Selective NR1/2B N-methyl-D-aspartate receptor antagonists among indole-2-carboxamides and benzimidazole-2-carboxamides

Article abstract of DOI:10.1021/jm060420k

(4-Benzylpiperidine-1-yl)-(6-hydroxy-1H-indole-2-yl)-methanone (6a) derived from (E)-1 -(4-benzylpiperidin-1-yl)-3-(4-hydroxy-phenyl)-propenone (5) was identified as a potent NR2B subunit-selective antagonist of the NMDA receptor. To establish the structu

Full text of DOI:10.1021/jm060420k

J. Med. Chem. 2007, 50, 901-914
901
Articles
Selective NR1/2B N-Methyl-D-aspartate Receptor Antagonists among Indole-2-carboxamides
and Benzimidazole-2-carboxamides
Istva´n Borza,* EÄ va Bozo´, Gizella Barta-Szalai, Csilla Kiss, Ga´bor Ta´rka´nyi, AÄ da´m Demeter, Tama´s Ga´ti, Viktor Ha´da,
Sa´ndor Kolok, Aniko´ Gere, La´szlo´ Fodor, Jo´zsef Nagy, Korne´l Galgo´czy, Ildiko´ Magdo´, Be´la AÄ gai,† Jo´zsef Fetter,†
Ferenc Bertha,† Gyo¨rgy M. Keseru¨, Csilla Horva´th, Sa´ndor Farkas, Istva´n Greiner, and Gyo¨rgy Doma´ny
Gedeon Richter Ltd., Budapest 10, POB 27, H-1475, Hungary, and Budapest UniVersity of Technology and Economics,
Budapest, POB 91, H-1521, Hungary
ReceiVed April 11, 2006
(4-Benzylpiperidine-1-yl)-(6-hydroxy-1H-indole-2-yl)-methanone (6a) derived from (E)-1-(4-benzylpiperidin-
1-yl)-3-(4-hydroxy-phenyl)-propenone (5) was identified as a potent NR2B subunit-selective antagonist of
the NMDA receptor. To establish the structure-activity relationship (SAR) and to attempt the improvement
of the ADME properties of the lead, a series of compounds were prepared and tested. Several derivatives
showed low nanomolar activity both in the binding and in the functional assay. In a formalin-induced
hyperalgesia model in mice, 6a and (4-benzylpiperidine-1-yl)-[5(6)-hydroxy-1H-benzimidazol-2-yl]-
methanone (60a) were as active as besonprodil (2) after oral administration. A CoMSIA model was developed
based on binding data of a series of indole- and benzimidazole-2-carboxamides.
Introduction
5, indicating that the basic nitrogen is not a condition of
activity10 (Figure 1). Numerous endogenous ligands of important
receptors in the CNS contain basic nitrogen, and basic nitrogen
is an important feature of the pharmacophore of several agents
acting on ion channels (e.g., hERG channels) as well. This may
result in the recognition of basic nitrogen containing exogenous
ligands by several of these receptors and ion channels and as a
consequence in off-target activities. The elimination of potential
off-target activities from lead structures is an important issue
in the NR2B antagonist field, too.11 To avoid or at least mitigate
possible adverse side effects, the nonbasic cinnamide derivative
5 was selected as a chemical starting point of our research aimed
at identifying novel, potent NR2B subtype-selective NMDA
receptor antagonists for the treatment of neuropathic pain. The
IC50 value of compound 5 for the inhibition of NMDA evoked
increase of intracellular Ca2+ level in rat primary cortical cell
culture was 131 nM, as measured in our laboratories. One of
our first modifications of this structure was the incorporation
of an NH group between the R carbon atom and the benzene
ring of the cinnamic acid part of the molecule, resulting in a
6-hydroxyindole-2-carboxamide derivative, compound 6a, with
more than 6-fold higher potency (IC50: 18 nM). Herein we
elaborate the structure-activity relationship (SAR) around
indole-2-carboxamide 6a. Our investigations were aimed at
clarifying the influence of the following features in general
formula A on the biological activity: a, nature and position of
the H-bond donor moiety Q; b, nature of X; c, position of the
substituent of the piperidine ring; d, nature of spacer Y; e, the
nature and position of Z; and f, possible substitution of the
pyrrole ring in the indole for other carbo- or heterocycles (V
and W). The goal of the lead optimization was to increase the
potency and to improve the drug-likeness, that is, the ADME
properties of the compounds. To achieve these goals, a series
of analogues of compound 6a were prepared and tested in vitro
and some representative members of the series in vivo as well
(Figure 2).
There is a high unmet medical need for new drugs in the
therapy of neuropathic pain. The principal cause of this fact is
that until recently little was known of the mechanisms under-
lying the various neuropathic pain conditions. The current
armamentarium of pharmacotherapy for neuropathic pain in-
cludes tricyclic antidepressants, anticonvulsants, opioids, and
unconventional agents like topical capsaicin. Suboptimal thera-
peutic efficacies and/or side effects are a serious limitation to
the use of these medications.1 Several compounds with novel
mechanisms of action are being studied to address this problem.
The already marketed gabapentin and its follow-up compound
pregabalin bind with high affinity to the R2δ accessory protein
of voltage-gated calcium channels widely distributed in the
central nervous system. Noradrenaline and serotonin reuptake
inhibitors, cannabinoid receptor agonists, and N-methyl-D-
aspartate (NMDA) receptor antagonists are also the focus of
current attention.2 The NMDA receptor is heteromeric and its
activity may be modulated by interaction at one of several
different binding sites. One of the most promising targets of
this receptor is the so-called ifenprodil binding site, situated on
the NR2B receptor subtype.3 Substantial effort has already been
invested in finding potent, selective, and drug-like NR2B
antagonists.4 Moreover, a recent clinical trial with 1 (traxoprodil,
(+) CP-101,606)5 provided additional impetus by demonstrating
the attenuation of neuropathic pain by NR2B subtype selective
NMDA antagonists in humans.6
A substantial proportion of the known NR2B subtype
selective NMDA antagonists are 1,4-disubstituted piperidines
like 1, 2 (besonprodil, CI-1041),7 3 (Ro-25-6981),8 or 4.9 There
are, however, examples of potent NR2B antagonists in which
the piperidine nitrogen is not basic, for example, in compound
* Corresponding author. Tel.: + 36-1-431-5139. Fax: +36-1-432-6002.
E-mail: i.borza@richter.hu.
† Budapest University of Technology and Economics.
10.1021/jm060420k CCC: $37.00 © 2007 American Chemical Society
Published on Web 02/10/2007

902 Journal of Medicinal Chemistry, 2007, Vol. 50, No. 5
Borza et al.
Figure 1. Structures of NR2B selective NMDA receptor antagonists.
Figure 2. Lead compound (6a) and the general formula of the prepared analogues.
Scheme 1a
a Reagents and conditions: (i) HBTU, TEA, DMF, 0 °C-rt, 16 h; (ii) H2, 10% Pd/C, MeOH, rt; (iii) PhCHO, Na(AcO)3BH3, AcOH, DCE, rt, 2 h; (iv)
MsCl, TEA, CHCl3, rt, 10 h.
Based on the data generated among indole- and benzimida-
zole-2-carboxamides, a CoMSIA model was constructed for the
facilitation of the design of further, more potent compounds.
Preliminary results of this work were published earlier.12
The preparation of some analogues (43, 44, and 19) was
started with Hemetsberger-Knittel indole synthesis.14 The
dihydroxy derivatives (10 and 11) were prepared from the
corresponding dibenzyloxy derivatives (43 and 44) by catalytic
hydrogenolysis (Scheme 2).
Chemistry
A related series of heterotricyclic carboxamides (20-22) were
synthesized according to the Fischer/Japp-Klingemann proce-
dure15 (Scheme 3).
Compounds 6a-6p, 7a-9a, 19-22, and 33a-35a were
prepared from appropriately substituted indole-2-carboxylic
acids (26-32), which were coupled to piperidines (a-p) using
a standard amide coupling reaction.13 Nitroindolecarboxamides
(33a-35a) were transformed via the corresponding amino
derivatives (12a-14a) to benzylamino derivative 15a or to
methansulfonamides (16a-18a) with standard procedures
(Scheme 1).
Amidine 23 was prepared from 6-benzyloxy-1H-indole-2-
carboxylic acid (51) via the corresponding nitrile (52) using a
Pinner-type procedure16 (Scheme 4).
Compound 24 was prepared by reducing carboxamide 6a with
LiAlH4 (Scheme 5).

NR1/2B N-Methyl-D-aspartate Receptor Antagonists
Journal of Medicinal Chemistry, 2007, Vol. 50, No. 5 903
Scheme 2a
a Reagents and conditions: (i) methyl azidoacetate, NaOMe, MeOH, 0 °C, 4 h; (ii) heating in xylene; (iii) 38, 39: KOSi(CH3)3, THF, reflux, 1 h; 41:
KOH, EtOH, reflux; (iv) 4-benzylpiperidine, HBTU, TEA, DMF, 0 °C-rt, 16 h; (v) H2, 10% Pd/C, MeOH, rt; (vi) ClCOCl, THF, TEA, rt.
Scheme 3a
a Reagents and conditions: (i) (1) NaNO2, H2O, HCL, 0 °C; (2) KOH, NaOAc, EtOH, MeCOCH(Me)COOEt, 0 °C; (ii) PPA, 120 °C; (iii) KOH, EtOH,
reflux; (iv) 4-benzylpiperidine, HBTU, TEA, DMF.
Scheme 4a
a Reagents and conditions: (i) (1) SOCl2, CHCl3, reflux, 1 h; (2) NH3; (ii) POCl3 CHCl3, reflux, 2 h; (iii) HCl, MeOH, 5 h; (iv) 4-benzylpiperidine.
Scheme 5a
a Reagents and conditions: (i) LiAlH4, THF, rt, 1 h.
Scheme 6a
a Reagents and conditions: (i) t-Boc2O, DMAP, DCM, rt, 2 h; (ii) (1) n-BuLi, SO2, THF, -70 °C-rt; (2) NCS, DCM, 5 °C; (iii) 4-benzylpiperidine, rt,
24 h; (iv) H2, 10% Pd/C, MeOH, rt.
The synthesis of sulfonamide 25 was started from 6-benzyl-
oxy-1H-indole (53). Lithiation was followed by the formation
of sulfonamide 54 in a one-pot procedure. Then hydrogenolysis
resulted in compound 25 (Scheme 6).
Piperidines used in the above syntheses were either com-
mercially available or prepared by procedures known from the
literature. 4-Phenoxypiperidines were prepared by reacting
4-chloropyridine with phenols, and then the obtained pyridine

