An Efficient Synthesis of Quinoxalinone Derivatives as Potent Inhibitors of Aldose Reductase

Article abstract of DOI:10.1002/cmdc.201200054

A novel and facile synthesis of quinoxalinone derivatives was developed in which a wide range of 3-chloroquinoxalin-2(1H)-ones as key intermediates can be generated chemo- and regioselectively in good yields from corresponding quinoxaline-2,3(1H,4H)-diones. This new protocol is arguably superior, as it allows the design and preparation of a variety of bioactive quinoxaline-based compounds, which are particularly effective in the treatment of diabetes and its complications. Through this procedure, a new class of quinoxalinone-based aldose reductase inhibitors were synthesized successfully. Most of the inhibitors, with an N1-acetic acid head group and a substituted C3-phenoxy side chain, proved to be potent and selective. Their IC₅₀ values ranged from 11.4 to 74.8nM. Among them, 2-(3-(4-bromophenoxy)-7-fluoro-2-oxoquinoxalin-1(2H)-yl)acetic acid and 2-(6-bromo-3-(4-bromophenoxy)-2-oxoquinoxalin-1(2H)-yl)acetic acid were the most active. Structure-activity relationship and molecular docking studies highlighted the importance of the ether spacer in the C3-phenoxy side chains, and provided clear guidance on the contribution of substitutions both at the core structure and the side chain to activity.

Full text of DOI:10.1002/cmdc.201200054

MED
DOI: 10.1002/cmdc.201200054
An Efficient Synthesis of Quinoxalinone Derivatives as
Potent Inhibitors of Aldose Reductase
Yanchun Yang, Shuzhen Zhang, Bobin Wu, Mingming Ma, Xin Chen, Xiangyu Qin,
Minlan He, Saghir Hussain, Chaojun Jing, Bing Ma, and Changjin Zhu*[a]
A novel and facile synthesis of quinoxalinone derivatives was
developed in which a wide range of 3-chloroquinoxalin-2(1H)-
ones as key intermediates can be generated chemo- and regio-
selectively in good yields from corresponding quinoxaline-
2,3(1H,4H)-diones. This new protocol is arguably superior, as it
allows the design and preparation of a variety of bioactive qui-
noxaline-based compounds, which are particularly effective in
the treatment of diabetes and its complications. Through this
procedure, a new class of quinoxalinone-based aldose reduc-
tase inhibitors were synthesized successfully. Most of the inhib-
itors, with an N1-acetic acid head group and a substituted C3-
phenoxy side chain, proved to be potent and selective. Their
IC50 values ranged from 11.4 to 74.8 nm. Among them, 2-(3-(4-
bromophenoxy)-7-fluoro-2-oxoquinoxalin-1(2H)-yl)acetic acid
and 2-(6-bromo-3-(4-bromophenoxy)-2-oxoquinoxalin-1(2H)-yl)-
acetic acid were the most active. Structure–activity relationship
and molecular docking studies highlighted the importance of
the ether spacer in the C3-phenoxy side chains, and provided
clear guidance on the contribution of substitutions both at the
core structure and the side chain to activity.
Introduction
Diabetes mellitus is a chronic disease caused by insulin defi-
ciency or insulin resistance. In this disease the abnormally high
levels of blood glucose trigger an enhancement in the polyol
pathway; this, in turn, causes longer-term complications such
as neuropathy, nephropathy, retinopathy, cataracts, and stroke
by damaging blood vessels and peripheral nerves. A growing
number of studies reveal a link between glucose metabolism
via the overactive polyol pathway and long-term diabetic com-
plications.[1] Aldose reductase (EC 1.1.1.21, ALR2a) catalyzes the
NADPH-dependent reduction of glucose to sorbitol in the first
and rate-controlling step of this metabolic pathway (Fig-
ure 1).[1a,2] Therefore, this enzyme has received much attention
as an important therapeutic target in the search for drugs that
Quinoxaline and quinoxalinone derivatives have attracted
considerable attention because they are endowed with a wide
spectrum of properties; they have been used as dyes,[5] re-
agents in organic synthesis,[6] photo- and electrochemical ma-
terials,[7] and pharmaceuticals. Typically, the quinoxaline moiety
is present as the scaffold of antibiotics such as echinomycin,
levomycin, and actinoleutin, which are known to inhibit the
growth of Gram-positive bacteria, block hepatitis C virus,[8] and
which are also active against various transplantable tumors,
probably owing to their ability to bind DNA.[9] In recent years
quinoxaline derivatives have seen increased application as anti-
malarial,[10] anti-inflammatory, anticancer,[11] and anti-mycobac-
terial agents.[12] Furthermore, quinoxaline derivatives were re-
ported to be promising therapeutics for the treatment of cere-
bral and cardiovascular diseases,[13] obesity and diabetes,[14]
and cytokine-driven disorders and tumors.[15] In particular, N-
substituted 2,3-dioxo-1-hydroquinoxaline 3 (Scheme 1), 3-mon-
osubstituted 2-oxo-1-hydroquinoxaline 7, and 1,3-disubstituted
2-oxo-quinoxaline 8 are essential building blocks or precursors
for the preparation of most of these antibiotics and
drugs,[11–14,15b] and for the synthesis of quinoxaline-based ARIs
in our work. These substituted quinoxalines must be prepared
from a specified derivative of benzene-1,2-diamine that already
Figure 1. The Polyol pathway of glucose metabolism.
can prevent or delay the onset and progression of diabetic
complications, independently of glycemic levels. In recent
years, a range of structurally varied aldose reductase inhibitors
(ARIs) have been developed (Figure 2).[3] We have been engag-
ed in the development of a variety of ARIs and in the study of
their structure–activity relationships (SARs). In an earlier study,
we designed a number of compound classes based on 1,2,4-
benzothiadiazine 1,1-dioxide, pyrido[2,3-e]-[1,2,4]-thiadiazine
1,1-dioxide, and 1,2-benzothiazine 1,1-dioxide (Figure 2).[4]
Herein we describe our further efforts toward novel and pow-
erful ARIs based on the quinoxaline scaffold, designed to con-
tribute to an improved understanding of their SARs and to
provide insight into their active conformations.
[a] Y. C. Yang,+ S. Z. Zhang,+ B. B. Wu, M. M. Ma, X. Chen, X. Y. Qin, M. L. He,
S. Hussain, C. J. Jing, B. Ma, Prof. Dr. C. J. Zhu
Department of Applied Chemistry, Beijing Institute of Technology
Zhongguancun South Street, 100081 Beijing (China)
Fax: (+86)10-68918506
E-mail: zcj@bit.edu.cn
[+] These authors contributed equally to this work.
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/cmdc.201200054.
ChemMedChem 2012, 7, 823 – 835
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
823

C. J. Zhu et al.
MED
Results and Discussion
General synthesis of 3-chloro-
quinoxalin-2(1H)-one deriva-
tives
As shown in Scheme 2, quinoxa-
line-2,3(1H,4H)-dione (9) was
prepared from oxalic acid (2)
and benzene-1,2-diamine (5);
this reacted readily with sulfonyl
dichloride to give 2,3-dichloro-
quinoxaline (11) in high yield.
Because our preliminary experi-
ment revealed that base is a criti-
cal factor in the chemoselective
hydrolysis of one of the 1,2-di-
chloro groups on dichloroqui-
noxaline 11 to form the key in-
termediate 3-chloroquinoxalin-
2(1H)-one (10), much effort was
Figure 2. Structures of aldose reductase inhibitors (ARIs).
bears
a
desired N-monosubstituted group (compound
1)[5,14,15b,16] or from the specified ketocarboxylate (compound 6)
or its equivalent.[7,11,13a–c,15,17] However, these two kinds of start-
ing compounds have low availability. 3-Chloroquinoxalin-2(1H)-
one (10) is a versatile intermediate for the formation of substi-
tuted quinoxalines 3, 7, and 8,[5a,11a,18] and its precursor qui-
noxaline-2,3(1H,4H)-dione (9) can be readily produced from
oxalic acid (2) and benzene-1,2-diamine (5). By the previous
methods, however, 9 can be converted into 10 in only very
poor yield along with the formation of a large quantity of 2,3-
dichloroquinoxaline (11) as a side product.[11a] Moreover, during
our studies on ARIs, a number of 1,4-disubstituted derivatives
of 9 were found to have inhibitory activity against ALR2, and
thus an urgent need arose to prepare more quinoxaline com-
pounds such as the 1,3-disubstituted derivatives 8 for further
structure–activity relationship studies. These issues prompted
us to develop new chemistry for improved access to quinoxa-
lines. Herein we report a novel and simple way to synthesize
key intermediates of the type 10, from which a series of novel
and potent ARIs were efficiently generated.
Scheme 2. Synthesis of 3-chloroquinoxalin-2(1H)-one derivatives. Reagents
and conditions: a) HCl, H2O, 1008C, 6 h, 96%; b) SOCl2, CH2Cl2, 458C, 6 h,
94%.
Table 1. Optimization of reaction conditions.[a]
Entry
Base (equiv)
Solvent (ratio)
t [h]
Yield [%][b]
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
NaOH (2)
LiOH (2)
KOH (2)
K2CO3 (2)
Cs2CO3 (2)
LiOH (1)
LiOH (2)
LiOH (3)
LiOH (2)
LiOH (2)
LiOH (2)
LiOH (2)
LiOH (2)
LiOH (2)
LiOH (2)
LiOH (2)
LiOH (2)
THF/H2O (10:1)
THF/H2O (10:1)
THF/H2O (10:1)
THF/H2O (10:1)
THF/H2O (10:1)
THF/H2O (10:1)
THF/H2O (10:1)
THF/H2O (10:1)
dioxane
12
12
12
12
12
24
24
24
12
12
12
24
24
24
24
24
24
25
68
–
–
–
20
61
27
18
50
46
82
90
88
69[c]
77[c]
85[c]
THF
H2O
THF/H2O (5:1)
THF/H2O (5:2)
THF/H2O (1:1)
dioxane/H2O (5:1)
dioxane/H2O (5:2)
dioxane/H2O (1:1)
[a] All reactions were carried out with compound 11 (2 mmol) at 658C.
[b] Following column chromatography. [c] At 558C.
Scheme 1. Overview of synthetic pathways for quinoxaline derivatives.
824
www.chemmedchem.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemMedChem 2012, 7, 823 – 835

Quinoxalinone Derivatives as ARIs
MED
put into the optimization of reaction conditions, including
bases and solvents. Detailed findings of the optimization pro-
cess are listed in Table 1. Notably, the performance of this reac-
tion depends significantly on the type of base, and lithium hy-
droxide was found to be favorable for the reaction, providing
10 in 68% yield (Table 1, Entry 2) whereas sodium hydroxide is
much less effective (Entry 1). Attempts with potassium hydrox-
ide, potassium carbonate, and cesium carbonate as base were
also unsuccessful, because after reaction for 12 h the entire
amount of starting material was recovered (Table 1, Entries 3–
5). Subsequent optimization of the amount of lithium hydrox-
ide showed that the use of LiOH at 2 equiv is essential
(Table 1, Entries 6–8). Decreasing or increasing the amount of
base to 1 or 3 equiv led to a significant decrease in yield. Fur-
thermore, investigation of solvent effect on the reaction
showed that the tested solvents dioxane, tetrahydrofuran, and
water all give low conversions (Table 1, Entries 9–11). After ex-
With the optimized reaction conditions in hand, we further
investigated the scope of the reaction, starting with various
2,3-dichloroquinoxalines bearing a substituent at the phenyl
ring, and the results are summarized in Table 2. As expected,
a variety of products were accessible under the optimized re-
action conditions, and good to excellent yields were typically
observed. Notably, chloro-, fluoro-, bromo-, and nitro-substitut-
ed 2,3-dichloroquinoxalines all showed greater reaction rates
than compound 11 (Table 2, Entries 1–4). The effects of sub-
stituents on the reaction rate fall in the rank order of NO2 >
ClꢀBr>F. These results indicate that the substrates with an
electron-withdrawing group on the phenyl ring are preferred
in reaction over the unsubstituted substrate and those bearing
an electron-donating group (Table 2, Entries 5 and 6). Reactions
of 2,3-dichloroquinoxalines containing an electron-donating
substituent were very slow, and after 24 h a large amount of
starting material remained. After numerous attempts the reac-
tion was greatly improved by using an alternate solvent
system of mixed dioxane/H2O (1:1) instead of THF/H2O (5:2)
(Table 2, Entries 7 and 8). It is likely that this alternate solvent
mixture did not work effectively for substrates containing an
electron-withdrawing group, as too many side reactions were
amining
a number of solvent combinations, significantly
higher conversions were observed with a mixed solvent of
THF/H2O, providing compound 10 at up to 90% yield (En-
tries 12–14).
Table 2. Scope of the hydrolytic reaction by LiOH.[a]
Entry
Substrate
Solvent (ratio)
t [h]
Product A[b]
Product B[b]
A/B[c]
81:19
Yield [%][c]
1
THF/H2O (5:2)
15
77
2
3
4
THF/H2O (5:2)
THF/H2O (5:2)
THF/H2O (5:2)
12
12
5
77:23
72:28
–
94
88
80
–
5
6
THF/H2O (5:2)
THF/H2O (5:2)
24
24
–
–
21
47
ND[d]
7
8
9
16
17
15
dioxane/H2O (1:1)
dioxane/H2O (1:1)
dioxane/H2O (1:1)
24
24
5
26
27
–
–
28
25
–
69:31[f]
–
76[e]
82[e]
64[e]
10
dioxane/H2O (1:1)
24
–
84[e]
[a] Reaction conditions: 2 mmol substrate, 2.0 equiv LiOH, 658C. [b] Structure determined by NOESY. [c] Regioisomeric ratio determined by column chroma-
tography. [d] Not detected. [e] At 558C. [f] Regioisomeric ratio determined by NMR spectroscopy.
ChemMedChem 2012, 7, 823 – 835
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemmedchem.org
825

