Synthesis and receptor binding studies of halogenated N,N-dialkylel-(2-phenyl-1H-indol-3-yl)glyoxylamides to visualize peripheral benzodiazepine receptors with SPECT or PET

Article abstract of DOI:10.1016/j.bmc.2006.07.001

A library of halogenated 2-arylindolyl-3-oxocarboxamides was prepared to develop radioligands to visualize cerebral PBR by SPECT and PET imaging. In vitro evaluation showed that most of the synthesized compounds were selective,high-affinity PBR ligands with adequate lipophilicity (log D_7.4 in the range of 1.6-2.4). The iodinated derivative 11 (K_i = 2.6 nM) and the fluorinated analog 26 (K_i = 6.2 nM) displayed higher affinity than reference compounds.

Full text of DOI:10.1016/j.bmc.2006.07.001

Bioorganic & Medicinal Chemistry 14 (2006) 7582–7591
Synthesis and receptor binding studies of halogenated
N,N-dialkylel-(2-phenyl-1H-indol-3-yl)glyoxylamides to visualize
peripheral benzodiazepine receptors with SPECT or PET
Idriss Bennacef,a Colin N. Haile,a Anne Schmidt,d Andrei O. Koren,c John P. Seibyl,a,c
Julie K. Staley,a Frederic Bois,a Ronald M. Baldwinb and Gilles Tamagnana,c,
*
aYale School of Medicine, VA Connecticut HCS (116A2), West Haven, CT 06516, USA
bVanderbilt University Medical Center, Department of Radiology and Radiological Sciences/PET Chemistry,
Nashville, TN 37232-2675, USA
cInstitute for Neurodegenerative Disorders, New Haven, CT 06510, USA
dPfizer Global Research & Development, Groton/New London Labs, CNS Discovery Biology, Groton, CT 06340, USA
Received 1 June 2006; revised 29 June 2006; accepted 1 July 2006
Abstract—A library of halogenated 2-arylindolyl-3-oxocarboxamides was prepared to develop radioligands to visualize cerebral
PBR by SPECT and PET imaging. In vitro evaluation showed that most of the synthesized compounds were selective,high-affinity
PBR ligands with adequate lipophilicity (logD7.4 in the range of 1.6–2.4). The iodinated derivative 11 (Ki = 2.6 nM) and the fluo-
rinated analog 26 (Ki = 6.2 nM) displayed higher affinity than reference compounds.
ꢀ 2006 Elsevier Ltd. All rights reserved.
1. Introduction
in cancer, auto-immune, infective, and neurodegenera-
tive disorders. More specifically, PBR reflects neuronal
injury and inflammatory lesions by increasing expres-
sion on proliferating and activated microglia. These
characteristics make PBR a promising target of efforts
aimed toward the diagnosis and treatment of patholo-
gies such Alzheimer’s disease,6 Huntington’s disease,
Wernicke’s encephalopathy, multiple sclerosis,5 and
stroke.
The peripheral benzodiazepine receptor (PBR) is an
18 kDa, five transmembrane protein primarily located
in the outer membrane of mitochondria. PBR forms a
trimeric complex that interacts in the mitochondrial per-
meability transition pore (MPTP) with adenosine nucle-
otide translocase (ANT) and voltage-dependent anion
channels (VDAC). The role of PBRs remains unknown
but their involvement in lipid metabolism and/or trans-
port, steroid regulation and cell proliferation is well
established.1 PBRs are distributed throughout the body.
High concentrations are observed in tissues such as
adrenal glands and gonads, while brain expresses low le-
vel of PBR’s primarily associated with the choroids plex-
us, ependymal lining, and microglia.2 The fact that PBR
knock-out mice die at an early stage of development
suggests that this receptor plays a critical role in physi-
ological processes.3 A great deal of research is being car-
ried out to determine PBRs involvement in normal and
pathophysiological condition.4 PBR has been implicated
Imaging studies using positron emission tomography
(PET) or single photon emission computed tomography
(SPECT) have provided valuable information regarding
the role of PBR. PET and SPECT are powerful imaging
techniques allowing the visualization of brain receptors
by recording the interaction of the targeted receptor and
a radioligand bearing a positron emitter for PET (car-
bon-11, t1/2 = 20.4 min; fluorine-18, t1/2 = 109.7 min) or
a gamma emitter for SPECT (iodine-123, t1/2 = 13.2 h).
To date, several PET radioligands for PBR have been
synthesized (PK11195 and DAA1106 families) but
only one SPECT probe ([123I]iodo-(R)-PK11195) has
been reported (Fig. 1).6
Keywords: Peripheral benzodiazepine receptor; PBR; SPECT; PET;
Arylindolyloxocarboxamides.
Recently, Primofiore et al.7 described a series of N,N-dial-
kyl-(2-phenyl-1H-lindol-3-yl)glyoxylamides I (Fig. 2) as
*
Corresponding author: E-mail: gtamagnan@indd.org
0968-0896/$ - see front matter ꢀ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2006.07.001

I. Bennacef et al. / Bioorg. Med. Chem. 14 (2006) 7582–7591
7583
X2
OCH3
X
N
X1
O
Ac
N
F
N
O
R
N
N
R
OR
H311C
OPh
X1 =Cl X2 = H R = 11CH3
X1
123I X2 = H R = CH3
1 = H X2
[
11C] PK 11195
[
[
[
11C]DAA1106
R = CH3
X = H R = CH2C6H5
[
[
[
11C] VC195
11C] VC193M
11C] VC198M
18F]FMDAA1106 R = 18FCH2
18F]FEDAA1106 R = 18F(CH2)2
=
[
123I] I-PK 11195
X = H R = CH(CH3)CH2CH3
X = F R = CH(CH3)CH2CH3
X
=
18F R = CH3
[
18F] F-PK 11195
Figure 1.
Y
Y
Bromopyridyl indole scaffold 20 was synthesized from
1-tert-butyloxycarbonylindole-2-boronic acid10 by
O
O
a
O
O
Suzuki cross coupling with 2,6-dibromopyridine.
Bromine-to-iodine exchange was performed using the
Klarpas and Buchwald conditions. At this stage, a
partial removal of the tert-butyloxycarbonyl moiety
was observed, hence the crude material adsorbed onto
silica was heated in a conventional microwave oven11
and iodopyridinyl indole 21 was obtained in good
yield. Compound 22 was finally obtained by the
two-step/one-pot acylation and amidation procedure
(Scheme 2).
X
N
H
N
H
X
"N"
I
II
Ia X = Cl, Y = NBu2
Ib X = Cl, Y = NHex2
Ic X = F, Y = NHex2
Y = NEt2, NBu2, NHex2, NHBn
or N(CH2CH2OCH2)2
X = I or F
Figure 2.
potent and selective PBR ligands. Most compounds of
this series displayed nanomolar affinity for PBR. Struc-
ture–activity relationship (SAR) studies showed that the
introduction of a halogen atom in the para-position of
the phenyl ring was beneficial and that modification of
the dialkylamide substituents could be performed without
significant loss of affinity. These results prompted us to
design new radioligands of general structure II where a
radionuclide (iodine-123 for SPECT or fluorine-18 for
PET) would reside in the phenyl ring while the dialkyl-
amide would help ‘fine-tune’ in vivo properties of the mol-
ecule. We also investigated replacing the 2-phenyl moiety
with a pyridyl ring.
Fluoropyridyl indole 24 was synthesized from 2-iodoin-
dole12 23 by Suzuki cross coupling with 2-fluoro-5-
(pinacol-borolan-2-yl)-pyridine. Acylation and amida-
tion were carried out to obtain compounds 25–27
(Scheme 3).
2.2. Structure–activity relationships
Physicochemical characterization of the new ligands
consisted of measuring their in vitro benzodiazepine
receptor binding affinity and lipophilicity. Competition
receptor binding assays were performed with rat kidney
membranes against [3H]PK11195 for PBR and with
guinea pig cortical membranes against [3H]flunitraze-
pam for the central benzodiazepine receptor (CBR).
The lipophilicity of compounds 6, 11, 12, and 15 was
determined experimentally at pH 7.4.
Herein, we describe the synthesis and in vitro evaluation
of the novel N,N-dialkyl-(2-(het)aryl-1H-indol-3-yl)gly-
oxyamide derivatives.
2. Results and discussion
2.1. Chemistry
In an initial examination, substitution of the chlorine
atom of molecule I (Table 1) by a bulkier iodine atom
resulted in the 2- and 3-fold decrease in PBR binding
affinity for Y = N(Bu)2 and Y = N(Hex)2, respectively
(compare Ia and 6, Ib and 7).
