Synthesis and α-glucosidase inhibitory activity of chrysin, diosmetin, apigenin, and luteolin derivatives

Article abstract of DOI:10.1016/j.cclet.2014.05.021

Several derivatives have been synthesized from chrysin, diosmetin, apigenin, and luteolin, which were isolated from diverse natural plants. The α-glucosidase inhibitory activity of these compounds was evaluated. The glucosidase inhibitory activity of all

Full text of DOI:10.1016/j.cclet.2014.05.021

G Model
CCLET 3002 1–5
Chinese Chemical Letters xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Chinese Chemical Letters
journal homepage: www.elsevier.com/locate/cclet
1
2
Original article
3
4
Synthesis and
diosmetin, apigenin, and luteolin derivatives
a
-glucosidase inhibitory activity of chrysin,
b,
Q1 Ning Cheng a, Wen-Bin Yi a, Qi-Qin Wang a, Sheng-Ming Peng a,b, , Xiao-Qing Zou
* *
5
6
7
8
a Key Laboratory of Environmentally Friendly Chemistry and Applications of Ministry of Education, College of Chemistry, Xiangtan University,
Xiangtan 411105, China
b Postdoctoral Programme of Chemical Engineering & Technology, Xiangtan University, Xiangtan 411105, China
A R T I C L E I N F O
A B S T R A C T
Article history:
Several derivatives have been synthesized from chrysin, diosmetin, apigenin, and luteolin, which were
isolated from diverse natural plants. The -glucosidase inhibitory activity of these compounds
was evaluated. The glucosidase inhibitory activity of all derivatives (IC50 < 24.396 mol/L) was
Received 13 March 2014
Received in revised form 29 April 2014
Accepted 30 April 2014
Available online xxx
a
m
higher compared with that of the reference drug, acarbose (IC50 = 563.601 ꢀ 40.492 mmol/L), and
1-deoxynojirimycin (IC50 = 226.912 ꢀ 12.573 mmol/L). O30,O7-Hexyl diosmetin (IC50 = 2.406 ꢀ 0.101
mmol/L) was the most potent inhibitor identified. These compounds showed a higher inhibitory ability
compared with their precursors except the luteolin derivatives. In general, the inhibitory activity of the
synthetic derivatives was enhanced with long alkyl chains at positions 30, 40 and 7 of the flavonoid.
ß 2014 Sheng-Ming Peng. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights
reserved.
Keywords:
Derivatives
Flavonoid
a-Glucosidase
Inhibition
9
10
1. Introduction
attractive drug target. At present, a number of a-glucosidase 28
inhibitors have been discovered and studied. Anti-diabetic agents 29
that are used in clinical practice, such as acarbose [10], voglibose, 30
and miglitol [11], competitively inhibit a-glucosidase in the brush 31
border of the small intestine, which consequently delay the 32
hydrolysis of carbohydrates and alleviate postprandial hypergly- 33
cemia. However, the continuous administration of these agents 34
may cause several adverse effects, such as diarrhea, abdominal 35
discomfort, flatulence [12–14], and hepatotoxicity [15]. Therefore, 36
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
Diabetes mellitus is a serious worldwide health problem. Each
year, the number of patients diagnosed with diabetes mellitus
increases. Diabetes mellitus is known to be a lifestyle-related
disease, which can cause numerous complications, such as
nephropathy, retinopathy, neuropathy, and cardiovascular dis-
eases. Diabetes mellitus is also one of the leading causes of patient
mortality. The International Diabetes Federation reported that
about 366 million people were diagnosed with diabetes in 2011,
and this number is expected to increase to up to 552 million by
2030 [1]. Type II diabetes mellitus is more prevalent in developed
countries is characterized by reduced insulin sensitivity and
impaired insulin secretion [2–6]. Type II diabetes mellitus can be
developing novel a-glucosidase inhibitors lacking these liabilities 37
is necessary given the therapeutic challenge of type II diabetes 38
mellitus [16–22]. Flavonoids are widely distributed in plants, for 39
example, vegetables and fruits. Researchers had focused their 40
efforts on a few pharmacological activities of flavonoids, such as, 41
scavenging free radicals and protecting against lipid peroxidation 42
[23,24]. Recently, researchers showed more interest in some 43
specific flavonoids because of modulating endothelial nitric 44
oxide metabolism and NADPH oxidase activity of them [25–31]. 45
The results from mechanistic research suggested that flavonoids 46
may also alleviate hyperglycemia, increase insulin secretion, and 47
improve insulin sensitivity [32]. Flavonoids, such as baicalein, 48
luteolin, kaempferol, apigenin, and chrysin, have the ability to 49
effectively treated by
ability to delay and reduce postprandial blood glucose spike [7–9].
-Glucosidase is involved in carbohydrate metabolism and
has a crucial function in diabetes, viral infection, and cancer.
-Glucosidase has diverse bioactivities and is considered an
a-glucosidase inhibitors, which have the
a
a
*
Corresponding author at: Key Laboratory of Environmentally Friendly
inhibit
and C rings are related to the activity of
-amylase inhibition. The unsaturated C ring, linkage of the B ring 52
at the 30 position, 3-OH, 4-CO, and the hydroxyl substitution on 53
a
-glucosidase activity [33,34]. The structure of the A, B, 50
Chemistry and Applications of Ministry of Education, College of Chemistry,
Xiangtan University, Xiangtan 411105, China.
