Sulfonate chalcone as new class voltage-dependent K+ channel blocker

Article abstract of DOI:10.1016/j.bmcl.2007.10.114

Chalcone derivatives 1-17 were synthesized and their voltage-dependent K⁺ channel inhibitory activities were investigated. The effective K⁺ channel blockers were shown to be sulfonate chalcones 9-17, in which the sulfonyloxy group is

Full text of DOI:10.1016/j.bmcl.2007.10.114

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Bioorganic & Medicinal Chemistry Letters 18 (2008) 137–140
Sulfonate chalcone as new class voltage-dependent
K+ channel blocker
Oleg V. Yarishkin,b Hyung Won Ryu,a Jae-Yong Park,b Min Suk Yang,a
Seong-Geun Hongb,* and Ki Hun Parka,*
aDivision of Applied Life Science (BK21 program), EB-NCRC, Institute of Agriculture & Life Science,
Gyeongsang National University, Jinju 660-701, Republic of Korea
bDepartment of Physiology, School of Medicine and Institute of Health Science, Gyeongsang National University,
Jinju 660-701, Republic of Korea
Received 20 August 2007; revised 10 October 2007; accepted 31 October 2007
Available online 4 November 2007
Abstract—Chalcone derivatives 1–17 were synthesized and their voltage-dependent K+ channel inhibitory activities were investi-
gated. The effective K+ channel blockers were shown to be sulfonate chalcones 9–17, in which the sulfonyloxy group is placed
on the A-ring. The 30-(p-aminobenzene-sulfonylhydroxy)-4-hydroxychalcone 17 (IC50 = 0.51 0.05 lM) was the most potent K+
channel blocker.
Ó 2007 Elsevier Ltd. All rights reserved.
Potassium ion channels play a peremptory role in a ser-
ies of cellular processes such as volume regulation, hor-
mone secretion, and electrical impulse formation.1 They
are grouped into three main families based on their
molecular structure: two transmembrane domains
(2TM), 4TM, and 6TM.2 Among them, the voltage-
gated Kv channels, which belong to the 6TM family, sta-
bilize the cell by effluxing K+ when opened by mem-
brane depolarization.3 Kv channels are normally of
importance in relaxing muscles, and preventing both
the heart and neurons from excessive excitation. Inap-
propriate opening and closure of the Kv channel directly
and rapidly lead to pathological conditions such as
hypertension, cardiac arrhythmia, and neural epilepsy.
Therefore, Kv channels have come to the fore of bio-
medical research as pharmacological tools and in poten-
tial therapeutic applications such as antihypertensives,4
antiarrhythmic drugs, and neuromodulators.5
have been developed, including peptidic toxins,7 bridged
bis-aminoquinolines,8 and benzopyran sulfon-amides.9
Recently, we found that sulfonate chalcones exhibit
the potential to act as a new class of voltage-dependent
K+ channel blockers, which can be obtained economi-
cally, using simple steps.
Chalcone is a biosynthetic product in shikimate pathway
and can be easily obtained through the Claisen-Schmidt
condensation of benzaldehyde and acetophenone using
either basic or acidic catalysis.10 Chalcone and its func-
tionalized derivatives have been shown to display
diverse medicinal properties including anti-inflamma-
tory,11 immunomodulatory,12 anticancer,13 anti-HIV,14
and a–glucosidase inhibitory activities.15
All chalcones were tested for their ability to block
delayed rectifying K+ currents in HEK293 cells, which
natively express five members of delayed rectifiers such
as Kv1.1, Kv1.2, Kv1.3, Kv1.6, and Kv3.1.16 By using
the patch clamp technique, we examined the blocking
potency of compounds for four kinds of delayed rectify-
ing K+ currents (except KV3.1) elicited by voltage steps
(200 ms duration) from ꢀ80 to +80 mV in 20 mV incre-
ments from a holding potential of ꢀ80 mV. All tests
were performed at room temperature.
Since apamin, the first naturally occurring, highly po-
tent, selective blocker of the SKCa channel, was discov-
ered,6 numerous ion channel blockers of various types
Keywords: Chalcone; Sulfonate chalcone; Potassium channel blocker;
K+ channel blocker; Ion channel.
*
Corresponding authors. Tel.: +82 55 751 5472; fax: +82 55 757 0178
(K.H.P.); tel.: +82 55 751 8740 (S.-G.H.); e-mail addresses:
hong149@gsnu.ac.kr; khpark@gsnu.ac.kr
All sulfonate chalcone products 9–17 were obtained
through sulfonation of hydroxyacetophenone with a
0960-894X/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2007.10.114

