Structure-activity relationships studies of quinoxalinone derivatives as aldose reductase inhibitors

Article abstract of DOI:10.1016/j.ejmech.2014.04.047

Novel quinoxalinone derivatives were synthesized and tested for their inhibitory activity against aldose reductase. Among them, N1-acetate derivatives had significant activity in a range of IC₅₀ values from low micromolar to submicromolar, and compound 15a bearing a C3-phenethyl side chain was identified as the most potent inhibitor with an IC₅₀ value of 0.143 μM. The structure-activity studies suggested that both C3-phenethyl and C6-NO₂ groups play an important role in enhancing the activity and selectivity of the quinoxalinone based inhibitors.

Full text of DOI:10.1016/j.ejmech.2014.04.047

European Journal of Medicinal Chemistry 80 (2014) 383e392
Contents lists available at ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Original article
Structureeactivity relationships studies of quinoxalinone derivatives
as aldose reductase inhibitors
Saghir Hussain, Shagufta Parveen, Xin Hao, Shuzhen Zhang, Wei Wang, Xiangyu Qin,
*
Yanchun Yang, Xin Chen, Shaojuan Zhu, Changjin Zhu , Bing Ma
Department of Applied Chemistry, Beijing Institute of Technology, No. 5, Zhongguancun South Street, 100081 Beijing, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Novel quinoxalinone derivatives were synthesized and tested for their inhibitory activity against aldose
reductase. Among them, N1-acetate derivatives had significant activity in a range of IC50 values from low
micromolar to submicromolar, and compound 15a bearing a C3-phenethyl side chain was identified as
the most potent inhibitor with an IC50 value of 0.143 mM. The structureeactivity studies suggested that
both C3-phenethyl and C6-NO2 groups play an important role in enhancing the activity and selectivity of
the quinoxalinone based inhibitors.
Received 5 December 2013
Received in revised form
11 April 2014
Accepted 15 April 2014
Available online 21 April 2014
Ó 2014 Elsevier Masson SAS. All rights reserved.
Keywords:
Quinoxalinone derivatives
Aldose reductase inhibitors
Structureeactivity relationships
1. Introduction
the strategy and an attractive approach to prevent and delay the
progression and development of diabetic complications [6].
Diabetes Mellitus (DM) is a complex and chronic metabolic
disease characterized by hyperglycemia. This disease is very com-
mon around the world and has major effect on public health. Hy-
perglycemia is the condition in which significant portion of the
glucose enters into polyol pathway which is considered as the
primary cause of pathogenesis of long-term diabetic complications,
including retinopathy, nephropathy, neuropathy and cataract [1e
3]. Aldose reductase (ALR2, EC 1.1.1.21) is a member of aldo-keto
reductase superfamily [4,5], which catalyzes the NADPH-
dependent reduction of glucose to sorbitol in the rate deter-
mining step of polyol pathway. Subsequently, the NADþ-dependent
sorbitol dehydrogenase oxidizes the sorbitol to fructose (Fig. 1). The
over production of sorbitol, imbalance of NADPH/NADPþ and
NADþ/NADH cofactors and subsequent oxidative stress inside the
cells are thought to be major causes of cellular damage that develop
diabetic complications. Recently, growing studies and evidences
reveal that ALR2 plays a pivotal role in the development of long-
term diabetic complications. Thus inhibition of ALR2 represents
In past few decades, structurally different Aldose reductase in-
hibitors (ARIs) have been developed and some of them are repre-
sented in Fig. 2, [7e17]. Unfortunately, only few of them are
advanced on clinical stages for evaluation of their potency and ef-
ficacy in the treatment of peripheral neuropathy. At present only
one drug, epalrestat is available in market and used in the treat-
ment of neuropathy in Japan [8], India [18] and China. Therefore,
development of more powerful ARIs is still needed.
We have been involved in the development and identification of
a suitable drug candidate for the prevention and treatment of long-
term diabetic complications. Recently, we have published a series of
different compounds based on aromatic thiadiazine 1,1-dioxide and
quinoxalinone as novel, potent and selective ARIs [19e22].
As our ongoing efforts aimed at the discovery of more phar-
macophores to further design of ARIs, we have developed a new
group of quinoxalinone derivatives. Herein we report their chem-
istry, inhibitory potency on aldose reductase and structureeactivity
relationships (SAR).
2. Chemistry
Abbreviations: ALR2, aldose reductase; ALR1, aldehyde reductase; ARIs, aldose
reductase inhibitors; AKR, aldo-keto reductase; NADPH,
dinucleotide phosphate reduced form; HNE, hydroxynoneal; SAR, structureeac-
tivity relationships.
* Corresponding author.
E-mail addresses: zcj@bit.edu.cn, zhuchangjin@tsinghua.org.cn (C. Zhu).
b-nicotinamide adenine
The synthetic methods illustrating the preparation of starting
materials 3-chloroquinoxlin-(1H)-one 5 and dichloroquinoxalin-
2(1H)-one 18 have been reported previously [19]. Syntheses of
target compounds 7aed, 8aed, 12, 14aed, 15aeb, 17, 22, and 23
http://dx.doi.org/10.1016/j.ejmech.2014.04.047
0223-5234/Ó 2014 Elsevier Masson SAS. All rights reserved.

384
S. Hussain et al. / European Journal of Medicinal Chemistry 80 (2014) 383e392
three series of compounds including p-nitrobenzyl derivatives
(7aed and 8aed), N1-acetate derivatives (14aed and 15aeb), and
C6- or C7-substituted N1-acetate derivatives (12, 17, 22, and 23) as
shown in Table 1. All of the newly synthesized quinoxalinone de-
rivatives were evaluated for their potential inhibitory effect on
ALR2 isolated from rat lenses. The IC50 values were determined by
linear regression analysis of log of the concentrationeresponse
curve [19e22].
Initially, compounds 7aed and 8aed series containing p-nitro-
benzyl group on the N1 position and various bulky lipophilic
moieties at the C3 position were prepared but all of them just
showed a moderate ALR2 inhibition. The p-nitrobenzyl group
seemed not suitable for the N1 position during the building of ALR2
inhibitors based on the quinoxalinone framework whereas the N1-
acetate substituent was still likely to be a favored strategy [19e22].
