Tricyclic indole-2-carboxylic acids: Highly in vivo active and selective antagonists for the glycine binding site of the NMDA receptor

Article abstract of DOI:10.1021/jm020239l

A series of tricyclic indole-2-carboxylic acid derivatives were synthesized and evaluated by the radioligand binding assay and the anticonvulsant effects in the mouse NMDA-induced seizure model. Among them, derivatives of 3S-(-)-4 such as 3a, 3f, and 3g which had certain zwitterionic anilides showed high affinity to the NMDA-glycine binding site. The absolute configuration of 3S-(-)-4 was confirmed by X-ray crystallographic analysis. In particular, 3g (SM-31900) was found to be a highly active glycine antagonist for both in vitro and in vivo assays (K_i = 1.0 ± 0.1 nM, ED₅₀ = 2.3 mg/kg, iv) and also showed high selectivity for the glycine site. In addition, 3g was soluble enough in aqueous media (> 10 mg/mL at pH 7.4) to use for medications by intravenous injection.

Full text of DOI:10.1021/jm020239l

J . Med. Chem. 2003, 46, 691-701
691
Tr icyclic In d ole-2-ca r boxylic Acid s: High ly in Vivo Active a n d Selective
An ta gon ists for th e Glycin e Bin d in g Site of th e NMDA Recep tor
Seiji Katayama,‡ Nobuyuki Ae,‡ Toru Kodo,‡ Shuji Masumoto,‡ Shinji Hourai,† Chika Tamamura,‡
Hiroyasu Tanaka,‡ and Ryu Nagata*,‡
Research Division, Sumitomo Pharmaceuticals Co., Ltd, 1-98 Kasugadenaka 3-chome, Konohana-ku, Osaka 554-0022, J apan,
and Environmental Health Science Laboratory, Sumitomo Chemical Co., Ltd, 4-2-1 Takatsukasa,
Takarazuka, Hyogo 665-8555, J apan
Received May 31, 2002
A series of tricyclic indole-2-carboxylic acid derivatives were synthesized and evaluated by the
radioligand binding assay and the anticonvulsant effects in the mouse NMDA-induced seizure
model. Among them, derivatives of 3S-(-)-4 such as 3a , 3f, and 3g which had certain
zwitterionic anilides showed high affinity to the NMDA-glycine binding site. The absolute
configuration of 3S-(-)-4 was confirmed by X-ray crystallographic analysis. In particular, 3g
(SM-31900) was found to be a highly active glycine antagonist for both in vitro and in vivo
assays (Ki ) 1.0 ( 0.1 nM, ED50 ) 2.3 mg/kg, iv) and also showed high selectivity for the
glycine site. In addition, 3g was soluble enough in aqueous media (>10 mg/mL at pH 7.4) to
use for medications by intravenous injection.
Sch em e 1. Synthetic strategy for tricyclic
indole-2-carboxylic acid derivatives 3.
In tr od u ction
The N-methyl-D-aspartate (NMDA) receptor is a
member of the glutamate receptor superfamily and
plays important roles for neurotransmission in the
central nervous system (CNS) and synaptic plasticity
that underlies learning processes and memory.1 The
NMDA receptor is associated with a ligand gated
calcium ion channel which is activated by cooperation
of glutamate and glycine2 and blocked by certain ion
channel blockers3 such as phencyclidine (PCP) and
dizocilpine (MK-801). Overactivation of the NMDA
receptor is, however, thought to be involved in neuronal
cell death caused by not only hypoxic conditions such
as stroke but also chronic neurodegenerative disorders
such as Alzheimer’s and Hungtington’s diseases.4 There-
fore, antagonists, especially, acting on the glycine bind-
ing site of the NMDA receptor have been recognized to
be potential therapeutic agents for such disorders.1b,5
The glycine antagonists discovered initially, however,
were found to show poor in vivo activities because the
structural features were unfavorable for penetration of
the blood-brain barrier.6 Although much effort has been
devoted to identifying in vivo active glycine antagonists
by many laboratories, only a few compounds such as
ACEA 1021,7 L-701,324,8 and ZD93799 have successfully
showed in vivo activities so far.10 GV150526A11 was also
reported to be in vivo active and entered clinical trials,
although the trials were terminated at the phase III.
We have synthesized a series of tricyclic quinoxalinedi-
ones 1 (Figure 1) as a new class of potent NMDA-
glycine antagonists including SM-18400 (1a ) which
showed extremely high affinity to the glycine site (Ki )
0.4 nM) and exhibited neuroprotective properties in
several animal models.12,13 We have also synthesized a
series of tricyclic azakynurenic acids 2 using a novel
Stille type coupling reaction.14 Moreover, we recently
identified another potent tricyclic series based on indole-
2-carboxylic acid, as exemplified by 3a (Ki ) 0.8 nM).15
Herein, we report the detailed study on this new series,
i.e., tricyclic indole-2-carboxylic acids 3, in which we
have further synthesized and evaluated the derivatives
of 3a and identified 3g as a potent glycine antagonist
in both in vitro and in vivo, as determined by the
radioligand binding assay and the anticonvulsant effects
in the mouse NMDA-induced seizure model.
Ch em istr y
Tricyclic indole-2-carboxylic acid derivatives (3) bear-
ing various anilide groups can be prepared by condensa-
tion of tricyclic indole monocarboxylic acid 3S-(-)-4 with
the corresponding anilines 5 followed by deprotections
(Scheme 1). Synthesis of common intermediate 3S-(-
)-4 was described in our previous report.15 Since we
succeeded in obtaining suitable crystals of (-)-4 by
recrystallization from 2-propanol, the absolute config-
uration of the (-)-isomer could be determined to be S
by single X-ray crystallographic analysis as shown in
Figure 2.
Aniline 5d was prepared as shown in Scheme 2.
Methyl 2-nitrophenylacetate (6), which was readily
prepared from commercially available 2-nitrophenylace-
tic acid, was hydrogenated with 10% palladium on
carbon in ethyl acetate to give 5d . Aniline 5e was
synthesized according to Scheme 3. Mesylation of 4-ni-
trobenzyl alcohol (7) followed by treatment with potas-
* To whom corresponding should be addressed. Tel: 81-6-6466-5193.
Fax: 81-6-6466-5483. E-mail: rnagata@sumitomopharm.co.jp.
‡ Sumitomo Pharmaceuticals Co., Ltd.
† Sumitomo Chemical Co., Ltd.
10.1021/jm020239l CCC: $25.00 © 2003 American Chemical Society
Published on Web 01/24/2003

692 J ournal of Medicinal Chemistry, 2003, Vol. 46, No. 5
Katayama et al.
F igu r e 1. Tricyclic NMDA antagonists acting on the glycine site.
catalyzed cyanation of 11 using zinc cyanide18 gave
compound 12 in practical yield. Selective reduction of
12 with a combination of borane-THF complex and
trimethylborate in THF followed by treatment with
Boc2O afforded desired nitrobenzene 13, which was then
hydrogenated as described above to give 5f. Anilines 5g
and 5h were respectively synthesized according to the
route shown in Scheme 5. At first, we used esters such
as ethyl or tert-butyl ester as a protecting group of
carboxylic acid at the side chain of the anilines. Such
anilines, however, readily underwent undesired lactam-
formation during storage or under coupling conditions
with 3S-(-)-4. To solve this problem, we chose mor-
pholinoamide as a protecting group that was stable
enough under storage or the coupling conditions and
was readily cleaved to the carboxylic acid by hydrolysis.
A mixture of methyl (S)-(-)-lactate (14g) and morpho-
line was heated in the presence of a catalytic amount
of sodium hydride and the resulting amide was con-
verted into tosylate 15g. The optical purity of 15g was
confirmed to be more than 99% ee after recrystallization,
as determined by HPLC analysis on a chiral stationary
column. 3-Hydroxy-4-nitrobenzoic acid (16) was reduced
with a combination of borane-pyridine complex/boron
trifluoride diethyl etherate/trimethyl borate in THF to
give benzyl alcohol 17 in high yield.19 This product was
coupled with 15g in the presence of potassium carbonate
to yield ether 18g. In this step, a SN2 type reaction
would take place with complete inversion at the stereo-
genic center because the chiral stationary phase HPLC
analysis of crude 18g showed an optical purity of more
than 99% ee without loss of the ee from 15g. The
absolute configuration of 18g must be R, as confirmed
by a model reaction.20 Similarly to the synthesis of 5e,
18g was converted into the desired aniline 5g in five
steps. The Boc-protected nitrobenzylamine 21g was
purified by recrystallization from toluene, and the chiral
stationary phase HPLC analysis of this product showed
99.9% ee. The isomer 5h was also prepared from methyl
(R)-(+)-lactate (14h ) as described above.
F igu r e 2. X-ray structure of 3S-(-)-4.
Sch em e 2a
a
Reagents and conditions: (i) H2, 10% Pd/C, EtOAc, rt, quant.
Sch em e 3a
a
Reagents and conditions: (i) MsCl, Et3N, toluene, 0 °C; (ii)
phthalimide-K, DMF, rt, 91% from 7; (iii) H2NNH2‚H2O, TsOH‚H2O,
THF, reflux; (iv) Boc2O, CH2Cl2, rt, 87% from 8; (v) H2, 10% Pd/C,
EtOAc, rt, 99%.
Preparation of compounds 3a -c in Table 1 was
described in the previous report.15 Compounds 3d -h
in Table 1 were prepared according to the route outlined
in Scheme 6. Condensation of 3S-(-)-4 with aniline 5d
using N,N-bis(2-oxo-3-oxazolidinyl)phosphinic chloride
(Bop-Cl) in dichloromethane in the presence of triethy-
lamine afforded anilide 22d . Both methyl esters of 22d
were hydrolyzed simultaneously with aqueous sodium
hydroxide in a mixed solvent of methanol and THF to
give 3d . In a similar way, 5f was condensed with 3S-
(-)-4 to afford anilide 22f, which was hydrolyzed as
described above and then treated with hydrogen chlo-
ride in 1,4-dioxane to give 3f as a hydrochloride salt.
sium phthalimide in DMF gave phthalimide 8. Depro-
tection of 8 with hydrazine monohydrate in THF in the
presence of p-toluenesulfonic acid followed by treatment
with di-tert-butyl dicarbonate (Boc2O) afforded 9, which
was then hydrogenated as described above to give 5e.
Although synthesis of aniline 5f was described in ref
16, we used a more convenient route as shown in
Scheme 4. Commercially available 1-iodo-4-nitrobenzene
(10) was treated with tert-butyl chloroacetate under the
conditions of the vicarious nucleophilic substitution
(VNS) reaction17 to afford compound 11. Palladium-

Tricyclic Indole-2-Carboxylic Acids
J ournal of Medicinal Chemistry, 2003, Vol. 46, No. 5 693
Sch em e 4a
a
Reagents and conditions: (i) tert-butyl chloroacetate, t-BuOK, DMF, 0 °C, 51%; (ii) Zn(CN)2, (Ph3P)4Pd, DMF, 80 °C, 84%; (iii) (MeO)3B,
BH3‚THF, THF, rt; (iv) Boc2O, THF, rt, 50% from 12; (v) H2, 10% Pd/C, EtOAc, rt, quant.
