Synthesis and biological evaluation of benzenesulfonamide-substituted 4-(6-alkylpyridin-2-yl)-5-(quinoxalin-6-yl)imidazoles as transforming growth factor-β type 1 receptor kinase inhibitors

Article abstract of DOI:10.1016/j.ejmech.2008.03.024

A series of benzenesulfonamide-substituted 4-(6-alkylpyridin-2-yl)-5-(quinoxalin-6-yl)imidazoles (15a-l) have been synthesized and evaluated for their ALK5 inhibitory activity in cell-based luciferase reporter assays. Among them, 4-[5-(6-methylpyridin-2-yl)-4-(quinoxalin-6-yl)-1H-imidazol-2-ylmethyl]b enzenesulfonamide (15b) and 4-[5-(6-ethylpyridin-2-yl)-4-(quinoxalin-6-yl)-1H-imidazol-2-ylmethyl]be nzenesulfonamide (15c) showed more than 90% inhibition at 0.5 μM in a luciferase reporter assay using HaCaT cells transiently transfected with p3TP-luc reporter construct, but inhibited p38α MAP kinase activity only 11 and 8% at a concentration of 10 μM, respectively.

Full text of DOI:10.1016/j.ejmech.2008.03.024

Available online at www.sciencedirect.com
European Journal of Medicinal Chemistry 44 (2009) 568e576
http://www.elsevier.com/locate/ejmech
Original article
Synthesis and biological evaluation of benzenesulfonamide-substituted
4-(6-alkylpyridin-2-yl)-5-(quinoxalin-6-yl)imidazoles as transforming
growth factor-b type 1 receptor kinase inhibitors
a
b
a
Dae-Kee Kim a, , Sun Hee Jung , Ho Soon Lee , Purushottam M. Dewang
*
a College of Pharmacy, Ewha Womans University, 11-1 Daehyun-dong, Seodaemun-gu, Seoul 120-750, South Korea
b In2Gen Co., Ltd., 608 Daerung Posttower II Building, 182-13 Guro-dong, Guro-gu, Seoul 152-050, South Korea
Received 21 December 2007; received in revised form 25 March 2008; accepted 27 March 2008
Available online 4 April 2008
Abstract
A series of benzenesulfonamide-substituted 4-(6-alkylpyridin-2-yl)-5-(quinoxalin-6-yl)imidazoles (15ael) have been synthesized and
evaluated for their ALK5 inhibitory activity in cell-based luciferase reporter assays. Among them, 4-[5-(6-methylpyridin-2-yl)-4-(quinoxalin-
6-yl)-1H-imidazol-2-ylmethyl]benzenesulfonamide (15b) and 4-[5-(6-ethylpyridin-2-yl)-4-(quinoxalin-6-yl)-1H-imidazol-2-ylmethyl]benzene-
sulfonamide (15c) showed more than 90% inhibition at 0.5 mM in a luciferase reporter assay using HaCaT cells transiently transfected with
p3TP-luc reporter construct, but inhibited p38a MAP kinase activity only 11 and 8% at a concentration of 10 mM, respectively.
Ó 2008 Elsevier Masson SAS. All rights reserved.
Keywords: Transforming growth factor-b (TGF-b); ALK5 inhibitors; Fibrosis; Cancer
1. Introduction
binding to the common mediator Smad4. This complex is shut-
tled into the nucleus and regulates transcription of specific
target genes involved in cell growth, differentiation, develop-
ment, and the immune response [1e4]. Dysregulated signaling
of TGF-b has been implicated in the pathogenesis of a number
of diseases, including fibrosis and carcinogenesis [4e6]. TGF-b
also plays important roles in wound healing and is possibly
deregulated in the related pathologies of hypertrophic scars
and keloids [7,8]. Attempts to block the effects of TGF-b con-
tributed to the development of molecules that inhibit TGF-
b binding to its receptor including decorin [9], soluble chimeric
TGF-b receptor [10], and neutralizing antibodies [11]. The
extensive knowledge regarding TGF-b-mediated ALK5-depen-
dent signaling pathway as an initiating point at the receptor
level has highlighted the therapeutic potential of TGF-b signal-
ing antagonist. Recent studies have shown that several small
molecule ATP-competitive ALK5 inhibitors (Fig. 1) such as 1
(SB-431542) [12], 2 (SB-505124) [13], 3 (SB-525334) [14], 4
(A-83-01) [15], 5 (GW6604) [16], 6 (LY580276) [17], and
SD-208 [18,19] inhibited autophosphorylation of ALK5 and
The TGF-b superfamily of ligands includes TGF-b, activins,
and bone morphogenetic proteins (BMPs) and regulates a wide
range of responses including cell proliferation, differentiation,
adhesion, migration, and apoptosis. Three TGF-b isoforms
(TGF-b1, TGF-b2, and TGF-b3) are expressed in mammals,
and each is encoded by a unique gene and expressed in a tis-
sue-specific manner. TGF-b1 is the prototypic member of this
family of cytokines that signals through two types of transmem-
brane receptor serine/threonine kinases, the type I and type II
TGF-b receptors (TbR-I and TbR-II, respectively). Generally,
ligand interaction with a homodimer of type II receptors
recruits and activates homodimers of type I receptors or activin
receptor-like kinase 5 (ALK5). Activated ALK5 phosphory-
lates a subset of downstream signaling molecules, the recep-
tor-activated Smad2/Smad3 proteins, which then enable their
* Corresponding author. Tel.: þ82 2 3277 3025; fax: þ82 2 3277 2467.
E-mail address: dkkim@ewha.ac.kr (D.-K. Kim).
0223-5234/$ - see front matter Ó 2008 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2008.03.024

D.-K. Kim et al. / European Journal of Medicinal Chemistry 44 (2009) 568e576
569
O
O
N
N
O
O
O
N
N
N
N
S
NH2
N
H
N
H
N
H
N
N
NH
N
N
N
N
1 (SB-431542)
2 (SB-505124)
3 (SB-525334)
4 (A-83-01)
F
N
N
N
O
CN
N
NH2
N
HN
N
N
N
N
N
H
N
H
NH
N
N
N
N
N
5 (GW6604)
6 (LY580276)
7 (IN-1130)
8 (IN-1166)
Fig. 1. Small molecule ATP-competitive ALK5 inhibitors.
TGF-b-induced transcription of matrix genes in reporter assays
at submolar concentrations. Among them, 3, 5 and SD-208
effectively retarded progressive fibrosis in kidney, liver and
lung, respectively, and SD-208 also strongly inhibited growth
and invasiveness of cancer cells in animal models. Earlier
reports from our laboratory described several 2-pyridyl-
substituted triazole [20,21], imidazole [22e24], and thiazole
derivatives [25]. These derivatives possess phenyl moiety as
one of the substituents on the central 5-membered heterocycle
attached directly or through methylene or aminomethylene
linkage. We have demonstrated that incorporation of a short
linkage, either methylene [21] or aminomethylene [22,25],
between a central triazole, an imidazole, or a thiazole and a phe-
nyl ring significantly enhances ALK5 inhibitory activity along
with selectivity. Moreover, introduction of a carbonitrile or
a carboxamide group at meta- or para-position on the phenyl
ring leads to the similar activity and selectivity enhancing
effects. These structural modifications have culminated in the
discovery of compound 8 (IN-1166), a highly potent and selec-
tive ALK5 inhibitor [22]. Based on similar modifications,
inhibitor 7 (IN-1130) was designed and synthesized. To our
delight, 7 effectively suppressed fibrogenic process of unilateral
ureteral obstruction in rats underscoring the potential clinical
benefits in the treatment of renal fibrosis [26] and ameliorated
experimental autoimmune encephalomyelitis (EAE) in SBE-
luc and GFAP-luc mice immunized with MOG35e55 [24].
