Pharmacological evaluation of a diarylmethylene-piperidine derivative: A new potent atypical antipsychotic?

Article abstract of DOI:10.1016/S0960-894X(01)00200-1

A new diaryl-methylene piperidine derivative, 2, displayed an atypical antipsychotic profile both in vitro and in vivo. The main pharmacological characteristics of this compound appears to reside in a more potent antagonism of the 5-HT₂ seroton

Full text of DOI:10.1016/S0960-894X(01)00200-1

Bioorganic & Medicinal Chemistry Letters 11 (2001) 1313–1316
Pharmacological Evaluation of a Diarylmethylene-Piperidine
Derivative: A New Potent Atypical Antipsychotic?
Patrice Talaga,* Alain Matagne and Henrik Klitgaard
UCB S.A., Pharma Sector, Chemin du Foriest, B-1420 Braine-l’Alleud, Belgium
Received 31 January 2001; revised 7 March2001; accepted 16 March2001
Abstract—A new diaryl-methylene piperidine derivative, 2, displayed an atypical antipsychotic profile both in vitro and in vivo. The
main pharmacological characteristics of this compound appears to reside in a more potent antagonism of the 5-HT2 serotonergic
receptor than of the D2 dopaminergic receptor. This confirms that molecules displaying a D2/5-HT2 binding ratio <1 possess
clozapine-like antipsychotic activity. # 2001 Elsevier Science Ltd. All rights reserved.
The notion of atypical antipsychotics is based on the
observation that classical neuroleptics produce extra-
pyramidal side effects (EPS), whereas atypical neuro-
leptics display antipsychotic activity without inducing
suchextrapyramidal side effects. Among the neurolep-
tics, the prototype atypical antipsychotic is clozapine, 1.
Although clozapine appears to be efficacious in patients
withnegative symptoms and in ethrapy-resistant
patients, its clinical use is hampered by the occurrence
of fatal agranulocytosis and seizures.1 Thus, there is an
urgent need for more tolerable antipsychotic drugs with
an atypical profile.2
at their therapeutic concentrations,8 whereas clozapine
primarily acts at D4 receptors.8 Besides blockade of
dopamine receptors, it also appears that antagonism of
serotonergic receptors is important, since coadministra-
tion of a 5-HT2 antagonist witha typical antipsychotic
has been suggested to reduce the appearance of EPS.9,10
A correlation between an atypical profile and the ratio
of D2/5-HT2 receptor binding has been proposed.11
Thus, it appears12 that clozapine-like antipsychotics
have a D2/5-HT2 binding ratio <1 (pKi values) whereas
typical antipsychotics have a ratio >1.
In this communication, we describe the in vitro and in
vivo pharmacological profile of a new diarylmethylene-
piperidine derivative, 2, which was identified via screen-
ing of UCB’s internal compound library. The discovery
approach was based upon the hypothesis that an atypi-
cal antipsychotic profile is related to a relatively higher
affinity (antagonism) for the D4 than for the D2 recep-
tor and to a relatively higher affinity (antagonism) for
the 5-HT2 than for the D2 receptor. We anticipated that
sucha binding profile would result in a relative selective
inhibition of behaviors in mice mediated through the
mesolimbic (A10) dopaminergic system (apomorphine-
induced climbing/amphetamine-induced hyperactivity)
in contrast to stereotyped behaviors mediated through the
nigro-striatal (A9) dopaminergic system (apomorphine
and d-amphetamine induced stereotypy).
A wide variety of neurochemical theories have been
proposed as an etiological abnormality in schizo-
phrenia.3,4 Among the numerous neurotransmitters
potentially involved in the pathogenesis of schizo-
phrenia, dopamine and serotonin still seem to be of
crucial importance.5 Thus, the importance of dopamine
antagonists in the treatment of schizophrenia has led the
most extensive investigation being aimed at dopamine
systems. Actually, most of the subtypes of dopamine
receptors including D1–D5 are targets for antipsychotic
drugs.3,5,6 The unique antipsychotic profile of clozapine
may relate to a relative selective blockade of subtypes of
dopamine receptors. An elevated concentration of D4
receptors has been reported in brains from patients with
schizophrenia.7 Moreover, it has been reported that
most typical neuroleptics primarily act at D2 receptors
Compound 2 may be regarded as belonging to the di-
arylbutylamine’s group of antipsychotic drugs (e.g.,
Pimozide). Specifically, 2 is a diarylmethylene piperidine
substituted on the nitrogen atom by a tetrahydrofuranoyl
*Corresponding author. Tel.: +32-2-386-2727; fax: +32-2-386-2704;
e-mail: patrice.talaga@ucb-group.com
0960-894X/01/$ - see front matter # 2001 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(01)00200-1