Sch em e 5a
a
Reagents and conditions: (i) morpholine, NaH, 50 °C; (ii) NaH, TsCl, THF, 0 °C, 73% from 14g,h , >99% ee; (iii) (MeO)3B, BF3‚OEt2,
BH3‚pyridine, 1,2-dichloroethane, rt 94%; (iv) K2CO3, DMF 50 °C, >99% ee; (v) MsCl, Et3N, CH2Cl2, 0 °C, 99% from 17; (vi) phthalimide-
K, DMF, rt, 67%; (vii) H2NNH2‚H2O, TsOH‚H2O, THF, reflux, 92%; (viii) Boc2O, EtOAc, rt, 93%, 99.9% ee; (ix) H2 10%, Pd/C, EtOAc, rt,
quant.
Condensation of 3S-(-)-4 with 5e was carried out with
a combination of 1-(3-(dimethylamino)propyl)-3-ethyl-
carbodiimide hydrochloride (WSC) and 1-hydroxyben-
zotriazole (HOBt) in DMF to afford 22e, which was then
subjected to the deprotection sequence as described
above to give 3e as a hydrochloride salt. Treatment of
3S-(-)-4 with oxalyl chloride in ethyl acetate in the
presence of DMF gave the corresponding acid chloride
which was then reacted with 5g in the presence of
triethylamine to afford anilide 22g. Succesive depro-
tection of 22g was performed at first with aqueous
lithium hydroxide in a mixed solvent of methanol and
THF and then treatment with hydrogen chloride in
acetic acid to give 3g as a hydrochloride salt. Under
these conditions no chromatographic purifications were
required through the entire sequence from starting
materials, 16 and 14g, to 3g. The final product 3g was
also analyzed by HPLC and both its ee and de were
estimated to be 99.9%. In a manner similar to 3g, 3h
was prepared from aniline 5h .
Biologica l Eva lu a tion s
The affinities of compounds 3a -h and 1a for the
glycine site of the NMDA receptor were determined by
the displacement of the tritium labeled selective glycine
site antagonist [3H] 1a (Kd ) 0.43 nM)13e from rat
cortical membrane preparations. The respective IC50
values are listed in Table 1. The affinity of the selected
compound 3g for the glycine site was also evaluated
by using [3H] 5,7-dichlorokynurenic acid (DCKA),21
[3H] glycine,22 as well as [3H] 1a (Table 2). The affinities
of 3g for the glutamate binding site of the NMDA
receptor and other glutamate receptor subtypes such as
2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl)propanoic
acid (AMPA) and kainic acid (KA) receptors were eval-
uated using [3H] glutamate,23 [3H] AMPA,24 and [3H]
KA25 as radiolabeled ligands, respectively (Table 2).
The in vivo activities of compounds 3a , 3c-h , and 1a
were measured in the mouse NMDA-induced seizure
model.12a,13b,26 A test compound was intravenously
administered at a given dose (usually 3 mg/kg, iv) into
each of 10 mice, 20 min prior to the intracerebroven-

694 J ournal of Medicinal Chemistry, 2003, Vol. 46, No. 5
Katayama et al.
Ta ble 1. Binding Affinity and Anticonvulsant Activity of Tricyclic Indole-2-carboxylic Acids 3a -h
mice NMDA-induced seizure modelb
number protected/number tested
(at 3 mg/kg, iv)
compd
R1
OCH2CO2H
OCH2CO2H
H
CH2CO2H
H
CH2CO2H
R2
IC50 (nM)a vs [3H] SM-18400
ED50 (mg/kg)
3a
3bd
3c
3d
3e
3f
3g
3h
1a
CH2NH2
CH2NH2
H
1.2
33
19
7.6
2/10
nte
5.0 (2.0-12.5)c
3/10
3/10
3/10
5/10
5/10
4/10
10/10
ndf
H
ndf
CH2NH2
CH2NH2
CH2NH2
CH2NH2
18
ndf
1.5 ( 0.3
2.7 ( 0.3
29.0 ( 0.5
1.0 ( 0.1
1.8 (0.63-5.1)c
2.3 (0.71-5.1)c
3.7 (2.5-10.0)c
0.41 (0.14-0.68)c
(1′R)-OC*H(CH3)CO2H
(1′S)-OC*H(CH3)CO2H
SM-18400
a
The values of 3a -e were determined from two independent experiments carried out in triplicate. The values of 3f-h , and 1a represent
b
the mean ( SEM from three separate assays carried out in triplicate. See ref 13e for detail assay procedures. See ref 12a, 13b, 26, 28
and see the text for detail assay procedures. c The values in parentheses show 95% confidence limits. Compound 3b was C-3 epimer of
d
3a and prepared from 3R-(+)-4. See ref 15. e This compound was not tested in vivo. f The values of ED50 for these compounds were not
determined.
Sch em e 6a
a
Reagents and conditions: (i) 5d or 5f, BopCl, Et3N, CH2Cl2, rt; (ii) 5e, WSC, HOBt, DMF, rt; (iii) (COCl)2, DMF, EtOAc, rt, then 5g
or 5h , Et3N, EtOAc, rt; (iv) aq 2 N NaOH, THF, MeOH, rt; (v) 2 N HCl, 1,4-dioxane, rt; (vi) aq 2 N LiOH, THF, MeOH, rt; (vii) 0.5 N HCl,
AcOH, rt.
tricular (icv) administration of NMDA (5 nmol). Under
the conditions without pretreatment with the test
compound, almost all of mice (9 to 10 of 10) exhibit tonic
seizures. The number of mice which did not exhibit tonic
seizures after icv administration of NMDA was counted
as considered to be protected. For the compounds 3a ,
3f-h , and 1a , the ED50 values were determined by
experiments at the doses of 1, 3, and 10 mg/kg under
the conditions described above. These results (the
number of protection at the given dose and/or the ED50
value) are summarized in Table 1.
Resu lts a n d Discu ssion
As revealed in the in vitro binding assays using [3H]
1a in Table 1 and [3H] DCKA as in the previous report,15
3S-(-)-isomer 3a (IC50 ) 1.2 nM) was more active than
its C-3 epimer 3b (IC50 ) 33 nM), and this result was
consistent with our previous observation in the series

Tricyclic Indole-2-Carboxylic Acids
J ournal of Medicinal Chemistry, 2003, Vol. 46, No. 5 695
Ta ble 2. Selectivity of 3g: Affinities for Glycine Binding Site, Glutamate Binding Site of NMDA Receptor and Other Glutamate
Receptor Subtypesa
NMDA-glycine site: Ki (nM)
vs [3H] DCKAb vs [3H] glycinec
11 ( 2
NMDA binding site: Ki (nM)
non-NMDA receptor: Ki (nM)
vs [3H] AMPAe vs [3H] KAf
>10000 >10000
vs [3H] glutamated
1.0 ( 0.1
>10000
a
b
d
See ref 28. DCKA: 5,7-dichlorokynurenic acid. See ref 21. c See ref 22. See ref 23. e AMPA: 2-amino-3-(3-hydroxy-5-methylisoxazol-
4-yl)propanoic acid. See ref 24. f KA: kainic acid. See ref 25.
of tricyclic quinoxalinediones.12a,d,13a In the previous
studies, we optimized tricyclic quinoxalinediones for
both in vitro and in vivo activity to obtain zwitterionic
compound 1a , which had an o-carboxymethoxy p-ami-
nomethylanilide at the side chain.13a As expected,
compound 3a (IC50 ) 1.2 nM, Ki ) 0.8 nM15) which had
the same anilide as 1a showed affinity as high as 1a
(IC50 ) 1.0 nM, Ki ) 0.4 nM13a,15). Unfortunately, in the
NMDA-induced seizure model, 3a (2/10 at 3 mg/kg, ED50
) 5.0 mg/kg), however, showed reduced activity com-
pared to 1a (10/10 at 3 mg/kg, ED50 ) 0.41 mg/kg). To
identify more in vivo active compounds in this new
series, we set a criterion that the anticonvulsant activity
of the test compound should reach 50% protection at
the dose of 3 mg/kg, iv (i.e. 5/10 at 3 mg/kg). Tricyclic
indole-2-carboxylic acid derivatives having various anil-
ide groups at the C-3 side chain were prepared and
evaluated to seek a compound beyond the criterion.
Selected examples are listed in Table 1. Among them,
derivatives whose anilide parts were not zwitterionic
such as 3c (unsubstituted anilide, IC50 ) 19 nM, 3/10
at 3 mg/kg), 3d (o-carboxymethylanilide, IC50 ) 7.6 nM,
F igu r e 3. Indole-2-carboxylate-based glycine antagonist, GV-
150526A.
cine antagonist, GV-150526A (23, Figure 3)11 was much
weaker than that of our series such as 3a -h in our
seizure model.27
We selected 3g (SM-31900) and evaluated further for
the biological activities and found that 3g had excellent
neuroprotective effects in neuronal cells28 and in several
animal models.29-31 In particular, 3g was more potent
than 3f in a permanent suture middle cerebral artery
occlusion (MCAo) model using normotensive rats.29 The
test compound was administered intravenously as a
bolus injection immediately after induction of the oc-
clusion followed by a continuous infusion for 24 h. The
percentage of cortical infarct volume reduction using 3g
and 3f were 84% (statistically significant) and 30% (not
significant) at the same dosage of 20 mg/kg bolus + 20
mg/kg/h continuous infusion, respectively. For compari-
son, 1a also significantly reduced the infarct volume by
50% at a dosage of 5 mg/kg bolus + 5 mg/kg/h continu-
ous infusion in the same test. Furthermore, 3g was also
neuroprotective in the permanent electrocoagulation
MCAo model using spontaneously hypertensive rats
(SHRs).30 In this test, 3g was administered 30 min after
the occlusion and still demonstrated significant infarct
reduction of 40% at a dosage of 1.5 mg/kg bolus + 6 mg/
kg/h continuous infusion for 24 h. As shown in Table 2,
3g showed high selectivity for the glycine site (Ki ) 1.0
( 0.1 nM vs [3H] DCKA, Ki ) 11 ( 2 nM vs [3H] glycine)
compared to the glutamate site (Ki >10 µM vs [3H]
glutamate) and other subtypes such as AMPA and KA
receptors (Ki >10 µM vs [3H] AMPA, Ki >10 µM vs [3H]
KA).28 In addition, 3g had no affinities for more than
160 other receptors, ion channels, and enzymes at 10µM.
Although we had already introduced another highly
potent candidate 1a , new candidate 3g turned out to
be superior to 1a in terms of pharmacokinetics and
solubility in aqueous media. Pharmacokinetic studies
for both compounds were carried out in rats at the same
dosage (10 mg/kg, iv) and showed that 3g had more
favorable pharmacokinetic parameters than 1a {clear-
ance (mL/min/kg), plasma half-life (min) for 3g: 4.5, 83;
for 1a : 39, 38, respectively}. The brain access of 3g was
also confirmed {the area under the concentration-time
curve from time zero to time infinity (AUC0-∞) in whole
brain homogenates for 3g: 10 µg‚min/g}, which was
better than that of 1a {the AUC value for the observed
time period (AUC0-2h) in whole brain homogenates for
3/10 at 3 mg/kg), and 3e (p-aminomethylanilide, IC50
)
18 nM, 3/10 at 3 mg/kg) showed only moderate activity
in both in vitro and in vivo. However, compound 3f (IC50
) 1.5 nM, 5/10 at 3 mg/kg, ED50 ) 1.8 mg/kg) which
had a zwitterionic o-carboxymethyl- p-aminomethya-
nilide showed not only a high affinity comparable to 3a ,
but excellent in vivo activity which could reach our
criterion. It was noteworthy that a subtle structural
difference between 3a and 3f affected their in vivo
activities, i.e. where the former possessed an o-phe-
noxyacetic acid moiety {calculated pKa ) 3.08, calcu-
lated log D (pH 7.4) ) -0.97}, whereas the latter had
an o-phenylacetic acid moiety {calculated pKa ) 4.02,
calculated log D (pH 7.4) ) -0.79}. We speculated that
the increased acidity and the existence of a hydrophilic
oxygen atom in the phenoxyacetic acid moiety of 3a
might result in the reduced in vivo activity compared
to 3f. Thus, it occurred to us to introduce an electron-
donating and lipophilic methyl group into the R position
of the carboxyl group of 3a . One isomer of such com-
pounds, 3g (IC50 ) 2.7 nM, 5/10 at 3 mg/kg, ED50 ) 2.3
mg/kg) retained affinity in in vitro and, indeed, signifi-
cantly improved the in vivo activity compared to 3a . The
absolute configuration of the second asymmetric center
of this compound was R, whereas the other epimer 3h
(IC50 ) 29 nM, 4/10 at 3 mg/kg, ED50 ) 3.7 mg/kg)
showed an at least 11-fold reduced affinity relative to
3g. Interestingly, 3h which had 24-fold lower affinity
than 3a was even more potent than 3a in in vivo. The
calculated pKa and log D (pH 7.4) for both 3g and 3h
were 3.13 and -0.62, respectively. The increase of log
D compared to 3a might mainly contribute to improve-
ment of the in vivo activity. It was also noteworthy that
the activity of another indole-2-carboxylate-based gly-

696 J ournal of Medicinal Chemistry, 2003, Vol. 46, No. 5
Katayama et al.