904 Journal of Medicinal Chemistry, 2007, Vol. 50, No. 5
Borza et al.
Scheme 7a
a Reagents and conditions: (i) MeI, KOt-Bu, DMF, rt, 24 h; (ii) KOSi(CH3)3, THF, reflux, 1 h; (iii) SOCl2, MeOH, 0 °C-rt, 10 h; (iv) BBr3, DCM, -15
°C-rt, 10 h; (v) KOH, MeOH, reflux 1 h; (vi) 33% HBr-AcOH, 10 min; (vii) H2, 10% Pd/C, MeOH, rt; (viii) MesCl, pyridine, DCM, rt, 5 h.
Scheme 8a
a Reagents and conditions: (i) ClCOCOOEt, Et3N, CH2Cl2, 0 °C-rt; (ii) n-BuNH2, toluene, rt, 10 h; (iii) H2, 10% Pd/C, MeOH, rt; (iv) 240 °C, 10 min;
(v) 48% HBr, reflux, 48 h.
derivatives were saturated.17 4-Benzyloxypiperidines were ob-
tained by O-benzylation of N-Boc-4-piperidinol,18 while 4-phe-
noxymethylpiperidines were prepared by alkylation of phenols
with N-Boc-4-mesyloxymethylpiperidine.19 For the preparation
of 2-, 3-, and 4-(substituted benzyl)piperidines, a new and
efficient method was developed.20
Compounds 74, 56, 57, 75, 59, and 76 were prepared from
the corresponding heterobicyclic carboxylic acids (67, 68, 70,
71, 72, and 73) and 4-benzylpiperidine, using a standard amide
coupling reaction.21 Reagents were commercially available or
prepared from commercially available starting materials with
standard procedures. Some of the products were further reacted,
like 74 and 75, that were debenzylated and demethylated,
respectively, to obtain the corresponding hydroxy derivatives
55 and 58. From 5(6)-nitro-1H-benzimidazole-2-carboxylic acid
amide 76, the 5(6)-MsNH-derivative 63 was prepared via the
5(6)-amino-derivative 62 (Scheme 7).
Heterotricyclic carboxamide 64 was prepared with a benz-
imidazole synthesis, similar to that depicted in Scheme 8,
starting from aniline derivative 89 and acid chloride 87, which
in turn were prepared from 6-aminobenzoxazolinone (88) and
4-benzylpiperidine (a), respectively (Scheme 9).
The synthesis of heterotricyclic carboxamide 65 started from
5(6)-hydroxy-1H-benzimidazole-2-carboxylic acid. Nitration at
position 4(7) and coupling with 4-benzylpiperidine resulted in
carboxamide 92, which was subsequently reduced to 93. Ring
closure with CDI led to the final product (Scheme 10).
Results and Discussion
All compounds described were evaluated in a functional assay
by a fluorimetric measurement of NMDA-evoked elevation of
cytoplasmic calcium concentration ([Ca2+]i) in primary rat
neocortical cell cultures.23 Neurons in these cultures express
NMDA receptors containing multiple types of NR2 subunits
of which NR2B is the predominant one.24 Compounds active
in this test were then evaluated in an NR2B-selective binding
assay using [3H]-Ro-25-6981 as radioligand.25 We found that
the results obtained from the functional test were suitable for
the establishment of SAR during lead-optimization, while
acceptable QSAR models could only be obtained using binding
The syntheses of 5(6)-hydroxy-1H-benzimidazole- and 4(7)-
hydroxy-1H-benzimidazole-2-carboxylic acid (85 and 86) were
performed analogously to the procedure described in the
literature.22 For acylation of piperidine derivatives a-u, HBTU
coupling was applied, resulting in hydroxybenzimidazole-2-
carboxamides 60a-u and 61a (Scheme 8).

NR1/2B N-Methyl-D-aspartate Receptor Antagonists
Journal of Medicinal Chemistry, 2007, Vol. 50, No. 5 905
Scheme 9a
a Reagents and conditions: (i) ClCOCOOEt, DIPEA, DCM, 0 °C; (ii) (1) KOH, MeOH, rt; (2) HCl; (iii) SOCl2, reflux, 2 h; (iv) NaNO3, TFA, rt; (v)
CHCl3, TEA, rt; (vi) H2, 10% Pd/C, MeOH, rt; (vii) 240 °C, 10 min.
Scheme 10a
a Reagents and conditions: (i) NaNO3, TFA, rt; (ii) 4-benzylpiperidine, HBTU, TEA, DMF; (iii) H2, 10% Pd/C, THF, rt; (iv) 1,1′-carbonyldiimidazole,
THF, rt.
metabolism of the phenol moiety26 and the mutagenetic liability
Table 1. In Vitro Data for Reference Compounds
of aniline derivatives,27 our objective was to identify phenol
and aniline replacements that might improve the drug-likeness
of our compounds. Analogues bearing a condensed heterocycle
on the indole part (19-22) showed acceptable to good activites,
proving that this mode of formation of an H-bond donor moiety
in this area was a viable option.
Replacing the carboxamide functionality in compound 6a by
carboxamidine (23) resulted in a somewhat more active
analogue, whereas compounds with CH2 or SO2 in place of CO
(24 and 25, respectively) almost completely lost their activity
(Table 3).
NMDA-evoked
[3H]Ro-25,6981
binding
IC50 ( S.E.M. (nM)
a
∆[Ca2+
]
i
IC50 ( S.E.M. (nM)
n
n
1
2
3
4
5
41 ( 5
7
3
3
10
2
7 ( 1
6
3
3
3
3
6.6 ( 1.2
159 ( 29
8.6 ( 1.7
131 ( 10
4 ( 1
6 ( 1
3.5 ( 1.1
196 ( 43
a NMDA-evoked changes of intracellular Ca2+
.
data. IC50 values of the reference compounds 1-5 measured in
the above assays are shown in Table 1.
The effect of varying the position of the benzyl group on the
piperidine ring was investigated on 4-methoxybenzyl derivatives
6b-6d. In this instance, substitution at either position 3 (6c)
or position 2 (6d) substantially decreased potency (Table 4).
Another sensitive region of compound 6a is the spacer (Y)
between position 4 of the piperidine and the terminal benzene
ring. Both elimination (6e) and elongation (6f) of the methylene
group resulted in less-active compounds. A similar reduction
in potency was found when CH2 was substituted for CO, CHOH,
or NH (6j-6l). Somewhat surprisingly, the activities of the
benzyloxypiperidine and the phenoxymethylpiperidine deriva-
tives (6h and 6i) are closer to that of compound 6a than to that
of the geometrically more similar phenylethylpiperidine deriva-
tive (6f). This is apparently a novel example for the Friedman’s
paradox28 (Table 5).
The results in Table 2 show that the 5- and 4-hydroxy
analogues of compound 6a (7a and 8a) had comparable
activities, while the 7-hydroxy analogue (9a) showed inferior
activity. This indicated that there is probably more than one
H-bond acceptor moiety in the corresponding area of the
receptor. Further evidence for this assumption came from the
observation that the 4,6-dihydroxy analogue (10) had enhanced
activity compared to the monohydroxy derivatives. This com-
pound was actually found to be equipotent with besonprodil
(2), as can be seen in Table 1. The reduced potency of compound
9a (over 6a-8a) and 11 (over 10) is likely to reflect poor
interaction of the 7-hydroxyl with the receptor, possibly because
of its probable intramolecular hydrogen bonding with the indole
NH group. Among the amino analogues (12a-14a), only the
4-amino derivative (12a) showed high activity, while among
the methansulfonamido isomers (16a-18a), the 6-MsNH de-
rivative was the most active. Due to the anticipated high
As far as the substitution pattern of the terminal benzene was
concerned, it was found after having prepared and tested a small

906 Journal of Medicinal Chemistry, 2007, Vol. 50, No. 5
Borza et al.
Table 2. In Vitro Data for Compounds with Various Q-s in Formula A
Table 4. Influence on the In Vitro Data of the Position of the Benzyl
Substituent on the Piperidine Ring in Formula A
NMDA-evoked
[3H]Ro-25,6981
binding
IC50 (nM)
a
∆[Ca2+
]
i
subst.
IC50 ( S.E.M. (nM)
n
n
6b 4-(4-MeO)Bn
80 ( 14
2206 ( 406
>8000 ( 2
3
7
2
17
N.D.
N.D.
2
6c
3-(4-MeO)Bn
6d 2-(4-MeO)Bn
a NMDA-evoked changes of intracellular Ca2+
.
Table 5. In Vitro Data for Compounds with Various Y in Formula A
NMDA-evoked
[3H]Ro-25,6981
binding
IC50 ( S.E.M. (nM)
a
∆[Ca2+
]
i
Y
IC50 ( S.E.M. (nM)
n
n
6e
6f
6g
6h
6i
6j
6k
6l
>8000 ( 2
875 ( 187
107 ( 27
16 ( 3
2
5
3
9
7
4
4
6
N.D.
359 ( 93
89
47 ( 4
19 ( 2
N.D.
60
1084
CH2CH2
O
OCH2
CH2O
CO
3
2
3
3
36 ( 6
744 ( 131
111 ( 23
348 ( 75
CH2OH
NH
2
2
a NMDA-evoked changes of intracellular Ca2+
.
Table 6. In Vitro Data for Compounds with Various Z in Formula A
NMDA-evoked
[3H]Ro-25,6981
binding
IC50 ( S.E.M. (nM)
∆[Ca2+
]
i
a
Z
IC50 ( S.E.M. (nM)
n
n
6m
6n
6o
4-F
90 ( 15
208 ( 34
249 ( 55
38 ( 8
6
3
3
6
12 ( 3
28
N.D.
31
3
2
4-Me
2-MeO
3-F
6p
1
a NMDA-evoked changes of intracellular Ca2+
.
Then we wanted to assess the importance of the NH group
in compound 6a. The N-Me analogue (55) was inactive.
Similarly, the corresponding benzofuran and benzothiazole
derivatives 56 and 57 had very weak activity. The 5-hydroxy-
benzo(b)thiophene-2-carboxamide (58) and the 5-hydroxy iso-
mer of benzofuran 56 (59) were also inactive. These results
indicated that the NH in compound 6a has a critical role in the
interaction with the receptor. This observation was supported
by the fact that benzimidazole-2-carboxamide 60a showed very
good activity. The additional N in the molecule resulted in a
9-fold increase in potency compared to 6a, making this
compound one of the most potent NR2B selective NMDA
antagonists reported (Table 7).
a NMDA-evoked changes of intracellular Ca2+
.
Table 3. In Vitro Data for Compounds with Various X-s in Formula A
NMDA-evoked
[3H]Ro-25,6981
binding
IC50 (nM)
a
∆[Ca2+
]
i
X
IC50 ( S.E.M. (nM)
n
n
23
24
25
CdNH
CH2
SO2
8.5 ( 1.7
1158 ( 231
>8000
5
3
1
10
N.D.
N.D.
2
After having identified 60a as an exceptionally potent NR2B
selective NMDA antagonist the optimization of this compound
started. A selection of the derivatives prepared and tested is
shown in Table 8. The 4(7)-hydroxy isomer of 60a (61a) was
practically equipotent with the lead. Substitution of the OH for
NH2 resulted in a less-active analogue (62). The corresponding
a NMDA-evoked changes of intracellular Ca2+
.
series of derivatives that substituents in all positions on the
benzene ring of the benzylpiperidine part of compound A
decreased the activity (6m-6p; Table 6).

