Lactam sulfonamides as potent inhibitors of the Kv1.5 potassium ion channel

Article abstract of DOI:10.1016/j.bmcl.2014.01.067

A series of lactam sulfonamides has been discovered and optimized as inhibitors of the Kv1.5 potassium ion channel for treatment of atrial fibrillation. In vitro structure-activity relationships from lead structure C to optimized structure 3y are described. Compound 3y was evaluated in a rabbit PD-model and was found to selectively prolong the atrial effective refractory period at submicromolar concentrations.

Full text of DOI:10.1016/j.bmcl.2014.01.067

Bioorganic & Medicinal Chemistry Letters 24 (2014) 1269–1273
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Lactam sulfonamides as potent inhibitors of the Kv1.5 potassium ion
channel
b
b
b
b
Roine I. Olsson a, , Ingemar Jacobson , Tommy Iliefski , Jonas Boström , Öjvind Davidsson ,
Ola Fjellström b, Annika Björe b, Christina Olsson b, Johan Sundell b, Ulrik Gran b, Jonna Gyll b,
Jesper Malmberg a, Olle Hidestål b, Hans Emtenäs b, Tor Svensson a, Zhong-Qing Yuan b,
Gert Strandlund b, Annika Åstrand a, Emma Lindhardt b, Gunilla Linhardt b, Elin Forsström b,
Ågot Högberg b, Frida Persson b, Birgit Andersson b, Anna Rönnborg b, Boel Löfberg b
⇑
a Respiratory, Inflammation & Autoimmunity iMed, AstraZeneca R&D Mölndal, SE-431 83 Mölndal, Sweden
b Cardiovascular & Metabolic Diseases iMed, AstraZeneca R&D Mölndal, SE-431 83 Mölndal, Sweden
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of lactam sulfonamides has been discovered and optimized as inhibitors of the Kv1.5 potassium
ion channel for treatment of atrial fibrillation. In vitro structure–activity relationships from lead structure
C to optimized structure 3y are described. Compound 3y was evaluated in a rabbit PD-model and was
found to selectively prolong the atrial effective refractory period at submicromolar concentrations.
Ó 2014 Elsevier Ltd. All rights reserved.
Received 5 December 2013
Revised 20 January 2014
Accepted 22 January 2014
Available online 30 January 2014
Keywords:
Atrial fibrillation
Kv1.5
IKur
Lactams
Sulfonamides
Atrial fibrillation (AF) is the most common cardiac arrhythmia
and patients suffering from AF generally have a reduced quality
of life with lower cardiac output and impaired ability to work
and exercise. AF patients also have an increased risk of stroke
and other cardiovascular diseases.1,2 Patients with AF commonly
need hospitalization, representing a considerable economic burden
to society. Several drug treatment options exist but they suffer
from poor efficacy or adverse effects that limit their use. Drugs that
inhibit the IKr (hERG) current may affect the ventricle repolariza-
tion and cause QT prolongation and life-threatening proarrhyth-
mias, such as Torsades de Pointes.3
Since a large unmet medical need still exists for AF patients, the
search for new treatments and new drugs continue. Kv1.5 is a volt-
age gated potassium ion channel conducting the ultra rapidly
activating delayed rectifier K+ current (IKur) and has received
attention since the channel protein is predominantly expressed
in the human atria. Blocking IKur has the potential to selectively
prolong atrium effective refractory period (ERP) over ventricular
ERP and reduce the risk of ventricular proarrhythmias. A number
of publications have summarized research around Kv1.5.4–9
However, whilst a block of IKur in animal models of AF has
been demonstrated to prolong the atrial refractory period,
one recent study has shown that this does not readily translate
into effects on human atrial refractory period in healthy volun-
teers.10 A number of factors such as high vagal tone in healthy
volunteers10 and lack of electrical remodeling11 could explain this
lack of effect. Ultimately, the final proof of whether or not Kv1.5 is
a suitable target for AF treatment will come from clinical studies in
AF patients.
In the presentpaper we describe the synthesis and evaluationof a
series of lactam sulfonamides with the aim to find a potent and hERG
selective inhibitor of Kv1.5. The start point of the program was
anthranilic amide A (Fig. 1), an inhibitor described in the early
literature with a Kv1.5 IC50 potency of 0.6 l
M.12 Using compound
A as a reference for automated shape-based molecular alignment
of single compounds,13–15 compound B (Fig. 1) was identified as an
interesting candidate for synthesis. Towards this goal, a direct ben-
zylation of N-(2-hydroxycyclohexyl)-4-methoxybenzene-sulfon-
amide failed, instead affording compound C (Fig. 1), as a racemate.
As an alternative, a literature synthetic method was adapted to
enable successful preparation of racemic B.16
⇑
Corresponding author. Tel.: +46 317065581.
E-mail address: Roine.I.Olsson@AstraZeneca.com (R.I. Olsson).
http://dx.doi.org/10.1016/j.bmcl.2014.01.067
0960-894X/Ó 2014 Elsevier Ltd. All rights reserved.

