Substituted indole-2-carboxylates as potent antagonists of the glycine binding site associated with the NMDA receptor

Article abstract of DOI:10.1002/(SICI)1521-4184(19998)332:8<271::AID-ARDP271>3.0.CO;2-X

A novel series of indole-2-carboxylate analogues of GV150526 (1) in which the propenoic double bond was substituted with different 'probes' or replaced by a isosteric cyclopropyl moiety were synthesized and evaluated for their affinity profile in order to obtain further information on the pharmacophoric model of the glycine binding site associated to the NMDA receptor.

Full text of DOI:10.1002/(SICI)1521-4184(19998)332:8<271::AID-ARDP271>3.0.CO;2-X

Substituted Indole-2-carboxylates
271
Substituted Indole-2-carboxylates as Potent Antagonists of the
Glycine Binding Site Associated with the NMDA Receptor
Fabrizio Micheli*, Romano Di Fabio*, Davide Baraldi, Nadia Conti, Alfredo Cugola, Paola Gastaldi, Simone Giacobbe,
Carla Marchioro, Manolo Mugnaini, Luciana Rossi, Angelo Pecunioso, Giorgio Pentassuglia
Glaxo Wellcome S.p.A., Medicines Research Centre, Via Fleming 4, 37100 Verona, Italy
Key Words: Neuroprotective agents; neurotransmitters
Summary
Results and Discussion
Synthesis
A novel series of indole-2-carboxylate analogues of GV150526(1)
in which the propenoic double bond was substituted with different
“probes” or replaced by a isosteric cyclopropyl moiety were syn-
thesized and evaluated for their affinity profile in order to obtain
further information on the pharmacophoric model of the glycine
binding site associated to the NMDA receptor.
The derivatives of the new series carrying the different
“probes” on the α,β-unsaturated double bond are listed below
(Table 1, 2–6) and were prepared exploiting alternatively
Horner-Emmons-Wittig or Knoevenagel reactions to insert
on the vinylic double bond different groups endowed with
steric and/or stereoelectonic differentiation in order to allow
a possible further mapping of the glycine binding site. The
stereochemistry of the double bond in the various derivatives
represented in the Schemes shown below was determined
using NMR techniques (namely J
ments).
and NOES experi-
Introduction
C,H
Glutamate is the most abundant excitatory neurotransmitter
Table 1
present in the CNS. It is now widely recognized that in
[1–4]
pathological conditions
, such as stroke, abnormal
amounts of glutamate are released into synaptic clefts causing
an over-stimulation of N-methyl-D-aspartate (NMDA) re-
ceptor which, ultimately, leads to a significant increase of the
++
intracellular level of Ca in the post-synaptic neurons, caus-
ing the activation of several neurotoxic cascades responsible
[5]
for irreversible neuronal damage
.
2+
——————————————————————————————
Entry pKi ED50 (i.v.) ED50 (p.o.)
mg/kg mg/kg
——————————————————————————————
Modulating the influx of Ca through the ion channel
[6]
X
associated with the NMDA receptor using competitive and
[7,8]
non-competitive NMDA antagonists
led to potential
therapeutic benefit according to animal models of stroke.
Recently, the glycine binding site has become one of the most
1
H
8.5
8.3
7.7
8.0
6.6
7.6
7.3
0.06
0.9
6.0
attractive targets for neuroprotection after stroke, in view of
2
Me
13.2
3.98
18.4
n.t.
[9–12]
the role of glycine as a co-agonist of the glutamate
in
3
Cl
0.055
0.14
n.t.
the activation of this ionotropic receptor complex and the
4
F (Z)
F(E)
NHAc
CN
[13–
favorable therapeutic index seen for glycine-antagonists
4a
5
21]
.
0.2
10
The indole-2-carboxylate derivative GV150526 (Entry 1,
6
n.t.
n.t.
[22–27]
Table 1) was identified by GlaxoWellcome
as a potent
—————————————————————————————
and selective glycine antagonist endowed with nanomolar
affinity in vitro and excellent in vivo activity in the MCAo
model in rats both pre and post-ischemia. The present paper
deals with the synthesis and the pharmacological charac-
terization of a novel series of analogues of the compound 1,
bearing different “probes” on the propenoic double bond or
with its replacement with a bioisosteric cyclopropyl group.
This new series of indole-2-carboxylates showed nanomolar
affinity forthe glycine binding site coupled withhigh receptor
selectivity. Some analogues prepared in our laboratories were
As depicted in Scheme 1, the starting point for the reactions
based on Horner-Wittig reaction was the aldehyde 7 which
was easily obtained in high yield submitting 2-ethoxycar-
bonyl-4,6-dichloroindole to Vilsmeyer-Haack (POCl /DMF)
3
conditions. This derivative was protected as (2-trimethyl-
silyl)ethoxymethyl (SEM) derivative using SEM chloride in
DMF at low temperature to give in almost quantitative yield
the intermediate 7c. This intermediate was submitted to Hor-
ner-Wittig reaction at RT with different phosphonates using
[29]
not reported because of disclosure in a patent reporting novel
DiazoBicycloUndecene (DBU) as base
. The desired
[28]
3-(indol-3-yl)propenoic acid derivatives analogues
.
methyl derivative was obtained as an E:Z mixture and the
Arch. Pharm. Pharm. Med. Chem.
© WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1999
0365-6233/99/0808/0271 $17.50 +.50/0

272
Micheli, Di Fabio, and co-workers
Scheme 1. a) LHMDS, SEMCl, DMF,
0
°C; b) LHMDS,
Scheme 3. a) t-BuOK, CH2Cl2 from -70 °C to r.t.; b) HCO2H, 40 °C; c) EDC,
HOBT, Aniline, CH3CN, r.t.; d) LiOH.H2O, THF/H2O, r.t. followed by acid
quenching.
(EtO)2OPC(H)(Me)CONHPh, DMF, 0 °C followed by chromatographic
separation; c) HCl 5M, reflux; d) LiOH.H2O, EtOH, 50 °C followed by acid
quenching.
isomer percentage was dependent on the equivalents of base
used and the reaction temperature; however, the desired pure
isomer was easily obtained by flash chromatography.
The synthesis of the chloro derivative is shown in Scheme 2
for the same aldehyde protected as phenylsulphonyl deriva-
tive 7b; on the vinyl derivative the acidic deprotection
(HCO H, RT) of the α,β-unsaturated tert-butyl ester gave in
2
high yield the corresponding acid which could be obtained as
pure isomer after crystallization from ethyl ether. The pure Z
isomer was subsequently transformed into the phenyl amide
1)
in high yield using EDC and aniline. Finally, a two step
deprotection was performed with ethanolic lithium hydroxide
to obtain the desired 2-carboxylic acid in quantitative yield.