C. J. Zhu et al.
MED
observed (Table 2, Entry 9). Inter-
estingly, it was found that in
most cases the hydrolytic reac-
tions occur at the 3-position of
the substrates, forming corre-
sponding 7-substituted 3-chloro-
quinoxalin-2(1H)-ones as favored
products (Table 2, Product A),
whereas only in the case of the
6-nitroquinoxaline substrate 15
did the reaction occur preferen-
Scheme 4. Synthesis of aldose reductase inhibitors. Reagents and conditions: a) PhNH2, CH3CN, 758C, 24 h, 80–
94%; b) PhOH, DMF, K2CO3, 758C, 24 h, 78–88%; c) BrCH2COOCH3, K2CO3, CH3CN, 558C, 0.5 h, 72–88%; d) LiOH,
THF, H2O, HCl, room temperature, 2 h, 71–84%.
tially at the 2-position to afford a single isomeric product of 3-
chloro-6-nitroquinoxalin-2(1H)-one (25). This finding suggests
that significant regioselectivity is present in the reaction.
tuted anilines and phenols to install anilino and phenoxy side
chains at the C3-position followed by N-alkylation at the N1-
position with methyl 2-bromoacetate, leading to methyl esters
32–39. Hydrolysis of the esters generated eight series of acetic
acid derivatives 40–47 serving as ARI candidates. This made it
possible for us to study the SARs of the quinoxalinone deriva-
tives as described in the following section; most of the com-
pounds proved to be potent ARIs.
Synthesis of 6,7-dichloro-3-(4-methylpiperazin-1-yl)quinoxa-
lin-2(1H)-one
To further demonstrate the utility of the 3-chloroquinoxalin-
2(1H)-ones, 6,7-dichloro-3-(4-methylpiperazin-1-yl)quinoxalin-
2(1H)-one (30), which has been reported to be a histamine H4
receptor ligand and thus to have significant anti-inflammatory
activity in vivo,[11c] was prepared from 18 via the key intermedi-
ate 29 in a total yield of 76%, as shown in Scheme 3. In the
previous synthesis, 30 was produced by reaction of 18 with 1-
Design, biological activity, and SAR studies of quinoxali-
none-based ARIs
In the cases of benzothiadiazine, pyridothiadiazine, and benzo-
thiazine core structures, it has been demonstrated that an ace-
tate and a substituted aromatic group are two essen-
tial side chains required for generating effective ARIs
(Figure 2).[4] In recent work, we found a series of qui-
noxaline-2,3-dione-based ARIs, such as compounds
48 and 49 (Figure 3), that still have the two side
chains, with the acetate group at the N1-position
and the aromatic moiety at the N4-position; however,
their ALR2 inhibition activity was not satisfied (IC50 >
200 nm). In comparing the structural features of the
successful benzothiadiazine- and pyridothiadiazine-
Scheme 3. Comparison of pathways for the synthesis of 6,7-dichloro-3-(4-methylpipera-
zin-1-yl)quinoxalin-2(1H)-one (30). Reagents and conditions: a) dioxane/H2O (1:1), LiOH,
558C, 24 h, 84%; b) 1-methylpiperazine, CH3CN, 858C, 24 h, 91%; c) 1-methylpiperazine,
(iPr)2NEt, THF, mw, 5 min, 1608C, 84%; d) NaOH(aq), THF, mw, 1208C, 5 min, 57%.
based ARIs (Figure 2), it was predicted that a shift of
the aromatic side chain to the C3-position of qui-
noxaline may result in more potent ARIs. Therefore,
in our initial design of the present work, the acetate
group was installed at the N1-position of the quinox-
alinone core, and the aromatic group onto the C3-
methylpiperazine in THF followed by hydrolysis of intermediate
31 with aqueous sodium hydroxide, giving a total yield of 48%
for the two steps. Moreover, the base diisopropylethylamine
and microwave irradiation (mw) were required for the first step
(Scheme 3).[11c] The present protocol proved arguably superior
given the significantly higher yield, avoidance of such reagents
as 1-methylpiperazine and diisopropylethylamine, and the lack
of need for microwave irradiation, indicating potential for ap-
plication of this protocol to large-scale syntheses.
position. This attempt led to compounds 40a–e (Scheme 4) in
which an amino group was used as a linker for the aromatic
side chain, because the similar side chains across different
series of effective ARIs were all associated with an amino
group (Figure 2).[4] However, the activities of these compounds
were moderate (IC50: 1204–124 nm, Table 3) in tests for their
General synthesis of ARIs
The new design and synthesis of quinoxalinone-based aldose
reductase inhibitors made efficient application of the obtained
3-chloroquinoxalin-2(1H)-ones, as shown in Scheme 4. Com-
pounds 10 and 19–24 reacted readily with a variety of substi-
Figure 3. Quinoxaline-2,3-dione-based ARIs.
826
www.chemmedchem.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemMedChem 2012, 7, 823 – 835

Quinoxalinone Derivatives as ARIs
MED
As listed in Table 3, the C3-
phenoxy derivatives 41–47 that
showed significantly potent
ALR2 inhibitory activity were
tested for their ability to inhibit
aldehyde reductase (ALR1), iso-
lated from rat kidneys, in order
to evaluate their selectivity. All
of the tested compounds were
found to be only slightly active
at ALR1 (IC50 >10 mm), demon-
strating their excellent selectivi-
ty for ALR2.
Table 3. Biological activity data for quinoxalinone derivatives.
Compd
Substituents
R2
ALR2 IC50 [nm][a]
ALR1 inh. [%][b]
R1
X
40a
40b
40c
40d
40e
41a
41b
41c
42a
42b
42c
43a
43b
43c
44a
44b
44c
45a
45b
45c
46a
46b
46c
47a
47b
47c
H
H
H
H
H
H
H
H
7-F
7-F
7-F
7-Cl
7-Cl
7-Cl
7-Br
7-Br
7-Br
6-F
6-F
6-F
6-Cl
6-Cl
6-Cl
6-Br
6-Br
6-Br
4-F
4-Br
2-F,4-Br
2,4-2F
3,4,5-3F
4-F
4-Br
2-F,4-Br
4-F
4-Br
2-F,4-Br
4-F
4-Br
2-F,4-Br
4-F
4-Br
2-F,4-Br
4-F
4-Br
2-F,4-Br
4-F
4-Br
2-F,4-Br
4-F
4-Br
2-F,4-Br
NH
NH
NH
NH
NH
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
493.50 (389.97–597.03)
150.31 (117.51–183.11)
124.05 (91.35–156.75)
1203.79 (936.62–1470.96)
986.85 (798.60–1175.10)
32.74 (24.70–40.78)
27.28 (16.80–37.77)
44.92 (27.47–62.36)
19.06 (13.51–24.60)
11.40 (10.55–12.56)
22.56 (19.54–25.58)
42.29 (38.48–46.11)
32.99 (17.72–48.25)
35.62 (27.99–43.25)
62.98 (54.92–70.05)
43.48 (32.99–53.98)
47.10 (40.08–54.11)
69.87 (54.57–85.17)
49.25 (36.64–61.86)
74.79 (66.46–83.12)
50.39 (38.55–62.23)
24.34 (17.52–31.16)
46.33 (40.97–51.69)
43.13 (34.29–51.98)
16.33 (14.15–18.51)
38.22 (26.74–49.70)
14.32 (12.26–16.08)
6.37
14.34
18.94
ND[c]
ND[c]
16.62
27.61
19.82
24.42
30.70
28.79
23.84
23.11
29.95
39.11
29.35
41.46
8.19
26.23
20.40
29.46
16.63
26.85
26.85
25.55
28.23
Apart from the role of the
spacer in the C3 side chain for
ALR2 inhibitory activity de-
scribed above, in which ether
groups are much preferred over
amino groups, substituents at
the phenoxy ring and quinoxali-
none core structure were stud-
ied for their effects on biological
activity. The SAR study regard-
ing substituents on the C3-
phenoxy side chain of all seven
phenoxy series 41–47 revealed
that regardless of the substitu-
ent at the quinoxalinone core
ring, 4’-bromophenoxy deriva-
tives (subseries b) in each series
demonstrated the most potent
activity (Table 3). The 4’-flouro-
phenoxy derivatives (subseries
a) and 2’-flouro,4’-bromophe-
epalrestat
[a] IC50 (95% CL) values represent the concentration required to effect 50% enzyme inhibition. [b] Percent in-
hibition determined at a test compound concentration of 10 mm. [c] Not determined.
potential inhibitory effect on ALR2 isolated from rat lens tissue.
We then decided to concentrate structural optimizations in the
linker of the C3 side chain by replacement of the amino group
with an ether oxygen atom. Accordingly, a redesign and syn-
thesis from the key intermediates of 3-chloroquinoxalin-2(1H)-
ones provided series 41a–c. As expected, the redesigned C3-
phenoxy compounds all showed dramatically enhanced inhibi-
tory activity against ALR2 in comparing individuals in series
41a–c with their counterparts in the C3-anilino series 40a–
c (Table 3). To further study the SARs and optimize the inhibi-
tors, fine-tuning of the ligand structure was done, and in turn,
six more series of C3-phenoxy derivatives 42–47 were generat-
ed in the same synthetic manner as used for 41 (Scheme 4). All
of the C3-phenoxy compounds showed potent ALR2 inhibitory
activity, with IC50 values ranging from 11.40 to 74.79 nm
(Table 3). Among these synthetic compounds, 2-(3-(4-bromo-
phenoxy)-7-fluoro-2-oxoquinoxalin-1(2H)-yl)acetic acid (42b)
was the most active (IC50 =11.40 nm). 2-(3-(4-Bromophenoxy)-
6-chloro-2-oxoquinoxalin-1(2H)-yl)acetic acid (47b) also
showed high ALR2 inhibition potency (IC50 =16.33 nm). These
results suggest that the C3-phenoxy compounds might take
up the conformational shape preferred for activity of the qui-
noxalinone-based ARIs.
noxy derivatives (subseries c), which were similar to each other
in potency, showed much lower activity than the 4’-bromophe-
noxy derivatives. This result suggests that the 4’-bromophenyl
side chain has a significant impact on the biological activity of
quinoxalinone-based ARIs. This differs from the results we re-
ported recently in which a 2’,4’,5’-triflourophenyl side chain
was found to be the most active, presumably because of the
core structures of benzothiadiazine 1,1-dioxide and pyridothia-
diazine 1,1-dioxide (Figure 2).[4]
For further SAR studies regarding substituents at the quinox-
alinone core ring, individual compounds in the unsubstituted
series 41 were compared with their counterparts in the C7-
substituted series 42–44 and those in the C6-substituted series
45–47. The results from both substitutions at the C6- and C7-
positions are mixed, with each substitution yielding increased
potency in ALR2 inhibition in some cases, but not in others. A
significant increase in ALR2 inhibitory activity was found with
C7-flouro and C6-bromo substitutions; for example, 42b (C7-
flouro, IC50 =11.40 nm) and 47b (C6-bromo, IC50 =16.33 nm)
are more potent than the unsubstituted 41b (IC50 =27.28 nm).
In addition, C7-flouro substitutions (series 42) provided greater
benefits to the enhancement of biological activity than C6-
bromo substitutions (series 47). It was also found that effects
ChemMedChem 2012, 7, 823 – 835
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemmedchem.org
827