2-(40-Iodophenyl)indole (1) and 2-(20-iodophenyl)indole
(4) were obtained from phenylhydrazine and 40- or
20-iodoacetophenone using the Fisher indole synthesis
(method A) or the modified procedure described by
Guy and Grette (method B);8 while 2-(30-iodophenyl)
indole (3) was prepared from 2-(30-bromophenyl)indole
(2) by the powerful bromine-to-iodine exchange
described by Klarpas and Buchwald.9 Finally, the hal-
ophenylindoles 1–4 were acylated with oxalyl chloride
and the resulting (2-arylindol-3-yl)glyoxyl chlorides
were reacted with proper amines (diethylamine, dibutyl-
amine, dihexylamine, benzylamine, and bis(2-methoxy-
ethyl)amine) to obtain desired products 5–9 and
11–19. Compound 15 was obtained from its bromo-an-
alog 10 by palladium-catalyzed stannylation followed by
iododestannylation (Scheme 1).
To extend the SAR in this series, a further library of
halogenated derivatives of general structure II was
synthesized and characterized. All new compounds
appeared to be selective PBR ligands.
In the first series, compounds bearing iodine in posi-
tion 20, 30 or 40 of the 2-phenyl ring were chosen as tar-
gets. We anticipated that the bulkier iodophenyl
moieties would affect docking of the molecule to the
receptor binding site but this might be compensated
by modifying the amide part of the molecule. Hence,
ethyl-, butyl-, hexyl-, and benzyl-amines were chosen
to map out the effect of the alkyl substituents (Table 1).

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I. Bennacef et al. / Bioorg. Med. Chem. 14 (2006) 7582–7591
Y
O
O
a
b
X
O
c
4'
X
+
NH2
4'
N
N
X
H
3'
2'
H
N
3'
H
2'
1 X = 4'-I Method A
2 X = 3'-Br Method B
3 X = 3'-I
5-9
X = 4'-I
10
X = 3'-Br
11-14 X = 3'-I
d,e
4 X = 2'-I Method B
15
X = 3'-I
16-19 X = 2'-I
Y = NEt2,NBu2, NHex2, NHCH2Ph,
N(CH2CH2OCH3)2 resp.
Scheme 1. Reagents and conditions: (a) Method A: PPA, D, 4 h, or method B: 1—AcOH, cat. EtOH, D; 2—PPA–xylenes, 85 ꢁC, 20 min; (b) NaI,
CuI, TMEDA, 1,4-dioxane, 110 ꢁC, 24 h; (c) 1—(COCl)2, THF, 0 ꢁC to rt, 1 h; 2—amine, THF, 0 ꢁC to rt, overnight; (d) Pd(PPh3)4, Me3SnSnMe3,
1,4-dioxane, D, 72 h; (e) I2, CH2Cl2, rt, overnight.
N(Bu)2
With the aim of finding a radioiodinated SPECT tracer
with lower lipophilicity, iodinated ligands with an oxy-
O
O
a
d
genated alkyl substituent (Y = N(CH2CH2OCH3)2)
were synthesized. The para-derivative 9 displayed
modest binding affinity (Ki = 72 nM) similar to that of
the non-oxygenated alkyl derivative 7 (Y = NHex2,
Ki = 90 nM). However, the meta-isomer 15 appeared
to be more potent (Ki = 16 nM) than its hexyl analog
13 (Ki = 51 nM) and as potent as 12 (Y = NBu2,
Ki = 10 nM) while displaying lower logD7.4 (1.7 vs 2.2).
OH
B
N
N
N
OH
N
H
N
Boc
Boc
X
I
20 X = Br
21 X = I
22
b, c
Scheme 2. Reagents and conditions: (a) 2,6-dibromopyridine, K2CO3,
THF/H2O, D, 6 h; (b) NaI, CuI,TMEDA, 1,4-dioxane,110 ꢁC, 24 h; (c)
MW, 1100 W, 2 min; (d) 1—(COCl)2, THF, 0 ꢁC to rt; 2—HNBu2,
THF, 0 ꢁC to rt.
Replacement of the 30-iodophenyl fragment by a 6-iodo-
2-pyridinyl moiety essentially did not change the binding
affinity (compare 22 and 12).
Compounds bearing the iodine atom in position 40 (5–8)
or 30 (11–14) displayed the same behavior with regard to
the amide nature. Here, the following order of affinities
was observed: NEt2 > NBu2 > NHBn ꢀ NHex2. When
examining the location of the iodo substituent (compare
5–8 and 11–14, respectively), it appeared that the meta-
position was the better placement. Compared to the
reference compounds, PBR affinity was increased by
introducing iodine in the meta-position and by shorten-
ing the length of the amide (compare I and 11).
For the design of a PET tracer, similar modifications of
the structure of a reported fluorinated ligand Ic
(Ki = 7.2 nM)7 were envisaged. To achieve efficient 18F
labeling, the phenyl ring was replaced with a 30-pyridyl
one. Thus, ligands 25–27 (Y = N(Bu)2, N(Hex)2, and
NHBn, respectively) were synthesized and evaluated.
As in the previous series, replacement of the meta-CH
with a nitrogen atom essentially did not change the affin-
ity (compare 26 and Ic). However, in the fluoropyridyl
series, the following order of affinities was observed:
N(Hex)2 > N(Bu)2 > NHBn. These results suggest that
the effect of the length of the amide alkyls on affinity
depends on the nature of the aromatic moiety attached
to position 2 of the indole scaffold.
When the iodine was in position 20 (16–19), the pattern
changed, and the affinities ranked in the following order:
NBu2 = NEt2 > NHex2 > NHBn.
Taken together, these data seem to indicate that the
30-position was best location for the iodo substituent,
and that the length of the amide alkyls should not
exceed four carbons.
3. Conclusion
With the aim to develop radioligands to visualize cere-
bral PBR by SPECT and PET imaging, a library of
halogenated 2-arylindolyl-3-oxocarboxamides was pre-
pared. In vitro evaluation showed that most of the
The logD7.4 values of compounds 6, 11, and 12 were
2.33, 2.18, and 2.25, respectively. These values are in
the accepted range for good blood–brain barrier perme-
ability (i.e., 0–3).
Y
O
O
d
c
a, b
I
N
H
N
H
N
H
N
H
N
F
N
F
23
25 Y = NBu2
26 Y = NHex2
24
27 Y =NHCH2Ph
Scheme 3. Reagents and conditions: (a) 1—n-BuLi, THF, ꢁ78 ꢁC, 30 min; 2—CO2(g), 10 min; (b) 1—t-BuLi, THF, ꢁ78 ꢁC, 1 h; 2—1,2-
diiodoethane, THF, ꢁ78 ꢁC, 1 h; (c) 5-B(pin)–2-F–pyridine, K2CO3, THF/H2O, D, 72 h; (d) 1—(COCl)2, THF, 0 ꢁC to rt; 2—amine, THF, 0 ꢁC to rt.

I. Bennacef et al. / Bioorg. Med. Chem. 14 (2006) 7582–7591
7585
Table 1. Physical properties and binding affinity of compounds I, 5–9, 11–19, 22 and 25–27 of General formula II
Y
O
O
Ar
N
H
II
Compound Ar
Y
Formula
Mp (ꢁC) Appearance
Anal.
Ki, PBRa Ki, CBRa logD7.4
(nM)
(nM)
PK11195
Ro-15-1788
—
—
—
—
—
—
—
—
—
—
—
—
6.9
>76.5
>65
1.3
—
—
Ia
Ib
NBu2
NHex2
C24H27ClN2O2
C28H35ClN2O2
—
—
White solid
Orange oil
C, H, N
C, H, N
7b
31b
>2070
>2070
Cl
F
Ic
NHex2
C28H35FN2O2
—
Orange oil
C, H, N
7.2
>2070
5
6
7
8
9
NEt2
NBu2
C20H19IN2O2
C24H27IN2O2
C28H35IN2O2
C23H17IN2O2
107
148
130
210
128
White solid
White solid
White solid
Yellow solid
White solid
C, H, N
C, H, N
C, H, N
C, H, N
C, H, N
9.8
15
>2070
>2070
>2070
>2070
>2070
2.33
NHex2
NHCH2Ph
90
46
I
I
N(CH2CH2OCH3)2 C22H23IN2O4
72
11
12
13
14
15
NEt2
NBu2
C20H19IN2O2
C24H27IN2O2
C28H35IN2O2
C23H17IN2O2
192
62
White solid
White foam
Yellow oil
White solid
White solid
C, H, N
C, H, N
H, N, Cc
C, H, N
C, H, N
2.6
10
255
2.18
2.25
>2070
>2070
>2070
>2070
NHex2
NHCH2Ph
—
51
21
232
<65
N(CH2CH2OCH3)2 C22H23IN2O4
16
1.69
I
16
17
18
19
NEt2
NBu2
C20H19IN2O2
C24H27IN2O2
C28H35IN2O2
C23H17IN2O2
225
77
Yellow foam C, H, N
Yellow foam C, H, N
Tanned foam C, H, N
Yellow foam C, H, N
14
9.5
27
22
>2070
>2070
>2070
>2070
NHex2
NHCH2Ph
52
204
N
I
22
NBu2
C23H26IN3O2
148
White solid
C, H, N
7
>2070
25
26
NBu2
NHex2
C23H26FN3O2
C27H34FN3O2
—
—
Yellow oil
Oil
C, H, N
C, H, N
16
>2070
>2070
6.2
N
F
27
NHCH2Ph
C22H16FN3O2
184
Yellow solid
C, H, N
45
>2070
a Average of 3–5 independent determinations.