Then, we attached nitro group at the C6 position of quinoxalinone
and this resulted in the preparation of N1-acetate derivatives 12
and 17. Both the C6-nitro substituted compounds showed signifi-
cant inhibitory activity. Based on comparison, compound 12 that
Fig. 1. The polyol pathway of glucose metabolism.
were accomplished as outlined in Schemes 1e3. As shown in
Scheme 1, the 3-chloroquinoxalinone-(1H)-one (5) was N-alkylated
with substituted p-nitrobenzyl bromides in the presence of K2CO3
producing intermediate 6. Further reaction of 6 with various pi-
perazines in the presence of K2CO3 produced the desired products
7aed. Alternatively, several olefines were attached, respectively, to
the C3 position of compound 6 by Heck coupling reaction to obtain
products 8aec with a vinyl linker at the C3 position, and a benzo-
thiophene group was attached to the C3 position by Suzuki
coupling reaction to yield 8d [23]. Similarly, N-alkylation of 5 with
2-bromoacetate produced key intermediate 9, which in turn led to
a variety of products 12, and 17, 14aed and 15aeb. The interme-
diate 9 was aminated with 2,4-difluoroaniline followed by nitration
with mixture of Cu(NO3)2.3H2O and Ac2O [24], and then by treat-
ment with LiOH to give 12 as shown in Scheme 2. Direct coupling of
9 with olefines led to 13aec and then 14aec, which having C3 vinyl
linker, and further Pd/C catalytic hydrogenation reaction by using
on the C3 double bond and the vinyl linker of 14aeb resulted in the
formation of 15aeb. Amination of 9 with 1-(4-methoxyphenyl)
piperazine produced 13d and then 14d. Separately,13b was nitrated
by the same way as that for the preparation of 11 to install a nitro
group at the C6 position producing 16 and 17. Products 22 and 23
having a chloro-substituent at C6 or C7 position of the quinox-
alinone core were similar compounds to 14aeb, and therefore
prepared by the same synthetic way (Scheme 3).
had a C6-nitro group and an IC50 value of 0.283 mM showed seven-
fold more potency than its counterpart, which lacked the C6eNO2
group reported in our previous work [19]. Also, compound 17 was
about four times higher potent than compound 14b that has no
substituent at the phenyl ring of the quinoxalinone framework.
Further, replacement of the C6-NO2 group of 17 with chloro group
led to compound 22, in which the inhibition was reduced to half of
17 but was still much stronger than that of 14b. In addition,
attachment of chloro to the C7 position forming compound 23
resulted in a significantly deactivated effect when comparing the
difference between 23 and 14a. These results suggest a large impact
of the N1-acetate and C3 substituents on biological activity, as well
as, an enhancing role for the C6 nitro group.
Compounds 14aed, with N1-acetate group, were prepared in
order to investigate the effect of C3 side chain on the ALR2 inhi-
bition. Among them, C3 styrenyl-containing compound (14a)
appeared to be the most active while the compound 14d with more
bulky C3 substituent was the least active. Hydrogenation reaction
on the C3 vinyl linker of 14aeb led to the corresponding C3 phe-
nethyl compounds 15aeb, respectively. Each of them was more
potent in the ALR2 inhibition than its precursor indicating a benefit
of the saturated linker over the vinyl linker for the biological ac-
tivity. However, the p-fluoro group of the C3-side chain is likely to
3. Results and discussion
Our recent work regarding effective quinoxalinone-based ARIs
indicated that the size of substituent groups attached to the C3
position might have an impact on the efficiency of ARIs [19]. The
present study focuses on the installation of various substituent
groups to quinoxalinone core structure and the activity evaluation
of the resulting compounds on ALR2. The synthetic work led to
Fig. 2. Chemical structures of aldose reductase inhibitors.

S. Hussain et al. / European Journal of Medicinal Chemistry 80 (2014) 383e392
385
Scheme 1. Reagents and conditions: (a) 4-nitrobenzyl bromide, CH3CN, K2CO3, 12 h, N2, 55 ꢀC; (b) Piperazines, DMF, K2CO3, 24 h, 75 ꢀC; (c) for the preparation of 8aec; Olefines,
Pd(OAc)2, P(o-tolyl)3, Et3N, DMF, 100 ꢀC, 24 h, for 8d; boronic acid reagent, Cs2CO3, Pd(OAc)2, P(Ph)3, N2, dioxane:water (30:3), 100 ꢀC, 12 h.
decrease the inhibitory efficiency as compared to 14a with 14b, and
15a with 15b (Table 1). The compounds, proven to be effective in
ALR2 inhibition were also tested for their ability to inhibit ALR1
(aldehyde reductase) isolated from rat kidney. ALR1 is present in all
tissues and plays an important role in detoxification, and therefore,
has been commonly employed in the selectivity evaluation of ALR2
inhibitors (ARIs). Interestingly, our results show that 15a and 17,
identified as significant ALR2 inhibitors, showed the least inhibi-
tory effect on ALR1 suggesting their good selectivity for ALR2.
Trp 111. The more flexible nature of saturated C3-linker in 15a
phenethyl group makes the compound a more favored conforma-
tion for the active site and thus stronger activity was found for 15a
over 14a. But, in contrast, docking of 14a (Fig. 3ced) showed that
the C2-carbonyl oxygen forms a hydrogen bond with Cys 298
ꢀ
(3.17 A) and in 17 (Fig. 3e, f) showed that the C2-carbonyl oxygen
ꢀ
forms a hydrogen bond with Cys 298 (3.11 A), the low bond length
of hydrogen bond in case of 17 was probably due to C6-NO2 which
favor the molecule to orientate slightly in to more stable way than
14a but in both, 14b and 17 the quinoxalinone core structures goes
somewhat away from the hydrophobic pocket instead of pene-
trating in it as case of 15a which indicate different interaction
patterns between these compounds. The docking results provide
support to 15a as more active inhibitor.