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R. I. Olsson et al. / Bioorg. Med. Chem. Lett. 24 (2014) 1269–1273
Table 1
O
Potency and lipophilicity of compounds 3a–3d
N
H
No. Structure
Kv1.5a
LogDb
O
HN
S
O
O
H2N
N
S
3ac
2.2
3.4
A
O
O
F
F
O
O
HO
N
S
HN
S
N
S
O
O
O
O
O
O
O
F
F
3bc
4.8
2.0
6.2
4.7
F
B
C
N
N
S
O
O
O
Figure 1. Structures of compounds A, B and C.
3c
Preliminary testing of both B and C against Kv1.5, using a Rb+-
efflux assay,17 showed that B had a blocking potency of 28
M,
whereas C had a blocking potency of 2 M. These results made
us choose the tertiary sulfonamide C as lead structure and a syn-
thetic program was started to explore structure–activity relation-
ship (SAR) around C.
l
F
l
H
N
N
O
O
O
S
F
3d
4.1
3.0
Different routes for synthesis of analogues to compound C are
shown in Scheme 1. Sulfonyl chloride 1 was reacted with the
appropriate primary amine under basic conditions. The formed
secondary sulfonamide 2 was then alkylated with the appropriate
alkyl halide under basic conditions to give the desired compound C
analogue 3. Alternatively, sulfonamide 3 was synthesized by react-
ing primary amine 4 under basic alkylation or reductive amination
conditions. The formed secondary amine 5 was then reacted with
the appropriate sulfonyl chloride under basic conditions to give 3.
The ion channel-blocking potency of synthesized compounds
on the Kv1.5 channel was assessed in a CHO cell line stably
expressing the human cardiac ion channel Kv1.5. Electrophysiolog-
ical studies were performed using a high throughput planar patch
clamp assay and standard extra- and intracellular solutions.18,19
Seven different concentrations of each compound were run in trip-
licates in the same plate to give the dose-response data from which
the IC50 value was determined.20 Human hERG channel blocking
potency was similarly assessed on selected compounds and most
F
a
b
c
IC50 values in
l
M.
Chromatographic lipophilicity.
Synthesized using routes c and d.
structure. The SAR of a first set of compounds is shown in Table 1.
Anilinic groups, like p-benzamide (3a) were found to be active but
anilinic fragments may pose a mutagenic risk.22 A benzyl group
(3b) was tolerated but gave a high lipophilicity. Replacing the ben-
zyl group with a (pyridin-2-yl)methyl group (3c) gave a slightly
higher activity with reduced lipophilicity. A (S)-(5-oxopyrrolidin-
2-yl)methyl ((S)-lactam) group (3d) was found to be active with
a LogD value of 3.0.
Compound 3d had the lowest lipophilicity and was most suit-
able for further optimization and we proceeded to explore varia-
tions in the benzene sulfone part of the molecule, as shown in
Table 2. An unsubstituted benzene sulfone ring (3e) gave a slight
drop in potency compared to compound 3d. A m-fluoro substituent
(3f) gave a similar potency as an unsubstituted ring, but a m-chloro
substituent (3g) gave a marked increase in potency. 3,5-Dichloro
substitution (3h) did not help to improve potency further but in-
stead gave a similar potency as the unsubstituted ring. Glutathione
trapping experiments in human liver microsomes23 also showed
that fluorine and possibly chlorine substitution on the benzene sul-
fone ring gave rise to reactive metabolites and we wished to avoid
these going forward.
tested compounds had IC50 values above 20 lM.
The lipophilicity of synthesized compounds was monitored
since the lead compound C possesses a high measured chromato-
graphic LogD21 of 4.6, deemed a potential weakness and source
of metabolic lability.
Compound C was also a racemate and trying to move away from
stereoisomeric compounds we varied the cyclohexanol part of the
Cl
O
O
R2
S
1
4
H2N
R1
A m-methoxy group (3i) was found active but linking the para
and meta positions together in a six membered ring gave an
inactive compound (3j). A m-methylsulfone group (3k) showed low-
er activity and a low lipophilicity. m-Cyano substitution (3l) gave an
active compound with a LogD value of 2.7. Varying the position of
the cyano group on the benzene sulfone ring showed that both p-cy-
ano (3m) and o-cyano (3n) substituted compounds were inactive.
Compound 3l showed a suitable combination of potency and
low lipophilicity and was used to further explore SAR around the
(S)-lactam, as shown in Table 3. Inversion of the stereochemistry
a
c
R2
O
R3
O
R2
O
R3
R2
HN
N
S
R1
d
b
N
O
H
S
2
3
5
R1
Scheme 1. Reagents and conditions: (a) R2NH2, NEt3, DCM, 20 °C, 18 h, 49–98%; (b)
R3X, K2CO3, MeCN, 80 °C, 18 h, 2–73%; (c) R3X, NEt3, DCM, 20 °C, 18 h, 49–69%, or
R3=O, NaBH(OAc)3, DCE, 18 h, 64–100%; (d) R1SO2Cl, NEt3, DCM, 2 h, or R1SO2Cl,
NaHCO3, MeCN, 18 h, 7–86%.

