Synthesis and biological evaluation of 3-styrylchromone derivatives as free radical scavengers and α-glucosidase inhibitors

Article abstract of DOI:10.1248/cpb.c14-00351

A series of 3-styrylchromone derivatives (4-20) were synthesized and the structure-activity relationships for α-glucosidase inhibition and antioxidant activities were analyzed. Among the synthesized compounds, compounds 15 and 20, which contain a catechol moiety, showed both potent 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging activity (15: EC₅₀ =17 μM; 20: EC₅₀ =23 μM) and α-glucosidase inhibitory activity (15: IC₅₀ =16 μM; 20: IC₅₀ =10 μM). Our data suggest that 3-styrylchromone derivatives are novel α-glucosidase inhibitors that have the potential to counteract diet-induced hyperglycemia in diabetes.

Full text of DOI:10.1248/cpb.c14-00351

810
Regular Article
Chem. Pharm. Bull. 62(8) 810–815 (2014)
Vol. 62, No. 8
Synthesis and Biological Evaluation of 3-Styrylchromone Derivatives as
Free Radical Scavengers and α-Glucosidase Inhibitors
Koichi Takao, Ryo Ishikawa, and Yoshiaki Sugita*
Laboratory of Bioorganic Chemistry, Department of Pharmaceutical and Health Sciences, Faculty of Pharmaceutical
Sciences, Josai University; 1–1 Keyaki-dai, Sakado, Saitama 350–0295, Japan.
Received May 6, 2014; accepted May 28, 2014
A series of 3-styrylchromone derivatives (4–20) were synthesized and the structure–activity relation-
ships for α-glucosidase inhibition and antioxidant activities were analyzed. Among the synthesized com-
pounds, compounds 15 and 20, which contain a catechol moiety, showed both potent 1,1-diphenyl-2-picrylhy-
drazyl (DPPH) free radical scavenging activity (15: EC50=17 µM; 20: EC50=23µM) and α-glucosidase inhibi-
tory activity (15: IC50=16 µM; 20: IC50=10 µM). Our data suggest that 3-styrylchromone derivatives are novel
α-glucosidase inhibitors that have the potential to counteract diet-induced hyperglycemia in diabetes.
Key words 3-styrylchromone; α-glucosidase inhibitor; antioxidant; structure–activity relationship
Diabetes mellitus is a metabolic disorder characterized by
Results and Discussion
hyperglycemia resulting from insufficiency of secretion or
Chemistry 3-Styrylchromone derivatives presented in
action of endogenous insulin. α-Glucosidase has been recog- this study were synthesized by Knoevenagel condensation of
nized as a therapeutic target for modulation of postprandial the appropriate 3-formylchromone with selected phenylacetic
hyperglycemia. α-Glycosidase inhibitors act to delay glucose acid derivatives, by means of a modified previous procedure22)
absorption, making them potent drugs to control blood glu- (Chart 1). This required the preparation of 3-formylchromone
cose levels.1) On the other hand, antioxidants function as free derivatives (2a, 2b and 2c) necessary for the synthesis of
radical scavengers, chelating agents for pro-oxidant metals, 3-styrylchromone derivatives (R1=H, OMe and OH). Synthe-
quenchers of singlet oxygen formation, and reducing agents.2,3) sis of 2a and 2b was prepared by Vilsmeier–Haack treatment
Because of their antioxidant characteristics, antioxidants of 2′-hydroxyacetophenones 1a and 1b, respectively, accord-
are important in the prevention of human diseases. The ac- ing to published procedures,29,30) and 2c was also synthesized
cumulated evidence suggests that diabetic patients are under from 1c according to the same procedure. Having 2a, 2b and
oxidative stress and that oxidative stress plays a major role 2c in hand, the final step was condensation with phenylacetic
in the pathogenesis of diabetes mellitus.4) Recently, several acid derivatives (3a–g) in the presence of tert-BuOK in dry
researchers have evaluated α-glucosidase inhibitors possessing pyridine to provide the 3-styrylchromone derivatives (4–13)
free-radical scavenging activity.5–11)
and allyl-protected products of 3-styrylchromones (14–20), re-
4H-1-Benzopyran-4-ones (chromones) are an important spectively. 3-Styrylchromones having the allyloxy group were
class of oxygenated heterocyclic compounds, and have at- submitted to a deprotection step, using Pd(PPh3)4 in the pres-
tracted the attention of organic chemists and biochemists due ence of morpholine in degassed anhydrated THF, for remov-
to their biological activities and occurrence in natural prod- ing the allyl group and affording 3-styrylchromones bearing
ucts. This chromone core structure is found in flavones, iso- the hydroxyl group (14–20).
flavones, and 2-styrylchromones. Flavones and isoflavones are
Biological Activity All synthesized compounds were
distributed in several species of plants. In contrast, 2-styryl- evaluated for their 1,1-diphenyl-2-picrylhydrazyl (DPPH) free
chromones constitute a small group of naturally occurring radical scavenging and α-glucosidase inhibitory activities.