4. Molecular modeling
In order to understand the mechanistic details of biological ac-
tivity and how 15a was more active than 14a and 17, docking of
compounds were performed with Lidorestat-bound conformation
of ALR2 (PDB code: 1Z3N). As shown in Fig. 3a, b, the results of 15a
revealed that ligand fits into the active site of enzyme. The
carboxylate group was fit for an anion-binding pocket through
three hydrogen bonds, of which two with the hydroxyl group of Tyr
5. Conclusion
The present effort to examine the ALR2 inhibition function of
substituent groups at different positions of quinoxalinone scaffold
resulted in the development of a new series of quinoxalinone ARIs
including 12, 14aed, 15aeb, 17, 22, and 23. They showed good to
ꢀ
ꢀ
ꢀ
48 (3.05 A and 3.56 A) and one with N2 atom of His 110 (3.04 A). The
carboxyl head makes stabilizing electro-stating interaction with the
positive charged nicotinamide moiety of the co-factor NADPþ (Ne
ꢀ
O ¼ 4.8 A). Additionally, the C2-carbonyl group interacts via
moderate activity with IC50 values of 0.143e7.53 mM. The most
ꢀ
hydrogen bonding with N1 of Trp 111 (2.39 A) while quinoxalinone
potent and selective inhibitor was found to be 15a with N1-acetate
and C3-phenethyl side chain. Besides, SAR studies suggested that
the C6-NO2 and particularly C3-phenethyl substitution were able to
increase the activity. However, the substitutions at the C7 position
of the scaffold and at the para-position of the phenethyl or of the
C3-strenyl ring may have a decreasing effect
core structure penetrates into hydrophobic pocket formed by the
side chains of Trp 20, Phe 122, Trp 79 and Trp 219. The C3-
phenethyl ring forms a stable stacking interaction against the
indol ring of Trp 111 side chain and penetrates into specificity
pocket formed by Leu 300, Cys 303, Cys 298, Thr 113, Phe 122, and

386
S. Hussain et al. / European Journal of Medicinal Chemistry 80 (2014) 383e392
Scheme 2. Reagents and conditions: (a) methyl 2-bromoacetate, CH3CN, K2CO3, 2 h, 55 ꢀC; (b) 2,4-difluoroaniline, DMF, K2CO3, 24 h, 75 ꢀC; (c) Cu(NO3)2e3H2O, Ac2O, CH2Cl2, 12 h,
rt; (d) LiOH, HCl; (e) for the preparation of 13aec: Olefines, Pd(OAc)2, P(o-tolyl)3, Et3N, DMF, 100 ꢀC; for 13d: Piperazine, Toluene, K2CO3, 12 h, 100 ꢀC; (f) Pd/C, H2, MeOH, 24 h, rt.
6. Experimental section
1H NMR spectra are values from CDCl3 (
d
¼ 7.26 ppm). Data for 1H
NMR spectra is represented as follows: chemical shifts (ppm),
multiplicity (s ¼ singlet, d ¼ doublet, t ¼ triplet, q ¼ quartet,
m ¼ multiplet), coupling constant J (Hz), and integration. 13C NMR
6.1. Materials
Melting points were taken on an X-4 microscopic melting points
apparatus and were uncorrected. All reactions and products mix-
tures purification and separation were performed by column chro-
matography on silica gel routinely checked by TLC on Merck60F254
Silica gel aluminum sheet. The purity of more potent acid derivatives
was checked by HPLC. 1H NMR and 13C NMR spectra were recorded,
at 400 MHz and 100 MHz in CDCl3 and DMSO-d6. Chemical shifts for
spectra data is represented in (
d
¼ ppm). All chemicals were re-
agents grade. 1-(3-trifluoromethyl) phenyl) piperazine, 1-(4-
methoxyphenyl) piperazine, 2-(piperazin-1-yl) pyrazine, benzo[b]
thiophen-3-yl boronic acid, tri-o-tolyl phosphine, and palladium
acetate were purchased from Alfa Aesar. D,L-glyceraldehydes and
NADPH were purchased from SigmaeAldrich. Wistar rats (250e
300 g) were supplied by Vital River, Beijing, China.
o
Reagents and conditions: (a) methyl 2-bromoacetate, CH3CN, K2CO3, 2 h, 55 C ; ( b)
Olefines , Pd(OAc)2, P(o-tolyl)3, Et3N, DMF, 100 oC; (c) LiOH, HCl.
Scheme 3. Reagents and conditions: (a) methyl 2-bromoacetate, CH3CN, K2CO3, 2 h, 55 ꢀC; (b) Olefines, Pd(OAc)2, P(o-tolyl)3, Et3N, DMF, 100 ꢀC; (c) LiOH, HCl.

S. Hussain et al. / European Journal of Medicinal Chemistry 80 (2014) 383e392
387
Table 1
Biological activity data of quinoxalinone derivatives.
b
Comp. no.
R1
R2
ALR2 inh. [%]a
42.85%
ALR2 IC50
[m
M]
ALR1 inh. [%]a
7a
7b
7c
24%
23%
7d
8a
26%
30%
8b
8c
24%
36.24%
8d
32%
14a
H
H
0.82 (0.77e0.87)
1.43 (1.39e1.47)
32%
47%
14b
14c
H
1.86 (1.78e1.94)
25%
(continued on next page)

388
S. Hussain et al. / European Journal of Medicinal Chemistry 80 (2014) 383e392
Table 1 (continued )
b
Comp. no.
R1
R2
ALR2 inh. [%]a
ALR2 IC50
[m
M]
ALR1 inh. [%]a
48%
14d
15a
15b
22
H
7.53 (6.93e8.13)
0.143 (0.125e0.161)
1.14 (1.05e1.23)
0.66 (0.51e0.81)
3.88 (2.90e4.86)
0.362 (0.314e4.10)
H
22%
40%
25%
35%
25%
H
6-Cl
7-Cl
6-NO2
23
17
12
6-NO2
0.283 (0.190e3.36)
0.12 (0.07e0.17)
41%
Epalrestat
a
Represents the percent inhibition of compounds determined at concentration of 10
IC50 (95% CL) values represent the concentration required to effect 50% enzyme inhibition.
m
M.
b
6.2. Synthesis of 3-chloro-1-(4-nitrobenzyl)-1, 2-
(s, 4H), 3.41 (s, 4H), 13C NMR (CDCl3, 100 MHz)
d
: 152.30, 151.37,
dihydroquinoxaline (6)
150.46, 147.51, 143.05, 137.8, 133.3, 132.95, 131.71, 129.76, 127.68,
125.74, 124.29,122.91, 121.99, 116.32, 113.62, 112.42, 109.86, 48.86,
46.81, 45.77; ESI-MS([MþH]þ) m/z: 510.0.
A mixture of compound 5 (3.600 g, 20 mmol), phenols
(22 mmol), DMF (10 mL) and K2CO3 (8.340 g, 60 mmol) was charged
in 250 mL flask and refluxed at 75 ꢀC. After 12 h the resulting
mixture was cooled down and filtered. After evaporating the sol-
vent, residue was purified by column chromatography using silica
gel eluted with ethyl acetate (EtOAc)/petroleum ether (P.E) ¼ 1:4 to
furnish compound 6. Yellow powder, yield 40%; mp: 90 ꢀC; 1H NMR
6.3.2. 1-(4-Nitrobenzyl)-3-(4-(pyrazin-2-yl) piperazin-1-yl)
quinoxalin-2(1H)-one (7b)
Dark yellow powder; yield: 85%; mp: 220e222 ꢀC; 1H NMR
(CDCl3, 400 MHz)
7.63 (m, 8H), 5.57 (s, 2H, eCH2e), 4.09e4.15 (m, 4H), 3.77e3.79 (m,
4H), 13C NMR (CDCl3, 100 MHz)
: 152.0. 152.34, 150.53, 147.56,
d: 8.10e8.19 (m, 3H), 7.38 (d, J ¼ 8 Hz, 2H), 7.01e
(CDCl3, 400 MHz)
2H), 7.37e7.54 (m, 4H), 5.67 (s, 2H).
d
: 8.19 (d, J ¼ 8 Hz, 2H), 7.85 (dd, J ¼ 9.2, 1.1 Hz,
d
143.02, 141.92, 133.52, 131.13, 129.81, 127.45, 125.83, 124.33, 113.65,
109.90, 46.63, 45.82, 44.50; ESI-MS([MþH]þ) m/z: 444.3.