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P. Talaga et al. / Bioorg. Med. Chem. Lett. 11 (2001) 1313–1316
amide group. This group may be considered as a rigidi-
fied bioisosteric analogue of the ethoxy-ethanol chain
found in another recently claimed atypical antipsychotic,
namely seroquel,13 3 (Fig. 1).
merically pure form (characterized by NMR and chiral
HPLC) and is assumed to have a cis configuration.15
The antipsychotic activity of 2 was determined by using
classical in vitro and in vivo assays, and was compared
to clozapine 1, seroquel 3, and haloperidol 4.
Chemical Synthesis
In Vitro Binding Studies
The diarylmethylene piperidine derivative 2 was pre-
pared from the known ester 5 as shown in Scheme 1.14
5-Chloromethyl-furan-2-carboxylic acid methyl ester 5
was completely hydrolyzed with 5 N sodium hydroxide
in dioxane to provide the corresponding 5-hydroxy-
methyl-furan-2-carboxylic acid. The acid was subse-
quently reesterified under acidic catalysis to provide 6 in
39% overall yield. 5-Chloromethyl-tetrahydrofuran-2-
carboxylic acid ethyl ester 7 was obtained by hydro-
genation of 6 in ethanol using Rh/C as catalyst followed
by chlorination of the hydroxymethyl group with thio-
nyl chloride in toluene. Compound 7 was not isolated
and was directly coupled to the diarylmethylene piper-
idine derivative 8 in xylene at reflux to provide the 5-(4-
[(4-fluoro-phenyl)-phenylmethylene]-piperidine-1-ylme-
thyl)-tetrahydrofuran-2-carboxylic ethyl ester derivative
in 31% yield. The ester was then saponified under basic
conditions and converted to the corresponding amide
derivative 2 (overall yield 56%) by treatment withethyl
chloroformate in THF followed by the addition of gas-
eous ammonia. 2 has been obtained in a diastereo-
Affinity for the D2, D4, and 5-HT2 receptors as well as
the binding ratios D2/5-HT2 and D2/D4 are listed in
Table 1. The affinity of 2 for the 5-HT2 receptor (pKi
7.5) was relatively higher when compared to the similar
affinities for the D2 or D4 receptors. This gives a D2/5-
HT2 ratio of 0.93 suggesting potential atypical
antipsychotic activity in vivo.
Apomorphine-Induced Climbing-Stereotypy in Mice
Activities of 2 and the reference antipsychotics in the
apomorphine-induced climbing-stereotypy model18 are
listed in Table 2. Among the reference molecules tested,
only the atypical antipsychotic clozapine showed a sig-
nificant separation between the doses that were active
against climbing and stereotypy. In contrast, the typical
neuroleptic haloperidol inhibited both apormophine
induced hyperactivity and stereotypy at similar doses.
Interestingly, a significant separation between the doses
active against climbing and stereotypy was also
observed for 2 (ED50 values for apomorphine induced
climbing/stereotypy: 140/290 mmol/kg).
Table 1. Affinities (pKi) for D2, D4, 5-HT2 receptors and D2/5-HT2,
D2/D4 binding ratios for 2 and reference molecules
Compounds
D2
D4
5-HT2
D2/5-HT2
D2/D4
1
2
3
4
7.5
7.0
7.2
9.1
7.8
6.8
nae
8.8
8.3a
7.5
220c
7.7a
0.8b
0.96
1.03
nae
0.93
0.95d
1.17b
1.03
aValues taken from ref 26.
bCalculated from ref 16.
cKi (nM) value taken from ref 4.
dCalculated from ref 17.
ena, not available.
Figure 1. Structure of compound 2 and reference antipsychotics.
Table 2. ED50 (mmol/kg) of 2 and reference molecules on apomor-
phine-induced climbing and stereotypy and DOI-induced head-twit-
ches in mice
Compounds
Inhibition
apomorphine-
Inhibition of
apomorphine-
Inhibition of
DOI-induced
induced climbinga induced stereotypya head-twitchesb
ip (po)
ip (po)
ip
1
2
3
4
28 (30)
46 (140)
51
67 (62)
69 (290)
60
1.5
16
9.0
0.61
0.32
0.31
aClimbing and stereotypy were induced by sc administration of
apomorphine at a dose of 2.5 mg/kg.
bHead-twitches were induced by ip administration of (Æ)-DOI, at a
Scheme 1. Synthesis of compound 2.
dose of 1.6 mg/kg.