chromones. Synthetic 2-styrylchromones possess a number
As shown in Table 1, modifications of 3-styrylchromones
of biological activities, including antioxidant,12,13) anti-aller- on the chromone ring (A-ring) and the phenyl group (B-ring)
gic,14) anti-inflammatory,15) antitumor,16–18) and antiviral19–21) of the styryl moiety revealed some interesting structure–activ-
effects. The synthesis and evaluation of biological activities ity relationships. As a result, the introduction of the methoxy
of 2-styrylchromones has been extensively investigated, while group or halogen atom (F or Cl) substituent (4–13) on the B-
studies dealing with 3-styrylchromones are few. Moreover, ring did not show DPPH radical scavenging activity, while the
although there are some examples of the synthesis of 3-styryl- introduction of the hydroxyl group did. It was evident that the
chromones,22–27) only a few studies have evaluated the bio- 3′,4′-dihydroxy derivatives (15 and 17) were more potent than
logical activity of 3-styrylchromones.22,28) In order to further the 4′-hydroxy derivatives (14 and 16). These compounds (15
explore novel biological activities, a series of 3-styrylchro- and 17) have in common a catechol group in the B-ring, which
mone derivatives were synthesized, containing newly prepared is known to be an important structural feature of the antioxi-
compounds, and structure–activity relationships in regards to dant activity.31,32) In contrast, it was noted that the introduction
antioxidant activity and α-glycosidase inhibition were investi- of a hydroxyl group at the 6-position on the chromone ring did
gated.
not increase the DPPH radical scavenging activity of 3-styryl-
chromones (4, 14 and 15 versus 18, 19 and 20, respectively).
These results indicate that hydroxyl groups on the B-ring play
a more vital role than those on the A-ring.
The authors declare no conflict of interest.
It was also found that the number of hydroxyl groups pref-
© 2014 The Pharmaceutical Society of Japan
*To whom correspondence should be addressed. e-mail: sugita@josai.ac.jp

August 2014
811
Reagents and conditions: (a) allylbromide, K2CO3, acetone, reflux; (b) DMF/POCl3; (c) tert-BuOK, dry pyridine, reflux; (d) allylbromide, K2CO3, EtOH and then KOH;
(e) Pd(PPh3)4, morpholine, THF, 60°C.
Chart 1. Protocol for the Synthesis 3-Styrylchromone Derivatives 4–20
erably attached to the B-ring might play an important role in in 3-styrylchromones. Of the synthesized compounds, com-
the α-glucosidase inhibitory activity (14 and 16 versus 15 and pounds 15, 19 and 20 showed potent activity, and exhibited
17, respectively). Interestingly, the introduction of a halogen superior antihyperglycemic activity to the commercial antihy-
at the 4′-position also increased the activity (10 and 11). It is perglycemic drug, acarbose, which has the structural features
known that halogens can impose molecular conformation or of a tetrasaccharide.
influence the potency of a product due to their steric and/or
The potency of α-glucosidase inhibition and the antioxidant
electronic effects. Conti and Desideri also reported on the in- activity of the synthesized 3-styrylchromones shared similar
hibition of anti-picornavirus activity with halogen-substituted chemical features and functional groups, such as the pres-
3-styrylchromone.22) It was also noted that the introduction ence of hydroxyl and methoxy groups, as shown in Table 1.
of a methoxy group at the 6-position on the chromone ring Introduction of the hydroxyl group on the phenyl group of the
decreased the activity (10 and 11 versus 12 and 13, 14 and styryl moiety increased both α-glucosidase inhibition and anti-
15 versus 16 and 17, respectively), while the introduction of oxidant activity, and 3′,4′-dihydroxy derivatives were more po-
a hydroxyl group on the chromone ring increased the activ- tent than the 4′-hydroxy derivatives (14 and 19 versus 15 and
ity (4, 14 and 15 versus 18, 19 and 20, respectively). These 20, respectively). In addition, the introduction of a hydroxyl
results indicate that the hydroxylation at the 6-position of group at the 6-position on the chromone ring resulted in even
the chromone ring is important for the α-glucosidase inhibi- greater increase in α-glucosidase inhibition (14 and 15 versus
tory activity. It has been reported that some flavonoids and 19 and 20, respectively), but a slight decrease in antioxidant
polyphenols, as well as sugar derivatives, were found to have activity. In contrast, a methoxy substitution at the 6-position
an effect on α-glucosidase inhibitory activity.6,7,33) It appears on the chromone ring resulted in a reduction of both activities
that this effect is associated with the polyphenols present (14 and 15 versus 16 and 17, respectively).