Q2
a
-glucosidase and 51
a
E-mail addresses: pengshengming@21cn.com (S.-M. Peng),
zouxq2002@gmail.com (X.-Q. Zou).
http://dx.doi.org/10.1016/j.cclet.2014.05.021
1001-8417/ß 2014 Sheng-Ming Peng. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Please cite this article in press as: N. Cheng, et al., Synthesis and
a-glucosidase inhibitory activity of chrysin, diosmetin, apigenin, and
luteolin derivatives, Chin. Chem. Lett. (2014), http://dx.doi.org/10.1016/j.cclet.2014.05.021

G Model
CCLET 3002 1–5
2
N. Cheng et al. / Chinese Chemical Letters xxx (2014) xxx–xxx
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
the B ring have been reported to increase the inhibitory activity
against -glucosidase and -amylase [35]. In addition, Hakamata
et al. [36] have shown that catechin derivatives showed potent
antioxidant activity and -glucosidase inhibitory activity with
alkyl side chains of various lengths, whereas Shin et al. [37] have
shown that a series of alkyl or acetyl derivatives of chrysin have
hypoglycemic effects. Based on the previous studies, we synthe-
sized a series of alkylated flavonoids such as chrysin, diosmetin,
1.00 (t, 3H, J = 7.4 Hz, –CH3); MALDI-TOF: m/z 311 ([M+H]+); Anal.
calcd. for C19H18O4: C, 73.53; H, 5.85; found: C, 73.42; H, 5.82.
O7-Hexyl chrysin (7): Yellowish powder; yield: 89.7%; mp:
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
a
a
a
143.3–143.6 8C; 1H NMR (400 MHz, CDCl3):
d
12.70 (s, 1H, 5-OH),
0
0
7.89 (d, 2H, J = 6.7 Hz, aromatic H2 ,6 ), 7.53 (d, 3H, J = 7.2 Hz,
0
0
0
aromatic H3 ,4 ,5 ), 6.66 (s, 1H, aromatic H8), 6.50 (s, 1H, aromatic
H3), 6.37 (s, 1H, aromatic H6), 4.04 (t, 2H, J = 6.5 Hz, –OCH2–),
1.94–1.71 (m, 2H, –CH2–), 1.71–1.32 (m, 2H, –CH2–), 1.26 (m, 4H, –
CH2CH2–), 0.92 (t, 3H, J = 6.4 Hz, –CH3); MALDI-TOF: m/z 339
([M+H]+); Anal. calcd. for C21H22O4: C, 74.54; H, 6.55; found: C,
74.24; H, 6.41.
apigenin, and luteolin, and studied their
activity.
a-glucosidase inhibitory
In this study, chrysin, diosmetin, apigenin, and luteolin
derivatives were synthesized from the corresponding naturally
General procedures for the synthesis of compounds 8–13 based
on the method used to obtain chrysin alkyl derivatives.
occurring flavonoids, and their yeast
a-glucosidase inhibitory
4
0
7
activity were evaluated. We attempted to study the relationship
between the structure of the derivatives and their inhibitory effect.
O ,O -Diethyl apigenin (8): Yellowish powder; yield: 62.3%; mp:
159.3–159.4 8C. 1H NMR (400 MHz, CDCl3):
12.80 (s, 1H, 5-OH),
7.82 (d, 2H, J = 8.9 Hz, aromatic H2 ,6 ), 7.00 (d, 2H, J = 8.9 Hz,
d
0
0
0
0
69
70
2. Experimental
aromatic H3 ,5 ), 6.56 (s, 1H, aromatic H8), 6.47 (s, 1H, aromatic H3),
6.34 (s, 1H, aromatic H6), 4.11 (dd, 4H, J = 6.9, 4.1 Hz, –OCH2–), 1.45
(t, 6H, J = 6.9 Hz, –CH3); MALDI-TOF: m/z 327 ([M+H]+); Anal. calcd.
for C19H18O5: C, 69.93; H, 5.56; found: C, 69.73; H, 5.49.
2.1. Reagents and instruments
4
0
7
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
All solvents used in this research were of analytical grade,
and the chemicals used for synthesizing the derivatives were of
reagent grade and commercially available. Chrysin, diosmetin,
apigenin and luteolin (>98% by HPLC) were purchased from Shanxi
Huike Co., Ltd., Jiangsu, China, and were used without further
O ,O -Dibutyl apigenin (9): Yellowish powder; yield: 70.6%;
mp: 130.9–131.5 8C. 1H NMR (400 MHz, CDCl3):
12.80 (s, 1H,
5-OH), 7.82 (d, 2H, J = 8.8 Hz, aromatic H2 ,6 ), 7.00 (d, 2H, J = 8.8 Hz,
d
0
0
0
0
aromatic H3 ,5 ), 6.56 (s, 1H, aromatic H8), 6.47 (s, 1H, aromatic H3),
6.35 (s, 1H, aromatic H6), 4.04 (t, 4H, J = 6.4 Hz, –OCH2), 2.02–1.68
(m, 4H, –CH2–), 1.68–1.21 (m, 4H, –CH2–), 0.99 (t, 6H, J = 7.3 Hz, –
CH3); MALDI-TOF: m/z 383 ([M+H]+); Anal. calcd. for C23H26O5: C,
72.23; H, 6.85; found: C, 72.14; H, 6.83.
