Synthesis and structure-activity relationship of 2-phenyliminochromene derivatives as inhibitors for aldo-keto reductase (AKR) 1B10

Article abstract of DOI:10.1016/j.bmc.2013.08.059

Inhibitors of a human member (AKR1B10) of the aldo-keto reductase superfamily are regarded as promising therapeutics for the treatment of cancer. Recently, we have discovered (Z)-2-(4-methoxyphenylimino)-7-hydroxy-N-(pyridin- 2-yl)-2H-chromene-3-carboxami

Full text of DOI:10.1016/j.bmc.2013.08.059

Bioorganic & Medicinal Chemistry 21 (2013) 6378–6384
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry
journal homepage: www.elsevier.com/locate/bmc
Synthesis and structure–activity relationship of
2-phenyliminochromene derivatives as inhibitors for aldo–keto
reductase (AKR) 1B10
b
a
a
c
c
Satoshi Endo a, , Dawei Hu , Miho Suyama , Toshiyuki Matsunaga , Kenji Sugimoto , Yuji Matsuya ,
⇑
Ossama El-Kabbani d, Kazuo Kuwata e, Akira Hara f, Yukio Kitade f, Naoki Toyooka g
a Laboratory of Biochemistry, Gifu Pharmaceutical University, Gifu 501-1196, Japan
b Graduate School of Innovative Life Science, University of Toyama, 3190 Gofuku, Toyama 930-8555, Japan
c Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, 2630 Sugitani, Toyama 930-0194, Japan
d Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria 3052, Australia
e United Graduate School of Drug Discovery and Medical Information Sciences, Gifu University, Gifu 501-1193, Japan
f Department of Biomolecular Science, Faculty of Engineering, Gifu University, Gifu 501-1193, Japan
g Graduate School of Science and Technology for Research, University of Toyama, 3190 Gofuku, Toyama 930-8555, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Inhibitors of a human member (AKR1B10) of the aldo–keto reductase superfamily are regarded as
promising therapeutics for the treatment of cancer. Recently, we have discovered (Z)-2-
(4-methoxyphenylimino)-7-hydroxy-N-(pyridin-2-yl)-2H-chromene-3-carboxamide (1) as the potent
competitive inhibitor using the virtual screening approach, and proposed its 4-methoxy group on the
2-phenylimino moiety as an essential structural prerequisite for the inhibition. In this study, 18
derivatives of 1 were synthesized and their inhibitory potency against AKR1B10 evaluated. Among them,
7-hydroxy-2-(4-methoxyphenylimino)-2H-chromene-3-carboxylic acid benzylamide (5n) was the most
potent inhibitor showing a Ki value of 1.3 nM. The structure–activity relationship of the derivatives
indicated that the 7-hydroxyl group on the chromene ring, but not the 4-methoxy group, was absolutely
required for inhibitory activity, The molecular docking of 5n in AKR1B10 and site-directed mutagenesis of
the enzyme residues suggested that the hydrogen-bond interactions between the 7-hydroxyl group of 5n
Received 29 July 2013
Revised 23 August 2013
Accepted 23 August 2013
Available online 6 September 2013
Keywords:
AKR1B10
Aldose reductase-like protein
Aldose reductase
Molecular docking
Structure–activity relationship
and the catalytic residues (Tyr49 and His111) of the enzyme, together with a
benzylamide moiety of 5n with Trp220, are important for the potent inhibition.
Ó 2013 Elsevier Ltd. All rights reserved.
p-stacking interaction of the
1. Introduction
in developing colon cancer cell resistance to anticancer drugs such
as mitomycin C12 and oxaliplatin.11 Due to its high catalytic
efficiency towards aliphatic aldehydes, retinals and isoprenyl alde-
hydes,1,6–8,13,14 the roles suggested for AKR1B10 in cell carcinogen-
esis and tumor development are the detoxification of cytotoxic
carbonyls derived from lipid peroxidation,6–8 decrease in retinoic
acid synthesis,13 and modulation of protein prenylation.6,11,15 In
addition, AKR1B10 is reported to promote fatty acid synthesis in
cancer cells by blocking the ubiquitin-dependent degradation of
acetyl CoA carboxylase.8,16 Thus, this enzyme has been recognized
not only as a potential diagnostic and/or prognostic marker, but
also as a potential therapeutic target for the treatment of the above
types of cancer and the colon cancer chemoresistance.
A
human member of the aldo–keto reductase (AKR)
superfamily, AKR1B10, is a NADPH-dependent reductase, which
was originally identified as an aldose reductase-like protein that
is up-regulated in hepatocellular carcinomas.1 Over-expression of
AKR1B10 has been also observed in other tumors, such as smokers’
non-small cell lung carcinomas,2 uterine carcinomas,3 cholangio-
carcinomas,4 pancreatic carcinoma,5 and breast cancer.6 The
silencing of the AKR1B10 gene results in growth inhibition of
cancer cells5–8 and hepatocellular carcinoma xenografts in mice,9
and its elevated expression in turn promotes proliferation of cancer
cells,10,11 indicating that the enzyme participates in tumor
development. Furthermore, AKR1B10 is suggested to be implicated
During the past five years, many synthetic and natural
compounds that show inhibitory effects on AKR1B10 have been
reported, as reviewed by Matsunaga et al.11,17 Among them, (Z)-
2-(4-methoxyphenylimino)-7-hydroxy-N-(pyridin-2-yl)-2H-chro-
mene-3-carboxamide (1) is the most potent competitive inhibitor
Abbreviations: AKR, aldo–keto reductase; FBS, fetal bovine serum; SAR, struc-
ture–activity relationship.
⇑
Corresponding author. Tel.: +81 58 237 5979; fax: +81 58 237 3931.
E-mail address: sendo@gifu-pu.ac.jp (S. Endo).