Hence being encouraged with these results, it was of our
immediate interest to observe the effect of introduction of
a sulfonamide group as a bioisoster for a carboxamide on the
phenyl substitution. It was previously observed by us that
compounds with a carboxamide substituent in the meta-position
on the phenyl ring showed slightly higher ALK5 inhibition
compared to the corresponding compounds that have that
substituent in the para-position [22,25]. To prepare compounds
with a sulfonamide substituent in the meta-position on the
phenyl ring, according to our synthetic scheme shown in
Scheme 1, 3-(2-oxoethyl)benzenesulfonamide and 3-(3-oxo-
propyl)benzenesulfonamide are requisite. However, these
unknown sulfonamides are not readily accessible, therefore,
we decided to prepare compounds having a sulfonamide sub-
stituent in the para-position. In combination with this structural
modification, the impact of linkage, either methylene (15aef)
or ethylene (15gel), between the central imidazole and a phenyl
ring was evaluated. Based on the previous observations
[22,25,27], 2-pyridyl substitution on the central imidazole
was also modified by incorporating a small alkyl functionality
at 6-position.
2. Results and discussion
2.1. Chemistry
A series of benzenesulfonamide-substituted 4-(6-alkylpyri-
din-2-yl)-5-(quinoxalin-6-yl)imidazoles, 15ael, were prepared
as shown in Scheme 1. Quinoxaline-6-carboxylic acid was
reacted with (COCl)2
in toluene to give quinoxaline-6-carbonyl
chloride (9) in quantitative yield. Coupling of 9 with the pyri-
dines 10aef in anhydrous THF in the presence of base
(n-BuLi and Et2AlCl in hexane) was carried out to obtain the
quinoxalinyl monoketones 11aef in 25e75% yields. Oxidation
of 11aef in DMSO with HBr (48 wt.% in water) gave the
quinoxalinyl diketones 12aef in 20e78% yields, which were
subsequently cyclized in MeOH/t-BuOMe with phenylacetal-
dehyde (13a) or hydrocinnamaldehyde (13b) in the presence
of NH4OAc to afford the pyridin-2-ylimidazoles 14ael in
23e72% yields. Chlorosulfonylation of 14ael with ClSO3H
in CH2Cl2 followed by amination of the resulting sulfonyl
chlorides with NH4OH yielded the pyridin-2-ylimidazole
sulfonamides 15ael in 12e59% yields.
2.2. Luciferase reporter assay and p38a
MAP kinase assay
To evaluate TGF-b-induced downstream transcriptional ac-
tivation to ALK5 signaling, cell-based luciferase activity of
15ael was measured using HaCaT cells transiently transfected

570
D.-K. Kim et al. / European Journal of Medicinal Chemistry 44 (2009) 568e576
N
N
N
N
N
N
O
O
O
a
b
c
N
OH
Cl
N
O
O
N
N
N
R
9
R
10a–f
R
12a–f
11a–f
10a: R = H
12a: R = H (20%)
12b: R = Me (66%)
12c: R = Et (50%)
12d: R = n-Pr (78%)
12e: R = i-Pr (76%)
12f: R = n-Bu (73%)
11a: R = H (75%)
10b: R = Me
10c: R = Et
10d: R = n-Pr
10e: R = i-Pr
10f: R = n-Bu
11b: R = Me (65%)
11c: R = Et (29%)
11d: R = n-Pr (38%)
11e: R = i-Pr (25%)
11f: R = n-Bu (45%)
SO2NH2
N
N
N
d
e
N
N
N
n
n
N
H
N
H
CHO
N
n
N
13
14a–l
R
15a–l
R
14a: R = H, n = 1 (62%)
14b: R = Me, n = 1 (25%)
14c: R = Et, n = 1 (23%)
14d: R = n-Pr, n = 1 (29%)
14e: R = i-Pr, n = 1 (24%)
14f: R = n-Bu, n = 1 (24%)
14g: R = H, n = 2 (72%)
14h: R = Me, n = 2 (56%)
14i: R = Et, n = 2 (44%)
14j: R = n-Pr, n = 2 (59%)
14k: R = i-Pr, n = 2 (20%)
14l: R = n-Bu, n= 2 (57%)
15a: R = H, n = 1 (30%)
15b: R = Me, n = 1 (27%)
15c: R = Et, n = 1 (15%)
15d: R = n-Pr, n = 1 (12%)
15e: R = i-Pr, n = 1 (21%)
15f: R = n-Bu, n = 1 (16%)
15g: R = H, n = 2 (46%)
15h: R = Me, n = 2 (37%)
15i: R = Et, n = 2 (59%)
15j: R = n-Pr, n = 2 (46%)
15k: R = i-Pr, n = 2 (20%)
15l: R = n-Bu, n = 2 (41%)
13a: n = 1
13b: n = 2
Scheme 1. Reagents and conditions: (a) (COCl)2, toluene, reflux, 2 h; (b) n-BuLi, Et2AlCl, anhydrous THF, ꢀ60 ꢁC; (c) HBr (48 wt.% in water), DMSO,
60e70 ꢁC, 2 h; (d) NH4OAc, MeOH, t-BuOMe, 60e70 ꢁC, 2 h; (e) (i) ClSO3H, CH2Cl2, rt, 2 h, Ar atmosphere; (ii) NH4OH (28%, aq.), dioxane, THF, rt, 2 h.
with two different luciferase receptor genes, p3TP-luciferase
reporter [28] and ARE-luciferase reporter [29], at a concentra-
tion of 0.5 mM. The selectivity of the synthesized compounds
was determined against p38a MAP kinase because this was
the only kinase to be significantly affected by SB-431542 in
vitro on a panel of 24 kinases unrelated to the ALKs [12].
A close look at the inhibitory activity (Table 1) as the
effect of change in length of linkage joining the central
imidazole ring and a phenyl ring reflects that generally the
methylene (n ¼ 1) linkage is favored over the ethylene link-
age (n ¼ 2) with the exception of compound 15d. In the case
of 15d, where n-propyl moiety was present on the pyridyl
substitution the reverse effect was observed. The activity
was increased with the lengthening of methylene (15d) to
ethylene linkage (15j). In another approach to optimize these
analogues, we concentrated on pyridyl substitution. A small
alkyl group at the 6-position of pyridyl ring has shown
crucial influence on the binding affinity in the cases of sev-
eral other closely related ALK5 inhibitors [22,27]. Motivated
by these reports, we wished to judge the optimal size of an
alkyl moiety best suitable to this series for the 6-position
of pyridyl substitution. Hence, the 6-position was derivatized
with different small alkyl moieties. The activities of resulted
compounds (15bef and 15hel) were compared within them-
selves and with unsubstituted analogues (15a and 15g).
Incorporation of a methyl substituent resulted in excellent
increase in both sets, one with methylene (15b) and another
with ethylene (15b) linkage, as compared, respectively, with
their counterpart compound (15a or 15g) which lack alkyl
substitutions. Extending methyl substitution further to ethyl
(15c and 15i) imparted additional binding interactions that
led to improvement in inhibitory activity. However, propyl
groups were too big to be accommodated beneficially and
hence the activities were dropped when ethyl (15c) was re-
placed with n-propyl (15d) and i-propyl (15e) groups. The
similar drop in activity was observed in the case of 15j
and 15k albeit to different order of magnitudes as compared
to the corresponding ethyl derivative (15i). The excellent
improvements in activity as evidenced by methyl (15b and
15h) and ethyl (15c and 15i) analogues proved that in this
series also 6-position on pyridyl ring offers a room for ap-
pending alkyl substitutions to increase activity. Nevertheless,
the limitations of the available space were indicated by lower
activity of compounds having propyl groups (15d, 15e, 15j
and 15k) than the corresponding methyl (15b and 15h) and
ethyl (15c and 15i) appended compounds. This was further
confirmed by n-butyl derivatives (15f and 15l) that exhibited
significant loss in ALK5 inhibitory activity compared to
n-propyl analogues (15d and 15j). Study of activities in
this series conclusively reveals that the methyl-, ethyl-, or
n-propyl-substituted analogues are more potent than parent
unsubstituted (15a or 15g) derivatives.