As far as the vinylic fluoro derivative is concerned, two
approaches were followed and they are reported in Schemes
3 and 4. It is worth noting that, as reported in Scheme 3, only
the pure E isomer was obtained using the phosphonate tert-
butyl ester on the protected aldehyde 7a, while to obtain the
Scheme 4. a) LHMDS, THF, –70 °C followed by chromatographic separa-
tion b) EDC, HOBT, Aniline, CH3CN, reflux; c) HCO2H, 40 °C; d)
LiOH.H2O, THF/H2O, 60 °C followed by acid quenching.
desired Z product, the Horner-Emmons reaction had to be
performed using the phosphonate carrying the free carboxylic
acid as shown in Scheme 4, according to literature refer-
[30–32]
ences
. The E/Z mixture obtained was then easily sepa-
rated and the Z acid 16 was coupled to aniline using EDC in
THF. Deprotection of the N-BOC derivative 17 with formic
acid and basic hydrolysis (LiOH/EtOH) of the esteric moiety
in position C-2 gave the desired product 4.
In order to obtain the acetamido derivative 5 without prob-
lems in the final basic hydrolysis, the 2-carboethoxy aldehyde
7a was replaced by the corresponding allyl ester derivative
19a as depicted in Scheme 5. The neutral deprotection of
intermediate 21 with Pd-tetrakis(triphenylphosphine) and di-
medone allowed a quantitative recovery of the desired pure
isomer.
As far the Knoevenagel reaction described in Scheme 6 is
concerned, the enamino intermediate 22 was obtained by
refluxing 3-formyl-2-ethoxycarbonyl-4,6-dichloroindole
with pyrrolidine in benzene under Dean-Stark conditions.
This intermediate could easily be separated and remained
———
1) It is worth noting that the transformation to give derivative 3 could have
been performed in a single step from intermediate 11 but this attempt allowed
the recovery of some propargylic derivative too because of a possible
β-elimination reaction. On the other hand, the two-step procedure allowed a
chromatographic purification of intermediate 12 and no elimination reaction
was observed on this substrate, thus permitting synthesis of the desired
derivative 3 as pure compound.
Scheme 2. a) LHMDS, THF, 0 °C; b) HCO2H, r.t.followed by crystallization
from Et2O; c) (PyS)2, PPh3, THF, Aniline, reflux; d)LiOH.H2O, EtOH, r.t.;
e) LiOH.H2O, EtOH, r.t. followed by acid quenching.
Arch. Pharm. Pharm. Med. Chem. 332, 271–278 (1999)

Substituted Indole-2-carboxylates
273
Finally, the removal of the vinylic double bond and its
substitution with an isosteric cyclopropyl moiety (30) was
performed as described in Scheme 7. Aldehyde 7 was pro-
tected as SEM derivative (7c) using SEMCl in DMF, the
formyl group transformed into the corresponding vinyl de-
rivative 27 which was then subjected to the cyclopropanation
reaction using rhodium acetate in dimethoxyethane. The re-
sulting amide 28 was then hydrolyzed to the ester derivative
29 using HCl and finally transformed into the desired product
30 using monohydrated lithium hydroxide. In order to over-
come the low yield obtained for the production of intermedi-
ate 28 from 27, an alternative route through intermediate 31
was set up and the product obtained in acceptable yield via
diazomethane cyclopropanation.
Scheme 5. a) DBU, CH2Cl2, r.t. b) TFA, CH2Cl2, r.t.; c) Dimedone,
Pd(PPh3)4, THF, r.t.
stable for weeks if stored at low temperature. The reaction of
22 with the N-phenyl 2-cyanoacetamide in pyridine led to the
isolation of the desired E product 23 only. Basic hydrolysis
of the ethyl ester with lithium hydroxide monohydrate unfor-
tunately led to a complete isomerization of the double bond
producing a 1:1 E:Z mixture of the desired 2-carboxylic acid
derivative 6. This problem was overcome using the corre-
sponding 2-allyl ester 19 to give intermediate 25 which, after
reaction with cyanophenylacetamide in pyridine led to the
isolation of the desired E product only also in this case.
Neutral hydrolysis of the allyl ester 26 using Pd tetrakis
triphenyl phosphine allowed the recovery the desired pure
2-carboxylic acid 6 as single E isomer. When intermediate 25
were submitted to Knoevenagel reaction using the ni-
trophenyl acetamide in pyridine, E/Z mixture of the desired
product were immediately obtained. Unfortunately, the nitro
derivative proved unstable to the different chromatographic
conditions used to isolate the pure E isomer; furthermore, any
attempt at deprotection on the isomeric mixture led to exten-
sive decomposition.
Scheme 7. a) LHMDS, MePPh3I, THF, 60 °C; b) Rh2(OAc)4, DME, N-
phenyl-diazoacetamide, r.t.; c) HCl 5M, reflux; d) LiOH.H2O, EtOH, 50 °C
followed by acid quenching; e) LHMDS, SEMCl, DMF, 0 °C; f) CH2N2;
Et2O; Rh2(OAc)4.
Table 2
——————————————————————————————
Entry
pKi
ED50 (i.v.)
ED50 (p.o.)
mg/kg
mg/kg
——————————————————————————————
30 6.7 0.27 n.t.
——————————————————————————————
Biology
The biological evaluation of the new chemical entities
(NCE) was performed using the following screening se-
Scheme 6. a) pyrrolidine, benzene, reflux; b) NCCH2CONHPh, Py, r.t.; c)
O2NCH2CONHPh, Py, r.t; d) LiOH.H2O, EtOH, r.t. followed by acid
quenching; e) pyrrolidine, benzene, reflux; f) NCCH2CONHPh, Py, r.t.; g)
Dimedone, Pd(PPh3)4, THF, r.t. h) AllylOH, pTSA, reflux.
[22]
[33]
quence previously described : a) binding assay
to
evaluate the affinity for the glycine site ; b) selectivity for the
Arch. Pharm. Pharm. Med. Chem. 332, 271–278 (1999)

274
Micheli, Di Fabio, and co-workers
glutamate receptors (NMDA/AMPA/KA); c) in vivo anticon-
Conclusions
vulsant activity in the NMDA induced convulsions model in
Different “probes” were used to test the ability of the
receptor to tolerate substitution on the double bond of ana-
logues of 1. The receptor seems to be extremely sensitive to
hindered EGW, leading to a reduced affinity. Among the
different compound tested, derivative 3, despite the reduced
in vitro affinity with respect to the unsubstituted analogue 1,
showed a promising preliminary in vivo pharmacological
profile.
[34]
mice (iv and po)
.
Discussion
Different “probes” in terms of steric hindrance and stereo-
electronic properties were used to evaluate the effect of the
substitution in the α position to the phenylamidic moiety of
the derivative 1. The results of this study are reported in
Table 1.
Acknowledgments
The replacement of a vinylic proton with a group exhibiting
a moderately increased steric bulk but with poor electronic
properties like a methyl probe (2) led to minimal variations
in terms of in vitro affinity.
We would like to thank Mr. S. Costa for the in vivo profiling. We also thank
the spectrometry and spectroscopy labs of GlaxoWellcome S.p.A. for their
fruitful collaboration in MS and NMR studies and Mrs. Maria Passarini for
her valuable support.
