Antioxidant and cytotoxic constituents from Wisteria sinensis

Article abstract of DOI:10.3390/molecules16054020

Chromatographic separation of an aqueous MeOH extract of Wisteria sinensis leaves has yielded six known flavonoids, two triterpene aglycones and the new acylated flavone glycoside chrysoeriol-7-O-[2″-O-(5?-O-caffeoyl)- β-Dapiofuranosyl]- β-D-glucopyranoside (1). All metabolites were isolated for the first time from the genus Wisteria. Their structures were established on the basis of their chromatographic properties, chemical and physicochemical methods including acid hydrolysis analysis, spectroscopic (UV, ¹H- and ¹³C-NMR) data and confirmed by ESI-MS analysis, as well as two-dimensional NMR (¹H-1HCOSY, HMQC and HMBC). Biological studies of the defatted aqueous 80% methanol leaf extract and the major isolates 1, 6 and 7 were undertaken and they are reported herein for the first time to have significant cytotoxic activity against the Hep-G2 tumor cell line in addition to antioxidant activity.

Full text of DOI:10.3390/molecules16054020

Molecules 2011, 16, 4020-4030; doi:10.3390/molecules16054020
OPEN ACCESS
molecules
ISSN 1420-3049
www.mdpi.com/journal/molecules
Article
Antioxidant and Cytotoxic Constituents from Wisteria sinensis
Mona A. Mohamed *, Manal M. Hamed, Allia M. Abdou, Wafaa S. Ahmed and Amal M. Saad
Department of Medicinal Chemistry, Theodor Bilharz Research Institute, P.O.B. 12411, Giza, Egypt;
E-Mails: manalayman@hotmail.com (M.M.H.); Allia.Mahmoud@yahoo.com (A.M.A.);
eb2003eg@hotmail.com (W.S.A.); Amal_badawy@hotmail.com (A.M.S.)
* Author to whom correspondence should be addressed; E-Mail: tbi20042003@yahoo.co.uk;
Fax: +20233388801.
Received: 5 February 2011; in revised form: 13 May 2011 / Accepted: 16 May 2011 /
Published: 17 May 2011
Abstract: Chromatographic separation of an aqueous MeOH extract of Wisteria
sinensis leaves has yielded six known flavonoids, two triterpene aglycones and
the new acylated flavone glycoside chrysoeriol-7-O-[2''-O-(5'''-O-caffeoyl)-β-D-
apiofuranosyl]-β-D-glucopyranoside (1). All metabolites were isolated for the
first time from the genus Wisteria. Their structures were established on the basis
of their chromatographic properties, chemical and physicochemical methods
including acid hydrolysis analysis, spectroscopic (UV, 1H- and 13C-NMR) data
and confirmed by ESI-MS analysis, as well as two-dimensional NMR
(1H-1HCOSY, HMQC and HMBC). Biological studies of the defatted aqueous
80% methanol leaf extract and the major isolates 1, 6 and 7 were undertaken and
they are reported herein for the first time to have significant cytotoxic activity
against the Hep-G2 tumor cell line in addition to antioxidant activity.
Keywords: Wisteria sinensis; fabeaceae; acylated flavone; cytotoxic; Hep-G2
1. Introduction
Wisteria is a genus of flowering plants belonging to the pea family (Fabaceae), that includes ten
species of woody climbing vines native to the eastern United States and the East Asian countries of
China, Korea, and Japan. It is also an extremely popular ornamental plant in China and Japan.
Wisteria sinensis (Sims.) DC. (Chinese wisteria), is a climbing plant that can reach a height of 20 m.