D.-K. Kim et al. / European Journal of Medicinal Chemistry 44 (2009) 568e576
3TP-Luc luciferase assay
571
Table 1
Inhibitory activity of benzenesulfonamide-substituted 4-(6-alkylpyridin-2-yl)-
5-(quinoxalin-6-yl)imidazoles, 15ael, on ALK5
20000
18000
16000
14000
12000
10000
8000
6000
4000
2000
0
1
15b
15c
7
SO2NH2
N
N
N
n
N
H
N
15a−l
R
Compound
R
n
Activitya (% control)
p3TP-luciferaseb ARE-luciferaseb p38a MAP
kinasec
Mock
TGF-b
15a
15b
15c
15d
15e
15f
15g
15h
15i
2
2
100 ꢂ 15
47 ꢂ 4
7 ꢂ 1
100 ꢂ 14
90 ꢂ 9
mock TGF-β1 0.0625
0.125
0.250 0.500 (μM)
H
1
1
1
1
1
1
2
2
2
2
2
2
95 ꢂ 5
89 ꢂ 6
Fig. 2. Effect of 15b and 15c on the activity of TGF-b-induced ALK5. HaCaT
cells were transiently transfected with p3TP-luciferase reporter construct.
Luciferase activity was determined in the presence of different concentrations
of each compound and is given as the mean ꢂ SD of three independent exper-
iments run in triplicate relative to control.
Me
Et
40 ꢂ 4
6
38 ꢂ 4
92 ꢂ 4
n-Pr
i-Pr
n-Bu
H
40 ꢂ 5
88 ꢂ 8
70 ꢂ 5
60 ꢂ 5
13 ꢂ 2
9 ꢂ 2
107 ꢂ 11
128 ꢂ 13
109 ꢂ 16
93 ꢂ 15
64 ꢂ 6
105 ꢂ 9
98 ꢂ 6
104 ꢂ 10
97 ꢂ 6
Me
Et
91 ꢂ 8
ALK5 in a dose-dependent manner as shown in Fig. 2. Also these
compounds were more potent than 1 at all four concentrations
tested. Compound 15c at concentrations of 0.125, 0.25 and
0.5 mM was at least two-fold more potent than 1. Also, the
inhibition at 0.5 mM concentration exhibited by 15b was twice
of that shown by compound 1. The comparison of ALK5 inhib-
itory activity of 15b and 15c with 7 demonstrates roughly the
influence of bioisosteric replacement of carboxamide with sul-
fonamide functionality. It can be realized from the higher activity
of 7 that m-carboxamide moiety present on the phenyl substitu-
tion interacts more favorably with the ATP binding pocket of
ALK5 than the corresponding p-sulfonamide moiety.
46 ꢂ 10
68 ꢂ 7
96 ꢂ 9
15j
15k
15l
n-Pr
i-Pr
n-Bu
16 ꢂ 2
102 ꢂ 15
123 ꢂ 8
25 ꢂ 4
103 ꢂ 12
105 ꢂ 9
97 ꢂ 8
114 ꢂ 13
147 ꢂ 12
76 ꢂ 7
1
49 ꢂ 5
a
Activity is given as the mean ꢂ SD of three independent experiments run
in triplicate relative to control incubations with DMSO vehicle.
b
Luciferase activity was determined at a concentration of 0.5 mM of inhibitor.
Kinase activity was determined at a concentration of 10 mM of inhibitor.
c
After achieving improvements in activities on introducing
alkyl substitutions in this series, it was of paramount interest
to know the selectivity of these analogues. As mentioned above,
to determine the selectivity p38a MAP kinase was chosen. In
vitro kinase assay of this enzyme was performed in the presence
of 10 mM of inhibitors. The most outstanding observation re-
garding selectivity profile was that all the compounds, 15ael,
exhibited weak or no measurable inhibition (<11%) for p38a
MAP kinase. This shows remarkably higher selectivity than
SB-431542 (1) which caused 51% inhibition of p38a MAP ki-
nase. The selectivity profile of these derivatives was not affected
to a great extent either by introduction of alky moiety on pyridyl
substitution or by change in the length of linkage that attaches
benzenesulfonamide group to central imidazole scaffold.
3. Conclusion
In this report, on the backdrop of the introduction of a p-
sulfonamide group on the phenyl substitution in tri-substituted
imidazole-based ALK5 inhibitors other two crucial structural
variations were investigated systematically. The structuree
activity relationships (SARs) regarding the optimal length of
an alkylene linkage between a phenyl and the central imidaz-
ole ring revealed that commonly a methylene is superior to an
ethylene linkage. Although our recent reports [22,25] and
other [27] suggest that a methyl is generally the best optimal
substituent for the 6-position of pyridyl ring, an ethyl substit-
uent is also equivalently beneficial in this series of compounds.
These modifications furnished compounds 15b and 15c that
are more potent than the known inhibitor 1. Albeit, compound
7 that contains a m-carboxamide group on the phenyl substitu-
tion was more potent in ALK5 inhibition than these p-sulfon-
amide analogues. All synthesized compounds were more
selective for ALK5 inhibition than p38a MAP kinase inhibi-
tion compared to 1. This manuscript reports the first exclusive
attempt to use p-sulfonamide functionality on the phenyl
substitution and ethylene linkage in the design of ATP-com-
petitive inhibitors of ALK5. The SAR disclosed here shall
The above series provided us with compounds 15b and 15c
which exhibited, respectively, 93 and 94% inhibition at 0.5 mM
in a p3TP-luciferase reporter assay. Moreover, these compounds
possess high selectivity against p38a MAP kinase causing only
11 (15b) and 8% (15c) inhibition. Hence, compounds 15b and
15c were selected for further studies and their inhibitory activity
was determined at four different concentrations (0.0625, 0.125,
0.25, and 0.5 mM) using HaCaT cells transiently transfected
with p3TP-luciferase reporter construct. The results were
compared with two different known small molecule ALK5 in-
hibitors, 1 and 7. The regulatory preclinical studies of compound
7 are currently under way. Compounds 15b and 15c inhibited

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D.-K. Kim et al. / European Journal of Medicinal Chemistry 44 (2009) 568e576
provide valuable insights to the medicinal chemists for design
and development of imidazole-based ALK5 inhibitors.
(t, 3H, J ¼ 7.6 Hz), 2.88 (q, 2H, J ¼ 7.6 Hz), 6.89 (d, 1H, J ¼
7.8 Hz), 6.98 (d, 1H, J ¼ 7.8 Hz), 7.60 (t, 1H, J ¼ 7.8 Hz), 8.12
(d, 1H, J ¼ 8.8 Hz), 8.26 (dd, 1H, J ¼ 8.8, 2.0 Hz), 8.60 (d, 1H,
J ¼ 1.6 Hz), 8.83 (d, 1H, J ¼ 2.0 Hz), 8.88 (d, 1H, J ¼ 1.6 Hz);
IR (neat) 1631 (CO) cmꢀ1; MS (EIS) m/z 278 (MHþ).
4. Experimental section
4.1. Chemistry
4.1.1.4.
2-(6-n-Propylpyridin-2-yl)-1-(quinoxalin-6-yl)etha-
1
none (11d). Yield 38%; mp 133e134 ꢁC; H NMR (CDCl3)
d 1.03 (t, 3H, J ¼ 7.4 Hz), 1.84e1.90 (m, 2H), 2.81 (t, 2H, J ¼
7.8 Hz), 6.92 (d, 1H, J ¼ 7.6 Hz), 6.98 (d, 1H, J ¼ 7.6 Hz), 7.58
(t, 1H, J ¼ 7.8 Hz), 8.12 (d, 1H, J ¼ 8.8 Hz), 8.25 (dd, 1H,
J ¼ 8.8, 2.0 Hz), 8.60 (d, 1H, J ¼ 2.0 Hz), 8.83 (d, 1H,
J ¼ 2.0 Hz), 8.87 (d, 1H, J ¼ 2.0 Hz); MS (EIS) m/z 292 (MHþ).
1H NMR spectra were recorded on a Varian Unity 400 spec-
trophotometer. The chemical shifts are reported in parts per
million (ppm) relative to internal tetramethylsilane in CDCl3.
Infrared spectra were recorded on an FT-infrared spectrometer
(Bio-Rad). Electrospray ionization mass spectra (ESI-MS)
were obtained on a Q-Tof2 mass spectrometer (Micromass).
All melting points were taken in Pyrex capillaries using an elec-
trothermal digital melting point apparatus (Buchi) and are not
corrected. Analytical thin-layer chromatography (TLC) was
performed on Merck silica gel 60F-254 glass plates. Medium-
pressure liquid chromatography (MPLC) was performed using
Merck silica gel 60 (230e400 mesh) with a YFLC-540 ceramic
pump (Yamagen). Elemental analyses were performed on
a Carlo Erba 1106 elemental analyzer.