0968-0896/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bmc.2013.08.059

S. Endo et al. / Bioorg. Med. Chem. 21 (2013) 6378–6384
6379
showing an IC50 value of 6.0 nM.18 Molecular docking of 1 in
AKR1B10 proposed that the interactions between the 4-methoxyl
group on the 2-phenylimino moiety of 1 and the enzyme’s active
site residues, His111 and Trp112, are important for the tight bind-
ing (Fig. 1A). However, this compound almost equally inhibits the
structurally similar human aldose reductase that is named AKR1B1
in the AKR superfamily. Because AKR1B1 plays distinct roles in glu-
cose and prostaglandin metabolism,19,20 selective inhibition of
AKR1B10 is ideally required for the development of drugs targeting
this enzyme. The structure–activity relationship (SAR) study on the
chromene-3-carboxamide derivatives has not been also reported
since its discovery by the virtual screening.18 In this study, we de-
signed and synthesized derivatives of 1 based on the molecular
docking result, and evaluated them for enzyme inhibitory activity,
in order to explore SAR of the 1-derived compounds as potent
inhibitors of ARK1B10.
confirm the interactions of the 4-methoxy group with His111
and Trp112 of AKR1B10, which was suggested by the previous
docking model of 1 in this enzyme.18 The Knoevenagel condensa-
tion of cyanoacetamide (2)21 with 2,4-dihydroxybenzaldehyde
(3) afforded the 2-iminochromene derivative (4). Reaction of 4
with anilines furnished the desired 2-phenyliminochromenes
(5a–g) (Scheme 1). All of the derivatives potently inhibited
AKR1B10, as evidenced by less than 2.2-fold increases in their
IC50 values compared to that of 1 (See Table 1). Surprisingly, the
des-methoxy derivative 5g also showed potent inhibition, in
contrast to the important interaction of the 4-methoxy group
suggested by the docking model of 1.18 Next, we examined the
effect of substituents of the 3-carboxamide moiety on AKR1B10
inhibition. Seven derivatives having isopropyl (5h) or acyclic alkyls
(5i–k), hydroxyalkyls (5l–m), and benzyl (5n) substituent instead
of the 2-pyridyl side chain of 1 were synthesized. Since these
substitutions also did not significantly affect the inhibitory potency
towards AKR1B10, we synthesized the different phenol derivatives
(5o–q) and deoxy-derivative (5r) at the 7-position of the chromene
ring system to examine the role of the 7-hydroxyl group on the
chromene ring of 1 and the above derivatives. The same procedures
for the synthesis of 5a–g were applied for the synthesis of 5o–r, as
shown in Schemes 2 and 3.
2. Results and discussion
2.1. Chemistry
First, we synthesized seven 1-based derivatives having different
substituents on the 2-phenylimino moiety at the 4-position to
Figure 1. Structures of 1 (A) and 5n (B), and their docked models in AKR1B10–NADP+ complex. The portion of NADP+ (yellow) and residues (green) within 4.0 Å from the
inhibitors are depicted with possible hydrogen bond interactions, which are shown in dotted lines with distances. The docked model of 1 (A) is the same as that previously
reported.18
Scheme 1. Synthesis of chromene derivatives 5a–g.

6380
S. Endo et al. / Bioorg. Med. Chem. 21 (2013) 6378–6384
the previous dock model.18 With respect to the moiety bound to
Table 1
Inhibition of AKR1B10 and AKR1B1 by the 1-based derivatives
the carboxyamide of the chromene ring, small alkyls (less than 3
carbons) or Bn substituent are better than c-Hex, n-Bu, or i-Bu as
the substituent on the amide nitrogen. Among the synthesized
compounds, the Bn derivative (5n) was the most potent and selec-
tive inhibitor of AKR1B10 (IC50 = 4.7 nM). The inhibition pattern of
5n was competitive with respect to the alcohol substrate, geraniol,
of AKR1B10, and its Ki value was 1.3 0.3 nM (Fig. 2), which is the
lowest among the values of the known inhibitors.10,11,13,14,17,18 In
contrast, the removal of the 7-hydroxyl group on the chromene ring
(5o–r) resulted in drastic decreases in inhibitory potency, suggest-
ing a crucial role of the 7-hydroxyl group in the tight binding of 1 to
AKR1B10.
a
Compound
IC50 (nM)
AKR1B10
Ratio
AKR1B1
11 1.0
1
5a
5b
5c
5d
5e
5f
5g
5h
5i
5j
5k
5l
5m
5n
5o
5p
5q
5r
6.0 0.1
1.8
3.5
2.5
3.0
1.8
0.9
1.5
2.8
0.7
1.6
1.8
2.5
1.8
3.3
5.1
–
6.8 0.3
7.6 1.0
8.6 0.8
14 0.8
13 2.1
13 1.6
12 2.3
9.7 1.6
18 3.3
16 2.1
11 0.5
11 0.5
8.8 1.0
24 1.1
19 1.3
26 3.0
25 4.4
12 1.5
20 2.4
34 1.5
6.7 0.4
28 2.7
28 3.3
27 4.6
20 1.1
29 0.4
24 2.4
2.3. Docking model of 5n in AKR1B10
4.7 0.04
The above SAR studies of 2-phenyliminochromene derivatives
(5a–r) revealed that the 7-hydroxyl group on the chromene ring
is an essential moiety for their potent inhibition of AKR1B10. The
underlying structural reasons for the high affinity of the 7-hydro-
xy-chromene derivatives were examined by constructing a model
of docked 5n in the AKR1B10-NADP+ complex (Fig. 1B). In this
model, 5n occupied the substrate-binding site of the enzyme, in
which its 7-hydroxyl group formed hydrogen-bond interactions
with the catalytically important residues, Tyr49 and His111
(2.9 Å and 3.0 Å, respectively), and the chromene ring was sur-
rounded by hydrophobic residues (Trp21, Val48, Trp112, and
Trp220). An additional hydrogen-bond interaction between the
oxygen in the chromene ring and the side chain of Trp21 (3.1 Å)
was suggested. The orientation of the chromene ring of 5n is
contrast to that in the previous 1-docked model (Fig. 1A), in which
the 7-hydroxy-chromene ring is oppositely positioned. The
b
>10,000
>10,000b
>10,000b
290 30
>10,000b
>10,000b
>10,000b
>10,000b
–
–
–
a
Selectivity is expressed as a ratio of AKR1B1/AKR1B10.
Inhibition percentages are less than 30% at 10,000 nM.
b
2.2. Biological evaluation and SAR of 5
Newly synthesized compounds (5), except for 5o–r, showed po-
tent inhibition for AKR1B10, with less than 3-fold increases in the
IC50 values compared with that of the original compound 1
(Table 1). While the replacement of the 4-methoxy group on the
2-phenylimino moiety of 1 with halogen (5d, 5e) or CH2CO2H group
(5f) slightly decreased the inhibitory potency, that with OH (5a),
CO2H (5b) or Me group (5c) had apparently no significant effect.
This indicates that the 4-methoxy group is not an essential struc-
tural prerequisite for the tight binding of 1, which is suggested by
benzylamide moiety of 5n formed a
p-stacking interaction with
the side chain of Trp220 (3.5 Å), which may account for the higher
inhibitory potency for AKR1B10 than other derivatives with
alkylamide and c-hexylamide moieties (5h–m). In fact, the
Scheme 2. Synthesis of chromene derivatives 5h–n.
Scheme 3. Synthesis of chromene derivatives 5o–r.