Molecules 2011, 16
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It is considered an invasive species in certain areas [1]. Its pendent racemes, with their many high
blue-violet scented flowers, make a striking picture. The flowers of W. sinensis are also cured in sugar
then mixed with flour and made into a famous local delicacy called "Teng Lo”. The leaves and
flowers are also used as a tea substitute [2]. In addition the fiber from its stems can be used to make
paper [3]. Wisteria species are used as a food source by the larvae of some Lepidoptera species of
moth including the brown-tail [4]. Interestingly, many oriental medicinists use Wisteria gall extracts
for treating gastric cancer [5] and cancer of breast and stomach, or rheumatoid arthritis patients [6-13].
Several Wisteria species have been also reported to have antioxidant [14] and antibacterial activities
[15]. A survey of the literature showed that in previous studies phenylpropanoids and β-chromenes
have been isolated from the oil of W. sinensis flowers [16] and several Wisteria species have been
found to contain triterpene saponins, [6-8], isoflavones [10-13], and lectins [17-19]. To the best of our
knowledge, there are no previous phytochemical investigations of this plant, thus we report herein our
phytochemical studies on a methanol extract of W. sinensis leaves and evaluate the anticancer activity
against Hep-G2 tumor cell lines and antioxidant activities of the investigated extract and its major
isolates 1, 6 and 7.
2. Results and Discussion
Based on chemical and physicochemical analyses, compounds 2-9 were identified as orientin (2),
isoorientin (3), vitexen (4), isovitixen (5), apigenin (6), luteolin (7), [20-23], oleanolic acid (8) and
hedragenin (9), respectively [24].
Compound 1, was determined to be a chrysoeriol caffeoyl diglycoside on the basis of its
chromatographic properties, UV spectra and acid hydrolysis results. Its UV spectrum (in methanol)
exhibited a characteristic band I at ≈ 330 nm, along with a band II masked by an extra strong
maximum at 262, 272 nm, which was indicative to the presence of a cinnamoyl moiety [23]. Upon
complete acid hydrolysis of 1, glucose and apiose were detected in the aqueous phase, while caffeic
acid was identified along with chrysoeriol in the organic phase. The negative ESI-MS of 1 exhibited a
molecular ion peak at m/z 755.30 [M-H]- corresponding to a molecular weight of 756, together with
five diagnostic fragment ion peaks at m/z 593.46 [M-H-deoxycaffeoyl]–, 575.3 [M- H –
deoxycaffeoyl-H2O]–, m/z 461.0 [M-H- deoxycaffeoyl apioside]–, m/z 299.4 [aglycone-H]–
corresponding to the loss of a glucoside from the last fragment and m/z 179.1 [caffeiate]–. Its 1H-NMR
spectrum (Table 1) showed signals at 7.50 (1H, brs), 7.34 (1H, dd, J = 8.0, 1.8 Hz) and 6.68 (1H, d,
J = 8.0 Hz) assigned to H-2', H-6' and H-5' respectively, in 1', 4'-disubstituted B-ring, two doublets at
6.67 (1H, d, J = 2.0 Hz) and 6.35 (1H, d, J = 2.0 Hz), attributed to H-8 and H-6, in 5,7- disubstituted
A-ring, and one singlet at 6.55 (1H, s) attributed to H-3 together with a methoxy at 3.73 (3H, s). All
the previous described signals were confirmative for a chrysoeriol moiety due to the deshielded
location of H-2' (~+0.2 ppm). An E-caffeoyl moiety was deduced in the structure of 1 through an AX
spin coupling system of two E-olefinic doublets at 7.29 H-7"" and 6.18 H-8"" (each, d, J = 16 Hz),
along with ABX spin coupling system of its phenyl protons at 6.87 (d, J = 1.8 Hz), 6.84 (dd, J = 8.0,
1.8 Hz) and 6.67 (d, J = 8.0 Hz) of H-2"", H-6"" and H-5"", respectively. A doublet signal at 5.19
(1H, d, J = 7.5 Hz, H-1'') and a singlet at 5.37 (1H, s) in the 1H-NMR spectrum revealed the presence
of two anomeric hydrogens from two sugar moieties. The 13C-NMR experiment showed 36 signals, of

