3-Substituted-(5-arylfuran-2-ylcarbonyl)guanidines as NHE-1 inhibitors

Article abstract of DOI:10.1016/j.bmcl.2006.12.012

The C-3 substituents effect on NHE-1 inhibitory activity of (5-arylfuran-2-ylcarbonyl)guanidines, previously identified as potent NHE-1 inhibitors, was investigated. The introduction of amine or alkyl groups at the 3-position of the furan ring, next to the acylguanidine moiety, remarkably improves NHE-1 inhibitory potency. Especially the important finding is that 5-(2,5-dichloro)phenyl and 5-(2-methoxy-5-chloro)phenyl derivatives exhibit high NHE-1 inhibitory activities (IC₅₀ < 0.02 μM) that match those of 3-unsubstituted derivatives.

Full text of DOI:10.1016/j.bmcl.2006.12.012

Bioorganic & Medicinal Chemistry Letters 17 (2007) 1291–1295
3-Substituted-(5-arylfuran-2-ylcarbonyl)guanidines as
NHE-1 inhibitors
Sunkyung Lee,a Taemi Kim,a Byung Ho Lee,a Sung-eun Yoo,a
Kyunghee Leeb and Kyu Yang Yia,*
aBio-organic Science Division, Korea Research Institute of Chemical Technology, Yuseong-gu, Daejeon 305-600, Republic of Korea
bCentral Research Center of Yuyu Inc., Anyang-si, Gyeonggi-do 430-804, Republic of Korea
Received 13 July 2006; revised 23 November 2006; accepted 4 December 2006
Available online 15 December 2006
Abstract—The C-3 substituents effect on NHE-1 inhibitory activity of (5-arylfuran-2-ylcarbonyl)guanidines, previously identified as
potent NHE-1 inhibitors, was investigated. The introduction of amine or alkyl groups at the 3-position of the furan ring, next to the
acylguanidine moiety, remarkably improves NHE-1 inhibitory potency. Especially the important finding is that 5-(2,5-dichlo-
ro)phenyl and 5-(2-methoxy-5-chloro)phenyl derivatives exhibit high NHE-1 inhibitory activities (IC50 < 0.02 lM) that match those
of 3-unsubstituted derivatives.
ꢀ 2007 Published by Elsevier Ltd.
The Na+/H+ exchanger isoform-1 (NHE-1) is known to
regulate intracellular pH (pHi) during ischemia. In spite
of its essential role in restoring normal pHi,1 activation
of NHE-1 has been implicated in deleterious conse-
quences that occur during ischemia and reperfusion,
such as contractile dysfunction, arrhythmia, and cell
death. Consequently, inhibition of the NHE-1 has been
identified as a strategy for reducing ischemia/reperfusion
injury.2
amine, alkyl and aryl groups at the 3-position of the fur-
an ring.
5-Aryl-3-aminofuran-2-carboxylate esters 3 (Scheme 1),
key intermediates in pathways for synthesis of the amine
substituted furan-2-carbonylguanidines, were prepared
from the corresponding acetophenones via a sequence
initiated by a-bromination7 and cyanide displacement
to form the 2-cyanoacetophenones 2.8 Reaction of 2
with methyl glycolate under Mitsunobu conditions
afforded the vinyl ethers which upon treatment with
sodium hydride cyclized to the 3-aminofurans 3 (40–
60%).9 The amine function in 3 was modified by using
conventional methods to produce N,N-dimethylamine
4, N-acetamide 5, N-methylacetamide 6, N-methylamine
7, pyrrolidine 8, piperidine 9, and pyrrole 10.
In an earlier study, we found that members of a series of
good
(5-arylfuran-2-ylcarbonyl)guanidines
exhibit
inhibitory activity toward NHE-1 and both in vitro
and in vivo cardioprotective efficacy against ischemia/re-
perfusion injury.3 The effect of substitution at the 5-aryl
position was examined in that effort. Earlier reports sug-
gest that functionality adjacent to the acylguanidine
moiety leads to improved NHE-1 inhibitory potency,
presumably due to an increase in hydrophobic interac-
tions and/or reduction in the conformational flexibility
of the acylguanidine group.4–6 Herein, we summarize
the results of studies evaluating NHE-1 inhibition by
The intermediate 3-alkyl or 3-arylfuran-2-carboxylate
esters 14–16 were prepared by Darzen condensation of
the corresponding b-keto acetals with methyl chloroace-
tate followed by thermolytic conversion of the resulting
glycidic esters 11–13 (Scheme 2).10 The furan rings in
14–16 were then brominated at C-5 setting the stage
for synthesis of 5-aryl derivatives 20–22 by Pd-catalyzed
Suzuki coupling.11
(5-arylfuran-2-ylcarbonyl)guanidines
that
contain
Keywords: Sodium hydrogen exchanger; 3-Substituted-(5-arylfuran-2-
ylcarbonyl)guanidine; Cardioprotective.
The 3-substituted (5-arylfuran-2-ylcarbonyl)guanidines
23–33 were then prepared from the corresponding car-
boxylate esters by the treatment with excess guanidine
*
Corresponding author. Tel.: +82 42 860 7143; fax: +82 42 861
1291; e-mail: kyyi@krict.re.kr
0960-894X/$ - see front matter ꢀ 2007 Published by Elsevier Ltd.
doi:10.1016/j.bmcl.2006.12.012