S. Endo et al. / Bioorg. Med. Chem. 21 (2013) 6378–6384
6381
Figure 2. Inhibition of wild-type and mutant AKR1B10s by 5n. The activity was determined with 0.25 mM NADP+ and geraniol (25–200
l
M for the wild-type and Gln303Ser
enzymes; and 50–800
concentrations, and replots of the slopes (
lM for Trp220Tyr enzyme) in the presence of the indicated concentrations of 5n. The velocities were plotted double-reciprocally versus the substrate
l
M mL munitÀ1) and intercepts (munit mLÀ1 Â 102) versus the inhibitor concentrations are shown in the figure.
Trp220Tyr mutagenesis of the enzyme resulted in a 39-fold
increase in the Ki value for 5n (51.0 1.0 nM) compared to that
determined with the wild-type enzyme (Fig. 2). The benzylamide
moiety of 5n is also close to the side-chain of Gln303 (3.3 Å), which
corresponds to Ser in AKR1B1, and the mutation of Gln303Ser
decreased the affinity for 5n (Ki = 3.8 0.1 nM, Fig. 2) by 3-fold.
Gln303 might be related to the highest AKR1B10-inhibitory
selectivity of 5n among the derivatives. The 4-methoxy group on
the 2-phenylimino moiety of 5n was located in the external region
of the substrate-binding pocket, in which only the side-chain of
Gln50 was close to the 4-methoxy group. This orientation may
explain the insignificant alteration in the inhibitory potency
following the replacement of the 4-methoxy group (5a–g).
J = 1.3, 7.3 Hz), 7.89 (1H, dd, J = 1.3, 7.3 Hz), 8.44–8.45 (1H, m),
8.76 (1H, br), 11.02 (1H, br).
4.1.1.3. 7-Hydroxy-2-imino-2H-chromene-3-carboxylic acid
butylamide (4i). Yield: 61%; 1H NMR (400 MHz, CDCl3) d 0.95
(3H, t, J = 7.1 Hz), 1.41 (2H, sext, J = 7.1 Hz), 1.60 (2H, quint,
J = 7.1 Hz), 3.42 (2H, t, J = 7.1 Hz), 6.64 (1H, s), 6.72 (1H, dd,
J = 2.4, 5.9 Hz), 7.33 (1H, d, J = 8.3 Hz), 8.81 (1H, s).
4.1.1.4. 7-Hydroxy-2-imino-2H-chromene-3-carboxylic acid
isobutylamide (4j). Yield: 49%; 1H NMR (400 MHz, DMSO-d6) d
0.94 (6H, d, J = 6.6 Hz), 1.81 (1H, m), 2.08 (2H, d, J = 6.6 Hz), 6.64
(1H, s), 6.72 (1H, dd, J = 2.4, 5.9 Hz), 7.33 (1H, d, J = 8.3 Hz), 8.81
(1H, s).
3. Conclusion
4.1.1.5. 7-Hydroxy-2-imino-2H-chromene-3-carboxylic acid
cyclohexylamide (4k). Yield: 68%; 1H NMR (400 MHz, DMSO-d6)
d 1.25–1.97 (10H, m), 3.95 (1H, quint, J = 7.8 Hz), 6.64(1H, s),
6.73 (1H, dd, J = 2.4, 6.2 Hz), 7.30 (1H, d, J = 8.6 Hz), 8.35 (1H, s),
10.03 (1H, br).
In this study, a series of 2-phenyliminochromene derivatives
(5a–r) were synthesized, and their inhibitory activities for
AKR1B10 were evaluated. The SAR of the synthesized compounds
revealed that the hydroxyl group on the chromene ring at the 7-po-
sition was essential to maintain the potent inhibitory effect. The
necessity of the 7-hydroxyl group was in agreement with the
molecular docking model of 5n in complex with AKR1B10–NADP+,
in which the 7-hydroxyl group forms strong hydrogen bond inter-
actions with catalytically important residues, Tyr49 and His111, of
the active site of the enzyme.
4.1.1.6. 7-Hydroxy-2-imino-2H-chromene-3-carboxylic acid
(2-hydroxyethyl)amide (4l). Yield: 81%; 1H NMR (400 MHz,
DMSO-d6) d 3.25 (2H, t, J = 7.1 Hz), 3.46 (2H, t, J = 7.1 Hz), 4.77
(1H, br), 6.53 (1H, s), 6.65 (1H, d, J = 8.5 Hz), 7.55 (1H, d,
J = 8.5 Hz), 8.3 (1H, s), 10.33 (1H, br).
4.1.1.7. 7-Hydroxy-2-imino-2H-chromene-3-carboxylic acid
(3-hydroxypropyl)amide (4m). Yield: 43%; 1H NMR (400 MHz,
DMSO-d6) d 1.62 (2H, quint, J = 6.5 Hz), 3.29 (2H, t, J = 6.5 Hz),
3.38 (2H, t, J = 6.5 Hz), 4.10 (1H, br), 6.54 (1H, s), 6.66 (1H, dd,
J = 2.1, 6.2 Hz), 7.55 (1H, d, J = 8.3 Hz), 8.29 (1H, s), 8.74 (1H, br),
10.24 (1H, br), 10.63 (1H, br).
4. Experimental section
4.1. Chemistry
4.1.1. General procedure for Knoevenagel condensation
To a stirred solution of cyanamide (2, 1.1 mmol) in ethanol
(2 mL) were added 2-hydroxybenzaldehyde (1 mmol) and piperi-
dine (catalytic amount), and the resulting mixture was stirred at
room temperature for 12 h. The suspension was then filtered to
give 4, which was used directly in the next step.
4.1.1.8. 7-Hydroxy-2-imino-2H-chromene-3-carboxylic acid
benzylamide (4n). Yield: 98%; 1H NMR (400 MHz, DMSO-d6) d
4.50 (2H, d, J = 5.9 Hz), 6.55 (1H, dd, J = 2.2, 6.3 Hz), 7.23–7.35
(5H, m), 7.56 (1H, d, J = 8.5 Hz), 8.42 (1H, s), 10.66 (1H, br).
4.1.1.1. 7-Hydroxy-2-imino-2H-chromene-3-carboxylic acid
pyridin-2-ylamide (4). Yield: 88%; 1H NMR (400 MHz, DMSO-d6)
d 6.59 (1H, s), 6.71 (1H, d, J = 8.5 Hz), 7.13 (1H, t, J = 8.9 Hz), 7.64
(1H, d, J = 8.5 Hz), 7.83 (1H, t, J = 8.9 Hz), 8.25 (1H, d, J = 8.9 Hz),
8.31–8.32 (1H, m), 8.50 (1H, s), 9.02 (1H, br), 13.14 (1H, s).
