug synthesis. Med Res Rev 1986;6(1):41–74.