138
O. V. Yarishkin et al. / Bioorg. Med. Chem. Lett. 18 (2008) 137–140
O
O
O
O
S O
O
O
S O
O
O
S O
O
b
a
O2N
H2N
O2N
15
Scheme 1. Reagents and condition: (a) benzaldehyde, H2SO4, MeOH, reflux (93%); (b) Fe powder, AcOH, reflux (95%).
sulfonyl chloride derivative and an ensuing condensa-
tion of the sulfonated acetophenone and benzaldehyde
using a catalytic amount of H2SO4 in MeOH. Aminated
chalcones (14, 15, and 17) were obtained from reduction
of the corresponding nitro-substituted species using Fe
powder in the presence of acetic acid (Scheme 1). 16
was formed from reaction of 14 with AcCl (Fig. 1).
Unsubstituted chalcone 1 (Fig. 2) has been found by us
to exert an inhibitory effect on the outward delayed rec-
tifying K+ current in HEK 293 cells. At 10 lM this com-
pound inhibited the outward current carried by K+ by
24.2 3.1% (n = 5). This effect was partially reversible.
Chalcone 1 thus gave the first clue that this class of mol-
ecules could act as K+ channel blockers. However, we
were interested that the presence of OH substituents of
4 at the 4 and 40-positions led to a diminution
(28.2 1.6% of inhibition) in the activity observed. We
thus resolved to examine this structure activity relation-
ship further.
Figure 3. Summary for inhibitory effects of chalcone compounds
tested on KV current in HEK 293 cells. The ratios of currents recorded
with test compound (10 lM each) to those without a compound
(control) are shown as mean values SE with number of cells for the
relative current (%). Current size was measured at the end of the
+80 mV step pulse from the holding potential of ꢀ80 mV. All
compounds were applied to bath solution.
As shown in Figure 3 and Table 1, when the effect of sul-
fonation at hydroxyl groups in the 4 and 40-positions
was systematically examined, a dramatic increase in
potencies was only observed in the 40-sulfonated prod-
ucts (9–16). For example, relative to compound 1
(IC50 > 50 lM), a huge increase in inhibitory activity
was attained with 9 (IC50 2.4 0.4 lM). However, when
the effect of sulfonyl substitution on the B-ring was as-
sayed, 4-sulfonated products 5–6 proved actually to be
slightly less potent than chalcones 1–4, none of which
contained a sulfonyl function. When the effect of a hy-
droxy group on the B-ring was examined in non-aminat-
ed chalcones (10 vs 11), a significant decrease in potency
was observed: IC50 increased from 2.4 lM (OH) to
>10 lM (OCH3). However, when the hydroxy group
was deleted in the aminated analogues (14 vs 15), the po-
tency was marginally increased (IC50, 1.1 vs 0.85 lM).
These two results possibly suggest that a hydroxy group
in the B-ring is not essential as long as another acidic
O
O
S O
O
R1
R2
Figure 1. Sulfonate chalcone.
O
O
O
A
B
O
O S
O
O
S O
O
R1
R2
R1
R2
4
R1
R2
4'
1 R1 = H, R2 = H
5 R1 = H, R2 = H
6 R1 = H, R2 = CH3
7 R1 = H, R2 = F
9
R1 = H, R2 = OH
2 R1 = H, R2 = OH
3 R1 = OH, R2 = H
4 R1 = OH, R2 = OH
10 R1 = CH3, R2 = OH
11 R1 = CH3, R2 = OCH3
12 R1 = F, R2 = OH
8 R1 = OH, R2 = CH3
13 R1 = NO2, R2 = OH
14 R1 = NH2, R2 = OH
15 R1 = NH2, R2 = H
16 R1 = NHAc, R2 = OH
O
S O
O
O
3'
H2N
OH
17
Figure 2. Target chalcones for K+ channel blocker.