4.1.1.9. 8-Hydroxy-2-imino-2H-chromene-3-carboxylic acid
pyridin-2-ylamide (4o). Yield: 78%; 1H NMR (400 MHz, DMSO-
d6) d 7.07–7.24 (4H, m), 7.83 (1H, t, J = 7.5 Hz), 8.26 (1H, d,
J = 8.5 Hz), 8.33 (1H, d, J = 7.5 Hz), 8.54 (1H, s), 9.14 (1H, br),
10.22 (1H, br), 13.26 (1H, br).
4.1.1.2. 7-Hydroxy-2-imino-2H-chromene-3-carboxylic acid
isopropylamide (4h). Yield: 45%; 1H NMR (400 MHz, DMSO-d6) d
1.17 (6H, s), 4.05 (1H, sept, J = 6.5 Hz), 6.78 (1H, s), 6.86 (1H, dd,
4.1.1.10. 6-Hydroxy-2-imino-2H-chromene-3-carboxylic acid
pyridin-2-ylamide (4p). Yield: 86%; 1H NMR (400 MHz, DMSO-
d6) d 6.99–7.17 (4H, m), 7.84 (1H, t, J = 8.4 Hz), 8.25 (1H, d,

6382
S. Endo et al. / Bioorg. Med. Chem. 21 (2013) 6378–6384
J = 8.4 Hz), 8.3–8.34 (1H, m), 8.52 (1H, s), 9.06 (1H, br), 9.74 (1H,
br).
143.29, 148.44, 149.83, 149.85, 151.45, 154.84, 160.25, 163.32; IR
(KBr): 3317, 1682, 1558, 1435 cmÀ1; MS (EI): m/z 435 (M+); HRMS:
Calcd for C21H14BrN3O3 435.0219. Found 435.0226.
4.1.1.11. 5-Hydroxy-2-imino-2H-chromene-3-carboxylic acid
pyridin-2-ylamide (4q). Yield: 81%; 1H NMR (400 MHz, DMSO-
d6) d 6.36 (1H, d, J = 7.9 Hz), 6.49 (1H, d, J = 8.4 Hz), 7.12 (1H, t,
J = 8.4 Hz), 7.24 (1H, t, J = 7.9 Hz), 7.80 (1H, t, J = 7.9 Hz), 8.26–
8.32 (2H, m), 13.19 (1H, br).
4.1.2.5.
7-Hydroxy-2-(4-iodophenylimino)-2H-chromene-3-
carboxylic acid pyridin-2-ylamide (5e: R = I). Yield: 60%; mp:
>300 °C; 1H NMR (400 MHz, DMSO-d6) d 6.55(1H, s), 6.78 (1H,
dd, J = 2.2, 6.3 Hz), 7.13–7.18 (3H, m), 7.71–7.77 (3H, m), 7.84
(1H, t, J = 8.1 Hz), 8.27 (1H, d, J = 8.1 Hz), 8.32–8.34 (1H, m), 8.66
(1H, s), 12.79 (1H, br); 13C NMR (100 MHz, DMSO-d6) d 100.11,
101.46, 111.12, 113.60, 113.72, 115.56, 119.91, 125.72, 131.80,
137.65, 138.46, 143.28, 143.66, 148.45, 149.79, 151.45, 154.85,
160.27, 163.33; IR (KBr): 3442, 1686, 1595, 1541, 1435 cmÀ1; MS
(EI): m/z 483 (M+); HRMS: Calcd for C21H14IN3O3 483.0080. Found
483.0074.
4.1.1.12. 2-Imino-2H-chromene-3-carboxylic acid pyridin-2-
ylamide (4r). Yield: 89%; 1H NMR (400 MHz, DMSO-d6) d 7.04–
7.27 (4H, m), 7.48–7.55 (2H, m), 7.74 (1H, t, J = 7.9 Hz), 8.36–8.39
(2H, m), 8.57 (1H, s), 13.09 (1H, br).
4.1.2. General procedure for synthesis of compounds (5a–r)
To a stirred solution of chromene (4, 1 mmol) in acetic acid
(2 mL) was added aniline (1 mmol), and the resulting mixture
was stirred at room temperature for 12 h. The solvent was re-
moved under reduced pressure, and the residue was chromato-
graphed on silica gel to give 5 as the yellow solid.
4.1.2.6.
{4-[7-Hydroxy-3-(pyridin-2-ylcarbamoyl)chromen-2-
ylideneamino]phenyl}-acetic acid (5f: R = CH2CO2H). Yield:
61%; mp: >300 °C; 1H NMR (400 MHz, DMSO-d6) d 3.57 (2H, s),
6.51 (1H, s), 6.73 (1H, d, J = 8.7 Hz), 7.14 (1H, t, J = 7.3 Hz), 7.28–
7.32 (4H, m), 7.67 (1H, d, J = 8.7 Hz), 7.83 (1H, t, J = 7.3 Hz), 8.27
(1H, d, J = 7.3 Hz), 8.33–8.35 (1H, m), 8.62 (1H, s), 13.00 (1H, br);
13C NMR (100 MHz, DMSO-d6) d 40.92, 48.63, 101.52, 110.69,
113.71, 115.26, 119.81, 123.13, 129.90, 131.69, 131.79, 138.39,
142.15, 142.82, 148.46, 149.16, 151.57, 155.01, 160.42, 163.94,
173.34; IR (KBr): 3402, 1668, 1543, 1437, 1229 cmÀ1; MS (EI):
m/z 415 (M+); HRMS: Calcd for C23H17N3O5 415.1168. Found
415.1172.
4.1.2.1.
7-Hydroxy-2-(4-hydroxyphenylimino)-2H-chromene-
3-carboxylic acid pyridin-2-ylamide (5a: R = OH). Yield: 52%;
mp: >300 °C; 1H NMR (400 MHz, DMSO-d6) d 6.62 (1H, s), 6.74
(1H, dd, J = 2.2, 6.1 Hz), 6.82 (2H, t, J = 8.8 Hz), 7.14 (1H, t,
J = 7.6 Hz), 7.33 (2H, d, J = 8.8 Hz), 7.65 (1H, d, J = 8.3 Hz), 7.83
(1H, t, J = 7.6 Hz), 8.27 (1H, d, J = 7.6 Hz), 8.36–8.36 (1H, m), 8.54
(1H, br); 13C NMR (100 MHz, DMSO-d6) d 100.11, 101.54, 110.94,
113.26, 113.69, 115.45, 115.95, 119.84, 125.24, 131.58, 134.89,
138.44, 147.58, 148.52, 151.62, 154.85, 154.98, 160.48, 163.15; IR
(neat): 3312, 1661, 1574, 1506, 1437 cmÀ1; IR (KBr): 3396, 1666,
1591, 1549, 1435 cmÀ1; MS (EI): m/z 373 (M+); HRMS: Calcd for
4.1.2.7. 7-Hydroxy-2-phenylimino-2H-chromene-3-carboxylic
acid pyridin-2-ylamide (5g: R = H). Yield: 52%; mp: 294–295 °C;
