Synthesis and biological evaluation of novel T-type Ca2+ channel blockers

Article abstract of DOI:10.1016/j.bmc.2004.06.011

A small molecule library of piperazinylalkylisoxazole derivatives containing about 600 compounds was designed, synthesized and evaluated for blocking effects on T-type Ca²⁺ channel. Several ligands were identified to possess high inhibitory activity against the T-type Ca ²⁺ channel. The compound 21 with trifluoromethyl substituents at C₃-position of phenyl group (R¹) and C₂- position of phenyl group (R²) showed the highest inhibitory activity with IC₅₀ value of 1.02μM, which is comparable to that of mibefradil.

Full text of DOI:10.1016/j.bmc.2004.06.011

Bioorganic & Medicinal Chemistry 12 (2004) 3965–3970
Synthesis and biological evaluation of novel
T-type Ca2+ channel blockers
Hee Kyung Jung,a Munikumar Reddy Doddareddy,a Joo Hwan Cha,a Hyewhon Rhim,a
Yong Seo Cho,a Hun Yeong Koh,a Bong Young Jungb and Ae Nim Paea,*
aLifescience Division, Korea Institute of Science and Technology, PO Box 131, Cheongryang, Seoul 130-650, South Korea
bDepartment of Chemistry, Korea University, 1-Anamdong, Seoul 136-701, South Korea
Received 17 May 2004; revised 8 June 2004; accepted 8 June 2004
Available online 24 June 2004
Abstract—A small molecule library of piperazinylalkylisoxazole derivatives containing about 600 compounds was designed, syn-
thesized and evaluated for blocking effects on T-type Ca2þ channel. Several ligands were identified to possess high inhibitory activity
against the T-type Ca2þ channel. The compound 21 with trifluoromethyl substituents at C3-position of phenyl group (R1) and C2-
position of phenyl group (R2) showed the highest inhibitory activity with IC50 value of 1.02 lM, which is comparable to that of
mibefradil.
ꢀ 2004 Elsevier Ltd. All rights reserved.
1. Introduction
tors of T-type calcium channel have been also reported
to play as antiepileptic drugs.5 Most of these Ca2þ
channel blockers interacts predominantly or exclusively
with the L-type calcium channel. However, these drugs
showed some extent feature of unwanted effects such as
negative inotropism, atrioventricular blockade or neu-
rohormonal activation.6 So recently more attention has
been paid on the development of active T-type blockers
for the reduction of these side effects.
Calcium is essential for life and is the most common
signal transduction element in cells. The calcium pene-
trates into plasma membrane ion channel on response to
membrane depolarization thereby transmitting the sig-
nal.1 The different subtypes of voltage-dependent Ca2þ
channels have been extensively investigated and classi-
fied into two main classes, one that responds to strong
depolarization also called as high voltage activated
(HVA) and the other, which responds to weak depo-
larization also called as low voltage activated (LVA).
Based on pharmacological studies, HVA Ca2þ channels
are again divided into L-, N-, P-, Q- and R-types and
LVA Ca2þ channel is also called as T-type.2 L-type
(long-lived) and T-type (transient) calcium channels
both coexist in neurons, heart, vascular smooth muscle
and endocrine cells. The rise of concentration of Ca2þ is
directly connected to cell death or damage and this is the
major causative factor in the progressive and delayed
death of nerve cells that occurs in cerebral injury and
cerebrovascular diseases.3;4 The Ca2þ channel blockers
have been used extensively in the treatment of neuro-
pathic pain, hypertension and angina pectoris. Inhibi-
The calcium channel blockers such as flunarizine,4b U-
92032,7 nicardipine8 and mibefradil,9 (Fig. 1) have been
reported as active T-type Ca2þ channel blockers. They
generally possess diphenylmethylpiperazine or dihydro-
pyridine moieties as the basic skeleton. Mibefradil, the
first marketed selective T-type Ca2þ channel blocker,
which depends on the cell type blocks T-type Ca2þ
channels 10–30 times more potently than L-type Ca2þ
channels. It was finally withdrawn due to its pharma-
cokinetic interactions with other drugs metabolized by
cytochromes P-450 3A4 and 2D6 (antihistamines such
as astemizole)10 So there is an urgent need for the
development of active T-type Ca2þ channel blockers,
which are structurally distinct from existing compounds.
