Piperidyl amides as novel, potent and orally active mGlu5 receptor antagonists with anxiolytic-like activity

Article abstract of DOI:10.1016/j.bmcl.2009.11.001

High throughput screening led to the identification of nicotinamide derivative 2 as a structurally novel mGluR5 antagonist. Optimization of the modular scaffold led to the discovery of 16m, a compound with high affinity for mGluR5 and excellent selectivit

Full text of DOI:10.1016/j.bmcl.2009.11.001

Bioorganic & Medicinal Chemistry Letters 20 (2010) 184–188
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Piperidyl amides as novel, potent and orally active mGlu5 receptor
antagonists with anxiolytic-like activity
a
b
a
Carsten Spanka a, Ralf Glatthar a, , Sandrine Desrayaud , Markus Fendt , David Orain ,
*
Thomas Troxler a, Ivo Vranesic b
a Novartis Institutes for Biomedical Research, Global Discovery Chemistry, Basel CH-4002, Switzerland
b Novartis Institutes for Biomedical Research, Neuroscience, Basel CH-4002, Switzerland
a r t i c l e i n f o
a b s t r a c t
Article history:
High throughput screening led to the identification of nicotinamide derivative 2 as a structurally novel
mGluR5 antagonist. Optimization of the modular scaffold led to the discovery of 16m, a compound with
high affinity for mGluR5 and excellent selectivity over other glutamate receptors. Compound 16m exhib-
its a favorable PK profile in rats, robust anxiolytic-like effects in three different animal models of fear and
anxiety, as well as a good PK/PD correlation.
Received 6 October 2009
Revised 30 October 2009
Accepted 1 November 2009
Available online 5 November 2009
Ó 2009 Elsevier Ltd. All rights reserved.
Keywords:
Metabotropic glutamate receptor
mGluR5 antagonist
Piperidylamides
Glutamate is the main excitatory neurotransmitter in the mam-
malian central nervous system and as such involved in a variety of
physiological and pathophysiological functions. Glutamate recep-
tors are classified into ionotropic (iGlu) receptors and metabotro-
pic glutamate (mGlu) receptors. The iGlu receptors form ligand-
gated ion channels (AMPA-, kainate-, and NMDA-type) which
mediate fast excitatory synaptic transmission. Metabotropic
glutamate receptors are G-protein-coupled receptors1 linked to
multiple second messenger systems modulating, for example, ion
channel functions in the neurons.2 Currently, eight distinct metab-
otropic receptor subtypes are known (mGluR1–mGluR8), which
are divided into three groups based on sequence homology, phar-
macological profiles, and signal transduction pathways. mGlu5
receptors are highly expressed in brain regions thought to mediate
and modulate emotions like fear and anxiety (amygdala, prefrontal
cortex, hippocampus, and basal ganglia).3 mGlu5 receptors are pre-
dominantly postsynaptically located and have been shown to play
a role in regulating glutamatergic transmission via potentiation of
NMDA receptor activity. Excessive glutamatergic transmission has
been proposed to play a role in psychiatric diseases like anxiety
disorders and depression.4 Additionally, mGlu5 receptor antago-
nism has been proposed as a potential approach for the treatment
of pain, obesity, Parkinson’s disease and drug abuse.5 Therefore, the
development of potent and selective mGlu5 receptor antagonists
as potential therapeutic agents has been the focus of significant re-
search in our laboratories.
Our previous research efforts for mGlu5 receptor antagonists
had been focused on alkyne derivatives such as MPEP (1) (Fig. 1)
which proved to be potent and highly selective mGlu5
receptor antagonist with in vivo activity in animal models of anx-
iety.6 In the course of our search for novel structural leads, com-
pound 2 was identified in a high-throughput screen, based on
the inhibition of agonist induced elevation of the intracellular
Ca2+ concentration.7a
In the present Letter, a detailed structure–activity relationship
(SAR) study will be discussed as well as the biological evaluation
of an optimized candidate in different animal models of anxiety.