R. I. Olsson et al. / Bioorg. Med. Chem. Lett. 24 (2014) 1269–1273
1271
Table 2
Table 2 (continued)
Potency and lipophilicity of compounds 3e–3n
No.
Structure
Kv1.5a
>30
LogDb
No.
Structure
Kv1.5a
8.8
LogDb
H
N
H
N
N
S
O
O
O
N
S
O
O
O
O
O
F
3n
2.5
N
3ec
2.7
F
a
b
c
IC50 values in
Chromatographic lipophilicity.
Synthesized using routes c and d.
lM.
H
N
N
S
O
F
3f
7.2
0.8
8.1
2.0
3.1
3.6
4.4
3.1
Table 3
F
Potency and lipophilicity of compounds 3o–3s
H
N
No.
Structure
Kv1.5a
LogDb
N
S
O
O
O
O
O
O
O
O
O
H
N
3gc
3hc
3ic
F
F
F
F
N
S
O
O
O
F
3oc
8.7
2.5
Cl
Cl
O
H
N
N
S
O
N
H
O
N
N
S
O
O
F
Cl
3p
7.6
2.7
2.9
2.9
H
N
N
S
O
O
N
H
N
N
S
O
O
O
F
3qc
H
N
N
S
N
3j
>10
3.0
N
N
S
O
O
O
O
O
F
3rc
0.81
3.1
H
N
N
S
O
O
O
N
F
3k
8.7
2.0
N
N
S
O
S
O
O
O
O
3sc
2.8
3.5
F
H
N
N
S
O
O
O
O
F
N
3lc
2.6
2.7
a
b
c
IC50 values in
Chromatographic lipophilicity.
Synthesized using routes c and d.
l
M.
N
H
N
N
S
of the (S)-lactam to (R)-configuration (3o) gave a drop in potency.
Expanding the (S)-lactam to a six membered ring (3p) gave a lower
potency. Extending the one-carbon linker of the (S)-lactam to a
two-carbon linker24 gave an equipotent compound (3q). Methyla-
tion of the (S)-lactam nitrogen (3r), using a literature method,25
gave a 3-fold increase in potency whereas ethylation (3s) gave a
similar potency as the unsubstituted nitrogen.
O
O
F
3mc
>30
2.6
N
The SAR of the benzyl part of compound 3l was further explored
in a final optimization, as shown in Table 4. Extending the