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S. Lee et al. / Bioorg. Med. Chem. Lett. 17 (2007) 1291–1295
N
Br
a
c (i)
b
O
O
O
X
O
X
X
1a - 1l
2a - 2l
N
NH2
O
N
c (ii)
d
O
O
O
O
O
X
X
X
O
O
3a - 3l
4f (X = 3-Cl)
4i (X = 2,5-diCl)
e
h
g
4k (X = 2-OMe-5-Cl)
n
O
N
NH
N
O
O
O
O
O
O
X
X
X
O
O
O
5f, 5i, 5k
8f , 8i (n = 1)
9f, 9i (n = 2)
10f
d
O
N
NH
f
O
O
O
O
X
X
O
O
6f, 6i, 6k
7f, 7i
Scheme 1. Reagents and conditions: (a) Br2, Et2O, rt, 70–90%; (b) NaCN, EtOH, H2O, rt, 80–90%; (c) i—Ph3P, DEAD, methyl glycolate, THF,
0 ꢁC ! rt; ii—NaH, rt, 40–60%; (d) CH3I, NaH, DMF, 0 ꢁC ! rt, 50–70%; (e) Ac2O, 90–95%; (f) 6 N HCl, reflux, 45–60%; (g) Br(CH2)nBr (n = 5, 6),
NaH, DMF, 0 ꢁC ! rt; 45–65%; (h) 2,5-dimethoxytetrahydrofuran, 4-chloropyridinium hydrochloride, dioxane, reflux, 60–80%.
O
R
R
R
O
R
O
a
O
O
b
Cl
+
O
O
N
NH2
NH2
O
O
O
O
a
O
O
X
X
O
O
11 (R = CH3)
12 (R = C2H5)
13 (R = Ph)
3-10, 20-22
23 (R = NH2), 24 (R = N(CH3)2)
25 (R = NH(COCH3))
26 (R = N(CH3)COCH3)
27 (R = NHCH3), 28 (R =
c
R
b
R
R
c
d
)
O
N
N
O
O
R
O
Br
O
14 (R = CH3)
15 (R = C2H5)
16 (R = Ph)
O
X
29 (R =
), 30 (R =
)
O
O
O
N
OH
O
17 (R = CH3)
18 (R = C2H5)
19 (R = Ph)
20f, 20h, 20i, 20k (R = CH3)
21f, 21i, 21k (R = C2H5)
22k (R = Ph)
X
31 (R = CH3), 32 (R = C2H5)
33 (R = Ph)
O
Scheme 3. Reagents and conditions: (a) guanidine, DMF, rt, 50–80%;
(b) 1 N NaOH, CH3OH, reflux, 85–95%; (c) i—CDI, THF, rt;
ii—guanidine, rt, 55–70%.
Scheme 2. Reagents and conditions: (a) NaOCH3, THF, ꢀ10 ꢁC to rt,
80%; (b) heating, 160 ꢁC, 85%; (c) Br2 Et2O, rt, 78%; (d) arylboronic
acid, Pd(Ph3)4, Ba(OH)2ÆH2O or K2CO3, toluene or DME, reflux, 60–
75%.
acidosis in PS120 variant cells in which the human
NHE-1 is selectively expressed.12 By using this method,
the IC50 value of cariporide was 1.2 lM (Table 1). The
IC50 values of 3-amino-5-phenylfurans 23 were com-
pared with those determined earlier for the correspond-
ing 3-unsubstituted derivatives.3 The results show
generally that introduction of a 3-amino group remark-
ably enhances NHE-1 inhibitory potency. This is
especially true for the 2,5-dichloro 23i and 2-methoxy-
5-choro 23k derivatives which have excellent inhibitory
in DMF (Scheme 3). Alternatively, these substances can
be produced by activation of the respective carboxylic
acids with 1,10-carbonyldiimidazole (CDI) followed by
treatment with guanidine.
The NHE-1 inhibitory activities of the synthesized com-
pounds were determined by measuring their effect on the
sodium-dependent recovery of pH following an imposed