Modifications of all three parts of scaffold 2, namely amide A,
aniline B, and ‘core’ C, have been explored. In a first round, each re-
gion was optimized separately. Then, in a second round, optimal
combinations were identified and further fine-tuned. The target
molecules can be synthesized by
a convenient two-step
synthetic process starting from readily available building blocks
O
Cl
N
N
N
N
H
A
C
B
1 MPEP
2
* Corresponding author.
E-mail address: ralf.glatthar@novartis.com (R. Glatthar).
Figure 1. mGluR5 antagonists.
0960-894X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2009.11.001

C. Spanka et al. / Bioorg. Med. Chem. Lett. 20 (2010) 184–188
185
X
can be reversed: First, a Buchwald reaction of nicotinic ester 8 with
aniline 6 followed by amide formation of intermediate 9 via corre-
sponding acid 10 and an amine 4 resulted in the formation of 7
(method B).
SAR evaluation started with variation of the amide functional-
ity. Tertiary amides carrying lipophilic substituents were clearly
preferred, in particular if R1 and R2 together form a ring. Small sub-
stituents at the cyclohexyl ring (11e–g) were tolerated, however
potency of the racemic derivatives did not further improve. Sec-
ondary amides resulted in compounds with significantly decreased
potency against the mGlu5 receptor (Table 1).
In a second sub-library, the influence of different aniline and
heteroarylamine moieties (fragment B) on the potency was studied
(Table 2). A very steep SAR was observed, with substitution of the
aromatic system only being tolerated in para-position. Best results
were obtained with small lipophilic fragments (e.g., Me, Cl). Inter-
estingly, the phenyl group could be replaced by a more polar 3-
pyridyl substituent which gave the most potent derivative 12k of
this set. The corresponding 2,20-dipyridylamines 12i–j that relate
Method A
Y
R3
R1
H2N
NH
R2
6
O
O
R1
4
X,Y = CH, N
Cl
N
R2
(b)
(a)
N
Cl
N
Cl
R1
3
5
O
X
N
Y
R3
R2
N
N
Method B
H
7
X
Y
R3
R1
O
H2N
Cl
O
NH
R2
(e)
6
4
X
MeO
RO
Y
R3
(c)
N
N
N
H
8
9 R = Me
10 R = H
(d)
Scheme 1. Reagents and conditions: (a) NEt3, DCM, 0 °C, 1 h; (b) AcOH/H2O 3:7,
95 °C, 18 h; (c) Pd(OAc)2, BINAP, K2CO3, toluene, 70 °C, 1.5 h; (d) 2 M NaOH, MeOH,
60 °C, 0.5 h; (e) HATU, DIPEA, DME, rt, 6 h.
Table 2
Optimization of aniline fragment B: in vitro hmGluR5 antagonism
(Scheme 1). In a first step, 6-chloronicotinoyl chloride (3) was re-
acted with an amine 4. Subsequent SNAr reaction of the 6-chloro
function of corresponding amide 5 with an aniline 6 afforded the
desired product 7 (method A). Alternatively, the reaction sequence
O
N
Ar
N
N
H
12
b
Compound
Ar
Ph
Methoda
A
IC50 (lM)
Table 1
Optimization of amide part A: in vitro hmGluR5 antagonism
Cl
2
0.31
O
R1
Cl
N
12a
12b
A
B
ꢀ10
R2
N
N
Cyclohexyl
>10
H
11
Cl
Compound
R1
R2
Methoda
A
IC50 (lM)
12c
12d
B
A
>10
>10
b
2
0.31
5.40
Cl
11a
11b
A
B
F
12e
12f
12g
B
A
A
2.30
2.30
1.80
0.25
11c
11d
B
A
2.30
0.46
OMe
Cl
Et
Et
12h
A
B
>10
11e
A
0.43
Cl
Cl
12i
12j
ꢀ10
11f
A
B
B
0.53
2.30
>10
N
B
B
>10
11g
N
N
11h
H
12k
0.42
a
a
See Scheme 1.