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which 16 were attributed to the aglycone moiety, nine to the E-caffeoyl moiety, six to the β-D-
glucopyranosyl moiety, and five possibly belonging to an apiofuranosyl moiety.
Table 1. 1H-, 13C-NMR and HMBC spectral data of 1 (500/125 MHz, DMSO-d6).
NO
2
δH
δC
HMBC correlation
164.3
103.7
181.7
161.2
99.5
3
6.55 s
4
5
6
6.35 d (2.0)
6.67 d (2.0)
H-8, 10
H-6, 10
7
162.3
94.3
8
9
156.7
105.4
121.6
113.7
147.6
149.3
115.0
115.4
55.5
10
1'
2'
7.50 (brs)
H-6', 4'
3'
4'
5'
6.68 d (8.0)
7.34 dd (8.0, 1.8)
3.73 s
H-3', 1'
H-2', 4'
H-3'
6'
OCH3
1''
2''
3''
4''
5''
6''a
6''b
1'''
2'''
3'''
4'''a
4'''b
5'''
1''''
2''''
3''''
4''''
5''''
6''''
5.19 d (7.5)
3.78 dd (10.5, 7.5 )
3.41 brd
99.1
H-7, 3''
H-1''', 4''
H-5'', 1''
H-2'', 6''
H-3''
75.8
76.6
3.20 t (10.5)
3.46 m
69.8
77.5
3.52 m
60.5
3.70 brd (12.0)
5.37 s
60.5
108.2
76.7
H-3''', 2''
H-4'''
3.58*
3.65*
77.0
H-1'''
3.75 d (9.5)
4.04 d (9.5)
4.07 brs
73.8
73.8
66.6
H-2'''
125.4
115.4
145.0
149.3
115.9
122.8
6.87 d (1.80)
H-6'''', 4'''', 7''''
6.67 d (8.0)
H-3'''', 1''''
6.84 d (8.0, 1.8)
H-2'''', 4'''', 7''''
7''''
8''''
9''''
7.29 d (16.0)
6.18 d (16.0)
144.9
113.4
167.5
H-5'''', 2'''', 9''''
H-1''''
* Unresolved proton resonances, δ in ppm and J values (Hz), were given in parentheses. All
carbon and proton resonances were assigned on the basis of 2D (1H-1H COSY, HMQC and
HMBC).

Molecules 2011, 16
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The apiose moiety was characterized through its one bond correlation in the HMQC spectrum with
its own proton signals compared to the literature data [25-27]. The glucosyl and apiosyl sugar
moieties were deduced to adopt β-D-pyranosyl and β-D-furanosyl stereostructures, respectively, on the
basis of J-values of their anomeric protons and δ-values of their 1H and 13C-resonances (Table 1).
Additional evidence for the chrysoeriol moiety was obtained from the deshielded shift of C-3'
(~ +3 ppm) (Table 1) and the observation of the three bond correlation peak between the methoxy
proton signal at δ 3.73 and the C-3' signal at δ 147.6 in the HMBC spectrum. The glycosidation at
7-OH was concluded from the downfield shift of both C-6 and C-8 (≈ + ∆ 0.2 ppm) and long-range
correlation between the hydrogen signal at 5.19 (H-1'' glucose) and the carbon signal at 162.3 (C-7
aglycone) in the HMBC spectrum. Besides, the chemical shift of the C-2'' of the glucose moiety at
75.8 was clearly deshielded (≈ + ∆3 ppm) compared to the chemical shift of the analogous carbon
resonance of a non-substituted moiety (72.9), led us to identify the glycoside moiety as 7-O-β–D-
glucopyranosyl (1'"→2") apiofuranoside. This was further confirmed from HMBC experiments
showing a long-range correlation between the hydrogen signal at 3.78 (H-2" glucose) and the carbon
signal at 108.2 (C-1''' apiose). In addition, the esterification of the E-caffeoyl group to C-5"' was
deduced from the characteristic downfield shift of C-5"' apiofuranosyl (66.6) relative to that of a
non-acylated analogue (62.4), together with the long range correlation between this protons and the
1
13
carbonyl carbon of the E-caffeoyl moiety (167.5) in HMBC spectrum. All other H- and C-NMR
resonances were also confirmed by the 1H-1H-COSY, HMQC and HMBC spectra and by comparison
with previously reported data for structurally related compounds [28-32]. Thus, 1 was identified as
chrysoeriol -7-O-[2''-O-(5'''-O-caffeoyl)-β-D-apiofuranosyl]-β- D-glucopyranoside (Figure 1).
Figure 1. Chemical structures of isolated compounds from the leaves of Wisteria sinensis.
5'
HO
4''
6''
5''
OH
4'
3'
6'
1'
O
HO
1
8
O
O
HO
9
2''
OCH3
3''
1''
2
O
7
6
2'
O
3
10
4
4''' 5'''
5
OH
1'''
O
3'''
O
2'''
HO
O
OH
6""
7""
9""
8""
5""
4""
1""
2""
HO
3""
OH
OH
R3
HO
R2
O
R1
O
H
OH
OH
O
HO
R
2- R1 = H, R2 = H, R3 = glucose
3- R1 = H, R2 = glucose, R3 = H
4 - R1 = OH, R2 = H, R3 = glucose
5- R1 = OH, R2 = glucose, R3 = H
6- R1 = H, R2 = H, R3 = H
8- R = H
9- R = OH
7- R1 = OH, R2 = H, R3 = H