NR1/2B N-Methyl-D-aspartate Receptor Antagonists
Journal of Medicinal Chemistry, 2007, Vol. 50, No. 5 907
Table 7. In Vitro Data for Compounds with Various V-s and W-s in
Formula B
convergence criterion. Conformational analyses were carried out
by random search with an energy cutoff of 10 kcal/mol.
The alignment of the molecules is a crucial step in the grid-
based 3D-QSAR techniques. The molecules employed in our
study were superimposed based on the pharmacophoric points
of the pharmacophore model built with the help of DISCO
technique.33 The resulting model (see Figure 3) consists of three
hydrophobic centers (H1-3), a donor atom (DA1) and the
corresponding acceptor site (AS1), and an acceptor atom (AA1)
and the corresponding donor site (DS1) as common to all
compounds involved in the model development. Additional
donor site (DS2) and acceptor sites (AS2, AS3) exist in some
subset of the compounds studied, improving their biological
activity. The molecules were aligned by least-square fitting to
the common pharmacophoric points.
NMDA-evoked
a
∆[Ca2+
]
i
[3H]Ro-25,6981
binding
IC50 (nM)
IC50 ( S.E.M.
subst.
V
W
(nM)
n
n
55
56
57
58
59
6-OH
6-OH
6-OH
5-OH
5-OH
NMe CH 5773 ( 958
4
4
3
5
5
7
N.D.
>10 000
N.D.
>10 000
>10 000
4
O
S
CH 6920 ( 1280
1
N
2597 ( 369
S
O
CH 5613 ( 1066
1
1
2
CH 1901 ( 295
60a 5(6)-OH NH
N
2.2 ( 0.4
The superimposed molecules were placed in a rectangular
regular grid with 2 Å spacing extending at least 4 Å beyond
each molecule in all directions. Molecular similarity indices were
used as descriptors (independent variables) in the 3D-QSAR
analyses. Steric, electrostatic, and hydrophobic as well as
hydrogen-bond donor and acceptor features were considered in
this CoMSIA study. Similarity indices were calculated at the
grid points between each compound and a probe atom with
radius of 1 Å and charge, hydrophobic, and hydrogen bond
properties of +1. The default setting of the attenuation factor
was applied (R ) 0.3).
Regression analysis of the resulting field matrix was per-
formed by partial least-square (PLS) method. The optimal
number of components was chosen by the leave-one-out (LOO)
cross-validation technique on the basis of the highest q2 value.
A minimum sigma standard deviation threshold (column filter-
ing) of 2.0 was used. A statistically significant CoMSIA model
was derived from the training set of 47 compounds. Good cross-
validated r2 (0.547) and conventional r2 (0.972) values were
obtained, that is, however, a necessary but not sufficient
condition for a model to be truly predictive. Cross-validated r2
(i.e., q2) is considered usually as a measure of the predictivity
of the method, although that is often not the case.34 External
validation is an absolute requirement for a predictive QSAR
model. The biological activities of the 12 test set molecules
were predicted with the above-described CoMSIA model, with
a predictive r2 of 0.666. The experimental and calculated activity
values (expressed as -log IC50) for the training and test set are
presented in the Supporting Information and graphically depicted
in Figure 4. The predicted values do not differ significantly from
the measured ones in that the deviations are well within one
logarithmic unit.
a NMDA-evoked changes of intracellular Ca2+
.
mesylamino derivative 63, however, was slightly more active
than 60a. Substitution the OH in 60a for NH as part of an
oxazolinone ring attached to the benzimidazole (64 and 65) led
to less-active compounds. Interestingly, modifications of Y and
Z (60m-60u) did not influence significantly the activity of the
compounds.
Selectivity toward 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 significant activity up to 15 µM concentration.
Compound 60a was selected for further examination of selectiv-
ity toward other NR2 subunit containing NMDA receptors.
Compound 60a, up to 10 µM concentration, did not inhibit
(inh. < 20%) NMDA-evoked current in NR1/NR2A and
NR1/NR2D transfected cells measured by standard patch clamp
technique.29
Reference compounds 1-3, 6a, and 60a were assayed in the
mouse formalin test adapted from Hunskaar et al.30 The first
phase (0-10 min) of the typical biphasic pain response is
regarded as acute nociception, while the second phase, lasting
generally from 10 to 60 min, represents persistent pain. NMDA
antagonists are known potent inhibitors of this late phase of
formalin response that represents persistent pain.31 Therefore,
we measured pain-related licking behavior at the peak of the
second phase of the typical biphasic pain response. ED50 values
after oral administration were >20 mg/kg, 2.4 mg/kg, 1.7
mg/kg, and 1.6 mg/kg for compounds 1, 2, 6a, and 60a,
respectively. Compound 3 was found inactive p.o., although it
had an ED50 value of 5.1 mg/kg after i.p. administration.
The 3D-QSAR study carried out using CoMSIA has led to
the identification of those regions important for interactions
between ligand and receptor and provided an insight into the
structural variations that enabled us to design further com-
pounds with high activity. CoMSIA contour maps are shown
in Figure 5.
Molecular Modeling
In total, 59 indole- and benzimidazole-carboxamide deriva-
tives were used for this CoMSIA32 study, for which IC50 values
were determined in an in vitro binding assay.23
The molecules were clustered by their UNITY fingerprints,
resulting in 12 clusters. From each cluster, one molecule was
selected for external validation of the QSAR model (test set),
with the condition to cover the biological activity range. The
remaining 47 molecules were used as a training set for the 3D-
QSAR analysis. The structures of compounds employed in this
study and their measured, as well as calculated, biological
activities (converted to -log IC50) can be found in the
Supporting Information.
Conclusion
The conformational constraint of cinnamide 5 via the
incorporation of an NH group resulted in indole-2-carboxamide
6a, having an additional H-bond donor moiety compared to 5.
It was found that these structural changes caused a significant
increase both in potency and in affinity. During the lead
optimization, it was found that the majority of numerous
structural modifications resulted in less-active compounds. The
most significant exception was the insertion of a further atom
into the indole skeleton, yielding 60a. The benzimidazole-2-
The structural energy minimization was performed using the
standard Tripos Force Field and Gasteiger-Hu¨ckel charges with
conjugate gradient method and a 0.05 kcal/mol energy gradient

908 Journal of Medicinal Chemistry, 2007, Vol. 50, No. 5
Table 8. In Vitro Data for Benzimidazole-2-carboxamides
Borza et al.
NMDA-evoked
[3H]Ro-25,6981
binding
IC50 ( S.E.M. (nM)
∆[Ca2+
]
i
a
Q
Y
Z
IC50 ( S.E.M. (nM)
n
n
61a
62
63
4(7)-OH
5(6)-NH2
5(6)-MsNH
CH2
CH2
CH2
H
H
H
3.0 ( 0.4
40 ( 10
1.3 ( 0.2
4
3
4
10 ( 4
143
3
3
2
2
64
65
CH2
CH2
H
H
193 ( 42
328 ( 70
11
3
N.D.
N.D.
60m
60q
60r
60s
60t
5(6)-OH
5(6)-OH
5(6)-OH
5(6)-OH
5(6)-OH
5(6)-OH
CH2
CH2
CH2
O
O
O
4-F
1.2 ( 0.3
2.4 ( 0.5
2.5 ( 0.6
1.1 ( 0.2
1.7 ( 0.4
2.9 ( 0.6
5
6
3
4
6
3
4
5
3
3
14
6
2
2
1
2
2
2
3-Me
3-MeO
4-Me
4-Cl
60u
4-F
a NMDA-evoked changes of intracellular Ca2+
.
of the affinities of a selection of the indole- and benzimidazole-
2-carboxamides measured in the [3H]-Ro-25,6981 binding assay,
a CoMSIA model was developed to facilitate the design of
further active analogues.
Experimental Section
General. All reagents and solvents were of commercial quality
and used without further purification, unless indicated otherwise.
1H NMR spectra were obtained on a Varian Unity Inova 300 or a
Varian Unity Inova 500 spectrometer. Chemical shifts are reported
in parts per million relative to TMS as internal standard. High-
resolution MS measurements (EI, 70 eV) were carried out on a
Finnigan MAT 95XP mass spectrometer; perfluorotributyl amine
was used as a reference compound. All prepared compounds (end
products and isolated intermediates) were characterized by high
performance liquid chromatography coupled to a mass selective
detector (LC/MS) using HP 1100 Binary Gradient chromatography
system with Microplate Sampler (Agilent, Waldbronn), controlled
by ChemStation software. HP diode array detector was used to
acquire UV spectra at 225 and 240 nm. All experiments were
performed using HP MSD (Agilent, Waldbronn) single quadruple
spectrometer equipped with an electrospray ionization source to
determine the structure. Melting points were determined in open
glass capillaries using a Bu¨chi 535 melting point apparatus and
are uncorrected. Column chromatography was performed on
Kieselgel 60 (Merck).
Figure 3. Pharmacophore model. AA, acceptor atom; DS, donor site;
DA, donor atom; AS, acceptor site; HY, hydrophobic center.
Measurement of [Ca2+]i. Primary cultures of cortical neurones
were initiated from neocortices of 17-day old Wistar rat embryos.
The cortical tissue was cut into small pieces, washed, and trypsinised
(0.25% trypsin, 4 min). The resulting suspension was filtered
through a 70 µm mesh and centrifuged at 125 g for 5 min. The
cell pellet was resuspended in DMEMa containing 10% foetal
bovine serum and antibiotics (0.25 µg/mL amphotericin B, 100
U/mL penicillin G, 100 µg/mL streptomycin). Cells were plated in
standard 96-well microplates previously coated with poly-D-lysine
at a concentration of 2 × 105 to 4 × 105 cells/cm2. Cultures were
kept at 37 °C in a humidified atmosphere of 95% air/5% CO2. After
3 days in culture, half of the culture medium was replaced with
Figure 4. Calculated vs experimental biological activity of training
[ and test 4 set molecules.
carboxamide analogues obtained in this way were more potent
derivatives than the corresponding indoles. In the case of the
one of most active compounds (60a), the NR2B versus NR2A,
NR2D subtype selectivities were determined. Compounds 6a
and 60a had antinociceptive effect in the mouse formalin test
after oral administration, and these effects were comparable to
that of the reference compound besonprodil (2). On the basis
a Abbreviations: DMEM, Dulbecco’s modified eagle medium; HEPES,
4-(2-hydroxyethyl)piperazine-1-ethanesulfonic acid; EGTA, ethylene glycol-
bis(2-aminoethylether)-N,N,N′,N′-tetraacetic acid; TRIS-HCl, tris(hy-
droxymethyl)aminomethane hydrochloride.