b In house data.
c C: calcd, 60.22; found, 59.45.
synthesized compounds were selective, high-affinity
PBR ligands with adequate lipophilicity (logD7.4 in the
range of 1.6–2.4). The iodinated derivative 11 and the
fluorinated analogs 26 and 27 displayed higher affinity
than reference compounds and could be used as a lead
for further modification of the N,N-dialkyl-(2-(het)-
aryl-1H-indol-3-yl)glyoxyamide motif. The optimal
combination of properties (affinity, selectivity, and lipo-
philicity) suggests that the novel PBR ligands are prom-
ising candidates for further investigation.
moisture-sensitive liquids were transferred by syringe
or stainless steel cannula. Thin layer chromatography
plates were visualized by exposure to ultraviolet light
(UV), and then were stained by submersion in etha-
nol–formaldehyde (35%) hydrochloric acid (25%) mix-
ture (2:1:1 v/v/v), followed by brief heating with a
heat gun. Flash chromatography was performed as
described by Still et al.13 employing silica gel (60 A
˚
pore size, 230–400 mesh, 40–63 lm). Proton nuclear
magnetic resonance (1H NMR) spectra and carbon
nuclear magnetic resonance (13C NMR) spectra were
recorded on a Bruker AMX-400 MHz or a Bruker
Advance 500 MHz spectrometer at 23 ꢁC. Proton
chemical shifts are expressed in parts per million
(ppm; d scale) downfield from tetramethylsilane in
the NMR solvent (CHCl3: d 7.26, (CH3)2SO: d
2.50). Carbon chemical shifts are expressed in parts
per million (ppm; d scale) downfield from tetrameth-
ylsilane and are referenced to the carbon resonance
4. Experimental
4.1. Chemistry
4.1.1. General considerations. All reactions were
performed in oven dried glassware fitted with rubber
septa under a positive pressure of argon. Air- and

7586
I. Bennacef et al. / Bioorg. Med. Chem. 14 (2006) 7582–7591
of the NMR solvent (CDCl3: d 77.16, (CD3)2SO: d
39.52). Data are represented as follows: Chemical
shift, multiplicity (s, singlet; d, doublet; t, triplet; m,
multiplet; br, broad), integration and coupling con-
stant (J) in hertz (Hz).14 Commercial reagents and
solvents were used as received except for ethyl ether
and tetrahydrofuran, which were distilled from sodi-
um/benzophenone immediately before use.
1 equiv), CuI (33.1 mg, 0.17 mmol, 0.09 equiv), and
NaI (636 mg, 4.23 mmol). After heating at 110 ꢁC dur-
ing 20 h, the suspension was cooled and ammonium
hydroxide (28–30%) was added. The mixture was
extracted with CH2Cl2 (3·). The combined organic lay-
ers were dried over MgSO4, filtered, and concentrated.
Purification by flash chromatography on silica gel (hex-
ane/EtOAc 100:1–98:2) yielded 3 as a white solid
(516 mg, 1.6 mmol, 81%). 1H NMR (DMSO-d6) d
11.65 (s, 1H), 8.30–8.29 (m, 1H), 7.94 (ddd,
J = 7.9 Hz, J = 0.8, J = 0.7 Hz, 1H), 7.71 (ddd,
J = 7.8 Hz, J = 0.8 Hz, J = 0.6 Hz, 1H), 7.58 (d,
J = 7.8 Hz, 1H), 7.45 (d, J = 8.1 Hz, 1H), 7.30 (t,
J = 7.9 Hz, 1H), 7.17 (dt, J = 8.0 Hz, J = 1.0 Hz, 1H),
7.06 (dd, J = 8.6 Hz, J = 0.8 Hz, 1H), 7.04–7.02 (m,
1H). 13C NMR (DMSO-d6) d 137.4, 136.8, 136.5,
134.9, 134.3, 131.0, 129.5, 124.8, 123.2, 121.3, 120.9,
111.5, 101.2, 95.4.
4.1.2. Cyclization
4.1.2.1. 2-(4-Iodophenyl)indole (1). 4-Iodoacetophe-
none (4.0 g,) and phenylhydrazine (2.64 g) were mixed
with polyphosphoric acid (34 g), and the mixture was
heated with stirring. The temperature of the reaction
mixture was kept at 105 ꢁC for 4 h. The mixture was
poured into crushed ice, stirred for 10 min, extracted
with CH2Cl2 (3·), dried over MgSO4, filtered, and con-
centrated. The crude, diluted in acetone, was triturated
with H2O. After suction filtration, desired product was
1
obtained as a brown solid (3.80 g, 12 mmol, 74%). H
4.1.2.4. 2-(Iodophenyl)-1H-indole (4). 2-Iodoacetoph-
enone (2.46 g, 10.0 mmol, 1 equiv) and phenyl hydra-
zine (1.30 g, 12.0 mmol, 1.2 equiv) were stirred in
ethanol (15 mL). Acetic acid (eight drops) was added
and the mixture was refluxed. After 5 h, solvent was
removed and the crude was taken up in EtOAc
(50 mL), washed with oxalic acid (5%), water, brine,
and dried over MgSO4. Filtration and evaporation
NMR (DMSO-d6) d 11.59 (s, 1H), 7.83–7.81 (m, 2H),
7.68–7.66 (m, 2H), 7.54 (d, J = 7.9 Hz, 1H), 7.41 (d,
J = 8.1 Hz, 1H), 7.12 (dt, J = 8.0 Hz, J = 1.0 Hz, 1H),
7.01 (dt, J = 7.2 Hz, J = 1.0 Hz, 1H), 6.94 (d,
J = 1.1 Hz, 1H). 13C NMR (DMSO-d6) d 138.0, 137.6,
136.9, 132.1, 128.9, 127.3, 122.3, 120.6, 119.9, 111.7,
99.7, 93.5.
yielded
1-[1-(2-iodophenyl)ethyliden]-2-phenylhydr-
4.1.2.2. 2-(3-Bromophenyl)-1H-indole (2). 30-Bromo-
acetophenone (2.0 g, 10.0 mmol, 1 equiv) and phen-
ylhydrazine (1.30 g, 12.0 mmol, 1.2 equiv) were stirred
in ethanol (15 mL). Acetic acid (eight drops) was added
and the mixture was refluxed. After 5 h, solvent was
removed and the crude was taken in EtOAc (50 mL),
washed with oxalic acid (5%), water, brine, and dried
over MgSO4. Filtration and evaporation yielded
1-[1-(3-bromophenyl)ethyliden]-2-phenylhydrazine (2.6 g,
9.0 mmol, 90%) as a light yellow solid. Crude (2.0 g,
6.9 mmol) in xylene (30 mL) and polyphosphoric acid
(15 g) was stirred at 85 ꢁC during 20 min. Water
(150 mL) was added to the warm crude, the mixture
was stirred for 10 min and poured into water (300 mL)
and stirred for 20 min. EtOAc was added, and the
organic layer was separated. The aqueous layer was
extracted with EtOAc (3· 100 mL), and the combined
organic layers were washed with H2O and brine, dried
over MgSO4, filtered, and concentrated. Purification
by flash chromatography on silica gel (hexane/EtOAc
98:2) yielded 2 as white powder (1.56 g, 5.75 mmol,
azine (3.36 g, 10.0 mmol, 100%) as a viscous brown
oil. Crude (3.36 g, 10 mmol) in xylene (45 mL) and
polyphosphoric acid (17 g) were vigorously stirred at
85 ꢁC during 20 min. Water (150 mL) was added to
the warm crude, the mixture was stirred for 10 min
and poured into water (300 mL) and stirred 20 min.
EtOAc was added, and the organic layer was separat-
ed. The aqueous layer was extracted with EtOAc (3·
100 mL), and the combined organic layers were
washed with H2O and brine, dried over MgSO4, fil-
tered, and concentrated. Purification by flash chroma-
tography on silica gel (hexane/EtOAc 98:2) yielded 4
(2.35 g, 7.37 mmol, 77%) as a brown oil. 1H NMR
(DMSO-d6) d 11.4 (s, 1H), 8.05 (dd, J = 7.8 Hz,
J = 0.8 Hz, 1H), 7.61 (d, J = 7.9 Hz, 1H), 7.57–7.49
(m, 2H), 7.44 (dd, J = 8.1 Hz, J = 0.7 Hz, 1H), 7.18–
7.14 (m, 2H), 7.05 (dt, 7.9 Hz, J = 0.9 Hz, 1H), 6.72
(dd, J = 2 Hz, J = 0.6 Hz, 1H). 13C NMR (DMSO-
d6) d 140.3, 139.4, 138.3, 136.6, 131.3, 130.1, 128.6,
128.1, 121.9, 120.6, 119.6, 111.8, 102.4, 98.8; Anal.