See Scheme 1.
b
hmGluR5 Ca2+ flux7 using glutamate as agonist, data are geometric means of
b
hmGluR5 Ca2+ flux7 using glutamate as agonist, data are geometric means of
n P 2.
n P 2.

186
C. Spanka et al. / Bioorg. Med. Chem. Lett. 20 (2010) 184–188
to a previously published class of potent mGluR5 antagonists8
exhibited surprisingly low potency.
hmGluR5
Ca2+ flux
IC50 [µM]
Modification of the 6-substituted nicotinamide, ‘core’ C showed
that potency could be gained by introduction of an electron-with-
drawing substituent in 5-position (13b). Benzamide 13a, pyrida-
zine-carboxamide 13d, and pyrimidine-5-carboxamide 13e were
only moderately active, whereas pyrazine-2-carboxamide 13f and
pyrazole-3-carboxamide 13g were completely inactive (Table 3).
Finally, the importance of the hydrogen bond donor on the
nitrogen bridge between the two aromatic rings was studied. Loss
of activity for the N-methylated derivative 14 and ether 15 in di-
rect comparison to 2 and 11f, respectively, confirmed the need
for a secondary amine functionality (Fig. 2).
Combination of optimal fragments identified for each region led
to the highly potent derivative 16a (Table 4). Since in the first opti-
mization round, potency could not be improved by modification of
fragment A, the potential for substitution of the piperidine ring (R1,
R2) was re-investigated, aiming at an improved potency as well as a
good balance of aqueous solubility at pH 6.8 and an acceptable
intrinsic clearance in human and rat liver microsomes (Table 4).
Whereas for substituent R2, chain length and stereochemistry
had not much influence on potency, the situation was different
for substituent R1, where the (R)-forms generally were more potent
in two functional assays on hmGluR5 than the corresponding (S)-
forms. In general, both solubility and microsomal stability de-
creased with increasing size of the substituents. The best balance
between potency, solubility and microsomal stability was achieved
O
2: R = H
14: R = H
X = NH
0.31
R
Cl
N
X = NMe >10
11f: R = Me X = NH
15: R = Me X = O
0.53
>10
N
X
Figure 2. Secondary amines 2, 11f and tertiary amine 14 and ether 15.
Table 4
Substitution of the piperidine ring: in vitro hmGluR5 antagonism, aqueous solubility
at pH 6.8 and intrinsic clearance in human and rat liver microsomes
R1
O
R2
Cl
N
N
N
16
N
H
Compd
R1
R2
H
rac-Me
rac-Et
rac-Pr
R-Et
S-Et
H
H
H
H
H
IC50 (nM)d
Ca2+flux/PI
Solubilitye
pH 6.8
CLintf (h/r)
16aa
16ba
16ca
16da
16ea
16fb
16gb
16hb
16ib
16jb
16kb
16lc
H
H
H
H
H
H
S-Me
R-Me
rac-Et
rac-Pr
rac-Bu
S-Et
R-Et
87/258
105/310
65/48
190/140
40/69
40/110
1400/–
240/430
110/90
90/16
150
—
15
—
95
33/48
60/38
171/417
ꢁ/ꢁ
322/643
174/687
39/68
<3
499
216
122
<3
<3
56
44/73
138/220
224/885
227/637
216/190
89/87
136/5
390/360
32/36
H
H
Table 3
16mc
58
Optimization of ‘core’ C: in vitro hmGluR5 antagonism
a
b
c
Synthesis method A.
Synthesis method B.
via separation of racemate 16i by chiral HPLC (Chiralpak AD-H, 30 ꢂ 250 mm,
O
R
Cl
N
hexane, 50% ethanol).
d
hmGluR5: Ca2+ flux using glutamate and phosphoinositol turnover using
N
quisqualate as agonist,7 data are geometric means of n P 2, IC50 (nM).
H
13
e
Solubility (mg/L) measured in a dissolution template potentiometric titration
approach.
Methoda
IC50 (lM)
b
Compound
R
‘Core’
f
CLint: intrinsic clearance (lL/min/mg protein).
