Rapid hit to lead evaluation of pyrazolo[3,4-d]pyrimidin-4-one as selective and orally bioavailable mGluR1 antagonists

Article abstract of DOI:10.1016/j.bmcl.2007.05.028

Our HTS effort yielded a preferential mGluR1 pyrimidinone antagonist 1 with lead-like characteristics. Rapid hit to lead (HTL) study identified compounds with improved functional activity and selectivity such as 1b with little improvements in ADME properties. Addition of an aminosulfonyl group on the N-1 aromatic ring led to 2f, a compound with similar in vitro biochemical profiles as those of 1b but drastically improved in vitro ADME properties. These improvements were paralleled by rat PK study characterized by low clearance and quantitative bioavailability. Compound 2f represented a true lead-like molecule that is amenable for further lead optimization (LO) evaluation.

Full text of DOI:10.1016/j.bmcl.2007.05.028

Bioorganic & Medicinal Chemistry Letters 17 (2007) 4303–4307
Rapid hit to lead evaluation of pyrazolo[3,4-d]pyrimidin-4-one
as selective and orally bioavailable mGluR1 antagonists
Xueqing Wang,* Teodozyi Kolasa, Odile F. El Kouhen, Linda E. Chovan,
Candace L. Black-Shaefer, Frank L. Wagenaar, Jennifer A. Garton, Robert B. Moreland,
Prisca Honore, Yau Yi Lau, Peter J. Dandliker, Jorge D. Brioni and Andrew O. Stewart
Neuroscience Research, Global Pharmaceutical Research and Development, AP9A/L16, Abbott Laboratories,
100 Abbott Park Road, Abbott Park, IL, USA
Received 6 April 2007; revised 4 May 2007; accepted 9 May 2007
Available online 16 May 2007
Abstract—Our HTS effort yielded a preferential mGluR1 pyrimidinone antagonist 1 with lead-like characteristics. Rapid hit to lead
(HTL) study identified compounds with improved functional activity and selectivity such as 1b with little improvements in ADME
properties. Addition of an aminosulfonyl group on the N-1 aromatic ring led to 2f, a compound with similar in vitro biochemical
profiles as those of 1b but drastically improved in vitro ADME properties. These improvements were paralleled by rat PK study
characterized by low clearance and quantitative bioavailability. Compound 2f represented a true lead-like molecule that is amenable
for further lead optimization (LO) evaluation.
ꢀ 2007 Elsevier Ltd. All rights reserved.
Hit to lead (HTL) is playing an increasingly important
role in drug discovery.1–3 At the onset of such processes,
biologically active molecules (hits) are first identified,
most often by high-throughput screening (HTS) of com-
pany or commercial libraries, and evaluated. When
selecting the hits for HTL study, special attention is gi-
ven to those so-called ‘lead-like’ molecules, namely com-
pounds with low molecular weight (MW < 450),
relatively low hydrophobicity (À4 < clogP < 4.5), and
synthetic accessibility.4,5 Through rapid structure–activ-
ity relationship (SAR) study of the hit series, the goal of
HTL is to not only improve the in vitro profile including
biochemical potency and sub-type selectivity, but also to
evaluate and address the absorption, distribution,
metabolism, and excretion (ADME) properties. Early
profiling of the ADME properties will enable the project
team to assess the likelihood of developing an orally bio-
available molecule in the ensuing lead optimization (LO)
stage, the goal of which is to generate potential drug
candidates. HTL will either provide high quality lead
to facilitate the LO or help disqualify a series of com-
pounds due to insurmountable liabilities, which will re-
duce unnecessary efforts and potential attrition in late
discovery phases.