Molecules 2011, 16
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Regarding their IC50 values (Figure 2), all tested compounds and the methanol extract exhibited
anticancer activity against HepG2 cells in the order 7, 6, 1 and methanol extract. The anti-cancer
activity of W. sinensis leaf methanol extract may be attributed to the corresponding activities of the
flavonoid extract constituents. Experimental animal studies indicate that certain flavonoids possess
antitumor activity. The hydroxylation pattern of the B ring of the flavones, such as luteolin and
quercetin, seems to critically influence their activities, especially the inhibition of protein kinase
antiproliferation activity [33]. Luteolin (7) is an important member of the flavonoid family. It has
been reported that this substance can inhibit the proliferation of a variety of tumor cells, including
solid tumors, ascties cancer and human myeloid leukemia. Luteolin can also sensitize a number of
apoptosis-inducing factors by unique mechanisms [34].
Figure 2. The cytotoxic activity of W. sinensis MeOH extract, 1, 6 and 7 against HepG2
cell line. DOX2 = doxorubicin (positive control).
1.2
Methanol Extract
Deox2
1
Compound 7
compound 6
compound 1
0.8
0.6
0.4
0.2
0
0
5
12
25
50
Conc; μg
The antioxidant properties of flavonoids are widely acknowledged [35-37]. The two classical
structural antioxidant features of flavonoids are the presence of a B-ring catechol group and the
presence of a C2-C3 double bond in conjugation with an oxo group at C4; the first serves to donate
hydrogen/electron to stabilize a radical species and the second serves to bind transition metal ions
such as iron and copper [37,38]. Because luteolin and some of its glycosides fulfill both structural
requirements, it is not surprising that many luteolin-containing plants possess antioxidant properties
[39]. The antioxidant activity of luteolin and its glycosides has been associated with their capacity to
scavenge reactive oxygen and nitrogen species [40], to chelate transition metals that may induce
oxidative damage through the fenton reaction [38], to inhibit proxidant enzymes [39,41,42] and to
induce antioxidant enzymes [43-45]. The antioxidant activity of luteolin has not only been observed

Molecules 2011, 16
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in vitro but also in vivo [46]. In line with this observation, all tested compounds and methanol extract
exhibited strong antioxidant activity (Table 2 and Figure 3).
Table 2. Maximum reactive reaction rate after 5 min. for compounds 1, 6 and 7 at
different concentrations.
Investigated
Maximum reactive reacting rate after 5 min concentration mL−1
materials
Methanol
2
-
4
-
8
-
10
-
20
82.9
40
861
60
74.5
80
79.4
100
65.1
extract
1
6
7
-
-
-
-
-
-
-
-
86.1
77.9
79.7
88.6
79.7
81.5
89.1
81.1
82. 9 82. 9
88.7
82.5
87.1
87.3
81.5
80.5
83.1
84.2
85.3
Figure 3. A. Antioxidant activity of methanol extract; B. Antioxidant activity of 1; C.
Antioxidant activity of 6; D. Antioxidant activities of 7.
A
B
RN-Antioxidant activity (in vitro )
100
90
80
70
60
50
40
30
20
10
0
Ascorbic acid
100 mg/ml
80 mg/ml
60 mg/ml
40 mg/ml
20 mg/ml
Time (sec.)
C
D
3. Experimental
3.1. General
NMR spectra for known compounds were recorded at 300 (1H) and 75 MHz (13C) on a Varian
Mercury 300, while those of the new compound 1 were recorded at 500 (1H) and 125 MHz (13C) on a
JEOL GX-500 NMR spectrometer and δ values are reported in ppm relative to TMS in the
corresponding solvent. ESI-MS analyses were measured on Finnigan LCQ deca LC/MS and double
focusing sector field MAT 90 MS spectrometers (Finnigan, Bremen, Germany). UV analyses of pure
samples were recorded, separately, in MeOH solutions on a Shimadzu UV 240 spectrophotometer.