NR1/2B N-Methyl-D-aspartate Receptor Antagonists
Journal of Medicinal Chemistry, 2007, Vol. 50, No. 5 909
Cells grown in standard 96-well microplates were loaded with
a fluorescent Ca2+-sensitive dye, fluo-4/AM (2-2.5 µM), for
60-90 min. To stop dye loading, cells were washed twice with
extracellular medium (145 mM NaCl, 5 mM KCl, 2 mM CaCl2,
10 mM HEPES, 20 mM glucose, 10 µM glycine, pH ) 7.4). After
washing, the test compounds (diluted in extracellular medium from
a DMSO stock solution, final DMSO concentration was <0.1%)
were added to the cells. Measurements [Ca2+]i were carried out
with a plate reader fluorimeter (Fluoroskan Ascent, Labsystems);
after recording baseline fluorescence (5 min), elevation of [Ca2+
]
i
was induced by application of 40 µM NMDA, and the fluorescence
was recorded for an additional 5 min. Conversion of raw fluores-
cence data to calcium concentration values was performed using
the equation
F - Fmin
[Ca2+]i ) Kd
Fmax - F
where Kd is the in vitro dissociation constant of fluo-4, Fmax and
Fmin are the maximal and minimal fluorescence (determined in the
presence of 5 µM ionomycin and 20 mM EGTA, respectively). In
some of the experiments this calibration was not performed and
raw fluorescence data was used for analysis. All treatments on a
single plate were measured in multiple wells, and the average value
of all wells of a treatment was used for analysis. Inhibitory potency
of a compound at a single concentration point was expressed as
percent inhibition of the control NMDA response. Sigmoidal
concentration-inhibition curves were fitted to the data derived from
at least three independent experiments using GraphPad Prism
software. IC50 values were determined as the concentration that
produced half of the maximal inhibition.
NR2B Receptor Binding. Rat forebrain was homogenized in
50 volumes of ice-cold 50 mM TRIS-HCl buffer at pH 7.4
containing 10 mM EDTA. The homogenate was centrifuged at
48 000 g for 10 min at 4 °C. The pellet was suspended in the same
buffer, and the homogenate was incubated at 37 °C for 10 min and
centrifuged at 48 000 g for 10 min at 4 °C. The pellet was
resuspended in the same buffer and frozen at -70 °C until use.
For the binding assay, membrane was thawed at 37 °C and
centrifuged at 48 000 g for 10 min at 4 °C, and the pellet was
washed two times in a 5 mM TRIS-HCl buffer (pH 7.4). The final
pellet was suspended in 5 mM TRIS-HCl buffer at pH 7.4 and
was used at a final concentration of 1 mg protein/mL. An amount
equal to 0.45 mL membrane suspension was incubated with 4 nM
[3H]Ro-25,6981 in the presence or absence of different concentra-
tions of compounds for 2 h at room temperature. The final
incubation volume was 500 µL. Nonspecific binding, assessed in
the presence of Ro-25,6981 (10 µM), was 5-15% of the total
binding. The assay was stopped by filtration on Whatman GF/B
glass fiber filter. The filters were washed three times with 5 mL
ice-cold 5 mM TRIS-HCl buffer, and radioactivity of the filters
was counted by liquid scintillation spectrometry in 2 mL HISafe
scintillation cocktail using a LKB-Wallac 1409 liquid scintillation
counter.
Figure 5. CoMSIA contour maps. A, steric field (green region, steric
bulk enhances activity; yellow region, sterick bulk detracts from
activity); B, electrostatic field (blue region, positive charge favored;
red region, positive charge unfavored); C, hydrophobic field (orange
region, hydrophobic groups favored; white region, hydrophobic groups
unfavored); D, hydrogen donor field (cyan region, hydrogen donor
favored; purple region, hydrogen donor unfavored); E, hydrogen
acceptor field (magenta region, hydrogen acceptor favored; blue region,
hydrogen acceptor unfavored).
All dilutions were made by 5% DMSO from 10 mM stock
solutions prepared in DMSO.
The ligand displacement by the compounds was determined using
a minimum of seven concentrations The specific radioligand binding
is defined as the difference between total binding and the
nonspecific binding determined in the presence of an excess of
unlabeled ligand. Results are expressed as a percent of inhibition
of specific binding obtained in the presence of compounds. IC50
values (i.e., concentration of compound giving 50% inhibition of
specific binding) were calculated from concentration-displacement
curves by sigmoidal fitting using Origin 6.0 software (Microcal).
Mouse Formalin Test. Male NMRI mice (20-25 g) from
Charles River (Isaszeg, Hungary) were used for tests. Prior to the
oral treatments, solid food was withdrawn for 14-16 h, but mice
had free access to 20% glucose solution.
fresh medium (DMEM containing 10% bovine serum and antibiot-
ics) containing 50 µM 5-fluoro-5′-deoxyuridine to stop the prolif-
eration of glial elements. On the fifth day, half of the medium was
replaced with serum-free (N2) medium (DMEM supplemented with
5 µg/mL insulin, 0.1 mg/mL transferrin, 5 µg/mL Na-selenite, 0.02
µg/mL progesterone, 0.1 mM putrescine, 25 mM D-glucose, 0.25
µg/mL amphotericin B, 100 U/mL penicillin G, 100 µg/mL
streptomycin). The cultures were used for the [Ca2+]i measurements
after 3-10 days in vitro.
An amount equal to 20 µL of 1% formalin in 0.9% saline was
injected subcutaneously into the dorsal surface of the right hindpaw.