6.3. General procedure for the synthesis of (7aed)
6.3.3. 1-(4-Nitrobenzyl)-3-(4-(2-morpholinoethyl) piperazin-1-yl)
quinoxalin-2(1H)-one (7c)
A mixture of compound 6 (150 mg, 0.5 mmol), K2CO3 (139 mg,
1 mmol), and appropriate piperazine and pyrazine (0.5 mmol) was
charged in 250 mL flask and refluxed in 5 mL CH3CN under argon
for 4 h. Then the resulting mixture was poured into H2O providing
yellowish precipitate, which was then filtered. The residue was
purified by column chromatography using silica gel eluted with
EtOAc/P.E ¼ 1:4e1:3 to afford desired products 7aec and 7d.
Yellow powder; yield: 85%; mp: 210e212 ꢀC; 1H NMR (CDCl3,
400 MHz)
3.85 (s, 4H), 3.56 (s, 4H), 2.36e2.52 (m, 12H), 13C NMR (CDCl3,
100 MHz) : 152.26, 150.51, 147.42, 134.31, 133.50, 129.64, 127.63,
d: 8.01 (d, J ¼ 8.4 Hz, 2H), 6.8e7.43 (m, 6H), 5.39 (s, 2H),
d
127.18, 125.33, 124.20, 113.50, 67.02, 56.45, 55.75, 54.24, 53.77,
46.98, 45.70; ESI-MS([MþH]þ) m/z: 479.1.
6.3.1. 1-(4-Nitrobenzyl)-3-(4-(3-(trifluoromethyl) phenyl)
piperazin-1-yl) quinoxalin-2(1H)-one (7a)
6.3.4. 1-(4-Nitrobenzyl)-3-(4-(4-methoxyphenyl) piperazin-1-yl)
quinoxalin-2(1H)-one (7d)
Orange powder; yield: 88%; mp: 88e90 ꢀC; 1H NMR (CDCl3,
Yellow powder; yield: 70%; mp: 220e225 ꢀC; 1H NMR (CDCl3,
400 MHz)
d: 8.14e8.19 (m, 4H), 7.01e7.63 (m, 8H), 5.57 (s, 2H), 4.18
400 MHz)
d: 9.1 (s, 1H), 8.15 (d, J ¼ 8.4 Hz, 2H), 6.83e7.5 (m, 9H),

S. Hussain et al. / European Journal of Medicinal Chemistry 80 (2014) 383e392
389
Fig. 3. Docking of inhibitors in to active site of ALR2. a) Docking of 15a in to ALR2 active site in ribbon diagram; b) in surface representation. The docked pose of 15a shown in cyan
(C), blue (N) and red (O); hydrogen bonds are shown as light yellow dashed lines; c) Docking of 14a in to ALR2 active site in ribbon diagram; d) in surface representation. The docked
pose of 14a shown in cyan (C), blue (N) and red (O); hydrogen bonds are shown as light yellow dashed lines; e) Docking of 17 in to ALR2 active site in ribbon diagram; f) in surface
representation. The docked pose of 17 shown in cyan (C), blue (N) and red (O); hydrogen bonds are shown as light yellow dashed lines.
5.54 (s, 2H), 4.1 (s, 4H), 3.2 (m, 4H), 3.7 (s, 3H), 13C NMR (CDCl3,
100 MHz) : 150.60, 145.64, 143.10, 129.76, 127.68,127.32, 125.56,
6.4.2. 3-(4-Fluorostyryl)-1-(4-nitrobenzyl) quinoxalin-2(1H) e one
(8b)
d
124.44, 118.62, 114.58, 113.58, 55.67, 50.99, 47.18, 45.76; ESI-
Orange solid; yield: 60%; mp: 200e202 ꢀC; 1H NMR (CDCl3,
MS([MþH]þ) m/z: 472.1.
400 MHz)
d: 8.12 (dd, J ¼ 22, 12.4 Hz, 2H), 7.90 (d, J ¼ 8 Hz, 2H), 7.0e
7.71 (m, 10H), 5.63 (s, 2H), 13C NMR (CDCl3, 100 MHz)
d
: 155.10,
152.55, 147.60, 137.54, 130.47, 130.15, 129.87, 127.81, 124.55, 121.86,
124.36, 121.62, 116.16, 115.94, 113.92, 45.62; ESI-MS([MþH]þ) m/z:
402.3.
6.4. General procedure for the synthesis of 8aec
A mixture of compound 6 (315 mg,1 mmol), appropriate olefinic
reagent (1.5 mmol), palladium acetate (0.3 mmol), tri-o-tolyl
phosphine (0.7 mmol) and triethylamine (2 mmol) in DMF (5 mL)
was refluxed for 24 h, and then poured into water and filtered. The
residue was purified by column chromatography eluted with
EtOAc/P.E ¼ 1:4 to afford products 8aec.
6.4.3. N-(Tert-butyl)-3-(4-(4-nitrobenzyl)-3-oxo-3, 4-
dihydroquinoxalin-2-yl) acryl amide (8c)
Pale yellow solid; yield: 60%; mp: 210 ꢀC; 1H NMR (CDCl3,
400 MHz)
d
: 8.18 (d, J ¼ 8 Hz, 2H), 7.90 (dd, J ¼ 12.2, 6.1 Hz, 2H),
7.26e7.48 (m, 4H), 7.11 (d, J ¼ 8 Hz, 2H), 5.63 (s, 2H), 1.45 (s, 9H), 13
C
NMR (CDCl3, 100 MHz) d: 164.44, 154.71, 151.30, 147.64, 142.54,
133.68, 133.54, 132.41, 131.46, 131.23, 127.82, 124.62, 113.97, 109.90,
6.4.1. 1-(4-Nitrobenzyl)-3-styrylquinoxalin-2(1H)-one (8a)
51.85, 45.58, 28.88; ESI-MS([MþH]þ) m/z: 407.4.