(C14H10IN) C, H, N.
1
83%), mp = 150 ꢁC. H NMR (DMSO-d6) d 11.68 (s,
1H), 8.14 (t, J = 1.7 Hz, 1H), 7.93 (dt, J = 7.7 Hz,
J = 1.0 Hz, 1H), 7.59 (d, J = 7.9 Hz, 1H), 7.56–7.57
(m, 1H), 7.48–7.44 (m, 2H), 7.17 (dt, J = 8.2 Hz,
J = 1.0 Hz, 1H), 7.08–7.04 (m, 2H). 13C NMR (CDCl3)
d 137.6, 136.2, 134.9, 131.4, 130.3, 128.8, 127.6, 124.3,
122.8, 122.5, 120.7, 119.9, 111.8, 100.3, Anal.
(C14H10BrN) C, H, N.
4.1.2.5. tert-Butyl 2-(6-bromopyridin-2-yl)-1H-indole-
1-carboxylate (20). 1-tert-Butoxycarbonylindole-2-
boronic acid (3 g, 11.5 mmol), 2,6-dibromopyridine
(3.28 g, 13.8 mmol), and Pd(PPh3)4 (417 mg, 0.36 mmol)
in THF/2 M K2CO3 (20 mL/20 mL) were refluxed over-
night. Purification by flash chromatography on silica gel
(hexane/EtOAc 98:2) yielded 20 (2.92 mg, 7.82 mmol,
68%) as
(DMSO-d6)
a
white solid, mp = 166 ꢁC. 1H NMR
d 8.12 (d, J = 8.3 Hz, 1H), 7.94 (t,
4.1.2.3. 2-(3-Iodophenyl)-1H-indole (3). N,N0-Dimeth-
ylethylenediamine (14.4 lL, 0.13 lmol) and then dry
dioxane (2 mL) were successively introduced in a sealed
tube with stirring bar (dried at 100 ꢁC) charged with
J = 7.8 Hz, 1H), 7.84 (d, J = 7.5 Hz, 1H), 7.76–7.72
(m, 2H), 7.47 (dt, J = 8.3 Hz, J = 1.1 Hz, 1H), 7.36 (t,
J = 7.7 Hz, 1H), 7.12 (s, 1H), 1.39 (s, 9H). 13C NMR
(DMSO-d6) d 153.4, 149.6, 140.8, 140.5, 137.6, 137.5,
2-(3-bromophenyl)-1H-indole
(544 mg,
2 mmol,

I. Bennacef et al. / Bioorg. Med. Chem. 14 (2006) 7582–7591
7587
128.4, 127.1, 125.9, 123.6, 122.4, 121.9, 114.4, 112.0,
84.0, 27.4.
fication by flash chromatography on silica gel (hexane/
EtOAc 80:20) yielded 5 (635 mg, 1.42 mmol, 89%) as a
white solid, mp = 107 ꢁC. 1H NMR (DMSO-d6) d
12.59 (s, 1H), 8.14 (d, J = 7.3 Hz, 1H), 7.96 (d,
J = 8.3 Hz, 2H), 7.57 (d, J = 7.3 Hz, 1H), 7.45 (d,
J = 8.3 Hz, 2H), 7.40–7.34 (m, 2H), 3.23 (q,
J = 7.0 Hz, 2H), 3.17 (q, J = 7.2 Hz, 2H), 1.10 (t,
J = 7.0 Hz, 3H), 0.91 (t, J = 7.2 Hz, 3H). 13C NMR
(DMSO-d6) d 187.5, 167.3, 146.6, 137.1, 136.1, 132.3,
130.6, 127.0, 123.9, 122.9, 121.2, 112.5, 110.1, 97.1,
42.1, 38.2, 14.0, 12.5. EI-MS m/z : 448 (21), 447 (100),
346 (5), 200 (4), 101 (33), Anal. (C20H19IN2O2) C, H, N.
4.1.2.6. 2-(6-Iodopyridin-2-yl)-1H-indole (21). N,N0-
Dimethylethylenediamine
(53.7 lL,
44.0 mg,
0.50 mmol), and then dry dioxane (5 mL) were succes-
sively introduced in a sealed tube with stirring bar
(dried at 100 ꢁC) charged with tert-butyl 2-(6-bromo-
pyridin-2-yl)-1H-indole-1-carboxylate (1.87 g, 5 mmol),
CuI (47.8, 0.25 mmol), and NaI (1.5 g, 62.5 mmol).
After heating at 110 ꢁC during 24 h, the suspension
was cooled and ammonium hydroxide (28–30%) was
added. The mixture was extracted with CH2Cl2 (3·).
The combined organic layers were dried (MgSO4), fil-
tered and adsorbed on SiO2 (20 g). The dry powder
was heated in a conventional microwave oven (1100
watts) during 2 min. Extraction with acetone, suction
filtration (3·), and concentration yielded 21 (1.34 g,
4.19 mmol, 84%) as an off-white solid, mp = 158 ꢁC.
1H NMR (DMSO-d6) d 11.60 (s, 1H), 8.03 (d,
J = 7.8 Hz, 1H), 7.76 (d, J = 7.7 Hz, 1H), 7.77–7.53
(m, 3H), 7.21–1.17 (m, 2H), 7.06 (t, J = 7.7 Hz, 1H).
13C NMR (DMSO-d6) d 152.4, 139.3, 137.8, 135.9,
133.1, 128.5, 123.2, 121.2, 120.1, 119.6, 119.0, 112.6,
102.2.
4.1.3.2. N,N-Dibutyl-2-(2-(4-iodophenyl)-1H-indol-3-
yl)-2-oxoacetamide (6). Compound 6 was obtained from
2-(4-iodophenyl)-1H-indole (400 mg, 1.25 mmol) in
THF (10 mL), oxalyl chloride (1.6 g, 12.5 mmol), and
dibutylamine (1.5 g, 11.6 mmol) in THF (5 mL). Purifi-
cation by flash chromatography on silica gel (hexane/
EtOAc 80:20) yielded 6 (473 mg, 0.94 mmol, 76%) as a
white solid, mp = 148 ꢁC. 1H NMR (CDCl3) d 10.12
(s, 1H), 8.08 (d, J = 7.9 Hz, 1H), 7.31 (d, J = 8.4 Hz,
2H), 7.25–7.21 (m, 1H), 7.16–7.14 (m, 2H), 6.85 (d,
J = 8.3 Hz, 2H), 3.06–3.02 (m, 4H), 1.47–1.43 (m, 2H),
1.21–1.07 (m, 4H), 0.88 (t, J = 7.0 Hz, 3H), 0.73 (t,
J = 7.4 Hz, 3H). 13C NMR (CDCl3) d 187.2, 168.3,
146.0, 137.7, 135.9, 131.5, 130.5, 127.5, 124.4, 123.7,
122.2, 112.1, 96.7, 48.5, 44.9, 30.8, 29.5, 20.8, 20.3,
14.5, 14.1. EI-MS m/z 504 (15), 503 (100). Anal.
(C24H27IN2O2) C, H, N.
4.1.2.7.
2-(6-Fluoropyridin-3-yl)-1H-indole
(24).
2-Iodoindole (1.22 g, 5.02 mmol), 2-fluoro-5-(4,4,5,5-tet-
ramethyl-[1,3,2]-dioxaborolan-2-yl)-pyridine (1.232 g,
5.52 mmol), and Pd(PPh3)4 (0.6 g, 0.52 mmol) in THF/
2 M K2CO3 (18 mL/12 mL) were refluxed for 72 h. The
organic layer was separated and the aqueous layer was
extracted with CH2Cl2 (3·). Combined organic layers
were washed with brine, dried over Na2SO4, filtered,
and concentrated. Purification by flash chromatography
on silica gel (hexane/EtOAc 85:15–80:20) yielded 24 as a
yellow solid (769 mg, 3.63 mmol, 72%), mp = 256 ꢁC. 1H
NMR (DMSO-d6) d 11.48 (s, 1H), 8.76–8.75 (m, 1H),
8.43 (dt, J = 8.3 Hz, J = 2.6 Hz, 1H), 7.57 (d,
J = 7.8 Hz, 1H), 7.43 (d, J = 8.1 Hz, 1H), 7.32 (dd,
J = 8.6 Hz, J = 2.9 Hz, 1H), 7.15 (t, J = 7.1 Hz, 1H),
7.05–7.00 (m, 2H). 13C NMR (DMSO-d6) d 162.0 (d,
J = 236.3 Hz), 144.1 (d, J = 15.3 Hz), 138.8 (d,
J = 8.3 Hz), 137.6, 133.8, 128.7, 127.3, 122.5, 120.7,
120.0, 111.8, 110.3 (d, J = 37.7 Hz), 100.3.