2
H
A
A
0.31
1.60
N
for analogue 16m, bearing a (R)-2-ethyl-piperidineamide as frag-
ment A.
13a
13b
Me
In vitro radioligand displacement assays utilizing [3H]-
ABP68811 showed that 16m is a high-affinity ligand at the previ-
ously characterized allosteric binding site located in the mem-
brane-spanning region of mGlu5 receptors12 with a Ki at the
human recombinant receptor of 38 nM.13 In addition, 16m showed
a high degree of selectivity over representatives of groups I–III
Cl
Me
H
B
0.095
2.10
N
OMe
13c
A9
metabotropic glutamate receptor subtypes (IC50 >10
hmGluR1, -2, -7) and ionotropic glutamate receptors (IC50
>10
M).14
A single-dose pharmacokinetic study of 16m in rats (Table 5)
lM for
N
N
l
13d
13e
Me
Me
B
B
0.72
0.98
N
revealed that after an oral dose of 30 lmol/kg, the mean maximal
N
N
N
Table 5
Pharmacokinetic parametersa of 16m
Absorptiona (30
lmol/kg po)
Disposition (10 lmol/kg iv)
13f
H
A
>10
>10
N
N
Cmax = 1230 pmol/mL
Tmax = 0.25 h
AUC = 7230 pmol h/mL
F = 54%
t1/2 1;2= 0.3; 0.9 h (54%)
MRT = 0.9 h
CL = 37.2 mL/min/kg
Vss = 2 L/kg
13g
Me
B10
HN
Brain/plasma-ratio = 1.3
AUC = 4480 pmol h/mL
brain/plasma-ratio = 1.36
a
See Scheme 1.
b
hmGluR5 Ca2+ flux7 using glutamate as agonist, data are geometric means of
a
n P 2.
n = 3 Sprague-Dawley rats/group.

C. Spanka et al. / Bioorg. Med. Chem. Lett. 20 (2010) 184–188
187
plasma concentration was reached quickly post-dose. A second in-
crease in plasma concentration between 4 and 8 h was observed
which points towards either a second absorption phase or ente-
ro-hepatic recirculation. Absolute oral bioavailability was esti-
cantly reduced stress-induced hyperthermia at 3 and 10 mg/kg,
while having no effect on baseline temperature (Fig. 3).
mated to 54%. After an iv bolus dose of 10 lmol/kg, the first and
second elimination half-lives amounted to 0.3 h and 0.9 h (t1/2,2:
55% of AUC), respectively. Compound 16m was moderately cleared
in rats and moderately distributed to tissues. After both oral and
intravenous dosages, the penetration of 16m into the brain was
significant with brain/plasma AUC ratios of 1.30 and 1.36,
respectively.
Given the good in vitro potency and pharmacokinetic profile in
rats, 16m was evaluated in three standard in vivo models for
assessing anxiolytic-like activity. In stress-induced hyperthermia,
exaggerated response of the autonomic nervous system to stress
is recorded using body-temperature measurements in mice.15 Oral
administration of 16m (1, 3, and 10 mg/kg, 1 h before T1) signifi-
Figure 5. Expression of fear-potentiated and baseline startle response (3–30 mg/kg
compound 16m): rats were fear-conditioned by 20 pairings of a light stimulus (5 s)
and an electric foot shock (0.5 mA, 0.5 s) on two successive days. On day three,
animals were orally treated (n = 10/group) and, 1 h later, the startle magnitude to a
noise burst was measured in the presence of the light stimulus as well as without
(12 presentations each). Depicted are mean startle magnitudes and SEMs of startle
stimulus alone and CS-startle stimulus trials, respectively, as well as the difference.
Statistics: multifactorial ANOVA: interaction treatment ꢂ trial type: F3,36 = 5.69,
p = 0.001; **p <0.01 (Dunnett post-hoc test vs 0 mg/kg).
