Oxamides as novel NR2B selective NMDA receptor antagonists

Article abstract of DOI:10.1016/j.bmcl.2004.05.053

A novel series of oxamides derived from indole-2-carboxamides was identified as potent NR2B selective NMDA receptor antagonists. Several members of this group showed good analgesic activity in the mouse formalin test.

Full text of DOI:10.1016/j.bmcl.2004.05.053

Bioorganic & Medicinal Chemistry Letters 14 (2004) 3953–3956
Oxamides as novel NR2B selective NMDA receptor antagonists
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Gizella Barta-Szalai, Istvan Borza, Eva Bozo, Csilla Kiss, Bela Agai,
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Agnes Proszenyak, Gyorgy M. Keseru, Aniko Gere, Sandor Kolok,
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Kornel Galgoczy, Csilla Horvath, Sandor Farkas and Gyorgy Domany
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aGedeon Richter Ltd, 10, PO Box 27, H-1475 Budapest, Hungary
bBudapest University of Technology and Economics, PO Box 91, H-1521 Budapest, Hungary
Received 19 April 2004; revised 19 May 2004; accepted 21 May 2004
Available online 17 June 2004
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Dedicated to Professor Karoly Lempert on his 80th birthday
Abstract—A novel series of oxamides derived from indole-2-carboxamides was identified as potent NR2B selective NMDA receptor
antagonists. Several members of this group showed good analgesic activity in the mouse formalin test.
Ó 2004 Elsevier Ltd. All rights reserved.
Over the last several years an increasing number of re-
ports have demonstrated the importance of NR2B
subunit-containing NMDA receptors in many physio-
logical and pathophysiological processes.1 These find-
ings made it attractive to choose this group of receptors
as targets of drug discovery aiming at the treatment of
several human diseases, among others of neuropathic
pain.2 Pharmacological investigations3 and very re-
cently, clinical observations4 have proved this concept.
NR2B subunit selective NMDA receptor antagonists fall
into several structural families.5;6 A rather populous
subclass of these compounds can be described as an
H-bond donor moiety containing benzene ring connected
to the N of a (substituted) phenyl- or benzylpiperidine via
a two or three-atom long spacer. Five characteristic
representatives of this class are (1R,2S)-3-(4-benzylpi-
peridin-1-yl)-1-(4-hydroxy-phenyl)-2-methyl-1-propanol
(Ro-25,6981),7 1-[2-(4-hydroxyphenoxy)ethyl]-4-(4-meth-
ylbenzyl)-piperidin-4-ol (Co-11,244),8 6-[3-[4-[(4-fluoro-
phenyl)-methyl]-1-piperidinyl]-1-oxopropyl]-2(3H)-benzo-
xazolone (EMD-95885),9 (+)-(1S,2S)-(4-hydroxyphenyl)-
2-(4-hydroxy-4-phenylpiperidin-1-yl)-propan-1-ol (CP-
101,606, traxoprodil)10 and 6-[2-[4-(4-fluoro-benzyl)-
piperidin-1-yl]ethansulfinyl]-3H-benzoxazol-2-one (CI-
1041, besonprodil).11
OH
HO
HO
CH3
N
N
O
Me
OH
Ro-25,6981
Co-101,244
HO
H
CH3
N
HO
HO
O
N
O
N
O
F
OH
N
N
N
H
N
H
O
OH
O
O
EMD-95885
CP-101,606
1
2
H
N
O
Recently we have reported on potent and selective
NR2B receptor antagonists among N-acylated 4-benz-
ylpiperidine derivatives, like compound 1, demonstrat-
ing that the basic nitrogen is not a condition of the
activity.12
N
O
S
F
O
CI-1041
It was found that the NHin the indole nucleus is a
beneficial feature of this structure and the nonbasic
* Corresponding author. Tel.: +36-1-431-4050; fax: +36-1-432-6002;
e-mail: gy.domany@richter.hu
0960-894X/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2004.05.053