4.1.3.3. N,N-Dihexyl-2-(2-(4-iodophenyl)-1H-indol-3-
yl)-2-oxoacetamide (7). Compound 7 was obtained
from 2-(4-iodophenyl)-1H-indole (400 mg, 1.25 mmol)
in THF (10 mL), oxalyl chloride (1.26 g, 9.84 mmol),
and dihexylamine (1.6 g, 8.7 mmol) in THF (5 mL).
Purification by flash chromatography on silica gel (elu-
ent: hexane/EtOAc 85:15) yielded 7 (565 mg, 1.0 mmol,
1
81%), as a white solid, mp = 130 ꢁC. H NMR (CDCl3)
d 11.34 (s, 1H), 7.99 (d, J = 7.1 Hz, 1H, H7), 7.20–7.17
(m, 1H), 7.09–7.06 (m, 1H), 7.03–7.00 (m, 3H), 6.58
(d, J = 7.7 Hz, 2H), 3.07–2.98 (m, 4H), 1.30–0.85 (m,
16H), 0.84 (t, J = 8.0 Hz, 3H), 0.71 (t, J = 7.1 Hz, 3H).
13C NMR (CDCl3) d 186.6, 168.7, 146.8, 137.5, 136.3,
131.2, 130.4, 127.5, 124.1, 123.6, 121.6, 112.9, 110.4,
96.4, 49.0, 45.5, 32.1, 31.7, 28.7, 27.4, 27.3, 26.7, 23.1,
22.8, 14.6, 14.3. EI-MS m/z 559 (MH+, 100), 560 (33).
Anal. (C28H35IN2O2) C, H, N.
4.1.3. General procedure for the synthesis of N,N-dialkyl-
[5-substituted-2-(4-substitutedphenyl)indol-3-yl]glyoxyla-
mide derivatives 5–14 and 16–19. At 0 ꢁC, oxalyl chloride
(10 equiv) was added dropwise to the appropriate indole
(1 equiv) in THF (0.15 M). The mixture was stirred for
1 h at room temperature and evaporated to dryness.
At 0 ꢁC, appropriate amine (10 equiv) in THF (0.3 M)
was added dropwise to the crude in THF (0.15 M). After
one night at rt, Et2O was added and the mixture was
washed with 2 N HCl (3·), NaHCO3 5%, H2O and
brine, dried over MgSO4, filtered, and concentrated.
4.1.3.4. N-Benzyl-2-(2-(4-iodophenyl)-1H-indol-3-yl)-
2-oxoacetamide (8). Compound 8 was obtained from 2-
(4-iodophenyl)-1H-indole (400 mg, 1.25 mmol) in THF
(10 mL), oxalyl chloride (1 g, 7.7 mmol), and benzyl-
amine (1.5 g, 14.0 mmol) in THF (5 mL). Purification
by flash chromatography on silica gel (hexane/EtOAc
60:40) yielded 8 (380 mg, 0.79 mmol, 63%) as a white sol-
id, mp = 210 ꢁC. 1H NMR (CDCl3) d 12.45 (s, 1H), 9.08
(t, J = 9.2 Hz, 1H), 8.01 (d, J = 8.0 Hz, 1H), 7.80 (d,
J = 8.2 Hz, 2H), 7.50 (d, J = 8.0 Hz, 1H), 7.38 (d,
J = 8.3 Hz, 2H), 7.34 (d, J = 7.6 Hz, 2H), 7.31–7.27 (m,
2H), 7.23–7.21 (m, 3H), 4.09 (d, J = 6.0 Hz, 2H). 13C
NMR (CDCl3) d 187.5, 166.7, 146.4, 138.7, 137.2, 136.2,
131.7, 128.7, 127.9, 127.6, 127.3, 123.8, 122.7, 121.2,
4.1.3.1. N,N-Diethyl-2-(2-(4-iodophenyl)-1H-indol-3-
yl)-2-oxoacetamide (5). Compound 5 was obtained from
2-(4-iodophenyl)-1H-indole (500 mg, 1.6 mmol) in THF
(10 mL), oxalyl chloride (300 mg, 2.36 mmol), and
diethylamine (490 mg, 10.0 mmol) in THF (5 mL). Puri-

7588
I. Bennacef et al. / Bioorg. Med. Chem. 14 (2006) 7582–7591
112.4, 109.6, 96.7, 42.1. EI-MS m/z 482 (8), 481 (25), 413
(15), 218 (100), 196 (29), Anal. (C23H17IN2O2) C, H, N.
(2.5 mL). Purification by flash chromatography on silica
gel (hexane/EtOAc 80:20) yielded 13 (157 mg,
0.28 mmol, 91%) as a yellow oil. H NMR (CDCl3) d
1
4.1.3.5. 2-(2-(4-Iodophenyl)-1H-indol-3-yl)-N,N-bis(2-
methoxyethyl)-2-oxoacetamide (9). Compound 9 was ob-
tained from 2-(4-iodophenyl)-1H-indole (479 mg,
1.5 mmol) in THF (7 mL), oxalyl chloride (1.91 g,
10.95 (br s, 1H), 8.04 (d, J = 7.8 Hz, 1H), 7.58 (s, 1H),
7.42 (d, J = 7.8 Hz, 1H), 7.15–7.11 (m, 1H), 7.06–7.05
(m, 2H), 7.70 (d, J = 6.1 Hz, 1H), 6.24–6.22 (m, 1H),
3.12 (t, J = 7.7 Hz, 2H), 3.03 (t, J = 7.3 Hz, 2H), 1.49–
1.47 (m, 2H), 1.23–1.07 (m, 14H), 0.81 (t, J = 7.1 Hz,
3H), 0.73 (t, J = 7.0 Hz, 3H). 13C NMR (CDCl3) d
186.9, 168.5, 145.9, 138.5, 138.4, 136.3, 133.3, 130.3,
129.0, 127.5, 124.2, 123.4, 121.9, 112.8, 110.8, 93.7,
49.3, 46.0, 32.0, 31.7, 28.9, 27.6, 27.3, 26.8, 23.0, 22.9,
14.5, 14.4, Anal. (C28H35IN2O2) H, N, C, calcd 60.22,
found 59.45.
15 mmol)
and
bis(2-methoxyethyl)amine
(2.5 g,
19 mmol) in THF (7 mL). Purification by flash chroma-
tography on silica gel (hexane/EtOAc 70:30) yielded 9
(538 mg, 1.06 mmol 71%) as a white solid, mp = 120 ꢁC.
1H NMR (CDCl3) d 9.18 (s, 1H), 8.09 (d, J = 7.9, 1H),
7.39 (d, J = 8.1 Hz, 2H), 7.25–7.21 (m, 1H), 7.17–7.13
(m, 2H), 6.95 (d, J = 8.1 Hz, 2H), 3.47–3.44 (m, 4H),
3.42 (t, J = 5.6 Hz, 2H), 3.29 (s, 3H), 3.27 (t, J = 5.7 Hz,
2H), 3.15 (s, 3H). 13C NMR (CDCl3) d 186.6, 168.9,
146.2, 137.8, 135.9, 131.4, 130.7, 127.5, 124.5, 123.7,
122.0, 112.1, 111.0, 96.7, 71.5, 70.4, 59.4, 59.1, 48.9,
46.2, Anal. (C22H23IN2O4) C, H, N.
4.1.3.9. N,N-Diethyl-2-(2-(3-iodophenyl)-1H-indol-3-
yl)-2-oxoacetamide (14). Compound 14 was obtained
from 2-(3-iodophenyl)-1H-indole (100 mg, 0.31 mmol)
in THF (5 mL), oxalyl chloride (519 mg, 4.09 mmol),
and benzylamine (513 mg, 5.37 mmol) in THF
(2.5 mL). Trituration into EtOAc yielded 14 (104 mg,
0.217 mmol, 70%) as a white solid, mp = 232 ꢁC. 1H
NMR (DMSO-d6) d 12.54 (s, 1H), 9.16 (t, J = 6.0 Hz,
1H), 8.07 (d, J = 7.9 Hz, 1H), 8.02 (s, 1H), 7.92
(d, J = 8.2, 1H), 7.65 (d, J = 7.7 Hz, 1H), 7.54
(d, J = 7.9 Hz, 1H), 7.39–7.22 (m, 8H), 4.12 (d,
J = 5.9 Hz, 2H). 13C NMR (DMSO-d6) d 187.6, 166.8,
145.7, 138.7, 138.3, 137.9, 136.2, 133.8, 130.4, 129.5,
128.7, 127.9, 127.5, 127.3, 123.9, 122.8, 121.3, 112.5,
109.7, 94.8, 42.2, Anal. (C23H17IN2O2) C, H, N.