On the other hand, compounds endowed with approxi-
mately the same steric hindrance of the methyl derivative 2,
but with electron-withdrawing properties (3, 5, 6) led to a
Experimental
significant decrease of the in vitro affinity (K ).
i
Infrared spectra were recorded on a Bruker IFS 48 spectrometer. 1H NMR
spectra were recorded on a Varian Unity400(400MHz);thedataarereported
as follows: chemical shift in ppm from the Me4Si line as external standard,
multiplicity (b = broad, s = singlet, d = doublet, t = triplet, q = quartet, m =
multiplet) and coupling constants.
Chromatography was carried out by use of the Merck Silica Gel 60
(230–400 mesh) as described by Still et al. Mass spectra were performed on
a Triple Quadrupole (VG-4 Fison Instrument, UK) equipped with Fast Atom
Bombardment (FAB) ionization . Elemental analyses were determined by a
EA 1108 Carlo Erba elemental analyzer and the analyses of the reported
compounds are in agreement with the calculated values. Melting points were
determined on a Büchi 530 apparatus (scale 0 °C–250 °C) and are uncor-
rected. All the reactions were carried out under a controlled atmosphere in
flame dried glassware. Anhydrous DMF was purchased from Aldrich; THF
was used after distillation over K/benzophenone; CH2Cl2 and CH3CN were
used after distillation over P2O5. Reactions were monitored by analytical
thin-layer chromatography (TLC) using Merck Silica Gel 60 F-254 glass
plates (0.25 mm).
This marked effect could be minimized using an electron-
withdrawing substituent but endowed with reduced steric
hindrance. Accordingly, when the vinylic proton was re-
placed by a fluorine atom as in derivative 4 a reversed effect
was observed.
A possible explanation (for this effect) could be offered in
accordance with the pharmacophoric interaction proposed in
[22]
ref.
. In particular, it was proposed that the carbonyl group
belonging to the phenylamidic moiety of 1 could behave as a
H-bonding acceptor group. Therefore, the introduction of
EWG in position α to this carbonyl group should reduce its
ability to interact with the receptor, resulting in a lower
affinity. Moreover, the increase of the steric hindrance in this
position probably should represent an additional penalty for
this series of compounds, making it more difficult to achieve
the right spatial orientation of the carbonyl.
Obviously, when the C-3 side chain cannot direct the
phenylamidic moiety to correctly achieve the above men-
tioned interaction, as in derivative 4a, a dramatic reduction
in affinity is observed.
1-tert-Butoxycarbonyl-3-formyl-4,6-dichloroindole-2-carboxylic Acid Ethyl
Ester (7a)
To a solution of aldehyde 7 (prepared according to the procedure reported
in ref. [22]) (858 mg, 3.0 mmol) in dry THF, DMAP (74 mg, 0.6 mmol) and
bis(tert-butoxy carbonate (380 mg, 3.6 mmol) were added at room tempera-
ture and stirred for 24 h. The solution was evaporated to dryness and the crude
product crystallized by cold AcOEt to give the desired product in 80% yield.–
Mp 141 °C.– IR (Nujol) ν = 3305–3288 cm–1 (NH).– 1H NMR (CDCl3): δ
= 10.77 (s, 1H), 8.24 (d, 1H), 7.42 (d, 1H), 4.50 (q, 2H), 1.65 (s, 9H), 1.43
(t, 3H).– MS m/z 386 [M]+.
To further evaluate the stereoelectronic effect of this olefin
moiety, the cyclopropyl derivative 29 was prepared. Accord-
ing to modeling studies, this compound showed the correct
spatial requirements necessary for the alignment with deriva-
[22]
tive 1 within the pharmacophoric model . Despite that, a
marked decrease in terms of in vitro affinity was observed as
reported in Table 2, suggesting once more the “ideal” features
of GV150526 (1).
1-(2-(Trimethylsilyl)ethoxymethyl)-3-formyl-4,6-dichloroindole-
Finally, these compounds were tested for their ability to
2-carboxylic Acid Ethyl Ester (7c)
inhibit the convulsions caused by “in vivo” administration of
To a solution of aldehyde 7 (prepared according to the procedure reported
in ref. [22]) (860 mg, 3.0 mmol) in dry DMF, LHMDS (sol. 1 M in hexanes)
(3.6 mL, 3.6 mmol) was slowly added at 0 °C; SEMCl (0.64 mL, 3.6 mmol)
was subsequently added at the same temperature and the solution was
allowed to warm to room temperature and stirred for an additional two hours.
The solution was quenched with aq. NH4Cl, extracted with AcOEt, and the
organic phase was dried over sodium sulphate; the solution was filtered and
the organic phase evaporated. The crude product was purified by flash
chromatography (CyH/AcOEt 90:10) to produce the desired product in 93%
[34]
NMDA
, a surrogate for stroke models, starting form the
basic assumption that NMDA receptor overactivation is the
key event in neurodegeneration following cerebral ischemia.
The ability of the new chemical entities to counteractNMDA-
induced convulsions was used as the end point of the model.
Some of the product described in Table 1, despite their
reduced affinity, showed excellent ED s in inhibiting con-
50
1
vulsions in mice. In particular, derivative 3 showed properties
quite similar to those of the lead compound 1, making it very
attractive in terms of further characterization.
yield.–. H NMR ([D6]DMSO): δ = 10.54 (s, 1H), 7.991 (d, 1H), 7.57 (d,
1H), 5.73 (s, 2H), 4.41 (q, 2H), 3.44 (t, 2H), 1.32 (t, 3H), 0.78 (t, 2H), –0.12
(s, 9H).
Arch. Pharm. Pharm. Med. Chem. 332, 271–278 (1999)

Substituted Indole-2-carboxylates
275
E-1-(2-(Trimethylsilyl)ethoxymethyl)-3-(2-methyl-2-phenylcarbamoyl)-
4,6-dichloroindole-2-carboxylic Acid Ethyl Ester (8)
1H), 7.71 (m, 2H), 7.65 (d, 1H), 4.34 (q, 2H), 1.23 (t, 3H). MS m/z 502 [M
+ H]+.
To a solution of (EtO)2PO(CH)(Me)CONHPh (430 mg, 1.5 mmol) in dry
DMF, KHMSD (0.5 M in toluene) (0.75 mL, 1.5 mmol) were slowly added
at 0 °C and the solution was left under stirring at the same temperature for
1 h. Aldehyde 7c (430 mg, 1 mmol) was slowly added the solution was
allowed to warm to room, quenched with aq. NH4Cl, extracted with AcOEt
and the organic phase was dried over sodium sulphate; the solution was
filtered and the organic phase evaporated. The crude product was purified by
flash chromatography (CyH/AcOEt 85:15) to isolate the desired E product
in 56% yield.– IR (Nujol) ν = 1678 cm–1 (C=O).– 1H NMR ([D6]DMSO):
δ = 12.48 (bs, 1H), 9.70 (s, 1H), 7.80–7.72 (m, 3H), 7.48 (d, 1H), 7.33 (t,
2H), 7.26 (d, 1H), 7.08 (m, 1H), 5.71 (s, 2H), 4.32 (q, 2H), 3.31 (t, 2H), 1.79
(d, 3H), 1.30 (t, 3H), –0.11 (s, 9H).