812
Vol. 62, No. 8
Table 1. DPPH Scavenging and α-Glucosidase Inhibitory Activities of 3-Styrylchromone Derivatives
DPPH scavenging activity
α-Glucosidase inhibitory activity
IC50 (μM)
Compound
R1
R2
R3
R4
EC50 (μM)
4
H
H
OMe
OMe
OMe
OMe
OMe
OMe
F
H
>200
>200
>200
>200
>200
>200
>200
>200
>200
>200
60
>100
>100
>100
>100
>100
>100
23
5
H
OMe
OMe
H
H
6
H
OMe
H
7
OMe
OMe
OMe
H
8
OMe
OMe
H
H
9
OMe
H
10
11
H
H
Cl
H
16
12
OMe
OMe
H
H
F
H
>100
57
13
H
Cl
H
14
H
OH
OH
OH
OH
OMe
OH
OH
H
39
15
H
OH
H
H
17
16
16
OMe
OMe
OH
OH
OH
H
78
>100
68
17
OH
H
H
22
18
19
H
>200
125
33
H
H
9
20
OH
H
23
10
Ascorbic acid
Acarbose
23
>100
(1H, dq, J=10.5, 1.5Hz, –CH=CH2), 4.66 (2H, dt, J=5.3,
Conclusion
A series of 3-styrylchromone derivatives (4–20) were syn- 1.5Hz, CH2). 13C-NMR (CDCl3, 100MHz) δ: 188.8, 175.8,
thesized and evaluated for DPPH free radical scavenging and 160.2, 156.8, 150.9, 132.2, 126.1, 124.8, 120.0, 119.6, 118.5,
α-glucosidase inhibitory activities. As a result, compounds 15 106.5, 69.5. High resolution mass spectrum (HR-MS) m/z:
and 20, possessing a catechol moiety in the B-ring, showed Calcd for C13H10O4 (M+): 230.0579; Found: 230.0571.
potent activity in both assays. This indicates that the introduc-
Synthesis of 4-(2-Propenyloxy)benzeneacetic Acid (3f)
tion of a hydroxyl group on the phenyl group of the styryl The compound (3f) was synthesized by a modified previous
moiety is important for the α-glucosidase inhibition and anti- procedure.34) Solid K2CO3 (16.6g, 120mol) was added to a so-
oxidant activities. This is the first report identifying the DPPH lution of 4-hydroxyphenylacetic acid (3h, 4.6g, 30mmol) and
free radical scavenging and α-glucosidase inhibitory activities allylbromide (9.4g, 75mmol) in EtOH (150mL) at room tem-
of 3-styrylchromone derivatives. These results suggest that perature, and the mixture was refluxed for 5h. To the cooled
3-styrylchromone derivatives are novel α-glucosidase inhibi- slurry was added KOH (6.7g, 120mmol) and stirring was con-
tors that may counteract diet-induced hyperglycemia.
tinued for 12h. The solvent was removed, the residue taken up
in H2O (500mL), washed with Et2O (100mL), acidified with
conc. HCl and extracted with EtOAc. The organic layer was
Experimental
Chemistry All reagents and solvents were purchased dried over Na2SO4 and the solvent was evaporated under re-
from commercial sources. Analytical thin-layer chromatogra- duced pressure. The residue was purified by silica gel column
phy was performed on silica-coated plates (silica gel 60F-254, chromatography (hexane:AcOEt=1:1) to give the title com-
Merck) and visualized under UV light. Column chromatogra- pound (3f) in 92% yield. Colorless solid. mp 76–77°C (lit.34)
1
phy was carried out using silica gel (Wakogel C-200, Wako). mp 69.5–71.9°C). H-NMR (CDCl3, 400MHz) δ: 7.19 (2H, d,
All melting points were determined using a Yanagimoto J=8.6Hz, H-2′ and H-6′), 6.88 (2H, d, J=8.6Hz, H-3′ and
1
micro-hot stage and are uncorrected. H-NMR and 13C-NMR H-5′), 6.05 (1H, ddt, J=17.2, 10.5, 5.3Hz, –CH=CH2), 5.41
spectra were recorded on a Varian 400-MR spectrometer (1H, dq, J=17.2, 1.5Hz, –CH=CH2), 5.28 (1H, dq, J=10.5,
using tetramethylsilane as the internal standard. MS spectra 1.5Hz, –CH=CH2), 4.52 (2H, dt, J=5.3, 1.5Hz, CH2), 3.58
were measured using a JEOL JMS-700 spectrometer. Elemen- (2H, s, CH2). MS (electron ionization (EI)) m/z: 192 [M]+. The
tal analyses were carried out on a Yanaco CHN MT-6 elemen- 1H-NMR spectrum was similar to that previously reported.34)
tal analyzer.
3,4-Bis(2-propenyloxy)benzeneacetic Acid (3g): Accord-
Synthesis of 3-Formylchromones 3-Formylchromones 2a– ing to the procedure for the preparation of compound (3f),
c were synthesized according to previous methods.29,30) The 3,4-dihydroxyphenylacetic acid (3i, 6.8g, 50mmol) and al-
products (2a, 2b) were identified by their melting points and lylbromide (24.2g, 200mmol) were treated with K2CO3 (41g,
1H-NMR spectra.
300mol) followed by KOH (11.2g, 200mmol) to give the title
1
3-Formyl-6-(2-propenyloxy)-4H-1-benzopyran-4-one (2c): compound (3g) in 92% yield. Colorless semisolid. H-NMR
Yield 53%. Yellow needles. mp 118–119°C. H-NMR (CDCl3, (CDCl3, 400MHz) δ: 6.86–6.75 (3H, m, aromatic), 6.06 (2H,
1
400MHz) δ: 10.40 (1H, s, CHO), 8.54 (1H, s, H-2), 7.66 (1H, m, –CH=CH2), 5.40 (2H, m, –CH=CH2), 5.27 (2H, m, –CH=
d, J=3.1Hz, H-5), 7.48 (1H, d, J=9.2Hz, H-8), 7.36 (1H, CH2), 4.59 (4H, m, CH2), 3.56 (2H, s, CH2). HR-MS m/z:
dd, J=9.2, 3.1Hz, H-7), 6.07 (1H, ddt, J=17.3, 10.5, 5.3Hz, Calcd for C14H16O4 (M+): 248.1049; Found: 248.1028.