To serve this purpose, we designed a new piper-
azinylalkylisoxazole scaffold (Fig. 2) and developed a
small molecule library containing about 600 com-
pounds. We selected a piperazinylalkyl group, based on
Keywords: T-type calcium channel; Synthesis.
* Corresponding author. Tel.: +82-295-85185; fax: +82-295-85189;
e-mail: author@institute.edu
0968-0896/$ - see front matter ꢀ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2004.06.011

3966
H. K. Jung et al. / Bioorg. Med. Chem. 12 (2004) 3965–3970
O
H
F
F
N
N
N
HO
N
N
H3C
CH3
F
F
Flunarizine
U-92032
H
O
H3CO
H3C
O
N
CH3
O
F
H
N
O
H3C
N
N
N
O
O
CH3
CH3
H3C
CH3
Mibefradil
Nicardipine
Figure 1. T-type Ca2þ calcium channel blockers.
R3
N
O
N
R2
O
R1
N
N
(b)
(a)
n
R1
N
NH
N
R1
N
N
NH2
R1
N
N
n = 2, 3
n
O
n
8 : R3 = H
3
1
2
9 : R3 = Me
n = 2 or 3
10 : R3 = Et
H
Figure 2. Piperazinylalkylisoxazole scaffold.
OH
O
O
OH
(e)
(c)
(d)
N
R2
O
R2
O
H
R2
R2
N
N
the information available on existing T-type blockers
and an isoxazole group as alternative to bioisosteres
such as amide,11 carbonyl,12 oxygen13 and hetero-
cycles.14 A biogenic amine was introduced as a linker
between the piperazine group and isoxazole group.
Substitutions of R1 and R2 on hydrophobic aromatic
groups on both sides and length of the alkyl chain (n ¼ 2
or 3) gave variation to the library. We designed a syn-
thetic scheme for piperazinylalkylisoxazole library by
combination of the substituted phenylpiperazinylalkyl-
amines with the substituted phenylisoxazole aldehydes.
4
7
5
6
Scheme 1. Reagents and conditions: (a) bromoethylphthalimide (for
n ¼ 2) or, bromopropylphthalimide (for n ¼ 3) K2CO3, DMF, 80 ꢁC
2 h, 50–85%; (b) hydrizine, EtOH, 70 ꢁC, 5 h, 85–99%; (c)
NH2OHÆHCl, Na2CO3, 60 ꢁC EtOH/H2O (2/1), 1 h, 90–100%; (d)
pyridine (cat.), NCS, 60 ꢁC, THF, 0.5 h, then 3-propynol, Et3N, 50 ꢁC,
rt, 2 h, 60–90%; (e) PCC, silica gel, CH2Cl2, 5 h, 50–95%.
aldehydes 4. Reaction of hydroxylamineÆHCl with
aldehydes 4 in ethanolic aqueous solution (EtOH/
H2O ¼ 2/1) gave the corresponding oximes 5 in 90–100%
yields. The 1,3-dipolar cycloaddition reaction of oximes
5 and 3-propyn-1-ol using NCS (N-chlorosuccinimide)
and pyridine provided substituted isoxazolyl methanols
6 in 60–90% yields. The oxidation of alcohols 6 with
PCC/SiO2 in CH2Cl2 gave corresponding aldehydes 7 in
50–95% yields (Scheme 1).