C. J. Zhu et al.
MED
of substituents at the C7-position on biological activity fall in
the rank order of F>Cl>Br, as deduced from the comparison
of compounds in subseries a of the C7-substituted series 42–
44 (42a>43a>44a), subseries b (42b>43b>44b), and
subseries c (42c>43c>44c). However, effects of substituents
at the C6-position fall into a reversed rank order of Br>Cl>F,
resulting from the comparison in subseries a of the C6-substi-
tuted series 45–47 (47a>46a>45a), subseries b (47b>
46b>45b), and subseries c (47c>46c>45c). These results
suggest that appropriate substituents at the C6- or C7-posi-
tions of the core structure are able to improve potency in
ALR2 inhibition, yet are not crucial for the activity of quinoxali-
none-based inhibitors.
pocket[20] formed by the side chains of Trp111, Leu300, Phe122,
Cys303, Thr113, Phe115, and Trp79. In addition, the C7-flouro-
phenyl ring of the quinoxalinone core is bound in an adjacent
hydrophobic pocket lined by the side chains of Leu300,
Trp219, Phe122, Trp20, and Trp79, and points toward the
opening of the active cleft. This manner of 42b binding to the
active site of ALR2 is similar to that of benzothiadiazine 1,1-di-
oxide-based ARI (Figure 2).[4a] On the other hand, in the dock-
ing of 42b with ALR1[19] (Figure 4e,f), the phenoxy side chain
and phenyl ring of the core appear to be mismatched, and this
may explain the selectivity of quinoxalinone derivatives for
ALR2 observed in the biological assays. These binding models
explain the SAR results described above for the quinoxalinone
compounds.
Docking studies
Conclusions
Through molecular docking methods, we examined the mech-
anistic details that underlie the biological activity of this novel
class of quinoxalinone-based inhibitors with the aim of design-
ing ARIs with more potent activity. The lidorestat-bound con-
formation of ALR2 (PDB code: 1Z3N)[3a] chosen from several
conformations was used for docking owing to the greater
structural similarity of inhibitors identified in the present study
to the ligand lidorestat over the other ligands. The docking be-
havior of 42b with the ALR1–NADP+–fidarestat complex (PDB
code: 3H4G)[19] was also investigated. Docking of the C3-anilino
compound 40b revealed that the ligand goes into the active
site of the enzyme primarily by a single hydrogen bond inter-
action between the C2-carbonyl group of the ligand and the
Trp111 residue of the anion binding pocket, which is common-
ly occupied by the carboxylate head group (Figure 4a,b). How-
ever, the carboxylate remains mismatched presumably due to
the conformational shape of 40b in which the phenyl ring of
the C3-anilino side chain is nearly coplanar with the quinoxali-
none core ring (Figure 4a). It was anticipated that the unfavor-
able direction of the carboxylate head may be attributed to
the conformationally restricted C3-amino spacer. In contrast,
docking of C3-phenoxy compound 42b, the most active as de-
scribed above, showed that the inhibitor appears to adopt
a twisted conformation, with the phenyl ring of the C3-phen-
oxy side chain perpendicular to the core; it is tightly bound in
the active site of ALR2 by a network that includes four hydro-
gen bonding interactions, an electrostatic interaction, a stack-
ing interaction, and two groups of hydrophobic interactions
(Figure 4c,d). Firstly, the carboxylate group is inserted deep
into the anion binding site by three hydrogen bonding interac-
tions with the side chains of residues Tyr48 (3.36 ꢁ), His110
(2.81 ꢁ), and Trp111 (2.94 ꢁ), and by a stabilizing electrostatic
interaction with the positively charged C4N atom of the nicoti-
namide moiety of the NADP+ cofactor (dNÀO =4.82 ꢁ). Second-
ly, the oxygen atom of the C2-carbonyl group of compound
42b core structure forms an additional hydrogen bond with
the side chain of Cys298 (2.08 ꢁ), indicating an important role
of the carbonyl in the tight binding of the inhibitor with ALR2.
Thirdly, the 4’-bromophenyl ring of C3-phenoxy of 42b forms
a stable stacking interaction against the indole ring of the
Trp111 side chain, and is well placed into the specificity
We developed a novel and efficient synthesis of quinoxaline
derivatives in which a group of key intermediates of 3-chloro-
quinoxalin-2(1H)-ones, represented by compound 10, were
chemoselectively and regioselectively formed. This synthetic
procedure has significant versatility, in that it can be used for
the facile introduction of various side chains at both the N1-
and C3-positions of the quinoxalinone core structure. More-
over, these side chains could be introduced at a very late or
even final stage. By using the synthetic procedure, a histamine
H4 receptor ligand was conveniently prepared via the C3 ami-
nation of the substituted quinoxalinone 29 with piperazine in
much higher yield, demonstrating the advantage of the syn-
thesis. The new synthetic approach has also proven useful in
the design and synthesis of novel aldose reductase inhibitors
by the introduction of a carboxylate group at the N1-position
and modifications to the C3 side chain. This, in turn, not only
resulted in the identification of the most potent inhibitors 42b
and 47b, but also allowed us to further study the structure–ac-
tivity relationships. The SAR study results significantly clarify
the essential role of the ether linker of the C3 side chain in the
quinoxalinone-based ARIs. Molecular docking studies revealed
the clear difference between C3-anilino compounds and C3-
phenoxy compounds, thus further supporting the SAR study
results. Our results, together with recent studies showing that
quinoxaline derivatives are inhibitors of glycogen phosphory-
lase and stearoyl-CoA desaturase (SCD)[14] and are activators of
insulin secretion,[21] suggest that quinoxalinone derivatives may
be emergent therapeutic agents for the treatment of diabetes
and associated complications.
Experimental Section
Chemistry
1
All reactions were carried out under air. H NMR spectra were re-
corded at 400 or 600 MHz. 1H NMR and13C NMR spectra were re-
corded in [D6]DMSO (unless otherwise stated). Chemical shifts for
1H NMR spectra are values from CDCl3 (d=7.26 ppm) or DMSO
(d=2.50 ppm). Chemical shifts for 13C NMR spectra are values from
CDCl3 (d=77.16 ppm), DMSO (d=9.52 ppm), or THF (d=67.21,
25.31 ppm). Data are presented as follows: chemical shift (ppm),
828
www.chemmedchem.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemMedChem 2012, 7, 823 – 835

Quinoxalinone Derivatives as ARIs
MED
Figure 4. Docking of inhibitors into the active site of ALR. a) Docking of 40b into the ALR2 active site. The protein structure is shown in ribbon and tube rep-
resentation with selected and labeled residues shown in line representation; ligand 40b and NADP are shown as stick models. The docked pose of 40b is
shown in cyan (C), red (O), blue (N), crimson (Br), and grey (F). Hydrogen bonds are shown as yellow dashed lines. b) Surface representation of protein resi-
dues in docking of 40b into the active site of ALR2. c) Docking of 42b into the active site of ALR2; the protein structure is shown as described for panel a).
d) Docking of 42b into the active site of ALR2; protein residues are in surface representation. e) Docking of 42b into the active site of ALR1; the protein struc-
ture is shown as described for panel a). f) Docking of 42b into the active site of ALR1; protein residues are in surface representation.
multiplicity (s=singlet, d=doublet, t=triplet, q=quartet, m=
multiplet), coupling constant, J (Hz) and integration. 13C NMR spec-
tra were recorded at 100 or 150 MHz. Data for 13C NMR are report-
ed in chemical shifts (d, ppm). HPLC analysis for data in Table 2
was performed with a Hitachi D-2000 Elite HPLC system: Inertsil
ODS-2 250 mmꢂ10 mm, 5 mm column; eluent: 75% CH3CN, 25%
H2O; flow rate: 2.5 mLminÀ1 with UV detection at l 254 nm. The
purity of all acetic acid derivatives was determined by the follow-
ing method: column, C18, 5 mm, 250 mmꢂ4.6 mm, a formic acid
(FA) gradient (CH3CN containing 5–100% 0.1% formic acid in H2O)
for 3 min with UV detection at l 254 nm.
Procedure for synthesis of quinoxaline-2,3(1H,4H)-dione (9). A
reaction solution of benzene-1,2-diamine (5) (100 mmol, 10.815 g),
oxalic acid (2) (150 mmol, 13.503 g), and concentrated HCl (10 mL)
in H2O (100 mL) was stirred at 1008C for 6 h. The resulting mixture
was cooled to room temperature. The crude product was filtered
off and washed with H2O to yield 15.602 g (96%) of the title com-
1
pound as colorless crystals. H NMR ([D6]DMSO, 400 MHz): d=7.063
(d, 2H, J=6.4 Hz), 7.114 (d, 2H, J=6.4 Hz), 11.893 ppm (s, 2H).
Procedure for synthesis of 2,3-dichloroquinoxaline (11). To a solu-
tion of compound 9 (8.107 g, 50 mmol) in a mixed solvent of DMF
(5 mL) and CH2Cl2 (50 mL) was added SOCl2 (11.900 g, 100 mmol).
ChemMedChem 2012, 7, 823 – 835
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemmedchem.org
829