Z-1-Benzenesulfonyl-3-(2-phenylcarbamoyl-2-chlorovinyl)-4,6-dichloroin
dole-2-Carboxylic Acid Ethyl Ester (11)
To a solution of 10 (1.05 g, 2 mmol) in dry THF were added 2,2’-dipyridyl
disulfide (506 mg, 2.3 mmol) and triphenyl phosphine (600 mg, 2.3 mmol)
and the resulting yellow solution was stirred at room temperature for 2.5 h.
Aniline (0.25 mL, 2.7 mmol) was added and the mixture heated at reflux for
24 h, then 1N hydrochloric acid was added and the mixture extracted with
EtOAc The combined organic phase was washed with brine, dried and
concentrated under reduced pressure. The resulting residue was adsorbed
onto silica and purified by flash chromatography to give the desired product
11.– IR (Nujol) ν = 3240 cm–1 (NH), 1724 (C=O).– 1H NMR ([D6]DMSO):
δ = 10.17 (bs, 1H), 8.08 –8.05 (m, 4H), 7.83–7.70 (m, 6H), 7.37 (m, 2H),
7.16 (m, 1H), 4.36 (q, 2H), 1.25 (t, 3H).
E-3-(2-Methyl-2-phenylcarbamoyl)-4,6-dichloroindole-2-carboxylic Acid
Ethyl Ester (8b)
Z-3-(2-Phenylcarabamoyl-2-chlorovinyl)-4,6-dichloroindole-2-carboxylic
Acid Ethyl Ester (12)
Derivative 8 (1.65g, 3 mmol) was suspended in 95% EtOH (10 mL) and
5N HCl (3 mmol) was slowly added. The resulting suspension was refluxed
for 3 h. AcOEt was added and the mixture extracted. The crude product was
dried over sodium sulphate and after evaporation it was chromatographed
(CyH/AcOEt 75:25) to give the desired product 8b in 80% yield.– IR (Nujol)
ν = 3317–3288 cm–1 (NH), 1678 (C=O).– 1H NMR ([D6]DMSO): δ = 12.48
(bs, 1H), 9.70 (s, 1H), 7.80–7.72 (m, 3H), 7.48 (d, 1H), 7.33 (t, 2H), 7.26 (d,
1H), 7.08 (m, 1H), 4.32 (q, 2H), 1.79 (d, 3H), 1.30 (t, 3H).
Intermediate 11 (276 mg, 0.5 mmol) was suspended in 80% EtOH and
LiOH.H2O (18 mg, 0.75 mmol) was added. The mixture was stirred for 6 h
and AcOEt was subsequently added. The organic phase was dried over
sodium sulphate and evaporated to dryness. The crude product was purified
by flash chromatography (CyH/AcOEt 75:25) to give the desired intermedi-
ate 12 in 88% yield.– 1H NMR ([D6]DMSO): δ = 12.67 (bs, 1H), 10.07 (s,
1H), 8.25 (s, 1H), 7.73 (d, 2H), 7.48–7.13 (m, 5H), 4.32 (q, 2H), 1.3 (t, 3H).
E-3-(2-Methyl-2-phenylcarbamoyl)-4,6-dichloroindole-2-carboxylic Acid
(2)
Z-3-(2-Phenylcarabamoyl-2-chlorovinyl)-4,6-dichloroindole-2-carboxylic
Acid Ethyl Ester (3)
Intermediate 8b (835 mg, 2 mmol) was suspended in 80% EtOH (10 mL)
and LiOH monohydrated (144 mg, 6 mmol) was added; the mixture was
warmed at 50 °C for 3 h, acidified to pH = 3 and extracted with AcOEt. The
organic solution wasdriedandthecrudeproductprecipitatedfromcoldEtOH
to give the desired product 2 in 90% yield.– IR (Nujol) ν = 3838 cm–1 (NH),
2725–2000 (COOH), 1703 (C=O).– 1H NMR ([D6]DMSO): δ = 13.45 (bs,
1H), 12.38 (s, 1H), 9.69 (s, 1H0, 7.76 (dd, 1H), 7.74 (d, 1H), 7.31 (t, 2H),
7.22 (d, 1H), 7.06 (tt, 1H), 1.78 (bs, 3H). MS m/z 389 [M]+.
Intermediate 12 (164 mg, 0.4 mmol) was suspended in 80% EtOH and
LiOH.H2O (14 mg, 0.6 mmol) was added. The mixture was stirred for 6 h
and subsequently acidified to pH = 3. AcOEt was subsequently added, and
the desired product 3 was precipitated as solid in 70% yield.– IR (Nujol) ν
= 3267 cm–1 NH, 1684 (C=O), 1599 (C=C).– 1H NMR ([D6]DMSO): δ =
13.5 (bs, 1H), 12.5 (s, 1H),10.00 (s, 1H), 8.26 (s, 1H), 7.75 (d, 2H), 7.48–7.37
(m, 3H), 7.29, (d, 1H), 7.03 (t, 1H). MS m/z 375 [M + H]+.
Z-1-tert-Butoxycarbonyl-3-(2-fluoro-2-carboxy)-4,6-dichloroindole-
2-carboxylic Acid Ethyl Ester (16)
E- and Z-1-Benzenesulfonyl-3-(2-tert-butoxycarbonyl-2-chlorovinyl)-
4,6-dichloroindole-2-carboxylic Acid Ethyl Ester (9)
A 1 M solution of LHMDS in THF (0.92 mL) was added dropwise to a
solution of diethyl 2-fluoro-(diethoxyphosphonyl)acetic acid (0.1 g,
0.46 mmol) in dry THF (4 mL) at –70 °C, and the reaction was stirred at
–40 °C for 15 min. After cooling at –70 °C, a solution of aldehyde 7a (0.15 g,
0.39 mmol) in THF (6 mL) was added dropwise and the stirring was contin-
ued at –40 °C for 1.5 h. Ethyl acetate was added and the organic phase was
washed with a 2N solution of HCl and brine, dried and concentrated under
reduced pressure to give a crude E/Z mixture and the isomers were separated
by flash chromatography (CyH/AcOEt 85:15). to give the desired isomer 16
in 57% yield.
A solution of 2-chloro-(diethoxyphosphonyl)acetic acid tert-butyl ester
(prepared in 94% overall yield from the commercially available
(diethoxyphosphonyl)acetic acid tert-butyl ester in two steps according to
ref. [35]) (0.9 g, 3.5 mmol) in dry THF (15 mL) was cooled to 0 °C and
1 M LHMDS (3.5 mL, 3.5 mmol) was added dropwise. The reaction was
stirred for 0.75 h at this temperature, then a suspension of 7b (prepared as
reported in ref. [36]) (1.5 g, 3.5 mmol) in dry THF (30 mL) was added.
