(S,E)-N-[1-(3-Heteroarylphenyl)ethyl]-3-(2-fluorophenyl)acrylamides: Synthesis and KCNQ2 potassium channel opener activity

Article abstract of DOI:10.1016/j.bmcl.2004.10.065

The synthesis and the KCNQ2 opener activity of a novel series of acrylamides are described. Replacement of the morpholinyl moiety in (S,E)-N-[1-(3-morpholinophenyl)ethyl]-3-phenylacrylamide (1) with heteroaryl groups led to the identification of (S,E)-N-1

Full text of DOI:10.1016/j.bmcl.2004.10.065

Bioorganic & Medicinal Chemistry Letters 15 (2005) 363–366
(S,E)-N-[1-(3-Heteroarylphenyl)ethyl]-3-(2-fluorophenyl)-
acrylamides: synthesis and KCNQ2 potassium
channel opener activity
Alexandre LꢀHeureux,a Alain Martel,a Huan He,b Jie Chen,b Li-Qiang Sun,b
John E. Starrett, Jr.,b Joanne Natale,c Steven I. Dworetzky,c Ronald J. Knox,d
David G. Harden,d David Weaver,d Mark W. Thompsond and Yong-Jin Wub,*
aDepartment of Medicinal Chemistry, Bristol-Myers Squibb Pharmaceutical Research Institute, 100 de l’Industrie Blvd.,
Candiac, Quebec, Canada, J5R 1J1
bDepartment of Neuroscience Chemistry, Bristol-Myers Squibb Pharmaceutical Research Institute, 5 Research Parkway,
Wallingford, CT 06492, USA
cDepartment of Neuroscience Biology, Bristol-Myers Squibb Pharmaceutical Research Institute, 5 Research Parkway,
Wallingford, CT 06492, USA
dDepartment of New Leads Biology, Bristol-Myers Squibb Pharmaceutical Research Institute, 5 Research Parkway,
Wallingford, CT 06492, USA
Received 24 September 2004; revised 20 October 2004; accepted 21 October 2004
Available online 11 November 2004
Abstract—Replacement of the morpholinyl moiety in (S,E)-N-[1-(3-morpholinophenyl)ethyl]-3-phenylacrylamide (1) with heteroar-
yl groups led to the identification of (S,E)-N-1-[3-(6-fluoropyridin-3-yl)phenyl]ethyl-3-(2-fluorophenyl)acrylamide (5) as a potent
KCNQ2 potassium channel opener. Among this series of heteroaryl substituted acrylamides, (S,E)-N-1-[3-(1H-pyrazol-1-yl)phen-
yl]ethyl-3-(2-fluorophenyl)acrylamide (9) exhibits balanced potency and efficacy. The syntheses and the KCNQ2 opener activity
of this series of acrylamides are described.
Ó 2004 Elsevier Ltd. All rights reserved.
1. Introduction
threshold, firing properties, and responsiveness of neu-
rons to synaptic inputs.
The identification of the KCNQ (K = potassium,
CN = channel, Q = long QT designation) channel family
was part of the surge in potassium channel cloning activ-
ity over the past decade that resulted in the discovery of
more than 70 potassium channel genes.1 In a landmark
study, Wang et al. identified the combination of
KCNQ2 with KCNQ3 as the underlying molecular com-
ponents of the M-channel.2 Additional studies suggest
that other KCNQ components can contribute to differ-
ent M-currents within the brain.3 The M-currents have
been shown to play a critical role in regulating neuronal
excitability as they determine, in part, the excitability
Without knowing the molecular components of the M-
current, two modulators of this current have been under
clinical investigation: the blocker linopirdine4 for cogni-
tion enhancement and the opener retigabine5 (Fig. 1) for
epilepsy. Retigabine was not known to be an opener of
the KCNQ channels at the time of development but was
known to increase potassium currents.
Over the past several years, we have seen the emergence
of novel molecules known as KCNQ openers (activa-
tors), such as benzanilides (e.g., ICA-D1, structure not
disclosed)6 and acrylamides (e.g., 1, Fig. 1).7,8 These
compounds have shown potential for the treatment of
CNS disorders characterized by hyperexcitability, such
as migraine, epilepsy, bipolar disorder, and neuropathic
pain.
Keywords: Acrylamides; KCNQ2.
*
Corresponding author. Tel.: +1 203 677 7485; fax: +1 203 677
7702; e-mail: yong-jin.wu@bms.com
0960-894X/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2004.10.065

