Synthesis and SAR study of T-type calcium channel blockers. Part II

Article abstract of DOI:10.1002/ardp.200800079

3,4-Dihydroquinazoline derivatives have been known to be the novel and potent T-type calcium channel blockers. From a systematic variation of 3,4-dihydroquinazoline derivative 5c (KYS05043), plausible SAR results were established. It was revealed that a 5-(dimethylamino)pentylamino group at R ¹, a biphenyl group at R², and a benzyl amido group at R³ in the 3,4-dihydroquinazoline backbone are closely related with the channel selectivity (T/N-type) as well as the potency based on the discovery of 6k (KYS05090).

Full text of DOI:10.1002/ardp.200800079

Arch. Pharm. Chem. Life Sci. 2008, 341, 661–664
Y. J. Choe et al.
661
Short Communication
Synthesis and SAR Study of T-Type Calcium Channel Blockers.
Part II
Yun Jeong Choe1, Han Na Seo1, Soo Yeon Jung1, Hyewhon Rhim2, Jungahn Kim1,
Dong Joon Choo1, and Jae Yeol Lee1
1 Research Institute for Basic Sciences and Department of Chemistry, College of Sciences, Kyung Hee
University, Seoul, Korea
2 Life Sciences Division, Korea Institute of Science & Technology, Cheongryang, Seoul, Korea
3,4-Dihydroquinazoline derivatives have been known to be the novel and potent T-type calcium
channel blockers. From a systematic variation of 3,4-dihydroquinazoline derivative 5c
(KYS05043), plausible SAR results were established. It was revealed that a 5-(dimethylamino)pen-
tylamino group at R1, a biphenyl group at R2, and a benzyl amido group at R3 in the 3,4-dihydro-
quinazoline backbone are closely related with the channel selectivity (T/N-type) as well as the
potency based on the discovery of 6k (KYS05090).
Keywords: Blockers / 3,4-Dihydroquinazoline / SAR study / T-type calcium channel /
Received: April 21, 2008; accepted: July 7, 2008
DOI 10.1002/ardp.200800079
Introduction
Calcium channels are the primary route for translating
electrical signals into the biochemical events underlying
key processes such as neurotransmitter release, cell excit-
ability, and gene expression [1]. Among calcium chan-
nels, T-type or low voltage activated (LVA) calcium chan-
Figure 1. Mibefradil and KYS05043.
nels are thought to contribute to neuronal excitability
and also play crucial roles in the control of blood pres-
sure [2], and they promise to provide the important ther-
apeutic targets for the treatment of epilepsy, neuro-
pathic pain, and cardiovascular diseases such as hyper-
tension and angina pectoris [3]. Therefore, many
researchers have been awaiting a specific T-type calcium
channel blocker for the exact understanding of the path-
ophysiological role of T-type channel since the with-
drawal of mibefradil in 1996 (Fig. 1). For this reason, we
have also tried to identify new compounds with higher
Figure 2. SAR study via the modifications of R1, R2, and R3 sub-
stituents.
potency and selectivity for T-type channel and reported the synthesis of novel T-type channel blockers based on a
3,4-dihydroquinazoline backbone [4–7]. Through an
intensive SAR (structure-activity relationship) study, we
had recently discovered the lead-like compound
Correspondence: Jae Yeol Lee, Research Institute for Basic Sciences
and Department of Chemistry, College of Sciences, Kyung Hee Univer-
KYS05090 starting form KYS05043 shown in Fig. 2 [5, 7].
Herein, we will discuss the detailed structure-activity
relationship of 3,4-dihydroquinazoline based on the dis-
covery of KYS05090 (Fig. 2).
sity, 1 Hoegi-Dong, Seoul 130-701, Korea.
E-mail: ljy@khu.ac.kr
Fax: +82-2-966-3701
Abbreviations: low voltage activated (LVA)
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Table 1. In vitro calcium channel blocking effects of 3,4-dihydroquinazoline derivatives.