4.1.1.5. 2-(6-Isopropylpyridin-2-yl)-1-(quinoxalin-6-yl)etha-
none (11e). Yield 25%; mp 129e130 ꢁC; H NMR (CDCl3)
1
d 1.40 (d, 6H, J ¼ 7.2 Hz), 3.05e3.15 (m, 1H), 6.29 (s, 1H),
6.90 (d, 1H, J ¼ 7.2 Hz), 6.97 (dd, 1H, J ¼ 8.0, 0.8 Hz), 7.59
(t, 1H, J ¼ 8.0 Hz), 8.11 (d, 1H, J ¼ 8.8 Hz), 8.25 (dd, 1H, J ¼
8.8, 2.0 Hz), 8.60 (d, 1H, J ¼ 2.0 Hz), 8.82 (d, 1H, J ¼
2.0 Hz), 8.86 (d, 1H, J ¼ 2.0 Hz); MS (EIS) m/z 292 (MHþ).
4.1.1.6. 2-(6-n-Butylpyridin-2-yl)-1-(quinoxalin-6-yl)ethanone
4.1.1. General procedure for the preparation of the
2-(pyridin-2-yl)-1-(quinoxalin-6-yl)ethanones (11aef)
1
(11f). Yield 45%; mp 89e90 ꢁC; H NMR (CDCl3) d 0.99 (t,
3H, J ¼ 7.2 Hz), 1.42e1.47 (m, 2H), 1.77e1.85 (m, 2H), 2.83
(t, 2H, J ¼ 8.0 Hz), 6.87 (d, 1H, J ¼ 8.0 Hz), 6.97 (d, 1H, J ¼ 8.0
Hz), 7.58 (t, 1H, J ¼ 8.0 Hz), 8.12 (d, 1H, J ¼ 8.8 Hz), 8.26 (dd,
1H, J ¼ 8.8, 2.0 Hz), 8.60 (d, 1H, J ¼ 2.0 Hz), 8.83 (d, 1H,
J ¼ 2.0 Hz), 8.87 (d, 1H, J ¼ 2.0 Hz); MS (EIS) m/z 306 (MHþ).
A stirred solution of pyridine 10aef (13 mmol) in anhydrous
THF (100 mL) at ꢀ60 ꢁC under Ar atmosphere was treated
dropwise with a solution of n-BuLi in hexanes (2.0 M, 13
mmol). After 30 min, a solution of Et2AlCl in hexane (1.0 M,
14 mmol) was added dropwise to the reaction mixture, and
the reaction mixture was allowed to warm to room temperature.
The reaction mixture was cooled to ꢀ60 ꢁC and transferred via
cannula to a stirred solution of quinoxaline-6-carbonyl chloride
(9) (10.3 mmol) in anhydrous THF (100 mL) at ꢀ60 ꢁC. Stir-
ring was continued for 20 min and the reaction mixture was
quenched with saturated aqueous NH4Cl solution. The mixture
was filtered through a pad of Celite and the filtered residue was
washed with EtOAc (100 mL). The combined filtrate was
concentrated under reduced pressure and the residue was puri-
fied by MPLC to afford the title compound 11aef as a solid.
4.1.2. General procedure for the preparation of the 1-
(pyridin-2-yl)-2-(quinoxalin-6-yl)ethane-1,2-diones (12aef)
A stirred suspension of 11aef (13 mmol) in DMSO was
treateddropwisewithHBr(48 wt.%inwater, 6 mL)andthemix-
turewas heated to 60e70 ꢁC. After 2 h, the reaction mixturewas
cooled to 0 ꢁC, poured onto ice water and brought to pH 10 with
K2CO3. The mixture was extracted with EtOAc (30 mL ꢃ 3),
and the EtOAc solution was dried over anhydrous Na2SO4, fil-
tered, and evaporated under reduced pressure. The residue was
purified by MPLC to afford the title compound 12aef as a solid.
4.1.1.1. 2-(Pyridin-2-yl)-1-(quinoxalin-6-yl)ethanone (11a).
4.1.2.1. 1-(Pyridin-2-yl)-2-(quinoxalin-6-yl)ethane-1,2-dione
(12a). Yield 20%; 1H NMR (CDCl3) d 7.55 (ddd, 1H, J ¼ 7.6,
4.8, 1.2 Hz), 7.99 (td, 1H, J ¼ 7.6, 1.6 Hz), 8.27 (d, 1H, J ¼
8.8 Hz), 8.28 (dq, 1H, J ¼ 7.6, 1.2 Hz), 8.43 (dd, 1H, J ¼ 8.8, 2.0
Hz), 8.55 (d, 1H, J ¼ 1.6 Hz), 8.65 (dq, 1H, J ¼ 4.8, 1.2 Hz), 8.92
(d, 1H, J ¼ 1.8 Hz), 8.95 (d, 1H, J ¼ 1.8 Hz).
1
Yield 75%; H NMR (CDCl3) d 7.06 (ddd, 1H, J ¼ 5.2, 2.4,
1.2 Hz), 7.17 (d, 1H, J ¼ 8.0 Hz), 7.68 (td, 1H, J ¼ 8.4, 1.2
Hz), 8.12 (d, 1H, J ¼ 8.8 Hz), 8.24 (dd, 1H, J ¼ 8.8, 2.0 Hz),
8.36 (d, 1H, J ¼ 4.8 Hz), 8.61 (d, 1H, J ¼ 1.6 Hz), 8.84 (d,
1H, J ¼ 1.6 Hz), 8.88 (d, 1H, J ¼ 2.0 Hz).
4.1.1.2. 2-(6-Methylpyridin-2-yl)-1-(quinoxalin-6-yl)ethanone
4.1.2.2.
1-(6-Methylpyridin-2-yl)-2-(quinoxalin-6-yl)ethane-
1
(11b) [30]. Yield 65%; mp 139e140 ꢁC; H NMR (CDCl3)
1,2-dione (12b) [30,31]. Yield 66%; mp 123e124 ꢁC; 1H
NMR (CDCl3) d 2.46 (s, 3H), 7.39 (dd, 1H, J ¼ 8.0, 0.4 Hz),
7.84 (t, 1H, J ¼ 7.6 Hz), 8.06 (dd, 1H, J ¼ 7.2, 0.4 Hz), 8.26 (d,
1H, J ¼ 8.8 Hz), 8.41 (dd, 1H, J ¼ 8.8, 2.0 Hz), 8.54 (d, 1H,
J ¼ 1.6 Hz), 8.92 (d, 1H, J ¼ 2.0 Hz), 8.95 (d, 1H, J ¼ 2.0 Hz);
IR (neat) 1698 (CO), 1684 (CO) cmꢀ1; MS (EIS) m/z 278 (MHþ).
d 2.59 (s, 3H), 6.88 (d, 1H, J ¼ 7.8 Hz), 6.97 (d, 1H, J ¼ 7.8
Hz), 7.57 (t, 1H, J ¼ 7.8 Hz), 8.12 (d, 1H, J ¼ 8.8 Hz), 8.25
(dd, 1H, J ¼ 8.8, 2.0 Hz), 8.60 (d, 1H, J ¼ 2.0 Hz), 8.83 (d,
1H, J ¼ 1.8 Hz), 8.88 (d, 1H, J ¼ 1.8 Hz); IR (neat) 1636
(CO) cmꢀ1; MS (EIS) m/z 264 (MHþ).
4.1.1.3.