4.1.3.6. N,N-Diethyl-2-(2-(3-iodophenyl)-1H-indol-3-
yl)-2-oxoacetamide (11). Compound 11 was obtained
from 2-(3-iodophenyl)-1H-indole (100 mg, 0.31 mmol)
in THF (5 mL), oxalyl chloride (632 mg, 5.0 mmol),
and diethylamine (400 mg, 5.5 mmol) in THF
(2.5 mL). Trituration into EtOAc yielded 11 (87 mg,
0.194 mmol, 64%) as a white solid, mp = 192 ꢁC. 1H
NMR (CDCl3) d 10.08 (s, 1H), 8.11 (d, J = 7.9 Hz,
1H), 7.65–7.64 (m, 1H), 7.55 (d, J = 8.0 Hz, 1H), 7.20–
7.13 (m, 3H), 6.96 (d, J = 7.7 Hz, 1H), 6.56 (t,
J = 7.8 Hz, 1H), 3.24 (q, J = 7.0 Hz, 2H), 3.13 (q,
J = 7.2 Hz, 2H), 1.11 (t, J = 7.0 Hz, 3H), 0.90 (t,
J = 7.2 Hz, 3H). 13C NMR (CDCl3) d 187.2, 168.0,
145.6, 138.7, 138.4, 136.0, 133.3, 130.3, 129.2, 127.4,
124.5, 123.6, 122.1, 112.3, 111.2, 93.8, 43.4, 39.9, 14.4,
13.0. EI-MS m/z 447 (12), 446 (38), 346 (20), 220 (17),
219 (10), 127 (8), 77 (9), 62 (100), 61 (27), Anal.
(C20H19IN2O2) C, H, N.
4.1.3.10. 2-(2-(3-Bromophenyl)-1H-indol-3-yl)-N,N-
bis(2-methoxyethyl)-2-oxoacetamide (10). Compound
10 was obtained from 2-(3-iodophenyl)-1H-indole
(816 mg, 3 mmol) in THF (15 mL), oxalyl chloride
(3.81 g, 30 mmol), and bis(2-methoxyethyl)amine (4 g,
30 mmol) in THF (7 mL). Purification by flash chroma-
tography on silica gel (hexane/EtOAc 60:40–1:1) yielded
10 (1.17 g, 2.55 mmol, 85%) as
a white solid,
1
4.1.3.7. N,N-Dibutyl-2-(2-(3-iodophenyl)-1H-indol-3-
yl)-2-oxoacetamide (12). Compound 12 was obtained
from 2-(3-iodophenyl)-1H-indole (100 mg, 0.31 mmol)
in THF (5 mL), oxalyl chloride (649 mg, 5.1 mmol),
and dibutylamine (667 mg, 5.2 mmol) in THF
(2.5 mL). Purification by flash chromatography on silica
gel (hexane/EtOAc 70:30) yielded 12 (133 mg,
0.27 mmol, 86%) as a white solid, mp = 62 ꢁC. 1H
NMR (CCl3) d 9.20 (s, 1H), 8.17 (d, J = 6.8 Hz, 1H),
7.75–7.74 (m, 1H), 7.65 (d, J = 8,0 Hz, 1H), 7.29 (d,
J = 7.7 Hz, 1H), 7.27–7.18 (m, 3H), 6.88 (t, J = 7.8 Hz,
1H), 3.10 (t, J = 7.8 Hz, 2H), 3.04 (t, J = 7.2 Hz, 2H),
1.50–1.45 (m, 2H), 1.22–1.08 (m, 6H), 0.83 (t,
J = 7.0 Hz, 3H), 0.76 (t, J = 7.3 Hz, 3H). 13C NMR
(CDCl3) d 186.9, 168.5, 145.9, 138.5, 138.4, 136.2,
133.2, 130.2, 129.0, 127.4, 124.2, 123.5, 121.8, 112.8,
110.8, 93.8, 49.0, 45.7, 31.0, 29.7, 20.8, 20.4, 14.3, 14.1,
Anal. (C24H27IN2O2) C, H, N.
mp = 120 ꢁC. H NMR (CDCl3) d 10.78 (s, 1H), 8.01
(d, J = 7.9 Hz, 1H), 7.50 (t, J = 1.7 Hz, 1H), 7.23 (m,
1H), 7.13–7.11 (m, 1H), 7.04–7.03 (m, 2H), 6.69 (d,
J = 7.6 Hz, m, 1H), 6.46 (t, 7.9 Hz, 1H), 3.51 (t,
5.6 Hz, 2H), 3.44–3.39 (m, 4H), 3.31 (t, J = 5.4 Hz,
2H), 3.21 (s, 3H), 3.11 (s, 3H). 13C NMR (CDCl3) d
186.3, 169.2, 146.0, 136.1, 133.2, 132.6, 130.1, 128.2,
127.4, 124.3, 123.5, 122.0, 121.7, 112.6, 110.6, 71.3,
70.2, 59.2, 59.0, 49.2, 46.5, Anal. (C22H23BrN2O4) C,
H, N.
4.1.3.11. N,N-Bis(2-methoxyethyl)-2-(2-(3-(trimethyl-
stannyl)phenyl)-1H-indol-3-yl)-2-oxoacetamide. 2-(2-(3-
Bromophenyl)-1H-indol-3-yl)-N,N-bis(2-methoxyethyl)-
2-oxoacetamide (10) (1 g, 2.18 mmol), Pd(PPh3)4 and
(Me3Sn)2 in 1,4-dioxane were refluxed for 72 h and
evaporated. Purification by flash chromatography on
silica gel (hexane/EtOAc/Et3N 98:2:0.1%–60:40:0.1%)
yielded desired compound (250 mg, 0.49 mmol, 99%)as
1
4.1.3.8. N,N-Dibutyl-2-(2-(3-iodophenyl)-1H-indol-3-
yl)-2-oxoacetamide (13). Compound 13 was obtained
from 2-(3-iodophenyl)-1H-indole (100 mg, 0.31 mmol)
in THF (5 mL), oxalyl chloride (600 mg, 4.72 mmol),
and dihexylamine (943 mg, 5.1 mmol) in THF
a white solid, mp <65 ꢁC. H NMR (CDCl3) d 8.43 (s,
1H), 8.07–8.05 (m, 1H), 7.48 (br s, 1H), 7.41–7.39 (m,
1H), 7.35–7.33 (m, 1H), 7.22–7.18 (m, 2H), 7.13–7.08
(m, 2H), 3.26 (t, J = 5.5 Hz, 2H), 3.19 (t, J = 6.1 Hz,
2H), 3.13 (t, J = 5.6 Hz, 2H), 3.09 (s, 3H), 3.05 (t,

I. Bennacef et al. / Bioorg. Med. Chem. 14 (2006) 7582–7591
7589
J = 6.0 Hz, 2H), 3.01 (s, 3H), 0.19–0.08 (m, 9H). 13C
NMR (CDCl3) d 181.5, 168.7, 147.6, 143.2, 137.8,
137.0, 135.6, 130.8, 130.2, 128.1, 127.6, 124.5, 123.6,
122.5, 111.5, 111.4, 71.6, 70.5, 59.1, 48.9, 45.9, ꢁ8.98.
Anal. (C25H32N2O4Sn) C, H, N.
4.1.3.15. N,N-Dibutyl-2-(2-(2-iodophenyl)-1H-indol-3-
yl)-2-oxoacetamide (18). Compound 18 was obtained
from 2-(2-iodophenyl)-1H-indole (348 mg, 1.09 mmol)
in THF (10 mL), oxalyl chloride (.26 g, 9.92 mmol),
and dihexylamine (1.28 g, 6.92 mmol) in THF (5 mL).
Purification by flash chromatography on silica gel (hex-
4.1.3.12.
2-(2-(3-Iodophenyl)-1H-indol-3-yl)-N,N-
ane/EtOAc
90:10–80:20)
yielded
18
(480 mg,
bis(2-methoxyethyl)-2-oxoacetamide (15). N,N-Bis(2-
methoxyethyl)-2-(2-(3-(trimethylstannyl)phenyl)-1H-
indol-3-yl)-2-oxoacetamide (272 mg, 0.50 mmol), iodine
(153 mg, 0.60 mmol) in CH2Cl2 were stirred overnight
at rt. Aqueous sodium thiosulfate was added, after dis-
coloration, MgSO4 was added, mixture was filtered
and concentrated. Purification by flash chromatography
on silica gel (hexane/EtOAc/Et3N 70:30:0.1%) yielded 15
(252 mg, 0.50 mmol, 99%) as a white solid, mp <65 ꢁC.