C. J. Zhu et al.
MED
The mixture was stirred at 458C for 6 h and then carefully poured
onto crushed ice. After vigorous stirring, the obtained suspension
was extracted with CH2Cl2. The combined organic extracts were
washed with brine, dried with MgSO4, and filtered. After evapora-
tion of the solvent under reduced pressure, the remaining residue
was purified by column chromatography on silica gel using CH2Cl2
as eluent to yield the product (9.357 g, 94%) as colorless crystals.
1H NMR ([D6]DMSO, 400 MHz): d=7.827 (d, 2H, J=6.4 Hz),
8.045 ppm (d, 2H, J=6.4 Hz).
J=8.4 Hz), 7.325 (s, 1H); 13C NMR ([D6]DMSO, 100 MHz): d=
150.959, 149.496, 134.828, 133.281, 129.608, 129.532, 123.847,
114.848 ppm; ESIMS: [MÀH]À m/z 213.0.[11c]
3,6-Dichloroquinoxalin-2(1H)-one (22). Eluent: PE/EtOAc (3:1);
yield: 93 mg (22%); white solid, mp: 253–2558C; 1H NMR
([D6]DMSO, 400 MHz): d=12.953 (s, 1H), 7.822 (s, 1H), 7.627 (d, 1H,
J=8.4 Hz), 7.343 (d, 1H, J=8.4 Hz); 13C NMR ([D6]DMSO, 100 MHz):
d=150.913, 150.654, 131.315, 131.231, 130.678, 127.368, 126.872,
117.214 ppm; HRMS (ESI) m/z calcd for [M+H]+ 214.97734, found
214.97742.
General procedure for synthesis of 2-oxo-3-chloro-1-hydroqui-
noxaline derivatives. Method A: A 25 mL flask equipped with
a magnetic stir bar was charged with substituted 2,3-dichloroqui-
noxaline (2 mmol) and LiOH (4 mmol) in THF/H2O (5:2, 7 mL). The
mixture was stirred at 658C for 5–24 h. The resulting mixture was
cooled to room temperature, and then to it was added brine
(10 mL). After extraction with THF (3ꢂ5 mL), the combined organic
layers were washed with brine (5 mL), dried over anhydrous
MgSO4, and filtered, followed by evaporation of the solvent in va-
cuo. The resulting residue was purified by column chromatography
on silica gel using petroleum ether (PE)/EtOAc (3:1 to 2:1) as
eluent to provide the desired product (10, 19, 20, 21, 22, 23, 24,
25).
7-Bromo-3-chloroquinoxalin-2(1H)-one (23). Eluent: PE/EtOAc
(3:1); yield: 329 mg (63%); white solid, mp: >3008C; 1H NMR
([D6]DMSO, 400 MHz): d=12.890 (s, 1H), 7.670 (d, 1H, J=8.0 Hz),
7.490 (m, 2H); 13C NMR ([D6]DMSO, 100 MHz): d=150.921, 149.637,
133.460, 129.878, 129.654, 126.640, 123.386, 117.854 ppm; HRMS
(ESI) m/z calcd for [M+H]+ 258.92683, found 258.92679.
6-Bromo-3-chloroquinoxalin-2(1H)-one (24). Eluent: PE/EtOAc
(3:1); yield: 128 mg (25%); white solid, mp: 267–2688C; 1H NMR
([D6]DMSO, 400 MHz): d=12.944 (s, 1H), 7.959 (s, 1H), 7.729 (d, 1H,
J=8.4 Hz), 7.280 ppm (d, 1H, J=8.4 Hz); 13C NMR ([D6]DMSO,
150 MHz): d=151.484, 151.081, 133.895, 132.219, 132.123, 130.371,
118.039, 115.549; HRMS (ESI) m/z calcd for [M+H]+ 258.92683,
found 258.92689.
Method B: A 25 mL flask equipped with a magnetic stir bar was
charged with substituted 2,3-dichloroquinoxaline (2 mmol) and
LiOH (4 mmol) in dioxane/H2O (1:1, 10 mL). The mixture was stirred
at 558C for 5–24 h. The resulting mixture was cooled to room tem-
perature, and then to it was added brine (10 mL). After extraction
with THF (3ꢂ5 mL), the combined organic layers were washed
with brine (5 mL), dried over anhydrous MgSO4, and filtered, fol-
lowed by evaporation of the solvent in vacuo. The resulting resi-
due was purified by column chromatography on silica gel using
PE/EtOAc (3:1 to 2:1) as eluent to provide the desired product (26,
27, 28, 29).
3-Chloro-6-nitroquinoxalin-2(1H)-one (25). Eluent: PE/EtOAc (2:1);
yield: 362 mg (80%); white solid, mp: 244–2468C; 1H NMR
([D6]DMSO, 400 MHz): d=13.297 (s, 1H), 8.529 (s, 1H), 8.401 (d, 1H,
J=8.8 Hz), 7.483 ppm (d, 1H, J=8.8 Hz); 13C NMR ([D6]DMSO,
100 MHz): d=151.969, 151.169, 142.771, 137.445, 129.817, 125.280,
123.451, 116.627 ppm; HRMS (ESI) m/z calcd for [M+H]+
226.00140, found 226.00144.
3-Chloro-7-methoxyquinoxalin-2(1H)-one (26). Eluent: PE/EtOAc
(2:1); yield: 322 mg (76%); white solid, mp: 236–2388C; 1H NMR
([D6]DMSO, 400 MHz): d=7.641 (d, 1H, J=8.8 Hz), 7.947 (d, 1H, J=
9.2 Hz), 6.781 (s, 1H), 3.832 ppm (s, 3H); 13C NMR ([D6]DMSO,
150 MHz): d=161.547, 151.867, 145.710, 134.402, 129.739, 126.187,
113.012, 98.507, 56.253 ppm; HRMS (ESI) m/z calcd for [M+H]+
211.02688, found 211.02693.
3-Chloroquinoxalin-2(1H)-one (10). Eluent: PE/EtOAc (2:1); yield:
325 mg (90%); white solid, mp: 275–2788C; 1H NMR ([D6]DMSO,
400 MHz): d=12.924 (s, 1H), 7.735 (d, 1H, J=7.2 Hz), 7.576 (d, 1H,
J=7.2 Hz), 7.352 ppm (m, 2H); 13C NMR ([D6]DMSO, 100 MHz): d=
151.115, 148.993, 132.183, 130.842, 130.781, 127.844, 123.782,
115.602 ppm; ESIMS: [M+H]+ m/z 181.0.[22]
3-Chloro-7-methylquinoxalin-2(1H)-one (27). Eluent: PE/EtOAc
(2:1); yield: 320 mg (82%) (23a+23b); separated by HPLC, yield
184 mg (47%); white solid, mp: 255–2568C; 1H NMR ([D6]DMSO,
400 MHz): d=7.668 (d, 1H, J=8.0 Hz), 7.206 (m, 2H), 2.565 ppm (s,
3H); 13C NMR ([D6]DMSO, 100 MHz): d=151.268, 147.732, 141.337,
132.134, 129.071, 127.604, 125.234, 115.198, 21.308 ppm; HRMS
(ESI) m/z calcd for [M+H]+ 195.03197, found 195.03210.
3-Chloro-7-fluoroquinoxalin-2(1H)-one (19). Eluent: PE/EtOAc
(3:1); yield: 248 mg (62%); white solid, mp: 243–2468C; 1H NMR
([D6]DMSO, 400 MHz): d=12.924 (s, 1H), 7.792 (m, 1H), 7.195 (d,
1H, J=8.8 Hz), 7.065 ppm (d, 1H, J=9.2 Hz); 13C NMR ([D6]DMSO,
100 MHz): d=162.536 (d, J=247.2 Hz), 151.051, 148.216, 133.789
(d, J=12.6 Hz), 130.284 (d, J=11 Hz), 127.901, 111.777 (d, J=
23.6 Hz), 101.544 ppm (d, J=26.7 Hz); ESIMS: [MÀH]À m/z 197.0;
Elemental analysis calcd for C8H4ClFN2O: C 48.39, H 2.03, N 14.11,
found: C 48.32, H 2.18, N 13.78.
3-Chloro-6-methylquinoxalin-2(1H)-one (28). Eluent: PE/EtOAc
(2:1); yield 320 mg (82%) (23a+23b); separated by HPLC, yield
67 mg (17%); white solid, mp: 252–2558C; 1H NMR ([D6]DMSO,
400 MHz): d=12.810 (s, 1H), 7.538 (d, 1H), 7.416 (d, 1H, J=7.6 Hz),
7.246 (d, 1H, J=8 Hz), 2.506 ppm (s, 3H); 13C NMR ([D6]DMSO,
100 MHz): d=151.013, 148.864, 133.265, 132.058, 130.758, 129.928,
127.371, 115.343, 20.310 ppm; HRMS (ESI) m/z calcd for [M+H]+
195.03197, found 195.03217.
3-Chloro-6-fluoroquinoxalin-2(1H)-one (20). Eluent: PE/EtOAc
(3:1); yield: 59 mg (15%); white solid, mp: 261–2638C; 1H NMR
([D6]DMSO, 400 MHz): d=12.907 (s, 1H), 7.619 (m, 1H), 7.504 (m,
1H), 7.356 ppm (m, 1H); 13C NMR ([D6]DMSO, 100 MHz): d=
157.934 (d, J=238.9 Hz), 150.818, 150.715, 131.037 (d, J=12.2 Hz),
129.147, 118.864 (d, J=24.4 Hz), 117.035 (d, J=9.2 Hz),
113.162 ppm (d, J=23.2 Hz); ESIMS: [MÀH]À m/z 197.0; Elemental
analysis calcd for C8H4ClFN2O: C 48.39, H 2.03, N 14.11, found: C
48.54, H 2.24, N 13.79.
3,6,7-Trichloroquinoxalin-2(1H)-one (29). Eluent: PE/EtOAc (2:1);
yield: 420 mg (84%); yellow solid, mp: >3008C; 1H NMR
([D6]DMSO, 400 MHz): d=12.960 (s, 1H), 8.057 (s, 1H), 7.477 ppm
(s, 1H); 13C NMR ([D4]THF, 100 MHz): d=152.563, 151.405, 134.542,
133.243, 131.448, 130.046, 127.249, 117.069 ppm; ESIMS: [MÀH]À
m/z 247.0; Elemental analysis calcd for C8H3Cl3N2O: C 38.51, H 1.21,
N 11.23, found: C 38.63, H 1.59, N 10.87.
3,7-Dichloroquinoxalin-2(1H)-one (21). Eluent: PE/EtOAc (3:1);
1
yield: 311 mg (72%); white solid, mp: >3008C; H NMR ([D6]DMSO,
400 MHz): d=12.910 (s, 1H), 7.743 (d, 1H, J=8.4 Hz), 7.366 (d, 1H,
830
www.chemmedchem.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemMedChem 2012, 7, 823 – 835