2-(6-Ethylpyridin-2-yl)-1-(quinoxalin-6-yl)ethanone
4.1.2.3. 1-(6-Ethylpyridin-2-yl)-2-(quinoxalin-6-yl)ethane-1,2-
1
1
(11c). Yield 29%; mp 109e110 ꢁC; H NMR (CDCl3) d 1.41
dione (12c). Yield 50%; mp 115e116 ꢁC; H NMR (CDCl3)

D.-K. Kim et al. / European Journal of Medicinal Chemistry 44 (2009) 568e576
573
d 1.07 (t, 3H, J ¼ 7.4 Hz), 2.72 (q, 2H, J ¼ 7.2 Hz), 7.39 (dt, 1H,
J ¼ 7.6, 0.6 Hz), 7.85 (t, 1H, J ¼ 7.6 Hz), 8.07 (dd, 1H, J ¼
7.6, 0.6 Hz), 8.26 (d, 1H, J ¼ 8.8 Hz), 8.40 (dd, 1H, J ¼ 8.8,
2.0 Hz), 8.53 (d, 1H, J ¼ 1.6 Hz), 8.91e8.92 (d, 1H, J ¼
2.0 Hz), 8.95e8.96 (d, 1H, J ¼ 2.0 Hz); IR (neat) 1687 (CO)
cmꢀ1; MS (EIS) m/z 292 (MHþ).
(CDCl3) d 2.47 (s, 3H), 4.23 (s, 2H), 6.95 (d, 1H, J ¼
7.2 Hz), 8.14 (br s, 2H), 8.42 (br s, 1H), 8.83 (d, 1H, J ¼ 1.6
Hz), 8.83 (d, 1H, J ¼ 2.0 Hz), 8.84 (d, 1H, J ¼ 2.0 Hz); MS
(EIS) m/z 378 (MHþ).
4.1.3.3. 6-[2-Benzyl-5-(6-ethylpyridin-2-yl)-1H-imidazol-4-yl]-
quinoxaline (14c). Yield 23%; mp 139e140 ꢁC; 1H NMR
(CDCl3) d 1.27 (t, 3H, J ¼ 7.6 Hz), 2.77 (q, 2H, J ¼ 7.6 Hz),
4.25 (s, 2H), 6.96 (d, 1H, J ¼ 7.6 Hz), 7.28e7.40 (m, 7H),
8.15e8.16 (m, 2H), 8.44 (d, 1H, J ¼ 0.8 Hz), 8.83 (d, 1H, J ¼
2.0 Hz), 8.85 (d, 1H, J ¼ 2.0 Hz), 9.91 (br s, 1H); MS (EIS) m/z
392 (MHþ).
4.1.2.4. 1-(6-n-Propylpyridin-2-yl)-2-(quinoxalin-6-yl)ethane-
1
1,2-dione (12d). Yield 78%; mp 87e88 ꢁC; H NMR (CDCl3)
d 0.73 (t, 3H, J ¼ 7.4 Hz), 1.48e1.57 (m, 2H), 2.66 (t, 2H, J ¼ 7.6
Hz), 7.36 (dt, 1H, J ¼ 8.0, 0.6 Hz), 7.85 (t, 1H, J ¼ 7.8 Hz), 8.06
(dt, 1H, J ¼ 7.6, 0.6 Hz), 8.26 (d, 1H, J ¼ 8.8 Hz), 8.40 (dd, 1H,
J ¼ 8.8, 2.0 Hz), 8.52 (d, 1H, J ¼ 2.0 Hz), 8.92 (d, 1H, J ¼ 2.0
Hz), 8.95 (d, 1H, J ¼ 2.0 Hz); IR (neat) 1684 (CO) cmꢀ1; MS
(EIS) 306 m/z (MHþ).
4.1.3.4. 6-[2-Benzyl-5-(6-n-propylpyridin-2-yl)-1H-imidazol-4-
yl]quinoxaline (14d). Yield 29%; mp 68e69 ꢁC; 1H NMR
(CDCl3) d 0.95 (t, 3H, J ¼ 7.2 Hz), 1.68e1.74 (m, 2H), 2.71
(t, 2H, J ¼ 7.6 Hz), 4.25 (s, 2H), 6.95 (d, 1H, J ¼ 7.2 Hz),
7.31e7.38 (m, 7H), 8.15 (m, 2H), 8.43 (s, 1H), 8.83 (d, 1H,
J ¼ 2.0 Hz), 8.84 (d, 1H, J ¼ 2.0 Hz), 9.92 (br s, 1H); MS
(EIS) m/z 406 (MHþ).
4.1.2.5. 1-(6-Isopropylpyridin-2-yl)-2-(quinoxalin-6-yl)ethane-
1
1,2-dione (12e). Yield 76%; mp 95e96 ꢁC; H NMR (CDCl3)
d 1.05 (d, 6H, J ¼ 6.4 Hz), 2.91e2.98 (m, 1H), 7.42 (d, 1H, J ¼
7.6 Hz), 7.87 (t, 1H, J ¼ 8.0 Hz), 8.06 (dd, 1H, J ¼ 8.0, 1.2 Hz),
8.26 (d, 1H, J ¼ 8.8 Hz), 8.39 (dd, 1H, J ¼ 8.8, 2.0 Hz), 8.53 (d,
1H, J ¼ 2.0 Hz), 8.92 (d, 1H, J ¼ 1.6 Hz), 8.95 (d, 1H, J ¼ 1.6
Hz); IR (neat) 1683 (CO) cmꢀ1; MS (EIS) m/z 306 (MHþ).
4.1.3.5. 6-[2-Benzyl-5-(6-isopropylpyridin-2-yl)-1H-imidazol-
1
4-yl]quinoxaline (14e). Yield 24%; mp 66e67 ꢁC; H NMR
(CDCl3) d 1.27 (d, 6H, J ¼ 6.8 Hz), 3.00e3.03 (m, 1H),
4.26 (s, 2H), 6.98 (d, 1H, J ¼ 7.2 Hz), 7.31e7.41 (m, 7H),
8.15e8.16 (m, 2H), 8.44 (br s, 1H), 8.83 (d, 1H, J ¼
2.0 Hz), 8.85 (d, 1H, J ¼ 2.0 Hz), 9.82 (br s, 1H); MS (EIS)
m/z 406 (MHþ).
4.1.2.6. 1-(6-n-Butylpyridin-2-yl)-2-(quinoxalin-6-yl)ethane-
1
1,2-dione (12f). Yield 73%; mp 59e62 ꢁC; H NMR (CDCl3)
d 0.64 (t, 3H, J ¼ 7.4 Hz), 1.08e1.14 (m, 2H), 1.41e1.49 (m,
2H), 2.68 (t, 2H, J ¼ 7.6 Hz), 7.37 (dd, 1H, J ¼ 7.6, 1.2 Hz),
7.84 (t, 1H, J ¼ 7.6 Hz), 8.06 (dd, 1H, J ¼ 7.6, 1.2 Hz), 8.26 (d,
1H, J ¼ 8.8 Hz), 8.40 (dd, 1H, J ¼ 8.8, 2.0 Hz), 8.51 (d, 1H,
J ¼ 2.0 Hz), 8.92 (d, 1H, J ¼ 1.6 Hz), 8.95 (d, 1H, J ¼ 1.6 Hz);
IR (neat) 1704 (CO) cmꢀ1; MS (EIS) m/z 320 (MHþ).
4.1.3.6. 6-[2-Benzyl-5-(6-n-butylpyridin-2-yl)-1H-imidazol-4-
yl]quinoxaline (14f). Yield 24%; mp 61e62 ꢁC; 1H NMR
(CDCl3) d 0.92 (t, 3H, J ¼ 7.2 Hz), 1.33e1.39 (m, 2H),
1.60e1.67 (m, 2H), 2.72 (t, 2H, J ¼ 7.6 Hz), 4.24 (s, 2H),
6.94 (d, 1H, J ¼ 7.2 Hz), 7.31 (d, 1H, J ¼ 7.2 Hz), 7.36e
7.38 (m, 6H), 8.15 (s, 1H), 8.16 (d, 1H, J ¼ 1.6 Hz), 8.43 (d,
1H, J ¼ 1.2 Hz), 8.83 (d, 1H, J ¼ 2.0 Hz), 8.85 (d, 1H, J ¼
2.0 Hz), 10.02 (br s, 1H); MS (EIS) m/z 420 (MHþ).
4.1.3. General procedure for the preparation of the
6-[2-benzyl-5-(pyridin-2-yl)-1H-imidazol-4-yl]quinoxalines
(14aef) and 6-[2-phenethyl-5-(pyridin-2-yl)-1H-imidazol-
4-yl]quinoxalines (14gel)
To a stirred solution of 12aef (1.44 mmol) in t-BuOMe (9 mL)
and MeOH (6 mL) were added ammonium acetate (7.20 mmol)
and phenylacetaldehyde (13a) (4.32 mmol) or hydrocinnamalde-
hyde (13b) (4.32 mmol) at room temperature. The mixture was
heated at 60e70 ꢁC for 2 h and then cooled to room temperature.
