A novel class of sodium/calcium exchanger inhibitors: Design, synthesis, and structure-activity relationships of 4-phenyl-3-(piperidin-4-yl)-3,4-dihydro- 2(1H)-quinazolinone derivatives

Article abstract of DOI:10.1016/j.bmcl.2005.10.012

Design, synthesis, and structure-activity relationships of 3,4-dihydro-2(1H)-quinazolinone derivatives as sodium/calcium (Na ⁺/Ca²⁺) exchanger inhibitors are described. In these studies, optimization of the substituents at the 3-posi

Full text of DOI:10.1016/j.bmcl.2005.10.012

Bioorganic & Medicinal Chemistry Letters 16 (2006) 727–730
A novel class of sodium/calcium exchanger inhibitors: Design,
synthesis, and structure–activity relationships of 4-phenyl-3-
(piperidin-4-yl)-3,4-dihydro-2(1H)-quinazolinone derivatives
Hirohiko Hasegawa,a,* Masami Muraoka,a Kazuki Matsuia and Atsuyuki Kojimab
aResearch Division, Sumitomo Pharmaceuticals Co. Ltd, 1-98, Kasugadenaka 3-Chome, Konohana-ku, Osaka 554-0022, Japan
bTakarazuka Organic Synthesis Department, Sumika Technoservice Co. Ltd, 2-1, Takarazuka 4-Chome,
Takarazuka City, Hyogo 665-0051, Japan
Received 12 August 2005; revised 25 September 2005; accepted 6 October 2005
Available online 24 October 2005
Abstract—Design, synthesis, and structure–activity relationships of 3,4-dihydro-2(1H)-quinazolinone derivatives as sodium/calcium
(Na+/Ca2+) exchanger inhibitors are described. In these studies, optimization of the substituents at the 3-position of this series of
compounds was carried out and dramatic effects of the substituent on the activities were observed. Based on these SAR studies,
a highly potent inhibitor of the Na+/Ca2+ exchanger, which showed single-digit-nanomolar activity, was discovered.
Ó 2005 Elsevier Ltd. All rights reserved.
The sodium/calcium (Na+/Ca2+) exchanger is a trans-
membrane carrier that plays a critical role in maintain-
ing calcium balance in cardiac myocytes. It is well
known that reperfusion injury is associated with a large
increase in intracellular Ca2+ content.1,2 Therefore, inhi-
bition of this Ca2+ overload is considered to be one of
the pharmacological interventions to prevent reperfu-
sion injury. It is proposed that the Na+/Ca2+ exchanger
plays an important role when Ca2+ overload occurs.3,4
We have been interested in developing novel inhibitors
of the Na+/Ca2+ exchanger with high potency and selec-
tivity, because we considered that inhibitors of the Na+/
Ca2+ exchanger would inhibit Ca2+ overload during
reperfusion and thus prevent reperfusion injury.
Furthermore, KB-R7943 (4),7 SEA0400 (5),8 benzyloxy-
phenyl derivative (6)9, and SN-6 (7)10 have been
reported.
We have already reported design, synthesis, and struc-
ture–activity relationships of 3,4-dihydro-2(1H)-quinaz-
olinone derivatives with the inhibitory activities of the
Na+/Ca2+ exchanger.11 In the previous article, we dis-
closed that these studies based on lead compound 8 with
a moderate potent inhibitory activity led to the identifi-
cation of a structurally novel and highly potent inhibitor
against the Na+/Ca2+ exchanger 9 (SM-15811), which
directly inhibited the Na+-dependent Ca2+ influx via
the Na+/Ca2+ exchanger in cardiomyocytes with high
potency and exerted the protective effect against myo-
cardial ischemic reperfusion injury (Fig. 2). We further
performed the optimization of this compound to find
more highly potent inhibitors of the Na+/Ca2+ exchang-
er. In this study, we found the dramatic effect of substit-
uents of 4-phenyl-3-(piperidin-4-yl)-3,4-dihydro-2(1H)-
quinazolinone derivatives and that based on this study
highly potent 4-phenyl-3-(piperidin-4-yl)-3,4-dihydro-
2(1H)-quinazolinone derivative was identified. Herein,
we wish to report interesting results.
A number of compounds, including peptidic and non-
peptidic, have been reported as Na+/Ca2+ inhibitors
(Fig. 1). As a peptidic inhibitor, Val-Met-Arg-Phe-
NH2 (1) with an IC50 value of 1.5 lM has been reported,
which is a non-selective inhibitor.5 As a non-peptidic
inhibitor, aroylguanidine derivative (2) with an IC50
value of 3.4 lM has been reported which is a modified
amiloride derivative like dimethylamiloride (3).6
Keywords: Sodium/calcium exchanger; Na+/Ca2+ exchanger; 4-Phenyl-
Synthesis of a series of 4-phenyl-3-(piperidin-4-yl)-3,4-
dihydro-2(1H)-quinazolinone derivatives is illustrated
in Scheme 1. Treatment of trichloroacetylamide 10 with
4-amino-1-benzylpiperidine in DMSO, followed by
3-(piperidin-4-yl)-3,4-dihydro-2(1H)-quinazolinone
Inhibitor.
derivatives;
*
Corresponding author. Tel.: +81 6 6466 5401; fax: +81 6 6466
5430; e-mail: hhasegaw@sumitomopharm.co.jp
0960-894X/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2005.10.012