1H NMR (CDCl3) d 10.76 (s, 1H), 8.01 (d, J = 7.9 Hz,
1H), 7.68 (t, J = 1.6 Hz, 1H), 7.43–7.41 (m, 1H), 7.13–
7.09 (m, 1H), 7.05–7.04 (m, 2H), 7.74 (d, J = 7.6 Hz,
1H), 6.33 (t, J = 7.8 Hz, 1H), 3.50 (t, J = 5.2 Hz, 2H),
3.43 (t, J = 5.1 Hz, 2H), 3.41 (t, J = 5.6 Hz, 2H), 3.31
(t, J = 5.5 Hz, 2H), 3.21 (s, 3H), 3.11 (s, 3H). 13C
NMR (CDCl3) d 186.4, 169.2, 145.9, 138.6, 138.2,
136.1, 133.3, 130.2, 128.9, 127.4, 124.3, 123.5, 121.8,
112.6, 110.6, 93.7, 71.4, 70.3, 59.2, 59.1, 49.2, 46.7, Anal.
(C22H23IN2O4) C, H, N.
0.86 mmol, 79%) as a tanned solid, mp = 52 ꢁC. 1H
NMR (CDCl3) d 9.90 (s, 1H), 8.17 (d, J = 7.6 Hz,
1H), 7.66 (d, J = 7.8 Hz, 1H), 7.27 (d, J = 7.8 Hz,
1H), 7.22–7.13 (m, 2H), 7.07 (dd, J = 7.5 Hz,
J = 0.9 Hz, 1H), 6.99 (t, J = 7.4 Hz, 1H), 6.89 (dt,
J = 7.8 Hz, J = 1.4 Hz, 1H), 3.13–2.92 (br m, 2H),
2.91–2.74 (br m, 2H), 1.44–1.39 (m, 2H), 1.24–0.93
(m, 14H), 0.82 (t, J = 6.9 Hz, 3H), 0.72 (t, J = 6.7 Hz,
3H). 13C NMR (CDCl3) d 187.2, 167.9, 147.7, 138.9,
136.6, 135.8, 132.8, 131.3, 127.7, 126.8, 124.4, 123.4,
122.6, 112.3, 111.8, 99.4, 49.5, 45.0, 32.0, 31.7, 28.9,
27.4, 27.2, 26.8, 23.0, 22.9, 14.5, 14.4. EI-MS m/z 558
(4), 347 (17), 346 (100), 273 (11), 271 (11), 220 (46),
219 (60), 191 (17), 190 (23), 85 (33), 57 (37), Anal.
(C28H35IN2O2) C, H, N.
4.1.3.16. N,N-Dibutyl-2-(2-(4-iodophenyl)-1H-indol-3-
yl)-2-oxoacetamide (19). Compound 19 was obtained
from 2-(2-iodophenyl)-1H-indole (316 mg, 0.99 mmol)
in THF (10 mL), oxalyl chloride (1.52 g, 12.0 mmol),
and benzylamine (1.20 g, 11.2 mmol) in THF (5 mL).
Trituration into EtOAc yielded 19 (321 mg, 0.669 mmol,
68%) as a yellow solid, mp = 204 ꢁC. 1H NMR (DMSO-
d6) d 12.48 (s, 1H), 8.97 (t, J = 6.1 Hz, 1H), 8.15 (d,
J = 7.5 Hz, 1H), 8.00 (d, J = 7.7 Hz, 1H), 7.53–7.50
(m, 3H), 7.36–7.27 (m, 5H), 7.24–7.22 (m, 2H), 4.09–
4.02 (m, 1H), 3.91–3.87 (m, 1H). 13C NMR (DMSO-
d6) d 187.0, 166.7, 148.8, 138.9, 138.6, 137.3, 135.8,
131.9, 131.1, 128.6, 127.8, 127.5, 127.2, 126.7, 123.8,
122.7, 121.6, 112.4, 110.5, 100.6, 41.9. EI-MS m/z 480
(9), 447 (24), 347 (11), 346 (61), 221 (13), 220 (76), 219
(100), 191 (15), 190 (28), 165 (10), 91 (28), 77 (12), Anal.
(C23H17IN2O2) C, H, N.
4.1.3.13. N,N-Diethyl-2-(2-(2-iodophenyl)-1H-indol-3-
yl)-2-oxoacetamide (16). Compound 16 was obtained
from 2-(2-iodophenyl)-1H-indole (309 mg, 0.969 mmol)
in THF (10 mL), oxalyl chloride (1.48 g, 11.6 mmol),
and diethylamine (1.26 g, 17.2 mmol) in THF (5 mL).
Trituration into EtOAc yielded 16 (272 mg, 0.61 mmol,
1
63%), white solid, mp = 225 ꢁC. H NMR (CDCl3) d
8.94 (s, 1H), 8.32–8.30 (m, 1H), 7.79 (dd,
J = 8.0 Hz,J = 0.8 Hz, 1H), 7.36–7.33 (m, 2H), 7.28–
7.24 (m, 3H), 7.04 (dt, J = 7.8 Hz, J = 1.7 Hz, 1H),
3.17–3.14 (br m, 2H), 3.0–2.95 (br m, 2H), 1.05 (t,
J = 7.0 Hz, 3H), 0.69 (t, J = 7.2 Hz, 3H). 13C NMR
(CDCl3) d 187.7, 167.4, 147.4, 139.1, 136.5, 135.5, 133.2,
131.6, 127.9, 126.9, 124.7, 123.7, 122.9, 112.2, 111.8,
99.3, 43.5, 38.8, 14.4, 12.8, Anal. (C20H19IN2O2) C, H, N.
4.1.3.17. N,N-Dibutyl-2-(2-(6-iodopyridin-2-yl)-1H-
indol-3-yl)-2-oxoacetamide
(22).
Oxalyl
chloride
4.1.3.14. N,N-Dibutyl-2-(2-(4-iodophenyl)-1H-indol-3-
yl)-2-oxoacetamide (17). Compound 17 was obtained
from 2-(2-iodophenyl)-1H-indole (330 mg, 1.03 mmol)
in THF (10 mL), oxalyl chloride (1.54 g, 12.1 mmol),
and dibutylamine (1.21 g, 9.38 mmol) in THF (5 mL).
Purification by flash chromatography on silica gel (hex-
anes/EtOAc 90:10–80:20) yielded 17 (322 mg,
(635 mg, 5 mmol) was added dropwise, over 1 h, to 2-
(6-iodopyridin-2-yl)-1H-indole (160 mg, 0.5 mmol) in
THF (2 mL) at 0 ꢁC. Four drops of DMF were added
and the crude was stirred for 1 more hour. Crude was
evaporated to give a brown solid that was reuptake in
THF (2 mL). Dibutylamine (645 mg, 5 mmol) in THF
(1 mL) was then added dropwise. The mixture was
stirred for one night at rt. Purification by column
1
0.64 mmol, 62%). White solid, mp = 77 ꢁC. H NMR
(CDCl3) d 9.44 (s, 1H), 8.22 (d, J = 7.4 Hz, 1H); 7.73
(dd, J = 7.9 Hz, J = 0.9 Hz, 1H), 7.30 (dd, J = 7.0 Hz,
J = 1.6 Hz, 1H), 7.24–7.18 (m, 3H), 7.11 (dt,
J = 7.5 Hz, J = 1.1 Hz, 1H), 6.97 (dt, J = 7.8 Hz,
J = 1.7 Hz, 1H), 3.11–2.94 (br m, 2H), 2.93–7.79 (br
m, 2H), 1.46–1.39 (m, 2H), 1.15–0.95 (m, 6H), 0.81–
0.72 (m, 6H). 13C NMR (CDCl3) d 187.4, 167.8, 147.4,
139.0, 136.6, 135.6, 132.9, 131.5, 127.8, 126.8, 124.5,
123.5, 122.7, 112.1, 112.0, 99.4, 49.2, 44.7, 31.0, 29.6,
20.7, 20.4, 14.3, 14.1. EI-MS m/z 502 (6), 347 (16), 346
(100), 329 (25), 220 (76), 219 (96), 190 (27), 164 (15),
160 (58), 156 (11), Anal. (C24H27IN2O2) C, H, N.
chromatography
(hexanes/EtOAc
75:25–70:30)
yielded 22 (114 mg, 0.23 mmol, 44%) as a white solid,
mp = 148 ꢁC. 1H NMR (CDCl3) d 10.36 (br s, 1H),
8.61 (d, J = 7.8 Hz, 1H), 7.77 (d, J = 8.1 Hz, 1H), 7.60
(t, J = 7.9 Hz, 1H), 7.38 (d, J = 8.1 Hz, 1H), 7.25–7.24
(m, 2H), 7.18–7.15 (m, 1H), 3.44 (t, J = 7.8 Hz, 2H),
3.17 (t, J = 7.8 Hz, 2H), 1.35–1.60 (m, 2H), 1.50–1.43
(m, 2H), 1.39–1.31 (m, 2H), 0.92 (t, J = 7.4 Hz, 3H),
0.68 (t, J = 7.3 Hz, 3H). 13C NMR (CDCl3) d 187.5,
169.1, 150.8, 149.1, 141.4, 140.3. 135.6, 128.0, 125.3,
125.2, 124.2, 123.5, 121.4, 112.5, 111.6, 48.5, 45.1,
30.9, 29.8, 20.8, 20.3, 14.3, 13.9.