–CH=CH2), 5.47 (1H, dq, J=17.3, 1.5Hz, –CH=CH2), 5.35
General Procedure for Preparation of (E)-3-Styryl-4H-1-

August 2014
813
benzopyran-4-one Derivative (4–13) To a solution of the
6-Methoxy-3-[(1E)-2-(3,4-dimethoxyphenyl)ethenyl]-4H-1-
corresponding 3-formylchromone (2, 2mmol) and phenylacetic benzopyran-4-one (8): Yield 63%. Light brown solid. mp
acid (3, 10mmol) in dry pyridine (20mL), tert-BuOK (3mmol) 135–136°C. 1H-NMR (CDCl3, 400MHz) δ: 8.11 (1H, d,
was added. The mixture was refluxed until complete disap- J=0.8Hz, H-2), 7.66 (1H, d, J=3.1Hz, H-5), 7.53 (1H, d,
pearance of 3-formylchromone (6–22h). After the reaction J=16.3Hz, H-β), 7.41 (1H, d, J=9.1Hz, H-8), 7.27 (1H, dd,
mixture was diluted with ice-water and acidified to pH 2 with J=9.1, 3.1Hz, H-7), 7.10 (1H, d, J=1.9Hz, H-2′), 7.07 (1H,
5N HCl, the sample was extracted with AcOEt. The combined dd, J=8.2, 1.9Hz, H-6′), 6.89 (1H, dd, J=16.3, 0.8Hz, H-α),
organic layer was washed with saturated NaHCO3 solution 6.86 (1H, dd, J=8.2Hz, H-5′), 3.95 (3H, s, OMe), 3.92 (3H,
and then with brine. The organic layer was dried over Na2SO4 s, OMe), 3.91 (3H, s, OMe). 13C-NMR (CDCl3, 100MHz) δ:
and the solvent was evaporated under reduced pressure. The 176.4, 156.9, 152.4, 150.7, 149.04 149.01, 131.1, 130.5, 124.6,
residue was purified by silica gel column chromatography 123.6, 121.1, 120.0, 119.4, 117.1, 111.1, 108.7, 105.1, 55.9 (2C),
(hexane:AcOEt=5:1) to give the corresponding 3-styryl-4H- 55.8. MS-EI m/z: 338 [M]+. Anal. Calcd for C20H18O5: C,
1-benzopyran-4-one derivative.
71.00; H, 5.36. Found: C, 71.04; H, 6.39.
3-[(1E)-2-(4-Methoxyphenyl)ethenyl]-4H-1-benzopyran-4-
6 -Methoxy-3-[(1E )-2-(3,4,5-t r imethoxy phenyl)-
one (4): Yield 40%. Pale yellow amorphous. mp 133–134°C ethenyl]-4H-1-benzopyran-4-one (9): Yield 83%. Pale yellow
1
(lit.24) 123–124°C). H-NMR (CDCl3, 400MHz) δ: 8.30 (1H, amorphous. mp 128–129°C. 1H-NMR (CDCl3, 400MHz) δ:
dd, J=8.0, 1.7Hz, H-5), 8.10 (1H, d, J=0.8Hz, H-2), 7.67 (1H, 8.12 (1H, d, J=0.8Hz, H-2), 7.66 (1H, d, J=3.1Hz, H-5), 7.57
ddd, J=8.5, 7.1, 1.7Hz, H-7), 7.56 (1H, d, J=16.4Hz, H-β), (1H, d, J=16.3Hz, H-β), 7.42 (1H, d, J=9.0Hz, H-8), 7.27 (1H,
7.47 (1H, m, H-8), 7.47 (2H, d, J=8.9Hz, H-2′ and H-6′), dd, J=9.0, 3.1Hz, H-7), 6.91 (1H, dd, J=16.3, 0.8Hz, H-α),
7.42 (1H, ddd, J=8.0, 7.1, 1.1Hz, H-6), 6.90 (2H, d, J=8.9Hz, 6.76 (2H, s, H-2′ and H-6′), 3.93 (3H, s, OMe), 3.92 (6H, s,
H-3′ and H-5′), 6.87 (1H, dd, J=16.4, 0.8Hz, H-α), 3.83 (3H, OMe), 3.87 (3H, s, OMe). 13C-NMR (CDCl3, 100MHz) δ:
1
s, OMe). MS-EI m/z: 278 [M]+. The H-NMR spectrum was 176.4, 157.0, 153.3, 152.8, 150.6, 138.0, 133.1, 131.4, 124.6,
similar to that previously reported.24)
123.7, 120.8, 119.5, 118.6, 105.1, 103.6, 61.0, 56.1, 55.9. MS-EI
3-[(1E )-2-(3,4 -Dimethoxy phenyl)ethenyl]- 4H-1- m/z: 368 [M]+. Anal. Calcd for C21H20O6: C, 68.47; H, 5.47.
benzopyran-4-one (5): Yield 63%. Pale yellow needles. mp Found: C, 68.67; H, 5.51.