Hz), 7.35 (d, 2H, J ) 8.3 Hz), 7.81 (d, 2H, J ) 8.3 Hz); MS m/z
313 (M+); HRMS (EI) calcd for C14H19NO5S 313.0984 found
313.0975.
1a : 3.3 µg‚min/g}. Solubility was a very important
character for intravenous administration that was
needed for the treatment of acute neurodegenerative
diseases such as stroke. Thus, it was also noteworthy
that 3g was highly soluble (>10 mg/mL) in aqueous
media at pH 7.4. In contrast, the solubility of 1a was
only 1.9 mg/mL at pH 7.4, though 1a could be more
soluble in alkaline conditions.
5-H yd r oxym et h yl-2-n it r op h en ol (17). To a solution of
3-hydroxy-4-nitrobenzoic acid (16, 50.0 g, 0.273 mol) in 1,2-
dichloroethane (1.0 L) were added trimethyl borate (45.4 g,
0.437 mol) and boron trifluoride diethyl etherate (62.0 g, 0.437
mol) followed by dropwise addition of borane-pyridine complex
(38.1 g, 0.410 mol). After stirring at room temperature for 4
h, methanol (100 mL) was added dropwise at 0 °C. The mixture
was concentrated, and toluene was added to the residue. The
resulting mixture was extracted with aqueous 1 N NaOH three
times, and the combined aqueous layers were acidified with
aqueous 12 N HCl to pH 1 and extracted with ethyl acetate
twice. The organic layers were combined, washed with water
and brine successively, dried over magnesium sulfate, and
concentrated in vacuo to give the title compound (43.3 g,
Con clu sion
We have successfully identified tricyclic indole-2-
carboxylic acids as a new class of potent NMDA-glycine
antagonists. Particularly, 3g was the most promising
one in terms of its neuroprotective effects, high selectiv-
ity for the glycine site, and high solubility in aqueous
media. Further pharmacological and toxicological evalu-
ations of 3g are in progress.
1
94%): mp 97-98 °C; H NMR (270 MHz, CDCl3) δ 1.94 (bs,
1H), 4.77 (s, 2H), 6.96 (dd, 1H, J ) 8.6, 1.7 Hz), 7.17 (d, 1H, J
) 1.7 Hz), 8.09 (d, 1H, J ) 8.6 Hz), 10.65 (s, 1H); MS (EI) m/z
169 (M+); Anal. (C7H7NO4): C, H, N.
Exp er im en ta l Section
2-((1R)-1-Mor p h olin oca r bon yleth oxy)-4-h yd r oxym eth -
yln itr oben zen e (18g). Potassium carbonate (52.7 g, 0.381
mol) was added to a solution of 17 (43.0 g, 0.254 mol) and 15g
(83.6 g, 0.267 mol) in DMF (150 mL), and the mixture was
stirred at 50 °C for 6 h. Water was added, and the resulting
mixture was extracted with dichloromethane twice. The
organic layers were combined and washed with aqueous 5%
potassium carbonate solution, aqueous 1 N HCl, and water
successively, dried over magnesium sulfate, and concentrated
in vacuo to give 18g (93.2 g, >99% ee). This product was used
in the following reaction without further purification. The
enantiomeric excess was estimated by using HPLC on a
CHIRALCEL OJ with 1:1 2-propanol/hexane as an eluent at
a flow rate of 0.4 mL/min (UV detection, 254 nm). The (R)-
enantiomer, 18g, eluted at the retention time of 17.7 min, and
the (S)-enantiomer, 18h , eluted at the retention time of 25.7
min. The crude product can be purified by silica gel column
chromatography with 1:1 chloroform/ethyl acetate to give the
Gen er a l Notes. Melting points were measured on either a
Thomas-Hoover or a Yanaco melting point apparatus and were
1
uncorrected. H NMR spectra were recorded on a J EOL GX-
270 or J EOL J NM-LA300 spectrometers using tetramethyl-
silane as an internal standard. LC mass spectra were obtained
on a PE SCIEX API 150EX spectrometer. Elemental analyses,
low-resolution mass spectra, and high-resolution mass spectra
were obtained from Sumitomo Analytical Center, Inc. Thin-
layer chromatography and flash column chromatography was
performed on silica gel glass-backed plates (5719, Merck & Co.)
and silica gel 60 (230-400 or 70-230 mesh, Merck & Co.),
respectively. Optical rotations were measured on a J ASCO
DIP-370. Optical purity was determined by HPLC using
Hitachi L 6000 pump and L 4000 UV detector or Shimadzu
LC-10A pump and SPD-10A UV detector with chiral columns
(CHIRALCEL OJ , Daicel; SUMICHIRAL OA-2500, Sumitomo
Analytical Center).
analytically pure sample: [R]25 ) -87.3° (c 0.25, MeOH); 1H
D
N-((2S)-2-Hyd r oxyp r op a n oyl)m or p h olin e. To a mixture
of methyl (S)-(-)-lactate (14g, 50.0 g, 0.480 mol) and morpho-
line (46.0 mL, 0.528 mol) with stirring at 0 °C was added
slowly portionwise 60% sodium hydride (1.92 g, 0.0480 mol),
and the resulting mixture was stirred at 50 °C for 3 h. Excess
morpholine was removed by azeotropic evaporation with
toluene to give the title compound (81.4 g) as crude material.
This product was used in the following reaction without further
NMR (270 MHz, CDCl3) δ 1.67 (d, 3H, J ) 6.9 Hz), 3.51 (m,
3H), 3.68 (m, 4H), 3.87 (m, 1H), 4.15 (t, 1H, J ) 5.6 Hz), 4.72
(d, 2H, J ) 5.6 Hz), 5.09 (q, 1H, J ) 6.9 Hz), 7.02 (dd, 1H, J
) 8.3, 1.6 Hz), 7.11 (d, 1H, J ) 1.6 Hz), 7.80 (d, 1H, J ) 8.3
Hz); MS (FAB) m/z 311 (MH+); HRMS (FAB) calcd for
C
14H19N2O6 (MH+) 311.1243 found 311.1238.
2-((1R)-1-Mor p h olin oca r bon yleth oxy)-4-m eth a n esu lfo-
purification: MS (EI) m/z 159 (M+); HRMS (EI) calcd for C7H13
-
n yloxym eth yln itr oben zen e (19g). Methanesulfonyl chloride
(36.1 g, 0.315 mol) was added dropwise slowly to a solution of
crude 18g (93.0 g) and triethylamine (50.1 mL, 0.360 mol) in
dichloromethane (500 mL) with stirring at 0 °C. After stirring
at 0 °C for 40 min, aqueous 1 N HCl (300 mL) was added, and
the organic layer was separated, washed with water, dried over
magnesium sulfate, and concentrated in vacuo to give the title
compound (97.0 g, 99% from 17). This product was used in
the following reaction without further purification: 1H NMR
(270 MHz, CDCl3) δ 1.70 (d, 3H, J ) 6.9 Hz), 3.09 (s, 3H),
3.48 (m, 3H), 3.69 (m, 4H), 3.92 (m, 1H), 5.08 (q, 1H, J ) 6.9
Hz), 5.24 (s, 2H), 7.09 (dd, 1H, J ) 8.2, 1.7 Hz), 7.11 (d, 1H, J
) 1.7 Hz), 7.85 (d, 1H, J ) 8.2 Hz); LC-MS (ESI) m/z 389
(MH+).
NO3 159.0895 found 159.0815.
N -((2 S )-2 -p -T o l u e n s u l fo n y l o x y p r o p a n o y l )m o r -
p h olin e (15g). To a suspension of 60% sodium hydride (20.2
g, 0.504 mol) in THF (400 mL) with stirring at 0 °C was added
dropwise a solution of N-((2S)-2-hydroxypropanoyl)morpholine
(81.4 g) obtained above in THF (400 mL), and the mixture was
warmed gradually and stirred at 50 °C for 30 min. After the
mixture was cooled to 0 °C, a solution of p-toluenesulfonyl
chloride (110 g, 0.576 mol) in THF (400 mL) was added
dropwise followed by stirring for 2 h at 0-5 °C. The reaction
mixture was diluted with water, acidified with aqueous 1 N
HCl to pH 1, and extracted with ethyl acetate. The organic
layer was washed with water and brine successively, dried over
sodium sulfate, and concentrated to afford the crude product.
To the residue were added diethyl ether (100 mL) and hexane
(30 mL). The precipitated crystals were collected by filtration,
washed with diethyl ether, and dried in vacuo to give 15g (110
g, >99% ee, 73% yield from methyl (S)-(-)-lactate). The
enantiomeric excess was determined by using HPLC on a
CHIRALCEL OJ with 1:5 ethanol/hexane as an eluent at a
flow rate of 1.0 mL/min (UV detection, 254 nm). The (-)-
enantiomer, 15g, eluted at the retention time of 22.9 min, and
2-((1R)-1-Mor p h olin oca r bon yleth oxy)-4-p h th a lim id o-
m eth yln itr oben zen e (20g). To a solution of 19g (96.7 g,
0.249 mol) in DMF (800 mL) was added potassium phthalimide
(50.8 g, 0.274 mol), and the mixture was stirred at room
temperature for 1.5 h. Water was added, and the resulting
mixture was extracted with 2:1 ethyl acetate/toluene twice.