7590
I. Bennacef et al. / Bioorg. Med. Chem. 14 (2006) 7582–7591
4.1.3.18. N,N-Dibutyl-2-(2-(6-fluoropyridin-3-yl)- 1H-
indol-3-yl)-2-oxoacetamide (25). Oxalyl chloride
4.2. Radioligand binding assays
(95.3 mg, 0.75 mmol) was added dropwise, over 1.5 h,
to 2-(6-fluoropyridin-3-yl)-1H-indole (106 mg, 0.5 mmol)
in THF (2 mL) at 0 ꢁC. Dibutylamine (300 mg,
2.33 mmol) in THF (2 mL) was then added dropwise.
After 2 h, EtOAc was added and the mixture was washed
with 2 N HCl (1·), 3% NaOH (1·) and brine, organic
layer was dried over MgSO4, filtered, and concentrated.
Purification by flash chromatography on silica gel (hex-
ane/EtOAc 80:20) yielded 25 (95 mg, 0.24 mmol, 48%)
as a yellow oil. 1H NMR (DMSO-d6) d 8.53 (d,
J = 2.2 Hz, 1H), 8.28 (dt, J = 8.1 Hz,J = 2.4 Hz, 1H),
8.10 (d, J = 6.7 Hz, 1H), 7.58 (d, J = 7.8 Hz, 1H), 7.43
(dd, J = 8.4 Hz, J = 2.5 Hz, 1H), 7.39–7.31 (m, 2H),
3.14–3.06 (m, 4H), 1.52–1.13 (m, 8H), 0.92 (t,
J = 7.1 Hz, 3H), 0.79 (t, J = 7.3 Hz, 3H). 13C NMR
(CDCl3) d 187.1, 167.6, 163.7 (d, J = 237 Hz), 148.8 (d,
J = 15.9 Hz), 144.2 (d, J = 8.5 Hz), 143.1, 136.5, 126.9,
126.0, 124.1, 123.0, 121.2, 112.7, 110.9, 109.2 (d,
J = 37.5 Hz), 47.5, 43.8, 30.4, 29.2, 20.1, 19.6, 14.0,
13.8, Anal. (C23H26FN3O2) C, H, N.
Peripheral and central benzodiazepine receptor binding
assays on membranes from rat kidney (PBR) and guinea
pig cortex (CBR) were performed according to standard
receptor binding procedures. Briefly, frozen rat kidney
(Pel-Freez) and guinea pig cortex were homogenized in
tissue (for PBR: 50 mM Tris–HCl buffer (pH 7.4 at
4 ꢁC) containing 2.0 mM MgCl2; for CBR: 50 mM Tris
acetate pH 7.4 at 4 ꢁC) using a Polytron and spun in a
centrifuge at 40,000g for 10 min. Membranes were
recovered after multiple rounds of separation by centri-
fugation and resuspension in fresh ice-cold tissue buffer.
The final pellets were resuspended in assay buffer (for
PBR assays: 50 mM Tris–HCl buffer (pH 7.4 at 22 ꢁC)
containing 2 mM MgCl2; for CBR assays: 50 mM Tris
Acetate (pH 7.4 at 4 ꢁC)). Incubations were initiated
by the addition of tissue to 96-well plates containing test
drugs and radioligand (for CBR assays: 1.0 nM [3H]PK-
11195 (Perkin Elmer); for CBR assays: 1.0 nM [3H]Flu-
nitrazepam (Amersham); final volume of 250 ll).
Non-specific binding was determined by radioligand
binding in the presence of a saturating concentration
of PK-11195 (10 lM) for PBR assays or Ro-15-1788
(10 lM) for CBR assays. After an appropriate incuba-
tion period (for PBR assays: 2 h at room temperature;
CBR assays: 90 min at 4 ꢁC), assay samples were rapidly
filtered through Whatman GF/B filters (pre-soaked in
0.5% polyethylenimine and dried) and rinsed with ice-
cold 50 mM Tris buffer (pH 7.7 at 4 ꢁC). Membrane-
bound [3H]PK-11195 and [3H]Flunitrazepam levels were
determined by liquid scintillation counting of the filters
in BetaScint using a Beta-plate counter. The IC50 value
(concentration at which 50% inhibition of specific bind-
ing occurs) was calculated by linear regression of the
concentration-response data. Ki values were calculated
according to the Cheng–Prusoff equation, Ki = IC50/
(1 + (L/Kd)), where L is the concentration of the radioli-
gand used in the experiment and the Kd value is the dis-
sociation constant for the radioligand (determined
previously by saturation analysis).
4.1.3.19. N,N-Hexyl-2-(2-(6-fluoropyridin-3-yl)-1H-
indol-3-yl)-2-oxoacetamide
(26).
Oxalyl chloride
(95.3 mg, 0.75 mmol) was added dropwise, over 1.5 h, to
2-(6-fluoropyridin-3-yl)-1H-indole (100 mg, 0.47 mmol)
in THF (2 mL) at 0 ꢁC. Dihexylamine (742 mg, 4.0 mmol)
in THF (2 mL) was then added dropwise. After 2 h, the
mixture was evaporated. Purification by flash chromatog-
raphy on silica gel (hexane/EtOAc 80:20) yielded 26
(188 mg, 0.42 mmol, 88%) as a yellow oil. 1H NMR
(CDCl3) d 11.3 (br s, 1H), 8.06 (d, J = 2.3 Hz, 1H), 7.82
(d, J = 6.85 Hz, 1H), 7.15–7.05 (m, 4H), 6.24 (d,
J = 8.2 Hz, 1H), 3.13 (t, J = 7.6 Hz, 2H), 3.08 (t,
J = 7.8 Hz, 2H), 1.46–1.42 (m, 2H), 1.26–1.20 (m, 2H),
1.24–1.98 (m, 6H), 0.83 (t, J = 7.0 Hz, 3H), 0.70 (t,
J = 7.1 Hz, 3H). 13C NMR (CDCl3) d 186.0, 169.0,
164.8 (d, J = 243.1 Hz), 148.2 (d, J = 15.1 Hz), 142.8 (d,
J = 8.4 Hz), 136.3, 126.9, 125.2 (d, J = 4.7 Hz), 124.4,
123.6, 121.2, 112.8, 110.8, 109.2 (d, J = 37.5 Hz), 48.8,
45.5, 31.5, 31.4, 28.6, 27.5, 27.1, 26.7, 23.0, 22.7, 14.4,
14.2. Anal. (C27H34FN3O2) C, H, N.
Acknowledgments
4.1.3.20.
indol-3-yl)-2-oxoacetamide
N-Benzyl-2-(2-(6-fluoropyridin-3-yl)-1H-
(27). Oxalyl chloride
This work was supported in part by the National
Institutes of Health (MH67066), the Department of
Veterans Affair, and National Center for PTSD Alcohol
Research Center.
(95.3 mg, 0.75 mmol) was added dropwise, over 1.5 h,
to 2-(6-fluoropyridin-3-yl)-1H-indole (106 mg, 0.5 mmol)
in THF (2 mL) at 0 ꢁC. Benzylamine (428 mg, 4.0 mmol)
in THF (2 mL) was then added dropwise. After 2 h, the
mixture was evaporated. Purification by flash chroma-
tography on silica gel (hexane/EtOAc 60:40) yielded 27
Supplementary data
(107 mg, 0.29 mmol, 58%) as
a
yellow solid,
1
mp = 184 ꢁC. H NMR (DMSO-d6) d 12.57 (br s, 1H),
9.13 (t, J = 6.1 Hz, 1H), 8.46 (d, J = 2.3 Hz, 1H), 8.19
(dt, J = 8.3 Hz, J = 2.5 Hz, 1H), 8.01 (d, J = 7.9 Hz,
1H), 7.52 (d, J = 8.0 Hz, 1H), 7.40–7.20 (m, 8H), 4.08
(d, J = 6.0 Hz, 2H). 13C NMR (DMSO-d6) d 187.2,
166.8, 163.5 (d, J = 138.7 Hz), 148.3 (d, J = 15.6 Hz),
143.6 (d, J = 8.6 Hz), 142.9, 138.6, 136.3, 128.9, 128.7,
127.9, 127.4, 127.2, 126.4, (d, J = 4.1 Hz), 124.1, 122.9,
121.3, 112.5, 110.5, 109.3 (d, J = 37.7 Hz), 42.1, Anal.
(C22H16FN3O2) C, H, N.
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/
j.bmc.2006.07.001.
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