1H NMR (400 MHz, DMSO-d6) d 6.51 (1H, s), 6.76 (1H, dd, J = 2.4,
6.2 Hz), 7.13–7.21 (2H, m), 7.32–7.46 (4H, m), 7.70 (1H, d,
J = 8.6 Hz), 7.86 (1H, t, J = 8.0 Hz), 8.29 (1H, d, J = 8.0 Hz), 8.32–
8.34 (1H, m), 8.65 (1H, s); 13C NMR (100 MHz, DMSO-d6) d
101.38, 110.86, 113.50, 113.71, 115.49, 119.80, 123.15, 124.52,
128.88, 131.68, 138.44, 142.95, 143.84, 148.32, 149.28, 151.52,
154.90, 160.34, 163.40; IR (KBr): 3442, 1684, 1582, 1541,
1437 cmÀ1; MS (EI): m/z 357 (M+); HRMS: Calcd for C21H15N3O3
357.1113. Found 357.1110.
C21H15N3O4 373.1063. Found 373.1060.
4.1.2.2. 4-[7-Hydroxy-3-(pyridin-2-ylcarbamoyl)-chromen-2-
ylideneamino]-benzoic acid (5b: R = CO2H). Yield: 34%; mp:
>300 °C; 1H NMR (400 MHz, DMSO-d6) d 6.51 (1H, s), 6.76 (1H,
dd, J = 2.4, 6.1 Hz), 7.14 (1H, t, J = 7.8 Hz), 7.38 (2H, d, J = 8.6 Hz),
7.71 (1H, d, J = 7.8 Hz), 7.84 (1H, t, J = 7.8 Hz), 7.99 (2H, d,
J = 8.6 Hz), 8.28–8.35 (2H, m), 8.68 (1H, s), 12.73 (1H, br); 13C
NMR (100 MHz, DMSO-d6) d 72.73, 93.77, 101.47, 111.00, 113.74,
115.35, 119.96, 123.09, 130.40, 131.89, 138.50, 143.72, 148.29,
148.47, 150.23, 151.45, 154.91, 160.30, 163.60, 167.17; IR (KBr):
3422, 1680, 1589, 1437 cmÀ1; MS (EI): m/z 401 (M+); HRMS: Calcd
for C22H15N3O5 401.1012. Found 401.1013.
4.1.2.8. 7-Hydroxy-2-(4-methoxyphenylimino)-2H-chromene-3-
carboxylic acid iso-propylamide (5h: R1 = i-Pr). Yield: 46%; mp:
229–231 °C; 1H NMR (400 MHz, DMSO-d6)
d 1.18 (6H, d,
J = 6.6 Hz), 3.99 (1H, sept, J = 6.6 Hz), 6.55 (1H, s), 6.71 (1H, d,
J = 8.3 Hz), 6.94 (2H, d, J = 8.5 Hz), 7.30 (2H, d, J = 8.5 Hz), 7.58
(1H, d, J = 8.3 Hz), 8.37 (1H, s), 10.18 (1H, d, J = 6.8 Hz), 10.72
(1H, br); 13C NMR (100 MHz, DMSO-d6) d 22.35, 22.45, 55.21,
101.33, 111.01, 112.97, 114.05, 116.84, 124.88, 131.08, 136.79,
140.51, 148.14, 154.56, 156.36, 160.74, 162.34; IR (KBr): 3321,
1655, 1570, 1558, 1506, 1246 cmÀ1; MS (EI): m/z 352 (M+); HRMS:
Calcd for C20H20N2O4 352.1423. Found 352.1426.
4.1.2.3. 7-Hydroxy-2-p-tolylimino-2H-chromene-3-carboxylic
acid pyridin-2-ylamide (5c: R = Me). Yield: 47%; mp: >300 °C;
1H NMR (400 MHz, DMSO-d6) d 2.33 (1H, s), 6.76 (1H, dd, J = 2.3,
6.1 Hz), 7.13–7.29 (5H, m), 7.70 (1H, d, J = 8.4 Hz), 7.84 (1H, t,
J = 8.2 Hz), 8.28 (1H, d, J = 8.2 Hz), 8.34–8.36 (1H, m), 8.62 (1H, s),
13.04 (1H, br); 13C NMR (100 MHz, DMSO-d6) d 20.67, 101.39,
110.94, 113.39, 113.71, 115.71, 119.85, 123.29, 129.39, 131.69,
133.78, 138.41, 141.06, 142.61, 148.46, 148.84, 151.54, 154.91,
160.38, 163.20; IR (KBr): 3421, 1676, 1593, 1551, 1437 cmÀ1; MS
(EI): m/z 371 (M+); HRMS: Calcd for C22H17N3O3 371.1270. Found
371.1273.
4.1.2.9. 7-Hydroxy-2-(4-methoxyphenylimino)-2H-chromene-3-
carboxylic acid butyl-amide (5i: R1 = n-Bu). Yield: 40%; mp:
257–259 °C; 1H NMR (400 MHz, DMSO-d6)
d 0.89 (3H, t,
J = 7.1 Hz), 1.33 (2H, sext, J = 7.1 Hz), 1.49 (2H, quint, J = 7.1 Hz),
3.35 (2H, t, J = 7.1 Hz), 3.74 (3H, s), 6.51 (1H, s), 6.70 (1H, d,
J = 8.1 Hz), 6.93 (2H, d, J = 8.9 Hz), 7.26 (2H, d, J = 8.9 Hz), 7.56
(1H, d, J = 8.1 Hz), 8.35 (1H, s), 10.15 (1H, d, J = 5.1 Hz), 10.64
(1H, br); 13C NMR (100 MHz, DMSO-d6) d 13.56, 19.71, 30.98,
55.13, 55.19, 101.29, 110.97, 112.90, 113.93, 114.00, 116.86,
124.72, 131.00, 136.91, 140.50, 148.21, 154.52, 156.25, 161.53,
162.27, 164.80; IR (KBr): 3373, 1665, 1570, 1504, 1246 cmÀ1; MS
(EI): m/z 366 (M+); HRMS: Calcd for C21H22N2O4 366.1580. Found
366.1585.