purification. Biotech-grade PNPG (4-nitrophenyl-
noside), -glucosidase from baker’s yeast, 1-deoxynojirimycin and
acarbose were purchased from Sigma Chemical Co., Ltd. (St. Louis,
MO, USA), and -glutathione (reduced) was obtained from Roche,
a-D-glucopyra-
a
4
0
7
L
O ,O -Dihexyl apigenin (10): Yellowish powder; yield: 78.4%;
mp: 88.5–88.6 8C; 1H NMR (400 MHz, CDCl3):
12.80 (s, 1H, 5-OH),
7.82 (d, 2H, J = 8.8 Hz, aromatic H2 ,6 ), 7.00 (d, 2H, J = 8.8 Hz,
Switzerland. Nuclear magnetic resonance (NMR) spectra were
recorded at 400 MHz for 1H on a Bruker Avance 400 spectrometer
in CDCl3 and DMSO-d6 with TMS as an internal standard (chemical
d
0
0
0
0
aromatic H3 ,5 ), 6.56 (s, 1H, aromatic H8), 6.47 (s, 1H, aromatic H3),
6.35 (s, 1H, aromatic H6), 4.17–3.93 (m, 4H, –OCH2–), 2.02–1.66 (m,
4H, –CH2–), 1.42 (dd, 4H, J = 48.2, 3.8 Hz, –CH2–), 1.25 (s, 8H, –
CH2CH2–), 0.92 (t, 6H, J = 6.7 Hz, –CH3); MALDI-TOF: m/z 439
([M+H]+); Anal. calcd. for C27H34O5: C, 73.94; H, 7.81; found: C,
73.79; H, 7.79.
shift in ppm, d). J values are reported in Hertz. Molecular mass was
determined by matrix-assisted laser desorption-ionisation time-
of-flight mass spectrometry (MALDI-TOF MS) using a Bruker
Aupoflex-III mass spectrometer. Elemental analysis (C, H) of the
targeted compounds was measured using an elementary Vario EL
III analyser. Melting points (mp) of derivatives were determined on
a Shanghai SHENGUANG WRS-1B digital melting-point apparatus,
China. The absorbance of samples was obtained using a Mapada
UV-1600 spectrophotometer, Shanghai, China.
3
7
0
O ,O -Diethyl diosmetin (11): Yellow powder; yield: 55.6%; mp:
191.9–192.2 8C; 1H NMR (400 MHz, CDCl3):
d
12.78 (s, 1H, 5-OH),
0
0
7.51 (d, 1H, J = 10.4 Hz, aromatic H6 ), 7.34 (s, 1H, aromatic H2 ),
0
6.98 (d, 1H, J = 8.5 Hz, aromatic H5 ), 6.57 (s, 1H, aromatic H8), 6.47
(s, 1H, aromatic H3), 6.35 (s, 1H, aromatic H6), 4.15 (dt, 4H, J = 30.8,
6.9 Hz, –OCH2–), 3.96 (s, 3H, –OCH3), 1.49 (dt, 6H, J = 27.5, 7.0 Hz, –
CH3); MALDI-TOF: m/z 357 ([M+H]+); Anal. calcd. for C20H20O6: C,
67.41; H, 5.66; found: C, 67.21; H, 5.56.
92
2.2. Synthesis
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
Chrysin (1.3 g, 5 mmol) in 120 mL of acetone was added to
anhydrous potassium carbonate (0.7 g, 5 mmol). The mixture was
stirred at reflux for 30 min, bromoethane (1.2 mL, 15 mmol)
was added dropwise, followed by refluxing for 24 h. The mixture
was cooled to room temperature, filtered, and was concentrated in
vacuo. The residue was purified with a silica gel column eluting
with a mixed solvent (EtOAc/CH2Cl2 = 1:10) to obtain O7-ethyl
chrysin (5). Yellowish powder; yield: 68.5%; mp: 163.2–163.7 8C;
3
7
0
O ,O -Dibutyl diosmetin (12): Yellow powder; yield: 66.7%; mp:
111.6–112.1 8C; 1H NMR (400 MHz, CDCl3):
d
12.78 (s, 1H, 5-OH),
0
0
7.49 (d, 1H, J = 8.4 Hz, aromatic H6 ), 7.34 (s, 1H, aromatic H2 ), 6.96
0
(d, 1H, J = 8.4 Hz, aromatic H5 ), 6.56 (s, 1H, aromatic H8), 6.48 (s,
1H, aromatic H3), 6.35 (s, 1H, aromatic H6), 4.07 (dt, 4H, J = 23.8,
6.3 Hz, –OCH2–), 3.94 (s, 4H, –OCH3), 1.98–1.71 (m, 4H, –CH2–),
1.66–1.38 (m, 4H, –CH2–), 1.12–0.93 (t, 6H, –CH3); MALDI-TOF: m/
z 413 ([M+H]+); Anal. calcd. for C24H28O6: C, 69.88; H, 6.84; found:
C, 69.58; H, 6.62.
1H NMR (400 MHz, CDCl3):
d 12.71 (s, 1H, 5-OH), 7.88 (d, 2H,
0
0
0
0
0
J = 7.9 Hz, aromatic H2 ,6 ), 7.53 (d, 3H, J = 7.4 Hz, aromatic H3 ,4 ,5 ),
6.66 (s, 1H, aromatic H8), 6.49 (s, 1H, aromatic H6), 6.36 (s, 1H,
aromatic H3), 4.11 (q, 2H, J = 7.0 Hz, –OCH2–), 1.46 (t, 3H, J = 7.0 Hz,
–CH3); MALDI-TOF: m/z 283 ([M+H]+); Anal. calcd. for C17H14O4: C,
72.33; H, 5.00; found: C, 72.10; H, 4.99.
3
7
0
O ,O -Dihexyl diosmetin (13): Yellow powder; yield: 75.9%; mp:
87.4–87.6 8C; 1H NMR (400 MHz, CDCl3):
d
12.78 (s, 1H, 5-OH), 7.50
0
0
(d, 1H, J = 6.7 Hz, aromatic H6 ), 7.34 (s, 1H, aromatic H2 ), 6.97 (d,
0
1H, J = 8.5 Hz, aromatic H5 ), 6.56 (s, 1H, aromatic H8), 6.48 (s, 1H,
Compounds 6 and 7 were obtained according to the method for
compound 5 [38].
aromatic H3), 6.35 (s, 1H, aromatic H6), 4.06 (dt, 4H, J = 23.7, 6.6 Hz,
–OCH2–), 3.94 (s, 3H, –OCH3), 1.97–1.74 (m, 4H, –CH2–), 1.67–1.38
(m, 4H, –CH2–), 1.36 (m, 8H, J = 6.8, 3.5 Hz, –CH2CH2–), 0.92 (t, 6H,
J = 1.4 Hz, –CH3); MALDI-TOF: m/z 469 ([M+H]+); Anal. calcd. for
O7-Butyl chrysin (6): Yellowish powder; yield: 74.5%; mp:
145.9–148.0 8C; 1H NMR (400 MHz, CDCl3):
d
12.70 (s, 1H, 5-OH),
0
0
7.89 (d, 2H, J = 7.7 Hz, aromatic H2 ,6 ), 7.53 (d, 3H, J = 7.4 Hz,
C
28H36O6: C, 71.77; H, 7.74; found: C, 71.42; H, 7.55.