910 Journal of Medicinal Chemistry, 2007, Vol. 50, No. 5
Borza et al.
Test drugs or the vehicle (5% Tween 80) were orally administered
15 min before the formalin injection. Time spent by licking or biting
of the injected paw was then registered 20-25 min post-formalin.
Increasing doses of drugs were administered and compared to a
parallel vehicle treated group (min 5 mice/dose group).
1H), 6.28-6.23 (m, 1H), 5.97 (d, J ) 1.9 Hz, 1H), 4.53-4.36 (m,
2H), 3.03-2.82 (m, 2H), 2.55 (d, J ) 7.2 Hz, 2H), 1.94-1.74 (m,
1H), 1.73-1.58 (m, 2H), 1.28-1.09 (m, 2H) ppm.
(4-Amino-1H-indol-2-yl)-(4-benzyl-piperidin-1-yl)-metha-
none (12a). Step 1: (4-Benzyl-piperidin-1-yl)-(4-nitro-1H-indol-
2-yl)-methanone (33a). A mixture of 4-nitroindole-2-carboxylic
acid (2.68 g, 13.0 mmol), triethylamine (1.5 mL, 10.8 mmol),
4-benzylpiperidine (1.88 g, 10.8 mmol), and HBTU (4.1 g, 10.8
mmol) in DMF (130 mL) was stirred at room temperature for 6 h.
The reaction mixture was concentrated and purified by column
chromatography (chloroform) and crystallized with diethyl ether
ED50 values were calculated by Boltzmann’s sigmoidal curve
fitting, using Microgal Origin 6.0 software. Licking time data were
statistically analyzed by Mann-Whitney U test.
Molecular Modeling. All calculations were performed using the
Sybyl 6.8 software package from Tripos.35
Chemistry. (4-Benzylpiperidine-1-yl)-(6-hydroxy-1H-indole-
2-yl)-methanone (6a). A mixture of 6-hydroxy-indole-2-carboxylic
acid (5.0 g, 28.2 mmol), triethylamine (4.4 mL, 31.6 mmol),
4-benzylpiperidine (5.0 g, 28.5 mmol), and HBTU (12.0 g, 31.6
mmol) in DMF (50 mL) was stirred at room temperature for 6 h.
The reaction mixture was concentrated, purified by column chro-
matography (4:1 toluene/methanol), and recrystallized from ethanol
1
to give 33a as a yellow solid (3.1 g, 79%): mp 139-142 °C; H
NMR (300 MHz, DMSO-d6) δ 1.10-1.32 (m, 2H), 1.62-1.78 (m,
2H), 1.78-1.97 (m, 1H), 2.57 (d, J ) 7.2 Hz, 2H), 3.02 (br m,
2H), 4.38 (br m, 2H), 7.14-7.34 (m, 6H), 7.41 (t, J ) 8.1 Hz,
1H), 7.90 (dt, J ) 8.1, 0.9 Hz, 1H), 8.11 (dd, J ) 8.1, 0.9 Hz, 1H),
12.43 (br s, 1H).
1
Step 2: (4-Amino-1H-indol-2-yl)-(4-benzyl-piperidin-1-yl)-
methanone (12a). To a solution of 33a (2.7 g, 7.5 mmol) in
methanol (110 mL), 10% Pd/C catalyst (0.5 g) was added and
hydrogenated for 3 h. The catalyst was filtered off, the filtrate was
concentrated, and the residue was crystallized with diethyl ether to
to give 6a as a white solid (6.75 g, 71%): mp 214-215 °C; H
NMR (300 MHz, DMSO-d6, 30 °C) δ 11.08 (d, J ) 1.5 Hz, 1H),
9.12 (s, 1H), 7.36 (d, J ) 8.5 Hz, 1H), 7.32-7.25 (m, 2H), 7.23-
7.15 (m, 3H), 6.79-6.75 (m, 1H), 6.63-6.60 (m, 1H), 6.57 (dd, J
) 8.5, 2.4 Hz, 1H), 4.49-4.38 (m, 2H), 3.03-2.82 (m, 2H), 2.55
(d, J ) 7 Hz, 2H), 1.92-1.74 (m, 1H), 1.72-1.59 (m, 2H), 1.27-
1.07 (m, 2H) ppm.
1
give 12a (1.96 g, 78.4%): mp 165-168 °C; H NMR (300 MHz,
DMSO-d6) δ 1.10-1.30 (m, 2H), 1.60-1.74 (m, 2H), 1.75-1.95
(m, 1H), 2.56 (d, J ) 6.9 Hz, 2H), 2.94 (br m, 2H), 4.47 (d, J )
13.5 Hz, 2H), 5.33 (s, 2H), 6.13 (dd, J ) 7.5, 0.6 Hz, 1H), 6.60 (d,
J ) 8.1 Hz, 1H), 6.84 (dd, J ) 8.1, 7.5 Hz, 1H), 7.14-7.33 (m,
5H), 11.08 (s, 1H).
(4-Benzylpiperidine-1-yl)-(4,6-dihydroxy-1H-indole-2-yl)-meth-
anone (10). Step 1: Methyl 4,6-Dibenzyloxy-1H-indole-2-car-
boxylate (39). To a solution of sodium methoxide (1.4 g, 60.8 mmol
sodium) in methanol (45 mL), a mixture of 2,4-dibenzyloxyben-
zaldehyde (36; 4.75 g, 14.9 mmol), methyl azidoacetate (6.9 g, 60.0
mmol), and methanol (20 mL) were added dropwise, at 0 °C, under
an Ar atmosphere. The mixture was stirred at 0 °C for 4 h, then
diluted with water (300 mL), and extracted with chloroform. The
organic layer was washed with water, dried over Na2SO4, and
concentrated, and the residue was crystallized with ethanol to give
methyl (Z)-2-azido-3-(2,4-dibenzyloxy)-acrylate (2.2 g, 38%): mp
94-95 °C. This material was added in small portions to a stirred
solution of boiling xylene (50 mL of 2.2 g, 5.7 mmol). After
completion of the addition, the reaction mixture was refluxed until
the gas formation (about 0.5 h), then cooled to room temperature.
The precipitated product was filtered off and recrystallized from
isopropanol to give 39 (1.3 g, 63.7%): mp 174 °C; 1H NMR (300
MHz, DMSO-d6, 30 °C) δ 11.74 (s, 1H), 7.55-7.25 (m, 10H),
7.08 (s, 1H), 6.61-6.55 (m, 1H), 6.41 (d, J ) 1.8 Hz, 1H), 5.22
(s, 2H), 5.10 (s, 2H), 3.83 (s, 3H) ppm.
(4-Benzylamino-1H-indol-2-yl)-(4-benzyl-piperidin-1-yl)-meth-
anone (15a). To a solution of 12a (0.33 g, 1.0 mmol), benzaldehyde
(0.1 g, 1.0 mmol), and acetic acid (0.12 mL, 2.0 mmol) in 1,2-
dichloroethane (10 mL) sodium triacetoxyborohydride (0.32 g, 1.5
mmol) was added below 10 °C, and the mixture was stirred at room
temperature for 2 h. The reaction mixture was poured into 8%
NaHCO3 (50 mL) and extracted with chloroform. The organic layer
was dried over Na2SO4 and concentrated, and the residue was
dissolved in EtOAc and HCl in EtOAc (2.5 M, 1 mL) was added.
The precipitated HCl salt was filtered off and washed with diethyl
ether to give 15a (0.3 g, 65.2%): mp 136-145 °C; 1H NMR (300
MHz, DMSO-d6) δ 1.10-1.30 (m, 2H), 1.60-1.75 (m, 2H), 1.75-
1.97 (m, 1H), 2.57 (d, J ) 7.2 Hz, 2H), 2.95 (br m, 2H), 4.40 (d,
J ) 12.6 Hz, 2H), 4.52 (s, 2H), 6.67 (br s, 1H), 7.00-7.46 (m,
14H), 11.63 (s, 1H).
N-[2-(4-Benzyl-piperidine-1-carbonyl)-1H-indol-4yl]-meth-
anesulfonamide (16a). To a stirred solution of 12a (0.33 g, 1.0
mmol) and triethylamine (0.21 mL, 1.5 mmol) in chloroform (10
mL), dropwise a solution of methanesulfonyl chloride (0.1 mL, 1.2
mmol) in chloroform (5 mL) was added below 10 °C, and the
mixture was stirred at room temperature for 10 h. The reaction
mixture was poured into water (30 mL) and extracted with
chloroform. The organic layer was dried over Na2SO4 and
concentrated, and the residue was treated with diethyl ether and
the crystals were filtered to give 16a (0.25 g, 61%): mp 228-230
°C; 1H NMR (300 MHz, DMSO-d6) δ 1.12-1.32 (m, 2H), 1.62-
1.76 (m, 2H), 1.76-1.98 (m, 1H), 2.58 (d, J ) 7.2 Hz, 2H), 2.94
(br m, 2H), 2.97 (s, 3H), 4.46 (d, J ) 13.2 Hz, 2H), 7.01 (dd, J )
7.5, 0.9 Hz, 1H), 7.08-7.33 (m, 8H), 9.60 (s, 1H), 11.60 (s, 1H).
(4-Benzylpiperidin-1-yl)-(1,6-dihydro-pirrolo[2,3-g]indazol-
7-yl)-methanone (20). Step 1: Ethyl 1,6-Dihydro-pyrrolo[2,3-
g]indazole-7-carboxylate (48). To a stirred mixture of 6-amino-
indazol (45; 6.66 g, 50.0 mmol), water (40 mL), and HCl (25 mL),
a solution of sodium nitrite (3.5 g, 50.7 mmol) in water (10 mL)
was added dropwise at 0 °C. The reaction mixture was stirred at 0
°C for 0.5 h. Then the so obtained solution was added to a mixture
of water (86 mL), KOH (5.0 g, 267 mmol), sodium acetate (15.0
g, 183 mmol), ethanol (60 mL), and ethyl 2-methyl-acetoacetate
(8.0 mL, 50.9 mmol, purity 90%). The reaction mixture was stirred
at 0 °C for 1 h. The precipitated product was filtered off, washed
with water, and dried to give ethyl 2-[(1H-indazol-6-yl)-hydrazono]-
propionate (8.16 g, 66%): mp 210-211 °C. A mixture of an aliquot
of this material (4.0 g, 16.25 mmol) and polyphosphoric acid (20
Step 2: (4-Benzylpiperidine-1-yl)-(4,6-dibenzyloxy-1H-indole-
2-yl)-methanone (43). A mixture of 39 (1.25 g, 3.5 mmol),
potassium trimethylsilanolate (0.5 g, 3.9 mmol), and THF (20 mL)
was refluxed for 2 h. The reaction mixture was cooled, poured into
water (100 mL), and acidified with HCl. The precipitated product
was filtered off, washed with water, and dried to give 4,6-
dibenzyloxy-1H-indole-2-carboxylic acid (1.0 g 83.2%): mp 180
°C.
A mixture of this material (1.0 g, 2.68 mmol), triethylamine (0.41
mL, 2.85 mmol), 4-benzylpiperidine (0.5 g, 2.85 mmol), and HBTU
(1.1 g, 2.9 mmol) in DMF (20 mL) was stirred at room temperature
for 6 h. The reaction mixture was concentrated and purified by
column chromatography (4:1 toluene/methanol) to give 43 as a
white solid (0.75 g, 52%): 1H NMR (300 MHz, DMSO-d6, 30 °C)
δ 11.35 (d, J ) 2.0 Hz, 1H), 7.56-7.08 (m, 15H), 6.66-6.62 (m,
1H), 6.60-6.57 (m, 1H), 6.37 (d, J ) 1.8 Hz, 1H), 5.21 (s, 2H),
5.07 (s, 2H), 4.50-4.36 (m, 2H), 3.08-2.80 (m, 2H), 2.54 (d, J )
7.0 Hz, 2H), 1.94-1.72 (m, 1H), 1.72-1.55 (m, 2H), 1.30-1.04
(m, 2H) ppm.
Step 3: (4-Benzylpiperidine-1-yl)-(4,6-dihydroxy-1H-indole-
2-yl)-methanone (10). To a solution of 43 (0.75 g, 1.4 mmol) in
methanol (20 mL), 10% Pd/C catalyst (0.05 g) was added and
hydrogenated for 2 h. The catalyst was filtered off, the filtrate was
concentrated, and the residue was recrystallized from isopropanol
to give (10; 0.3 g, 60.7%): mp 245-246 °C; 1H NMR (300 MHz,
DMSO-d6, 30 °C) δ 10.92 (d, J ) 2.0 Hz, 1H), 9.43 (s, 1H), 8.91
(s, 1H), 7.35-7.24 (m, 2H), 7.24-7.13 (m, 3H), 6.69-6.65 (m,