128–129°C. 1H-NMR (CDCl3, 400MHz) δ: 8.31 (1H, dd,
3-[(1E)-2-(4-Fluorophenyl)ethenyl]-4H-1-benzopyran-4-
J=8.0, 1.7Hz, H-5), 8.12 (1H, d, J=0.7Hz, H-2), 7.68 (1H, one (10): Yield 80%. Colorless amorphous. mp 142–143°C.
ddd, J=8.5, 7.1, 1.7Hz, H-7), 7.54 (1H, d, J=16.3Hz, H-β), 1H-NMR (CDCl3, 400MHz) δ: 8.31 (1H, dd, J=8.0, 1.7Hz,
7.48 (1H, dd, J=8.5, 1.1Hz, H-8), 7.43 (1H, ddd, J=8.0, 7.1, H-5), 8.11 (1H, d, J=0.7Hz, H-2), 7.68 (1H, ddd, J=8.5, 7.1,
1.1Hz, H-6), 7.10 (1H, d, J=2.0Hz, H-2′), 7.07 (1H, dd, J=8.2, 1.7Hz, H-7), 7.62 (1H, d, J=16.3Hz, H-β), 7.48 (1H, dd,
2.0Hz, H-6′), 6.88 (1H, dd, J=16.3, 0.7Hz, H-α), 6.86 (1H, J=8.5, 1.1Hz, H-8), 7.48 (2H, m, H-2′ and H-6′), 7.43 (1H,
d, J=8.2Hz, H-5′), 3.95 (3H, s, OMe), 3.91 (3H, s, OMe). ddd, J=8.0, 7.1, 1.1Hz, H-6), 7.05 (2H, m, H-3′ and H-5′), 6.88
13C-NMR (CDCl3, 100MHz) δ: 176.7, 155.8, 152.5, 149.1, (1H, dd, J=16.3, 0.7Hz, H-α). 13C-NMR (CDCl3, 100MHz) δ:
1
133.5, 131.3, 130.4, 126.2, 125.2, 124.0, 122.0, 120.0, 118.0, 176.6, 162.4 (d, JC-F=248Hz), 155.8, 153.1, 133.6, 133.5, 130.5,
3
116.9, 111.1, 108.7, 55.9, 55.8. MS (EI) m/z: 308 [M]+. Anal. 128.1 (d, JC-F=8Hz), 126.2, 125.3, 124.1, 121.6, 118.8, 118.0,
2
Calcd for C19H16O4: C, 74.01; H, 5.23. Found: C, 74.26; H, 115.5 (d, JC-F=22Hz). MS-EI m/z: 266 [M]+. Anal. Calcd for
5.26.
3-[(1E)-2-(3,4,5-Trimethoxyphenyl)ethenyl]-4H-1-
C17H11FO2: C, 76.68; H, 4.16. Found: C, 76.64; H, 4.21.
3-[(1E)-2-(4-Chlorophenyl)ethenyl]-4H-1-benzopyran-4-one
benzopyran-4-one (6): Yield 62%. Yellow solid. mp (11): Yield 82%. Colorless amorphous. mp 157–158°C (lit.25)
156–157°C. 1H-NMR (CDCl3, 400MHz) δ: 8.30 (1H, dd, 159–160°C). 1H-NMR (CDCl3, 400MHz) δ: 8.30 (1H, dd,
J=8.0, 1.7Hz, H-5), 8.13 (1H, d, J=0.8Hz, H-2), 7.69 (1H, J=8.0, 1.7Hz, H-5), 8.11 (1H, d, J=0.8Hz, H-2), 7.68 (1H,
ddd, J=8.5, 7.1, 1.7Hz, H-7), 7.58 (1H, d, J=16.2Hz, H-β), ddd, J=8.5, 7.1, 1.7Hz, H-7), 7.64 (1H, d, J=16.3Hz, H-β),
7.48 (1H, dd, J=8.5, 1.1Hz, H-8), 7.43 (1H, ddd, J=8.0, 7.1, 7.48 (1H, dd, J=8.5, 1.1Hz, H-8), 7.46–7.41 (1H, m, H-6),
1.1Hz, H-6), 6.90 (1H, dd, J=16.2, 0.8Hz, H-α), 6.76 (2H, 7.45 (2H, d, J=8.5Hz, H-2′ and H-6′), 7.32 (2H, d, J=8.5Hz,
s, H-2′ and H-6′), 3.92 (6H, s, OMe), 3.87 (3H, s, OMe). H-3′ and H-5′), 6.93 (1H, dd, J=16.3, 0.8Hz, H-α). 13C-NMR
13C-NMR (CDCl3, 100MHz) δ: 176.6, 155.8, 153.3, 153.0, (CDCl3, 100MHz) δ: 176.5, 155.7, 153.4, 135.9, 133.6, 133.4,
138.0, 133.6, 133.1, 131.6, 126.2, 125.3, 124.0, 121.6, 118.4, 130.4, 128.8, 127.7, 126.2, 125.3, 124.0, 121.4, 119.7, 118.1.