General procedures for the synthesis of O ,O -ethylidene
3
4
0 0
0
0
0
aromatic H3 ,4 ,5 ), 6.66 (s, 1H, aromatic H8), 6.50 (s, 1H, aromatic
H3), 6.37 (s, 1H, aromatic H6), 4.05 (t, 2H, J = 6.5 Hz, –OCH2–),
1.94–1.68 (m, 2H, –CH2–), 1.50 (dt, 2H, J = 14.7, 7.4 Hz, –CH2–),
luteolin [30]: Firstly, to a mixture of luteolin (1.5 g, 5 mmol)
and K2CO3 (0.4 g, 2.5 mmol) in 30 mL of DMSO was added 1,
Please cite this article in press as: N. Cheng, et al., Synthesis and
a
-glucosidase inhibitory activity of chrysin, diosmetin, apigenin, and
luteolin derivatives, Chin. Chem. Lett. (2014), http://dx.doi.org/10.1016/j.cclet.2014.05.021

G Model
CCLET 3002 1–5
N. Cheng et al. / Chinese Chemical Letters xxx (2014) xxx–xxx
3
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
2-dibromoethane dropwise, followed by heating at 70 8C for 1 h.
The mixture was poured into ice water, filtered, washed with
water, the precipitates were dried in vacuo. The residue was
chromatographed on silica gel to afford compound 14. Yellow
powder; yield: 32.4%; mp: 307.3–308.0 8C; 1H NMR (400 MHz,
and reaction lasted for 20 min. An aliquot (200
m
L) was added to a 230
sodium carbonate solution (9.8 mL, 100 mmol/L) to stop the 231
reaction. The glucosidase activity was detected using a silica dish, 232
and the absorbance was determined at 400 nm (for pNP). The 233
inhibitory degree (%) of the targeted compounds upon 234
DMSO-d6):
d
12.90 (s, 1H, 5-OH), 10.87 (s, 1H, 7-OH), 7.60–7.57 (m,
a
D
-glucosidase addition was calculated using [(1 ꢁ
D
Atest
/
235
0
0
0
2H, aromatic H2 ,6 ), 7.04–7.02 (d, 1H, J = 8 Hz, aromatic H5 ), 6.87
(s, 1H, aromatic H8), 6.51 (s, 1H, J = 1.7 Hz, aromatic H3), 6.20–6.19
Acontrol) ꢂ 100], where
D
A indicates the absorbance increase in 236
20 min. The 50% inhibitory concentration values (IC50) were 237
expressed as mean ꢀ SD (n = 3), which were obtained using the 238
Sigmaplot 12.0 software. All the tests were performed in triplicate. 239
(s, 1H, J = 4 Hz, aromatic H6), 4.33–4.32 (d, 4H, J = 4 Hz,
OCH2CH2O–); MALDI-TOF: m/z 313 ([M+H]+).
–
General procedures for synthesis of compounds 15–17 based on
Acarbose and 1-deoxynojirimycin were used as positive controls.
240
the method used to obtain chrysin alkyl derivatives.
7
3
4
0
0
O -Ethyl-O ,O -ethylidene luteolin (15): Yellow powder; yield:
3. Results and discussion
241
70.2%; mp: 174.1–174.6 8C; 1H NMR (400 MHz, CDCl3):
d
7.41–7.37
0
0
0
(m, 2H, aromatic H2 ,6 ), 6.98–6.96 (d, 1H, J = 8 Hz, aromatic H5 ),
6.54 (s, 1H, aromatic H8), 6.45 (s, 1H, aromatic H3), 6.34 (s, 1H,
aromatic H6), 4.33–4.32 (d, 4H, J = 4 Hz, –CH2CH2–), 4.13–4.08 (q,
2H, J = 6.7 Hz, –CH2–), 1.47–1.43 (t, 3H, J = 8 Hz, –CH3);
MALDI-TOF: m/z 341 ([M+H]+); Anal. calcd.Anal. calcd. for
C19H10O6: C, 67.05; H, 4.74; found: C, 67.25; H, 4.79.
The synthesis of derivatives 5–13 was achieved by coupling 242
various bromoalkanes with their respective precursors in anhy- 243
drous acetone (Scheme 1). Chrysin derivatives 5–7 were derived at 244
the C-7 position, diosmetin derivatives 8–10 were derived at the C- 245
7 and C-30 positions, and apigenin derivatives 11–13 were obtained 246
by alkylating the C-7 and C-40 positions. Luteolin derivatives 15–17 247
were conveniently prepared using the method described in 248
literature (Scheme 2). The structures of all the derivatives were 249
7
3
4
0
0
O -Butyl-O ,O -ethylidene luteolin (16): Yellow powder; yield:
80.4%; mp: 153.9–154.5 8C; 1H NMR (400 MHz, CDCl3):
d
7.41–7.37
characterized by 1H NMR, MALDI-TOF, and elemental analyses.