NR1/2B N-Methyl-D-aspartate Receptor Antagonists
Journal of Medicinal Chemistry, 2007, Vol. 50, No. 5 911
g) was slowly warmed to 120 °C and kept at this temperature for
0.5 h. The reaction mixture was cooled to room temperature and
water (30 mL) and HCl (15 mL) were added. The so obtained
mixture was extracted with ethyl acetate, dried over Na2SO4, and
8.73 (s, 1H), 7.33-7.21 (m, 2H), 7.20-7.09 (m, 4H), 6.70-6.67
(m, 1H), 6.45 (dd, J ) 8.4, 2.4 Hz, 1H), 6.08-6.03 (m, 1H), 3.46
(s, 2H), 2.88-2.71 (m, 2H), 2.49 (d, J ) 7.0 Hz, 2H), 1.95-1.78
(m, 2H), 1.60-1.38 (m, 3H), 1.30-1.09 (m, 2H) ppm.
1
concentrated to give 48 (1.6 g, 43%): mp 120-121 °C; H NMR
2-(4-Benzyl-piperidin-1-sulfonyl)-1H-indol-6-ol (25). Step 1:
6-Benzyloxy-2-(4-Benzyl-piperidin-1-sulfonyl)-1H-indol (54). A
mixture of 6-benzyloxy-1H-indole (3.51 g, 15.7 mmol), t-Boc2O
(3.68 g, 16.9 mmol), and DMAP (0.18 g, 1.4 mmol) in dichlo-
romethane (50 mL) was stirred at room temperature for 2 h. The
reaction mixture was concentrated and purified by column chro-
matography (4:1 hexane/ethyl acetate) to give 6-benzyloxy-indole-
1-carboxylic acid tert-butyl ester as a white solid (5.03 g, 99.0%):
mp 105 °C. Under an Ar atmosphere to a solution of the above
t-Boc intermediate (1.0 g, 3.1 mmol) in dry THF (10 mL), 2.5 M
n-butyllithium in hexane (1.25 mL, 3.12 mmol) was added dropwise
at -70 °C. After an additional 0.5 h, dry SO2 gas was introduced
over the solution surface for 15 min to give a copious precipitate.
This suspension was allowed to warm to room temperature over 2
h and diluted with hexane (30 mL), and the white precipitate was
collected by filtration to give lithium sulfinate salt. The salt was
suspended in dichloromethane (10 mL) and cooled to 5 °C, and
N-chlorosuccinimide (0.45 g, 3.37 mmol) was added portionwise.
After 2 h, the mixture was filtered and the solvent was evaporated
to give a brown oil. This crude sulfonyl chloride was dissolved in
THF (10 mL), and 4-benzyl-piperidin (1.1 g, 6.1 mmol) was added.
The reaction mixture was stirred for 24 h, concentrated, and purified
by column chromatography (4:1 toluene/MeOH) to give 54 as a
white solid (0.25 g, 17.5%): 1H NMR (300 MHz, DMSO-d6, 30
°C) δ 11.95 (s, 1 H), 7.56 (d, J ) 8.7 Hz, 1H), 7.50-7.06 (m,
10H), 6.98-6.94 (m, 1H), 6.91-6.84 (m, 2H), 5.14 (s, 2H), 3.70-
3.58 (m, 2H), 2.45 (d, J ) 7.0 Hz, 2H), 2.35-2.20 (m, 2H), 1.70-
1.40 (m, 3H), 1.32-1.10 (m, 2H) ppm.
(300 MHz, DMSO-d6) δ 1.37 (t, J ) 7.2 Hz, 3H), 4.36 (q, J ) 7.2
Hz, 2H), 7.25 (dd, J ) 8.7, 0.9 Hz, 1H), 7.42 (dd, J ) 0.9, 0.6 Hz,
1H), 7.58 (d, J ) 8.7 Hz, 1H), 8.10 (s, 1H), 12.30 (br s, 1H).
Step 2: (4-Benzylpiperidin-1-yl)-(1,6-dihydro-pirrolo[2,3-g]-
indazol-7-yl)-methanone (20). A stirred mixture of 48 (1.6 g, 7.0
mmol), ethanol (160 mL), water (10 mL), and KOH (1 g, 17.8
mmol) was refluxed for 5 h. The mixture was concentrated, and
the residue was dissolved in water and acidified with 1 N HCl
solution. The precipitated crystals were filtered off and washed with
water to give 1,6-dihydro-pyrrolo[2,3-g]indazole-7-carboxylic acid
(1.1 g, 78%): mp 270-275 °C. A mixture of an aliquot of this
material (0.38 g, 1.9 mmol), triethylamine (0.3 mL, 2.1 mmol),
4-benzylpiperidine (0.35 mL, 2.2 mmol), and HBTU (0.76 g, 2.0
mmol) in DMF (10 mL) was stirred at room temperature for 6 h.
The reaction mixture was concentrated, purified by column gel
chromatography (95:5 chloroform/methanol), and crystallized with
diethyl ether to give 20 as a white solid (0.25 g, 37%): mp 209-
1
210 °C; H NMR (300 MHz, DMSO-d6) δ 1.10-1.32 (m, 2H),
1.64-1.77 (m, 2H), 1.79-2.00 (m, 1H), 2.58 (d, J ) 7.2 Hz, 2H),
3.00 (br m, 2H), 4.49 (d, J ) 13.2 Hz, 2H), 7.00 (dd, J ) 2.4, 0.9
Hz, 1H), 7.16-7.34 (m, 6H), 7.47 (d, J ) 9.0 Hz, 1H), 7.99 (d, J
) 1.5 Hz, 1H), 11.90 (s, 1H), 13.19 (s, 1H). HRMS (C22H22N4O)
calcd, 358.1788; found, 358.1784.
2-[(4-Benzyl-piperidin-1-yl)-imino-methyl]-1H-indol-6-ol (23).
Step 1: 6-Benzyloxy-1H-indole-2-carbonitrile (52). To a suspen-
sion of 6-benzyloxy-1H-indole-2-carboxylic acid (51; 3.0 g, 11.2
mmol) in chloroform (60 mL), thionyl chloride (3.0 mL, 41.1 mmol)
and DMF (1 drop) were added at ambient temperature, and the
mixture was refluxed for 1 h. The reaction mixture was poured
into a mixture of 25% ammonia solution (20 mL) and ice. After
evaporation of the chloroform, the precipitated product was filtered
off and washed with water to yield 2.72 g (90.6%) of the
6-benzyloxy-1H-indole-2-carboxylic acid amide: mp 186 °C. A
mixture of this material (2.72 g, 10.2 mmol) and POCl3 (2.72 mL,
29.1 mmol) in chloroform (20 mL) was refluxed for 2 h. The
reaction mixture was poured into ice. The organic layer was
separated and concentrated in vacuo. The residue was purified by
column chromatography (4:1 hexane/ethyl acetate) to give 52 as a
white solid (1.63 g, 64.2%): mp 123-124 °C; 1H NMR (500 MHz,
DMSO-d6, 30 °C) δ 12.15 (s, 1 H), 7.56 (d, J ) 7.8 Hz, 1 H),
7.50-7.45 (m, 2 H), 7.43-7.37 (m, 2 H), 7.36-7.31 (m, 1 H),
7.27 (s, 1 H), 6.98 (d, J ) 2.0 Hz, 1 H), 6.89 (dd, J ) 7.8, 2.0 Hz,
1 H), 5.16 (s, 2 H) ppm.
Step 2: 2-(4-Benzyl-piperidin-1-sulfonyl)-1H-indol-6-ol (25).
To a solution of 54 (0.2 g, 0.43 mmol) in methanol (20 mL), 10%
Pd/C catalyst (0.2 g) was added and hydrogenated for 6 h. The
catalyst was filtered off, the filtrate was concentrated, and the
residue was purified by column chromatography (4:1 toluene/
aceton) and crystallized with hexane to give 25 (20 mg): mp 92
1
°C; H NMR (300 MHz, DMSO-d6, 30 °C) δ 11.60 (s, 1H), 9.38
(s, 1H), 7.44 (d, J ) 8.7 Hz, 1H), 7.28-7.20 (m, 2H), 7.19-7.07
(m, 3H), 6.84-6.81 (m, 1H), 6.80-6.76 (m, 1H), 6.65 (dd, J )
8.7, 2.2 Hz, 1H), 3.68-3.58 (m, 2H), 2.64 (d, J ) 7.0 Hz, 2H),
2.34-2.20 (m, 2H), 1.68-1.40 (m, 3H), 1.30-1.10 (m, 2H) ppm.
(4-Benzylpiperidin-1-yl)-(6-hydroxy-1-methyl-1H-indol-2-yl)-
methanone (55). Step 1: 6-Benzyloxy-1-methyl-1H-indole-2-
carboxylic Acid (67). Under an Ar atmosphere to a solution of
6-benzyloxy-1H-indole-2-carboxylic acid methyl ester (66; 1.0 g,
3.5 mmol) in DMF (10 mL), KOt-Bu (1.0 g, 8.9 mmol) and
iodomethane (0.5 mL, 8.0 mmol) were added at room temperature.
The mixture was stirred at this temperature for 24 h and then diluted
with water (100 mL). The precipitated crystals were filtered off,
washed with water, and recrystallized from isopropanol to give
6-benzyloxy-1-methyl-1H-indole-2-carboxylic acid methyl ester
(0.85 g, 81%): mp 80-81 °C; 1H NMR (300 MHz, DMSO-d6, 30
°C) δ 7.56 (d, J ) 8.7 Hz, 1H), 7.53-7.47 (m, 2H), 7.45-7.31
(m, 3H), 7.22-7.16 (m, 2H), 6.87 (dd, J ) 8.7, 2.4 Hz, 1H), 5.19
(s, 2H), 5.07 (s, 2H), 3.98 (s, 3H), 3.83 (s, 3H) ppm. A mixture of
6-benzyloxy-1-methyl-1H-indole-2-carboxylic acid methyl ester
(7.22 g, 24.4 mmol), potassium trimethylsilanolate (4.33 g, 33.7
mmol), and THF (140 mL) was refluxed for 1 h. The reaction
mixture was cooled, poured into water (100 mL), and acidified with
HCl. The precipitated product was filtered off, washed with water,
Step 2: 2-[(4-Benzyl-piperidin-1-yl)-imino-methyl]-1H-indol-
6-ol (23). A mixture of 52 (1.0 g, 4.0 mmol) and saturated HCl
solution in MeOH (20 mL, 52%) was stirred at room temperature
for 5 h. The reaction mixture was concentrated in vacuo. The residue
was dissolved in MeOH (20 mL). To this solution was added
4-benzyl-piperidin (5.0 g, 28.0 mmol), and the mixture was stirred
at the same temperature for 24 h. The reaction mixture was
concentrated and purified by column chromatography (3:1 CHCl3/
MeOH) and crystallized with diethyl ether to give the HCl salt of
1
23 as a white solid (61 mg): mp 219 °C; H NMR (300 MHz,
DMSO-d6, 30 °C) δ 11.90 (vbr s, 1H), 7.36 (d, J ) 8.6 Hz, 1H),
7.33-7.24 (m, 2H), 7.23-7.14 (m, 3H), 6.78-6.73 (m, 1H), 6.66-
6.62 (m, 1H), 6.59 (dd, J ) 8.6, 2.1 Hz, 1H), 4.09-3.90 (m, 2H),
3.01-2.85 (m, 2H), 2.55 (d, J ) 7.1 Hz, 2H), 1.91-1.71 (m, 1H),
1.69-1.55 (m, 2H), 1.40-1.20 (m, 2H) ppm.
1
and dried to give 67 (4.43 g, 64.4%): mp 210-212 °C; H NMR
(300 MHz, DMSO-d6, 30 °C) δ 13.50-11.50 (vbr s, 1H), 7.56 (d,
J ) 8.7 Hz, 1H), 7.53-7.47 (m, 2H), 7.45-7.30 (m, 3H), 7.20-
7.16 (m, 2H), 6.85 (dd, J ) 8.7, 2.4 Hz, 1H), 5.19 (s, 2H), 3.98 (s,
3H) ppm.
Step 2: (4-Benzylpiperidin-1-yl)-(6-hydroxy-1-methyl-1H-
indol-2-yl)-methanone (55). A mixture of 67 (0.8 g, 2.8 mmol),
triethylamine (0.4 mL, 2.8 mmol), 4-benzylpiperidine (0.6 g, 3.4
mmol), and HBTU (1.1 g, 2.9 mmol) in DMF (20 mL) was stirred
2-(4-Benzyl-piperidin-1-ylmethyl)-1H-indol-6-ol (24). To a
solution of 6a (1.0 g, 3.0 mmol) in THF (20 mL), LiAlH4 (0.2 g,
5.2 mmol) was added at room temperature under an Ar atmosphere.
The mixture was stirred for 1 h and decomposed with ethanol (5
mL). The reaction mixture was concentrated and purified by column
chromatography (4:1 toluene/methanol) and crystallized with etha-
1
nol to give 24 as a white solid (0.15 g, 15.6%): mp 180 °C; H
NMR (300 MHz, DMSO-d6, 30 °C) δ 10.48 (d, J ) 1 Hz, 1H),