Figure 3. Stress-induced hyperthermia: individually housed mice (n = 14/group)
were orally treated and, 1 h later, the initial temperature (T1) was determined via a
rectal thermistor. Fifteen minutes later core-temperature were re-determined (T2)
and SIH was defined as T2 ꢁ T1. Depicted are means (T2 ꢁ T1) and SEM. Statistics:
Kruskal–Wallis ANOVA on ranks: H = 39.9, p <0.001; *p <0.05 (Dunn’s post-hoc test
vs 0 mg/kg).
Figure 4. Vogel conflict test (punished drinking): after a 24 h water-deprivation,
rats were re-exposed to the boxes and had free access to the drinking spout and
then returned back to the home-cage where they had access to water for an
additional 30 min period. After another 24 h period of water deprivation rats were
orally treated (n = 12/group) and, 1 h later re-exposed to the boxes and now every
lick was punished by a shock (0.5 mA; 0.6 s duration). The number of punished licks
throughout this 10 min session was used as experimental parameter and is
depicted in the figure. Statistics: Kruskal–Wallis ANOVA on ranks: H = 22.4, p
<0.001; *p < 0.05 (Dunn’s post-hoc test vs 0 mg/kg).
Figure 6. (A) Expression of fear-potentiated and baseline startle response (0.08–
30 mg/kg compound 16m), for methods see Fig. 5. Multifactorial ANOVA: interac-
tion treatment x trial type: F5,54 = 5.50, p <0.001, p = 0.001; **p <0.01 (Dunnett
post-hoc test vs 0 mg/kg). (B) Immediately after the behavioral test, the animals
were sacrified and the brains were removed for HPLC analysis of compound ꢂ con-
centration in the brain. Depicted are the mean ( SEM) brain concentration of
compound 16m in the different treatment groups as well as the mean percent
startle difference ( SEM). Compound 16m brain levels are nicely correlated with
the expression of fear-potentiated startle (sigmoid fit: r2=0.85).

188
C. Spanka et al. / Bioorg. Med. Chem. Lett. 20 (2010) 184–188
2. (a) Knöpfel, T.; Kuhn, R.; Allgeier, H. J. Med. Chem. 1995, 38, 1417; (b) Conn, P. J.;
Compound 16m was further evaluated in the Vogel conflict
Pin, J. P. Annu. Rev. Pharmacol. Toxicol. 1997, 37, 205.
test16 in which drinking is punished in water-deprived rats by a
mild electrical shock. Compound 16m (3, 10, and 30 mg/kg, oral
administration 1 h before test), significantly increased the number
of punished licks at doses of 10 or 30 mg/kg but not at 3 mg/kg,
(Fig. 4), suggesting a strong anxiolytic-like effect at the two doses.
In the fear-potentiated startle test (FPS), the effects of 16m were
evaluated on the expression of FPS in rats.17 Vehicle-treated ani-
mals displayed a potentiated startle magnitude in the presence
of the light stimulus which had previously been paired with an
electric footshock, indicating the presence of conditioned fear un-
der control conditions. Rats, following an oral pre-treatment
(ꢁ1 h) at doses of 3, 10, and 30 mg/kg showed a significant and
dose-dependent decrease of FPS. The baseline startle response
was not modified at any dose tested (Fig. 5).
In conclusion, robust efficacy of 16m in three different animal
models of fear and anxiety was observed. We were further inter-
ested whether brain and plasma levels of compound 16m can be
correlated with its anxiolytic-like activity of compound 16m. This
was investigated in a further experiment using the FPS model
(Fig. 6).
Analysis of plasma and brain concentrations of 16m showed a
good dose-proportionality from 0.4 to 30 mg/kg in plasma and
brain. Furthermore, a clear relationship between plasma and brain
levels and the behavioral effects could be observed. The half-max-
imal behavioral effect for 16m could be observed at a dose of 2 mg/
kg, corresponding to a brain concentration of 127 56 pmol/g.