2. Chemistry
The synthetic strategy for obtaining a series of piper-
azinylalkylisoxazoles was adopted from the solution
phase combinatorial synthesis by the reductive amina-
tion.15;16 The preparation of starting materials was out-
lined in Scheme 1. The phenylalkylpiperazinyl amines
were prepared from the commercially available substi-
tuted phenylpiperazines 1. By the reaction of phenyl-
alkylamine 1 using bromoalkylphthalimide and K2CO3
in DMF at 80 ꢁC, corresponding piperazinylalkyl
phthalimide 2 was obtained after chromatographic
purification on silica gel in 50–85% yields.
The final step of the synthesis was accomplished by the
reductive amination17 of the prepared primary amines 3
with aldehydes 7 using NaBH(OAc)3 as shown in
Scheme 2. To a solution of amines 3 and aldehydes 7 in
CH2Cl2 were added NaBH(OAc)3 (3 equiv) and molec-
ular sieves (four beads). The reaction mixture was stir-
red for 1 h at room temperature, quenched with
saturated sodium bicarbonate solution and extracted
with CH2Cl2. Subsequent chromatographic purification
on silica gel gave the product 8 in 60–90% yields. Ter-
tiary amines 9 and 10 were prepared from the secondary
amine 8 by the reductive amination once again. The
reaction of compound 8 with formaldehyde and
NaBH(OAc)3 in CH2Cl2 at room temperature gave the
product 9 (R3 ¼ methyl) in 90% to quantitative yields.
The treatment of hydrazine on piperazinylphthalimide 2
in ethanol at 70 ꢁC gave phenylethyl(propyl)piperazinyl
ethyl (or propyl) amines 3 in 85–99% yield (Scheme 1).
The phenylalkylisoxazole aldehydes 7 for the reductive
amination were prepared from the substituted phenyl-

H. K. Jung et al. / Bioorg. Med. Chem. 12 (2004) 3965–3970
3967
Table 1. IC50 values of selected compounds
R3
N
N
O
O
+
O
N
(a)
R2
R1
N
N
R1
N
N
NH2
R3
N
O
N
n
R2
n
R2
R1
N
N
8 : R3 = H
n = 2 or 3
3
7
n
Compds
n
Substituentb
R2
IC50 (lMa)
R3
O
(b)
N
N
R1
R3
R2
R1
N
N
N
N
n
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
Mibefradil
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
3
3
3
3
a
a
b
b
c
c
d
d
e
e
e
e
e
f
l
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
Me
Me
Me
Me
Me
Et
Et
Et
H
H
H
H
7.49
25.49
33.48
11.20
53.2
8.24
75.79
3.04
2.98
2.04
1.02
3.33
3.06
2.02
1.53
10.41
2.54
9.26
19.13
5.82
7.62
8.19
2.51
4.08
7.55
3.03
4.82
23.86
8.46
7.48
60.54
8.82
4.36
5.49
10.71
4.21
10.56
8.18
18.00
7.01
2.71
1.55
4.17
4.75
0.84
m
l
9 : R3 = Me
m
l
R3
N
O
(c)
R2
R1
N
l
n
l
10 : R3 = Et
m
k
l
Scheme 2. Reagents and conditions: (a) NaBH(OAc)3 (3 equiv),
molecular sieves (four beads), CH2Cl2, rt, 1 h, 60–90%; (b) formalde-
hyde, NaBH(OAc)3 (3 equiv), 4 A molecular sieves, CH2Cl2, rt, 1 h,
90% ꢀ quant.; (c) acetaldehyde, NaBH(OAc)3 (3 equiv), molecular
sieves, CH2Cl2, rt, 1 h, 90% ꢀ quant.
m
n
r
l
f
m
l
g
g
g
h
h
i
Compound 10 (R3 ¼ ethyl) was obtained from reductive
amination using acetaldehyde. All the prepared com-
pounds were characterized by 1H NMR, 13C NMR,
HPLC, IR and HRMS methods.
m
r
k
l
k
l
i
i
m
n
o
q
r
i
3. Results and discussion
i
i
i
The biological activities of the generated phenyl-
piperazinylalkylisoxazole analogues were evaluated in
vitro for the inhibition of T-type Ca2þ current as IC50
values on HEK 293 cell with stabilized a1G T-type
calcium channel.
i
t
i
p
s
i
j
l
j
m
l
g
h
h
h
j
The activities of 44 selected compounds were shown in
Table 1. The activities of this class of compounds for the
T-type Ca2þ channel inhibition were largely dependent
on substitution pattern on phenyl groups of R1 and R2.