4.1.2.4. 2-(4-Bromophenylimino)-7-hydroxy-2H-chromene-3-
carboxylic acid pyridin-2-ylamide (5d: R = Br). Yield: 49%; mp:
>300 °C; 1H NMR (400 MHz, DMSO-d6) d 6.56 (1H, s), 6.78 (1H, d,
J = 8.4 Hz), 7.15 (1H, t, J = 7.5 Hz), 7.31 (2H, d, J = 8.7 Hz), 7.60
(2H, d, J = 8.7 Hz), 7.72 (1H, d, J = 8.4 Hz), 7.85 (1H, t, J = 7.5 Hz),
8.28 (1H, d, J = 7.5 Hz), 8.32–8.34 (1H, m), 8.67 (1H, s), 12.80 (1H,
br); 13C NMR (100 MHz, DMSO-d6) d 101.45, 111.00, 113.60,
113.71, 115.53, 116.70, 119.92, 125.45, 131.78, 138.44, 143.21,

S. Endo et al. / Bioorg. Med. Chem. 21 (2013) 6378–6384
6383
4.1.2.10. 7-Hydroxy-2-(4-methoxphenylino)-2H-chromene-3-
carboxylic acid isobutyl-amide (5j: R1 = i-Bu). Yield: 62%; mp:
>300 °C; 1H NMR (400 MHz, DMSO-d6) d 0.94 (6H, d, J = 6.6 Hz),
1.81 (1H, m), 2.08 (2H, d, J = 6.6 Hz), 3.77 (3H, s), 6.54 (1H, s),
6.72 (1H, d, J = 8.7 Hz), 6.95 (2H, d, J = 7.7 Hz), 7.28 (2H, d,
J = 7.7 Hz), 7.60 (1H, d, J = 8.7 Hz), 8.39 (1H, s), 10.25 (1H, br); 13C
NMR (100 MHz, DMSO-d6) d 20.12, 27.99, 30.71, 46.35, 55.22,
101.34, 110.83, 113.15, 114.06, 116.67, 124.66, 131.12, 136.95,
140.72, 148.46, 154.61, 156.28, 161.70, 162.76; IR (KBr): 3420,
1663, 1558, 1506, 1244 cmÀ1; MS (EI): m/z 366 (M+); HRMS: Calcd
for C21H22N2O4 366.1580. Found 366.1584.
(1H, d, J = 7.9 Hz), 8.41–8.43 (1H, m), 8.59 (1H, s), 13.48 (1H, br);
13C NMR (100 MHz, DMSO-d6) d 55.26, 113.73, 114.05, 119.62,
119.66, 119.85, 119.98, 120.55, 124.60, 126.36, 135.96, 138.46,
141.54, 141.57, 144.37, 147.10, 148.60, 151.51, 153.14, 157.01,
159.99; IR (KBr): 3369, 1678, 1601, 1506, 1435 cmÀ1; MS (EI):
m/z 387 (M+); HRMS: Calcd for C22H17N3O4 387.1219. Found
387.1214.
4.1.2.16. 6-Hydroxy-2-(4-methoxy-phenylimino)-2H-chromene-3-
carboxylic acid pyridin-2-ylamide (5p: R1, R3 = H, R2 =
OH). Yield: 59%; mp:>300 °C; 1H NMR (400 MHz, DMSO-d6) d
3.79 (3H, s), 6.99–7.04 (3H, m), 7.15–7.18 (3H, m), 7.45 (2H, d,
J = 8.9 Hz), 7.87 (1H, t, J = 8.1 Hz), 8.28 (1H, d, J = 8.1 Hz), 8.37–
8.39 (1H, m), 8.60 (1H, s), 9.80 (1H, br); 13C NMR (100 MHz,
4.1.2.11. 7-Hydroxy-2-(4-methoxy-phenylimino)-2H-chromene-3-
carboxylic acid cyclohexylamide (5k: R1 = c-Hex). Yield: 63%;
mp: 240–242 °C; 1H NMR (400 MHz, DMSO-d6) d 1.31–1.84 (10H,
m), 3.76 (3H, s), 3.79–3.81 (1H, m), 6.54 (1H, s), 6.71 (1H, dd,
J = 2.2, 6.3 Hz), 6.95 (2H, d, J = 9.1 Hz), 7.29 (2H, d, J = 9.1 Hz),
7.59 (1H, d, J = 8.5 Hz), 8.38 (1H, s). 10.32 (1H, d, J = 7.8 Hz),
10.67 (1H, br); 13C NMR (100 MHz, DMSO-d6) d 23.81, 25.22,
32.45, 55.22, 101.32, 111.04, 112.98, 114.09, 116.88, 124.81,
131.11, 136.79, 140.62, 148.28, 154.55, 156.35, 160.59, 162.33; IR
(KBr): 3450, 1653, 1558, 1506 cmÀ1; MS (EI): m/z 392 (M+); HRMS:
Calcd for C23H24N2O4 392.1736. Found 392.1740.
DMSO-d6)
d 55.24, 113.77, 114.15, 114.27, 116.15, 119.14,
120.02, 120.52, 121.11, 125.14, 136.38, 138.49, 141.73, 146.30,
148.18, 148.55, 151.45, 153.96, 156.63, 160.03; IR (KBr): 3312,
1661, 1574, 1506 cmÀ1; MS (EI): m/z 387 (M+); HRMS: Calcd for
C22H17N3O4. Found 387.1214.
4.1.2.17. 5-Hydroxy-2-(4-methoxy-phenylimino)-2H-chromene-3-
carboxylic acid pyridin-2-ylamide (5q: R1, R2 = H, R3 =
OH). Yield: 49%; mp: 294–296 °C; 1H NMR (400 MHz, DMSO-d6)
d 3.79 (3H, s), 6.71 (1H, d, J = 8.6 Hz), 6.74 (1H, d, J = 8.6 Hz), 7.01
(2H, d, J = 8.8 Hz), 7.16 (1H, t, J = 7.3 Hz), 7.39–7.45 (3H, m),
7.86 (1H, t, J = 7.3 Hz), 8.28 (1H, d, J = 7.3 Hz), 8.36–8.38 (1H, m),
8.75 (1H, s); 13C NMR (100 MHz, DMSO-d6) d 55.22, 105.66,
107.98, 110.57, 113.73, 114.13, 117.86, 119.94, 125.09, 134.38,
136.28, 136.61, 138.45, 147.79, 148.52, 151.46, 153.82, 156.09,
156.65, 160.09; IR (KBr): 3319, 1684, 1541, 1506 cmÀ1; MS (EI):
m/z 387 (M+); HRMS: Calcd for C22H17N3O4 387.1219. Found
387.1221.