Glutamic acid (Glu) is the major excitatory amino acid
(EAA) neurotransmitter in the central nervous system
(CNS) and is implicated in pathological processes lead-
ing to a number of neurological and psychiatric dis-
eases.6–8 The transmitter function of Glu is modulated
by two types of receptors: the ionotropic glutamate
receptors (iGluRs) and metabotropic glutamate recep-
tors (mGluRs).9–11 mGluRs belong to the type 3 super-
family of G-protein coupled receptors (GPCRs) with
seven transmembrane (TM) domains and comprise eight
members that can be subdivided into three groups
according to sequence homology, signal transduction
mechanism, and pharmacological profile12,13: group I
(mGluRs1/5), group II (mGluRs2/3), and group III
(mGluRs4/6/7/8). A specific role for group I mGluRs in
nociceptive processing has been demonstrated by phar-
macological, immunohistochemical, and in situ hybrid-
ization.14–21 A role of dorsal horn group I mGluRs,
particularly the mGluR1 receptor, in acute nociception
has been described in behavioral22–24 and electrophysio-
logical studies in vitro25 or in vivo,26 suggesting that
selective mGluR1 antagonists may serve as novel anal-
gesics. Recently, non-amino acid, selective mGluR1
antagonists have been reviewed.27 Some of them, includ-
Keywords: mGluR1 antagonist; Hit to lead; ADME.
*
Corresponding author. Tel.: +1 847 936 0362; fax: +1 847 937
9195; e-mail: xueqing.wang@abbott.com
0960-894X/$ - see front matter ꢀ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2007.05.028

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X. Wang et al. / Bioorg. Med. Chem. Lett. 17 (2007) 4303–4307
ing CPCCOEt (7-(hydroxyimino)cyclopropa[b]chro-
men-1a-carboxylate ethyl ester),28 BAY36-7620,29 R-
21412730, 1625958531, and dicarboxypyrroles32, have
been shown to inhibit receptor activity in a non-compet-
itive manner by interacting with the transmembrane do-
main VII, a location remote from the glutamate binding
site. Some of the most recently reported potent, non-
competitive mGluR1 antagonists include quinoline
derivatives,33 b-carbolines,34 thiazolo [3,2-a]benzimid-
azole-2-carboxamide (YM-298198) analogs35, and triaz-
fluorenone analogs, which had been shown to be
effective in different pain models.36
compounds 1 to improve in vitro potency, subtype selec-
tivity, and ADME properties is presented herein.
HTS hit 1 is a small lead-like molecule (MW = 336,
clogP = 4.2)4,5 with a rigid structure scaffold and poten-
tial multiple points to introduce diversity and therefore
represents a valid starting point for HTL study. Our
strategy was to keep the pyrazolopyrimidine pharmaco-
phore intact and modulate two cyclic appendage groups
(R1 and R2) sequentially. Analogs with different R1
groups (1a–1i), shown in Scheme 1, were prepared under
solvent-free conditions in moderate to good yields using
POCl337 to assist the condensation and cyclization from
4 and the corresponding amines. Analogs with alkyl R2
(2a and 2b) were generated using a modified Mitsunobu
procedure38 shown in Scheme 2. Compounds with aryl
R2 groups (2c–2l) were prepared by copper-catalyzed
C–N bond formation39 under microwave conditions.
Despite moderate yield (20–40%), this synthesis allowed
rapid access to these analogs that otherwise would re-
quire multi-step synthesis. In these reactions K3PO4
was a superior base to K2CO3. For both alkylation pro-
cedures, N-2 regioisomers were produced in about 1:3
ratio with respect to the desired N-1 isomers and they
were isolated by HPLC.
Despite the structure diversity of known mGluR1 antag-
onists, only poor to modest oral bioavailabilities were
achieved.32,33,36 To identify additional novel, potentially
orally bioavailable small-molecule mGluR1-selective
antagonists, a high-throughput screening (HTS) effort
on Abbott compound collection was carried out. A un-
ique pyrazolopyrimidinone analog 1 (Fig. 1) was shown
to be a preferred mGluR1 non-competitive antagonist
(IC50 = 242 nM) exhibiting much weaker potency
against mGluR5 (IC50 = 9600 nM). Our HTL study on
These compounds were evaluated in a calcium influx
Fluorometric Imaging Plate Reader (FLIPR) assay
employing 1321N1 cells transfected with human
mGluR1 or human mGluR5 receptors (co-expressing
rat GLAST).40 The antagonist potency, expressed as
IC50, is the concentration at which 50% of the Ca2+ flux
induced by 10 lM glutamate is blocked.