118.0, 103.6, 61.0, 56.1. HR-MS m/z: Calcd for C20H18O5 (M+): MS-EI m/z: 282 [M]+. The 1H and 13C-NMR spectra were
338.1154; Found: 338.1127.
similar to that previously reported.25)
6-Methoxy-3-[(1E)-2-(4-methoxyphenyl)ethenyl]-4H-1-
3-[(1E)-2-(4-Fluorophenyl)ethenyl]-6-methoxy-4H-1-
benzopyran-4-one (7): Yield 69%. Yellow needles. mp benzopyran-4-one (12): Yield 86%. Pale yellow amorphous.
137–138°C. 1H-NMR (CDCl3, 400MHz) δ: 8.09 (1H, d, mp 154–155°C. 1H-NMR (CDCl3, 400MHz) δ: 8.09 (1H,
J=0.8Hz, H-2), 7.65 (1H, d, J=3.1Hz, H-5), 7.55 (1H, d, d, J=0.8Hz, H-2), 7.65 (1H, d, J=3.1Hz, H-5), 7.61 (1H, d,
J=16.3Hz, H-β), 7.47 (2H, d, J=8.7Hz, H-2′ and H-6′), 7.41 J=16.3Hz, H-β), 7.49 (2H, m, H-2′ and H-6′), 7.41 (1H, d,
(1H, d, J=9.1Hz, H-8), 7.26 (1H, dd, J=9.1, 3.1Hz, H-7), 6.90 J=9.1Hz, H-8), 7.27 (1H, dd, J=9.1, 3.1Hz, H-7), 7.05 (2H,
(2H, d, J=8.7Hz, H-3′ and H-5′), 6.88 (1H, dd, J=16.3, 0.8Hz, m, H-3′ and H-5′), 6.90 (1H, dd, J=16.3, 0.8Hz, H-α), 3.92
H-α), 3.92 (3H, s, OMe), 3.83 (3H, s, OMe). 13C-NMR (CDCl3, (3H, s, OMe). 13C-NMR (CDCl3, 100MHz) δ: 176.4, 162.4
1
100 MHz) δ: 176.4, 159.4, 156.9, 152.4, 150.7, 130.9, 130.2, (d, JC-F=247Hz), 157.0, 152.9, 150.6, 133.6, 130.3, 128.1
3
127.8, 124.6, 123.6, 121.2, 119.4, 116.9, 114.1, 105.1, 55.9, 55.3. (d, JC-F=8Hz), 124.6, 123.7, 120.8, 119.5, 119.0, 115.5 (d,
MS-EI m/z: 308 [M]+. Anal. Calcd for C19H16O4: C, 74.01; H, 2JC-F=22Hz), 105.1, 55.9. MS-EI m/z: 296 [M]+. Anal. Calcd
5.23. Found: C, 74.12; H, 5.28.
for C18H13FO3: C, 72.97; H, 4.42. Found: C, 73.20; H, 4.47.

814
Vol. 62, No. 8
3-[(1E)-2-(4-Chlorophenyl)ethenyl]-6-methoxy-4H-1- H-2′ and H-6′), 6.84 (1H, dd, J=16.4, 0.7Hz, H-α), 6.78 (2H,
benzopyran-4-one (13): Yield 80%. Pale yellow needles. d, J=8.6Hz, H-3′ and H-5′), 3.88 (3H, s, OMe). 13C-NMR
1
mp 134–135°C. H-NMR (CDCl3, 400MHz) δ: 8.10 (1H, d, (DMSO-d6, 100MHz) δ: 175.7, 157.8, 157.0, 154.6, 150.5,
J=0.8Hz, H-2), 7.65 (1H, d, J=3.1Hz, H-5), 7.63 (1H, d, 131.0, 128.7, 128.1, 124.5, 123.6, 120.6, 120.5, 116.6, 116.1,
J=16.3Hz, H-β), 7.45 (2H, d, J=8.5Hz, H-2′ and H-6′), 7.42 105.4, 56.2. MS (EI) m/z: 294 [M]+. Anal. Calcd for C18H14O4:
(1H, d, J=9.1Hz, H-8), 7.33 (2H, d, J=8.5Hz, H-3′ and H-5′), C, 73.46; H, 4.80. Found: C, 73.27; H, 4.81.
7.27 (1H, dd, J=9.1, 3.1Hz, H-7), 6.95 (1H, dd, J=16.3, 0.8Hz,
3-[(1E)-2-(3,4-Dihydroxyphenyl)ethenyl]-6-methoxy-4H-1-
H-α), 3.92 (3H, s, OMe). 13C-NMR (CDCl3, 100MHz) δ: 176.3, benzopyran-4-one (17): Yield 55% (2 steps). Ocher amor-
1
157.1, 153.2, 150.6, 135.9, 133.3, 130.2, 128.8, 127.7, 124.6, phous. mp 219–221°C. H-NMR (DMSO-d6, 400MHz) δ: 9.10
123.7, 120.6, 119.9, 119.5, 105.1, 55.9. MS-EI m/z: 312 [M]+. (2H, br s, OH), 8.64 (1H, s, H-2), 7.65 (1H, d, J=9.1Hz, H-8),
Anal. Calcd for C18H13ClO3: C, 69.13; H, 4.19. Found: C, 69.31; 7.51 (1H, d, J=3.1Hz, H-5), 7.50 (1H, d, J=16.4Hz, H-β), 7.41
H, 4.19.