4.1.2.12. 7-Hydroxy-2-(4-methoxyphenylimino)-2H-chromene-3-
carboxylic acid (2-hydroxyethyl)amide (5l: R1 = (CH2)2
OH). Yield: 80%; mp: 213–214 °C; 1H NMR (400 MHz, DMSO-d6)
d 3.39 (2H, t, J = 5.2 Hz), 3.54 (2H, t, J = 5.2 Hz), 3.77 (3H, s), 4.86
(1H, br), 6.56 (1H, s), 6.71 (1H, dd, J = 2.2, 6.1 Hz), 6.94 (2H, d,
J = 9.0 Hz), 7.37 (2H, d, J = 9.0 Hz), 7.60 (1H, d, J = 8.3 Hz), 8.40
(1H, s), 10.41 (1H, br); 13C NMR (100 MHz, DMSO-d6) d 41.75,
55.19, 59.73, 101.33, 110.99, 112.92, 113.91, 116.97, 125.15,
131.08, 136.81, 140.49, 147.77, 154.59, 156.33, 161.70, 162.30; IR
(KBr): 3368, 1661, 1559, 1506 cmÀ1; MS (EI): m/z 354 (M+); HRMS:
Calcd for C19H18N2O5 354.1216. Found 354.1213.
4.1.2.18. 2-(4-Methoxy-phenylimino)-2H-chromene-3-carboxylic
acid pyridin-2-ylamide (5r: R1, R2, R3 = H). Yield: 75%; mp: 249–
250 °C; 1H NMR (400 MHz, DMSO-d6) d 3.83 (3H, s), 6.94 (2H, d,
J = 9.0 Hz), 7.03 (1H, t, J = 6.7 Hz), 7.14–7.24 (2H, m), 7.45–7.52
(4H, m), 7.72 (1H, t, J = 6.7 Hz), 8.32–8.34 (2H, m). 8.56 (1H, s),
13.25 (1H, br); 13C NMR (100 MHz, DMSO-d6) d 55.46, 114.00,
114.78, 115.47, 119.07, 119.75, 121.47, 124.45, 125.55, 129.43,
132.85, 136.56, 137.80, 141.15, 147.42, 148.38, 151.89, 153.55,
157.17, 160.56; IR (KBr): 1676, 1541, 1506, 1437 cmÀ1; MS (EI):
m/z 371 (M+); HRMS: Calcd for C22H17N3O3 371.1270. Found
371.1271.
4.1.2.13. 7-Hydroxy-2-(4-methoxyphenylimino)-2H-chromene-3-
carboxylic acid (3-hydroxypropyl)amide (5m: R1 = (CH2)3-
OH). Yield: 72%; mp: 229–231 °C; 1H NMR (400 MHz, DMSO-d6)
d 1.67 (2H, quint, J = 6.6 Hz), 3.38 (2H, d, J = 6.6 Hz), 3.51 (2H, d,
J = 6.6 Hz), 3.77 (3H, s), 4.56 (1H, br), 6.53 (1H, s), 6.71 (1H, dd,
J = 2.3, 6.2 Hz), 6.95 (2H, d, J = 6.7 Hz), 7.32 (2H, d, J = 6.7 Hz),
7.60 (1H, d, J = 8.5 Hz), 8.39 (1H, s), 10.188 (1H, t, J = 5.6 Hz); 13C
NMR (100 MHz, DMSO-d6) d 32.11, 36.21, 55.16, 58.53, 101.29,
110.98, 112.91, 113.92, 113.94, 116.88, 124.83, 131.04, 136.93,
140.09, 148.09, 154.54, 156.25, 161.70, 162.28; IR (KBr): 3371,
1665, 1570, 1504, 1242 cmÀ1; MS (EI): m/z 368 (M+); HRMS: Calcd
for C20H20N2O5 368.1372. Found 368.1371.
4.2. Biological assays
4.2.1. Preparation of recombinant enzymes
Recombinant AKR1B122 and AKR1B10 with the N-terminal 6-
His tag,14 and Trp220Tyr and Gln303Ser mutant AKR1B10s23 were
expressed in Escherichia coli cells harboring their cDNAs, and puri-
fied to homogeneity, as described previously.
4.1.2.14. 7-Hydroxy-2-(4-methoxyphenylimino)-2H-chromene-3-
carboxylic acid benzylamide (5n: R1 = Bn). Yield: 40%; mp: 257–
259 °C; 1H NMR (400 MHz, DMSO-d6) d 3.75 (3H, s), 4.55 (2H, d,
J = 5.9 Hz), 6.52 (1H, s), 6.71 (1H, dd, J = 2.2, 6.2 Hz), 6.91–6.93
(2H, m), 7.24–7.26 (3H, m), 7.32–7.36 (4H, m), 7.61 (1H, d,
J = 8.4 Hz), 8.42 (1H, s), 10.55 (1H, t, J = 5.9 Hz); 13C NMR
4.2.2. Assay of enzyme activity
The reductase and dehydrogenase activities of the enzymes
were determined at 25 °C by measuring the rate of change in
NADPH absorbance (at 340 nm) and fluorescence (at 455 nm with
an excitation wavelength of 340 nm), respectively.14 The IC50 val-
ues for inhibitors were determined in the reaction mixture that
consisted of 0.1 M potassium phosphate, pH 7.4, 0.1 mM NADPH,
0.2 mM pyridine-3-aldehyde (approximately 15 Â Km concentra-
tion), and enzyme, in a total volume of 2.0 mL. The inhibitor
constant, Ki, for 5n was determined by kinetic analysis in the
NADP+-linked geraniol oxidation, because the reaction of AKR1B10
follows an order bi bi mechanism14 and many competitive
(100 MHz, DMSO-d6)
d 42.78, 55.20, 101.35, 110.93, 113.06,
113.96, 116.74, 124.81, 126.95, 127.25, 128.48, 131.17, 136.86,
139.07, 140.86, 148.21, 154.66, 156.28, 161.92, 162.58; IR (KBr):
3407, 1661, 1558, 1506 cmÀ1; MS (EI): m/z 400 (M+); HRMS: Calcd
for C24H20N2O4 400.1423. Found 400.1426.
4.1.2.15. 8-Hydroxy-2-(4-methoxy-phenylimino)-2H-chromene-3-
carboxylic acid pyridin-2-ylamide (5o: R1 = OH, R2 = H, R3 = H).
Yield: 88%; mp: 253–255 °C; 1H NMR (400 MHz, DMSO-d6) d 3.80
(3H, s), 7.02 (2H, d, J = 8.9 Hz), 7.12–7.19 (3H, m), 7.27 (1H, d,
J = 6.6 Hz), 7.75 (2H, d, J = 8.9 Hz), 7.87 (1H, t, J = 7.9 Hz), 8.41
inhibitors including
1 show mixed-type or noncompetitive

6384
S. Endo et al. / Bioorg. Med. Chem. 21 (2013) 6378–6384
5. Chung, Y. T.; Matkowskyj, K. A.; Li, H.; Bai, H.; Zhang, W.; Tsao, M. S.; Liao, J.;
Yang, G. Y. Mod. Pathol. 2012, 25, 758.
inhibition with respect to pyridine-3-aldehyde in the reduction
reaction.10,11,13,14,17,18 The Ki value was estimated from the replots
of the slopes and intercepts of double reciprocal plot of the five
geraniol concentrations versus velocities, which were determined
in the presence of a saturating NADP+ concentration (0.25 mM)
and three concentrations of the inhibitor. The IC50 and Ki values
are expressed as the means of at least three determinations.