In conclusion, high-throughput screening led to the identifica-
tion of 2 as a structurally novel mGlu5 receptor antagonist with
modest in vitro potency. Optimization of the modular lead scaffold
led to the discovery of 16m, a compound showing high affinity at
mGluR5 and selectivity over other glutamate receptors. Character-
ization in vivo revealed a good pharmacokinetic profile in rats, ro-
bust anxiolytic-like effects in three different animal models of fear
and anxiety as well as a good PK/PD correlation. In view of the ro-
bust anxiolytic-like properties in different animal models, com-
pound 16m was considered for further development.
3. (a) Shigemoto, R.; Nomura, S.; Ohishi, H.; Sugihara, H.; Nakanishi, S.; Mizuno, N.
Neurosci. Lett. 1993, 163, 53; (b) Romano, C.; Sesma, M. A.; McDonald, C. T.;
O’Malley, K.; Van den Pol, A. N.; Olney, J. W. J. Comp. Neurol. 1995, 355, 455; (c)
Rodrigues, S. M.; Bauer, E. P.; Farb, C. R.; Schafe, G. E.; LeDoux, J. E. J. Neurosci.
2002, 22, 5219.
4. (a) Phan, K. L.; Fitzgerald, D. A.; Cortese, B. M.; Seraji-Bozorgzad, N.; Tancer, M.
E.; Moore, G. J. NeuroReport 2005, 16, 183; (b) Mathew, S. J.; Price, R. B.;
Charney, D. S. Am. J. Med. Genet. C Semin. Med. Genet. 2008, 148, 89.
5. (a) Bradbury, M. J.; Campbell, U.; Giracello, D.; Chapman, D.; King, C.; Tehrani,
L.; Cosford, N. D. P.; Anderson, J.; Varney, M. A.; Strack, A. M. J. Pharmacol. Exp.
Ther. 2005, 313, 395; (b) Breysse, N.; Baunez, C.; Spooren, W.; Gasparini, F.;
Amalric, M. J. Neurosci. 2002, 22, 5669; (c) Zhu, C. Z.; Wilson, S. G.; Mikusa, J.
P.; Wismer, C. T.; Gauvin, D. M.; Lynch, J. L., III; Wade, C. L.; Decker, M. W.;
Honore, P. Eur. J. Pharmacol. 2004, 506, 107; (d) Mutel, V. Expert Opin. Ther.
Pat. 2002, 12, 1845; (e) Chiamulera, C.; Epping-Jordan, M. P.; Zocchi, A.;
Marcon, C.; Cottiny, C.; Tacconi, S.; Corsi, M.; Orzi, F.; Conquet, F. Nat.
Neurosci. 2001, 4, 873.
6. (a) Gasparini, F.; Lingenhöhl, K.; Stoehr, N.; Flor, P. J.; Heinrich, M.; Vranesic, I.;
Biollaz, M.; Allgeier, H.; Heckendorn, R.; Urwyler, S.; Verney, M. A.; Johnson, E.
C.; Hess, S. D.; Rao, S. P.; Sacaan, A. I.; Santori, E. M.; Velicelebi, G.; Kuhn, R.
Neuropharmacology 1999, 38, 1493; (b) Spooren, W. P. J. M.; Vassout, A.; Neijt,
H. C.; Kuhn, R.; Gasparini, F.; Roux, S.; Porsolt, R. D.; Gentsch, C. Pharmacol. Exp.
Ther. 2000, 295, 1267; (c) Schulz, B.; Fendt, M.; Gasparini, F.; Lingenhöhl, K.;
Kuhn, R.; Koch, M. Neuropharmacology 2001, 41, 1.
7. (a) Daggett, L. P.; Sacaan, A. I.; Akong, M.; Rao, S. P.; Hess, S. D.; Liaw, C.; Urrutia,
A.; Jachec, C.; Ellis, S. B. Neuropharmacology 1995, 34, 871; (b) Flor, P. J.;
Gomeza, J.; Tones, M. A.; Kuhn, R.; Pin, J.-P.; Knoepfel, T. J. Neurochem. 1996, 67,
58; (c) Knopfel, T.; Sakaki, J.; Flor, P. J.; Baumann, P.; Sacaan, A. I.; Velicelebi, G.;
Kuhn, R.; Allgeier, H. Eur. J. Pharmacol. 1994, 288, 389.