Orange solid; yield: 60%; mp: 200e205 ꢀC; 1H NMR (CDCl3,
400 MHz)
(d, J ¼ 16 Hz, 2H), 7.40e7.44 (m, 6H), 7.10 (d, J ¼ 8 Hz, 2H), 5.63 (s,
2H), 13C NMR (CDCl3, 100 MHz)
: 155.11, 152.65, 147.61, 138.88,
d
: 8.16e8.21 (m, 3H), 7.69 (d, J ¼ 8 Hz, 2H, aromatic), 7.77
6.5. Synthesis of 3-(Benzo[b] thiophen-3-yl)-1-(4-nitrobenzyl)
quinoxalin-2(1H)-one (8d)
d
136.34, 133.81, 131.95, 130.10, 129.61, 129, 128.1, 127.82, 124.38,
A mixture of compound 6 (315 mg, 1 mmol), appropriate
boronic acid reagent (196 mg, 1.1 mmol), palladium acetate (5 mg,
121.86, 113.90, 45.63; ESI-MS([MþH]þ) m/z: 384.3.

390
S. Hussain et al. / European Journal of Medicinal Chemistry 80 (2014) 383e392
0.05 mmol), triphenyl phosphine (20 mg, 0.015 mmol) and Cesium
carbonate (650 mg, 2 mmol) in solution of dioxane:water (30:3)
was refluxed under inert atmosphere at 100 ꢀC for 12 h and
monitored by TLC, then washed the mixture with aqueous sodium
chloride solution and extracted with THF. Dried the organic layer
with MgSO4, and filtered off. After evaporating the solvent in vacuo,
the residue was purified by column chromatography using silica gel
eluted EtOAc/P.E ¼ 1:3 to afford 8d. Pale yellow solid; yield: 70%;
6.9.2. 2-(3-(4-Fluorostyryl)-2-oxoquinoxalin-1(2H)-yl) acetic acid
methyl ester (13b)
Yellow powder; yield: 70%; mp: 165 ꢀC; 1H NMR (400 MHz,
DMSO-d6)
d
: 8.05 (d, J ¼ 16.2 Hz, 1H), 7.61 (dd, J ¼ 19.5, 11.8 Hz, 2H),
7.25e7.40 (m, 6H), 7.08 (d, J ¼ 7.9 Hz, 1H), 5.2 (s, 2H), 3.4 (s, 3H).
6.9.3. Methyl 2-(3-(3-(tert-butylamino)-3-oxoprop-1-en-1-yl)-2-
oxoquinoxalin-1(2H)-yl) acetate (13c)
mp: 195e200 ꢀC; 1H NMR (CDCl3, 400 MHz)
d
: 8.88 (s, 1H), 7.15e
Synthesized and used immediately for next step to prepare 14c.
8.19 (m, 12H), 5.69 (s, 2H), 13C NMR (CDCl3, 100 MHz)
d
: 153.25,
148.16, 151.30, 147.28, 142.32, 141.57, 140.18, 140.07, 133.04, 132.73,
131.51, 130.35, 127.49, 126.19, 125.16, 124.27, 122.75, 113.54, 45.58;
ESI-MS([MþH]þ) m/z: 415.4.
6.9.4. 2-(3-(4-Fluorostyryl)-6-nitro-2-oxoquinoxalin-1(2H)-yl)
acetic acid methyl ester (16)
Orange powder; Yield: 70%; mp: 130 ꢀC; 1H NMR (400 MHz,
DMSO-d6)
2H), 3.6 (s, 3H).
d
: 8.90 (s, 1H), (d, J ¼ 8 Hz, 1H), 7.22e7.60 (m, 7H), 5.17 (s,
6.6. Compounds 9 and 10
Procedure and data reported previously [19].
6.9.5. Compound 19
Procedure and data reported previously [19].
6.7. Synthesis of 2-(3-(2,4-difluorophenylamino)-6-nitro-2-
oxoquinoxalin-1(2H)-yl) acetic acid methyl ester 11
6.9.6. 2-(6-Chloro-2-oxo-3-styrylquinoxalin-1(2H)-yl) acetic acid
methyl ester (20)
Synthesized and used immediately for next step to prepare 22.
A solution of Cu (NO3)2.3H2O (223 mg, 1 mmol) in acetic an-
hydride (10 mL) was stirred for 2 h at room temperature, and then a
solution of compound 10 (173 mg, 0.5 mmol) [21] in CH2Cl2 (10 mL)
was added in it. The reaction solution was stirred for 12 h at room
temperature. After it, MeOH (10 mL) added to the resulting solution
and the stirring was continued until the mixture becomes clear
solution. Solvent was evaporated, and the residue was neutralized
with aqueous solution of NaHCO3 to PH 6. The precipitate was
collected by filtration, washed with water and purified with column
chromatography eluted with EtOAc/P.E ¼ 1:3 to furnish the product
11. Yellow powder; yield: 55%; mp: 225 ꢀC; 1H NMR (CDCl3,
6.9.7. 2-(7-Chloro-2-oxo-3-styrylquinoxalin-1(2H)-yl) acetic acid
methyl ester (21)
Yellow powder; yield: 45%; mp: 180 ꢀC; 1H NMR (CDCl3,
400 MHz)
d
: 7.60 (d, J ¼ 8 Hz, 2H), 7.59 (s, 1H), 7.18e7.36 (m, 6H),
6.90 (d, J ¼ 12 Hz, 1H), 4.96 (s, 2H), 3.6 (s, 3H).
6.10. Synthesis of methyl 2-(3-(4-(4-methoxyphenyl) piperazin-1-
yl)-2-oxoquinoxalin-1(2H)-yl) acetate (13d)
400 MHz)
(m, 4H), 5.63 (s, 2H), 3.74 (s, 3H).
d
: 10.48 (s, 1H), 8.34 (s, 1H), 7.85 (d, J ¼ 8.9 Hz, 1H), 8.19
A mixture of compound 9 (252 mg, 1 mmol), K2CO3 (278 mg,
2 mmol), and 1-(4-methoxyphenyl) piperazine (192 mg, 1 mmol)
was charged in 100 mL flask and refluxed in 10 mL Toluene under
argon for 12 h. After evaporating the solvent, the residue was pu-
rified by column chromatography using silica gel eluted with
EtOAc/P.E ¼ 1:3 to get desired product. Off-white powder; yield:
6.8. Synthesis of 2-(3-(2,4-difluorophenylamino)-6-nitro-2-
oxoquinoxalin-1(2H)-yl) acetic acid (12)
70%; mp: 185e190 ꢀC; 1H NMR (400 MHz, DMSO-d6)
d: 6.08e7.27
To a solution of ester 11 (195 mg, 0.5 mmol) in THF (5 mL)
was added saturated aqueous LiOH (5 mL). The mixture was
stirred at room temperature for 2 h, and then acidified to pH 1e
2. The precipitate was filtered off and washed with water to
afford the product. Yellow powder; yield: 70%; mp: 290 ꢀC; 1H
(m, 8H), 5.08 (s, 2H), 4.09 (s, 4H), 3.67 (s, 4H), 2.59 (s, 6H).