The reaction mixture was concentrated under reduced pressure
and the residue was neutralized with saturated aqueous NaHCO3
solution (pH 8) at 0 ꢁC. The mixture was diluted with water and
extracted with CH2Cl2 (15 mL ꢃ 3). The CH2Cl2 solution was
washed with brine (25 mL), dried over anhydrous Na2SO4, fil-
tered, and concentrated under reduced pressure. The residue was
purified by MPLC to afford the title compound 14ael as a solid.
4.1.3.7. 6-[2-Phenethyl-5-(pyridin-2-yl)-1H-imidazol-4-yl]qui-
noxaline (14g). Yield 72%; mp 62e65 ꢁC; 1H NMR
(CDCl3) d 3.15 (s, 4H), 7.11 (dd, 1H, J ¼ 9.0, 4.6 Hz), 7.23
(dd, 3H, J ¼ 12.0, 7.0 Hz), 7.31 (q, 2H, J ¼ 7.4 Hz), 7.50 (d,
2H, J ¼ 3.6 Hz), 8.14 (dd, 2H, J ¼ 12.0, 8.4 Hz), 8.42 (s,
1H), 8.51 (dt, 1H, J ¼ 5.2, 1.4 Hz), 8.85 (d, 2H, J ¼ 5.2 Hz);
MS (EIS) m/z 378 (MHþ).
4.1.3.8. 6-[5-(6-Methylpyridin-2-yl)-2-phenethyl-1H-imidazol-
1
4-yl]quinoxaline (14h). Yield 56%; mp 47e49 ꢁC; H NMR
(CDCl3) d 2.54 (s, 3H), 3.17 (s, 4H), 6.97 (d, 1H, J ¼ 7.2
Hz), 7.23e7.41 (m, 7H), 8.13 (s, 2H), 8.42 (s, 1H), 8.83 (d,
1H, J ¼ 2.0 Hz), 8.85 (d, 1H, J ¼ 2.0 Hz); MS (EIS) m/z 392
(MHþ).
4.1.3.1.
6-[2-Benzyl-5-(pyridin-2-yl)-1H-imidazol-4-yl]qui-
1
noxaline (14a). Yield 62%; mp 59e62 ꢁC; H NMR (CDCl3)
d 4.21 (s, 2H), 7.07e7.09 (m, 1H), 7.22e7.24 (m, 1H), 7.29e
7.32 (m, 4H), 7.51 (br m, 2H), 8.14 (s, 2H), 8.40e8.43 (br m,
2H), 8.83e8.85 (m, 2H); MS (EIS) m/z 364 (MHþ).
4.1.3.9. 6-[5-(6-Ethylpyridin-2-yl)-2-phenethyl-1H-imidazol-4-
yl]quinoxaline (14i). Yield 44%; mp 48e49 ꢁC; 1H NMR
(CDCl3) d 1.32 (t, 3H, J ¼ 7.6 Hz), 2.81 (q, 2H, J ¼ 7.6 Hz),
3.19 (s, 4H), 6.98 (d, 1H, J ¼ 7.2 Hz), 7.27e7.41 (m, 7H),
4.1.3.2. 6-[2-Benzyl-5-(6-methylpyridin-2-yl)-1H-imidazol-4-
yl]quinoxaline (14b). Yield 25%; mp 61e62 ꢁC; 1H NMR

574
D.-K. Kim et al. / European Journal of Medicinal Chemistry 44 (2009) 568e576
8.13 (s, 2H), 8.42 (s, 1H), 8.83 (d, 1H, J ¼ 2.0 Hz), 8.85 (d,
1H, J ¼ 2.0 Hz); MS (EIS) m/z 406 (MHþ).
(br d, 2H, J ¼ 7.6 Hz), 7.47e7.59 (m, 4H), 8.09 (br s, 2H),
8.27 (d, 1H, J ¼ 0.8 Hz), 8.35 (br t, 1H), 8.80e8.82 (br m,
2H); IR (neat) 3282, 3175, 1334, 1158 cmꢀ1; MS (EIS) m/z
443 (MHþ). Anal. Calcd for C23H18N6O2S: C, 62.43; H, 4.10;
N, 18.99. Found: C, 62.72; H, 4.02; N, 18.81.
4.1.3.10. 6-[2-Phenethyl-5-(6-n-propylpyridin-2-yl)-1H-imida-
zol-4-yl]quinoxaline (14j). Yield 59%; mp 53e54 ꢁC; 1H
NMR (CDCl3) d 0.98 (t, 3H, J ¼ 7.4 Hz), 1.69e1.76 (m,
2H), 2.73 (t, 2H, J ¼ 7.6 Hz), 3.17 (q, 4H, J ¼ 2.8 Hz), 6.96
(d, 1H, J ¼ 7.6 Hz), 7.24e7.34 (m, 6H), 7.40 (t, 1H, J ¼ 7.6
Hz), 8.13 (d, 2H, J ¼ 1.2 Hz), 8.42 (s, 1H), 8.83 (d, 1H,
J ¼ 2.0 Hz), 8.85 (d, 1H, J ¼ 2.0 Hz); MS (EIS) m/z 420
(MHþ).
4.1.4.2. 4-[5-(6-Methylpyridin-2-yl)-4-(quinoxalin-6-yl)-1H-
imidazol-2-ylmethyl]benzenesulfonamide (15b). Two-step yield
1
27%; mp 140e143 ꢁC; H NMR (CDCl3) d 2.38 (br s, 3H),
4.17 (br s, 2H), 6.99 (d, 1H, J ¼ 7.6 Hz), 7.33 (d, 3H,
J ¼ 7.6 Hz), 7.43 (t, 1H, J ¼ 7.6 Hz), 7.73 (br s, 2H), 8.15 (s,
2H), 8.35 (br s, 1H), 8.85e8.86 (br m, 2H); IR (neat) 3411,
3244, 1341, 1169 cmꢀ1; MS (EIS) m/z 457 (MHþ). Anal. Calcd
for C24H20N6O2S: C, 63.14; H, 4.42; N, 18.41. Found: C, 62.99;
H, 4.53; N, 18.25.
4.1.3.11. 6-[5-(6-Isopropylpyridin-2-yl)-2-phenethyl-1H-imi-
1
dazol-4-yl]quinoxaline (14k). Yield 20%; mp 58e60 ꢁC; H
NMR (CDCl3) d 1.30 (d, 6H, J ¼ 6.4 Hz), 3.01e3.05 (m,
1H), 3.18 (t, 4H, J ¼ 4.6 Hz), 6.98 (d, 1H, J ¼ 7.6 Hz),
7.23e7.37 (m, 6H), 7.41 (t, 1H, J ¼ 7.6 Hz), 8.14 (s, 2H),
8.42 (s, 1H), 8.83 (d, 1H, J ¼ 1.6 Hz), 8.85 (d, 1H, J ¼
1.6 Hz); MS (EIS) m/z 420 (MHþ).
4.1.4.3. 4-[5-(6-Ethylpyridin-2-yl)-4-(quinoxalin-6-yl)-1H-
imidazol-2-ylmethyl]benzenesulfonamide (15c). Two-step yield
15%; mp 155e156 ꢁC; 1H NMR (CDCl3) d 1.14 (t, 3H,
J ¼ 7.6 Hz), 2.69 (q, 2H, J ¼ 7.6 Hz), 4.14 (s, 2H), 5.22 (br s,
2H), 7.02 (d, 1H, J ¼ 7.6 Hz), 7.31 (br s, 2H), 7.34 (d, 1H,
J ¼ 8.0 Hz), 7.48 (t, 1H, J ¼ 8.0 Hz), 7.70 (br s, 2H), 8.13 (s,
2H), 8.33 (s, 1H), 8.84e8.85 (m, 2H); IR (neat) 3046, 1325,
1153 cmꢀ1; MS (EIS) m/z 471 (MHþ). Anal. Calcd for
C25H22N6O2S: C, 63.81; H, 4.71; N, 17.86. Found: C, 63.63;
H, 4.85; N, 17.69.