Entry
R1
R2
HEK293 cells T-Type (a1G)
HEK293 cell
N-Type (a1B)
% Inhibition (10 lM)
Selectivity
(T/N-Type)c)
% Inhibitiona)
IC50
(10 lM)
(lM)b)
5a
(CH2)5NH2
51.9 l 1.1
90.0 l 0.7
84.1 l 1.6
88.5 l 0.4
84.1 l 0.6
87.7 l 1.2
59.5 l 1.1
82.5 l 0.7
86.5 l 0.5
94.9 l 1.2
90.1 l 2.3
92.9 l 1.7
67.4 l 1.1
88.5 l 0.6
91.8 l 1.9
97.5 l 1.2
72.4 l 0.3
68.1 l 0.5
88.3 l 1.5
83.8 l 1.4
88.1 l 1.7
98.0 l 1.6
95.9 l 1.7
9.16 l 0.32
2.27 l 0.49
0.30 l 0.09
0.37 l 0.08
1.84 l 0.15
2.02 l 0.15
5.84 l 0.44
0.56 l 0.10
0.68 l 0.18
0.34 l 0.04
0.23 l 0.03
1.20 l 0.12
4.54 l 0.62
0.17 l 0.03
0.14 l 0.01
0.57 l 0.05
3.13 l 0.27
4.20 l 0.20
0.16 l 0.02
0.13 l 0.01
0.26 l 0.01
0.04 l 0.00
1.34 l 0.49
3.0 l 2.6
54.2 l 2.1
7.5 l 0.7
17.3
1.6
5b
(CH2)5NHBoc
(CH2)5NH2
5c (KYS05043)
11.2
0.9
5d
(CH2)5NHBoc
94.9 l 1.7
4.3 l 2.6
5e
NH(CH2)4NH2
19.5
1.7
5f
NH(CH2)4NHBoc
53.1 l 2.5
10.7 l 2.3
No Blockingd)
98.6 l 1.3
36.5 l 0.2
24.4 l 2.8
35.0 l 1.8
No Blockingd)
30.1 l 1.1
15.2 l 2.4
75.1 l 0.1
1.7 l 1.1
5g
5.6
5h
NH(CH2)4NH2
S100
0.9
5i
NH(CH2)4NHBoc
5j
2.6
5k
3.7
6a
(CH2)5NHBoc
(CH2)5NH2
2.7
6b
S 100
2.9
6c
(CH2)5NHBoc
(CH2)5NH2
6d
6.0
6e
NH(CH2)4NHBoc
NH(CH2)4NH2
1.3
6f
42.5
1.5
6g
46.3 l 0.3
16.6 l 0.7
8.3 l 1.8
6h
NH(CH2)4NHBoc
NH(CH2)4NH2
5.3
6i
10.1
6j
11.7 l 5.8
70.6 l 3.1 (4.9 lM)e)
67.6 l 1.2
7.5
6k (KYS05090)
Mibefradil
1.4 (119.5)f)
1.4
a)
Percent inhibition value (l SE) was obtained by repeated procedures (n F 4).
IC50 value was determined from the dose-response curve.
% inhibition ratio at 10 lM.
“No blocking” means that the inhibition was less than 1%.
IC50 value against N-type channel.
b)
c)
d)
e)
f)
Selectivity value based on IC50 value ratio.
phosphorane derivative 3 was directly prepared by the
Appel's method (PPh3-C2CI6-Et3N reagent system) from
methyl 2-aminocinnamate 2 [8], which was derived from
commercially available 2-nitrocinnamic acid 1 using a
procedure described earlier [6]. The intermolecular aza-
Synthesis
Referring to the structures listed in Table 1, 3,4-dihydro-
quinazoline derivatives were easily prepared according
to Scheme 1 using our set-up procedure [4–6]. The imino-
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Arch. Pharm. Chem. Life Sci. 2008, 341, 661–664
Synthesis and SAR Study of T-Type Calcium Channel Blockers
663
Reactants: R1-NCO = Ph-NCO, 4-Ph-Ph-NCO; R2H = H2N(CH2)5NH2, H2N(CH2)5NHBoc, 1-pyrrolidinyl(CH2)5NH(CH3), Bn2N(CH2)5NH(CH3).