Generally the compounds with shorter chain length
(n ¼ 2) and with secondary amine group (R3 ¼ H)
showed higher activity than their corresponding ana-
logues with longer chain length (n ¼ 3) and tertiary
amine group (R3 ¼ methyl or ethyl). Compound 21 with
trifluoromethyl groups at 3-position of phenyl group
(R1 ¼ e) and at 2-position of phenyl group (R2 ¼ m)
showed highest IC50 value of 1.02 lM. 2,4-Dimethyl-
phenylpiperazine (R1 ¼ f) analogues showed higher
activity (24 and 25) than mono methylphenylpiperazine
(R1 ¼ i) analogues (32 and 33). Compounds 13, 15 and
41 with less hydrophobic groups like p-methoxyphenyl,
pyridine and pyrimidine showed lower activity. The
cyano group substitution in piperazine ring drastically
decreased the activity (17). Whereas in case of substi-
tutions on isoxazole side phenyl ring (R2), 2-methoxy
group (R2 ¼ l), 2-trifluoromethyl group18 (R2 ¼ m), 2, 3-
dimethoxy groups (R2 ¼ n) and 2-nitro group (R2 ¼ r),
which all act as hydrogen bond acceptors showed good
inhibitory activity. From above observations we suggest
that hydrogen bond accepting group of the phenyl ring
(R2) at 2-position of isoxazole side is very important for
k
l
m
m
n
m
n
m
l
e
j
j
e
f
f
m
m
i
a IC50 values on HEK 293 cell with stabilized a1G T-type calcium
channel.
b see Figure 3 for structures.
T-type Ca2þ channel blocking activity in this class of
compounds. Whereas hydrogen bond acceptor group at
other positions like that in substituents k, q and t
showed lower activity than when it was present in 2-
position. Bulkier substituents like p-benzyloxy group
(R2 ¼ t) decreased the activity (38). Compounds with
secondary amine group (R3 ¼ H) showed higher activity
than their methyl or ethyl analogues with very few
exceptions like compounds 26 and 43. Compounds 51,

3968
H. K. Jung et al. / Bioorg. Med. Chem. 12 (2004) 3965–3970
R1
:
using KBr pellet, CHCl3 or neat. GC/MSD was ob-
OCH3
tained on a Hewlett Packard 5890. HRMS spectra were
obtained on a JMS-700 mass spectrometer (Jeol). Ana-
lytical thin layer chromatographies (TLC) were carried
out on precoated silica gel plates (Merck Kieselgel
60F254, layer thickness 0.25 mm). Flash column chro-
matographies were conducted with silica gel grade 230–
400 mesh (Merck Kiesegel 60 Art 9385).
CF3
Cl
N
N
NC
a
b
c
d
e
CH3
F
CH3
N
CH3
5.1. 5-[4-(2-Trifluoromethylphenyl)-piperazin-1-yl-ethyl-
amino methyl]-3-(2-methoxyphenyl)-isoxazole (20)
f
g
h
i
j
To a solution of 2-[4-(3-trifluoromethyl-phenyl)-piper-
azin-1-yl]-ethylamine (50.0 mg, 0.183 mmol) and 3-(2-
R2
:
O
methoxyphenyl)-isoxazole-5-carbaldehyde
0.183 mmol) in CH2Cl2 (5 mL)
(37.5 mg,
added
H3CO
H3CO
O
H3CO
was
F3C
NaBH(OAc)3 (154.8 mg, 0.730 mmol) and molecular
sieves (four beads) at room temperature. After stirring
for 1 h, the reaction mixture was quenched with a
saturated sodium bicarbonate solution and extracted
with CH2Cl2 (5 mL · 3). The collected organic layer
was washed with brine, dried over anhydrous MgSO4,
evaporated and purified by column chromatography
(EtOAc/MeOH ¼ 10:1) to give the product 20 (60.0 mg,
71.2%).