N
N
N
N
O
Cl
1
hmGluR1 FLIPR EC50 = 242 nM
hmGluR5 FLIPR EC50 = 9600 nM
Concurrent with the antagonist activity characteriza-
tion, we decide to start evaluating the ADME properties
of the project compounds to identify possible orally bio-
available compounds. Aqueous solubility, in vitro sta-
bility in liver microsomes, and passive membrane
permeability41 were measured on the most potent ana-
logs to monitor such progress.
Figure 1.
O
a
b
NH2
N
O
NH
N
N
N
N
N
N
N
O
O
O
R1
O
Different R1 groups were first investigated as shown in
Table 1. During the HTS, a closely related analog 1a,
a meta-chloro isomer of 1, was found to be inactive.
Subsequent modifications of R1 groups were focused
3
4
1b-1k
Scheme 1. Reagents and conditions: (a) i—Ac2O, reflux, overnight;
ii—NH4OH, MeOH, 2 h; (b) R1NH2, POCl3, 165 ꢁC, 2 h.
R2
N
O
N
O
N
N
R2
N
N
+
N
N
c
Cl
H
N
Cl
N
CN
a-b
2a-2b
N
N
EtO
CO2Et
d
O
Cl
R2
N
N
N
+
N
R2
5
6
N
N
N
N
O
O
Cl
2c-2k, R2 = Aryl
N
-2 Regionisomer
Scheme 2. Reagents and conditions: (a) NH2NH2, EtOH, 75 ꢁC, 2 h; (b) i—Ac2O, reflux, overnight; ii—step b in Scheme 1; (c) R2OH, DBAD, P-
PPh3, THF, DMF; (d) R2X, CuI, ligand, K3PO4, THF, DMSO, 180 ꢁC, microwave, 30 min.

X. Wang et al. / Bioorg. Med. Chem. Lett. 17 (2007) 4303–4307
Table 1. Antagonist potencies of 5-substituted pyrazolo[3,4-d]pyrimidin-4-ones
4305
R2
N
N
1
3
N
5
N
R1
2
O
1a-i, 2a-l
Compound R1
R2
FLIPR IC50 SEMa (nM) clogPc Solubility Microsomal
Permeability
clearanced (L/h/kg) (·10À6 cm/s)
(lM)
hmGluR1
hmGluR5
1
4-Cl–C6H4
3-Cl–C6H4
Ph
Ph
Ph
Ph
Ph
242 60
>100,000
9600 1200 4.20
NDb
18
7.0
6.9
29.6
19.4
1a
1b
1c
1d
1e
1f
1g
1h
1i
4-Br–C6H4
4-OH–C6H4
4-CF3O–C6H4
78
7
>100,000
>100,000
>100,000
>100,000
>100,000
NDb
4.35
14
2400 160
>100,000
>100,000
800 160
760 160
91 20
4-NH2SO2–C6H4 Ph
3-F-4-Cl–C6H4
Cycloheptyl
Piperidin-1-yl
Azepan-1-yl
4-Cl–C6H4
4-Cl–C6H4
4-Cl–C6H4
4-Cl–C6H4
4-Cl–C6H4
4-Cl–C6H4
4-Cl–C6H4
4-Cl–C6H4
4-Cl–C6H4
4-Cl–C6H4
4-Cl–C6H4
4-Cl–C6H4
Ph
Ph
4.34
2.55
18
19
11
NDb
5.49
Ph
Ph
2800 800
3600 370
>100,000
>100,000
9500 2200
>100,000
>100,000
>100,000
>100,000
>100,000
>100,000
>100,000
108
240 50
520 130
Cyclohexylmethyl >100,000
2a
2b
2c
2d
2e
2f
2g
2h
2i
Cycloheptyl
2-CH3–C6H4
3-CH3–C6H4
3-Cl–C6H4
350 70
180
220 30
127
3
4.69
4.91
2.70
30
11
42
24
11
13.4
5.6
3-NH2SO2–C6H4
4-NH2SO2–C6H4
4-Cl–C6H4
6
< 2.5
17.6
1412 200
1100 250
>100,000
230 16
Pyridin-2-yl
Pyridin-3-yl
2j
2.79
73
4.0
21.4
2k
2l
Pyrimidin-5-yl
Pyrazin-2-yl
9800 1730 >100,000
>100,000 >100,000
a Mean value for antagonist IC50 calculated from at least three determinations SEM in FLIPR assay using 1321N1 cells expressing either human
mGluR1 or mGluR5 receptors.