The -glucosidase inhibition effect of the precursors and 251
250
0
0
0
(m, 2H, aromatic H2 ,6 ), 6.98–6.96 (d, 1H, J = 8 Hz, aromatic H5 ),
6.54 (s, 1H, aromatic H8), 6.45 (s, 1H, aromatic H3), 6.34 (s, 1H,
aromatic H6), 4.33–4.32 (d, 4H, J = 4 Hz, –CH2CH2–), 4.04–4.01
(t, 2H, J = 6.2 Hz, –CH2O–), 1.81–1.78 (t, 2H, J = 7 Hz, –CH2–),
1.53–1.47 (q, 2H, J = 7.2 Hz, –CH2–), 1.01–0.97 (t, 3H, J = 7.2 Hz, –
CH3); MALDI-TOF: m/z 369 ([M+H]+); Anal. calcd. for C21H20O6: C,
68.47; H, 5.47; found: C, 68.35; H, 5.50.
a
their derivatives were determined using similar protocols de- 252
scribed in literature [39,43,44]. 1-Deoxynojirimycin (a clinically 253
used a-glucosidase inhibitor) and acarbose were used as reference 254
drugs. The IC50 values of all compounds are shown in Table 1, 255
which shows that the precursors 1–4 and their derivatives 5–13 256
7
3
0
4
0
O -Hexyl-O ,O -ethylidene luteolin (17): Yellow powder; yield:
75.9%; mp: 125.6–125.9 8C. 1H NMR (400 MHz, CDCl3):
and 15–17 were more active against yeast
a-glucosidase than 257
d
7.40–7.36
1-deoxynojirimycin (IC50 = 226.912 ꢀ 12.573 mmol/L) and acarbose 258
(IC50 = 563.601 ꢀ 40.492 mmol/L). The a-glucosidase inhibition of 259
chrysin 1 (IC50 = 77.730 ꢀ 3.490 mmol/L) was weaker compared with 260
its derivatives 5–7 (IC50 < 24.396 mmol/L). Similarly, apigenin 261
derivatives 8–10 (IC50 < 7.350 mmol/L) and diosmetin derivatives 262
11–13 (IC50 < 22.051 mmol/L) are more potent that the parent 263
0
0
0
(m, 2H, aromatic H2 ,6 ), 6.97–6.95 (d, 1H, J = 8 Hz, aromatic H5 ),
6.52 (s, 1H, aromatic H8), 6.44 (s, 1H, aromatic H3), 6.33 (s, 1H,
aromatic H6), 4.32–4.31 (d, 4H, J = 4 Hz, –CH2CH2–), 4.03–4.00
(t, 2H, J = 6.5 Hz, –OCH2–), 1.82–1.78 (t, 2H, J = 8 Hz, –CH2–),
1.46–1.34 (m, 6H, –CH2CH2CH2–), 0.91 (s, 3H, –CH3); MALDI-TOF:
m/z 397 ([M+H]+); Anal. calcd. for C23H24O6: C, 69.68; H, 6.10;
found: C, 69.45; H, 6.15.
apigenin
2
(IC50 = 16.780 ꢀ 0.257 mmol/L) and diosmetin
3
264
(IC50 = 22.764 ꢀ 3.503 mmol/L). The inhibitory activity of luteolin 265
derivatives 15–17 did not exceed that of luteolin 4. But increasing the 266
hydrophobicity or the alkyl chain length led to more potent analogs 267
219
2.3. a-Glucosidase inhibitory activity
(IC50: 15 > 16 > 17).
268
220
221
222
223
224
225
226
227
228
229
An improved methodology used in the assessment of
-glucosidase inhibitory activity has been reported in previous
Transition states of the reactions catalyzed by glycosidase 269
involve covalent intermediates [45,46]. Hydrogen bonding is a 270
crucial factor for the interactions between the enzyme and its 271
substrates and the conformation and orientations of the 272
inhibitors in the active site [47]. Previous studies have reported 273
that the hydroxyl group has an important function in 274
a
studies [39–42]. pNP-
a
-Glu was hydrolyzed into pNP by
a
-glucosidase. The absorption of pNP at 400 nm was determined
using
a
spectrophotometer, which indicated the activity of
L of the
-glucosidase (200 L,
a
-glucosidase. Sodium phosphate buffer (pH 6.8), 50
samples in various concentrations, and
m
a
m
a-glucosidase inhibition at position 5 of the flavonoids [48,49], 275
0.3 U/mL) were mixed at 37 8C and the mixture was allowed to stir
for 10 min. The reaction was started with the addition of
4-nitrophenyl-a-D-glucopyranoside (500 mL, 10 mmol/L) at 37 8C
and the hydroxyl substitution on the B ring by particular groups 276
could enhance inhibitory activity [35]. Compared with that of 277
chrysin 1 (IC50 = 26.417 ꢀ 0.485 mmol/L), the inhibitory effect of 278
Scheme 1. Preparation of derivatives 5–13, reagents and conditions: (a) bromoalkane, K2CO3, acetone, reflux.
Please cite this article in press as: N. Cheng, et al., Synthesis and
a-glucosidase inhibitory activity of chrysin, diosmetin, apigenin, and
luteolin derivatives, Chin. Chem. Lett. (2014), http://dx.doi.org/10.1016/j.cclet.2014.05.021

G Model
CCLET 3002 1–5
4
N. Cheng et al. / Chinese Chemical Letters xxx (2014) xxx–xxx
Scheme 2. Preparation of derivatives 15–16, reagents and conditions: (a) dibromoethane, K2CO3, DMSO, 70 8C; (b) bromoalkane, K2CO3, acetone, reflux.