912 Journal of Medicinal Chemistry, 2007, Vol. 50, No. 5
Borza et al.
at room temperature for 6 h. The reaction mixture was concentrated
and purified by column chromatography (4:1 toluene/methanol) to
give 74 as a white solid (0.5 g, 40%). A mixture of 74 (0.5 g, 1.1
mmol) and 33% HBr solution in AcOH (5 mL) was stirred at room
temperature for 10 min. The reaction mixture was diluted with
diethyl ether. The precipitated crystals were filtered off, purified
by column chromatography (4:1 toluene/MeOH), and crystallized
with isopropanol to give 55 as a white solid (0.18 g, 45%): mp
Step 2: (4-Benzylpiperidin-1-yl)-(5-hydroxybenzothiophen-
2-yl)-methanone (58). To a solution of 75 (0.68 g, 1.9 mmol) in
dichloromethane (10 mL), BBr3 solution in dichloromethane (4 mL,
1 M) was added dropwise at -20 °C. The reaction mixture was
stirred at room temperature for 10 h and concentrated. The residue
was stirred with 20 mL of 5% aqueous NaHCO3 solution. The
precipitated crystals were filtered off and washed with water to
1
give 58 (0.63 g, 94%): mp 162 °C (dec); H NMR (300 MHz,
1
DMSO-d6) δ 1.10-1.30 (m, 2H), 1.59-1.73 (m, 2H), 1.74-1.92
(m, 1H), 2.55 (d, J ) 7.2 Hz, 2H), 2.94 (br m, 2H), 4.25 (br m,
2H), 6.94 (dd, J ) 8.7, 2.4 Hz, 1H), 7.14-7.33 (m, 6H), 7.49 (d,
J ) 0.6 Hz, 1H), 7.75 (d, J ) 8.7 Hz, 1H), 9.50 (br s, 1H).
(4-Benzylpiperidin-1-yl)-[5(6)-hydroxy-1H-benzimidazol-2-
yl]-methanone (60a). Step 1: N-(4-Methoxy-2-nitro-phenyl)-
oxalamic Acid Ethyl Ester (79). To a solution of 77 (33.6 g, 0.2
mol) and Et3N (30.8 mL, 0.22 mol) in dichloromethane (1000 mL),
ethyl chlorooxoacetate (23.4 mL, 0.21 mol) was added dropwise
below 5 °C. The reaction mixture was stirred at room temperature
for 24 h, washed with water, dried over Na2SO4, and concentrated.
The residue was stirred with n-hexane (500 mL) and filtered to
give 79 (55.1 g, 96.2%): mp 136 °C; 1H NMR (500 MHz, DMSO-
d6, 30 °C) δ 11.12 (s, 1H), 7.89 (d, J ) 9.1 Hz, 1H), 7.59 (d, J )
3.0 Hz, 1H), 7.39 (dd, J ) 9.1, 3.0 Hz, 1H), 4.33 (q, J ) 7.2 Hz,
2H), 3.86 (s, 3H), 1.33 (t, J ) 7.2 Hz, 3H) ppm.
180 °C; H NMR (300 MHz, DMSO-d6, 30 °C) δ 9.22 (s, 1H),
7.36 (d, J ) 8.7 Hz, 1H), 7.32-7.24 (m, 2H), 7.23-7.14 (m, 3H),
6.76-6.73 (m, 1H), 6.63 (dd, J ) 8.7, 2.1 Hz, 1H), 6.48 (d, J )
1 Hz, 1H), 4.38-4.16 (m, 2H), 3.61 (s, 3H), 3.04-2.76 (m, 2H),
2.55 (d, J ) 7.2 Hz, 2H), 1.91-1.72 (m, 1H), 1.70-1.54 (m, 2H),
1.27-1.08 (m, 2H) ppm.
(4-Benzylpiperidin-1-yl)-(6-hydroxybenzofuran-2-yl)-metha-
none (56). A mixture of 6-hydroxybenzofuran-2-carboxylic acid
(68; 0.36 g, 2.0 mmol), triethylamine (0.3 mL, 2.1 mmol),
4-benzylpiperidine (0.35 g, 2.0 mmol), and HBTU (0.76 g, 2.0
mmol) in DMF (10 mL) was stirred at room temperature for 6 h.
The reaction mixture was concentrated, and the residue was purified
by column chromatography (4:1 toluene/aceton) and crystallized
with methanol to give 56 (0.37 g, 55%): mp 183-186 °C; 1H NMR
(300 MHz, DMSO-d6) δ 1.08-1.30 (m, 2H), 1.59-1.74 (m, 2H),
1.74-1.94 (m, 1H), 2.55 (d, J ) 7.2 Hz, 2H), 2.94 (br m, 2H),
4.22-4.42 (m, 2H), 6.81 (dd, J ) 8.5, 2.1 Hz, 1H), 6.92-6.96 (m,
1H), 7.13-7.34 (m, 6H), 7.49 (dd, J ) 8.5, 0.5 Hz, 1H), 9.79 (br
s, 1H).
Step 2: N-(2-Amino-4-methoxy-phenyl)-N’-butyl-oxalamide
(81). To a suspension of 79 (44.0 g, 164 mmol) in toluene (330
mL), n-butylamine (16.8 mL, 170 mmol) was added at room
temperature. The reaction mixture was stirred for 10 h and
concentrated, and the residue was crystallized with diethyl ether.
The precipitated product was filtered off, washed with diethyl ether,
and dried to give N-butyl-N’-(4-methoxy-2-nitro-phenyl)-oxalamide
(4-Benzylpiperidin-1-yl)-(6-hydroxybenzothiazol-2-yl)-metha-
none (57). Step 1: 6-Hydroxybenzothiazole-2-carboxylic Acid
(70). To a stirred solution of 6-methoxybenzothiazole-2-carboxylic
acid (69; 8.3 g, 40.0 mmol) in methanol (80 mL), thionyl chloride
(4.8 mL, 65.8 mmol) was added dropwise at 0 °C. The reaction
mixture was stirred at room temperature for 10 h. The precipitated
crystals were filtered off and washed with methanol to give methyl
6-methoxybenzothiazole-2-carboxylate (6.0 g, 67%): mp 130-135
°C. To a stirred solution of methyl 6-methoxybenzothiazole-2-
carboxylate (6.0 g, 27 mmol) in dichloromethane (60 mL), a
solution of BBr3 (2.6 mL, 27.5 mmol) in dichloromethane (10 mL)
was added dropwise at -15 °C. The reaction mixture was stirred
at room temperature for 10 h, poured into ice water, and extracted
with ethyl acetate. The organic layer was dried over Na2SO4 and
concentrated. The residue was purified by column chromatography
(2:1 hexane/EtOAc) to give methyl 6-hydroxybenzothiazole-2-
1
(45.3 g, 93.3%): mp 127-128 °C; H NMR (500 MHz, DMSO-
d6, 30 °C) δ 10.25 (vbr s, 1H), 9.06 (t, J ) 6.2 Hz, 1H), 8.22 (d,
J ) 9.1 Hz, 1H), 7.61 (d, J ) 3.1 Hz, 1H), 7.39 (dd, J ) 9.1, 3.1
Hz, 1H), 3.86 (s, 3H), 3.28-3.20 (m, 2H), 1.56-1.49 (m, 2H),
1.37-1.27 (m, 2H), 0.91 (t, J ) 7.3 Hz, 3H) ppm.
Step 3: A mixture of N-butyl-N’-(4-methoxy-2-nitro-phenyl)-
oxalamide (27.0 g, 91 mmol) and Pd/C (7.3 g, 5%) catalyst in
methanol (1200 mL) was hydrogenated for 3 h. Acetone (600 mL)
was added to the reaction mixture. The catalyst was filtered off
and washed with acetone, the filtrate was concentrated, and the
residue was crystallized with diethyl ether to give 81 (21.8 g,
90.1%): mp 180-181 °C; 1H NMR (500 MHz, DMSO-d6, 30 °C)
δ 9.72 (s, 1H), 8.81 (t, J ) 6.1 Hz, 1H), 7.13 (d, J ) 8.6 Hz, 1H),
6.38 (d, J ) 2.8 Hz, 1H), 6.20 (dd, J ) 8.6, 2.8 Hz, 1H), 4.94 (br
s, 2H), 3.68 (s, 3H), 3.24-3.16 (m, 2H), 1.54-1.45 (m, 2H), 1.35-
1.24 (m, 2H), 0.89 (t, J ) 7.3 Hz, 3H) ppm.
1
carboxylate (2.0 g, 36%): mp 200-206 °C; H NMR (300 MHz,
DMSO-d6) δ 3.95 (s, 3H), 7.12 (dd, J ) 9.0, 2.7 Hz, 1H), 7.49
(dd, J ) 2.7, 0.6 Hz, 1H), 8.01 (dd, J ) 9.0, 0.6 Hz, 1H), 10.24
(br s, 1H).
Step 4: 5(6)-Methoxy-1H-benzimidazole-2-carboxylic Acid
Butylamide (83). Compound 81 (41.0 g, 154 mmol) was stirred at
240 °C for 10 min under N2. The mixture was cooled to room
temperature, diethyl ether (300 mL) was added, and the mixture
was stirred for 1 h. The precipitated product was filtered off, washed
with diethyl ether, and dried to give 83 (26.5 g, 69.5%): mp 125-
A stirred mixture of methyl 6-hydroxybenzothiazole-2-carboxy-
late (2.0 g, 9.6 mmol), ethanol (100 mL), and KOH (1.1 g, 16.9
mmol) was refluxed for 1 h. The reaction mixture was cooled to
10 °C and the precipitated crystals were filtered off, washed with
ethanol, dissolved in water, and acidified with 20% aqueous sulfuric
acid. The precipitated crystals were filtered off and washed with
1
126 °C; H NMR (500 MHz, DMSO-d6, 50 °C) δ 12.41 (vbr s,
1
water to give 70 (1.85 g, 99%): mp 128-132 °C; H NMR (300
1H), 8.65 (t, J ) 6.0 Hz, 1H), 7.55 (br s, 1H), 7.08 (br s, 1H), 6.94
(dd, J ) 8.8, 1.6 Hz, 1H), 3.82 (s, 3H), 3.39-3.30 (m, 2H), 1.62-
1.52 (m, 2H), 1.40-1.30 (m, 2H), 0.91 (t, J ) 7.3 Hz, 3H) ppm.
Step 5: 5(6)-Hydroxy-1H-benzimidazole-2-carboxylic Acid
(85). A mixture of 83 (26.0 g, 105 mmol) and 48% aqueous
hydrobromic acid (780 mL) was refluxed for 12 h. The mixture
was cooled to room temperature, and the precipitated product was
filtered off, washed with water until pH neutral, and dried to give
MHz, DMSO-d6) δ 7.10 (dd, J ) 9.0, 2.4 Hz, 1H), 7.46 (d, J )
2.4 Hz, 1H), 8.00 (d, J ) 9.0 Hz, 1H), 10.20 (br s, 1H).
Step 2: (4-Benzylpiperidin-1-yl)-(6-hydroxybenzothiazol-2-
yl)-methanone (57). Compound 57 was prepared from 70 and
4-benzylpiperidine according to the procedure described above for
1
56: mp 68-70 °C; H NMR (300 MHz, DMSO-d6) δ 1.08-1.36
(m, 2H), 1.59-1.98 (m, 3H), 2.55 (d, J ) 7.1 Hz, 2H), 2.83 (t, J
) 12.2 Hz, 1H), 3.19 (J ) 12.3 Hz, 1H), 4.45 (d, J ) 12.3 Hz,
1H), 5.21 (d, J ) 12.5 Hz, 1H), 7.04 (dd, J ) 8.9, 2.5 Hz, 1H),
7.13-7.34 (m, 5H), 7.42 (d, J ) 2.5 Hz, 1H), 7.91 (d, J ) 8.9 Hz,
1H), 10.07 (br s, 1H).
1
85 (14.3 g, 76.2%): mp 206-207 °C; H NMR (300 MHz, D2O
+ NaOD, 30 °C) δ 7.38 (m, 1H), 6.70 (m, 2H) ppm.
Step 6: (4-Benzylpiperidin-1-yl)-[5(6)-hydroxy-1H-benzimi-
dazol-2-yl]-methanone (60a). Compound 60a was prepared from
85 and 4-benzylpiperidine according to the procedure described
above for 56: mp 186 °C (toluene); 1H NMR (300 MHz, DMSO-
d6, 30 °C) δ 12.61 (s, 1H), 9.40 (s, 1H), 7.50 (d, J ) 8.9 Hz, 1H),
7.36-7.24 (m, 2H), 7.23-7.14 (m, 3H), 6.84 (d, J ) 2.4 Hz, 1H),
6.74 (dd, J ) 8.9, 2.4 Hz, 1H), 5.68-5.50 (m, 1H), 4.61-4.43 (m,
(4-Benzylpiperidin-1-yl)-(5-hydroxybenzothiophen-2-yl)-metha-
none (58). Step 1: 1-(4-Benzylpiperidin-1-yl)-1-(5-methoxyben-
zothiophen-2-yl)-methanone (75). Compound 75 was prepared from
71 and 4-benzylpiperidine according to the procedure described
above for 56: mp 128-130 °C (diethyl ether).