S. Lee et al. / Bioorg. Med. Chem. Lett. 17 (2007) 1291–1295
1293
Table 1. NHE-1 inhibition by 3-amino (23) and 3-methyl (31) furanylcarbonyl-guanidines
R
N
NH2
NH2
O
X
O
X
R = NH2
R = CH3
R = H
a
a,b
IC50 (lM)
Compound
IC50a(lM)
Compound
IC50 (lM)
Cariporide
H
2-F
1.2
2.3
23a
23b
23c
23d
23e
23f
23g
23h
23i
3.1
3.5
1.2
2-CH3
0.24
0.15
0.68
0.15
0.77
0.41
0.008
0.072
0.015
0.12
0.34
2.3
2-OMe
3-F
3-Cl
2.4
31f
0.024
0.75
6.0
3-CH3
2,5-DiF
2-5-DiCl
2,5-DiCH3
2-OMe-5-Cl
2-OMe-5-F
31h
31i
0.13
0.016
1.3
0.12
0.65
0.081
0.48
23j
23k
23l
31k
0.010
a Values are means of three experiments.
b Values are from previous report.
properties (IC50 < 0.02 lM). Moreover, the effects of C-
5 aryl ring substituents in the 3-aminofuran series on
IC50 values parallel those of the 3-unsubstituted com-
pounds. Additionally, the 3-methylfurans 31 show simi-
larly increased inhibitory activities. These results are in
accord with the earlier suggestion that introduction of
an additional substituent adjacent to the acylguanidine
would lead to increased NHE-1 inhibition.4
30 min global ischemia followed by 30 min reperfusion.
The evaluation of the cardioprotective effect was mea-
sured as an index of cardiac contractile function based
on the percent recovery of rate pressure product (RPP,
HR · LVDP, heart rate · left ventricular developing
pressure) at the end of reperfusion to the pre-ischemic
value. Additionally left ventricular end diastolic pres-
sure (LVEDP) was used as an indicator of cardiac con-
tracture. In this model, cariporide significantly improves
the recovery of contractile function (48% RPP) and
diminishes LVEDP (24 mmHg) compared with the vehi-
cle group (13% RPP, 56 mmHg LVEDP). Cardioprotec-
tive in vivo efficacy was determined by measuring a ratio
of myocardial infarction size to area at risk (IS/AAR) by
using a rat myocardial infarction model15 that was sta-
bilized for 20 min after a left thoracotomy operation,
subjected to 45 min coronary artery occlusion, following
90 min reperfusion. The compounds (0.1 mg/kg) were
administered by bolus intravenous injection 5 min be-
fore onset of ischemia. In this model, cariporide has a
41% of IS/AAR corresponding to a significant reduction
of the infarct size compared with the vehicle group (59%
of IS/AAR). Among the 3-amino derivatives, 2-fluor-
ophenyl 23b (62% RPP, 20 mmHg LVEDP) and 3-fluor-
ophenyl 23e (49% RPP, 25 mmHg LVEDP) showed a
significant effect on recovery of cardiac contractility,
that is similar to or slightly better than that of cariporide
(48% RPP, 24 mmHg LVEDP). In a manner strikingly
different from the 3-unsubstituted substances, most of
the 3-amino analogs did not show any significant protec-
tive activity against ischemia–reperfusion injury in the
Langendorff model. Especially, the most potent deriva-
tives against NHE-1, 2-methoxy-5-chloro compounds
(23k, 24k, 31k), were not active in the isolated rat heart
model. The 3-unsubstituted analogs represented good
correlation between NHE-1 inhibitory activity and
cardioprotective efficacy,3a but not the 3-unsubstitued
The influence of various 3-substituents on the NHE-1
inhibitory activity was determined (Table 2). The
3-N,N-dimethylamino compounds 24 are as potent
inhibitors as the corresponding primary amines, while
3-N-monomethylamine analogs 27 have slightly lower
potencies. Inhibition by the 3-acetamides 25 and 26 is
dramatically lower than that of the related amines, an
observation which differs from that described in a pub-
lished report.13 The 3-pyrrolidine 28, piperidine 29, and
pyrrole 30 analogs do not have improved activities. In
addition, the 3-phenyl analog 33k (IC50 = 5.6 lM) was
not as active as its 3-unsubstituted counterpart
(IC50 = 0.081 lM). Although the 3-ethyl derivative 32f
(IC50 = 0.23 lM) is three-times more potent than the
unsubstituted analog (IC50 = 0.75 lM), it is not as active
as the 3-methyl compound 31f (IC50 = 0.024 lM). The
combined results demonstrate that the 3-amino, 3-N,
N-dimethylamino, 3-methyl compounds have greatly
increased NHE-1 inhibitory activities and similar
responses to C-5 phenyl ring substitution as compared
to 3-unsubstituted derivatives.
The in vitro and in vivo cardioprotective efficacies
against ischemia/reperfusion injury of the furan-2-car-
bonylguanidines that have good NHE-1 inhibitory
activities were evaluated (Table 3). The isolated rat heart
model was used.14 Each isolated rat heart was treated
with 10 lM of the compound for 10 min, subjected to