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
the 7-methylated compound 5 (IC50 = 24.396 ꢀ 0.665 mmol/L) was
minimally increased, whereas butylated and hexylated analogs 6 and
7 (6: IC50 = 7.040 ꢀ 1.634 mmol/L; 7: IC50 = 4.476 ꢀ 1.109 mmol/L)
showed excellent activity against the yeast a-glucosidase (Fig. 1).
Therefore, a-glucosidase inhibitory activity was improved when the
hydrophobicity of chrysin was enhanced. To further study the effect
of flavone hydrophobicity on inhibitory activity, we analyzed the
inhibitory activity of apigenin derivatives (IC50: 8 > 9 > 10) and
diosmetin derivatives (IC50: 11 > 12 > 13) from Fig. 1. The results
indicated that hydrophobicity has an important function in
increasing inhibitory activity. Inhibitory activity was dramatically
enhanced when the alkyl chain was longer than or equal to two
carbons. In addition, We found that the OH groups at positions 30 and
40 of benzopyran that were alkylated by ethylidene did not improve
a-glucosidase inhibitory activity; the inhibitory activity of luteolin
derivatives 15–17 did not exceed that of luteolin 4. But increasing
the hydrophobicity or the elongation of alkyl chains improved the
inhibitory activity (IC50: 15 > 16 > 17).
Fig. 1. Effect of compounds on
a-glucosidase activity in vitro.
Kumar et al. [49] reported that replacement of the OH group at
positions 30, 40 and 7 of benzopyran by any electron-withdrawing
group (NO2, OCH3 etc.) favors
a-glucosidase inhibitory activity.
Therefore, the substitution of the hydrogen of OH by alkyls at
position 7 of benzopyran would enhance the inhibitory activity,
which is dependent on the alkyl chain lengths. The lengths were
found to be positively correlated with the IC50 values of derivatives
300
301
302
303
304
305
306
Table 1
Structures and in vitro
a-glucosidase inhibitory activity of targeted compounds.
(IC50
develop novel
:
5 > 6 > 7, 8 > 9 > 10, 11 > 12 > 13, 15 > 16 > 17). To
-glucosidase inhibitor, the results of this study
a
could provide a series of potential compounds.
4. Conclusion
307
In summary, twelve chrysin, diosmetin, apigenin, and luteolin
308
309
310
311
312
313
314
315
316
317
318
319
320
321
alkyl derivatives were synthesized as novel inhibitors of yeast
a-
glucosidase. All compounds were verified by 1H NMR, MALDI-TOF,
and elemental analyses. The glucosidase inhibitory activity of all
derivatives is higher compared with those of the positive control
drugs, acarbose, and 1-deoxynojirimycin. O7-Hexyl chrysin 7,
Compound
R1
R2
R3
IC50 (m
mol/L)a
4
7
3
7
7
0
0
0
O ,O -hexyl apigenin 10, O ,O -hexyl diosmetin 13, O -hexyl-
1 (Chrysin)
OH
H
H
77.730 ꢀ 3.490
16.780 ꢀ 0.257
22.764 ꢀ 3.503
3.652 ꢀ 0.077
24.396 ꢀ 0.665
7.040 ꢀ 1.634
4.476 ꢀ 1.109
7.350 ꢀ 0.998
6.897 ꢀ 0.263
4.426 ꢀ 0.281
22.051 ꢀ 3.596
2.940 ꢀ 0.051
2.406 ꢀ 0.101
15.952 ꢀ 1.013
13.733 ꢀ 0.299
5.180 ꢀ 0.451
563.601 ꢀ 40.492
226.912 ꢀ 12.573
3
4
0
2 (Apigenin)
OH
H
OH
O ,O -ethylidene luteolin 17 were the most effective among the
inhomogeneous derivatives. From a structural–activity relation-
ship perspective, replacing the hydrogen of OH group at positions
30, 40, and 7 of benzopyran with various alkyl chains was the critical
factor in altering the inhibition activity of flavonoids. To develop
3 (Diosmetin)
OH
OH
OCH3
OH
4 (Luteolin)
OH
OH
5
OC2H5
OC4H9
OC6H13
OC2H5
OC4H9
OC6H13
OC2H5
OC4H9
OC6H13
OC2H5
OC4H9
OC6H13
H
H
6
H
H
7
H
H
8
H
OC2H5
OC4H9
OC6H13
OCH3
OCH3
OCH3
_
novel
a-glucosidase inhibitor, the results of this study could
9
H
provide a series of potential compounds.
10
H
11
OC2H5
12
OC4H9
Acknowledgments
322
13
OC6H13
15
_
_
_
16
_
This work was financially supported by the Research Fund for Q3 323
17
Acarboseb
1-Deoxynojirimycinb
_
the Doctoral Program of Higher Education of China (no.
20114301120004), Hunan Provincial Natural Science Foundation
of China (no. 12JJ6081), Dr.’s Start-up Foundation of Xiangtan
University (no. 06KZjKZ08035), and Natural Science Foundation of
Xiangtan University (no. 2011XZX09).
324
325
326
327
328
a
Data represents means ꢀSD of triplicate samples obtained from the dose
inhibition curve.
b
This compound was used as a positive control.
Please cite this article in press as: N. Cheng, et al., Synthesis and
a
-glucosidase inhibitory activity of chrysin, diosmetin, apigenin, and
luteolin derivatives, Chin. Chem. Lett. (2014), http://dx.doi.org/10.1016/j.cclet.2014.05.021

G Model
CCLET 3002 1–5
N. Cheng et al. / Chinese Chemical Letters xxx (2014) xxx–xxx
5
329
References
[25] H.D. Ly, S.G. Withers, Mutagenesis of glycosidases, Annu. Rev. Biochem. 68 (1999) 390
487–522.
[26] T. Schewe, Y. Steffen, H. Sies, How do dietary flavanols improve vascular function? 392
A position paper, Arch. Biochem. Biophys. 476 (2008) 102–106.