The organic layers were combined, washed with water (three
times) and brine successively, dried over magnesium sulfate,
and concentrated to give the crude product (108 g). To the
residue thus obtained were added diethyl ether (400 mL) and
toluene (50 mL). The precipitated crystals were collected by
filtration, washed with diethyl ether and dried in vacuo to give
the (+)-enantiomer, 15h , eluted at the retention time of 21.6
1
min: mp 77-78 °C; [R]25 ) -26.6° (c 1.0, MeOH); H NMR
D
(270 MHz, CDCl3) δ 1.47 (d, 3H, J ) 6.6 Hz), 2.46 (s, 3H),
3.42 (m, 1H), 3.57 (m, 3H), 3.63 (m, 4H), 5.27 (q, 1H, J ) 6.6
20g (73.6 g, 67%): mp 124-125 °C; [R]25 ) -85.1° (c 0.22,
D

Tricyclic Indole-2-Carboxylic Acids
J ournal of Medicinal Chemistry, 2003, Vol. 46, No. 5 697
MeOH); 1H NMR (270 MHz, CDCl3) δ 1.65 (d, 3H, J ) 6.9 Hz),
3.49-3.31 (m, 3H), 3.71-3.51 (m, 4H), 3.88 (m, 1H), 4.81 (d,
1H, J ) 15.2 Hz), 4.88 (d, 1H, J ) 15.2 Hz), 5.02 (q, 1H, J )
6.9 Hz), 7.08 (dd, 1H, J ) 7.3, 1.7 Hz), 7.10 (d, 1H, J ) 1.7
Hz), 7.75 (m, 2H), 7.80 (d, 1H, J ) 7.3 Hz), 7.87 (m, 2H); MS
(FAB) m/z 440 (MH+); HRMS (FAB) calcd for C22H22N3O7
(MH+) 440.1458 found 440.1462.
solution of 5g (57.7 g, 152 mmol) in ethyl acetate (880 mL)
was added triethylamine (26.5 mL, 190 mmol) followed by
dropwise addition of the solution obtained above of the acid
chloride of 3S-(-)-4 in ethyl acetate with stirring at 0 °C. The
reaction mixture was stirred at 0 °C for 1 h and at room
temperature for a further 1 h. The reaction mixture was
acidified with aqueous 5% KHSO4 and extracted with ethyl
acetate. The organic layer was washed with water, saturated
aqueous NaHCO3, water, and brine successively, dried over
magnesium sulfate, and concentrated in vacuo to give crude
product (88.5 g). The crude product thus obtained was dis-
solved in hot toluene (450 mL). The resulting solution was
cooled gradually and stirred at room temperature. The pre-
cipitated crystals were collected by filtration, washed with
toluene, and dried in vacuo at 40 °C to give the title compound
2-((1R)-1-Mor p h olin oca r b on ylet h oxy)-4-a m in om et h -
yln itr oben zen e. To a solution of 20g (73.4 g, 0.167 mol) in
THF (800 mL) were added hydrazine monohydrate (32.4 mL,
0.668 mol) and p-toluenesulfonic acid monohydrate (3.18 g,
0.0167 mol). The mixture was heated under reflux for 6 h. The
resulting mixture was cooled to room temperature, basified
with aqueous 5% potassium carbonate solution to pH 10, and
extracted with dichloromethane three times. The organic
layers were combined, washed with water, dried over magne-
sium sulfate, and concentrated in vacuo to give the title
(83.0 g, 98%): mp 189-190 °C, dec; [R]25 ) -68.4° (c 0.23,
D
MeOH); 1H NMR (270 MHz, CDCl3) δ 1.46 (s, 9H), 1.57 (d,
3H, J ) 6.6 Hz), 2.04 (m, 1H), 2.29 (m, 1H), 2.59 (dd, 1H, J )
14.0, 10.1 Hz), 2.84 (m, 2H), 3.12 (m, 1H), 3.43 (m, 2H), 3.59
(m, 6H), 3.83 (s, 3H), 4.03 (m, 1H), 4.23 (m, 2H), 4.88 (m, 1H),
4.95 (q, 1H, J ) 6.6 Hz), 6.86 (m, 2H), 6.93 (d, 1H, J ) 8.3
Hz), 7.18 (s, 1H), 8.36 (d, 1H, J ) 8.3 Hz), 8.82 (s, 1H), 9.02 (s,
1H); MS (FAB) m/z 669 (MH+); HRMS (FAB) calcd for
compound (47.3 g, 92%): mp 116-117 °C; [R]25 ) -57.8° (c
D
0.19, MeOH); 1H NMR (270 MHz, CDCl3) δ 1.50 (bs, 2H), 1.69
(d, 3H, J ) 6.9 Hz), 3.56-3.38 (m, 3H), 3.69 (m, 4H), 3.93 (s,
2H), 3.96 (m, 1H), 5.09 (q, 1H, J ) 6.9 Hz), 7.05 (d, 1H, J )
8.3 Hz), 7.13 (s, 1H), 7.83 (d, 1H, J ) 8.3 Hz); MS (FAB) m/z
310 (MH+); HRMS (FAB) calcd for C14H20N3O5 (MH+) 310.1403
found 310.1426.
C
34H42N4O8Cl (MH+) 669.2691 found 669.2724.
Meth yl (3S)-7-Ch lor o-3-(2-((1R)-1-car boxyeth oxy)-4-ter t-
2-((1R)-1-Mor p h olin oca r b on ylet h oxy)-4-ter t-b u t oxy-
ca r bon yla m in om eth yln itr oben zen e (21g). Di-tert-butyl di-
carbonate (36.6 g, 0.167 mol) was added to a solution of 2-((1R)-
1-morpholinocarbonylethoxy)-4-aminomethylnitrobenzene (47.1
g, 0.152 mol) in ethyl acetate (800 mL), and the mixture was
stirred at room temperature for 1 h. After the solvent was
removed in vacuo, the residue was dissolved in hot toluene
(400 mL). The solution thus obtained was allowed to cool to
room temperature, then further cooled to 0 °C and stirred for
2 h. The precipitated crystals were collected by filtration,
washed with toluene, and dried at 50 °C in vacuo to give 21g
(58.1 g, 93%, 99.9% ee). The enantiomeric excess was deter-
mined by using HPLC on a CHIRALCEL OJ with 1:1 2-pro-
panol/hexane as an eluent at a flow rate of 0.4 mL/min (UV
detection, 254 nm). The (R)-enantiomer, 21g, eluted at the
retention time of 18.4 min, and the (S)-enantiomer, 21h , eluted
b u t oxyca r b on yla m in om e t h ylp h e n yl)a m in oca r b on yl-
m eth yl-1,3,4,5-tetr a h yd r oben z[cd ]in d ole-2-ca r boxyla te.
To a solution of 22g (86.4 g, 129 mmol) in a mixed solvent of
THF (440 mL) and methanol (440 mL) was added aqueous 2
N LiOH (440 mL, 880 mmol), and the mixture was stirred at
room temperature for 16 h. The organic solvents were removed
in vacuo, and the resulting aqueous layer was washed with
toluene (three times), acidified with aqueous 13% KHSO4 to
pH 2 and extracted with 3:1 ethyl acetate/THF three times.
The organic layers were combined, washed with water and
brine successively, treated with activated charcoal and mag-
nesium sulfate, and filtered. The filtrate was concentrated in
vacuo to give crude product (73.1 g). The crude product (72.0
g) was suspended in acetonitrile (360 mL), heated under reflux,
cooled gradually, and stirred at room temperature for 1 h. The
crystals formed were collected by filtration, washed with ice-
cooled acetonitrile, and dried in vacuo to give the title
at the retention time of 14.8 min: mp 147-148 °C; [R]25
)
D
1
-58.7° (c 1.0, MeOH); H NMR (270 MHz, CDCl3) δ 1.46 (s,
9H), 1.68 (d, 3H, J ) 6.9 Hz), 3.55-3.37 (m, 3H), 3.69 (m, 4H),
3.91 (m, 1H), 4.32 (d, 2H, J ) 6.4 Hz), 5.06 (q, 1H, J ) 6.9
Hz), 5.07 (m, 1H), 7.00 (m, 2H), 7.82 (d, 1H, J ) 8.6 Hz); MS
(FAB) m/z 410 (MH+); HRMS (FAB) calcd for C19H28N3O7
(MH+) 410.1927 found 410.1923.
compound (70.3 g, 94%): mp 228-229 °C; [R]25 ) -61.6° (c
D
1
0.22, MeOH); H NMR (270 MHz, CDCl3) δ 1.40 (s, 9H), 1.56
(d, 3H, J ) 6.6 Hz), 1.85 (m, 1H), 2.13 (m, 1H), 2.81-2.62 (m,
3H), 3.10 (m, 1H), 3.87 (m, 1H), 4.04 (m, 2H), 4.75 (q, 1H, J )
6.6 Hz), 6.84 (m, 3H), 7.15 (s, 1H), 7.31 (m, 1H), 7.89 (d, 1H,
J ) 8.3 Hz), 9.07 (s, 1H), 11.42 (s, 1H), 12.99 (bs, 2H); MS
(FAB) m/z 586 (MH+); HRMS (FAB) calcd for C29H33N3O8Cl
(MH+) 586.1956 found 586.1956.
2-((1R)-1-Mor p h olin oca r b on ylet h oxy)-4-ter t-b u t oxy-
ca r bon yla m in om eth yla n ilin e (5g). Compound 21g (20.0 g,
48.9 mmol) in ethyl acetate (500 mL) was hydrogenated over
10% palladium on carbon (including 50% of water, 5.0 g) at
room temperature under an atmospheric pressure of hydrogen
for 3 h. The reaction mixture was dried over magnesium
sulfate and filtered through a Celite pad, and the filtrate was
(3S )-7-Ch lor o-3-(2-((1R )-1-ca r b oxye t h oxy)-4-a m in o-
m eth ylp h en yl)a m in oca r bon ylm eth yl-1,3,4,5-tetr a h yd r o-
ben z[cd ]in d ole-2-ca r boxylic Acid Hyd r och lor id e (3g).
To a solution of methyl (3S)-7-chloro-3-(2-((1R)-1-carboxy-
ethoxy)-4-tert-butoxycarbonylaminomethylphenyl)amino-
ca r bon ylm et h yl-1,3,4,5-t et r a h ydr oben z[cd ]in dole-2-ca r -
boxylate (70.0 g, 119 mmol) in acetic acid (280 mL) was added
1 N HCl in acetic acid (240 mL, 240 mmol) at room temper-
ature, and the mixture was stirred at the same temperature
for 2 h. Toluene (1.04 L) was added and stirring was continued
for 30 min. The precipitated solid was collected by filtration,
washed with toluene, and dried in vacuo to give the title
compound (61.2 g, 99%) as an amorphous solid. The enantio-
meric excess was determined to be 99.9% ee by chiral HPLC.
Chiral HPLC conditions: column, SUMICHIRAL OA-2500;
mobile phase, acetonitrile/5 mM aqueous 1-heptanesulfonic
acid, sodium salt (adjusted to pH 2.5 with H3PO4) (27:73); flow
rate: 1.0 mL/min; UV detection, 240 nm; tR for (-)-enantiomer
3g, 26.3 min; (+)-enantiomer, 30.5 min. The diastereomeric
excess and the purity were determined to be 99.9% de and 98.8
area %, respectively, by reverse phase HPLC. HPLC condi-
tions: column, SUMIPAX ODS A-212; mobile phase, acetoni-
trile/5 mM aqueous 1-heptanesulfonic acid, sodium salt (ad-
justed to pH 2.5 with H3PO4) (33: 66 for 20 min, then gradient
concentrated in vacuo to give the title compound (18.6 g,
1
100%): [R]D ) -11.3° (c 0.40, CHCl3); H NMR (270 MHz,
25
CDCl3) δ 1.45 (s, 9H), 1.60 (d, 3H, J ) 6.6 Hz), 3.63-3.52 (m,
8H), 3.89 (bs, 2H), 4.14 (d, 2H, J ) 7.3 Hz), 4.80 (bs, 1H), 4.98
(q, 1H, J ) 6.6 Hz), 6.66 (d, 1H, J ) 7.6 Hz), 6.70 (s, 1H), 6.73
(d, 1H, J ) 7.6 Hz); LC-MS (ESI) m/z 380 (MH+); MS (FAB)
m/z 379 (M+); HRMS (FAB) calcd for C19H29N3O5 (M+) 379.2107
found 379.2109.