F
o
k
l
m
n
OCF3
BnO
O
O
NO2
q
r
s
t
p
Figure 3. Aromatic substituents R1; piparazinyl side phenyl ring, R2;
isoxazolyl side phenylring.
1H NMR (300 MHz, CDCl3): d 7.90 (m, 1H), d 7.44 (m,
2H), d 7.06 (m, 5H), d 6.70 (s, 1H), d 4.03 (s, 2H), d 3.91
(m, 3H), d 3.26 (m, 4H), d 2.84 (m, 2H), d 2.63 (m, 6H).
IR (KBr, cmꢁ1): 2822, 1606, 1450, 1314, 1250, 1162,
1118, 758. 13C NMR (75 MHz, CDCl3): 171.0, 160.9,
157.6, 151.7, 135.0, 131.6, 129.9, 121.3, 119.1, 116.2,
112.6, 111.8, 103.9 57.9, 55.9, 53.3, 49.0, 45.8, 45.4.
HRMS (FAB, M+H): Cacld for C24H28F3N4O2
461.2164, found 461.2178.
53 and 54 with longer chain length (n ¼ 3) showed lower
activity when compared to the corresponding analogues
21, 25 and 33 with shorter chain length (n ¼ 2). In gen-
eral, compounds with hydrophobic substituents like 3-
trifluoromethyl group (R1 ¼ e) on R1 and hydrogen
bond acceptor groups like methoxy, trifluoromethyl and
nitro groups (R2 ¼ l, m and r) at 2-position of R2, with
shorter chain length (n ¼ 2) showed appreciable T-type
Ca2þ channel blocking activity.
5.2. 5-[4-(2-Trifluoromethylphenyl)-piperazin-1-yl-ethyla-
mino methyl]-3-(2-trifluoromethylphenyl)-isoxazole (21)
4. Conclusions
To a solution of 2-[4-(3-trifluoromethyl-phenyl)-piper-
azin-1-yl] ethylamine (56.7 mg, 0.207 mmol) and 3-(2-
trifluoromethyl-phenyl)-isoxazole-5-carbaldehyde (50.0
mg, 0.207 mmol) in CH2Cl2 (5 mL) was added NaBH-
(OAc)3 (131.8 mg, 0.622 mmol) and molecular sieves
(four beads) at room temperature. After stirring for 1 h,
the reaction mixture was quenched with a saturated
sodium bicarbonate solution and extracted with CH2Cl2
(5 mL · 3). The collected organic layer was washed with
brine, dried over anhydrous MgSO4, evaporated and
purified by column chromatography (EtOAc/
MeOH ¼ 10:1) to give the product 21 (92.0 mg, 89.1%).
1H NMR (300 MHz, CDCl3): d 7.72 (m, 1H), d 7.54 (m,
3H), d 7.24 (m, 1H), d 6.98 (m, 3H), d 6.30 (s, 1H), d 3.95
(s, 2H), d 3.15 (m, 4H), d 2.72 (m, 2H), d 2.50 (m, 6H).
IR (KBr, cmꢁ1): 2822, 1450, 1316, 1166, 1124, 768. 13C
NMR (75 MHz, CDCl3): 171.9, 161.8, 151.7, 132.3,
132.1, 130.1, 129.9, 129.4, 129.0, 128.8, 126.9, 126.8,
119.1, 116.1, 112.5, 103.8, 57.9, 53.3, 49.0, 45.7, 45.2.
HRMS (FAB, M+H): Cacld for C24H25F6N4O
499.1933, found 499.1932.