Quinoxalinone Derivatives as ARIs
MED
Procedure for synthesis of 6,7-dichloro-3-(4-methylpiperazin-1-
yl)quinoxalin-2(1H)-one (30). A 25 mL flask equipped with a mag-
netic stir bar was charged with 3,6,7-trichloroquinoxalin-2(1H)-one
(29) (1 mmol, 250 mg) and 1-methylpiperazine (1.1 mmol, 110 mg)
in CH3CN (10 mL). The mixture was stirred at 858C for 24 h. After
concentration in vacuo, the residue was washed with EtOAc to
Removal of the solvent in vacuo gave the resulting residue, which
was purified by column chromatography on silica gel (PE/EtOAc,
3:1) to provide the desired product.
Methyl 2-(3-(4-fluorophenoxy)-2-oxoquinoxalin-1(2H)-yl)acetate
1
(33a). Yield: 215 mg (65%); white solid, mp: 160–1628C; H NMR
1
([D6]DMSO, 400 MHz): d=7.392 (m, 8H), 5.190 (s, 2H), 3.738 ppm
(s, 3H).
yield 285 mg (91%) of an off-white solid; mp: 262–2638C; H NMR
(CDCl3, 400 MHz): d=10.199 (s, br, 1H), 7.585 (s, 1H), 7.142 (s, 1H),
4.084 (s, 4H), 2.573 (s, 4H), 2.358 ppm (s, 3H); 13C NMR ([D6]DMSO,
100 MHz): d=151.576, 151.111, 132.030, 129.360, 126.357, 125.847,
124.864, 115.343, 52.454, 43.699, 42.743 ppm; ESIMS: [M+H]+ m/z
313.0.[11c]
Methyl 2-(3-(4-bromophenoxy)-2-oxoquinoxalin-1(2H)-yl)acetate
1
(33b). Yield: 247 mg (63%); white solid, mp: 189–1908C; H NMR
([D6]DMSO, 400 MHz): d=7.690 (d, J=2 Hz, 2H), 7.479 (m, 3H),
7.307 (m, 3H), 5.190 (s, 2H), 3.736 ppm (s, 3H).
General procedure for synthesis of methyl 2-(2-oxo-3-(phenyla-
mino)quinoxalin-1(2H)-yl)acetate derivatives (32a–e). A 25 mL
flask equipped with a magnetic stir bar was charged with 3-chloro-
quinoxalin-2(1H)-one (10) (1 mmol, 181 mg) and aniline (1.1 mmol)
in CH3CN (10 mL). The mixture was stirred at 858C for 24 h, cooled
to room temperature, and then H2O (100 mL) was added. The re-
sulting mixture was filtered off, washed with H2O, and suspended
in CH3CN (25 mL). To the suspension were added methyl 2-bro-
moacetate (1 mmol, 153 mg) and K2CO3 (3 mmol, 415 mg), and the
reaction mixture was stirred at 558C for 0.5 h. The resulting mix-
ture was filtered, and the solvent was removed in vacuo. Purifica-
tion of the residue by column chromatography on silica gel (PE/
EtOAc 3:1) provided the desired product.
Methyl 2-(3-(4-bromo-2-fluorophenoxy)-2-oxoquinoxalin-1(2H)-
yl)acetate (33c). Yield: 273 mg (67%); white solid, mp: 169–
1718C; 1H NMR ([D6]DMSO, 400 MHz): d=7.838 (d, J=10 Hz, 1H),
7.510 (m, 5H), 7.308 (m, 1H), 5.204 (s, 2H), 3.740 ppm (s, 3H).
Methyl 2-(7-fluoro-3-(4-fluorophenoxy)-2-oxoquinoxalin-1(2H)-
yl)acetate (34a). Yield: 213 mg (62%); white solid, mp: 174–
1
1768C; H NMR ([D6]DMSO, 400 MHz): d=7.544 (dd, J=10.8 Hz, J=
2 Hz, 1H), 7.464 (dd, J=8.8 Hz, J=6 Hz, 1H), 7.340 (m, 4H), 7.140
(dd, J=12 Hz, J=8.4 Hz, 1H), 5.204 (s, 2H), 3.740 ppm (s, 3H).
Methyl 2-(3-(4-bromophenoxy)-7-fluoro-2-oxoquinoxalin-1(2H)-
yl)acetate (34b). Yield: 259 mg (64%); white solid, mp: 175–
1
1788C; H NMR ([D6]DMSO, 400 MHz): d=7.671 (d, J=9.6 Hz, 2H),
Methyl 2-(3-((4-fluorophenyl)amino)-2-oxoquinoxalin-1(2H)-yl)a-
cetate (32a). Yield: 226 mg (69%); white solid, mp: 230–2138C;
1H NMR ([D6]DMSO, 400 MHz): d=9.662 (s, 1H), 8.169 (dd, J=
9.2 Hz, J=5.2 Hz, 2H), 7.57 (m, 1H), 7.406 (m, 1H), 7.304 (m, 2H),
7.209 (t, J=8.8 Hz, 2H), 5.181 (s, 2H), 3.726 ppm (s, 3H).
7.549 (dd, J=11 Hz, J=1.2 Hz, 1H), 7.486 (dd, J=8.8 Hz, J=5.6 Hz,
1H), 7.315 (d, J=9.6 Hz, 2H), 7.152 (m, 1H), 5.145 (s, 2H),
3.741 ppm (s, 3H).
Methyl 2-(3-(4-bromo-2-fluorophenoxy)-7-fluoro-2-oxoquinoxa-
lin-1(2H)-yl)acetate (34c). Yield: 273 mg (64%); white solid, mp:
168–1708C; 1H NMR ([D6]DMSO, 400 MHz): d=7.833 (dd, J=
10.2 Hz, J=1.6 Hz, 1H), 7.529 (m, 4H), 7.166 (m, 1H), 5.122 (s, 2H),
3.745 ppm (s, 3H).
Methyl 2-(3-((4-bromophenyl)amino)-2-oxoquinoxalin-1(2H)-yl)a-
cetate (32b). Yield: 289 mg (74%); white solid, mp: 275–2768C;
1H NMR ([D6]DMSO, 400 MHz): d=9.734 (s, 1H), 8.146 (d, J=8.8 Hz,
2H), 7.590 (d, J=9.2 Hz, 1H), 7.540 (d, J=8.8 Hz, 2H), 7.426 (d, J=
9.2 Hz, 1H), 7.327 (m, 2H), 5.183 (s, 2H), 3.724 ppm (s, 3H).
Methyl 2-(7-chloro-3-(4-fluorophenoxy)-2-oxoquinoxalin-1(2H)-
yl)acetate (35a). Yield: 277 mg (77%); white solid, mp: 174–
Methyl 2-(3-((4-bromo-2-fluorophenyl)amino)-2-oxoquinoxalin-
1
1768C; H NMR ([D6]DMSO, 400 MHz): d=7.734 (d, J=1.6 Hz, 1H),
1(2H)-yl)acetate (32c). Yield: 307 mg (76%); white solid, mp: 215–
7.366 (m, 6H), 5.172 (s, 2H), 3.748 ppm (s, 3H).
1
2168C; H NMR ([D6]DMSO, 400 MHz): d=9.044 (s, 1H), 8.254 (t, J=
8.4 Hz, 1H), 7.685 (d, J=10.4 Hz, 1H), 7.480 (m, 3H), 7.327 (m, 2H),
5.196 (s, 2H), 3.730 ppm (s, 3H).
Methyl 2-(3-(4-bromophenoxy)-7-chloro-2-oxoquinoxalin-1(2H)-
yl)acetate (35b). Yield: 295 mg (70%); white solid, mp: 173–
1758C; H NMR ([D6]DMSO, 400 MHz): d=7.737 (d, J=1.6 Hz, 1H),
7.678 (dd, J=6.6 Hz, J=2 Hz, 2H), 7.593 (d, J=8.8 Hz, 1H), 7.320
(m, 3H), 5.172 (s, 2H), 3.746 ppm (s, 3H).
1
Methyl 2-(3-((2,4-difluorophenyl)amino)-2-oxoquinoxalin-1(2H)-
yl)acetate (32d). Yield: 263 mg (76%); white solid, mp: 187–
1
1888C; H NMR ([D6]DMSO, 400 MHz): d=9.079 (s, 1H), 8.122 (dd,
J=15.4 Hz, J=8.8 Hz, 1H), 7.433 (m, 3H), 7.304 (m, 2H), 7.168 (t,
J=8.4 Hz, 1H), 5.191 (s, 2H), 3.732 ppm (s, 3H).
Methyl 2-(3-(4-bromo-2-fluorophenoxy)-7-chloro-2-oxoquinoxa-
lin-1(2H)-yl)acetate (35c). Yield: 299 mg (67%); white solid, mp:
184–1858C; 1H NMR ([D6]DMSO, 400 MHz): d=7.834 (dd, J=
10.2 Hz, J=1.6 Hz, 1H), 7.777 (d, J=2 Hz, 1H), 7.609 (m, 3H), 7.335
(dd, J=8.8 Hz, J=1.2 Hz, 1H), 5.186 (s, 2H), 3.750 ppm (s, 3H).
Methyl
2-(2-oxo-3-((3,4,5-trifluorophenyl)amino)quinoxalin-
1(2H)-yl)acetate (32e). Yield: 256 mg (71%); white solid, mp: 261–
1
2628C; H NMR ([D6]DMSO, 400 MHz): d=10.101 (s, 1H), 8.305 (dd,
J=11.2 Hz, J=6.4 Hz, 2H), 7.753 (d, J=7.6 Hz, 1H), 7.540 (d, J=
8 Hz, 1H), 7.441 (m, 2H), 5.274 (s, 2H), 3.824 ppm (s, 3H).
Methyl 2-(7-bromo-3-(4-fluorophenoxy)-2-oxoquinoxalin-1(2H)-
yl)acetate (36a). Yield: 301 mg (74%); white solid, mp: 177–
1788C; H NMR ([D6]DMSO, 400 MHz): d=7.847 (d, J=1.6 Hz, 1H),
1
General procedure for synthesis of methyl 2-(2-oxo-3-phenoxy-
quinoxalin-1(2H)-yl)acetate derivatives (33–39). A mixture of
K2CO3 (139 mg, 1 mmol) and phenol (1.1 mmol) in DMF (10 mL)
was stirred at 858C for 12 h, then to which substituted 3-chloroqui-
noxalin-2(1H)-one (1 mmol) was added. The reaction mixture was
stirred at 758C for 12 h and cooled to room temperature. Then
H2O (100 mL) was added. The residue was filtered off, washed with
H2O, and then added to a suspension of methyl 2-bromoacetate
(1 mmol, 153 mg) and K2CO3 (3 mmol, 415 mg) in CH3CN (25 mL).
The reaction mixture was stirred at 558C for 0.5 h and then filtered.
7.372 (m, 6H), 5.756 (s, 2H), 3.749 ppm (s, 3H).
Methyl 2-(7-bromo-3-(4-bromophenoxy)-2-oxoquinoxalin-1(2H)-
yl)acetate (36b). Yield: 324 mg (69%); white solid, mp: 192–
1938C; 1H NMR ([D6]DMSO, 400 MHz): d=7.851 (s, 1H), 7.678 (d,
J=8.8 Hz, 2H), 7.380 (m, 4H), 5.171 (s, 2H), 3.746 ppm (s, 3H).
Methyl 2-(7-bromo-3-(4-bromo-2-fluorophenoxy)-2-oxoquinoxa-
lin-1(2H)-yl)acetate (36c). Yield: 342 mg (70%); white solid, mp:
1
197–2008C; H NMR ([D6]DMSO, 400 MHz): d=7.892 (d, J=1.2 Hz,
ChemMedChem 2012, 7, 823 – 835
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemmedchem.org
831