Stirring was continued for 3 h at 0 °C resulting in the gradual formation of a
clear solution to which was added saturated NH4Cl (10 mL). The layers were
separated and the aqueous phase extracted with CH2Cl2 (3 × 50 mL). The
combined extracts were washed with brine, dried, and concentrated under
reduced pressure. The resulting crude product was purified by flash chroma-
tography (CyH/EtOAc 85:15) to give 9 (68% yield, 62/38 mixture of isomers
of unassigned stereochemistry) as a white solid. – IR (Nujol) ν = 1736 and
1718 cm–1 (C=O).– 1H NMR (CDCl3): Major isomer δ = 8.04 (dd, 2H), 8.01
(d, 1H), 8.00 (s, 1H), 7.65 (tt, 1H), 7.55 (td, 2H), 7.28 (d, 1H), 4.41 (q, 2H),
1.56 (s, 9H), 1.37 (t, 3H); Minor isomer: 8.09 (dd, 2H), 8.0 (d, 1H), 7.55 (td,
2H), 4.41 (q, 2H), 1.37 (t, 3H). MS m/z 558 [M + H]+.
Isomer E: mp > 220 °C. 1H NMR ([D6]DMSO): δ = 7.93 (d, 1H), 7.41 (d,
1H), 6.39 (d, 1H), 4.24 (q, 2H), 1.53 (s, 9H), 1.24 (t, 3H). MS m/z 447
[M+H]+.
Isomer Z (16): mp > 220 °C. 1H NMR ([D6]DMSO): δ = 8.03 (d, 1H), 7.54
(d, 1H), 6.90 (d, 1H), 4.28 (q, 2H), 1.58 (s, 9H), 1.27 (t, 3H). MS m/z 447
[M+H]+.
Z-1-tert-Butoxycarbonyl-3-(2-fluoro-2-phenylcarbamoyl)-4,6-dichloroind
ole-2-carboxylic Acid Ethyl Ester (17)
1-Hydroxybenzotriazole hydrate (0.047 g, 0.35 mmol), 1-(3-dimethylami-
nopropyl)-3-ethylcarbodiimide hydrochloride (0.085 g, 0.43 mmol) and ani-
line (0.04 g, 0.43 mmol) were added to a suspension of the compound 16
(0.13 g, 0.29 mmol) in acetonitrile (15 mL) and the reaction was refluxed for
1.5 h. Ethyl acetate was added and the organic phase was washed with a 2N
solution of HCl and brine, dried and concentrated under reduced pressure.
The crude product which was purified by flash chromatography to yield the
desired compound 17 in 66% yield.– Mp> 220 °C.– IR (Nujol) ν = 3360 cm–1
(NH), 1745 and 1676 (C=O), 1603 (C=C).– 1H NMR ([D6]Acetone): δ =
Z-1-Benzenesulfonyl-3-(2-carboxy-2-chlorovinyl)-4,6-dichloroindole-2-ca
rboxylic Acid Ethyl Ester (10)
A suspension of 9 (3.1 g, 5.42 mmol) in formic acid (150 mL) was stirred
overnight at room temperature. After evaporation of the formic acid, product
10 (100% yield, mixture of E- and Z-isomers) was obtained as a white solid.
The pure Z-isomer was obtained by trituration with diethyl ether.– Mp
229.5–232.1 °C.– IR (Nujol) ν = 2900–2790 cm–1 (OH), 1736 (C=O).– 1H
NMR ([D6]DMSO): δ = 8.09 (dd, 2H), 8.06 (s, 1H), 8.04 (d, 1H), 7.82 (m,
Arch. Pharm. Pharm. Med. Chem. 332, 271–278 (1999)

276
Micheli, Di Fabio, and co-workers
9.68 (s, 1H), 8.15 (d, 1H), 7.84 (m, 1H), 7.52 (d, 1H), 7.47 (d, 1H), 7.38 (t,
E-3-(2-Fluoro-2-phenylcarbamoyl)-4,6-dichloroindole-2-carboxylic Acid
(4a)
2H), 7.17 (tt, 1H), 4.41 (q, 2H), 1.65 (s, 9H), 1.35 (s, 3H MS m/z 552 [M+H]+.
Lithium hydroxide monohydrated (0.015 g, 0.36 mmol) was added to a
solution of the compound 15 (0.04 g, 0.095 mmol) in THF/H2O (6 mL/4 mL)
and the reaction mixture was stirred at r.t. overnight. Ethyl acetate was added
and the solution was washed with a 2N solution of HCl and brine. The organic
layer was dried and concentrated under reduced pressure. The crude product
was purified by trituration in diethyl ether to give the desired compound 4a
in 40% yield.– Mp >220 °C.– IR (Nujol) ν = 3427 and 3317 cm–1 (NH +
OH), 1699 and 1670 (C=O), 1600 (C=C).– 1H NMR ([D6]DMSO): δ = 13.38
(bs, 1H), 12.28 (bs, 1H), 10.34 (bs, 1H), 7.56 (d, 2H), 7.41 (d, 1H), 7.25 (t,
2H), 7.17 (d, 1H), 7.12 (d, 1H), 7.05 (t, 1H). MS m/z 393 [M+H]+.
Z-3-(2-Fluoro-2-phenylcarbamoyl)-4,6-dichloroindole-2-carboxylic Acid
Ethyl Ester (18)
A suspension of compound 17 (0.1 g, 0.19 mmol) in formic acid (5 mL)
was heated at 40 °C for 2 h. The precipitate was filtered and washed with
diethyl ether to give the desired compound 18 in 62% yield.– Mp > 200 °C.–
IR (Nujol) ν = 3312 cm–1 (NH), 1678 and 1659 (C=O),1600 (C=C) cm–1.–
1H NMR ([D6]Acetone): δ = 11.63 (bs, 1H), 9.71 (bs, 1H), 7.86 (d, 2H), 7.62
(s, 1H), 7.58 (d, 1H), 7.37 (t, 2H), 7.25 (d, 1H), 7.15 (t, 1H), 4.38 (q, 2H),
1.35 (t, 3H). MS m/z 421 [M+H]+.
Z-1-tert-Butoxycarbonyl-3-(2-phenylcarbamoyl-2-acetamido)-4,6-dichlor
oindole-2-carboxylic Acid Allyl Ester (20)
Z-3-(2-Fluoro-2-phenylcarbamoyl)-4,6-dichloroindole-2-carboxylic Acid
(4)
DBU (0.12 mL, 0.8 mmol) was added to a solution of commercially
available N-acetyl-(dimethoxyphosphonyl)phenylacetamide (0.12 g,
0.39 mmol) in dry dichloromethane (10 mL) and the reaction mixture was
stirred at r.t. for 30 min. After cooling at –20 °C, a solution of aldehyde 19a
(115 mg, 0.3 mmol) in dry dichloromethane (10 mL) was added dropwise
and the stirring was continued at –20 °C for 7 h. The reaction mixture was
washed with a 2N solution of HCl and brine, then dried and concentrated
under reduced pressure. The crude product was purified by flash chromatog-
raphy (CyH/AcOEt 85:15) to give the desired compound 20 in 52% yield.–
Mp > 250 °C . IR (Nujol) ν = 3302 cm–1 (NH), 1745 and 1695 and 1648
(C=O).– 1H NMR ([D6]Acetone): δ = 9. 26 (bs, 1H), 8.77 (bs, 1H), 8.11 (d,
1H), 7.75 (d, 2H), 7.41 (d, 1H), 7.32 (t, 2H), 7.19 (s, 1H), 7.08 (t, 1H), 6.06
(m, 1H), 5.5–5.2 (m, 2H), 4.79 (m, 1H), 1.89 (s, 3H), 1.64 (s, 9H). MS m/z
572 [M+H]+.