8. Kamenecka, T. M.; Bonnefous, C.; Govek, S.; Vernier, J.-M.; Hutchinson, J.;
Chung, J.; Reyes-Manalo, G.; Anderson, J. J. Bioorg. Med. Chem. Lett. 2005, 15,
4350.
9. 6-Chloro-5-methoxynicotinic acid required for the preparation of 13c was
prepared in analogy to Stump, C. A.; Williams, T. M. PCT International Patent
Application WO 00/51614, example 4.
10. 5-(4-Chloro-phenylamino)-2H-pyrazole-3-carboxylic acid required for the
synthesis of 13i was prepared in analogy to a procedure published by Radl,
S. Coll. Czech. Chem. Commun. 1992, 57, 656.
11. Hintermann, S.; Vranesic, I.; Allgeier, H.; Bruelisauer, A.; Hoyer, D.; Lemaire, M.;
Moenius, T.; Urwyler, S.; Whitebread, S.; Gasparini, F.; Auberson, Y. P. Bioorg.
Med. Chem. 2007, 15, 903.
12. Pagano, A.; Ruegg, D.; Litschig, S.; Stoehr, N.; Stierlin, C.; Heinrich, M.;
Floersheim, P.; Prezeau, L.; Carroll, F.; Pin, J. P.; Cambria, A.; Vranesic, I.; Flor, P.
J.; Gasparini, F.; Kuhn, R. J. Biol. Chem. 2000, 275, 33750.
13. A similar binding affinity (Ki: 30 nM) was observed in membranes prepared
from cells expressing rat brain tissue (cortex/hippocampus).
14. Selectivity to ionotropic glutamate receptors was assessed with radioligand
displacement assays in rat brain membranes at the AMPA (glutamate binding
site), kainate (glutamate binding site) and NMDA (glutamate and glycine
binding sites) subtypes.
Acknowledgments
15. (a) Spooren, W. P. J. M.; Gasparini, F.; Salt, T. E.; Kuhn, R. Trends Pharmacol. Sci.
2001, 22, 331; (b) Adriaan Bouwknecht, J.; Olivier, B.; Paylor, R. E. Neurosci.
Biobehav. Rev. 2007, 31, 41.
16. (a) Vogel, J. R.; Beer, B.; Clody, D. E. Psychopharmacology 1971, 21, 1; (b) Millan,
M. J.; Brocco, M. Eur. J. Pharm. 2003, 463, 67.
17. (a) Brown, J. S.; Kalish, H. I.; Farber, I. E. J. Exp. Psychol. 1951, 41, 317; (b) Davis,
M. Behav. Neurosci. 1986, 100, 814; (c) Davis, M.; Falls, W. A.; Campeau, S.
Behav. Brain Res. 1993, 58, 175; (d) Fendt, M.; Fanselow, M. S. Neurosci.
Biobehav. Rev. 1999, 23, 743; (e) Koch, M. Prog. Neurobiol. 1999, 59, 107; (f)
Davis, M. Biol. Psychiat. 1998, 44, 1239; (g) Grillon, C.; Davis, M.
Psychophysiology 1997, 34, 451.
The excellent technical assistance of Christian Boesch, Hugo
Bürki, Riccardo Canova, Stefan Imobersteg, David Kolarik, Nicole
Reymann, Patrick Seitzer, Christine Stierlin, Engin Tasdelen, Roland
Wermuth, Peter Wipfli, Francis Risser, Pierrette Guntz, and Valerie
Cordier is gratefully acknowledged.
References and notes
1. (a) Swanson, C. J.; Bures, M.; Johnson, M. P.; Linden, A.-M.; Monn, J. A.; Schoepp,
D. D. Nat. Rev. Drug Disc. 2005, 4, 131; (b) Ritzen, A.; Mathiesen, J. M.; Thomsen,
C. Basic Clin. Pharmacol. Toxicol. 2005, 97, 202.