O. V. Yarishkin et al. / Bioorg. Med. Chem. Lett. 18 (2008) 137–140
Table 1. Inhibitory activities of chalcone derivatives
139
Compound
Inhibition IC50, lMa
1
>50
>50
2
3
>50
>50
4
5
>50
>50
6
7
>50
>50
8
9
2.4 ( 0.4)
1.6 ( 0.4)
>10
10
11
12
13
14
15
16
17
2.7 ( 0.4)
10.7 ( 1.9)
1.1 ( 0.1)
0.85 ( 0.04)
>10
Figure 4. Dose-response curve for inhibitory effect of 13 (circles) and
14 (triangles) on the delayed rectifier K+ current. Values are
means SE from the data of 3–7 cells and fitted with logistic function
0.51 ( 0.05)
a Values are means of three experiments, standard deviation is given in
parentheses.
for calculating IC50
.
proton remains in the molecule. These results in total
suggest that a sulfonate function in the A-ring of the
chalcone is a key structural requirement for blocking
KV channels. The activity of sulfonate chalcones was af-
fected by subtle changes in functionality. When the effect
of differing substituents on the phenyl ring within the A-
sulfonyloxy group (9–17) was compared, the following
potency hierarchy was noted: NH2 (14, IC50 = 1.1
0.1 lM) > CH3 (10, IC50 = 1.6 0.4 lM) > H (9,
IC50 = 2.4 0.4 lM) > F (12, IC50 = 2.7 0.4 lM) >
NO2 (13, IC50 = 10.7 1.9 lM). The amino group obvi-
ously transpired to be the most favorable substituent for
K+ channel blocking activity. This trend is directly
linked to the electron releasing effect of the substituent.
To further validate this pattern, N-acyl equivalent 16,
with drastically reduced electron releasing capacity,
was shown to be of low potency. Interestingly, chalcone
17, the 30 regioisomer of chalcone 14, was shown to be
approximately 2 times more effective than 14 (in lM,
0.51 0.05 vs 1.1 0.1).
Figure 5. Inhibition property of compound 17 on four KV currents.
(A) Representative traces of KV1.1 current before (left) and after
application of 10 lM compound 17 (right). (B) Progressive inhibition
of KV1.1 currents with time after adding 10 lM compound 17. Note
that decay phase accelerated with time lapse as shown in the right (in
min). This was taken from the currents observed in KV1.1-overex-
pressed CHO cells. (C) Summary for the suppressive effect of
compound 17 on KV1.1, KV1.2, KV1.3, and KV1.6 currents overex-
pressed in CHO cells. Relative inhibition was obtained as described in
Figure 3. Scale bars are equal to 1 nA and 100 ms. Asterisks (*) are
differences from control (p < 0.05). Number of cells is shown in
brackets.
All sulfonate chalcones dose-dependently reduced the
delayed rectifying K+ current (Fig. 4). To have more
convincing evidence that the sulfonate chalcones inhibit
delayed rectifier K+ channels, the blocking potency of
sulfonate chalcone 17 was assayed on KV1.1, KV1.2,
KV1.3, and KV1.6 overexpressed in CHO cells, which
do not express any endogenous KV channels.17,18
(ss). Compound 17 inhibited this current by accelerating
both phases of sr from 26.64 10.77 ms to
7.20 1.02 ms and ss from 457.06 76.34 ms to
42.57 5.94 ms, respectively, at 80 mV (n = 3, see
Fig. 5C). The inhibition was progressively intensified
and reached its maximum after ꢁ5 min (Fig. 5B), which
is consistent with that of khellinone chalcones19 and
cyclohexyl-substituted benzamides20 on KV1.X-induced
currents, even though there are differences among them
in specificity and potency for KV family.
Among the delayed rectifier K+ currents examined, KV1.1
and KV1.2 were inhibited more potently than KV1.3 and
KV1.6. As shown in Figure 5C, compound 17 (10 lM)
inhibited KV1.1 and KV1.2 currents by 87.53 3.98%
(n = 7) and 87.39 4.97% (n = 5), whereas KV1.3 and
KV1.6 were done by 20.6 3.54% (n = 5) and
44.23 5.74% (n = 6), respectively (see also sppl. figure).
These suppressions were due to enhancement in the decay
of currents, which was profound in KV1.1-mediated cur-
rents in CHO cells (Fig. 5). Overexpressed in CHO cells,
KV1.1 current was relaxed so that its decay could be fitted
with two phases, of the rapid phase (sr) and of slow phase
Characterized by acceleration of the decay phase and
progressive reduction of the current size, this kind of
inhibition may be caused by either blocking open pore
or modification of gating process in the KV channel.
More preference of compound 17 on KV1.1 and KV1.2 is
of interest in view of probable therapeutic effects for

140
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Acknowledgments
This work was financially supported by the MOST/KO-
SEF to the Environmental Biotechnology National
Core Research Center (Grant R15-2003-012-02001-0),
Korea. Oleg V. Yarishkin was supported by Korea Re-
search Foundation Grant (KRF-2004-005-E00008).
Also, Hyung Won Ryu is the recipient of a BK21 fellow-
ship from the Ministry of Education.
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