Meth yl (3S)-7-Ch lor o-3-(2-((1R)-1-m or ph olin ocar bon yl-
e t h oxy)-4-t er t -b u t oxyca r b on yla m in om e t h ylp h e n yl)-
a m in oca r b on ylm e t h yl-1,3,4,5-t e t r a h yd r ob e n z[cd ]in -
d ole-2-ca r boxyla te (22g). Oxalyl chloride (16.9 g, 133 mmol)
was added dropwise slowly to a suspension of methyl (3S)-(-
)-7-chloro-3-carboxymethyl-1,3,4,5-tetrahydrobenz[cd]indole-
2-carboxylate (3S-(-)-4, 39.0 g, 127 mmol) in ethyl acetate (390
mL) and DMF (0.196 mL) with stirring at 0 °C, and then the
mixture was stirred at room temperature for 2 h. The solvent
and the excess oxalyl chloride were removed in vacuo, and the
residue was dissolved in ethyl acetate (260 mL) to give a
solution of the acid chloride of 3S-(-)-4 in ethyl acetate. To a

698 J ournal of Medicinal Chemistry, 2003, Vol. 46, No. 5
Katayama et al.
to 95:5 over 20 min); flow rate: 1.0 mL/min; UV detection, 240
nm; tR for 3g and its enantiomer, 16.2 min; diastereomers (3h
and its enantiomer), 18.0 min. Although the material obtained
above was pure enough to use for pharmacological tests, 3g
could also be recrystallized from 1:10 water/2-propanol to
give white crystals as monohydrate: mp 210-214 °C dec
(for amorphous), 231-237 °C, dec (for crystals); [R]25D ) -68.7
(c 1.0, MeOH);1H NMR (300 MHz, DMSO-d6) δ 1.56 (d, 3H, J
) 6.6 Hz), 1.87 (m, 1H), 2.10 (m, 1H), 2.60-2.80 (m, 3H), 3.08
(m, 1H), 3.89 (m, 1H), 3.93 (s, 2H), 4.84 (q, 1H, J ) 6.6 Hz),
6.83 (s, 1H), 7.06 (d, 1H, J ) 8.1 Hz), 7.15 (s, 1H), 7.19 (s,
1H), 8.02 (d, 1H, J ) 8.1 Hz), 8.34 (bs, 3H), 9.22 (s, 1H), 11.45
(s, 1H); Anal. (C24H25N3O6Cl2 ‚ H2O): C, H, N (for crystals).
(d, 1H, J ) 7.9 Hz), 9.38 (s, 1H), 11.44 (s, 1H), 12.52 (bs, 2H);
MS (FAB) m/z 427 (MH+); HRMS (FAB) calcd for C22H20N2O5-
Cl (MH+) 427.1061 found 427.1047; Anal. (C22H19N2O5Cl‚1/
5H2O): C, H, N.
2-(4-Nit r ob en zyl)-1H -isoin d ole-1,3(2H )-d ion e
(8).
A procedure similar to that described in synthesis of 20g from
18g was carried out with 4-nitrobenzyl alcohol (7, 2.24 g, 14.6
mmol) to give 3.76 g of the title compound (91% from 4-ni-
trobenzyl alcohol): mp 171-174 °C; 1H NMR (270 MHz,
CDCl3) δ 4.93 (s, 2H), 7.59 (d, 2H, J ) 8.6 Hz), 7.73-7.78 (m,
2H), 7.84-7.91 (m, 2H), 8.18 (d, 2H, J ) 8.6 Hz); LC-MS (ESI)
m/z 283 (MH+); MS (FAB) m/z 283 (MH+); HRMS (FAB) calcd
for C15H11N2O4 (MH+) 283.0719 found 283.0732.
2-((1S)-1-Mor p h olin oca r b on ylet h oxy)-4-ter t-b u t oxy-
ca r bon yla m in om eth yla n ilin e (5h ). The title compound was
prepared from methyl (R)-(+)-lactate by the procedure similar
ter t-Bu tyl 4-Nitr oben zylca r ba m a te (9). A procedure
similar to that described in synthesis of 21g from 20g was
carried out with 8 (772 mg, 2.74 mmol) to give 600 mg of the
to that described above in the preparation of 5g: [R]D
)
1
25
title compound (87% from 8): mp 105-108 °C; H NMR (270
+11.2° (c 0.40, CHCl3); The other spectral properties of the
title compound were identical with those of 5g.
MHz, CDCl3) δ 1.46 (s, 9H), 4.41 (d, 2H, J ) 5.9 Hz), 5.00 (bm,
1H), 7.44 (d, 2H, J ) 8.6 Hz), 8.19 (d, 2H, J ) 8.6 Hz); LC-MS
(ESI) m/z 253 (MH+); MS (FAB) m/z 253 (MH+); HRMS (FAB)
calcd for C12H17N2O4 (MH+) 253.1188 found 253.1181.
(3S )-7-Ch lor o-3-(2-((1S )-1-ca r b oxye t h oxy)-4-a m in o-
m eth ylp h en yl)a m in oca r bon ylm eth yl-1,3,4,5-tetr a h yd r o-
ben z[cd ]in d ole-2-ca r boxylic Acid Hyd r och lor id e (3h ).
The title compound was prepared from 3S-(-)-4 and 5h by
ter t-Bu tyl 4-Am in oben zylca r ba m a te (5e). A procedure
similar to that described in synthesis of 5g from 21g was
carried out with 9 (134 mg, 0.533 mmol) to give the title
compound (118 mg, 99%): mp 60-64 °C; 1H NMR (270 MHz,
CDCl3) δ 1.45 (s, 9H), 3.64 (bs, 2H), 4.18 (d, 2H, J ) 5.6 Hz),
4.71 (bm, 1H), 6.64 (d, 2H, J ) 8.6 Hz), 7.07 (d, 2H, J ) 8.6
Hz); LC-MS (ESI) m/z 223 (MH+); MS (FAB) m/z 223 (MH+);
HRMS (FAB) calcd for C12H19N2O2 (MH+) 223.1447 found
223.1461.
the procedure similar to that described above in synthesis of
1
3g: mp 204-206 °C, dec; [R]25 ) -34.0° (c 0.22, MeOH); H
D
NMR (300 MHz, DMSO-d6) δ 1.57 (d, 3H, J ) 6.8 Hz), 1.84
(m, 1H), 2.07 (m, 1H), 2.67-2.81 (m, 3H), 3.10 (m, 1H), 3.86
(m, 1H), 3.93 (s, 2H), 4.81 (q, 1H, J ) 6.4 Hz), 6.84 (s, 1H),
7.05 (d, 1H, J ) 8.2 Hz), 7.15 (s, 1H), 7.17 (s, 1H), 7.99 (d, 1H,
J ) 8.2 Hz), 8.32 (bs, 3H), 9.31 (s, 1H), 11.45 (s, 1H); Anal.
(C24H27N3O7Cl2‚6/5H2O): C, H, N.
Met h yl (3S)-3-{2-[(4-{[(ter t-Bu t oxyca r b on yl)a m in o]-
m et h yl}p h en yl)a m in o]-2-oxoet h yl}-7-ch lor o-1,3,4,5-t et -
r a h yd r oben z[cd ]in d ole-2-ca r boxyla te (22e). To a solution
of 3S-(-)-4 (50.0 g, 0.162 mmol) and 5e (40.0 mg, 0.179 mmol)
in DMF (1.0 mL) were added 1-hydroxybenzotriazole (30.0 mg,
0.195 mmol) and 1-(3-(dimethylamino)propyl)-3-ethylcarbodi-
imide hydrochloride (37 mg, 0.195 mmol), and the mixture was
stirred at room temperature for 20 h. The resulting mixture
was acidified with aqueous 5% KHSO4, and extracted with 1:1
toluene/ethyl acetate. The organic layer was washed succes-
sively with water, aqueous 5% NaHCO3, and brine, dried over
magnesium sulfate, and concentrated in vacuo to give the title
compound (100 mg) as a crude material. This product was used
in the following reaction without further purification: 1H NMR
(270 MHz, CDCl3) δ 1.46 (s, 9H), 2.05 (m, 1H), 2.30 (m, 1H),
2.52 (dd, 1H, J ) 13.7, 9.2 Hz), 2.71 (dd, 1H, J ) 13.7, 4.3
Hz), 2.88 (m, 1H), 3.01 (m, 1H), 3.90 (s, 3H), 3.95 (m, 1H),
4.27 (d, 2H, J ) 5.3 Hz), 4.81 (bm, 1H), 6.91 (s, 1H), 7.20 (s,
1H), 7.24 (d, 2H, J ) 8.4 Hz), 7.50 (d, 2H, J ) 8.4 Hz), 7.79 (s,
1H), 8.60 (s, 1H); LC-MS (ESI) m/z 512 (MH+); MS (FAB) m/z
512 (MH+); HRMS (FAB) calcd for C27H31N3O5Cl (MH+)
512.1952 found 512.1961.
(3S)-3-{2-[(4-{[(ter t-Bu t oxyca r b on yl)a m in o]m et h yl}-
p h en yl)a m in o]-2-oxoet h yl}-7-ch lor o-1,3,4,5-t et r a h yd r o-
ben z[cd ]in d ole-2-ca r boxylic Acid . To a solution of 22e
(100 mg) obtained above in a mixed solvent of THF (2.0 mL)
and methanol (2.0 mL) was added aqueous 2 N NaOH (2.0
mL, 4.0 mmol), and the mixture was stirred at room temper-
ature for 21 h. The reaction mixture was acidified with aqueous
5% KHSO4, and the precipitated crystals were collected by
filtration and dried in vacuo at 40 °C to give the title compound
(72.0 mg, 89% from 3S-(-)-4): mp 213-218 °C, dec; 1H NMR
(270 MHz, DMSO-d6) δ 1.39 (s, 9H), 1.85 (m, 1H), 2.04 (m,
1H), 2.49 (m, 1H), 2.67 (dd, 1H, J ) 14.5, 3.6 Hz), 2.79 (m,
1H), 3.05 (m, 1H), 3.90 (m, 1H), 4.03 (d, 2H, J ) 6.4 Hz), 6.84
(s, 1H), 7.16 (d, 2H, J ) 8.4 Hz), 7.33 (t, 1H, J ) 6.4 Hz), 7.52
(d, 2H, J ) 8.4 Hz), 9.86 (s, 1H), 11.41 (s, 1H), 12.91 (bs, 1H);
LC-MS (ESI) m/z 498 (MH+); MS (FAB) m/z 498 (MH+); HRMS
(FAB) calcd for C26H29N3O5Cl (MH+) 498.1796 found 498.1807.
Meth yl (2-Am in op h en yl)a ceta te (5d ). A procedure simi-
lar to that described in synthesis of 5g from 21g was carried
out with methyl (2-nitrophenyl)acetate (6, 174 mg, 0.893 mmol)
to give the title compound (148 mg, 100%): 1H NMR (270 MHz,
CDCl3) δ 3.57 (s, 2H), 3.69 (s, 3H), 4.06 (bs, 2H), 6.70-6.78
(m, 2H), 7.07-7.13 (m, 2H); MS (FAB) m/z 165 (M+); HRMS
(FAB) calcd for C9H11NO2 (M+) 165.0790 found 165.0781.