b ND, not determined.
c Calculated logP.
d Rat microsomal scaled intrinsic clearance.
on para-substituted analogs accordingly. The para-
chloro group of R1 could be replaced by a bromo to give
1b, which is more potent and selective. Other substitu-
ents at this position such as hydroxy (1c), trifluorometh-
oxy (1d), and aminosulfonyl (1e), however, either
decreased or abolished the mGluR1 antagonist activity,
although they were not active against mGluR5 either.
Additional substitution on the phenyl ring did not im-
prove the antagonist activity (1f). Saturated cycloalkyl
groups and their variants were also prepared and tested.
Those compounds with ring sizes of 6 and above were
active (1g–1i), indicating a putative large hydrophobic
pocket on the receptor that can accommodate these
non-polar cycloalkyl R1 rings. Despite being more po-
tent than 1, 1h and 1i were weakly active against
mGluR5, therefore less selective.
metabolism profile. Based on the above observations
our focus was switched to R2 modifications, keeping
the para-chloro on the R1 phenyl ring. One postulation
was to introduce electron-withdrawing groups at R2 to
slow down the metabolism while maintaining or improv-
ing the in vitro profile.
In vitro testing indicated that all the N-2 regioisomers
were inactive (data not shown), highlighting that right
spatial alignment of different fragments is critical to gen-
erating favorable interactions with the receptor. Like
R1, large hydrophobic groups such as cycloheptyl were
favored over smaller rings. The bioisosteric cyclo-
hexylmethyl R2 (2b) was inactive. In contrast to the
para-substitution preference of the R1 phenyl ring, com-
pounds with meta-substituted R2 groups were more ac-
tive (2d–2f) with no detectable mGluR5 antagonism,
with 2f being the most potent. Similar substitution at
the para-position led to weaker compounds (2g vs 2f,
2h vs 2e) than their meta-cogeners. Substitution at the
ortho-position (2c) provided a weaker and less selective
mGluR1 antagonist. Meanwhile, different nitrogen-con-
taining heterocycles were also surveyed. While 2-pyridyl
R2 (2i) was inactive, the 3-pyridyl analog (2j) showed
comparable mGluR1 antagonism as 1, consistent with
the previous observation that meta-substituents were
beneficial to the antagonist activity. Two meta-embed-
The initial hit 1 had relatively low solubility and high
microsomal clearance but good membrane permeability.
More active and selective analog 1b showed no signifi-
cant improvement in solubility and microsomal stabil-
ity. Compound 1h exhibited much higher microsomal
clearance and poorer permeability comparing to 1, indi-
cating faster metabolism of the piperidine ring. Addition
of a fluoro group (1f) did not slow down the microsomal
clearance, suggesting that modification of R2 might be
necessary to improve both antagonist activity and

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X. Wang et al. / Bioorg. Med. Chem. Lett. 17 (2007) 4303–4307
Table 2. Mean pharmacokinetic parameters in Sprague–Dawley rats (iv, ip, po 1 mg/kg)
AUCb
Vb
CLd
Cmax
tmax
t1/2
F
c
e
Compound
(h)
(h)
(%)
1b
2f
iva
ipa
1285
6150
389
3.1
0.4
0.8
0.2
2.5
1.5
0.25
1.7
1.3
1.2
1b
2f
0.17
1.54
0.03
2.1
0.25
1.7
1.3
1.2
30
Quantf
8
Quantf
7790
100
1b
2f
poa
6240
a n = 9 animal per study.