6. Ma, J.; Luo, D. X.; Huang, C.; Shen, Y.; Bu, Y.; Markwell, S.; Gao, J.; Liu, J.; Zu, X.;
Cao, Z.; Gao, Z.; Lu, F.; Liao, D. F.; Cao, D. Int. J. Cancer 2012, 131, 862.
7. Yan, R.; Zu, X.; Ma, J.; Liu, Z.; Adeyanju, M.; Cao, D. Int. J. Cancer 2007, 121, 2301.
8. Wang, C.; Yan, R.; Luo, D.; Watabe, K.; Liao, D. F.; Cao, D. J. Biol. Chem. 2009, 284,
26742.
9. Satow, R.; Shitashige, M.; Kanai, Y.; Takeshita, F.; Ojima, H.; Jigami, T.; Honda,
K.; Kosuge, T.; Ochiya, T.; Hirohashi, S.; Yamada, T. Clin. Cancer Res. 2010, 16,
2518.
10. Soda, M.; Hu, D.; Endo, S.; Takemura, M.; Li, J.; Wada, R.; Ifuku, S.; Zhao, H. T.;
El-Kabbani, O.; Ohta, S.; Yamamura, K.; Toyooka, N.; Hara, A.; Matsunaga, T.
Eur. J. Med. Chem. 2012, 48, 321.
11. Matsunaga, T.; Wada, Y.; Endo, S.; Soda, M.; El-Kabbani, O.; Hara, A. Front.
Pharmacol. 2012, 3, 5.
12. Matsunaga, T.; Yamane, Y.; Iida, K.; Endo, S.; Banno, Y.; El-Kabbani, O.; Hara, A.
Anticancer Drugs 2011, 22, 402.
13. Crosas, B.; Hyndman, D. J.; Gallego, O.; Martras, S.; Pares, X.; Flynn, T. G.; Farres,
J. Biochem. J. 2003, 373, 973.
14. Endo, S.; Matsunaga, T.; Mamiya, H.; Ohta, C.; Soda, M.; Kitade, Y.; Tajima, K.;
Zhao, H. T.; El-Kabbani, O.; Hara, A. Arch. Biochem. Biophys. 2009, 487, 1.
15. Li, H.; Yang, A. L.; Chung, Y. T.; Zhang., W.; Liao, J.; Yang, G. Y. Carcinogenesis
2013, 34, 2090.
4.2.3. Molecular modeling and energy minimization
The coordinates for AKR1B10 (PDB code: 1ZUA)24 were
obtained from the RCSB Protein Data Bank. The structure was
prepared using the Maestro (Schrödinger, LLC, Portland, OR) soft-
ware package Version 8.5, as described previously.14 The docking
calculations were performed using the program Glide 5.043 on a
Linux workstation under the conditions described previously.14
The docked models shown in Figure 1 were generated using
PyMOL (DeLano Scientific, San Carlos, CA, USA).
16. Ma, J.; Yan, R.; Zu, X.; Cheng, J. M.; Rao, K.; Liao, D. F.; Cao, D. J. Biol. Chem. 2008,
283, 3418.
Acknowledgement
17. Matsunaga, T.; El-Kabbani, O.; Hara, A. In Molecular Mechanisms of Tumor Cell
Resistance to Chemotherapy; Bonavida, B., Ed.; Springer: New York, 2013; pp
109–134.
18. Endo, S.; Matsunaga, T.; Kuwata, K.; Zhao, H. T.; El-Kabbani, O.; Kitade, Y.; Hara,
A. Bioorg. Med. Chem. 2010, 18, 2485.
19. Baba, S. P.; Barski, O. A.; Ahmed, Y.; O’Toole, T. E.; Conklin, D. J.; Bhatnagar, A.;
Srivastava, S. Diabetes 2009, 58, 2486.
20. Nagata, N.; Kusakari, Y.; Fukunishi, Y.; Inoue, T.; Urade, Y. FEBS J. 2011, 278,
1288.
This work is supported in part by JSPS Grant-in-Aid for Young
Scientists (B) from the Japan Society for the Promotion of Science
Grant Number 24790114.
References and notes
1. Cao, D.; Fan, S. T.; Chung, S. S. J. Biol. Chem. 1998, 273, 11429.
2. Fukumoto, S.; Yamauchi, N.; Moriguchi, H.; Hippo, Y.; Watanabe, A.; Shibahara,
J.; Taniguchi, H.; Ishikawa, S.; Ito, H.; Yamamoto, S.; Iwanari, H.; Hironaka, M.;
Ishikawa, Y.; Niki, T.; Sohara, Y.; Kodama, T.; Nishimura, M.; Fukayama, M.;
Dosaka-Akita, H.; Aburatani, H. Clin. Cancer Res. 2005, 11, 1776.
21. Gorobets, N. Y.; Yousefi, B. H.; Belaj, F.; Kappe, C. O. Tetrahedron 2004, 60, 8633.
22. Iino, T.; Tabata, M.; Takikawa, S.; Sawada, H.; Shintaku, H.; Ishikura, S.; Hara, A.
Arch. Bichem. Biohys. 2003, 416, 180.
23. Matsunaga, T.; Endo, S.; Soda, M.; Zhao, H. T.; El-Kabbani, O.; Tajima, K.; Hara,
A. Biochem. Biophys. Res. Commun. 2009, 389, 128.
3. Yoshitake, H.; Takahashi, M.; Ishikawa, H.; Nojima, M.; Iwanari, H.; Watanabe,
A.; Aburatani, H.; Yoshida, K.; Ishi, K.; Takamori, K.; Ogawa, H.; Hamakubo, T.;
Kodama, T.; Araki, Y. Int. J. Gynecol. Cancer 2007, 17, 1300.
24. Gallego, O.; Ruiz, F. X.; Ardevol, A.; Dominguez, M.; Alvarez, R.; de Lera, A. R.;
Rovira, C.; Farres, J.; Fita, I.; Pares, X. Proc. Natl. Acad. Sci. U.S.A. 2007, 104,
20764.
4. Heringlake, S.; Hofdmann, M.; Fiebeler, A.; Manns, M. P.; Schmiegel, W.;
Tannapfel, A. J. Hepatol. 2010, 52, 220.