C. J. Zhu et al.
MED
1H), 7.826 (dd, J=10 Hz, J=1.6 Hz, 1H), 7.472 (m, 4H), 5.185 (s,
2-(3-((4-Bromophenyl)amino)-2-oxoquinoxalin-1(2H)-yl)acetic
2H), 3.750 ppm (s, 3H).
acid (40b). Yield: 291 mg (78%); white solid, mp: >3008C;
1H NMR ([D6]DMSO, 400 MHz): d=9.690 (s, 1H), 8.151 (d, J=8 Hz,
2H), 7.546 (m, 3H), 7.309 (m, 3H), 4.947 ppm (s, 2H); 13C NMR
([D6]DMSO, 100 MHz): d=169.127, 150.938, 146.111, 139.035,
132.189, 131.309, 129.727, 126.237, 125.319, 123.757, 121.940,
114.590, 114.312, 45.376 ppm; HRMS (ESI) m/z calcd for [M+H]+
374.01348, found 374.01294.
Methyl 2-(6-fluoro-3-(4-fluorophenoxy)-2-oxoquinoxalin-1(2H)-
yl)acetate (37a). Yield: 259 mg (75%); white solid, mp: 163–
1
1648C; H NMR ([D6]DMSO, 400 MHz): d=7.560 (dd, J=9.2 Hz, J=
5.2 Hz, 1H), 7.340 (m, 6H), 5.187 (s, 2H), 3.739 ppm (s, 3H).
Methyl 2-(3-(4-bromophenoxy)-6-fluoro-2-oxoquinoxalin-1(2H)-
yl)acetate (37b). Yield: 293 mg (72%); white solid, mp: 158–
2-(3-((4-Bromo-2-fluorophenyl)amino)-2-oxoquinoxalin-1(2H)-yl)-
acetic acid (40c). Yield: 287 mg (73%); white solid, mp: >3008C;
1H NMR ([D6]DMSO, 400 MHz): d=9.014 (s, 1H), 8.283 (t, J=8.4 Hz,
1H), 7.672 (d, J=10.4 Hz, 1H), 7.401 (m, 5H), 5.059 ppm (s, 2H);
13C NMR ([D6]DMSO, 100 MHz): d=168.766, 153.918 (d, J=
248.4 Hz), 150.923, 145.772, 132.116, 129.537, 127.627 (d, J=
3.4 Hz), 126.516, 126.367 (d, J=10.6 Hz), 125.795, 124.614, 124.172,
118.747 (d, J=22.9 Hz), 115.318 (d, J=9.1 Hz), 114.502,
44.233 ppm; HRMS (ESI) m/z calcd for [M+H]+ 392.00406, found
392.00468.
1
1608C; H NMR ([D6]DMSO, 400 MHz): d=7.695 (m, 2H), 7.561 (dd,
J=9.2 Hz, J=4.8 Hz, 1H), 7.374 (m, 4H), 5.184 (s, 2H), 3.736 ppm
(s, 3H).
Methyl 2-(3-(4-bromo-2-fluorophenoxy)-6-fluoro-2-oxoquinoxa-
lin-1(2H)-yl)acetate (37c). Yield: 314 mg (74%); white solid, mp:
153–1558C; 1H NMR ([D6]DMSO, 400 MHz): d=7.843 (d, J=10 Hz,
1H), 7.478 (m, 5H), 5.319 (s, 2H), 3.740 ppm (s, 3H).
Methyl 2-(6-chloro-3-(4-fluorophenoxy)-2-oxoquinoxalin-1(2H)-
yl)acetate (38a). Yield: 276 mg (76%); white solid, mp: 148–
1
2-(3-((2,4-Difluorophenyl)amino)-2-oxoquinoxalin-1(2H)-yl)acetic
acid (40d). Yield: 258 mg (78%); white solid, mp: 270–2718C;
1H NMR ([D6]DMSO, 400 MHz): d=9.032 (s, 1H), 8.181 (dd, J=
15.2 Hz, J=8 Hz, 1H), 7.307 (m, 6H), 4.977 ppm (s, 2H); 13C NMR
([D6]DMSO, 100 MHz): d=168.987, 158.456 (d, J=252.9 Hz),
154.650 (d, J=246.9 Hz), 150.873, 146.320, 132.288, 129.655,
126.260, 125.295 (d, J=14.1 Hz), 123.932, 123.445, 114.548, 112.220
(d, J=21.8 Hz), 104.373 (d, J=24.0 Hz), 103.987, 44.770 ppm;
HRMS (ESI) m/z calcd for [M+H]+ 332.08412, found 332.08397.
1508C; H NMR ([D6]DMSO, 400 MHz): d=7.519 (m, 3H), 7.352 (m,
4H), 5.179 (s, 2H), 3.737 ppm (s, 3H).
Methyl 2-(3-(4-bromophenoxy)-6-chloro-2-oxoquinoxalin-1(2H)-
yl)acetate (38b). Yield: 313 mg (74%); white solid, mp: 158–
1
1598C; H NMR ([D6]DMSO, 400 MHz): d=7.681 (d, J=8.8 Hz, 2H),
7.526 (m, 3H), 7.326 (d, J=8.8 Hz, 2H), 5.176 (s, 2H), 3.733 ppm (s,
3H).
Methyl 2-(3-(4-bromo-2-fluorophenoxy)-6-chloro-2-oxoquinoxa-
lin-1(2H)-yl)acetate (38c). Yield: 332 mg (75%); white solid, mp:
178–1808C; 1H NMR ([D6]DMSO, 400 MHz): d=7.841 (d, J=10 Hz,
1H), 7.549 (m, 5H), 5.191 (s, 2H), 3.738 ppm (s, 3H).
2-(2-Oxo-3-((3,4,5-trifluorophenyl)amino)quinoxalin-1(2H)-yl)ace-
tic acid (40e). Yield: 249 mg (71%); white solid, mp: >3008C;
1H NMR ([D6]DMSO, 400 MHz): d=9.932 (s, 1H), 8.175 (m, 2H),
7.592 (d, J=7.2 Hz, 6H), 7.315 (m, 3H), 5.006 ppm (s, 2H); 13C NMR
([D6]DMSO, 100 MHz): d=168.796, 150.793, 149.914 (d, J=
246.1 Hz), 145.779, 136.010, 135.526, 135.378, 130.595 (d, J=
226.7 Hz), 126.657, 125.994, 124.085, 114.312, 103.924 (d, J=
24.8 Hz), 44.199 ppm; HRMS (ESI) m/z calcd for [M+H]+ 350.07470,
found 350.07542.
Methyl 2-(6-bromo-3-(4-fluorophenoxy)-2-oxoquinoxalin-1(2H)-
yl)acetate (39a). Yield: 319 mg (78%); white solid, mp: 154–
1
1558C; H NMR ([D6]DMSO, 400 MHz): d=7.622 (m, 2H), 7.490 (d,
J=9.2 Hz, 1H), 7.352 (m, 4H), 5.173 (s, 2H), 3.735 ppm (s, 3H).
Methyl 2-(6-bromo-3-(4-bromophenoxy)-2-oxoquinoxalin-1(2H)-
yl)acetate (39b). Yield: 374 mg (80%); white solid, mp: 168–
1
General procedure for synthesis of 2-(2-oxo-3-phenoxyquinoxa-
lin-1(2H)-yl)acetic acid derivatives (41–47). A mixture of the ap-
propriate substituted acetate2-(2-oxo-3-phenoxyquinoxalin-1(2H)-
yl)acetate (33–39)(1 mmol) and saturated aqueous LiOH (5 mL) in
THF (5 mL) was stirred at room temperature for 2 h. The alkaline
suspension was adjusted to an acidic pH value with 0.1n HCl. The
residue was filtered off and washed with H2O to give the product.
1708C; H NMR ([D6]DMSO, 400 MHz): d=7.655 (m, 4H), 7.491 (d,
J=8.8 Hz, 1H), 7.327 (dd, J=6.8 Hz, J=2 Hz, 2H), 5.171 (s, 2H),
3.733 ppm (s, 3H).
Methyl 2-(6-bromo-3-(4-bromo-2-fluorophenoxy)-2-oxoquinoxa-
lin-1(2H)-yl)acetate (39c). Yield: 363 mg (75%); white solid, mp:
183–1858C; 1H NMR ([D6]DMSO, 400 MHz): d=7.836 (d, J=10 Hz,
1H 1H), 7.671 (m, 2H), 7.521 (m, 3H), 5.185 (s, 2H), 3.738 ppm (s,
3H).
2-(3-(4-Fluorophenoxy)-2-oxoquinoxalin-1(2H)-yl)acetic
acid
(41a). Yield: 244 mg (78%); white solid, mp: >3008C; 1H NMR
([D6]DMSO, 400 MHz): d=7.374 (m, 8H), 5.073 ppm (s, 2H);
13C NMR ([D6]DMSO, 100 MHz): d=168.712, 159.517 (d, J=
239.7 Hz), 153.540, 149.813, 148.279, 131.595, 129.552, 128.078,
127.350, 123.986, 123.685 (d, J=8.4 Hz), 116.345 (d, J=23.3 Hz),
114.598, 44.153 ppm; HRMS (ESI) m/z calcd for [M+H]+ 315.07756,
found 315.07813.
General procedure for synthesis of 2-(2-oxo-3-(phenylamino)qui-
noxalin-1(2H)-yl)acetic acid derivatives (40). A mixture of the ap-
propriate substituted methyl 2-(2-oxo-3-(phenylamino)quinoxalin-
1(2H)-yl)acetate (32) (1 mmol) and saturated aqueous LiOH (5 mL)
in THF (5 mL) was stirred at room temperature for 2 h. The alkaline
suspension was adjusted to an acidic pH value with 0.1n HCl. The
residue was filtered off and washed with H2O to give the product.
2-(3-(4-Bromophenoxy)-2-oxoquinoxalin-1(2H)-yl)acetic
acid
2-(3-((4-Tluorophenyl)amino)-2-oxoquinoxalin-1(2H)-yl)acetic
acid (40a). Yield: 252 mg (81%); white solid, mp: 253–2558C;
1H NMR ([D6]DMSO, 400 MHz): d=9.642 (s, 1H), 8.193 (dd, J=
8.8 Hz, J=5.2 Hz, 2H), 7.437 (m, 1H), 7.240 (m, 5H), 5.032 ppm (s,
2H); 13C NMR ([D6]DMSO, 100 MHz): d=169.025, 157.861 (d, J=
239.1 Hz), 151,132, 146.000, 135.980, 132.425, 129.419, 126.241,
125.171, 123.997, 121.848 (d, J=7.6 Hz), 115.128 (d, J=22.1 Hz),
114.339, 44.313 ppm; HRMS (ESI) m/z calcd for [M+H]+ 314.09355,
found 314.09241.
(41b). Yield: 310 mg (83%); white solid, mp: >3008C; 1H NMR
([D6]DMSO, 400 MHz): d=7.682 (d, J=8 Hz, 2H), 7.596 (m, 3H),
7.390 (m, 3H), 5.062 ppm (s, 2H); 13C NMR ([D6]DMSO, 100 MHz):
d=168.687, 153.271, 151.564, 149.857, 132.609, 131.672, 129.477,
128.178, 127.385, 124.238, 123.987, 117.929, 114.625, 44.234 ppm;
HRMS (ESI) m/z calcd for [M+H]+ 374.99750, found 374.99647.
2-(3-(4-Bromo-2-fluorophenoxy)-2-oxoquinoxalin-1(2H)-yl)acetic
acid (41c). Yield: 303 mg (77%); white solid, mp: 255–2568C;
832
www.chemmedchem.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemMedChem 2012, 7, 823 – 835