Lithium hydroxide monohydrate (0.024 g, 0.57 mmol) was added to a
solution of the compound 18 (0.04 g, 0.095 mmol) in THF/H2O (6 mL/4 mL)
and the reaction was stirred at 60 °C for 7 h and at r.t. for 15 h. Ethyl acetate
was added and the solution was washed with a 2N solution of HCl and brine.
The organic layer was dried and concentrated at reduced pressure to give the
crude product which was purified by trituration in diethyl ether/petroleum
ether to give the desired product (4) in 60% yield.– IR (Nujol) ν = 3418–
3315cm–1 (NH, OH), 1664 (C=O).– 1H NMR ([D6]DMSO): δ = 13.67 (bs,
1H), 12.54 (bs, 1H), 10.33 (s, 1H), 7.77 (d, 2H), 7.48 (s, 1H), 7.46 (d, 1H),
7.34 (t, 2H), 7.28 (d, 1H), 7.12 (t, 1H). MS m/z 392 [M]+.
E-1-tert-Butoxycarbonyl-3-(2-fluoro-2-tert-butoxycarbonyl)-4,6-dichloro-
indole-2-carboxylic Acid Ethyl Ester (13)
Z-3-(2-Phenylcarbamoyl-2-acetamido)-4,6-dichloroindole-2-carboxylic
Acid Allyl Ester (21)
A solution of diethyl 2-fluoro-(diethoxyphosphonyl)acetic acid tert-butyl
ester (0.2 g, 0.74 mmol) in dry dichloromethane (5 mL) was added to a
suspension of potassium tert-butoxyde (0.09 g; 0.74 mmol) in dry dichlo-
romethane (5 mL) at –70 °C; the reaction was stirred for 20 min and a
solution of the aldehyde 7a (0.23 g; 0.62 mmol) in dry dichloromethane
(10 mL) was added. The temperature was raised to r.t. and after 1.5 h the
solution washed with a 2N solution of HCl and brine, dried and concentrated
under reduced pressure to give the crude compound which was purified by
flash chromatography (CyH/AcOEt 70:30) to give the desired product 13 in
Trifluoroacetic acid (6 mL) was added dropwise to a solution of the
compound 20 (0.125 g, 0.21 mmol) in dry dichloromethane (6 mL) at 0 °C,
then the reaction mixture was stirred at r.t. for 1 h. The solvent was evapo-
rated under reduced pressure and the residue was dissolved in ethyl acetate
and washed with a saturated solution of NaHCO3. The organic layer was
dried and concentrated under reduced pressure. The crude product was
purified by trituration in diethyl ether to give the compound 21 in 60% yield.–
Mp> 200 °C.– IR (Nujol) ν = 3331 cm–1 (NH), 1720 and1656 (C=O).– 1H
NMR ([D6]DMSO): δ = 12.48 (s, 1H), 9.74 (s, 1H), 9.05 (s, 1H), 7.75 (d,
2H), 7.48 (d, 1H), 7.32 (t, 2H), 7.25 (d, 1H), 7.13 (s, 1H), 7.07 (t, 1H), 6.03
(m, 1H), 5.40 (dq, 1H), 5.25 (dq, 1H), 4.80 (d, 2H), 1.78 (s, 3H). MS m/z 472
[M+H]+.
1
75% yield.– Isomer Z: H NMR ([D6]Acetone): δ = 8.12 (d, 1H), 7.44 (d,
1H), 7.03 (d, 1H), 4.38 (q, 2H), 1.63 (s, 9H), 1.34 (t, 3H), 1.12 (s, 9H). MS
m/z 502 [M+H]+.
E-3-(2-Fluoro-2-carboxy)-4,6-dichloroindole-2-carboxylic Acid Ethyl Ester
(14)
Z-3-(2-Phenylcarbamoyl-2-acetamido)-4,6-dichloroindole-2-carboxylic
A solution of the compound 13 (0.23 g, 0.46 mmol) in formic acid (5 mL)
was heated at 40 °C for 1.5 h. The formed precipitated was filtered and
washed with diethyl ether to give the desired compound 14 in 94% yield. –
Mp > 238–240 °C.– IR (Nujol) ν = 3321 cm–1 (NH), 1711 and 1672 (C=O).–
1H NMR ([D6]Acetone): δ = 13.35 (bs, 1H), 12.45 (s, 1H), 7.44 (d, 1H), 7.23
(d, 1H), 7.23 (s, 1H), 4.30 (q, 2H), 1.29 (t, 3H). MS m/z 345 [M]+.
Acid (5)
Dimedone (0.023 g, 0.17 mmol) and tetrakis(triphenylphosphine)palla-
dium(0) (0.024 g, 0.011 mmol) were added to a solution of compound 21
(0.02 g, 0.042 mmol) in THF (2 mL) and the reaction was stirred for 1 h.
Ethyl acetate was added and the solution was washed with a saturated
solution of NaHCO3, a 2N solution of HCl and brine. The organic layer was
dried and concentrated under reduced pressure to give a crude product which
was purified by trituration in diethyl ether to give compound 5 in 55% yield.–
IR (Nujol) ν = 3321 cm–1 (NH).– 1H NMR ([D6]DMSO): δ = 13.44 (bs, 1H),
12.32 (bs, 1H), 9.73 (s, 1H), 9.02 (bs, 1H), 7.76 (d, 2H), 7.45 (d, 1H), 7.32
(t, 2H), 7.21 (s, 1H), 7.3–7.1 (bs, 1H), 7.06 (t, 1H), 1.80 (s, 3H). MS m/z 432
[M+H]+.
E-3-(2-Fluoro-2-phenylcarbamoyl)-4,6-dichloroindole-2-carboxylic Acid
Ethyl Ester (15)
1-Hydroxybenzotriazole hydrate (0.071 g, 0.53 mmol), 1-(3-dimethylami-
nopropyl)-3-ethylcarbodiimide hydrochloride (0.1 g, 0.5 mmol) and aniline
(0.52 g, 0.56 mmol) were added to a suspension of the compound 14 (0.13 g,
0.43 mmol) in acetonitrile (15 mL) and the reaction was stirred at r.t. over-
night. Ethyl acetate was added and the organic phase was washed with a 2N
solution of HCl and brine, dried and concentrated at reduced pressure. The
crude product was purified by flash chromatography (CyH/AcOEt 80:20) to
give the desired compound 15 in 50% yield.– Mp> 199–201 °C.– IR (Nujol)
ν = 3342 cm–1 (NH), 1707 and 1661 (C=O), 1601 (C=C).– 1H NMR
([D6]acetone): δ = 11.43 (bs, 1H), 9.46 (bs, 1H), 7.66 (dd, 2H), 7.54 (d, 1H),
7.28 (t, 2H), 7.16 (d, 1H), 7.15 (d, 1H), 7.08 (tt, 1H), 4.31 (q, 2H), 1.32 (t,
3H). MS m/z 421 [M+H]+.