4.1.3.12. 6-[5-(6-n-Butylpyridin-2-yl)-2-phenethyl-1H-imida-
zol-4-yl]quinoxaline (14l). Yield 57%; mp 54e55 ꢁC; 1H
NMR (CDCl3) d 0.95 (t, 3H, J ¼ 7.4 Hz), 1.39 (m, 2H),
1.64e1.72 (m, 2H), 2.75 (t, 2H, J ¼ 7.8 Hz), 3.16 (br s, 4H),
6.96 (d, 1H, J ¼ 7.2 Hz), 7.23e7.34 (m, 6H), 7.40 (t, 1H,
J ¼ 7.8 Hz), 8.13 (d, 2H, J ¼ 0.8 Hz), 8.42 (s, 1H), 8.83 (d,
1H, J ¼ 2.0 Hz), 8.85 (d, 1H, J ¼ 2.0 Hz); MS (EIS) m/z 434
(MHþ).
4.1.4.4. 4-[5-(6-n-Propylpyridin-2-yl)-4-(quinoxalin-6-yl)-1H-
imidazol-2-ylmethyl]benzenesulfonamide (15d). Two-step yield
12%; mp 150 ꢁC; 1H NMR (CDCl3) d 0.88 (t, 3H,
J ¼ 8.0 Hz), 1.50e1.68 (m, 2H), 2.62e2.70 (m, 2H), 4.17 (s,
2H), 5.08 (br s, 2H), 7.01 (d, 1H, J ¼ 7.2 Hz), 7.34e7.36
(m, 3H), 7.46 (t, 1H, J ¼ 7.6 Hz), 7.73 (br s, 2H), 8.13 (s,
2H), 8.35 (s, 1H), 8.85 (s, 2H); IR (neat) 3390, 1298,
1046 cmꢀ1; MS (EIS) m/z 485 (MHþ). Anal. Calcd for
C26H24N6O2S: C, 64.44; H, 4.99; N, 17.34. Found: C, 64.53;
H, 4.80; N, 17.29.
4.1.4. General procedure for the preparation of the
4-[5-(pyridin-2-yl)-4-(quinoxalin-6-yl)-1H-imidazol-2-
ylalkyl]benzenesulfonamides (15ael)
To a stirred solution of 14ael (0.14 mmol) in CH2Cl2
(3 mL) was added ClSO3H (3.00 mmol) at 0 ꢁC under Ar
atmosphere. After 10 min, the mixture was allowed to warm
to room temperature and stirred for an additional 2 h. The
reaction mixture was dropped into ice water and neutralized
with 6 N NaOH, and it was extracted with CH2Cl2 (10 mL ꢃ 5).
The CH2Cl2 solution was dried over anhydrous Na2SO4, filtered,
and concentrated under reduced pressure to give the sulfonyl
chloride derivatives as a brown foam, which was used in the
next step without further purification. To a stirred solution of
the sulfonyl chloride derivatives in dioxane (3 mL) and THF
(3 mL) was added 28% aqueous ammonia solution (0.5 mL)
at 0 ꢁC. After 10 min, the mixture was allowed to warm to
room temperature and stirred for an additional 2 h. The reac-
tion mixture was concentrated under reduced pressure and
then extracted with CH2Cl2 (10 mL ꢃ 3). The CH2Cl2 solution
was washed with brine (20 mL), dried over anhydrous
Na2SO4, filtered, and concentrated under reduced pressure.
The residue was purified by MPLC to afford the title com-
pound 15ael as a solid.
4.1.4.5.
4-[5-(6-Isopropylpyridin-2-yl)-4-(quinoxalin-6-yl)-
1H-imidazol-2-ylmethyl]benzenesulfonamide (15e). Two-step
1
yield 21%; mp 147e148 ꢁC; H NMR (CDCl3) d 1.26 (d,
6H, J ¼ 6.8 Hz), 3.04 (br s, 1H), 4.25 (s, 2H), 4.94 (br s,
2H), 7.04 (d, 1H, J ¼ 7.6 Hz), 7.36 (d, 1H, J ¼ 8.0 Hz),
7.46e7.47 (m, 3H), 7.83 (br d, 2H, J ¼ 8.0 Hz), 8.13 (s,
2H), 8.38 (s, 1H), 8.84e8.85 (m, 2H); IR (neat) 3406,
1030 cmꢀ1; MS (EIS) m/z 485 (MHþ). Anal. Calcd for
C26H24N6O2S: C, 64.44; H, 4.99; N, 17.34. Found: C, 64.33;
H, 5.10; N, 17.29.
4.1.4.6. 4-[5-(6-n-Butylpyridin-2-yl)-4-(quinoxalin-6-yl)-1H-
imidazol-2-ylmethyl]benzenesulfonamide (15f). Two-step yield
16%; mp 135e136 ꢁC; 1H NMR (CDCl3) d 0.76 (t, 3H,
J ¼ 7.6 Hz), 1.15e1.24 (m, 2H), 1.40 (br s, 2H), 2.62 (br s,
2H), 4.05 (br s, 2H), 5.45 (br s, 2H), 7.01 (d, 1H,
J ¼ 7.6 Hz), 7.16 (br s, 2H), 7.32 (d, 1H, J ¼ 7.2 Hz), 7.47 (t,
1H, J ¼ 7.6 Hz), 7.56 (br s, 2H), 8.12 (br s, 2H), 8.30 (s, 1H),
8.83 (d, 1H, J ¼ 2.0 Hz), 8.84 (d, 1H, J ¼ 2.0 Hz); IR (neat)
4.1.4.1. 4-[5-(Pyridin-2-yl)-4-(quinoxalin-6-yl)-1H-imidazol-2-
ylmethyl]benzenesulfonamide (15a). Two-step yield 30%; mp
1
137e144 ꢁC; H NMR (CDCl3) d 4.09 (s, 2H), 5.69 (br s,
2H), 5.88 (br s, 1H), 7.10 (td, 1H, J ¼ 7.2, 1.2 Hz), 7.15e7.21

D.-K. Kim et al. / European Journal of Medicinal Chemistry 44 (2009) 568e576
575
3422, 1422, 1035 cmꢀ1; MS (EIS) m/z 499 (MHþ). Anal. Calcd
for C27H26N6O2S: C, 65.04; H, 5.26; N, 16.86. Found: C, 65.23;
H, 5.10; N, 16.69.
J ¼ 2.0 Hz); IR (neat) 3399, 3067, 1337, 1160 cmꢀ1; MS
(EIS) m/z 499 (MHþ). Anal. Calcd for C27H26N6O2S: C,
65.04; H, 5.26; N, 16.86. Found: C, 64.83; H, 5.40; N, 16.79.
4.1.4.7. 4-[2-[5-(Pyridin-2-yl)-4-(quinoxalin-6-yl)-1H-imida-
4.1.4.12. 4-[2-[5-(6-n-Butylpyridin-2-yl)-4-(quinoxalin-6-yl)-
zol-2-yl]ethyl]benzenesulfonamide (15g). Two-step yield
1H-imidazol-2-yl]ethyl]benzenesulfonamide (15l). Two-step
1
1
46%; mp 139e140 ꢁC; H NMR (CDCl3) d 3.07 (t, 2H, J ¼
yield 41%; mp 208e210 ꢁC; H NMR (CDCl3) d 0.94 (t, 3H,
7.2 Hz), 3.14 (t, 2H, J ¼ 7.2 Hz), 7.14 (ddd, 1H, J ¼ 6.0, 3.6,
1.2 Hz), 7.23 (d, 2H, J ¼ 8.4 Hz), 7.52e7.58 (m, 2H), 7.74
(d, 2H, J ¼ 8.4 Hz), 8.03 (d, 1H, J ¼ 8.8 Hz), 8.09 (d, 1H,
J ¼ 8.8 Hz), 8.19 (br s, 1H), 8.45 (dt, 1H, J ¼ 4.8, 1.2 Hz),
J ¼ 7.2 Hz), 1.40 (m, 2H), 1.69 (m, 2H), 2.78 (t, 2H, J ¼ 7.6
Hz), 3.17 (d, 2H, J ¼ 6.6 Hz), 3.22 (d, 2H, J ¼ 6.6 Hz), 7.01 (d,
1H, J ¼ 7.6 Hz), 7.36 (d, 2H, J ¼ 8.4 Hz), 7.24e7.49 (m, 2H),
7.86 (d, 2H, J ¼ 8.0 Hz), 8.09e8.12 (m, 2H), 8.23 (br s, 1H),
8.84 (d, 1H, J ¼ 2.0 Hz), 8.85 (d, 1H, J ¼ 2.0 Hz); IR (neat)
3411, 3062, 1333, 1156 cmꢀ1; MS (EIS) m/z 513 (MHþ). Anal.