728
H. Hasegawa et al. / Bioorg. Med. Chem. Lett. 16 (2006) 727–730
O
NH
NH2
O
NH
Me2N
Cl
N
N
Cl
N
H
N
H
N
H
NH2
O2N
NH2
3
2
F
O2N
OEt
O
O
F
NH
NH2
CH3SO3H
O
S
NH2
5
4
O2N
O
N
H
N
CO2Et
O
F
N
HN
O
O
S
6
7
Figure 1. Chemical structures of non-peptidic inhibitor of the Na+/Ca2+ exchanger: (2) aroylguanidine derivative; (3) dimethylamiloride; (4)
KB-R7943; (5) SEA0400; (6) benzyloxyphenyl derivative; (7) SN-6.
which are known inhibitors of the Na+/Ca2+ exchanger,
showed inhibitory activities with IC30 values of 10 lM
and 30 lM, respectively.
Ph
Ph
4
N
Ph
Cl
4
N
NMe2
6
N
6
citrate
N
H
O
N
H
O
Table 1 summarizes our results in exploring heteroaryl
groups like pyridyl, thienyl, or furyl as replacements for
the phenyl group. 2-, 3-, or 4-pyridyl methyl (15–17) were
almost 10–30 times weaker than 9. 2- or 3-Thienyl methyl
(18, 19) were almost 2 orders weaker than 9. Interestingly,
although 2-furyl methyl 20 reduced activity markedly,
3-furyl methyl 21 was almost equipotent as 9.
9
8
Figure 2. Chemical structures of 3,4-dihydro-2(1H)-quinazolinone
derivatives 8 and 9.
reduction of imine and removal of the trichloroacetyl 11
with NaBH4, gave diamine 12. Treatment of diamine 12
with 1,10-carbonyldiimidazole led to cyclization to
afford 3-[4-(1-benzyl)piperidinyl]-2(1H)-quinazolinone
13. Debenzylation of 13 gave 14,11 which was subse-
quently reductively alkylated to afford 15–32.
The effect of substituents on the phenyl ring of com-
pound 9 was then investigated. Table 2 summarizes
the results of this investigation. At first, both methoxy
groups, which are electron-donating groups, and chlo-
rine atoms, which are electron-withdrawing groups,
were introduced at each position of the phenyl ring.
Introduction of chlorine atoms at the 2-, 3-, or 4-posi-
tions (22–24) reduced the activity dramatically. On the
other hand, concerning the methoxy groups, introduc-
tion at the 4-position 27 resulted in decrease in activity
and introduction at the 2-position 25 resulted in a com-
plete loss of activity. Introduction at the 3-position 26,
The inhibitory activity of test compounds on the Na+/
Ca2+ exchange was measured by the inhibition of Na+-
and K+-free contracture in isolated guinea pig left atria,
performed as described previously.12 The inhibitory
activities were calculated as IC30 values. In this system,
Val-Met-Arg-Phe-NH2 (1) and dimethylamiloride (3),
Ph
Ph
NBn
Ph
NBn
c
a
b
O
N
N
H
NHCOCCl3
10
NHCOCCl3
NH2
11
12
Ph
Ph
NBn
NH
Ph
N
R
d
e
N
N
N
N
H
O
N
H
O
N
H
O
15-32
13
14
Scheme 1. Reagents: (a) 4-amino-1-benzyl piperidine, DMSO; (b) NaBH4, EtOH; (c) 1,10-carbonyldiimidazole, THF, reflux; (d) HCO2NH4, Pd/C,
MeOH, reflux; (e) R-CHO, NaBH3CN, HCl, MeOH.