4,6-Dichloropyrrolidin-1-ylmethylene-3H-indole-2-carboxylic Acid Ethyl
Ester (22)
Intermediate 7 (2.0 g, 7 mmol) was treated with pyrrolidine (0.71 mL,
1.2 mmol) in refluxing benzene under Dean-Stark conditions for 2 h. The
solution was cooled to room temperature and evaporated to dryness to give
the desired product 22 in 80% yield.– 1H NMR ([D6]DMSO): δ = 9.29 (s,
1H), 7.68 (d, 1H), 7.21 (d, 1H), 4.40 (m, 2H), 4.01–3.50 (m, 4H), 2.05 (m,
4H), 1.38 (t, 3H).
Arch. Pharm. Pharm. Med. Chem. 332, 271–278 (1999)

Substituted Indole-2-carboxylates
277
E-3-(2-Phenylcarbamoyl-2-cyano)-4,6-dichloroindole-2-carboxylic Acid
Ethyl Ester (23)
The reaction was cooled to room temperature, poured into water, and
extracted with AcOEt. The organic phase dried over sodium sulphate, filtered
and evaporated to dryness. The crude product was purified by flash chroma-
tography (CyH/AcOEt 75:25) to give the desired product 27 in 42% yield.–
1H NMR ([D6]DMSO): δ = 7.89 (d, 1H), 7.32 (d, 1H), 7.14 (dd, 1H), 5.77
(s, 2H), 5.48 (dd, 1H), 5.33 (dd, 1H), 4.32 (q, 2H), 3.36 (t, 2H), 1.24 (t, 3H),
0.74 (t, 2H), –0.13 (s, 9H).
Intermediate 22 (500 mg, 1.48 mmol) was treated with NCCH2CONHPh
(237 mg, 1.48 mmol) in pyridine at room temperature for 1 h. The solution
was evaporated to dryness and the residue precipitated from 95% EtOH to
give the desired product 23 in 85% yield.– IR (Nujol) ν = 3414–3283 cm–1
(NH), 1700–1676 (C=O), 1606 (C=C).– 1H NMR ([D6]DMSO): δ = 13.07
(bs, 1H), 10.38 (bs, 1H), 8.83 (s, 1H), 7.68 (d, 2H), 7.54 (d, 1H), 7.41–7.36
(m, 3H), 7.14 (t, 1H), 4.37 (q, 2H), 1.31 (t, 3H).
E-1-(2-(Trimethylsilyl)ethoxymethyl)-3-(2-phenylcarbamoylcyclopropyl)-
4,6-dichloroindole-2-carboxylic Acid Ethyl Ester (28)
To a solution of compound 27 (120 mg, 0.29 mmol) and Rh2(OAc)4
(2.6 mg, 0.0058 mmol) in 1,2 – dimethoxyethane was added a solution of
N-phenyl diazoacetamide (70 mg, 0.435 mmol) in 1,2-dimethoxyethane by
a motor-driven syringe pump over a 4 h period. The solvent was evaporated
and the crude product was purified by a gradient elution to give the desired
intermediate 28 in 7% yield. – IR (CDCl3) ν = 1720–1709 cm–1 (C=O), 1601
(C=C).– 1H NMR (CDCl3): δ = 7.55 (d, 2H), 7.42 (d, 1H), 7.34 (t, 2H), 7.18
(d, 1H), 7.12 (t, 1H), 5.73 (d, 1H), 5.65 (d, 1H), 4.55–4.10 (m, 2H), 3.50–3.40
(m, 2H), 2.83 (m, 1H), 1.80 (m, 1H), 1.70 (m, 1H), 1. 42 (t, 3H), 1.15 (m,
1H), 0.86 (m, 2H), –0.06 (s, 9H).
E/Z-3-(2-Phenylcarbamoyl-2-nitro)-4,6-dichloroindole-2-carboxylic Acid
Ethyl Ester (24)
Intermediate 25 (370 mg; 1.24 mmol) was treated with O2NCH2CONHPh
(225 mg, 1.24 mmol) in pyridine at room temperature for 12 h. The product
was isolated as a crude E/Z mixture, but the desired E product was not
obtained because of the chromatographic instability of the mixture to any of
the attempted purification conditions.
3-Formyl-4,6-dichloroindole-2-carboxylic Acid Allyl Ester (19)
Intermediate 7 (1 g, 3.5 mmol) was suspended in allyl alcohol, p-toluene-
sulphonic acid monohydrate (665 mg, 3.5 mmol) was added and the mixture
refluxed for 2h. The resulting solution was evaporated to dryness and the
crude product was purified by precipitation from CyH to give the desired
product 19 in 60% yield.– IR (Nujol) ν = 3305–3288 cm–1 (NH).– 1H NMR
([D6]DMSO): δ = 11.4 (s, 1H), 7.41 (d, 1H), 7.05 (d, 1H), 6.1–5.9 (m, 1H),
5.4–5.2 (m, 2H), 4.8 (m, 2H).
Alternative Procedure to Prepare E-1-(2-(Trimethylsilyl)ethoxymethyl)-
3-(2-phenylcarbamoylcyclopropyl)-4,6-dichloroindole-2-carboxylic Acid
Ethyl Ester (28)
Intermediate 31 (602 mg, 1.13 mmol) was dissolved in dry Et2O under an
argonatmosphere, Pd(OAc)2 (10%) and an ethereal solution ofdiazomethane
was added at 0 °C. The mixture was carefully warmed at room temperature
and stirring continued for 1 h. The solution was evaporated using a stream
of dry nitrogen, the crude product was washed carefully with dry Et2O and
dry DCM and finally purified by flash chromatography to give the desired
product in 82% yield.
4,6-Dichloropyrrolidin-1-ylmethylene-3H-indole-2-carboxylic Acid Allyl
Ester (25)
Intermediate 19 (450 mg, 1.51 mmol) was refluxed in benzene under
Dean-Stark conditions with pyrrolidine (0.16 mL, 1.8 mmol) for 4 h. The
solution was evaporated to dryness to give the desired intermediate 25 in 80%
yield.– 1H NMR ([D6]DMSO): δ = 9.12 (s, 1H), 7.70 (d, 1H), 7.20 (d, 1H),
6.20 (m, 1H), 5.50-5.20 (m, 2H), 4.85 (m, 2H), 4.00–3.50 (m, 2H), 2.05 (m,
4H).