6.11. Synthesis of 14aed, 17, 22, and 23
Same procedure as for 12.
NMR (400 MHz, DMSO-d6) d: 10.31 (s, 1H), 7.71e8.17 (m, 5H),
7.68 (d, J ¼ 4 Hz, 1H), 5.1 (s, 2H), 13C NMR (100 MHz, DMSO-d6)
d:
169.94, 151.47, 151.20, 149.10, 147.97, 144.41, 137.55, 136.61, 135.42,
129.92, 119.52, 110.47, 105.65, 105.40, 19.9; ESI-MS([MþH]þ) m/z:
377.1; HRMS (ESI) m/z calcd for [MꢁH]ꢁ 375.0939 found
376.9744.
6.11.1. 2-(2-Oxo-3-styrylquinoxalin-1(2H)-yl) acetic acid (14a)
Yellow powder; yield: 70%; mp: 215 ꢀC; 1H NMR (400 MHz,
DMSO-d6)
d
: 8.05 (d, J ¼ 16.2 Hz, 1H), 7.4e7.8 (m, 10H), 5.07 (s, 2H),
13C NMR (100 MHz, DMSO-d6)
d
: 168.78, 154.09, 151.43, 137.55,
135.83, 132.62, 130.35, 129.58, 129.41, 129.07, 127.77, 124.04, 112.83,
114.60, 53.0; ESI-MS([MꢁH]ꢁ) m/z: 305.1; HRMS (ESI) m/z calcd for
[MꢁH]ꢁ 305.095 found 305.0943.
6.9. General procedure for the synthesis of compounds 13aec, 16,
19, 20 and 21
6.11.2. 2-(3-(4-Fluorostyryl)-2-oxoquinoxalin-1(2H)-yl) acetic acid
(14b)
Same procedure as for 8aec.
Yellow powder, yield: 70% mp: 215 ꢀC; 1H NMR (400 MHz,
6.9.1. 2-(2-Oxo-3-styrylquinoxalin-1(2H)-yl) acetic acid methyl
ester (13a)
DMSO-d6)
7.53 (m, 6H), 7.41 (t, J ¼ 7.5 Hz, 1H), 7.28 (t, J ¼ 8.8 Hz, 1H) 5.09 (s,
2H), 13C NMR (100 MHz, DMSO-d6)
: 168.83, 164, 161.54, 154.
d
: 8.07 (d, J ¼ 16.3 Hz, 1H), 7.84 (dd, J ¼ 16.8, 8.2 Hz, 1H),
Yellow powder; yield: 70%; mp: 160 ꢀC; 1H NMR (CDCl3,
d
400 MHz)
d
: 8.18 (d, J ¼ 16.2 Hz,1H), 7.91 (d, J ¼ 7.9 Hz,1H), 7.71 (dd,
151.38, 136.31, 132.60, 132.51, 132.28, 130.32, 130, 129.92, 129.38,
124, 121.74, 116.11, 115.90, 114.61, 53.8; ESI-MS([MꢁH]ꢁ) m/z: 323.1;
HRMS (ESI) m/z calcd for [MꢁH]ꢁ 323.0837 found 323.0836.
J ¼ 19.5, 11.8 Hz, 2H), 7.50 (t, J ¼ 7.7 Hz, 1H), 7.25e7.40 (m, 5H), 7.08
(d, J ¼ 7.9 Hz, 1H), 5.09 (s, 2H), 3.8 (s, 3H).

S. Hussain et al. / European Journal of Medicinal Chemistry 80 (2014) 383e392
391
6.11.3. 2-(3-(3-(Tert-butylamino)-3-oxoprop-1-en-1-yl)-2-
oxoquinoxalin-1(2H)-yl) acetic acid (14c)
MS([MꢁH]ꢁ) m/z: 307.3; HRMS (ESI) m/z calcd for [MꢁH]ꢁ
307.1088 found 307.1070.
Brown powder; yield: 50%; mp: 115 ꢀC; 1H NMR (400 MHz,
DMSO-d6)
d
: 7.83 (s, 1H), 7.46e7.81 (m, 3H), 7.43 (d, J ¼ 12 Hz, 1H),
6.12.2. 2-(3-(4-Fluorophenethyl)-2-oxoquinoxalin-1(2H)-yl) acetic
acid (15b)
7.39 (d, J ¼ 8 Hz, 1H), 5.00 (s, 2H), 1.29 (s, 9H), 13C NMR (100 MHz,
DMSO-d6)
d
: 171.11, 169.71, 169.22, 164.14, 154.37, 151.12, 133.20,
Off-white powder; yield: 70%; mp: 130 ꢀC; 1H NMR (400 MHz,
132.82, 132.60, 132.31, 132.12, 131.99, 131.95, 131.80, 130.24, 129.10,
124.59, 115.18, 67.49, 65.53, 30.28, 28.89, 28.84, 25.55; ESI-
MS([MþH]þ) m/z: 330.3.
DMSO-d6)
d
: 7.75 (dd, J ¼ 7.9, 1.3 Hz, 1H), 7.06e7.50 (m, 8H), 4.68 (s,
2H), 3.01e3.12 (m, 4H), 13C NMR (100 MHz, DMSO-d6)
d: 160.31,
158.37, 154.12, 140.99, 132.24, 132.35, 129.09, 128.41, 129.11, 125.55,
123.45, 115.33, 53.0, 35.34, 32.23; ESI-MS([MꢁH]ꢁ) m/z: 325.3.
6.11.4. 2-(3-(4-(4-Methoxyphenyl) piperazin-1-yl)-2-
oxoquinoxalin-1(2H)-yl) acetic acid (14d)
6.13. Biological methods
Off-white powder; yield: 50%; mp: 200 ꢀC; 1H NMR (400 MHz,
ALR2 and ALR1 were obtained from Wistar rats containing about
200e250 g body weight, supplied by Vital River, Beijing China.
glyceraldehyde, Sodium -glucuronate and NADPH were obtained
from Sigma Aldrich. ALR2 and ALR1 were prepared by methods of
La Motta et al. [16] and Kinoshita [25]. All chemical used were of
reagent grade. Enzyme and target compounds inhibition activities
were tested using Shimadzu UV-1800 Spectrophotometer by
monitoring change in absorption at
of NADPH by ALR2 and ALR1.