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G. Barta-Szalai et al. / Bioorg. Med. Chem. Lett. 14 (2004) 3953–3956
Table 1. Results of receptor binding, functional assay and in vivo activity for compounds 1–3
X
O
Q
N
N
H
Y
O
3a-3l
Q
X
Y
Mp (°C)
[3H]Ro-25,6981
bindinga
IC50 (nM)
NMDA-evoked
a;b
NR1/NR2Aa Formalin test, p.o.
D[Ca2þ
IC50 (nM)
]
inhib. %
ED50 (mg/kg)
i
1
2
31 10
42 13
18
1.4
HO
CH2
CH2
H167–169
16
2
31
6
20
9.4
H
N
O
3a
3b
3c
F
297–300
5
1
2
1
2
)1
2
>20
14
N
H
H
N
O
O
CH2
H289–291
4
1
6 1
N
H
H
N
O
Cl
286–288
26
7
8
1
>20
N
H
H
N
3d
3e
CH2
CH2
H192–194
8
2
3
1
9
0.9
O
O
O
H
N
F
223–225
6
1
3
4
7
1
2
5
3
7.7
4.4
O
H
N
3f
3g
3h
3i
O
Cl
244–245
40
O
O
O
O
H
N
CH2
O
H201-203
17
4
9
2
17
0.4
S
H
N
Me
Me
215–217
17
54
1
6
8
1
2
15
7
0.2
0.5
S
H
N
CH2
208–209
15
O
S
H
N
3j
O
Me
311–314
131 31
10
2
14
>20
N
H
H
O
N
3k
CH2
CH2
H206–207
139
6
29
9
15
<0.1
O
H
N
O
3l
Me
228–231
17
2
18
5
15
10
O
Ro-25,6981
Co-101,244
EMD 95885
CP-101,606
CI-1041
6
4
8
7
4
1
1
1
1
1
57
5
5
1
p.o. inactive 5.1 (ip)
p.o. inactive 5.9 (ip)
3.7
48
4
30
8
>20 (s.c. and p.o.)
2.4
1
a Values represent the means SEM. The number of experiments is 3–4 for [3H]Ro-25,6981 binding, 2–5 for NMDA-evoked D[Ca2þ
NR1/NR2A measurements.
]
and 1–2 for
a
i
b NMDA-evoked changes of intracellular Ca2þ
.

G. Barta-Szalai et al. / Bioorg. Med. Chem. Lett. 14 (2004) 3953–3956
3955
Figure 1. Conformational and electrostatic potential differences between compounds 2 and 1.
nitrogen of the 4-benzylpiperidine part is also advanta-
geous because it improves selectivity over many other
different receptors.
derivatives used are either commercially available or
were prepared by analogy with the procedure developed
recently for the preparation of 3-benzylpiperidines.16
The 4-phenoxy-piperidines were prepared following
known procedures17 as depicted in Scheme 2. Aniline
derivatives (QNH2) were prepared by catalytic reduction
of the corresponding nitro derivatives that were in turn
prepared by nitration of the commercially available
heterobicycles.
One of our modifications aiming at new structures, but
keeping as much of the characteristics of compound 1 as
possible, resulted in a new oxamide derivative 2 that was
almost twice as potent as compound 1 in both binding
and functional tests (see Table 1).
Global minimum conformations of 1 and 2 were found
to be rather similar, however, negative regions of the
calculated Poisson–Boltzmann potential revealed
remarkably different electrostatic pattern (Fig. 1).13
Introduction of the negative site by the carbonyl group
of 2 gives further opportunity for receptorial interac-
tions and increases binding affinity, as it was demon-
strated for a number of analogues.
Biological activity of the prepared compounds was
measured in a binding assay using tritiated Ro-25,6981
as radioligand7;18;19 and in a functional assay where the
inhibition of NMDA-evoked increase of intracellular
Ca2þ level was determined on cells expressing
recombinant NR1/NR2B receptors20 (Table 1). Baseline
and NMDA-evoked changes of intracellular Ca2þ were
monitored by fluorimetry using a Ca2þ-selective fluo-
rescent dye (Fluo-4/AM) and a plate reader fluorime-
ter.20 Selectivity towards NR2A subunit-containing
NMDA receptors was tested by the same functional
assay using cells expressing recombinant NR1/NR2A
receptors and none of the compounds exhibited signifi-
cant activity up to 15 lM concentration. In vivo anal-
Since compounds containing phenolic OHgroups have
generally unfavourable metabolic properties14 it was
decided that condensed heterobicycles with at least one
NHshould substitute the phenol moiety on the left-
hand side of structure 1.
gesic activity was tested in the mouse formalin test21;22
a
A series of oxamide derivatives has been prepared and
tested. A representative selection of those (3a–l) is pre-
sented in Table 1.
model of persistent pain. It is known that the second
phase response can be blocked by NMDA antagonists
probably via spinal site.23
Compounds 2 and 3a–l were synthesised in a straight-
forward manner (Scheme 1).15 The 4-benzylpiperidine
Benzimidazolones and benzoxazolones containing 4-
benzylpiperidines (3a,b,d,e) showed better affinities to-
wards the NR2B subunit than compound 2 and their
IC50 values were comparable to that of the reference
compounds. The 4-chlorophenoxypiperidine containing
analogues (3c and 3f), however, had weaker activities in
this assay. The other heterobicycles (3g–l) showed sim-
ilar or weaker affinities than compound 2.
X
X
(ii)
(i)
O
3a-3l
N
N
H
Y
HO
Y
O
Scheme 1. Synthesis of compounds 2 and 3a–l. Reagents and condi-
tions: (i) (1) ClCOCOOEt, TEA, CHCl3, 10 °C, 2 h; (2) KOH, EtOH/
H2O, 20 °C, 2 h; (3) 6 N HCl, 10 °C, 2 h; (ii) QNH2, HBTU, TEA,
DMF, 20 °C, 20 h.
The substitution of the OHgroup in 2 for condensed
heterocycles increased the potency of the new derivatives
Cl
OH
O
O
(i)
(ii)
+
N
N
Y
Y
N
Y
Br
(iii)
O
O
(iv)
HN
N
Y
Y
Scheme 2. Synthesis of 4-phenoxy-piperidines. Reagents and conditions: (i) cat. 1-(4-pyridyl)pyridinium chloride hydrochloride, 220 °C, 6 h;
(ii) benzyl bromide, diethyl ether, 20 °C, 48 h; (iii) NaBH4, EtOH; (iv) H2, 10% Pd/C, MeOH, rt.