(1H, dd, J=9.1, 3.1Hz, H-7), 6.95 (1H, d, J=2.0Hz, H-2′),
General Procedure for Preparation of 3-Styrylchro- 6.80 (1H, m, H-6′), 6.77 (1H, d, J=16.4Hz, H-α), 6.74 (1H,
mones Having the Hydroxyl Group (14–20) According to m, H-5′), 3.88 (3H, s, OMe). 13C-NMR (DMSO-d6, 100MHz)
the general procedure for preparation of (E)-3-styryl-4H-1- δ: 175.7, 157.0, 154.5, 150.5, 146.2, 145.9, 131.2, 129.3, 124.4,
benzopyran-4-one derivative, the corresponding 3-formyl- 123.6, 120.6, 120.5, 118.9, 116.3, 116.2, 113.3, 105.4, 56.2.
chromone (2, 2mmol) and phenylacetic acid (3a, 3f or 3g, MS-EI m/z: 310 [M]+. Anal. Calcd for C18H14O5: C, 69.67; H,
10mmol) were treated with tert-BuOK (3mmol) and then the 4.55. Found: C, 69.60; H, 4.65.
residue was passed once through a short silica gel column
6-Hydroxy-3-[(1E)-2-(4-methoxyphenyl)ethenyl]-4H-1-
(hexane:AcOEt=5:1) and the solvent was evaporated. The benzopyran-4-one (18): Yield 53% (2 steps). Colorless amor-
obtained allyl protected compound (1.0mmol) was dissolved phous. mp 236–237°C. 1H-NMR (DMSO-d6, 400MHz) δ:
in degassed anhydrated tetrahydrofuran (THF) (50mL) and 10.06 (1H, br s, OH), 8.59 (1H, d, J=0.7Hz, H-2), 7.65 (1H,
morpholine (10 equiv. per allyl group to be cleaved) was d, J=16.4Hz, H-β), 7.55 (1H, d, J=9.0Hz, H-8), 7.41 (1H, d,
added Pd(PPh3)4 (5mol%). The green mixture was stirred at J=3.0Hz, H-5), 7.48 (2H, d, J=8.7Hz, H-2′ and H-6′), 7.24
60°C (monitored by TLC) and concentrated under reduced (1H, dd, J=9.0, 3.0Hz, H-7), 6.90 (1H, dd, J=16.4, 0.7Hz,
pressure. The residue was treated with saturated NH4Cl solu- H-α), 6.96 (2H, d, J=8.7Hz, H-3′ and H-5′), 3.78 (3H, s,
tion and extracted with AcOEt. The organic layer was dried OMe). 13C-NMR (DMSO-d6, 100MHz) δ: 175.8, 159.4, 155.3,
over Na2SO4 and the solvent was evaporated under reduced 155.0, 149.5, 130.40, 130.37, 127.9, 124.7, 123.5, 120.2, 120.1,
pressure. The residue was purified by silica gel column chro- 118.0, 114.7, 108.2, 55.6. MS (EI) m/z: 294 [M]+. Anal. Calcd
matography (hexane:AcOEt=2:1) to give the title compound. for C18H14O4: C, 73.46; H, 4.80. Found: C, 73.22; H, 4.83.
3-[(1E)-2-(4-Hydroxyphenyl)ethenyl]-4H-1-benzopyran-4-
6-Hydroxy-3-[(1E)-2-(4-hydroxyphenyl)ethenyl]-4H-1-
one (14): Yield 30% (2 steps). Ocher amorphous. mp benzopyran-4-one (19): Yield 41% (2 steps). Ocher amorphous.
1
1
209–211°C. H-NMR (DMSO-d6, 400MHz) δ: 9.63 (1H, br s, mp 293–295°C. H-NMR (DMSO-d6, 400MHz) δ: 10.00 (1H,
OH), 8.64 (1H, d, J=0.7Hz, H-2), 8.15 (1H, dd, J=8.0, 1.7Hz, br s, OH), 9.63 (1H, br s, OH), 8.57 (1H, d, J=0.7Hz, H-2),
H-5), 7.81 (1H, ddd, J=8.5, 7.1, 1.7Hz, H-7), 7.68 (1H, dd, 7.58 (1H, d, J=16.4Hz, H-β), 7.54 (1H, d, J=9.0Hz, H-8),
J=8.5, 1.0Hz, H-8), 7.61 (1H, d, J=16.4Hz, H-β), 7.52 (1H, 7.40 (1H, d, J=3.0Hz, H-5), 7.36 (2H, d, J=8.6Hz, H-2′ and
ddd, J=8.0, 7.1, 1.1Hz, H-6), 7.37 (2H, d, J=8.6Hz, H-2′ H-6′), 7.23 (1H, dd, J=9.0, 3.0Hz, H-7), 6.82 (1H, dd, J=16.4,
and H-6′), 6.84 (1H, dd, J=16.4, 0.7Hz, H-α), 6.78 (2H, d, 0.7Hz, H-α), 6.77 (2H, d, J=8.6Hz, H-3′ and H-5′). 13C-NMR
J=8.6Hz, H-3′ and H-5′). 13C-NMR (DMSO-d6, 100MHz) (DMSO-d6, 100MHz) δ: 175.8, 157.8, 155.3, 154.7, 149.5,
δ: 176.2, 157.9, 155.7, 154.9, 134.4, 131.2, 128.7, 128.1, 125.9, 130.8, 128.8, 128.0, 124.7, 123.4, 120.3, 120.2, 116.8, 116.1,
125.8, 123.8, 121.4, 118.9, 116.5, 116.1. HR-MS m/z: Calcd for 108.2. MS (EI) m/z: 280 [M]+. Anal. Calcd for C17H12O4: C,
C17H12O3 (M+): 264.0786; Found: 264.0774.