DMSO-d6)
d
: 6.85e7.51 (m, 8H), 4.98 (s, 2H), 4.04 (s, 4H), 3.69 (s,
3H), 3.19 (s, 4H), 13C NMR (100 MHz, DMSO-d6)
d: 168.95, 151.39,
D,L-
D
149.98, 132.36, 130.11, 126.20, 125.31, 123.72, 114.35, 114.01, 55.26,
50.13, 46.13, 43.93, 39.72, 39.25; HRMS (ESI) m/z calcd for [M_H]-
393.1568 found 393.1581.
6.11.5. 2-(3-(4-Fluorostyryl)-6-nitro-2-oxoquinoxalin-1(2H)-yl)
acetic acid (17)
l
¼ 340 nm, resulting oxidation
Orange powder; yield: 45%; mp: 190 ꢀC; 1H NMR (400 MHz,
DMSO-d6)
d
: 8.64 (s, 1H), 7.31e7.95 (m, 7H), 7.27 (d, J ¼ 8 Hz, 1H),
5.28 (s, 2H), 13C NMR (100 MHz, DMSO-d6)
d
: 168.06, 142.94, 138.01,
6.14. Enzymatic assay
134.30, 133.57, 133.50, 132.66, 132.55, 130.97, 130.25, 129.1, 126.36,
126.24, 125.18, 116.97, 116.76, 115.63, 65.51; ESI-MS([MþH]þ) m/z:
372.3; HRMS (ESI) m/z calcd for [MþH]þ 372.3018 found 372.0939.
ALR2 was prepared by methods of La Motta et al. [16] and
Kinoshita [25]. The freshly acquired rat eye lenses were homoge-
nized (Glass-potter) in three volumes of deionized water in an ice
bath. The homogenate was then centrifuged for 30 min at
12,000 rpm (rotor type: 12154-H) at 0e4 ꢀC. The supernatant was
precipitated with (NH4)2SO4 at 40% and at 50% saturation. The
combined supernatant of both 40% and at 50% saturation then
precipitated with (NH4)2SO4 at 75%. The final precipitated obtained
from the 75% saturated fraction, which was determined to possess
ALR2 activity, was dissolved in 0.05 M NaCl and dialyzed overnight
and stored at ꢁ20 ꢀC. The dialyzed material was used for enzymatic
assay.
6.11.6. 2-(6-Chloro-3-(4-fluorostyryl)-2-oxoquinoxalin-1(2H)-yl)
acetic acid (22)
Yellow powder; yield: 45%; mp: 280 ꢀC; 1H NMR (400 MHz,
DMSO-d6)
d
: 7.63 (d, J ¼ 12 Hz, 1H), 7.51e7.42 (m, 4H), 7.40 (d,
J ¼ 8 Hz, 1H), 7.23e7.39 (m, 3H), 5.00 (s, 2H), 13C NMR (100 MHz,
DMSO-d6) d: 196.17, 164.51, 162.04, 154.32, 152.02, 137.23, 135.16,
133.82, 132.83, 132.80, 130.51, 130.42, 124.59, 121.94, 116.57, 116.35,
114.93, 67.48; ESI-MS([MþH]þ) m/z: 359.3; HRMS (ESI) m/z calcd
for [M_H]- 339.0542 found 339.056.
The ALR2 activity was performed at 30 ꢀC in a reaction mixture
of I mL solution containing 0.25 mL NADPH (0.10 mM), 0.25 mL
sodium phosphate buffer (0.1 M, pH 6.2), 0.1 mL enzyme extract,
6.11.7. 2-(7-Chloro-2-oxo-3-styrylquinoxalin-1(2H)-yl) acetic acid
(23)
0.15 mL deionized water and 0.25 mL
as a substrate. The reaction mixture was incubated at 30 ꢀC for
10 min except for Glyceraldehyde. Then substrate added to start
D-L Glyceraldehyde (10 mM)
Yellow powder, yield: 35%; mp: 270 ꢀC; 1H NMR (400 MHz,
DMSO-d6)
d
: 8.041 (d, J ¼ 10.8, 1H), 8.02 (d, J ¼ 5.2, 1H), 7.39e7.88
D-L
(m, 8H), 5.10 (s, 2H), 13C NMR (100 MHz, DMSO-d6)
d
: 169.21,
the reaction and monitored for 4 min. The ALR1 activity assay was
done at 37 ꢀC in a reaction mixture containing 0.25 mL NADPH
(0.10 mM), 0.25 mL sodium phosphate buffer (0.1 M, pH 7.2), 0.1 mL
154.30, 153.26, 139.17, 138.80, 136.10, 136.01, 133.76, 133.68, 131.98,
131.62, 130.30, 129.54, 128.08, 122.07, 117.08, 116.90, 53.02; ESI-
MS([MþH]þ) m/z: 341.1; HRMS (ESI) m/z calcd for [MꢁH]ꢁ
339.0542 found 339.0560.
enzyme extract, 0.15 mL deionized water and 0.25 mL sodium D-
Glucuronate (20 mM) as a substrate inꢀa final volume of 1 mL. The
reaction mixture was incubated at 37 C for 10 min except for so-
6.12. General procedure of synthesis of 15a and 15b
dium D-Glucuronate. After it substrate was added to start the re-
action and monitored for 4 min.
The inhibitory activity of newly synthesized compounds against
ALR2 and ALR1 were assayed by adding 5 mL inhibitor solution to
To a suspension of 10% palladium over carbon (50 mg) in
methanol was added a solution of appropriate compound 14a or
14b (0.25 mmol) in EtOAc (10 mL). The mixture was stirred at room
temperature under hydrogen atmosphere for 18 h. The catalyst was
filtered off through celite. The filtrate was concentrated and the
residue was purified by column chromatography using CH2Cl2/
MeOH (40:2) as eluent to obtain products as off-white powder.
the above mentioned reaction mixture. All compounds were dis-
solved in DMSO and diluted with deionized water. To correct for
non-enzymatic oxidation of NADPH, the rate of NADPH oxidation in
the presence of all of the reaction mixture components except the
substrate was subtracted from each experimental rate. The inhibi-
tory effect of synthetic compounds was routinely estimated at
concentration of 10ꢁ5 M (The concentration is referenced to that of
compounds in the reaction mixture). The active compounds were
tested at an additional concentration between 10ꢁ6 and 10ꢁ7 M.
Each dose effect curve was generated with at least three concen-
trations of inhibitors between 20 and 80%, with three replicates at
each concentration.