3956
G. Barta-Szalai et al. / Bioorg. Med. Chem. Lett. 14 (2004) 3953–3956
in the NMDA evoked Ca2þ assay. This improvement
was generally higher and included more derivatives than
in the case of the binding test. Even compounds with 4-
phenoxypiperidine (3c and 3f) had IC50 values lower
than 10 nM.
8. Zhou, Z.; Cai, S. X.; Whittemore, E. R.; Konkoy, C. S.;
Espitia, S. A.; Tran, M.; Rock, D. M.; Coughenour, L. L.;
Hawkinson, J. E.; Boxer, P. A.; Bigge, C. F.; Wise, L. D.;
Weber, E.; Woodward, R. M.; Keana, J. F. W. J. Med.
Chem. 1999, 42, 2993–3000.
9. Leibrock, J.; Prucher, H.; Rautenberg, W. Pharmazie
1997, 52, 479–480.
Several known NR2B selective antagonists have been
synthesised and tested in vivo in our formalin test (Table
1). Co-101,244, Ro-25,6981, CP-101,606 were inactive
after oral administration. Since the former two com-
pounds were potent given ip those have probably poor
oral bioavailability. CI-1041 and EMD 95885 had good
oral potency. Comparing oral efficacy of our com-
pounds with the examined NR2B selective compounds
of various structural families, we can conclude that
several oxamide structures have outstanding oral effi-
cacy with ED50 value below 1 mg/kg. It should be noted,
however that in vivo activities did not parallel those in
vitro. Of course, besides in vitro potency, there are
several other yet unexamined features that can modify
the in vivo observed effect, like oral bioavailability,
brain penetration, metabolic stability, etc.
10. Chenard, B. L.; Bordner, J.; Butler, T. W.; Chambers, L.
K.; Collins, M. A.; De Costa, D. L.; Ducat, M. F.;
Dumont, M. L.; Fox, C. B.; Mena, E. E.; Menniti, F. S.;
Nielsen, J.; Pagnozzi, M. J.; Richter, K. E. G.; Ronau, R.
T.; Shalaby, I. A.; Stemple, J. Z.; White, W. F. J. Med.
Chem. 1995, 38, 3138–3145.
11. Wright, J. L.; Kesten, S. R.; Upasani, R. B.; Lan, N. C.
PCT Int. Appl. WO2000000197-A1. 2000; Chem. Abstr.
2000, 132, 64255.
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ꢀ
12. Borza, I.; Kolok, S.; Gere, A.; Agai-Csongor, E.; Agai, B.;
ꢀ
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Tarkanyi, G.; Horvath, Cs.; Barta-Szalai, G.; Bozo, E.;
Kiss, Cs.; Bielik, A.; Nagy, J.; Farkas, S.; Domany, Gy.
ꢀ
ꢀ
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Bioorg. Med. Chem. Lett. 2003, 13, 3859–3861.
13. Conformational analysis of 1 and 2 was performed by
Low-Mode search as implemented in MacroModel 6.0.
Calculation of electrostatic potentials was carried out by
MOLCAD in Sybyl 6.9.
14. Wright, J. L.; Gregory, T. F.; Kesten, S. R.; Boxer, P. A.;
Serpa, K. A.; Meltzer, L. T.; Wise, L. D. J. Med. Chem.
2000, 43, 3408–3419.
In summary, a series of new oxamide derivatives were
prepared and found to be potent and selective antago-
nists of the NR2B subtype of NMDA receptors. Their in
vitro activities were comparable with those of the most
potent literature compounds, while some representatives
of this class showed outstanding activity in vivo. Results
of detailed biological investigations will be published
under separate cover.
15. The IR, 1HNMR, 13C NMR and MS spectra for all
intermediates and final compounds were consistent with
the assigned structures. Purity of the samples was checked
by HPLC and HRMS analysis.
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F. Tetrahedron 2003, 59, 7897–7900.
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21. Licking behaviour was counted 20–25 min after injection
of formalin into the hindpaw of mice pretreated orally
with test compounds suspended in 5% Tween-80,
except Ro-25,6981 and Co-101,244 that was given ip
Percentage inhibition was calculated for each dose and
the dose producing half-maximal effect (ED50) was
determined. Maximal inhibition ranged from 59% to
93%.
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