72.85; H, 4.32. Found: C, 72.66; H, 4.45.
3-[(1E )-2-(3,4 -Dihyd roxy phenyl)ethenyl]- 4H-1-
6-Hydroxy-3-[(1E)-2-(3,4-dihydroxyphenyl)ethenyl]-4H-1-
benzopyran-4-one (15): Yield 49% (2 steps). Ocher amor- benzopyran-4-one (20): Yield 36% (2 steps). Brown solid. mp
1
phous. mp 186–188°C. 1H-NMR (DMSO-d6, 400MHz) δ: 258–260°C. H-NMR (DMSO-d6, 400MHz) δ: 9.90 (1H, br s,
9.11 (2H, br s, OH), 8.66 (1H, s, H-2), 8.14 (1H, dd, J=8.0, OH), 9.18 (2H, br s, OH), 8.59 (1H, d, J=0.8Hz, H-2), 7.54
1.7Hz, H-5), 7.82 (1H, ddd, J=8.5, 7.1, 1.7Hz, H-7), 7.68 (1H, (1H, d, J=9.0Hz, H-8), 7.49 (1H, d, J=16.4Hz, H-β), 7.40 (1H,
dd, J=8.5, 1.0Hz, H-8), 7.52 (1H, d, J=16.4Hz, H-β), 7.52 d, J=3.0Hz, H-5), 7.23 (1H, dd, J=9.0, 3.0Hz, H-7), 6.94 (1H,
(1H, m, H-6), 6.95 (1H, d, J=2.0Hz, H-2′), 6.81 (1H, dd, d, J=2.0Hz, H-2′), 6.79 (1H, dd, J=8.1, 2.0Hz, H-6′), 6.74
J=8.1, 2.0Hz, H-6′), 6.76 (1H, d, J=16.4Hz, H-α), 6.73 (1H, (1H, dd, J=16.4, 0.8Hz, H-α), 6.73 (1H, d, J=8.1, H-5′), 3.88
d, J=8.1Hz, H-5′). 13C-NMR (DMSO-d6, 100MHz) δ: 176.0, (3H, s, OMe). 13C-NMR (DMSO-d6, 100MHz) δ: 175.8, 155.3,
155.7, 154.7, 146.2, 145.9, 134.4, 131.4, 129.2, 125.9, 125.8, 154.6, 149.5, 146.1, 145.9, 131.0, 129.4, 124.7, 123.4, 120.3,
123.8, 121.4, 118.9, 118.8, 116.22, 116.20, 113.4. MS-EI m/z: 120.2, 118.8, 116.6, 116.2, 113.3, 108.2. HR-MS m/z: Calcd for
280 [M]+. Anal. Calcd for C17H12O4: C, 72.85; H, 4.32. Found: C17H12O5 (M+): 296.0685. Found: 296.0672.
C, 72.75; H, 4.39.
Biological Assay α-Glucosidase from Saccharomyces
3-[(1E)-2-(4-Hydroxyphenyl)ethenyl]-6-methoxy-4H-1- cerevisiae and 4-nitrophenyl α-D-glucopyranoside (PNP-G)
benzopyran-4-one (16): Yield 64% (2 steps). Ocher needles. were purchased from Sigma Chemical Co., St. Louis, MO,
1
mp 209–211°C. H-NMR (DMSO-d6, 400MHz) δ: 9.61 (1H, U.S.A. DPPH radical was purchased from Tokyo Chemical
br s, OH), 8.62 (1H, d, J=0.7Hz, H-2), 7.65 (1H, d, J=9.1Hz, Industry Co., Tokyo, Japan.
H-8), 7.58 (1H, d, J=16.4Hz, H-β), 7.50 (1H, d, J=3.1Hz,
DPPH Radical Scavenging Assay DPPH radical scaveng-
H-5), 7.41 (1H, dd, J=9.2, 3.1Hz, H-7), 7.37 (2H, d, J=8.6Hz, ing activity was measured according to the method of Nile

August 2014
815
et al.35) with minor modifications. Briefly, 180µL of 100µM
DPPH solution in MeOH was mixed with 20µL of various
concentrations of the sample solution in MeOH. The absor-
bance of the mixture was measured at 517nm using a micro-
plate reader (Molecular Devices SPECTRA MAX 190). The
sample solution was replaced by MeOH as a control. Ascorbic
acid was used as a positive control.
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