Scheme 1. Synthesis of the 3,4-dihydroquinazoline derivative 6.
Wittig reaction of iminophosphorane 3 with aryl isocya-
nate (R1-NCO) in benzene provided carbodiimide 4, which
was treated with an amine nucleophile to afford the 3,4-
dihydroquinazoline 5. In the case of the primary amine
(R2H) attack on carbodiimide 4, the resulting two regio-
isomers 5 could be separated by silica gel column chro-
matography and their structures could be completely
elucidated by 1H-NMR technique such as NOESY as
Figure 3. Pharmacophores of 3,4-dihydroquinazlone compound
reported earlier [5]. The hydrolysis of compound 5 with
LiOH provided the free carboxylic compound, which was
coupled with benzylamine in the presence of EDC and
HOBT, afforded the benzyl amide 6 [9]. Finally, deprotec-
tion of tert-butoxy (50% TFA in CH2Cl2) or dibenzyl group
(H2, Pd/C, MeOH, aq. HCHO) was carried out to provide
the corresponding 3,4-dihydroquinazoline derivative 6
as depicted in Scheme 1 [7].
for T-type channel blocking.
respect to IC50 values, both of percent inhibition and IC50
values showed linear relationships except for 5b. More-
over, fourteen synthetic compounds are more potent
than mibefradil. In particular, compound 6k (KYS05090)
is most potent and approximately 33-fold more potent
(IC50 = 40 nM) than the reference. Based on this structure-
activity relationship, more hydrophobic moieties are
required at both R1 and R2 substituents irrespective of the
position when comparing the phenyl group with the
biphenyl group (for example, 5a–b vs. 5c–d & 6a–b vs.
6c–d).
Secondly, the benzylamido group exhibited a higher
potency than the methyl ester group at the R3 substituent
(5 vs. 6), which means that a hydrophobic moiety is also
required at R3 position. In the case of the R1 position, the
terminal part of the chain is required to have a proper
hydrophobic moiety, when comparing the activity of 6k
(IC50 = 40 nM) with that of 6j (IC50 = 0.26 lM). With regard
to the N-type channel (a1B), in the meanwhile, two com-
pounds (5d and 5i) showed higher inhibitory activity
against the N-type channel and, thus, poor channel selec-
tivity. However, two compounds (5h and 6b) did not
block the N-type channel (less than 1%) and thus showed
the highest selectivity for the T-type channel. However,
Results and discussion
The in-vitro calcium channel blocking activities of 3,4-
dihydroquinazoline derivatives were determined in T-
type (a1G) and N-type channels (a1B), respectively, stably
expressed in HEK293 cells, by whole-cells patch-clamp
methods at 10 lM concentration [10]. For the exact
potency of the compounds, their IC50 values required to
produce 50% inhibition of a1G T-type currents were again
determined from fitting raw data into dose-response
curves. In-vitro blocking data of the compounds are sum-
marized in Table 1.
Compared to mibefradil (96%), most of compounds
showed good inhibitory activity (A84%) against T-type cal-
cium channel (a1G) at a concentration of 10 lM except 5a,
5g, 6b, 6f, and 6g. Among them, compounds 6e and 6k
showed better activity (A97%) than mibefradil. With
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Arch. Pharm. Chem. Life Sci. 2008, 341, 661–664
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This work was supported by the Korea Research Foundation
Grant funded by the Korean Government (MOEHRD) (KRF-
2007-313-C00475) and Vision 21 Program from Korea Institute
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