H. Hasegawa et al. / Bioorg. Med. Chem. Lett. 16 (2006) 727–730
729
Table 1. Inhibitory activity of 3,4-dihydro-2(1H)-quinazolinones
against the Na+/Ca2+ exchanger
Table 2. Inhibitory activity of 3,4-dihydro-2(1H)-quinazolinones
against the Na+/Ca2+ exchanger
Ph
N
R
Ph
N
R
N
N
N
H
O
N
H
O
a
Compound
RCH2-
Val-Met-Arg-Phe-NH2
IC30 (lM)b
Compounda
RCH2-
PhCH2-
2-Cl-PhCH2-
IC30 (lM)b
1
10
9c
22
0.017
9.0
O
NH
NH2
23
24
3-Cl-PhCH2-
4-Cl-PhCH2-
0.54
0.62
>10
Me2N
N
N
3
9c
N
H
30
25
26
2-MeO-PhCH2-
3-MeO-PhCH2-
4-MeO-PhCH2-
Cl
NH2
0.0084
0.25
>10
27
PhCH2-
0.017
0.39
0.16
0.48
1.7
28d
29d
30d
31d
32
3,5-Di-MeO-PhCH2-
3,4,5-Tri-MeO-PhCH2-
3-EtO-PhCH2-
>10
N
0.58
0.49
0.56
15d
16d
17
3-MeOCH2-PhCH2-
3-Me-PhCH2-
a All the compounds tested were racemic.
N
b IC30 values are expressed as means from three to five preparations.
c Compound tested as the citrate.
d Compound tested as the hydrochloride.
N
ents on the phenyl group, to optimize the 3,4-dihydro-
2(1H)-quinazolinone derivative 9. (1) Concerning the
replacement of the phenyl group with heteroaryl group
like pyridyl, thienyl, and furyl groups, most of the hetero-
aryl groups reduced the activity. Only 3-furyl was as po-
tent as phenyl group. (2) Concerning the introduction of
substituents, both chlorine atoms which are electron-
withdrawing groups and alkoxyl groups which are elec-
tron-donating groups were introduced to investigate the
preferred substituent systematically. These studies led to
the finding of the highly potent Na+/Ca2+ exchanger
inhibitor in which methoxy group was substituted at the
3-position of the phenyl group. (3) According to results
of (1) and (2), there is a possibility that the oxygen atom
might interact with amino acid(s). (4) Based on these re-
sults, various types of alkoxyl groups were introduced;
however, all introduced substituents reduced the activi-
ties, suggesting that the size of the substituent is limited.
(5) In the course of this study, dramatic effects of the sub-
stituents on the inhibitory activity were observed. These
compounds showed great variations in activities, ranging
from compounds with no activities even at a concentra-
tion of up to 10 lM to a compound with an activity in
the nanomolar range. Thus, we discovered the structural-
ly novel 3,4-dihydro-2(1H)-quinazolinone derivative as
the highly potent inhibitor of the Na+/Ca2+ exchanger
(26) with an IC30 value of 0.0084 lM, which is a single-
digit-nanomolar activity. Compound (26) would be a use-
ful tool for studying the Na+/Ca2+ exchanger inhibitor as
well as indicating the potential for generating a novel class
of highly potent Na+/Ca2+ exchanger inhibitors.
18d
19d
20d
21
S
3.9
S
8.3
O
0.017
O
a All the compounds tested were racemic.
b IC30 values are expressed as means from three to five preparations.
c Compound tested as the citrate.
d Compound tested as the hydrochloride.
however, enhanced the activity with an IC30 value of
0.0084 lM. Introduction of a methyl group 32 to see if
steric effects would alter the activity reduced the activity,
indicating that alkoxyl groups were important. These
results including the fact that only 3-furyl methyl 21
showed strong activity among the heteroaryl groups dis-
cussed above suggest that there might be interaction of
oxygen atom with amino acid(s). To investigate further
the steric effects of alkoxyl groups, various kinds of alk-
oxyl groups were introduced. 3,5-Dimethoxy group 28
and 3,4,5-trimethoxy group 29 diminished the activity.
One carbon extended substituent 3-ethoxy group 30
reduced the activity. 3-Methoxymethyl 31 lowered
the activity. These results suggested that although intro-
duction of an alkoxyl group at the 3-position on the
phenyl ring is preferred, the size of the substituent is
limited and only 3-methoxy group enhanced the activity.
Acknowledgment
We thank Ms. Hitomi Sakanaka for evaluating the
inhibitory activities of the compounds against the Na+/
Ca2+ exchanger.
In summary, we synthesized various types of compounds
to replace a benzyl group with heteroarylalkyl and to
introduce chlorine atom and alkoxyl groups as substitu-

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H. Hasegawa et al. / Bioorg. Med. Chem. Lett. 16 (2006) 727–730
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