364
A. L’Heureux et al. / Bioorg. Med. Chem. Lett. 15 (2005) 363–366
N
F
O
Me
Me
O
Me
Me
F
N
a,b
Br
N
H
BocHN
H2N
CO2Et
HN
1
11
12
F
O
N
F
H2N
N
H
F
O
Me
N
O
c
N
H
retigabine
N
H
2
5
Cl
F
O
Me
Me
Scheme 1. Reagents and conditions: (a) (6-fluoropyridin-3-yl)boronic
acid, Pd(PPh3)4, Cs2CO3, ethylene glycol dimethyl ether, sealed tube,
100°C, 18h, 85%; (b) TFA, CH2Cl2, 100%; (c) 2-fluorocinnamic acid,
EDACÆHCl, DIPEA, HOBT, DMF, 52%.
O
O
N
H
3
O
Het
N
H
Me
Me
N
4
a
B(OH)2
b,c
HN
Boc
11
H2N
Figure 1.
13
14
F
O
Me
N
As part of our continuous efforts toward the identifica-
tion of KCNQ2 openers with improved potency over
retigabine and acrylamide 1, we identified (S,E)-N-[1-
(4-cyclopropylmethyl-3,4-dihydro-2H-benzo[1,4]oxazin-
6-yl)ethyl]-3-(2-fluorophenyl)acrylamide (2) as a potent
and efficacious KCNQ2 opener.9 This compound was
effective in reducing neuronal hyperexcitability in rat
hippocampal slices, and the inhibition mediated by 2
was reversed by the KCNQ blocker linopirdine.
Subsequent SAR studies culminated in the discovery
of (S,E)-N-(1-(benzo[d][1,3]dioxol-5-yl)ethyl)-3-(2-chlo-
rophenyl)acrylamide (3) as a potent KCNQ2 opener.10
Prompted by the potency of 2 and 3 in augmenting
KCNQ2 channels, we explored the replacement of the
morpholinyl moiety of 1 with various heteroaryl
groups. We have previously shown that 2-fluoro
substitution of the styrene phenyl generally increases
the potency and yet maintains the physical properties
of nonfluorinated acrylamides. Therefore, our prelimi-
nary studies were directed at 2-fluoro heteroaryl
substituted analogs with structure 4. Herein, we wish
to report the synthesis and KCNQ2 opener activity of
this series of 2-fluorophenylheteroaryl substituted
acrylamides.
d
N
H
6
Scheme 2. Reagents and conditions: (a) MeLi; t-BuLi, B(OMe)3,
NH4Cl, 61%; (b) 2-bromopyridine, Pd(PPh3)4, Cs2CO3, ethylene glycol
dimethyl ether, sealed tube, 100°C, 18h, 30%; (c) TFA, CH2Cl2, 100%;
(d) 2-fluorocinnamic acid, EDACÆHCl, DIPEA, HOBT, DMF, 58%.
Me
N
a, b
c
N
13
H2N
O
15
Me
F
N
N
N
H
7
Scheme 3. Reagents and conditions: (a) 2-chloropyrazine, Pd(PPh3)4,
Cs2 CO3, ethylene glycol dimethyl ether, sealed tube, 100°C, 18h, 57%;
(b) TFA, CH2Cl2, 100%; (c) 2-fluorocinnamic acid, EDACHCl,
DIPEA, HOBT, DMF, 40%.
2. Chemistry
Acrylamides 5–10 for this study were prepared accord-
ing to Schemes 1–5. The synthesis of acrylamide 5
started with (S )-tert-butyl 1-(3-bromophenyl)ethyl-carb-
amate (11),8 which was prepared from the commercially
available (S)-1-(3-bromophenyl)ethylamine (Scheme 1).
Palladium-catalyzed Suzuki coupling reaction of 11 with
(6-fluoropyridin-3-yl)boronic acid provided 3-phenylpy-
ridine 12, after deprotection of the NH–Boc group.
Compound 12 was coupled with 2-fluorocinnamic
acid in the presence of 1-(3-dimethylaminopropyl)-
Me
N
N
F
O
Me
N
N
N
N
a
H2N
N
H
8
16
Scheme 4. Reagents and conditions: (a) 2-fluorocinnamic acid,
EDACÆHCl, DIPEA, HOBT, DMF, 43%.
3-ethylcarbodiimide
hydrochloride
(EDACÆHCl),