Quinoxalinone Derivatives as ARIs
MED
1H NMR ([D6]DMSO, 400 MHz): d=7.841 (dd, J=10 Hz, J=4 Hz,
1H), 7.504 (m, 5H), 7.289 (m, 1H), 5.035 ppm (s, 2H); 13C NMR
([D6]DMSO, 100 MHz): d=168.754, 153.811 (d, J=239.7 Hz),
152.142, 149.338, 138.731 (d, J=12.2 Hz), 131.903, 129.122,
128.565, 127.543, 126.028, 124.104, 120.464, 120.248, 118.395 (d,
J=8.7 Hz), 114.864, 44.652 ppm; HRMS (ESI) m/z calcd for [M+H]+
392.98807, found 392.98710.
120.282, 118.522 (d, J=8.4 Hz), 114.834, 45.338 ppm. HR-MS: [M+
H]+ m/z calcd for C8H5Cl2N2O 426.94910, found 426.94734.
2-(7-Bromo-3-(4-fluorophenoxy)-2-oxoquinoxalin-1(2H)-yl)acetic
acid (44a). Yield: 315 mg (80%); white solid, mp: 262–2638C;
1H NMR ([D6]DMSO, 400 MHz): d=7.760 (s, 1H), 7.366 (m, 6H),
5.060 ppm (s, 2H); 13C NMR ([D6]DMSO, 100 MHz): d=168.647,
159.578 (d, J=239.7 Hz), 153.826, 149.761, 148.142, 132.928,
128.973, 128.786, 126.847, 123.664 (d, J=8.8 Hz), 120.713, 117.307,
116.368 (d, J=23.3 Hz), 44.553 ppm; HRMS (ESI) m/z calcd for [M+
H]+ 392.98807, found 392.98675.
2-(7-Fluoro-3-(4-fluorophenoxy)-2-oxoquinoxalin-1(2H)-yl)acetic
acid (42a). Yield: 277 mg (83%); white solid, mp: >3008C;
1H NMR ([D6]DMSO, 400 MHz): d=7.463 (m, 2H), 7.342 (m, 4H),
7.127 (m, 1H), 5.028 ppm (s, 2H); 13C NMR ([D6]DMSO, 100 MHz):
d=168.525, 161.567 (d, J=271.9 Hz), 159.155 (d, J=169.5 Hz),
152.927, 149.864, 148.233, 133.078 (d, J=11.8 Hz), 129.158 (d, J=
10.3 Hz), 126.310, 123.616 (d, J=8.4 Hz), 116.322 (d, J=23.3 Hz),
111.319 (d, J=23.2 Hz), 101.836(d, J=28.6 Hz), 44.793 ppm; HRMS
(ESI) m/z calcd for [M+H]+ 333.06814, found 333.06693.
2-(7-Bromo-3-(4-bromophenoxy)-2-oxoquinoxalin-1(2H)-yl)acetic
acid (44b). Yield: 378 mg (83%); white solid, mp: >3008C;
1H NMR ([D6]DMSO, 400 MHz): d=7.678 (m, 3H), 7.362 (m, 4H),
4.996 ppm (s, 2H); 13C NMR ([D6]DMSO, 100 MHz): d=168.766,
153.620, 151.454, 149.673, 133.073, 132.642, 128.962, 128.691,
126.756, 124.237, 120.785, 118.072, 117.394, 44.961 ppm; HRMS
(ESI) m/z calcd for [M+H]+ 452.90801, found 452.90605.
2-(3-(4-Bromophenoxy)-7-fluoro-2-oxoquinoxalin-1(2H)-yl)acetic
acid (42b). Yield: 316 mg (80%); white solid, mp: >3008C;
1H NMR ([D6]DMSO, 400 MHz): d=7.677 (d, J=8.8 Hz, 2H), 7.479
(m, 2H), 7.313 (d, J=8.8 Hz, 2H), 7.137 (m, 1H), 5.031 ppm (s, 2H);
13C NMR ([D6]DMSO, 100 MHz): d=168.567, 161.322 (d, J=
242.7 Hz), 152.683, 151.521, 149.864, 133.146 (d, J=11.8 Hz),
132.631, 129.257 (d, J=10.3 Hz), 126.726, 124.218, 117.977, 111.424
(d, J=23.6 Hz), 101.899 (d, J=28.7 Hz), 44.755 ppm; HRMS (ESI) m/
z calcd for [M+H]+ 392.98807, found 392.98789.
2-(7-Bromo-3-(4-bromo-2-fluorophenoxy)-2-oxoquinoxalin-1(2H)-
yl)acetic acid (44c). Yield: 386 mg (82%); white solid, mp:
>3008C; 1H NMR ([D6]DMSO, 400 MHz): d=7.828 (d, J=9.6 Hz,
1H), 7.502 (m, 3H), 7.325 (m, 2H), 4.749 ppm (s, 2H); 13C NMR
([D6]DMSO, 100 MHz): d=168.918, 153.755 (d, J=250.7 Hz),
152.679, 148.984, 138.715 (d, J=12.2 Hz), 133.598, 128.701 (d, J=
24 Hz), 128.242, 126.401, 126.005, 120.922, 120.477, 120.263,
118.422 (d, J=8.4 Hz), 117.863, 46.633 ppm; HRMS (ESI) m/z calcd
for [M+H]+ 470.89859, found 470.89689.
2-(3-(4-Bromo-2-fluorophenoxy)-7-fluoro-2-oxoquinoxalin-1(2H)-
yl)acetic acid (42c). Yield: 309 mg (75%); white solid, mp: 257-
2588C; H NMR ([D6]DMSO, 400 MHz): d=7.540 (dd, J=10 Hz, J=
2-(6-Fluoro-3-(4-fluorophenoxy)-2-oxoquinoxalin-1(2H)-yl)acetic
acid (45a). Yield: 279 mg (84%); white solid, mp: 276–2788C;
1H NMR ([D6]DMSO, 400 MHz): d=7.536 (m, 1H), 7.372 (m, 6H),
5.079 ppm (s, 2H); 13C NMR ([D6]DMSO, 100 MHz): d=168.674,
159.660 (d, J=240.1 Hz), 158.342 (d, J=239.3 Hz), 154.565,
149.662, 148.153, 130.549 (d, J=11.9 Hz), 128.504, 123.710 (d, J=
8.7 Hz), 116.451 (d, J=23.2 Hz), 116.194, 115.421 (d, J=23.7 Hz),
112.935 (d, J=13.3 Hz), 44.485 ppm; HRMS (ESI) m/z calcd for [M+
H]+ 333.06814, found 333.06961.
1
2 Hz, 2H), 7.513 (m, 4H), 7.155 (m, 1H), 5.026 ppm (s, 2H); 13C NMR
([D6]DMSO, 100 MHz): d=168.552, 161.537 (d, J=243.5 Hz),
153.785 (d, J=250.7 Hz), 151.502, 149.353, 138.674 (d, J=12.2 Hz),
133.370 (d, J=12.2 Hz), 129.421(d, J=10.3 Hz), 128.547 (d, J=
3.1 Hz), 125.967 (d, J=7.4 Hz), 120.473, 120.259, 118.438 (d, J=
8.4 Hz), 111.649 (d, J=23.6 Hz), 102.080 (d, J=25.8 Hz),
44.961 ppm; HRMS (ESI) m/z calcd for [M+H]+ 410.97865, found
410.97791.
2-(3-(4-Bromophenoxy)-6-fluoro-2-oxoquinoxalin-1(2H)-yl)acetic
acid (45b). Yield: 301 mg (77%); white solid, mp: 285–2888C;
1H NMR ([D6]DMSO, 400 MHz): d=7.688 (d, J=8.8 Hz, 2H), 7.542
(dd, J=9.2 Hz, J=4.8 Hz, 1H), 7.353 (m, 4H), 5.080 ppm (s, 2H);
13C NMR ([D6]DMSO, 100 MHz): d=168.640, 158.315 (d, J=
233.9 Hz), 154.287, 151.418, 149.586, 132.680, 130.444 (d, J=
12.2 Hz), 128.550, 124.260, 118.164, 116.242 (d, J=9.5 Hz), 115.497
(d, J=23.6 Hz), 112.958 (d, J=23.3 Hz), 44.446 ppm; HRMS (ESI) m/
z calcd for [M+H]+ 392.98807, found 392.98747.
2-(7-Chloro-3-(4-fluorophenoxy)-2-oxoquinoxalin-1(2H)-yl)acetic
acid (43a). Yield: 288 mg (83%); white solid, mp: 286–2888C;
1H NMR ([D6]DMSO, 400 MHz): d=7.660 (s, 1H), 7.362 (m, 6H),
5.062 ppm (s, 2H); 13C NMR ([D6]DMSO, 100 MHz): d=168.628,
159.583 (d, J=240.0 Hz), 153.720, 149.807, 148.126, 132.745,
132.395, 128.786, 128.478, 123.986, 123.673 (d, J=8.4 Hz), 116.379
(d, J=243.5 Hz), 114.533, 44.538 ppm; HRMS (ESI) m/z calcd for
[M+H]+ 349.03859, found 349.03925.
2-(3-(4-Bromo-2-fluorophenoxy)-6-fluoro-2-oxoquinoxalin-1(2H)-
yl)acetic acid (45c). Yield: 312 mg (76%); white solid, mp: 270–
2718C; H NMR ([D6]DMSO, 400 MHz): d=7.838 (m, 1H), 7.454 (m,
2-(3-(4-Bromophenoxy)-7-chloro-2-oxoquinoxalin-1(2H)-yl)acetic
acid (43b). Yield: 342 mg (83%); white solid, mp: 288–2908C;
1H NMR ([D6]DMSO, 400 MHz): d=7.637 (m, 3H), 7.428 (d, J=
8.8 Hz, 1H), 7.266 (m, 3H), 5.051 ppm (s, 2H); 13C NMR ([D6]DMSO,
100 MHz): d=168.651, 153.468, 151.433, 149.768, 132.814, 132.654,
132.516, 128.824, 128.409, 124.241, 124.005, 118.099, 114.571,
44.622 ppm; HRMS (ESI) m/z calcd for [M+H]+ 408.95852, found
408.95769.
1
5H), 5.091 ppm (s, 2H); 13C NMR ([D6]DMSO, 100 MHz): d=168.579,
158.391 (d, J=240 Hz), 153.705 (d, J=250.7 Hz), 153.064, 149.083,
138.559 (d, J=12.2 Hz), 130.049 (d, J=11.8 Hz), 128.653 (d, J=
11.4 Hz), 125.978, 120.515, 120.298, 118.594 (d, J=8.4 Hz), 116.278
(d, J=26.6 Hz), 116.027 (d, J=13.7 Hz), 113.102 (d, J=23.2 Hz),
44.568 ppm; HRMS (ESI) m/z calcd for [M+H]+ 410.97865, found
410.97947.
2-(3-(4-Bromo-2-fluorophenoxy)-7-chloro-2-oxoquinoxalin-1(2H)-
yl)acetic acid (43c). Yield: 337 mg (79%); white solid, mp:
>3008C; 1H NMR ([D6]DMSO, 400 MHz): d=7.830 (d, J=9.2 Hz,
1H), 7.492 (m, 4H), 7.284 (d, J=8.4 Hz, 1H), 4.972 ppm (s, 2H);
13C NMR ([D6]DMSO, 100 MHz): d=168.781, 153.764 (d, J=
251.1 Hz), 152.363, 149.201, 138.622 (d, J=12.6 Hz), 132.993 (d, J=
24.4 Hz), 128.878, 128.578, 128.013, 126.013, 124.024, 120.496,
2-(6-Chloro-3-(4-fluorophenoxy)-2-oxoquinoxalin-1(2H)-yl)acetic
acid (46a). Yield: 277 mg (79%); white solid, mp: 255–2568C;
1H NMR ([D6]DMSO, 400 MHz): d=7.434 (m, 7H), 5.075 ppm (s,
2H); 13C NMR ([D6]DMSO, 100 MHz): d=168.579, 159.620 (d, J=
240.5 Hz), 154.424, 149.738, 148.088, 130.646, 130.569, 127.914,
127.685, 126.306, 123.648 (d, J=8.7 Hz), 116.392, 116.387 (d, J=
ChemMedChem 2012, 7, 823 – 835
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemmedchem.org
833

C. J. Zhu et al.
MED
23.3 Hz), 44.370 ppm; HRMS (ESI) m/z calcd for [M+H]+ 349.03859,
found 349.03899.
(0.1m, pH 6.2), 0.1 mL enzyme extract, 0.15 mL deionized water,
and 0.25 mL d,l-glyceraldehyde (10 mm) as substrate in a final
volume of 1 mL. The reaction mixture, except for d,l-glyceralde-
hyde, was incubated at 308C for 10 min. The substrate was then
added to start the reaction, which was monitored for 4 min. ALR1
activity assays were performed at 378C in a reaction mixture con-
taining 0.25 mL NADPH (0.12 mm), 0.1 mL enzyme extract, 0.25 mL
sodium phosphate buffer (0.1m, pH 7.2), 0.15 mL deionized water,
and 0.25 mL sodium d-glucuronate (20 mm) as substrate in a final
volume of 1 mL. The reaction mixture, except for sodium d-glucur-
onate, was incubated at 378C for 10 min. The substrate was then
added to start the reaction, which was monitored for 4 min.
2-(3-(4-Bromophenoxy)-6-chloro-2-oxoquinoxalin-1(2H)-yl)acetic
acid (46b). Yield: 318 mg (78%); white solid, mp: 285–2878C;
1H NMR ([D6]DMSO, 400 MHz): d=7.686 (d, J=8.8 Hz, 2H), 7.515
(m, 3H), 7.327 (d, J=8.8 Hz, 2H), 5.026 ppm (s, 2H); 13C NMR
([D6]DMSO, 100 MHz): d=168.541, 154.196, 151.395, 149.654,
132.638, 130.760, 130.470, 127.853, 127.750, 126.310, 124.199,
118.122, 116.442, 44.633 ppm; HRMS (ESI) m/z calcd for [M+H]+
408.95852, found 408.95944.
2-(3-(4-Bromo-2-fluorophenoxy)-6-chloro-2-oxoquinoxalin-1(2H)-
yl)acetic acid (46c). Yield: 314 mg (73%); white solid, mp: 260–
The inhibitory activity of the newly synthesized compounds
against ALR2 and ALR1 was assayed by adding 5 mL inhibitor solu-
tion to the reaction mixture described above. All compounds were
dissolved in dimethyl sulfoxide (DMSO) and diluted with deionized
water. To correct for any non-enzymatic oxidation of NADPH, the
rate of NADPH oxidation in the presence of all of the reaction mix-
ture components except the substrate was subtracted from each
experimental rate. The inhibitory effect of the synthetic com-
pounds was routinely estimated at a concentration of 10À4 m (the
concentration is referenced to that of the compound in the reac-
tion mixture). Those compounds found to be active were tested at
additional concentrations between 10À4 and 10À8 m. Each dose–
effect curve was generated with at least four concentrations of in-
hibitor causing inhibition between 20 and 80%, with three repli-
cates at each concentration. The 95% confidence limits (95% CL)
were calculated from t values for nÀ2, where n is the total number
of determinations.
1
2628C; H NMR ([D6]DMSO, 400 MHz): d=7.851 (dd, J=10 Hz, J=
2.4 Hz, 1H), 7.506 (m, 5H), 4.991 ppm (s, 2H); 13C NMR ([D6]DMSO,
100 MHz): d=168.590, 153.703 (d, J=251.1 Hz), 153.053, 149.113,
138.555 (d, J=12.2 Hz), 130.996, 130.051, 128.543, 128.082 (d, J=
20.5 Hz), 126.390, 125.955, 120.496, 120.282, 118.568 (d, J=8.4 Hz),
116.697, 45.094 ppm; HRMS (ESI) m/z calcd for [M+H]+ 426.94910,
found 426.94835.
2-(6-Bromo-3-(4-fluorophenoxy)-2-oxoquinoxalin-1(2H)-yl)acetic
acid (47a). Yield: 305 mg (78%); white solid, mp: 238–2408C;
1H NMR ([D6]DMSO, 400 MHz): d=7.544 (m, 2H), 7.356 (m, 5H),
5.055 ppm (s, 2H); 13C NMR ([D6]DMSO, 100 MHz): d=168.583,
159.616 (d, J=240.1 Hz), 154.348, 149.746, 148.115, 131.053,
130.851, 130.429, 129.213, 123.648 (d, J=8.7 Hz), 116.697, 116.379
(d, J=23.2 Hz), 115.600, 44.405 ppm; HRMS (ESI) m/z calcd for [M+
H]+ 392.98807, found 392.98834.
2-(6-Bromo-3-(4-bromophenoxy)-2-oxoquinoxalin-1(2H)-yl)acetic
acid (47b). Yield: 363 mg (80%); white solid, mp: 266–2678C;
1H NMR ([D6]DMSO, 400 MHz): d=7.647 (m, 4H), 7.439 (d, J=
8.8 Hz, 1H), 7.328 (d, J=8.4 Hz, 2H), 5.032 ppm (s, 2H); 13C NMR
([D6]DMSO, 100 MHz): d=168.598, 154.093, 151.384, 149.685,
132.638, 131.133, 130.764, 130.516, 129.247, 124.207, 118.133,
116.724, 115.588, 44.553 ppm; HRMS (ESI) m/z calcd for [M+H]+
452.90801, found 452.90928.
Docking studies
Docking was performed using Molegro Virtual Docker, version 5.0.
The crystal structure of human aldose reductase with bound inhibi-
tor (lidorestat) retrieved from the RCSB Protein Data Bank (PDB
code: 1Z3N)[3a] and aldehyde reductase alone (PDB code: 3H4G)[19]
were used for docking. All solvent molecules within the protein
structure were removed for the docking procedure. All structural
parameters of ligands such as bond orders, hybridization, explicit
hydrogen atoms, and charges were assigned when necessary in
Molegro Virtual Docker software. To obtain better potential binding
sites in the protein, detecting possible binding cavities was imple-
mented, and four cavities were obtained. The cavity around the
anion binding site (volume of ~182 ꢁ3) was used for docking calcu-
lations and further modified using side chain minimization. All
docking calculations were carried out using the grid-based Mol-
Dock score (GRID) function with a grid resolution of 0.30 ꢁ. The
best ligand poses were chosen on the basis of the MolDock score
and ReRank score. The docking calculations were performed with
a dual processor Windows 7 based computer with 4 GB RAM, and
each docking process took 4–6 min.
2-(6-Bromo-3-(4-bromo-2-fluorophenoxy)-2-oxoquinoxalin-1(2H)-
yl)acetic acid (47c). Yield: 372 mg (79%); white solid, mp:
>3008C; 1H NMR ([D6]DMSO, 400 MHz): d=7.836 (d, J=9.2 Hz,
1H), 7.536 (m, 4H), 7.317 (d, J=8.4 Hz, 2H), 4.831 ppm (s, 2H);
13C NMR ([D6]DMSO, 100 MHz): d=168.868, 153.762 (d, J=
250.7 Hz), 153.125, 149.033, 138.641 (d, J=12.6 Hz), 131.629,
130.775, 130.291, 129.129, 128.562, 125.975, 120.445 (d, J=
21.7 Hz), 118.575, 117.227, 115.394, 46.047 ppm; HRMS (ESI) m/z
calcd for [M+H]+ 470.89859, found 470.89614.
Biological methods
ALR2 and ALR1 were obtained from Wistar rats, body weight 200–
250 g, supplied by Vital River, Beijing (China). d,l-Glyceraldehyde,
sodium d-glucuronate, and NADPH were obtained from Sigma–Al-
drich. All other chemicals were of reagent grade. ALR1 and ALR2
were prepared according to the methods of Kinoshita[23] and La
Motta et al.[3f] Enzyme activity was assayed spectrophotometrically
on a Shimadzu UV-1800 UV spectrophotometer by measuring the
decrease in absorption of NADPH at l 340 nm, which accompanies
the oxidation of NADPH catalyzed by ALR2 and ALR1.
The Supporting Information contains general information regard-
ing NOESY data for some compounds.
Acknowledgements
Enzyme assays
This work was supported by the Beijing Natural Science Founda-
tion (no. 7102091) and the Research Fund for the Doctoral Pro-
gram of Higher Education of China (no. 20111101110042).
ALR2 activity was performed at 308C in a reaction mixture contain-
ing 0.25 mL NADPH (0.10 mm), 0.25 mL sodium phosphate buffer
834
www.chemmedchem.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemMedChem 2012, 7, 823 – 835