[27] M.N. Clifford, Chlorogenic acids and other cinnamates – nature, occurrence and 394
dietary burden, J. Sci. Food Agric. 79 (1999) 362–372.
391
393
395
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
[1] D.R. Whiting, L. Guariguata, C. Weil, J. Shaw, IDF diabetes atlas: global estimates of
the prevalence of diabetes for 2011 and 2030, Diabetes Res. Clin. Pract. 94 (2011)
311–321.
[2] S.I. Taylor, D. Accili, Y. Imai, Insulin resistance or insulin deficiency: which is the
primary cause of NIDDM? Diabetes 43 (1994) 735–740.
[3] D. Porte Jr., b-Cells in type II diabetes mellitus, Diabetes 40 (1991) 166–180.
[4] A.E. Butler, J. Janson, S. Bonner-Weir, et al., b-Cell deficit and increased b-cell
apoptosis in humans with type 2 diabetes, Diabetes 52 (2003) 102–110.
[5] P.C. Tang, Z.G. Lin, Y. Wang, et al., Design and synthesis of DPP-4 inhibitor for the
treatment of type 2 diabetes, Chin. Chem. Lett. 21 (2010) 253–256.
[6] Y.H. Wu, Synthesis of (S)-2-ethoxy-3-phenylpropanoic acid derivatives and their
insulin-sensitizing activity, Chin. J. Chem. 25 (2007) 265–267.
[7] A.H. Samad, T.S.T. Willing, K.G.M. Alberti, R. Taylor, Effects of BAYm 1099, new a-
glucosidase inhibitor, on acute metabolic responses and metabolic control in
NIDDM over 1 mo, Diabetes Care 11 (1988) 337–344.
[8] N. Asano, Glycosidase inhibitors: update and perspectives on practical use,
Glycobiology 13 (2003) 93R–104R.
[9] K. O’Dea, J. Turton, Optimum effectiveness of intestinal alpha-glucosidase inhi-
bitors: importance of uniform distribution through a meal, Am. J. Clin. Nutr. 41
(1985) 511–516.
[10] P. Lefebvre, A. Scheen, The use of acarbose in the prevention and treatment of
hypoglycaemia, Eur. J. Clin. Invest. 24 (1994) 40–44.
[11] L.J. Scott, C.M. Spencer, Miglitol: a review of its therapeutic potential in type 2
diabetes mellitus, Drugs 59 (2000) 521–549.
[28] M. Richelle, I. Tavazzi, E. Offord, Comparison of the antioxidant activity of 396
commonly consumed polyphenolic beverages (coffee, cocoa, and tea) prepared 397
per cup serving, J. Agric. Food Chem. 49 (2001) 3438–3442.
[29] A. Crozier, I.B. Jaganath, M.N. Clifford, Dietary phenolics: chemistry, bioavailabil- 399
ity and effects on health, Nat. Prod. Rep. 26 (2009) 1001–1043.
398
400
[30] Q.Q. Wang, N. Cheng, X.W. Zheng, S.M. Peng, X.Q. Zou, Synthesis of organic 401
nitrates of luteolin as a novel class of potent aldose reductase inhibitors, Bioorg. 402
Med. Chem. 21 (2013) 4301–4310.
[31] J.H. Cui, D. Hu, X. Zhang, Z. Jing, et al., Design and synthesis of new 7, 8-dimethoxy- 404
a-naphthoflavones as CYP1A1 inhibitors, Chin. Chem. Lett. 24 (2013) 215–218.
[32] K. Hanhineva, R. To¨rro¨nen, I. Bondia-Pons, et al., Impact of dietary polyphenols on 406
carbohydrate metabolism, Int. J. Mol. Sci. 11 (2010) 1365–1402.
[33] T. Nishioka, J. Kawabata, Y. Aoyama, Baicalein, an a-glucosidase inhibitor from 408
Scutellaria baicalensis, J. Nat. Prod. 61 (1998) 1413–1415.
403
405
407
409
[34] H.W. Ryu, B.W. Lee, M.J. Curtis-Long, et al., Polyphenols from Broussonetia 410
papyrifera displaying potent a-glucosidase inhibition, J. Agric. Food Chem. 58 411
(2009) 202–208.
[35] K. Tadera, Y. Minami, K. Takamatsu, T. Matsuoka, Inhibition of a-glucosidase and 413
a-amylase by flavonoids, J. Nutr. Sci. Vitaminol. (Tokyo) 52 (2006) 149–153.
412
414
[36] W. Hakamata, I. Nakanishi, Y. Masuda, et al., Planar catechin analogues with alkyl 415
side chains: a potent antioxidant and an a-glucosidase inhibitor, J. Am. Chem. Soc. 416
[12] L.K. Campbell, D.E. Baker, R.K. Campbell, Miglitol: assessment of its role in the
treatment of patients with diabetes mellitus, Ann. Pharmacother. 34 (2000)
1291–1301.
[13] A.J. Krentz, C.J. Bailey, Oral antidiabetic agents, Drugs 65 (2005) 385–411.
[14] D. Nathan, J. Buse, M. Davidson, et al., Management of hyperglycaemia in type 2
diabetes: a consensus algorithm for the initiation and adjustment of therapy,
Diabetologia 49 (2006) 1711–1721.
128 (2006) 6524–6525.
417
[37] J.S. Shin, K.S. Kim, M.B. Kim, J.H. Jeong, B.K. Kim, Synthesis and hypoglycemic 418
effect of chrysin derivatives, Bioorg. Med. Chem. Lett. 9 (1999) 869–874.
[38] D.C. Wan, J.J. Yuan, Z.L. Yang, et al., Facile O-alkylation of highly hydrophilic 420
hyperbranched polyglycerol, Chin. Chem. Lett. 18 (2007) 192–194.