A small molecule library of piperazinylalkylisoxazole
derivatives containing about 600 compounds was de-
signed, synthesized and evaluated for blocking effects on
T-type Ca2þ channel. Among them, four compounds
(20, 21, 25 and 52) showed high T-type calcium channel
blocking activity.
5. Experimental
All the commercially available reagents were obtained
from Aldrich, Fluka, and generally used without further
purification. Anhydrous procedures were performed
with purified solvents. Reaction was performed under
1
nitrogen atmosphere. H NMR and 13C NMR spectra
were obtained on a Varian Gemini 300 and Bruker
Advance 300 spectrometers. Nuclear magnetic reso-
nance spectra were acquired at 300 (or 200) MHz for 1H,
and 75 MHz for 13C NMR. Infrared spectra were ob-
tained on a Perkin Elmer 16FPC FT-IR spectrometer

H. K. Jung et al. / Bioorg. Med. Chem. 12 (2004) 3965–3970
3969
5.3. 5-[4-(2,4-Dimethylphenyl)-piperazin-1-yl-ethylamino
methyl]-3-(2-trifluoromethylphenyl)-isoxazole (25)
References and notes
1. For a review: Brini, M.; Carafoli, E. Cell Mol. Life Sci.
2000, 57, 354.
To a solution of 2-[4-(2,4-dimethyl-phenyl)-piperazin-
1-yl]-ethylamine (48.3 mg, 0.207 mmol) and 3-(2-trifluo-
2. For review: (a) Perez-Reyes, E. Phyisol. Rev. 2003, 83, 117;
(b) Vanhoutte, P. M.; Paoletti, R. The WHO classification
of calcium antagonists. TIPS 1987, 8, 4; (c) Randall,
A.; Tsien, R. W. Pharmacological dissection of
multiple types of Ca2þ channel currents in rat
cerebellar granule neurons. J. Neurosci. 1995, 15,
2995.
3. For reviews: (a) Farber, J. L. Life Sci. 1981, 29, 1289; (b)
Meyer, F. B. Brain Res. Rev. 1989, 14, 227; (c) Hugten-
burg, E. B.; Jap, W.; Heynis, J.; van Zwieten, P. Trends
Pharmacol. Sci. 1989, 10, 397; (d) Choi, D. W. Trends
Neurosci. 1995, 18, 58; (e) Kristian, T.; Siesjo, B. K. Life
Sci. 1996, 59, 357; (f) Kristian, T.; Siesjo, B. K. Stroke
1998, 29, 705.
4. (a) Pauwels, P. J.; Van Assouw, H. P.; Leysen, J. E.;
Janssen, P. A. J. Mol. Pharmacol. 1989, 36, 525; (b)
Pauwels, P. J.; Leysen, J. E.; Janssen, P. A. J. Life Sci.
1991, 48, 1881; (c) Peters, T.; Wilffert, B.; Vanhoutte, P.
M.; van Zwieten, P. A. J. Cardiovasc. Pharmacol. 1991,
18(Suppl. 8), S1; (d) Takahashi, K.; Akaike, N.
J. Pharmacol. Exp. Ther. 1991, 256, 169; (e) Urenjak,
J.; Obrenovitch, T. P. Pharmacol. Rev. 1996, 48, 21.
5. Gomora, J. C.; Daud, A. N.; Weiergraber, M.; Perez-
Reyes, E. Mol. Pharmacol. 2001, 60, 1121.
romethyl-phenyl)-isoxazole-5-carbaldehyde
(50.0 mg,
0.207 mmol) in CH2Cl2 (5 mL) was added NaBH(OAc)3
(131.8 mg, 0.642 mmol) and molecular sieves (four
beads) at room temperature. After stirring for 1 h, the
reaction mixture was quenched with a saturated sodium
bicarbonate solution and extracted with CH2Cl2
(5 mL · 3). The collected organic layer was washed with
brine, dried over anhydrous MgSO4, evaporated and
purified by column chromatography (EtOAc/
MeOH ¼ 10:1) to give the product 25 (88.0 mg, 92.7%).