Quinoxalinone Derivatives as ARIs
MED
derveld, E. Guaita, M. Adami, G. Coruzzi, R. Leurs, L. J. P. de Esch, J. Med.
Chem. 2008, 51, 2457–2467.
Keywords: chemoselectivity
·
enzymes
·
inhibitors
·
[12] L. E. Seitz, W. J. Suling, R. C. Reynolds, J. Med. Chem. 2002, 45, 5604–
5606.
quinoxalines · regioselectivity · structure–activity relationships
[13] a) D. Catarzi, V. Colotta, F. Varano, O. Lenzi, G. Filacchioni, L. Trincavelli,
C. Martini, C. Montopoli, S. Moro, J. Med. Chem. 2005, 48, 7932–7945;
b) B. Hu, R. J. Unwalla, I. Goljer, J. W. Jetter, E. M. Quinet, T. J. Berrodin,
M. D. Basso, I. B. Feingold, A. G. Nilsson, A. Wilhelmsson, M. J. Evans, J. E.
Wrobel, J. Med. Chem. 2010, 53, 3296–3304; c) J. A. Willardsen, D. A.
Dudley, W. L. Cody, L. G. Chi, T. B. McClanahan, T. E. Mertz, R. E. Potoczak,
L. S. Narasimhan, D. R. Holland, S. T. Rapundalo, J. J. Edmunds, J. Med.
Chem. 2004, 47, 4089–4099; d) J. Deng, E. Feng, S. Ma, Y. Zhang, X. Liu,
H. Li, H. Huang, J. Zhu, W. Zhu, X. Shen, L. Miao, H. Liu, H. Jiang, J. Li, J.
Med. Chem. 2011, 54, 4508–4522.
[14] a) J. Dudash, Y. Z. Zhang, J. B. Moore, R. Look, Y. Liang, M. P. Beavers,
B. R. Conway, P. J. Rybczynski, K. T. Demarest, Bioorg. Med. Chem. Lett.
2005, 15, 4790–4793; b) D. O. Koltun, E. Q. Parkhill, N. I. Vasilevich, A. I.
Glushkov, M. Zilbershtein, A. V. Ivanov, A. G. Cole, I. Henderson, N. A.
Zautke, S. A. Brunn, N. Mollova, K. Leung, J. W. Chisholm, J. Zablocki,
Bioorg. Med. Chem. Lett. 2009, 19, 2048–2052.
[15] a) P. Koch, H. Jahns, V. Schattel, M. Goettert, S. Laufer, J. Med. Chem.
2010, 53, 1128–1137; b) D. S. Lawrence, J. E. Copper, C. D. Smith, J. Med.
Chem. 2001, 44, 594–601.
[16] R. O. Hughes, J. K. Walker, J. W. Cubbage, Y. M. Fobian, D. J. Rogier, S. E.
Heasley, R. M. Blevis-Bal, A. G. Benson, D. R. Owen, E. J. Jacobsen, J. N.
Freskos, J. M. Molyneaux, D. L. Brown, W. C. Stallings, B. A. Acker, T. M.
Maddux, M. B. Tollefson, J. M. Williams, J. B. Moon, B. V. Mischke, J. M.
Rumsey, Y. Zheng, A. MacInnes, B. R. Bond, Y. Yu, Bioorg. Med. Chem.
Lett. 2009, 19, 4092–4096.
[17] D. Bandyopadhyay, S. Mukherjee, R. R. Rodriguez, B. K. Banik, Molecules
2010, 15, 4207–4212.
[18] a) J. Liu, A. E. Fitzgerald, N. S. Mani, J. Org. Chem. 2008, 73, 2951–2954;
b) L. Hintermann, L. Xiao, A. Labonne, Angew. Chem. 2008, 120, 8370–
8374; Angew. Chem. Int. Ed. 2008, 47, 8246–8250; c) A. Katoh, T. Yoshi-
da, J. Ohkanda, Heterocycles 2000, 52, 911–920.
[19] O. El-Kabbani, V. Carbone, C. Darmanin, M. Oka, A. Mitschler, A. Podjar-
ny, C. Schulze-Briese, R. P. T. Chung, J. Med. Chem. 2005, 48, 5536–5542.
[20] A. Urzhumtsev, F. TeteFavier, A. Mitschler, J. Barbanton, P. Barth, L. Urz-
humtseva, J. F. Biellmann, A. D. Podjarny, D. Moras, Structure 1997, 5,
601–612.
[1] a) J. H. Kinoshita, C. Nishimura, Diabetes Metab. Rev. 1988, 4, 323–337;
b) C. Yabe-Nishimura, Pharmacol. Rev. 1998, 50, 21–33; c) S. S. M.
Chung, S. K. Chung, Curr. Med. Chem. 2003, 10, 1375–1387.
[2] K. H. Gabbay, L. O. Merola, R. A. Field, Science 1966, 151, 209–210.
[3] a) M. C. Van Zandt, M. L. Jones, D. E. Gunn, L. S. Geraci, J. H. Jones, D. R.
Sawicki, J. Sredy, J. L. Jacot, A. T. DiCioccio, T. Petrova, A. Mitschler, A. D.
Podjarny, J. Med. Chem. 2005, 48, 3141–3152; b) F. Da Settimo, G. Pri-
mofiore, C. La Motta, S. Sartini, S. Taliani, F. Simorini, A. M. Marini, A. Lav-
ecchia, E. Novellino, E. Boldrini, J. Med. Chem. 2005, 48, 6897–6907; c) P.
Alexiou, V. J. Demopoulos, J. Med. Chem. 2010, 53, 7756–7766; d) C. La
Motta, S. Sartini, S. Salerno, F. Simorini, S. Taliani, A. M. Marini, F. Da Set-
timo, L. Marinelli, V. Limongelli, E. Novellino, J. Med. Chem. 2008, 51,
3182–3193; e) F. Da Settimo, G. Primofiore, A. Da Settimo, C. La Motta,
F. Simorini, E. Novellino, G. Greco, A. Lavecchia, E. Boldrini, J. Med.
Chem. 2003, 46, 1419–1428; f) C. La Motta, S. Sartini, L. Mugnaini, F. Si-
morini, S. Taliani, S. Salerno, A. M. Marini, F. Da Settimo, A. Lavecchia, E.
Novellino, M. Cantore, P. Failli, M. Ciuffi, J. Med. Chem. 2007, 50, 4917–
4927.
[4] a) X. Chen, C. J. Zhu, F. Guo, X. W. Qiu, Y. C. Yang, S. Z. Zhang, M. L. He,
S. Parveen, C. J. Jing, Y. Li, B. Ma, J. Med. Chem. 2010, 53, 8330–8344;
b) X. Chen, Y. C. Yang, B. Ma, S. Z. Zhang, M. L. He, D. Q. Gui, S. Hussain,
C. J. Jing, C. J. Zhu, Q. Yu, Y. Liu, Eur. J. Med. Chem. 2011, 46, 1536–
1544; c) X. Chen, S. Zhang, Y. Yang, S. Hussain, M. He, D. Gui, B. Ma, C.
Jing, Z. Qiao, C. Zhu, Q. Yu, Bioorg. Med. Chem. 2011, 19, 7262–7269.
[5] a) J. Fleischhauer, R. Beckert, Y. Juttke, D. Hornig, W. Gunther, E. Birckner,
U. W. Grummt, H. Gorls, Chem. Eur. J. 2009, 15, 12799–12806; b) A. S. R.
Koti, B. Bhattacharjee, N. S. Haram, R. Das, N. Periasamy, N. D. Sona-
wane, D. W. Rangnekar, J. Photochem. Photobiol. A 2000, 137, 115–123.
[6] S. Mayadevi, P. G. Prasad, K. K. M. Yusuff, Synth. React. Inorg. Met.-Org.
Chem. 2003, 33, 481–496.
[7] a) K. R. J. Thomas, M. Velusamy, J. T. Lin, C. H. Chuen, Y. T. Tao, Chem.
Mater. 2005, 17, 1860–1866; b) P. Karastatiris, J. A. Mikroyannidis, I. K.
Spiliopoulos, A. P. Kulkarni, S. A. Jenekhe, Macromolecules 2004, 37,
7867–7878; c) T. Dallos, M. Hamburger, M. Baumgarten, Org. Lett. 2011,
13, 1936–1939.
[8] R. Liu, Z. Huang, M. G. Murray, X. Guo, G. Liu, J. Med. Chem. 2011, 54,
5747–5768.
[9] a) P. Marques-Gallego, M. A. Gamiz-Gonzalez, F. R. Fortea-Perez, M. Lutz,
A. L. Spek, A. Pevec, B. Kozlevcar, J. Reedijk, Dalton Trans. 2010, 39,
5152–5158; b) N. E. Mollegaard, C. Bailly, M. J. Waring, P. E. Nielsen, Bio-
chemistry 2000, 39, 9502–9507.
[21] G. Botton, E. Valeur, M. Kergoat, C. Charon, S. Elbawab, (Merck Patent
GmbH, Germany), Application: WO, 2009, 70 pp.
[22] M. B. Deshmukh, A. R. Mali, S. D. Jadhav, A. W. Suryawarishi, Indian J.
Chem. Sect. B 2007, 46, 1211–1213.
[23] S. Hayman, J. H. Kinoshita, J. Biol. Chem. 1965, 240, 877–882.
[10] B. Zarranz, A. Jaso, I. Aldana, A. Monge, S. Maurel, E. Deharo, V. Jullian,
M. Sauvain, Arzneim.-Forsch. 2005, 55, 754–761.
[11] a) S. A. Galal, A. S. Abdelsamie, H. Tokuda, N. Suzuki, A. Lida, M. M. ElHef-
nawi, R. A. Ramadan, M. H. E. Atta, H. I. El Diwani, Eur. J. Med. Chem.
2011, 46, 327–340; b) D. P. Singh, S. R. Hashim, R. G. Singhal, Int. J. Drug
Dev. Res. 2010, 2, 810–815; c) R. A. Smits, H. D. Lim, A. Hanzer, O. P. Zui-
Received: January 27, 2012
Revised: February 18, 2012
Published online on March 13, 2012
ChemMedChem 2012, 7, 823 – 835
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemmedchem.org
835