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S. Lee et al. / Bioorg. Med. Chem. Lett. 17 (2007) 1291–1295
Table 3. Cardioprotective efficacy against ischemia–reperfusion injury
R
N
NH2
NH2
Langendorffa
O
X
O
Compound
R
X
In vivob
RPP (%) LVEDP IS/AAR
(mmHg) (%)
Control
Cariporide
23b
13 1.3
48 5.1
62 10.7 20 5.2
56 2.2 59 1.5
24 3.2 41 2.1
NH2
NH2
NH2
NH2
NH2
NH2
2-F
23c
23d
2-CH3
2-OMe
3-F
30 6.3
30 9.7
49 8.1
33 3.4
28 4.2 47 1.8
31 8.8 55 1.0
25 4.7
23e
23f
3-Cl
27 7.8 53 0.9
29 2.9
23k
2-OMe- 27 4.3
5-Cl
24k
31k
N(CH3)2 2-OMe- 6.4 3.3
5-Cl
40 6.1
34 6.0
CH3
2-OMe- 0.3 0.3
5-Cl
a In vitro cardioprotective effect was evaluated by measuring % RPP
(LVDP · HR) to pre-ischemic value, LVEDP (10 lM). n = 3 or
higher.
b In vivo cardioprotective effect was determined by measuring a ratio
of myocardial infarct size to area at risk (IS/AAR) in rat myocardial
infarction model (0.1 mg/kg). Values are means, n = 3 or higher.
derivatives. Even none of compounds display protective
efficacies in the rat myocardial infarction model. The
discrepancy between NHE-1 inhibition and cardiopro-
tective efficacy associated with these substances is not
clear. However, since these properties are well-correlat-
ed in 3-unsubstituted analogs,3a the protective efficacy
may be due to the inhibitory activity on NHE-1. There
may be a possibility that the differences are presumably
attributable to the 3-substituents, but it still needs more
investigation.
In summary, a series of 3-substituted (5-arylfuran-2-
ylcarbonyl)guanidines were synthesized and evaluated
for their NHE-1 inhibitory activities and in vitro and
in vivo cardioprotective efficacies. The NHE-1 inhibito-
ry potencies of the 3-substituted analogs, especially
3-amino, 3-N,N-dimethylamino, and 3-methyl com-
pounds, are much stronger than those of the 3-unsubsti-
tuted analogs. However, both the in vitro and in vivo
cardioprotective efficacies against ischemia/reperfusion
injury of these substances were not as good as that of
the 3-unsubstituted analogs. Continuing studies are
underway to identify the source of the discrepancy and
to uncover new compounds with better cardioprotective
profiles.
Acknowledgments
This research was supported by grants from the Center
for Biological Modulators of the 21st Century Frontier
R&D program, the Ministry of Science and Technology
(CBM-01-A100-001-1-0-0) and the Ministry of Health &
Welfare, Korea.

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