Meth yl 7-Ch lor o-(3S)-3-(2-{[2-(2-m eth oxy-2-oxoeth yl)-
p h en yl]a m in o}-2-oxoeth yl)-1,3,4,5-tetr a h yd r oben z[cd ]in -
d ole-2-ca r boxyla te (22d ). To a solution of methyl (3S)-(-)-
7-chloro-3-carboxymethyl-1,3,4,5-tetrahydrobenz[cd]indole-2-
carboxylate (3S-(-)-4, 36.5 mg, 0.125 mmol), 5d (20.8 mg,
0.126 mmol), and triethylamine (53 µL, 0.38 mmol) in dichlo-
romethane (1.5 mL) was added N,N-bis(2-oxo-3-oxazolidinyl)-
phosphinic chloride (35.3 mg, 0.139 mmol) followed by stirring
at room temperature for 16 h. The reaction mixture was
acidified with aqueous 5% KHSO4 and extracted with ethyl
acetate. The organic layer was washed with brine, dried over
magnesium sulfate, and concentrated in vacuo. The residue
was purified by silica gel column chromatography with 6:1
chloroform/ethyl acetate to give the title compound (45.2 mg,
79%): mp 215-218 °C; 1H NMR (270 MHz, DMSO-d6) δ 1.79-
1.94 (m, 1H), 2.07-2.15 (m, 1H), 2.55-2.66 (m, 2H), 2.78-
2.87 (m, 1H), 3.01-3.14 (m, 1H), 3.60 (s, 3H), 3.72 (s, 2H), 3.85
(s, 3H), 3.86 (m, 1H), 6.89 (s, 1H), 7.14-7.19 (m, 2H), 7.25-
7.29 (m, 2H), 7.41 (d, 1H, J ) 7.6 Hz), 9.36 (s, 1H), 11.61 (s,
1H); LC-MS (ESI) m/z 455 (MH+); MS (FAB) m/z 455 (MH+);
HRMS (FAB) calcd for C24H24N2O5Cl (MH+) 455.1374 found
455.1372.
(3S)-3-(2-{[2-(Ca r b oxym et h yl)p h en yl]a m in o}-2-oxo-
et h yl)-7-ch lor o-1,3,4,5-t et r a h yd r ob en z[cd ]in d ole-2-ca r -
boxylic Acid (3d ). To
a solution of 22d (37.4 mg,
0.0822 mmol) in 1,2-dimethoxyethane (3.0 mL) was added
aqueous 1 N NaOH (1.50 mL, 1.50 mmol), and the mixture
was stirred at room temperature for 4 h. The reaction mixture
was acidified with aqueous 5% KHSO4 and extracted with
ethyl acetate. The organic layer was washed with brine, dried
over magnesium sulfate, and concentrated in vacuo to give the
title compound (35.1 mg, 100%): mp 211-213 °C, dec; [R]25
(3S)-3-(2-{[4-(Am in om eth yl)ph en yl]am in o}-2-oxoeth yl)-
7-ch lor o-1,3,4,5-t et r a h yd r ob en z[cd ]in d ole-2-ca r b oxylic
Acid Hyd r och lor id e (3e). To a suspension of 3-{2-[(4-{[(tert-
butoxycarbonyl)amino]methyl}phenyl)amino]-2-oxoethyl}-7-
chloro-1,3,4,5-tetrahydrobenz[cd]indole-2-carboxylic acid (65.0
D
) -87.2° (c 0.03, MeOH); 1H NMR (270 MHz, DMSO-d6) δ
1.78-1.91 (m, 1H), 2.04-2.13 (m, 1H), 2.55-2.70 (m, 2H),
2.74-2.85 (m, 1H), 3.01-3.15 (m, 1H), 3.62 (s, 2H), 3.87 (m,
1H), 6.86 (s, 1H), 7.12-7.17 (m, 2H), 7.23-7.28 (m, 2H), 7.45

Tricyclic Indole-2-Carboxylic Acids
J ournal of Medicinal Chemistry, 2003, Vol. 46, No. 5 699
mg, 0.130 mmol) in a mixture of 1,4-dioxane (3.0 mL) and
acetic acid (2.0 mL) was added 4 N HCl in 1,4-dioxane (4.0
mL, 16 mmoL). The mixture was stirred at room temperature
for 3 h and concentrated. The residual solid was rinsed with
diethyl ether, collected by filtration, and dried in vacuo at 40
ca r boxyla te (22f). A procedure similar to that described
in synthesis of 22d was carried out with 5f (3.94 g, 11.7 mmol)
and 3S-(-)-4 (3.00 g, 9.75 mmol) to give the title compound
1
(4.32 g, 71%): mp 156-161 °C; H NMR (270 MHz, CDCl3) δ
1.39 (s, 9H), 1.46 (s, 9H), 2.08 (m, 1H), 2.33 (m, 1H), 2.55 (dd,
1H, J ) 13.9, 10.4 Hz), 2.85 (m, 2H), 3.10 (m, 1H), 3.47 (s,
2H), 3.93 (s, 3H), 4.04 (m, 1H), 4.26 (d, 2H, J ) 5.6 Hz), 4.80
(bm, 1H), 6.90 (s, 1H), 7.12 (s, 1H), 7.19-7.23 (m, 2H), 7.90
(d, 1H, J ) 8.3 Hz), 8.67 (s, 1H), 8.93 (s, 1H); LC-MS (ESI)
m/z 626 (MH+); MS (FAB) m/z 626 (MH+); HRMS (FAB) calcd
for C33H41N3O7Cl (MH+) 626.2633 found 626.2629.
(3S)-3-(2-{[4-(Am in om eth yl)-2-(ca r boxym eth yl)p h en yl]-
a m in o}-2-oxoeth yl)-7-ch lor o-1,3,4,5-tetr a h yd r oben z[cd ]-
in d ole-2-ca r boxylic Acid Hyd r och lor id e (3f). A procedure
similar to that described in synthesis of 3e from 22e was
carried out with 22f (4.32 g. 6.90 mmol) to give the title
compound (3.04 g, 98%): mp 217-218 °C, dec; [R]25D ) -78.6°
(c 0.21, MeOH); 1H NMR (270 MHz, DMSO-d6) δ 1.82 (m, 1H),
2.09 (md, 1H, J ) 12.9 Hz), 2.60 (m, 2H), 2.80 (md, 1H, J )
17.2 Hz), 3.11 (mt, 1H, J ) 14.5 Hz), 3.60 (d, 1H, J ) 16.5
Hz), 3.68 (d, 1H, J ) 16.5 Hz), 3.89 (m, 1H), 3.97 (bs, 2H),
6.83 (s, 1H), 7.16 (s, 1H), 7.35 (s, 1H), 7.37 (d, 1H, J ) 8.3
Hz), 7.52 (d, 1H, J ) 8.3 Hz), 8.35 (bs, 3H), 9.49 (s, 1H), 11.44
(s, 1H); Anal. (C23H23N3O5Cl2‚6/5H2O): C, H, N.
°C to give 3e (56.0 mg, 99% yield): mp 206-214 °C, dec; [R]25
D
) -56.0° (c 0.07, MeOH); 1H NMR (270 MHz, DMSO-d6) δ
1.86 (m, 1H), 2.04 (m, 1H), 2.51 (dd, 1H, J ) 14.5, 11.2 Hz),
2.68 (dd, 1H, J ) 14.5, 3.6 Hz), 2.79 (m, 1H), 3.07 (m, 1H),
3.89 (m, 1H), 3.96 (s, 2H,), 6.83 (s, 1H), 7.16 (s, 1H), 7.39 (d,
2H, J ) 8.4 Hz), 7.64 (d, 2H, J ) 8.4 Hz), 8.23 (bs, 3H), 10.05
(s, 1H), 11.43 (s, 1H), 12.89 (bs, 1H); MS (FAB) m/z 398 (MH+
- HCl); Anal. (C21H21N3O3Cl2‚3/2H2O): C, H, N.
ter t-Bu tyl (5-Iod o-2-n itr op h en yl)a ceta te (11). To a sus-
pension of potassium tert-butoxide (56.3 g, 0.508 mol) in DMF
(1.00 L) with stirring at 0 °C was added dropwise a solution
of 1-iodo-4-nitrobenzene (10, 50.0 g, 0.201 mol) and tert-butyl
chloroacetate (33.3 g, 0.221 mol) in DMF (500 mL), and the
mixture was stirred at 0 °C for 6 h. The resulting mixture was
acidified with aqueous 5% KHSO4 and extracted with 1:1
toluene/ethyl acetate. The organic layer was washed succes-
sively with water and brine, dried over magnesium sulfate,
and concentrated in vacuo. The residue was purified by silica
gel column chromatography with 50:1 and then 40:1 hexane/
ethyl acetate to give the title compound (37.2 g, 51%): mp 89-
94 °C; 1H NMR (270 MHz, CDCl3) δ 1.44 (s, 9H), 3.89 (s, 2H),
7.72 (s, 1H), 7.81 (s-like, 2H); LC-MS (ESI) m/z 364 (MH+),
290 (M+ - t-BuO); MS (FAB) m/z 364 (MH+); HRMS (FAB)
calcd for C12H15NO4I (MH+) 364.0045 found 364.0040.
ter t-Bu tyl (5-Cya n o-2-n itr op h en yl)a ceta te (12). To a
solution of 11 (36.2 g, 99.7 mmol) in DMF (350 mL) were added
60% zinc cyanide (11.7 g, 59.8 mmol) and tetrakis(triph-
enylphosphine)palladium(0) (6.91 g, 5.98 mmol), and the
mixture was stirred at 80 °C for 3 h. After cooling to room
temperature, water was added and the resulting mixture was
extracted with 1:1 toluene/ethyl acetate. The organic layer was
washed successively with water and brine, dried over magne-
sium sulfate, and concentrated in vacuo. The residue was
purified by silica gel column chromatography with 20:1 to 5:1
hexane/ethyl acetate to give the title compound (22.0 g, 84%):
mp 88-90 °C; 1H NMR (270 MHz, CDCl3) δ 1.44 (s, 9H), 3.98
(s, 2H), 7.67 (d, 1H, J ) 1.7 Hz), 7.78 (dd, 1H, J ) 8.2, 1.7
Hz), 8.17 (d, 1H, J ) 8.2 Hz); LC-MS (ESI) m/z 263 (MH+);
MS (FAB) m/z 263 (MH+); HRMS (FAB) calcd for C13H15N2O4
(MH+) 263.1032 found 263.1016.
Ack n ow led gm en t. We are grateful to Prof. Y.
Yoneda of Kanazawa University for ligand binding
assays. We also wish to thank Messrs. K. Ohtani and
H. Yasuda for pharmacological assays ([3H] SM-18400
binding and rat MCAo model). We appreciate Mr. Y.
Saito for pharmacokinetic study and Dr. K. Yanagi for
discussion concerning X-ray crystallography. We ac-
knowledge Drs. H. Kishimoto, A. Dan, W. E. Hume,
Messrs. T. Toyoda, N. Sawada, T. Umezome, T. Tokuna-
ga, and K. Shimago for their valuable discussions and
contributions to the synthetic study. We thank Ms. Y.
Saida for her technical assistance in biological evalua-
tions. We also appreciate Dr. M. Nakamura for his
helpful discussion of the pharmacology.
Su p p or tin g In for m a tion Ava ila ble: X-ray crystallo-
graphic analysis. This material is available free of charge via
the Internet at http://pubs.acs.org.