P. Talaga et al. / Bioorg. Med. Chem. Lett. 11 (2001) 1313–1316
1315
Amphetamine-Induced Hyperactivity and Stereotypy in
Mice
(À32%) at the dose of 32.7 mg/kg at 0.5–2.5 h
post-administration. In contrast, 2 given orally
(43.1–431 mg/kg) had no significant effect on heart
rate, and blood pressure throughout the 24 h post-
administration.
The typical neuroleptic haloperidol inhibited both
amphetamine-induced hyperactivity19 and stereotypy20
at similar doses. In contrast, 2 decreased d-ampheta-
mine-induced hyperactivity from a dose of 10 mmol/kg
(decrease of 44%; p<0.01), while a dose of 100 mmol/kg
was required to slightly antagonize the stereotyped
behavior induced by d-amphetamine (decrease of 13%;
p<0.05). This was similar to clozapine which also
antagonized amphetamine induced hyperactivity and
stereotypy at doses of 10 and 100 mmol/kg, respectively.
. Anticholinergic side effects were evaluated in mice
using the oxotremorine-induced tremors/salivation
test.24 As for clozapine (ED50 values, mmol/kg ip
salivation/tremor inhibition: clozapine 12/8; 2 32/
20), no important separation between tremors and
salivation inhibitory activity was detected. In con-
trast to clozapine, 2 displayed no affinity for mus-
carinic receptors. Thus, an indirect effect obviously
mediates the anticholinergic action induced by
compound 2.
. Testing in the IRWIN test25 showed that 2, com-
pared to clozapine, induced effects like sedation
(100/3.2), convulsions (320/180) and lethality
(1000/320) at markedly higher doses (mmol/kg ip).
DOI-Induced Head-Twitches in Mice
All reference antipsychotics were potent inhibitors of
DOI-induced head-twitches,21 a 5-HT2 mediated behavior
(Table 2).
Taken together, these results demonstrate that 2 reveals
a profile similar to that of the atypical antipsychotic
clozapine in mice. This was confirmed in rats using the
catalepsy test22 and the Sidman Avoidance paradigm.23
Oral administration of 2 (40–160 mg/kg) dose-depen-
dently decreased the number of avoidance responses in
the Sidman Avoidance test (Fig. 2). It also clearly
increased the number of shocks received and the num-
ber of escape failures. A similar activity was observed
withclozapine from a dose of 20 mg/kg po in this
model. No induction of catalepsy was observed with 2
(up to 160 mg/kg po) and clozapine (up to 40 mg/kg
po). In contrast, the typical antipsychotic haloperidol
both decreased the conditioned avoidance behavior (0.5
mg/kg po) and induced catalepsy (2 mg/kg po).
In conclusion, the present study provides support that a
more potent antagonism at the 5-HT2 receptor as com-
pared to the D2 receptor is important for an atypical
profile of an antipsychotic. In contrast, a relatively
selective antagonism of the D4 receptor appears not to
be important. This finding seems in accordance with a
study published by Roth et al.,12 which reported that
affinity for the D4 receptor is unable to distinguish
between typical and atypical antipsychotics. Lead
molecule 2 presented a favorable binding ratio between
the 5-HT2 and the D2 receptor in vitro and a relatively
selective inhibition of mesolimbic versus nigro-striatal
dopamine behaviors in vivo. The latter was comparable to
the separation observed with clozapine. Thus, 2 should be
considered for further preclinical investigations in order to
delineate its clinical potential as an atypical antipsychotic.
Adverse Effect Profile Evaluation in Mice and Rats
Acknowledgements
. Cardiovascular effects of 2 as well as of clozapine
were evaluated in the awake rats (unpublished
data). Oral administration of clozapine transiently
increased heart rate (+49%) from the dose of
10.5 mg/kg, and decreased arterial blood pressure
We are grateful to Yves Lamberty, Michel Guyaux and
Martine Vandevelde for performing the oxotremorine-
induced tremors/salivation, Irwin, and cardiovascular
tests, respectively. Furthermore, we wish to thank C.
Chaussee and A. C. Michaux as well as B. Lallemand
for their skillful technical assistance.
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Figure 2. Effect of
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2 and clozapine on conditioned avoidance

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