b ng h/mL.
c L/kg.
d ng/mL.
e lg/mL.
f Quantitative.
ded nitrogens (2k) resulted in much weaker activity, and
compound with ortho- and meta-embedded nitrogens
(2l) was inactive.
Acknowledgments
The authors thank the Abbott HTS group, Renjie
Chang, Loan Miller, and Marie Uchic for preparing
1321N1 cells and conducting functional and binding
studies, Dr. Kennan Marsh for conducting PK studies,
and Dr. Tom Pagano for helpful NMR
characterizations.
Among these active analogs, 2d had better solubility but
faster clearance. The electron-withdrawing meta-chloro
analog (2e) had higher clogP, similar solubility and
clearance as 1 but much lower permeability. Incorpora-
tion of aminosulfonyl (2f), a polar, electron-withdraw-
ing group, however, decreased clogP, improved
solubility and stability in microsomes significantly while
maintained relative good permeability. The meta-
embedded pyridyl (2j) exhibited similar ADME profile.
Supplementary data
Experimental procedures, compound characterization
data, and ADME assay methods associated with this
article can be found, in the online version. Supple-
mentary data associated with this article can be found
in the online version, at doi:10.1016/j.bmcl.
2007.05.028.
The overall favorable in vitro characteristics of 2f
prompted us to evaluate its pharmacokinetic (PK) pro-
file in rat (Table 2). Comparing to 1b, intravenous (iv)
administration of 2f in rat revealed a much lower clear-
ance (0.2 L/h/kg vs 0.8 L/h/kg), agreeing in rank order
with their in vitro microsomal metabolism rate. The cal-
culated volume of distribution of 2f was much less than
that of 1b, which contributes to its lower iv half-life
(1.5 h vs 2.5 h). Despite this, compound 2f has substan-
tially improved intraperitoneal (ip) and oral (po) plasma
exposure and peak concentrations of those of 1b. The
bioavailabilities of 2f are quantitative in both cases.
References and notes
1. Bleicher, K. H.; Boehm, H.-J.; Muller, K.; Alanine, A. I.
Nat. Rev. Drug. Disc. 2003, 2, 369.
2. Davis, A. M.; Keeling, D. J.; Steele, J.; Tomkinson, N. P.;
Tinker, A. C. Curr. Top. Med. Chem. 2005, 5, 421.
3. Gillespie, P.; Goodnow, R. A., Jr. Annu. Rep. Med. Chem.
2004, 39, 293.
4. Teague, S. J.; Davis, A. M.; Leeson, P. D.; Oprea, T. I.
Angew. Chem., Int. Ed. 1999, 38, 3743.
5. Oprea, T. I.; Davis, A. M.; Teague, S. J.; Leeson, P. D.
J. Chem. Inf. Comput. Sci. 2001, 41, 1308.
6. Excitatory Amino Acids and Synaptic Transmission;
Wheal, H. V., Thomson, A. M., Eds.; Academic Press:
London, 1995.
7. The Ionotropic Glutamate Receptor; Monaghan, D. T.,
Wenthold, R. J., Eds.; Humana Press: Totowa, NJ, 1997.
8. Parsons, C. G.; Danysz, W.; Quack, G. Drug News
Perspect. 1998, 11, 523.
9. The Metabotropic Glutamate Receptors; Conn, P. J., Patel,
J., Eds.; Humana Press: Totowa, NJ, 1994.