Refer en ces
ter t-Bu tyl (5-{[(ter t-Bu toxyca r bon yl)a m in o]m eth yl}-2-
n itr op h en yl)a ceta te (13). To a solution of 12 (8.0 g, 30.5
mmol) and trimethyl borate (30.0 mL, 268 mmol) in THF (160
mL) was added dropwise 1.0 M borane-THF complex in THF
solution (46.0 mL, 46.0 mmol), and the mixture was stirred
at room temperature for 5 h. Methanol (50 mL) was added
dropwise, and the resulting mixture was concentrated in
vacuo. The residue was dissolved in THF (100 mL), to the
solution was added di-tert-butyl dicarbonate (8.4 mL, 36.6
mmol), and the mixture was stirred at room temperature for
15 h. After the solvent was removed in vacuo, the residue was
purified by silica gel column chromatography with 5:1 hexane/
ethyl acetate to give the title compound (5.60 g, 50%): 1H NMR
(270 MHz, CDCl3) δ 1.44 (s, 9H), 1.46 (s, 9H), 3.93 (s, 2H),
4.37 (d, 2H, J ) 7.3 Hz), 5.04 (bs, 1H), 7.23 (s, 1H), 7.35 (d,
1H, J ) 8.6 Hz), 8.08 (d, 1H, J ) 8.6 Hz).
ter t-Bu tyl (2-Am in o-5-{[(ter t-bu toxyca r bon yl)a m in o]-
m eth yl}p h en yl)a ceta te (5f). A procedure similar to that
described in synthesis of 5g from 21g was carried out with 13
(5.20 g, 14.2 mmol) to give the title compound (4.78 g, 100%):
mp 77-80 °C; 1H NMR (270 MHz, CDCl3) δ 1.44 (s, 9H), 1.45
(s, 9H), 3.44 (s, 2H), 4.05 (bs, 2H), 4.17 (d, 2H, J ) 5.6 Hz),
4.70 (bs, 1H), 6.66 (d, 1H, J ) 8.3 Hz), 6.98 (s, 1H), 7.00 (d,
1H, J ) 8.3 Hz); LC-MS (ESI) m/z 337 (MH+); MS (FAB) m/z
336 (M+); HRMS (FAB) calcd for C18H28N2O4 (M+) 336.2049
found 336.2029.
(1) (a) The NMDA Receptor, 2nd ed.; Watkins, J . C., Collingridge,
G. L., Eds.; IRL Press: Oxford, England, 1994. (b) Danysz, W.;
Parsons, C. G. Glycine and N-methyl-D-aspartate receptors:
Physiological significance and possible therapeutic applications.
Pharmacol. Rev. 1998, 50, 597-664, and references therein.
(2) (a) J ohnson, J . W.; Ascher, P. Glycine potentiates the NMDA
response in cultured mouse brain neurons. Nature (London)
1987, 325, 529-531. (b) Kleckner, N. W.; Dingledine, R. Re-
quirements for glycine in activation of NMDA receptors ex-
pressed in Xenopus oocytes. Science 1988, 241, 835-837.
(3) (a) Rogawski, M. A. Therapeutic potential of excitatory amino
acid antagonists: Channel blockers and 2,3-benzodiazepines.
Trends Pharmacol. Sci. 1993, 14, 325-331. (b) Parsons, C. G.;
Quack, G.; Bresink, I.; Baran, L.; Przegalinski, E.; Kostowski,
W.; Krzascik, P.; Hartmann, S.; Danysz, W. Comparison of the
potency, kinetics and voltage-dependency of a series of uncom-
petitive NMDA receptor antagonists in vitro with anticonvulsive
and motor impairment activity in vivo. Neuropharmacology
1995, 34, 1239-1258.
(4) (a) Meldrum, B.; Garthwaite, J . Excitatory amino acid neuro-
toxicity and neurodegenerative disease. Trends Pharmacol. Sci.
1990, 11, 379-387. (b) Lipton, S. A.; Rosenberg, P. A. Excitatory
amino acids as a final common pathway for neurologic disorders.
N. Engl. J . Med. 1994, 330(9), 613-622. (c) Rothman, S. M.;
Olney, J . W. Excitotoxicity and the NMDA receptor-still lethal
after eight years. Trends Neurosci. 1995, 18, 57-58.
(5) (a) Wood, P. L.; Hawkinson, J . E. N-Methyl-D-aspartate antago-
nists for stroke and head trauma. Expert Opin. Invest. Drugs
1997, 6, 389-397. (b) Dannhardt, G.; Kohl, B. K. The glycine
site on the NMDA receptor: Structure-activity relationships
and possible therapeutic applications. Curr. Med. Chem. 1998,
5, 253-263. (c) Tranquillini, M. E.; Reggiani, A. Glycine an-
tagonists and stroke. Exp. Opin. Invest. Drugs 1999, 8, 1837-
1848.
Meth yl (3S)-3-(2-{[4-{[(ter t-Bu toxyca r bon yl)a m in o]-
m et h yl}-2-(2-ter t-b u t oxy-2-oxoet h yl)p h en yl]a m in o}-2-
oxoet h yl)-7-ch lor o-1,3,4,5-t et r a h yd r ob en z[cd ]in d ole-2-

700 J ournal of Medicinal Chemistry, 2003, Vol. 46, No. 5
Katayama et al.
(6) (a) Leeson, P. D.; Iversen, L. L. The glycine site on the NMDA
receptor: Structure-activity relationships and therapeutic po-
tential. J . Med. Chem. 1994, 37, 4053-4067. (b) Rowley, M.;
Kulagowski, J . J .; Watt, A. P.; Rathbone, D.; Stevenson, G. I.;
Carling, R. W.; Baker, R.; Marshall, G. R.; Kemp, J . A.; Foster,
A. C.; Grimwood, S.; Hargreaves, R.; Hurley, C.; Saywell, K. L.;
Tricklebank, M. D.; Leeson, P. D. Effect of plasma protein
binding on in vivo activity and brain penetration of glycine/
NMDA receptor atagonists. J . Med. Chem. 1997, 40, 4053-4068,
and references therein.
(7) (a) Keana, J . F. W.; Kher, S. M.; Xiong, Cai, S.; Dinsmore, C.
M.; Glenn, A. G.; Guastella, J .; Huang, J . C.; Ilyin, V.; Lu, Y.;
Mouser, P. L.; Woodward, R. M.; Weber, E. Synthesis and
structure-activity relationships of substituted 1,4-dihydroqui-
noxaline-2,3-diones: Antagonists of N-methyl-D-aspartate (NMDA)
receptor glycine sites and non-NMDA glutamate receptors. J .
Med. Chem. 1995 38, 4367-4379. (b) Lutfy, K.; Weber, E.
Attenuation of nociceptive responses by ACEA 1021, a competi-
tive NMDA receptor/glycine site antagonist, in the mice. Brain
Res. 1996, 743, 17-23. (c) Albers, G. W.; Clark, W. M.; Atkinson,
R. P.; Madden, K.; Data, J . L.; Whitehouse, M. J . Dose escalation
study of the NMDA glycine-site antagonist licostinel in acute
ischemic stroke. Stroke 1999, 30, 508-513.
(8) (a) Kulagowski, J . J .; Baker, R.; Curtis, N. R.; Leeson, P. D.;
Mawer, I. M.; Moseley, A. M.; Ridgill, M. P.; Rowley, M.;
Stansfield, I.; Foster, A. C.; Grimwood, S.; Hill, R. G.; Kemp, J .
A.; Marshall, G. R.; Saywell, K. L.; Tricklebank, M. D. 3′-
(Arylmethyl)- and 3′-(aryloxy)-3-phenyl-4-hydroxyquinolin-2(1H)-
ones: Orally active antagonists of the glycine site on the NMDA
receptor. J . Med. Chem. 1994 37, 1402-1405. (b) Bristow, L. J .;
Hutson, P. H.; Kulagowski, J . J .; Leeson P. D.; Matheson, S.;
Murray, F.; Rathbone, D.; Saywell, K. L.; Thorn, L.; Watt, A.
P.; Tricklebank, M. D. Anticonvulsant and behavioral profile of
L-701,324, a potent, orally active antagonist at the glycine
modulatory site on the N-methyl-D-aspartate receptor complex.
J . Pharmacol. Exp. Ther. 1996, 279, 492-501.
(9) (a) Bare, T. M.; Smith, R. W.; Draper, C. W.; Sparks, R. B.;
Pullan, L. M.; Goldstein, J . M.; Patel, J . B. Pyridazino[4,5-b]-
quinolinediones: A series of novel glycine site NMDA antago-
nists with potent in vitro and in vivo properties. Abstracts of
Papers, 205th Meeting of the American Chemical Society; March
1993; Medi 79. (b) Takano, K.; Tatlisumak, T.; Formato, J . E.;
Carano, R. A. D.; Bergmann, A. G.; Pullan, L. M.; Bare, T. M.;
Sotak, C. H.; Fisher, M. Glycine site antagonist attenuates
infarct size in experimental focal ischemia. Stroke 1997, 28,
1255-1263. (c) Bare, T. M. Pyridazino[4,5-b]quinolinediones:
Novel glycine/N-methyl-D-aspartate antagonists for the treat-
ment of stroke. J . Heterocycl. Chem. 1998, 35, 1171-1186.
(10) For recent reports on investigation of in vivo active glycine
antagonists: (a) Carling, R. W.; Leeson, P. D.; Moore, K. W.;
Moyes, C. R.; Duncton, M.; Hudson, M. L.; Baker, R.; Foster, A.
C.; Grimwood, S.; Kemp, J . A.; Marshall, G. R.; Tricklebank, M.
D.; Saywell, K. L. 4-Substituted-3-phenylquinolin-2(1H)-ones:
Acidic and nonacidic glycine site N-methyl-D-aspartate antago-
nists with in vivo activity. J . Med. Chem. 1997, 40, 754-765.
(b) J imonet, P.; Ribeill, Y.; Bohme, G. A.; Boireau, A.; Cheve´,
M.; Damour, D.; Doble, A.; Genevois-Borella, A.; Herman, F.;
Imperato, A.; Guern, S. L.; Manfre´, F.; Pratt, J .; Randle, J . C.
R.; Stutzmann, J .-M.; Mignani, S. Indeno[1,2-b]pyrazin-2,3-
diones: A new class of antagonists at the glycine site of the
NMDA receptor with potent in vivo activity. J . Med. Chem. 2000,
43, 2371-2381. (c) Fray, M. J .; Bull, D. J .; Carr, C. L.; Gautier,
E. C. L.; Mowbray, C. E.; Stobie, A. structure-activity relation-
ships of 1,4-dihydro-(1H, 4H)-quinoxaline-2,3-diones as N-meth-
yl-D-aspartate (glycine site) receptor antagonists. 1. Heterocyclic
substituted 5-alkyl derivatives. J . Med. Chem. 2001, 44, 1951-
1962.
(12) (a) Nagata, R.; Tanno, N.; Kodo, T.; Ae, N.; Yamaguchi, H.;
Nishimura, T.; Antoku, F.; Tatsuno, T.; Kato, T.; Tanaka, H.;
Nakamura, M.; Ogita, K.; Yoneda, Y. Tricyclic quinoxalinedi-
ones: 5,6-Dihydro-1H-pyrrolo[1,2,3-de]quinoxaline-2,3-diones and
6,7-dihydro-1H,5H-pyrido[1,2,3-de]quinoxaline-2,3-diones as po-
tent antagonists for the glycine binding site of the NMDA
receptor. J . Med. Chem. 1994, 37, 3956-3968. (b) Nagata, R.;
Ae, N.; Tanno, N. Structure-activity relationships of tricyclic
quinoxalinediones as potent antagonists for the glycine binding
site of the NMDA receptor 1. Bioorg. Med. Chem. Lett. 1995, 5,
1527-1532. (c) Nagata, R.; Kodo, T.; Yamaguchi, H.; Tanno, N.