A. L’Heureux et al. / Bioorg. Med. Chem. Lett. 15 (2005) 363–366
365
Table 1. Whole cell patch-clamping data (À40mV)
Compd
Me
N
N
X
O
Me
N
N
EC50 (lM)a
E/Eref
1.4 0.1
a,b
a
H2N
N
H
1
3.2 0.6
0.06 0.01
0.020 0.001
0.010 0.001
1.20 0.03
0.37 0.06
0.33 0.01
0.12 0.02
1.20 0.05
1.30 0.04
2
1.83 0.02
1.1 0.1
9: X = F
10: X = H
17
3
5
0.85+0.01
1.8 0.1
6
Scheme 5. Reagents and conditions: (a) EDACÆHCl, DIPEA, HOBT,
DMF, 2-fluorocinnamic acid, 49% (9) or cinnamic acid, 58% (10).
7
1.57 0.10
1.20 0.01
1.60 0.04
1.9 0.2
8
9
10
Retigabine
1.60 0.05
1-hydroxybenzotrazole (HOBT) and diisopropylethyl-
amine (DIPEA) to furnish acrylamide 5.
a These values are the mean SEM (n = 2–5).
b The efficacy of the test compound relative to ( )-3.10
The synthesis of acrylamide 6 is shown in Scheme 2.
Deprotonation of the NH–Boc hydrogen of bromide
11 with 1equiv methyllithum, halogen lithium exchange
with 2equiv t-butyllithium, and quenching of the result-
ing phenyllithium with trimethyl borate, followed by
hydrolysis, provided the boronic acid 13 (Scheme 2).
This acid was coupled with 2-bromopyridine to afford
2-phenylpyridine 14, after deprotection of the NH–Boc
group. Compound 6 was obtained from 14 via coupling
with 2-fluorocinnamic acid.
efficacies of test compounds were normalized to the effi-
cacy of ( )-3 (reference compound) (Fig. 1)10 to yield an
E/Eref ratio (Table 1). The ratio was calculated by divid-
ing the maximum current amplitude produced by the
test compound by the maximum current amplitude pro-
duced by the reference compound. Compounds which
provide a higher E/Eref ratio are more efficacious
KCNQ2 channel openers.
Acrylamide 7 was prepared from boronic acid 13 in the
same fashion as 6 with the exception that 2-chloropyr-
azine was used in the Suzuki coupling reaction instead
of 2-bromopyridine (Scheme 3).
Among this series of heteroaryl substituted acrylamides,
the 6-fluoro-3-pyridyl analog 5 was the most potent
(EC50: 10nM), but least efficacious opener of KCNQ2
channels, while the 2-pyridyl counterpart 6 exhibited
the lowest potency (EC50: 1.2lM), but highest efficacy
(E/Eref: 1.8). As shown in Table 1, compound 5 has im-
proved potency over 2 and 3 by approximately 6- and 2-
fold, respectively, and it is the most potent KCNQ2
opener that we have identified to date.
Acrylamide 8 was prepared through the coupling reac-
tion of (S)-1-(3-[1,2,4]triazol-1-yl-phenyl)ethylamine
(16) with 2-fluorocinnamic acid (Scheme 4). Amine 16
was obtained in 96% yield using the copper-catalyzed
N-arylation of 1,2,4-triazole with (S)-1-(3-bromophen-
yl)ethylamine under microwave conditions recently re-
ported from this laboratory.11
It is important to note that the pyrazole analog 9 was
approximately 3-fold more potent and also 33% more
efficacious than the corresponding triazole derivative 8
in augmenting mKCNQ2 currents. Because of its
balanced potency and efficacy, acrylamide 9 warrants
further investigation. Consistent with our prior
observation on acrylamides that 2-fluoro substitution
of the styrene phenyl generally increased the
potency of acrylamides, the fluoro pyrazole analog 9
was 10-fold more potent than the unsubstituted
counterpart 10.
Acrylamides 9 and 10 were prepared through the cou-
pling reaction of (S)-1-(3-pyrazol-1-yl-phenyl)ethyl-
amine (17)11 with 2-fluorocinnamic acid and cinnamic
acid, respectively (Scheme 5).
3. Results and discussion
The effects of test compounds on outward potassium
currents were determined using the whole-cell patch-
clamp recordings from HEK 293 cells stably expressing
cloned mouse (m) KCNQ2 channels as described previ-
ously.7 Baseline currents were evoked by stepping from
À80mV holding potential to À40mV. Compounds were
rapidly applied to cells by local superfusion, and channel
opening efficacy was determined from the concentration
dependent increase in the baseline current measured
prior to compound addition. Compound effects were ex-
pressed as the percent of compound free control current
using current responses measured at À40mV. The data
at À40mV were used for preliminary structure activity
relationship studies as this membrane potential is most
likely related to physiological conditions. The EC50’s
shown in Table 1 were calculated from the concentra-
tion response relationship of the test compounds. The
Preliminary studies using thallium(I) influx assay12
showed that this series of acrylamides, like other mem-
bers of acrylamides reported previously from this labo-
ratory,8 also activated other members of the KCNQ
family. Further electrophysiological characterization is
required in order to understand the activation of other
KCNQ channels.
4. Conclusion
Compound 5 was identified as a potent KCNQ2 opener.
The pyrazole analog 9 displayed balanced potency and
efficacy and thus deserves further evaluation. Both com-
pounds, along with 2 and 3, are expected to be valuable
tools in further studying the pharmacology of KCNQ2

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A. L’Heureux et al. / Bioorg. Med. Chem. Lett. 15 (2005) 363–366
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and possibly other KCNQ channels as well as decipher-
ing the correlation between KCNQ opening activity and
the efficacy observed in animal models of CNS disorders
associated with neuronal excitability.
7. Wu, Y.-J.; Boissard, C. G.; Greco, C.; Gribkoff, V. K.;
Harden, D. G.; He, H.; LꢀHeureux, A.; Kang, S. H.;
Kinney, G. G.; Knox, R. J.; Natale, J.; Newton, A. E.;
Lehtinen-Oboma, S.; Sinz, M. W.; Sivarao, D. V.;
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son, W. P.; Weaver, D.; Wong, H. S.; Zhang, L.;
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Q.; Gribkoff, V. K.; Harden, D. G.; He, H.; Knox, R. J.;
Natale, J.; Pieschl, R. L.; Starrett, J. E., Jr.; Sun, L.-Q.;
Thompson, M. W.; Weaver, D.; Wu, D.; Dworetzky, S. I.
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