Calcd for C28H28N6O2S: C, 65.60; H, 5.51; N, 16.39. Found: C,
65.93; H, 5.30; N, 16.09.
8.82e8.83 (m, 2H); IR (neat) 3275, 3180, 1331, 1158 cmꢀ1
;
MS (EIS) m/z 457 (MHþ). Anal. Calcd for C24H20N6O2S: C,
63.14; H, 4.42; N, 18.41. Found: C, 62.93; H, 4.60; N, 18.29.
4.1.4.8. 4-[2-[5-(6-Methylpyridin-2-yl)-4-(quinoxalin-6-yl)-1H-
imidazol-2-yl]ethyl]benzenesulfonamide (15h). Two-step yield
4.2. Biological activity testing
1
37%; mp 130e131 ꢁC; H NMR (CDCl3) d 2.56 (s, 3H), 3.17
(t, 2H, J ¼ 6.8 Hz), 3.24 (t, 2H, J ¼ 6.8 Hz), 7.01 (d, 1H,
J ¼ 8.0 Hz), 7.31e7.35 (m, 1H), 7.37 (d, 2H, J ¼ 8.8 Hz),
7.44 (t, 1H, J ¼ 8.2 Hz), 7.88 (d, 2H, J ¼ 8.4 Hz), 8.07 (d, 1H,
J ¼ 8.4 Hz), 8.12 (d, 1H, J ¼ 8.8 Hz), 8.22 (br s, 1H), 8.84e
8.85 (m, 2H); IR (neat) 3460, 3320, 1336, 1158 cmꢀ1; MS
(EIS) m/z 471 (MHþ). Anal. Calcd for C25H22N6O2S: C,
63.81; H, 4.71; N, 17.86. Found: C, 63.63; H, 4.90; N, 17.69.
4.2.1. Luciferase reporter assay
Biological activity of the test compounds was determined
by measuring their ability to inhibit TGF-b-induced p3TP-lu-
ciferase reporter activity and ARE-luciferase reporter activity
in HaCaT cells. HaCaT cells were seeded at concentrations of
5 ꢃ 104 in 24-well plates. And the next day, when they reach
approximately 90% confluence, the cells were transfected with
0.1 mg of p3TP-Luc reporter construct or ARE-Luc reporter
construct and 0.1 mg of b-galactosidase using Lipofectamine
2000 (Invitrogen). At 24 h after transfection, ALK5 inhibitors
of various concentrations were added to the cells. After 2 h,
the cells were treated with 5 ng/mL of TGF-b for 18e24 h.
Cell lysates were harvested according to the manufacturer’s
instruction and luminescence was measured by a luminometer
VICTOR (PerkineElmer Life).
4.1.4.9. 4-[2-[5-(6-Ethylpyridin-2-yl)-4-(quinoxalin-6-yl)-1H-
imidazol-2-yl]ethyl]benzenesulfonamide (15i). Two-step yield
1
59%; mp 130 ꢁC; H NMR (CDCl3) d 1.25 (t, 3H, J ¼ 7.6
Hz), 2.78 (q, 2H, J ¼ 7.6 Hz), 3.11 (t, 2H, J ¼ 6.4 Hz), 3.17
(t, 2H, J ¼ 6.4 Hz), 7.03 (d, 1H, J ¼ 8.0 Hz), 7.30 (d, 2H,
J ¼ 8.4 Hz), 7.35 (br s, 1H), 7.48 (t, 1H, J ¼ 7.8 Hz), 7.80
(d, 2H, J ¼ 8.0 Hz), 8.06e8.11 (m, 2H), 8.22 (br s, 1H),
8.84 (d, 1H, J ¼ 2.0 Hz), 8.85 (d, 1H, J ¼ 2.0 Hz); IR (neat)
3434, 1331, 1153 cmꢀ1; MS (EIS) m/z 485 (MHþ). Anal.
Calcd for C26H24N6O2S: C, 64.44; H, 4.99; N, 17.34. Found:
C, 64.53; H, 4.90; N, 17.29.
4.2.2. p38a MAP kinase inhibition assay
p38a kinase assay was performed according to the instruc-
tion manual of assay kit provided by the manufacturer (Upstate
Biotechnology). Briefly, to activate MAPKAP kinase-2, 10 mL
of reaction mixture containing 200 ng of inactive MAPKAP ki-
nase-2, 0.06 U of purified p38a kinase and 2 mL of magnesium/
ATP cocktail (75 mM MgCl2/500 mM cold ATP) were mixed by
vortexing and incubated for 15 min at 30 ꢁC with agitation.
Before activation reaction was started, inhibitors dissolved in
DMSO were added to the reaction tube with 10 mM of final
concentration. After activation, 10 mCi [g-32P]ATP and 10 mL
of 0.86 mM MAPKAP kinase-2 substrate were added, and the
mixture was incubated for 10 min at 30 ꢁC with agitation.
Then, 40 mL of reaction mixture was transferred into P81 phos-
phocellulose paper. After extensively washing the paper three
times with 40 mL of 0.75% phosphoric acid, the bound radioac-
tivity was determined by liquid scintillation counter.
4.1.4.10. 4-[2-[5-(6-n-Propylpyridin-2-yl)-4-(quinoxalin-6-yl)-
1H-imidazol-2-yl]ethyl]benzenesulfonamide (15j). Two-step
yield 46%; mp 215e217 ꢁC; 1H NMR (CDCl3) d 0.98 (t,
2H, J ¼ 7.6 Hz), 1.69e1.76 (m, 3H), 2.77 (t, 2H, J ¼ 7.6
Hz), 3.19 (d, 2H, J ¼ 6.2 Hz), 3.24 (d, 2H, J ¼ 6.2 Hz), 7.01
(d, 1H, J ¼ 7.2 Hz), 7.38 (d, 2H, J ¼ 8.4 Hz), 7.44 (br s,
2H), 7.88 (d, 2H, J ¼ 8.0 Hz), 8.11 (br s, 2H), 8.24 (br s,
1H), 8.84 (d, 1H, J ¼ 2.0 Hz), 8.85 (d, 1H, J ¼ 2.0 Hz); IR
(neat) 3387, 3222, 1332, 1156 cmꢀ1; MS (EIS) m/z 499
(MHþ). Anal. Calcd for C27H26N6O2S: C, 65.04; H, 5.26; N,
16.86. Found: C, 65.23; H, 5.10; N, 16.79.
4.1.4.11. 4-[2-[5-(6-Isopropylpyridin-2-yl)-4-(quinoxalin-6-yl)-
1H-imidazol-2-yl]ethyl]benzenesulfonamide (15k). Two-step
1
yield 20%; mp 124e127 ꢁC; H NMR (CDCl3) d 1.31 (d,
Acknowledgment
6H, J ¼ 6.4 Hz), 3.03e3.05 (m, 1H), 3.18 (d, 2H, J ¼ 6.2
Hz), 3.23 (d, 2H, J ¼ 6.2 Hz), 7.03 (d, 1H, J ¼ 8.0 Hz), 7.37
(d, 2H, J ¼ 8.4 Hz), 7.87 (d, 2H, J ¼ 8.4 Hz), 8.10 (br s,
2H), 8.23 (br s, 1H), 8.84 (d, 1H, J ¼ 2.0 Hz), 8.85 (d, 1H,
This work was supported in part by the grants from
Ministry of Commerce, Industry and Energy, Korea
(M1-0310-43-0001 and M1-0310-43-0002).

576
D.-K. Kim et al. / European Journal of Medicinal Chemistry 44 (2009) 568e576
S. Parsons, E.C.R. Smith, J.R. Wagner, L. Yan, F. Zhanga,
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