Structure-activity relationships of tricyclic quinoxalinediones
as potent antagonists for the glycine binding site of the NMDA
receptor 2. Bioorg. Med. Chem. Lett. 1995, 5, 1533-1536. (d)
Katayama, S.; Ae, N.; Nagata, R. Enzymatic resolution of
2-substituted tetrahydroquinolines. Convenient approaches to
tricyclic quinoxalinediones as potent NMDA-glycine antagonists.
Tetrahedron: Asymmetry 1998, 9, 4295-4299.
(13) For SM-18400 (1a ): (S)- 9-chloro-5-[p-aminomethyl-o-(car-
boxymethoxy)phenylcarbamoylmethyl]-6,7-dihydro-1H,5H-pyrido-
[1,2,3-de]quinoxaline-2,3-dione hydrochloride, see: (a) Nagata,
R.; Tanno, N.; Yamaguchi, H.; Kodo, T.; Ae, N.; Tanaka, H.;
Nakamura, M.; Ogita, K.; Yoneda, Y. Tricyclic quinoxalinedi-
ones: Highly in vivo active antagonists for the glycine binding
site of the NMDA recepter. Abstracts of papers, 210th National
Meeting of the American Chemical Society; Chicago, IL, August
1995; American Chemical Society: Washington, DC, 1995; Medi
150. (b) Tanaka, H.; Yasuda, H.; Kato, T.; Maruoka, Y.; Kawabe,
A.; Kawashima, C.; Ohtani, K.; Nakamura, M. Neuroprotective
and anticonvulsant actions of SM-18400, a novel strychnine-
insensitive glycine site antagonist. J . Cereb. Blood Flow Metab.
1995, 15, Suppl. 1, S431. (c) Yasuda, H.; Tanaka, H.; Ohtani,
K.; Kato, T.; Maruoka, Y.; Kawabe, A.; Kawashima, C.; Saka-
moto, H.; Tojo, S.; Nakamura, M. Neuroprotective effects of a
novel NMDA glycine site antagonist, SM-18400, in the rat model
of cerebral ischemia. Soc. Neurosci. Abstr. 1995, 21, 996. (d)
Maruoka, Y.; Ohno, Y.; Tanaka, H.; Yasuda, H.; Ohtani, K.;
Tamamura, C.; Nakamura, M. Effects of the novel tricyclic
quinoxalinedione derivatives, SM-18400 and its analogues, on
N-methyl-D-aspartate (NMDA) receptor-mediated synaptic trans-
mission in the isolated neonatal rat spinal cord in vitro. J pn. J .
Pharmacol. 1998, 76, 265-270. (e) Ohtani, K.; Tanaka, H.;
Yasuda, H.; Tamamura, C.; Maruoka, Y.; Ito, A.; Ohno, Y.;
Nakamura, M.; Noguchi, H. In vitro pharmacological properties
of the N-methyl-D-aspartate (NMDA) receptor glycine site
antagonist, SM-18400, Soc. Neurosci. Abstr. 1998, 24, 574. (f)
Ohtani, K.; Tanaka, H.; Yasuda, H.; Maruoka, Y.; Kawabe, A.;
Nakamura, M. Blocking the glycine-binding site of NMDA
receptors prevents the progression of ischemic pathology induced
by bilateral carotid artery occlusion in spontaneously hyperten-
sive rats. Brain Res. 2000, 871, 311-318.
(14) Hume, W. E.; Nagata, R. Synthesis of tricyclic azakynurenic
acids as a new class of NMDA-glycine antagonists using novel
Stille coupling reaction. Synlett 1997, 5, 473-474.
(15) Katayama, S.; Ae, N.; Nagata, R. Synthesis of tricyclic indole-
2-carboxylic acids as potent NMDA-glycine antagonists. J . Org.
Chem. 2001, 66, 3474-3483.
(16) Nagata, R.; Tanno, N.; Ae, N. Preparation of 1,3,4,5-tetrahy-
drobenz[cd]indole-2-carboxylate antagonists of glycine binding
in NMDA receptors. U.S. Patent 5,496,843, 1996.
(17) Mudryk, B.; Makosza, M.; Mudryk, B.; Makosza, M. Reactions
of organic anions. 156. A simple and efficient synthesis of alkyl
(2-nitroaryl)acetates and alkyl 2-(2-nitroaryl)propanoates via
vicarious nucleophilic substitution of hydrogen in nitroarenes
by carbanions of alkyl chloroacetates or alkyl 2-chloropro-
panoates. Synthesis 1988, 1007-1009.
(18) Tschaen, D. M.; Desmond, R.; King, A. O.; Fortin, M. C.; Pipik,
B.; King, S.; Verhoeven, T. R. An improved procedure for
aromatic cyanation. Synth. Commun. 1994, 24, 887-890.
(19) For the practical synthesis of SM-18400 aromatic fragment (5a )
which contains improved method to prepare 17: Kodo, T.;
Nishihara, T.; Nagata, R. Practical synthesis of the aniline part
of SM-18400, a tricyclic quinoxalinedione derivative, as a NMDA
glycine site antagonist. Abstracts of Papers, 219th National
Meeting of the American Chemical Society, San Francisco,
March 2000; American Chemical Society: Washington, DC,
2000; Orgn 610. For initial synthetic routes of 5a , also see ref
16.
(20) As a model reaction, m-iodophenol was coupled with 15h under
similar conditions to give the corresponding ether, 4-(2-(3-
iodophenoxy)propanoyl)morpholine. The absolute configuration
of the ether at R-position was unambiguously determined to be
S by X-ray crystallographic analysis. For similar reactions with
SN2 inversion, for example, see following papers: (a) Canceill,
J .; Collet, A.; Gabard, J .; Gottarelli, G.; Spada, G. P. Exciton
approach to the optical activity of C3-cyclotriveratrylene deriva-
tives. J . Am. Chem. Soc. 1985, 107, 1299-1308. (b) Biedermann,
J .; Leon-Lomeli, A.; Borbe, H. O.; Prop, G. Two stereoisomeric
(11) (a) Di Fabio, R.; Capelli, A. M.; Conti, N.; Cugola, A.; Donati,
D.; Feriani, A.; Gastaldi, P.; Gavirighi, G.; Hewkin, C. T.;
Micheli, F.; Missio, A.; Mugnaini, M.; Pecunioso, A.; Quaglia,
A. M.; Ratti, E.; Rossi, L.; Tedesco, G.; Trist, D. G.; Reggiani, A.
Substituted indole-2-carboxylates as in vivo potent antagonists
acting at the strychnine-insensitive glycine binding site. J . Med.
Chem. 1997, 40, 841-850. (b) Di Fabio, R.; Cugola, A.; Donati,
D.; Feriani, A.; Gaviraghi, G.; Ratti, E.; Trist, D. G.; Reggiani,
A. Identification and pharmacological characterization of
GV150526, a novel glycine antagonist as a potent neuroprotec-
tive agent. Drugs Future 1998, 23, 61-69. (c) Dyker, A. G.; Lees,
K. R. Safety and tolerability of GV150526 (a glycine site
antagonist at the N-methyl-D-aspartate receptor) in patients
with acute stroke. Stroke 1999, 30, 986-992. (d) Sacco, R. L.;
DeRosa, J . T.; Haley, E. C., J r.; Levin, B.; Ordronneau, P.;
Phillips, S. J .; Rundek, T.; Snipes, R. G.; Thompson, J . L. Glycine
antagonist in neuroprotection for patients with acute stroke:
GAIN Americas: a randomized controlled trial. J AMA 285, 2001,
1719-1728.

Tricyclic Indole-2-Carboxylic Acids
J ournal of Medicinal Chemistry, 2003, Vol. 46, No. 5 701
imidazoline derivatives. Synthesis, optical, and R2-adrenoceptor
activities. J . Med. Chem. 1986, 29, 1183-1188. (c) Otera, J .;
Nakazawa, K.; Sekoguchi, K.; Orita, A. CsF in organic synthesis.
Inversion of secondary mesylates and tosylates, Tetrahedron
1997, 53, 13633-13640.
(26) Moreau, J .-L.; Pieri, L.; Prud’hon, B. Convulsions induced by
centrally administered NMDA in mice: effects of NMDA an-
tagonists, benzodiazepines, minor tranquilizers and anticonvul-
sants. Br. J . Pharmacol. 1989, 98, 1050-1054.
(27) The in vivo activity of 23 in our seizure model was 3/10 at 30
mg/kg, iv (ED50 > 30 mg/kg, IC50 ) 24 nM vs [3H] 1a ). Workers
at Merck also reported that 23 had no activity in their DBA/2
anticonvulsant assay even at 10 mg/kg, ip (ref 6b).
(28) Ohtani, K.; Tanaka, H.; Yoneda, Y.; Yasuda, H.; Ito, A.; Nagata,
R.; Nakamura, M. In vitro and in vivo antagonistic activities of
SM-31900 for the NMDA receptor glycine-binding site. Brain
Res. 2002, 944, 165-173.
(29) Ohtani, K.; Yasuda, H.; Tanaka, H. Unpublished observations.
The detailed results will be published elsewhere.
(30) Ohtani, K.; Tanaka, H.; Ohno, Y. SM-31900, a novel NMDA
receptor glycine-binding site antagonist, reduces infarct volume
induced by permanent middle cerebral artery occlusion in
spontaneously hypertensive rats. Neurochem. Int. 2002, in press.
(31) Katayama, S.; Ae, N.; Tanaka, H.; Nagata, R. Tricyclic indole-
2-carboxylic acids, highly in vivo active antagonists for the
glycine binding site of the NMDA receptor. Abstracts of papers,
220th National Meeting of the American Chemical Society,
Washington, DC, August 2000; American Chemical Society:
Washington, DC, 2000, Medi 215.
(21) Yoneda, Y.; Suzuki, T.; Ogita, K.; Han, D. Support for radiola-
beling of a glycine recognition domain on the N-methyl-D-
aspartate receptor ionophore complex by 5,7-[3H] dichloro-
kynurenate in rat brain. J . Neurochem. 1993, 60, 634-645.
(22) Ogita, K.; Suzuki, T.; Yoneda, Y. Strychnine-insensitive binding
of [3H] glycine to synaptic membranes in rat brain, treated with
Triton X-100. Neuropharmacology 1989, 28, 1263-1270.
(23) (a) Ogita, K.; Yoneda, Y. Disclosure by Triton X-100 of NMDA-
sensitive [3H] glutamate binding sites in brain synaptic mem-
branes. Biochem. Biophys. Res. Commun. 1988, 153, 510-517.
(b) Yoneda, Y.; Ogita, K. Microbial methodological artifacts in
[3H] glutamate receptor binding assays. Anal. Biochem. 1989,
177, 250-255.
(24) (a) Murphy, D. E.; Snowhill, E. W.; Williams, M. Characteriza-
tion of quisqualate recognition sites in rat brain tissue using
DL-[3H]-R-amino-3-hydroxy-5-methylisoxazole-4-propionic acid
(AMPA) and a filtration assay. Neurochem. Res. 1987, 12, 755-
782. (b) Olsen, R. W.; Szamraj, O.; Houser, C. R. [3H] AMPA
binding to glutamate receptor subpopulation in rat brain. Brain
Res. 1987, 402, 243-254.
(25) London, E. D.; Coyle, J .-T. Specific binding of [3H] kainic acid
to receptor sites in rat brain. Mol. Pharmacol. 1979, 15, 492-
505.
J M020239L