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R. I. Olsson et al. / Bioorg. Med. Chem. Lett. 24 (2014) 1269–1273
Table 4
Table 5
Potency and lipophilicity of compounds 3t–3y
Selected PK-parameters of 3y in rat and dog
No.
Structure
Kv1.5a
>10
LogDb
Rata
45
0.53
45
Dogb
CL (mL/min/kg)
t1/2 (h)
F (%)
31
0.87
44
H
N
N
S
O
O
O
O
O
O
O
a
3t
2.9
Sprague Dawley, dosed at 2
Beagle, dosed at 1
l
mol/kg iv and 6
mol/kg iv and 2 mol/kg p.o.
lmol/kg p.o.
F
b
l
l
N
N
H
N
Table 6
N
S
O
Selected in vitro and in vivo PD data of 3y in human and rabbit
Cl
3uc
2.2
4.3
3.1
Measure
3y
Rabbit atrium ERP Ceu20
Human Kv1.5 IC50
Human hERG IC50
(l
M)
0.35
0.21
30
(
(
l
M)
l
M)
Rabbit QT-interval (ms)
<10
H
N
Cl
N
S
O
3v
3
the unbound steady-state plasma concentration (Ceu20) giving a
20% change in the atrium ERP. The maximum observed change in
the QT-interval during the drug exposure period was also modeled
to give a measure of the effects on ventricular repolarization.
Compound 3y caused a marked increase in the atrium ERP with
N
Cl
H
N
N
S
O
a Ceu20 of 0.35
as the IC50 value from the human cellular assay. The human hERG
channel was blocked by compound 3y with an IC50 value of 30 M,
lM (Table 6), that is, at the same order of magnitude
O
O
3x
>10
2.7
l
indicating a 140-fold margin of the hERG and Kv1.5 in vitro values.
No measurable change was noted in the QT-interval in the rabbit
experiments, which also indicates a good margin to block of the
hERG channel. The compound was well tolerated in rabbits with
no signs of the CNS-like side effects observed for other Kv1.5 block-
ers.28 No other compound in the series was tested in the rabbit
model.
N
N
O
N
S
O
O
Cl
3y
0.21
3.6
Overall, compound 3y was judged to have too short half-life to
be selected as a clinical candidate but was used as a tool compound
for further pharmacological evaluation, which will be reported in a
future publication.
In conclusion, we have discovered a series of lactam sulfona-
mides that are potent inhibitors of the Kv1.5 channel. The opti-
mized compound 3y was evaluated in a rabbit PD model and
showed a marked prolongation of ERP in the atrium at submicrom-
olar concentrations.
N
a
b
c
IC50 values in
Chromatographic lipophilicity.
Synthesized using routes c and d.
lM.
p-fluorobenzyl group of 3l to a p-fluorophenethyl group gave an
inactive compound (3t). A p-chlorobenzyl group (3u) was toler-
ated, whereas m-chloro substitution (3v) reduced potency and o-
chloro substitution (3x) gave an inactive compound. Methylation
of the (S)-lactam nitrogen was earlier found to increase potency
in the series (compound 3l vs 3r). Applying the same strategy to
compound 3u, yielding compound 3y, was found to give a 10-fold
increase in potency. Overall, compound 3y was found to be the
most potent compound in the series and was selected for pharma-
cokinetic (PK) and pharmacodynamic (PD) evaluations.
Acknowledgments
We thank the Separation Science group at AstraZeneca Mölndal
for help with compound purification. We also thank Mark Furber
for useful comments concerning this manuscript.
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