NR1/2B N-Methyl-D-aspartate Receptor Antagonists
Journal of Medicinal Chemistry, 2007, Vol. 50, No. 5 913
1H), 3.23-3.07 (m, 1H), 2.85-2.70 (m, 1H), 2.55 (d, J ) 7.0 Hz,
2H), 1.98-1.61 (m, 3H), 1.36-1.03 (m, 2H) ppm.
poured into ice water, and the precipitated product was filtered off,
washed with water, and dried to give 91 (1.7 g, 68%): mp 218 °C.
Step 2: (4-Benzylpiperidin-1-yl)-(5(6)-hydroxy-4(7)-nitro-1H-
benzimidazol-2-yl)methanone (92). Compound 92 was prepared
from 91 and 4-benzylpiperidine according to the procedure
described above for 56: mp 102 °C (diethyl ether); 1H NMR (500
MHz, DMSO-d6, 50 °C) δ 12.68 (s, 1H), 7.84 (br s, 1H), 7.32-
7.24 (m, 3H), 7.22-7.13 (m, 2H), 7.08-6.91 (m, 1H), 5.40-4.30
(m, 2H), 3.24-3.06 (m, 1H), 2.83-2.72 (m, 1H), 2.56 (d, J ) 7.1
Hz, 2H), 1.94-1.81 (m, 1H), 1.79-1.56 (m, 2H), 1.33-1.12 (m,
2H) ppm.
6-(4-Benzylpiperidin-1-carbonyl)-3,5-dihydro-imidazo[4′,5′:
4,5]benzo[1,2-d]-oxazol-2-one (64). Step 1: 6-Amino-5-nitro-3H-
benzoxazol-2-one (89). To a solution of 6-amino-3H-benzoxazol-
2-one (88; 2.0 g, 13.3 mmol) in trifluoroacetic acid (20 mL), sodium
nitrate (1.2 g, 14.1 mmol) was added below 20 °C. The reaction
mixture was stirred at room temperature overnight and then
concentrated. The residue was purified by column chromatography
1
(4:1 toluene/MeOH) to give 89 (2.50 g, 96.0%): mp 198 °C; H
NMR (300 MHz, DMSO-d6, 30 °C) δ 11.64 (br s, 1H), 7.54 (s,
2H), 7.50 (s, 1H), 6.85 (s, 1H) ppm.
Step 3: (4(7)-Amino-5(6)-hydroxy-1H-benzimidazol-2-yl)-(4-
benzylpiperidin-1-yl)methanone (93). A mixture of 92 (1.0 g, 2.6
mmol) and Pd/C (0.4 g, 10%) catalyst in methanol (30 mL) was
hydrogenated for 2 h. The catalyst was filtered off, and the filtrate
was concentrated. The residue was treated with diethyl ether, and
the crystalline product was filtered, washed with diethyl ether, and
Step 2: (4-Benzylpiperidin-1-yl)-oxoacetyl Chloride (87). To
a solution of 4-benzylpiperidine (10.0 g 57 mmol) and N-
ethyldiisopropylamine (10 mL, 57.4 mmol) in dichloromethane (100
mL), ethyl oxalyl chloride (7.05 mL, 63.1 mmol) was added
dropwise at 0 °C. The mixture was stirred at this temperature for
30 min. The organic phase was washed with water, dried on
Na2SO4, and concentrated to give (4-benzylpiperidin-1-yl)-oxoacetic
acid ethyl ester (15.5 g, 99%) as a brown oil. A mixture of (4-
benzylpiperidin-1-yl)-oxoacetic acid ethyl ester (15.5 g, 56 mmol)
and KOH (5.0 g, 75.9 mmol) in methanol (250 mL) was stirred at
room temperature for 6 h. The reaction mixture was concentrated,
and the residue was taken up in water and acidified with 1 N HCl.
The precipitated product was filtered off, washed with water, and
dried to give (4-benzylpiperidin-1-yl)-oxoacetic acid (11.95 g,
1
dried to give 93 (0.5 g, 54%): mp 108 °C; H NMR (500 MHz,
DMSO-d6, 30 °C) δ 12.43 (br s, 1H), 8.72 (br s, 1H), 7.32-7.25
(m, 3H), 7.22-7.15 (m, 2H), 6.81 (d, J ) 8.6 Hz, 1H), 6.75 (d, J
) 8.6 Hz, 1H), 5.79-5.67 (m, 1H), 4.75 (s, 2H), 4.65-4.44 (m,
1H), 3.22-3.10 (m, 1H), 2.83-2.71 (m, 1H), 2.55 (d, J ) 7.1 Hz,
2H), 1.94-1.76 (m, 1H), 1.76-1.61 (m, 2H), 1.31-1.08 (m, 2H)
ppm.
Step 4: 7-(4-Benzylpiperidin-1-carbonyl)-1,6-dihydro-3-oxa-
1,6,8-triaza-as-indacen-2-one (65). To a solution of 93 (0.45 g,
1.28 mmol) in THF (5 mL), 1,1′-carbonyldiimidazole (0.2 g, 1.37
mmol) was added at 20 °C. The reaction mixture was stirred at
room temperature for 2 h and then concentrated. The residue was
purified by column chromatography (4:1 toluene/MeOH) and
crystallized with isopropanol to give 65 (0.45 g, 93.5%): mp >270
1
85%): mp 115 °C; H NMR (300 MHz, DMSO-d6) δ 0.91-1.23
(m, 2H), 1.51-1.92 (m, 3H), 2.53 (d, J ) 7.1 Hz, 2H), 2.64 (td, J
) 12.7, 3.0 Hz, 2H), 3.05 (td, J ) 12.4, 2.7 Hz, 2H), 3.46-3.58
(m, 2H), 4.12-4.27 (m, 2H), 7.12-7.35 (m, 5H), 13.96 (br s, 1H).
A mixture of (4-benzylpiperidin-1-yl)-oxoacetic acid (26.2 g, 106
mmol) and thionyl chloride (50 mL) was refluxed for 2 h. The
mixture was cooled and concentrated to give 87 (28.0 g, 99.5%)
as an oil.
1
°C; H NMR (300 MHz, DMSO-d6, 30 °C) δ 13.30 (br s, 1H),
12.22 (br s, 1H), 7.40-7.15 (m, 7H), 5.40-5.25 (m, 1H), 4.60-
4.46 (m, 1H), 3.28-3.14 (m, 1H), 2.89-2.75 (m, 1H), 2.56 (d, J
) 7.0 Hz, 2H), 1.98-1.60 (m, 3H), 1.35-1.10 (m, 2H) ppm.
Step 3: 2-(4-Benzylpiperidin-1-yl)-N-(5-nitro-2-oxo-2,3-di-
hydro-benzoxazol-6-yl)-2-oxo-acetamide (90). To a solution of
89 (3.23 g, 16.56 mmol) and triethylamine (2.58 mL, 18.5 mmol)
in chloroform (100 mL), 87 (5.25 g, 19.75 mmol) in chloroform
(20 mL) was added dropwise at 20 °C. The reaction mixture was
stirred at room temperature for 2 h. The organic phase was washed
with water, dried on Na2SO4, and concentrated. The residue was
purified by column chromatography (4:1 toluene/MeOH) to give
90 (3.3 g, 47.0%) as an amorphous solid foam: 1H NMR (300
MHz, DMSO-d6, 30 °C) δ 12.16 (br s, 1H), 11.15 (s, 1H), 7.73-
7.69 (m, 2H), 7.34-7.25 (m, 2H), 7.24-7.14 (m, 3H), 4.41-4.19
(m, 1H), 4.15-3.97 (m, 1H), 3.16-2.99 (m, 1H), 2.80-2.64 (m,
1H), 2.55 (d, J ) 7.1 Hz, 2H), 1.95-1.75 (m, 1H), 1.75-1.53 (m,
2H), 1.33-1.02 (m, 2H) ppm.
Acknowledgment. The authors are indebted to Derek R.
Buckle for the valuable consultations and to Ma´rta Meszle´nyi-
Sipos for analytical support.
Supporting Information Available: Experimental details and
data for compounds 6b-6p, 7, 8, 9, 11, 13a-14a, 17a, 18a, 19,
21, 22, 59, 60m-60u, 61a, 62, and 63. HPLC and HRMS analysis
of the final compounds. Experimental and calculated biological
activities (expressed as -log IC50) of compounds used in the
CoMSIA study. Structures of molecules in the CoMSIA study. This
material is available free of charge via the Internet at http://
pubs.acs.org.
Step 4: 6-(4-Benzylpiperidin-1-carbonyl)-3,5-dihydro-imi-
dazo[4′,5′:4,5]benzo-[1,2-d]oxazol-2-one (64). A mixture of 90 (3.3
g, 7.7 mmol) and Pd/C (0.3 g, 10%) catalyst in methanol (30 mL)
was hydrogenated for 8 h. The catalyst was filtered off, and the
filtrate was concentrated. The residue was purified by column
chromatography (2:1 toluene/acetone) to give N-(5-amino-2-oxo-
2,3-dihydro-benzoxazol-6-yl)-2-(4-benzylpiperidin-1-yl)-2-oxo-
acetamide (1.06 g, 34.5%): mp 296 °C. An aliquot of this material
(1.0 g, 2.5 mmol) was heated to 240 °C for 10 min and then cooled.
The obtained mixture was purified by column chromatography (1:1
toluene/acetone) to give 64 (0.16 g, 17%): mp >290 °C; 1H NMR
(300 MHz, DMSO-d6, 30 °C) δ 13.00 (vbr s, 1H), 11.70 (vbr s,
1H), 7.53 (br s, 1H), 7.40-7.04 (m, 6H), 5.68-5.43 (m, 1H), 4.65-
4.42 (m, 1H), 3.28-3.09 (m, 1H), 2.87-2.71 (m, 1H), 2.55 (d, J
) 7.0 Hz, 2H), 1.97-1.77 (m, 1H), 1.77-1.60 (m, 2H), 1.37-
1.05 (m, 2H) ppm.
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