10. Dingledine, R.; Borges, K.; Bowie, D.; Traynelis, S. F.
Pharmacol. Rev. 1999, 51, 7.
In conclusion, efficient HTL study, characterized by the
parallel evaluations of both the biochemical and
in vitro ADME profiles, was carried out on the HTS
hit 1 as novel mGluR1 antagonists. The distinctive pref-
erence of para-substituents at R1 and meta-groups at R2
is noteworthy. R1 modifications offered compounds with
better potency and subtype selectivity but similar ADME
properties. Nevertheless, careful choosing and incorpo-
ration of electron-withdrawing group at R2 led to signif-
icant improvements of ADME properties. Within this
structure class the in vitro ADME data were predictive
of what was observed in in vivo PK study in terms of
clearance and bioavailability. This HTL effort quickly
turned a ‘lead-like’ HTS hit 1 into a true lead molecule
2f with high in vitro potency and superb physicochemical
properties. The identification of orally bioavailable
mGluR1 selective antagonists will aid the understanding
of mGluR1 related pharmacology and potentially benefit
the discovery of therapies from selective mGluR1
modulation.
11. Bra¨uner-Osborne, H.; Egebjerg, J.; Nielsen, E. Ø.; Madsen,
U.; Krogsgaard-Larsen, P. J. Med. Chem. 2000, 43, 2609.
12. Nakanishi, S.; Masu, M. Annu. Rev. Biophys. Biomol.
Struct. 1994, 23, 319.
13. Pin, J. P.; Duvoisin, R. Neuropharmacology 1995, 34, 1.

X. Wang et al. / Bioorg. Med. Chem. Lett. 17 (2007) 4303–4307
4307
14. Vidnyanszky, Z.; Hamori, J.; Negyessy, L.; Ruegg, D.;
Knopfel, T.; Kuhn, R.; Gorcs, T. J. NeuroReport 1994, 6,
209.
15. 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.
16. Romano, C.; Van den Pol, A. N.; O’Malley, K. J. Comp.
Neurol. 1996, 367, 403.
17. Valerio, A.; Rizzonelli, P.; Paterlini, M.; Moretoo, G.;
Knopfel, T.; Kuhn, R.; Memo, M.; Spano, P. Neurosci.
Res. 1997, 28, 49.
31. Lavreysen, H.; Wouters, R.; Bischoff, F.; Nobrega Pereira,
S.; Langlois, X.; Blokland, S.; Somers, M.; Dillen, L.;
Lesage, A. S. J. Neuopharmacology 2004, 47, 961.
32. Micheli, F.; Di Fabio, R.; Cavanni, P.; Rimland, J. M.;
Capelli, A. M.; Chiamulera, C.; Corsi, M.; Corti, C.;
Donati, D.; Feriani, A.; Ferraguti, F.; Maffeis, M.; Missio,
A.; Ratti, E.; Paio, A.; Pachera, R.; Quartaroli, M.;
Reggiani, A.; Sabbatini, F. M.; Trist, D. G.; Ugolini, A.;
Vitulli, G. Bioorg. Med. Chem. 2003, 11, 171.
33. Mabire, D.; Coupa, S.; Adelinet, C.; Poncelet, A.;
Simonnet, Y.; Venet, M.; Wouters, R.; Lesage, A. S. J.;
Beijsterveldt, L. V.; Bischoff, F. J. Med. Chem. 2005, 48,
2134.
18. Fisher, K.; Fundytus, M. E.; Cahill, C. M.; Coderre, T. J.
Pain 1998, 77, 59.
19. Boxall, S. J.; Berthele, A.; Laurie, D. J.; Sommer, B.;
Zieglgansberger, W.; Urban, L.; Tolle, T. R. Neuroscience
1998, 82, 591.
20. Berthele, A.; Boxall, S. J.; Urban, A.; Anneser, J. M. H.;
Zieglgansberger, W.; Urban, L.; Tolle, T. R. Dev. Brain
Res. 1999, 112, 39.