6.12.1. 2-(2-Oxo-3-phenethylquinoxalin-1(2H)-yl) acetic acid (15a)
Off-white powder; yield: 70%; mp: 120 ꢀC; 1H NMR (400 MHz,
DMSO-d6)
7.32 (m, 7H), 4.70 (s, 2H), 3.01e3.11 (m, 4H), 13C NMR (100 MHz,
DMSO-d6) : 159.68, 154.27, 141.99, 133.30, 132.31, 130.01, 129.28,
128.85, 128.79, 126.35, 123.55, 115.43, 53.0, 35.66, 32.12; ESI-
d: 7.75 (d, J ¼ 7.9 Hz, 1H), 7.49 (t, J ¼ 10.1 Hz, 1H), 7.17e
d

392
S. Hussain et al. / European Journal of Medicinal Chemistry 80 (2014) 383e392
[4] Y.L. Kao, K. Donaghue, A. Chan, J. Knight, M. Silink, Diabetes 48 (1999) 1338e
6.15. Molecular docking
1340.
[5] D.K. Moczulski, W. Burak, A. Doria, M. Zychma, E. Zukow-ska-Szczechowska,
J.H. Warram, W. Grzeszczak, Diabetologia 42 (1999) 94e97.
[6] V.F. Carvalho, E.O. Barreto, M.F. Serra, R.S. Cordeiro, M.A. Maritus, Z.B. Fortes,
P.M. e Silva, European Journal of Pharmacology 549 (2006) 173e178.
[7] R. Kikkawa, I. Hatanaka, H. Yasuda, N. Kobayashi, Y. Shigeta, H. Tarashima,
T. Morimua, M. Tsuboshima, Diabetologia 24 (1983) 290e292.
[8] M.A. Ramirez, N.L. Borja, Pharmacotherapy 28 (2008) 646e655.
[9] S. Ao, Y. Shingu, C. Kikuchi, Y. Takano, K. Nomura, T. Fujiwara, Y. Ohkubo,
Y. Notsu, I. Yamaguchi, Metabolism 40 (1991) 77e87.
[10] 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, Journal
of Medicinal Chemistry 48 (2005) 3141e3152.
[11] C. La Motta, S. Sartini, S. Salerno, F. Si-morini, S. Taliani, A.M. Marini, F. Da
Settimo, L. Marinelli, V. Limongelli, E. Novellino, Journal of Medicinal Chem-
istry 51 (2008) 3182e3193.
[12] W.G. Robison Jr., N.M. Laver, J.L. Jacot, J.P. Glover, Investigative Ophthalmology
&Visual Science 36 (1995) 2368e2380.
[13] T. Asano, Y. Saito, M. Kawakami, N. Yamada, Journal of Diabetes and its
Complication 16 (2002) 133e138.
[14] T. Negoro, M. Murata, S. Ueda, B. Fujitani, Y. Ono, A. Kuromiya, M. Komiya,
K. Suzuki, J.-i. Matsumoto, Journal of Medicinal Chemistry 41 (1998) 4118e
4129.
Docking studies were performed using Molegro Virtual Docker,
version 5.0. The crystal structure of the human aldose reductase
with bound inhibitor (PDB code: 1Z3N) retrieved from the RCSB
Protein Data Bank [10] and used for docking. Water and other
solvents within the protein structure were removed for docking
procedure. All the structural parameters of the ligands such as bond
order, hybridization, explicit hydrogen atoms and charges were
assigned when necessary in the Molegro Virtual Docker software.
For the better potential, binding sites in protein, and five binding
cavities were selected, the cavity around the anion binding site
(volume of w124 Å3) was chosen for the docking calculations. All
docking calculations were carried out using the grid-based Mol-
ꢀ
Dock score (GRID) function with a grid resolution of 0.30 A. From
the MolDock score and ReRank score best ligand poses were
chosen.
[15] B.L. Mylari, S.J. Armento, D.A. Beebe, E.L. Conn, J.B. Coutcher, M.S. Dina,
M.T. O’Gorman, M.C. Linhares, W.H. Martin, P.J. Oates, D.A. Tess, G.J. Withbroe,
W.J. Zembrowski, Journal of Medicinal Chemistry 48 (2005) 6326e6339.
[16] C. La Motta, S. Sartini, L. Mugnaini, F. Simorini, S. Taliani, S. Salerno,
A.M. Marini, F. Da Settimo, A. Lavecchia, E. Novellino, M. Can-tore, P. Failli,
M. Ciuffi, Journal of Medicinal Chemistry 50 (2007) 4917e4927.
[17] P. Alexiou, V.J. Demopoulos, Journal of Medicinal Chemistry 53 (2010) 7756e
7766.
Acknowledgments
This work was supported by the National Natural Science
Foundation of China (grant no. 21272025), the Research Fund for
the Doctoral Program of Higher Education of China (grant no.
20111101110042), and the Science and Technology Commission of
Beijing (China) (grant no. Z131100004013003).
[18] S.R. Sharma, N. Sharma, Annals of Indian Academy of Neurology 11 (2008)
231e235.
[19] Y. Yang, S. Zhang, B. Wu, X. Chen, X. Qin, M. He, S. Hussain, C. Jing, B. Ma,
C. Zhu, Chemistry Medicinal Chemistry 7 (2012) 823e835.
[20] X. Chen, S. Zhang, Y. Yang, S. Hussain, M. He, D. Gui, B. Ma, C. Jing, Z. Qiao,
C. Zhu, Q. Yu, Bioorganic & Medicinal Chemistry 19 (2011) 7262e7269.
[21] X. Chen, Y. Yang, B. Ma, S. Zhang, M. He, D. Gui, S. Hussain, C. Jing, C. Zhu,
Q. Yu, Y. Liu, European Journal of Medicinal Chemistry 46 (2011) 1536e1544.
[22] X. Chen, C. Zhu, F. Guo, X. Qiu, Y. Yang, S. Zhang, M. He, S. Parveen, C. Jing, Y. Li,
B. Ma, Journal of Medicinal Chemistry 53 (2010) 8330e8344.
[23] M. Azaam, W.M. De Borggraeve, F. Compernolle, G.J. Hoornaert, Tetrahedron
61 (2005) 3953e3962.
Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.ejmech.2014.04.047.
References
[24] P. Romea, M. Aragones, J. Garcia, J. Vilarrasa, Organic Letters 56 (1991) 7038e
7042.
[1] P. Alexiou, K. Pegklidou, M. Chatzopoulou, I. Nicolaou, V.J. Demopoulos, Cur-
rent Medicinal Chemistry 16 (2009) 734e752.
[25] S. Hayman, J.H. Kinoshita, Journal of Biological Chemistry 240 (1965) 877e
882.
[2] C. Yabe-Nishimura, Pharmacological Reviews 50 (1998) 21e33.
[3] S.M. Chung, S.K. Chung, Current Medicinal Chemistry 10 (2003) 1375e1387.