419
421
[39] Y. Kashima, H. Yamaki, T. Suzuki, M. Miyazawa, Structure–activity relationships 422
of bergenin derivatives effect on a-glucosidase inhibition, J. Enzyme Inhib. Med. 423
[15] S.H. Hsiao, L.H. Liao, P.N. Cheng, T.J. Wu, Hepatotoxicity associated with acarbose
therapy, Ann. Pharmacother. 40 (2006) 151–154.
Chem. 28 (2013) 1162–1170.
424
[40] Y.Q. Li, F.C. Zhou, F. Gao, J.S. Bian, F. Shan, Comparative evaluation of quercetin, 425
[16] Z.Y. Du, R.R. Liu, W.Y. Shao, et al., a-Glucosidase inhibition of natural curcumi-
noids and curcumin analogs, Eur. J. Med. Chem. 41 (2006) 213–218.
[17] E.B. de Melo, A. da Silveira Gomes, I. Carvalho, a- and b-glucosidase inhibitors:
chemical structure and biological activity, Tetrahedron 62 (2006)
10277–10302.
[18] Y.I. Kwon, E. Apostolidis, K. Shetty, In vitro studies of eggplant (Solanum melon-
gena) phenolics as inhibitors of key enzymes relevant for type 2 diabetes and
hypertension, Bioresour. Technol. 99 (2008) 2981–2988.
isoquercetin and rutin as inhibitors of a-glucosidase, J. Agric. Food. Chem. 57 426
(2009) 11463–11468.
427
[41] W. Li, K. Wei, H. Fu, K. Koike, Structure and absolute configuration of clerodane 428
diterpene glycosides and a rearranged cadinane sesquiterpene glycoside from the 429
stems of Tinospora sinensis, J. Nat. Prod. 70 (2007) 1971–1976.
430
[42] S. Adisakwattana, P. Charoenlertkul, S. Yibchok-anun, a-Glucosidase inhibitory 431
activity of cyanidin-3-galactoside and synergistic effect with acarbose, J. Enzyme 432
Inhib. Med. Chem. 24 (2009) 65–69.
433
[19] R. Tundis, M. Loizzo, F. Menichini, Natural products as-amylase and-glucosidase
inhibitors and their hypoglycaemic potential in the treatment of diabetes: an
update, Mini-Rev. Med. Chem. 10 (2010) 315–331.
[43] C.M. Ma, M. Hattori, M. Daneshtalab, L. Wang, Chlorogenic acid derivatives with 434
alkyl chains of different lengths and orientations: potent a-glucosidase inhibi- 435
tors, J. Med. Chem. 51 (2008) 6188–6194.
436
[20] L.G. Ranilla, Y.I. Kwon, E. Apostolidis, K. Shetty, Phenolic compounds, antioxidant
activity and in vitro inhibitory potential against key enzymes relevant for
hyperglycemia and hypertension of commonly used medicinal plants, herbs
and spices in Latin America, Bioresour. Technol. 101 (2010) 4676–4689.
[21] M. Liu, W. Zhang, J. Wei, X. Lin, Synthesis and a-glucosidase inhibitory mecha-
nisms of bis(2, 3-dibromo-4, 5-dihydroxybenzyl) ether, a potential marine bro-
mophenol a-glucosidase inhibitor, Mar. Drugs 9 (2011) 1554–1565.
[22] R.R. Rao, A.K. Tiwari, P.P. Reddy, et al., Synthesis of antihyperglycemic, a-gluco-
sidase inhibitory, and DPPH free radical scavenging furanochalcones, Med. Chem.
Res. 21 (2012) 760–774.
[23] J.D. Xu, L.W. Zhang, Y.F. Liu, Synthesis and antioxidant activities of flavonoids
derivatives, troxerutin and 30, 40, 7-triacetoxyethoxyquercetin, Chin. Chem. Lett.
24 (2013) 223–226.
[24] J.B. Zheng, H.F. Zhang, H. Gao, Investigation on electrochemical behavior and
scavenging superoxide anion ability of chrysin at mercury electrode, Chin. J.
Chem. 23 (2005) 1042–1046.
[44] G.L. Li, J.Y. He, A. Zhang, et al., Toward potent a-glucosidase inhibitors based on 437
xanthones: a closer look into the structure–activity correlations, Eur. J. Med. 438
Chem. 46 (2011) 4050–4055.
439
[45] T.D. Heightman, A.T. Vasella, Recent insights into inhibition, structure, and 440
mechanism of configuration – retaining glycosidases, Angew. Chem. Int. Ed. 38 441
(1999) 750–770.
[46] A. Vasella, G.J. Davies, M. Bo¨hm, Glycosidase mechanisms, Curr. Opin. Chem. Biol. 443
6 (2002) 619–629.
[47] D.L. Zechel, S.G. Withers, Glycosidase mechanisms: anatomy of a finely tuned 445
catalyst, Acc. Chem. Res. 33 (2000) 11–18.
442
444
446
[48] H. Gao, T. Nishioka, J. Kawabata, T. Kasai, Structure–activity relationships for a- 447
glucosidase inhibition of baicalein, 5, 6, 7-trihydroxyflavone: the effect of A-ring 448
substitution, Biosci. Biotechnol. Biochem. 68 (2004) 369–375.
449
[49] V. Kumar, S. Kumar, P. Rani, Pharmacophore modeling and 3D-QSAR studies on 450
flavonoids as a-glucosidase inhibitors, Der Pharma Chemica 2 (2010) 324–335. 451
Please cite this article in press as: N. Cheng, et al., Synthesis and
a-glucosidase inhibitory activity of chrysin, diosmetin, apigenin, and
luteolin derivatives, Chin. Chem. Lett. (2014), http://dx.doi.org/10.1016/j.cclet.2014.05.021