34. Di Fabio, R.; Micheli, F.; Alvaro, G.; Cavanni, P.;
Donati, D.; Gagliardi, T.; Fontana, G.; Giovannini, R.;
Maffeis, M.; Mingardi, A.; Tranquillini, M. E.; Vitulli, G.
Bioorg. Med. Chem. Lett. 2007, 17, 2254.
35. Kohara, A.; Toya, T.; Tamura, S.; Watabiki, T.; Nagak-
ura, Y.; Shitaka, Y.; Hayashibe, S.; Kawabata, S.; Okada,
M. J. Pharmacol. Exp. Ther. 2005, 315, 163.
36. Zheng, G. Z.; Bhatia, P.; Daanen, J.; Kolasa, T.; Patel,
M.; Latshaw, S.; El-Kouhen, O. F.; Chang, R.; Uchic, M.
E.; Miller, L. N.; Nakane, M.; Lehto, S. G.; Honore, M.
P.; Moreland, R. B.; Brioni, J. D.; Stewart, A. O. J. Med.
Chem. 2005, 48, 7374.
37. Vaidya, N. A.; Blanton, J. C. D. J. Org. Chem. 1982, 47,
1777.
38. Gentles, R. G.; Wodka, D.; Park, D. C.; Vasudevan, A.
J. Comb. Chem. 2002, 4, 442.
39. Antilla, J. C.; Baskin, J. M.; Barder, T. E.; Buchwald, S. L.
J. Org. Chem. 2004, 69, 5578.
21. Jia, H.; Rustinoi, A.; Valtschanoff, J. G. J. Comp. Neurol.
1999, 410, 627.
22. Fisher, K.; Coderre, T. J. Pain 1996, 68, 255.
23. Fisher, K.; Coderre, T. J. NeuroReport 1996, 2743.
24. Young, M. R.; Fleetwood Walker, S. M.; Dickinson, T.;
Blackburn Munro, G.; Sparrow, H.; Birch, P. J.; Bountra,
C. Brain Res. 1997, 777, 161.
25. Boxall, S. J.; Berthele, A.; Tolle, T. R.; Zieglgansberger,
W.; Urban, L. NeuroReport 1998, 9, 1201.
26. Neugebauer, V.; Lucke, T.; Schaible, H. G. Eur. J.
Neurosci. 1994, 6, 1179.
27. Layton, M. E. Curr. Top. Med. Chem. 2005, 5, 859.
28. Annoura, H.; Fukunaga, A.; Uesugi, T.; Tatsuoka, T.;
Horikawa, Y. Bioorg. Med. Chem. Lett. 1996, 6, 763.
29. Carroll, F. Y.; Stolle, A.; Beart, P. M.; Voerste, A.;
Brabet, I.; Mauler, F.; Joly, C.; Antonicek, H.; Bockaert,
40. El-Kouhen, O.; Lehto, S. G.; Pan, J. B.; Chang, R.; Baker,
S. J.; Zhong, C.; Hollingsworth, P. R.; Mikusa, J. P.;
Cronin, E. A.; Chu, K. L.; McGaraughty, S. P.; Uchic,
M.; Miller, L. N.; Rodell, N. M.; Patel, M.; Bhatia, P.;
Mezler, M.; Kolasa, T.; Zheng, G. Z.; Fox, G. B.; Stewart,
A. O.; Decker, M. W.; Moreland, R. B.; Brioni, J. D.;
Honore, P. Br. J. Pharmacol. 2006, 149, 761.
´
J.; Muller, T.; Pin, J. P.; Prezeau, L. Mol. Pharmacol.
¨
2001, 59, 965.
30. Lavreysen, H.; Janssen, C.; Bischoff, F.; Langlois, X.; Leysen,
J. E.; Lesage, A. S. J. Mol. Pharmacol. 2003, 63, 1082.
41. Avdeef, A. Curr. Top. Med. Chem. 2001, 1, 277.