E-3-(2-Phenylcarbamoylcyclopropyl)-4,6-dichloroindole-2-carboxylic
Acid Ethyl Ester (29)
5N HCl (2 mL) was added to a suspension of intermediate 28 (201 mg,
0.5 mmol) in 95% EtOH and the resulting mixture was refluxed for 5 h. The
mixture was cooled to room temperature, concentrated at reduced pressure
and extracted with AcOEt. The organic phase dried over sodium sulphate,
filtered and evaporated to dryness. The crude product was purified by flash
chromatography (CyH /AcOEt 50:50) to give the desired product 29 in 70%
yield.– IR (Nujol) ν = 3312 cm–1 (NH), 1672 and 1649 (C=O).– 1H NMR
([D6]DMSO): δ = 12.1 (bs, 1H), 10.2 (bs, 1H), 7.60 (d, 2H), 7.40 (d, 1H),
7.28 (t, 2H), 7.20 (d, 1H), 7.01 (m, 1H), 4.4–4.25 (m, 2H), 2.55 (m, 1H), 1.98
(m, 1H), 1.49 (m, 1H), 1.27 (t, 3H), 1.22 (m, 1H).
E-3-(2-Phenylcarbamoyl-2-cyano)-4,6-dichloroindole-2-carboxylic Acid
Allyl Ester (26)
Intermediate 25 (420 mg, 1.51 mmol) was treated with NCCH2CONHPh
(350 mg, 1.8 mmol) in pyridine at room temperature for 1 h. The solution
was evaporated to dryness and the crude product purified by flash chroma-
tography (CyH/AcOEt 50:50) to give the desired product 26 in 60% yield.–
IR (Nujol) ν = 3283 cm–1 (NH), 1676 (C=O), 1599 (C=C).– 1H NMR
([D6]DMSO): δ = 13.1 (bs, 1H), 10.4 (bs, 1H), 8.83 (s, 1H), 7.70 (d, 2H),
7.55 (d, 1H), 7.41–7.36 (m, 3H), 7.14 (t, 1H), 6.02 (m, 1H), 5.35 (m, 2H),
4.86 (m, 2H).
E-3-(2-Phenylcarbamoylcyclopropyl)-4,6-dichloroindole-2-carboxylic
Acid (30)
LiOH. H2O (21 mg, 0.9 mmol) was added to a suspension of intermediate
29 (125 mg, 0.3 mmol) in 80% EtOH and the resulting mixture was stirred
at 50 °C for 3 h. The mixture was cooled to room temperature, the pH
adjusted to 3 and the desired product 30 was obtained for precipitation in
almost quantitative yield.– IR (Nujol) ν = 3400–3150 cm–1 (NH), 1670 and
1597 (C=O).– 1H NMR ([D6]DMSO): δ = 11.2 (bs, 1H), 10.8 (bs, 1H), 7.59
(d, 2H), 7.29 (d, 1H), 7.26 (t, 2H), 6.97(t, 1H), 6.95 (d, 1H), 2.32 (m, 1H),
2.21 (m, 1H), 1.40 (m, 1H), 1.31 (m, 1H). MS m/z 390 [M + H]+.
E-3-(2-Phenylcarbamoyl-2-cyano)-4,6-dichloroindole-2-carboxylic Acid
(6)
Intermediate 26 (20 mg, 0.046 mmol) were dissolved in dry THF under
nitrogen and dimedone (7.5 mg, 0.06 mmol) and Pd(PPh3)4 (1.3 mg,
0.001 mmol) were subsequently added at room temperature. The solution
was left under stirring for 2 h, poured into AcOEt, extracted with 0.5 N
NaOH. The aqueous phase was acidified with 0.5 N HCl and extracted with
AcOEt, the organic phase dried over sodium sulphate, filtered andevaporated
to dryness to give the desired product 6 in 80% yield.– 1H NMR
([D6]DMSO): δ = 14. 0 (bs, 1H), 12.95 (bs, 1H), 10.39 (bs, 1H), 8.82 (s, 1H),
7.70 (m, 2H), 7.52 (d, 1H), 7.39–7.36 (m, 3H), 7.14 (m, 1H). MS m/z 401 [M
+ H]+.
E-1-(2-(Trimethylsilyl)ethoxymethyl)-3-(2-phenylcarbamoylvinyl)-
4,6-dichloroindole-2-carboxylic Acid Ethyl Ester (31)
To a solution of 1 (120 mg, 0.3 mmol) (prepared according to ref. [22] in
dry DMF, a 1 M solution of LHMDS in THF (0.36 mL, 0.36 mmol) was
added at 0 °C followed by SEMCl (0.0 64 mL, 0.36 mmol). The solution was
left under stirring at room temperature for 1h, concentrated, poured onto
water and extracted with AcOEt. The organic phase dried over sodium
sulphate, filtered and evaporated to dryness. The crude product was purified
by flash chromatography (CyH/AcOEt 90:10) to give the desired product 31
in 80% yield.– IR (Nujol) ν = 3206 cm–1 (NH), 1703 and 1659 (C=O), 1618
and 1603 (C=C).– 1H NMR ([D6]DMSO): δ = 10.22 (s, 1H), 8.13 (d, 1H),
1-(2-(Trimethylsilyl)ethoxymethyl)-3-vinyl-4,6-dichloroindole-2-carboxylic
Acid Ethyl Ester (27)
To a 1M solution of LHMDS (0.3 mL, 0.3 mmol) in dry THF, methyl-
triphenylphosphonium bromide (107 mg, 0.3 mmol) was added at room
temperature and the mixture stirred for 4 h. Intermediate 7c (125 mg,
0.3 mmol) was subsequently added and the reaction warmed to 60 °C for 9 h.
Arch. Pharm. Pharm. Med. Chem. 332, 271–278 (1999)

278
Micheli, Di Fabio, and co-workers
7.97 (d, 1H), 7.70 (d, 2H), 7.44 (d, 1H), 7.33 (t, 2H), 7.07 (t, 1H), 6.44 (d,
1H), 5.83 (s 2H), 4. 39 (q, 2H), 3.41 (t, 2H), 1.29 (t, 3H), 0.77 (t, 2H), -0.12
(s, 9H).
[21] R. Di Fabio, G. Gaviraghi, A. Reggiani, La Chimica e l’Industria 1996,
78, 283–289.
[22] R. Di Fabio, A.M. Capelli, N. Conti, A. Cugola, D. Donati, A. Feriani,
P. Gastaldi, G. Gaviraghi, C.T. Hewkin, F. Micheli, A. Missio,
M. Mugnaini, A. Pecunioso, A.M. Quaglia, E. Ratti, L. Rossi, G.
Tedesco, D. G. Trist, A. Reggiani, J. Med. Chem. 1997, 40, 841–850.
References and Notes
[1] B. Meldrum, J. Trends Pharmacol. 1990, 11, 379–387.
[2] D. W. Choi, J. Neurosci. 1990, 10, 2493–2501.
[23] R. Di Fabio, A. Cugola, D. Donati, A. Feriani, G. Gaviraghi, E.Ratti,
D. Trist, ACS Book of Abstracts, 211th ACS National Meeting, New
Orleans, LA, 24–28 March 1996, Abstract 107.
[3] B. Meldrum, Cerebrovasc. Brain Metab. Rev. 1990, 2, 27–57.
[4] J. McCullogh, Br. J. Clin. Pharmacol. 1992, 34, 106–114.
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Received: April 15, 1999 [FP384]
Arch. Pharm. Pharm. Med. Chem. 332, 271–278 (1999)