1H NMR (300 MHz, CDCl3): d 7.71 (m, 1H), d 7.54 (m,
3H), d 6.87 (m, 3H), d 6.31 (s, 1H), d 3.95 (s, 2H), d 2.75
(m, 6H), d 2.51 (m, 6H), d 2.18 (s, 6H). IR (KBr, cmꢁ1):
2938, 2816, 1504, 1456, 1374, 1316, 1176, 1130, 770. 13C
NMR (75 MHz, CDCl3): 172.0, 161.8, 149.3, 133.0,
132.9, 132.3, 132.2, 132.1, 130.0, 127.4, 126.9, 126.8,
119.4, 103.8, 58.0, 54.1, 52.1, 45.8, 45.3, 21.1, 18.0.
HRMS (FAB, M+H): Cacld for C25H30F3N4O
459.2372, found 459.2361.
6. Opie, L. H. Calcium channel antagonists. Parts IV : side
effects and contraindications drug interactions and com-
binations. Cardiovasc. Drugs Ther. 1988, 2, 177.
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K.; Liou, S.-Y.; Kunihara, M. Eur. J. Pharmacol. 1994,
257, 203.
8. Richard, S.; Diochot, S.; Nargeot, J.; Baldy-Moulinier,
M.; Valmier, J. Neurosci. Lett. 1991, 132(2), 229.
9. (a) McDonough, S. I.; Bean, B. P. Mol. Pharmacol. 1998,
54, 1080; (b) Mishra, S. K.; Hermsmeyer, K. Circ. Res.
1994, 75, 144.
5.4. 5-[4-(2,4-Dimethylphenyl)-piperazin-1-yl-ethylamino
methyl]-3-(2-methoxyphenyl)-isoxazole (52)
To a solution of 3-[4-(2,4-dimethyl-phenyl)-piperazin-1-
yl]-propylamine (120.0 mg, 0.485 mmol) and 3-(2-meth-
oxy-phenyl)-isoxazole-5-carbaldehyde (99.6 mg, 0.485
mmol) in CH2Cl2 (5 mL) was added NaBH(OAc)3
(308.5 mg, 1.455 mmol) and molecular sieves (four
beads) at room temperature. After stirring for 1 h, the
reaction mixture was quenched with a saturated sodium
bicarbonate solution and extracted with CH2Cl2
(5 mL · 3). The collected organic layer was washed with
brine, dried over anhydrous MgSO4, evaporated and
purified by column chromatography (EtOAc/
MeOH ¼ 10:1) to give the product 52 (123.0 mg, 58.5%).
1H NMR (300 MHz, CDCl3): d 7.91 (m, 1H), d 7.42 (m,
1H), d 6.97 (m, 5H), d 6.70 (s, 1H), d 3.99 (s, 2H), d 3.87
(s, 3H), d 2.91 (m, 4H), d 2.79 (m, 2H), d 2.62 (m, 4H), d
2.51 (m, 2H), d 2.28 (m, 6H), d 1.78 (m, 2H). IR (KBr,
cmꢁ1): 2957, 2812, 1604, 1504, 1470, 1376, 1250, 1116,
1024, 756. 13C NMR (75 MHz, CDCl3): 170.8, 160.4,
157.6, 149.3, 133.0, 132.9, 132.1, 131.6, 129.9, 127.4,
121.3, 119.4, 111.8, 104.0, 57.4, 55.9, 54.2, 52.2, 48.6,
45.3, 26.8, 21.1, 18.1. HRMS (FAB, M+H): Cacld for
C26H35N4O2 435.2760, found 435.2760.
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Acknowledgements
We would like to thank Professor Jung Ha Lee of So-
gang University for biological assay. This work was
supported by Korea Institute of Science and Techno-
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