Molecules 2011, 16
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3.2. Plant material
Leaves of Wisteria sinensis were collected in Spring from plants growing in the El-Orman
Botanical Garden, Giza, Egypt. The plant was authenticated by Prof. Wafaa M. Amer, Department of
Botany, Faculty of Science, Cairo University, Giza, Egypt. A voucher specimen (Reg. No.: P–I) was
deposited in the herbarium, Medicinal Chemistry Department, Theodor Bilharz Research Institute,
Giza, Egypt.
3.3. Extraction and isolation
Air-dried ground powders leaves of W. sinensis (750 g) were extracted with hot 85% aqueous
methanol (4 × 3 L) under reflux (70 °C). The extract was then dried under reduced pressure and
redissolved in methanol. The methanol-soluble portion (75 g) was suspended in water and
preliminarily fractionated on a Polyamide S column (Ø 7 × 110 cm, 350 g, Fluka, St. Louis, MO,
USA), using a step gradient from water 100% to methanol 100% for elution to yield 56 fractions of 1
L each, which were concentrated under reduced pressure. On the basis of comparative thin layer
chromatography (TLC) and paper chromatography (PC) using solvent systems S1, S2 and S3 [S1,
n-butanol–acetic acid– water (4:1:5, top layer), S2, 15% aqueous acetic acid and S3, CHCl3 - MeOH
(8:2)] with the use of UV light, 10% H2SO4, FeCl3 and Naturstoff spray reagents, the 56 individual
fractions were grouped into four major fractions (I–IV). The dry material of fraction I was redissolved
in methanol and filtered to remove some free sugars and salts. A part of the methanol soluble portion
of fraction I (320 mg) was subjected to repeated column chromatography (CC) on Sephadex LH-20
(Pharmacia, Uppsala, Sweden) and eluted with methanol to give pure 1 (65 mg). Fraction II (eluted
with 30%–60% methanol, 9 g) was subjected to CC on Sephadex LH-20 twice, followed by
individual precipitation of both main subfractions from ethanol by excess ethyl acetate to give pure
samples of 2 (19 mg) and 3 (20 mg). Fraction III (eluted with 60%–80% methanol, 12 g) was
fractionated on cellulose C (Merck) with 60% MeOH as an eluent, followed by a Sephadex LH-20
column using BIW (n-BuOH/2-propanoI/H2O, 4:1:5 v/v/v, organic layer) to afford pure 4 (27 mg) and
5 (22 mg). Fraction IV, (80%–100% methanol, 15 g) gave two dark purple spots on PC under long
UV, which change to dark green color with the use of FeCl3 and two pink color spots with sulphuric
acid spray reagent on TLC when heated at 120 °C for three min. Fraction IV was dried under vacuum
and was subjected to separation over a silica gel 60 column (Sigma, 28–200 mesh, Ø 3.0 × 50 cm,
100 g) using a gradient of CHCl3-MeOH (8:2, 7:3, 1:1, 4:6 and 0:1) to give 20 individual fractions of
75 mL each. On the basis of comparative TLC and PC using the previously described solvent systems,
the individual 20 fractions were pooled in two collected fractions (A and B) according to the
differences in composition. Fraction A eluted with (20%–30% MeOH in CHCl3) was subjected to
(CC) on Sephadex LH-20 to give pure samples of 6 (55 mg) and 7 (63 mg). Pure 8 (24 mg) and 9
(32 mg) were isolated from fraction B (30%–100% MeOH in CHCl3) using a Sephadex column and
EtOH for elution. All separation processes were followed up by comp-PC and TLC using S1, S2 and
S3. Silica gel powder (F254, Merck; Darmstadt, Germany) were used for TLC. For paper
chromatography Whatman No. 1 sheets (Whatman Ltd., England) were used. All aglycones and
sugars obtained by acid hydrolysis were identified by comp-TLC and PC with authentic samples,

Molecules 2011, 16
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using the previously described solvent systems, in addition to EtOAc-C5H5N-H2O (12:5:4), and
specific spray reagents (e.g., vanillin HCl and aniline hydrogen phthalate).
3.4. Chrysoeriol -7-O-[2''-O-(5'''-O-caffeoyl)-β-D-apiofuranosyl]-β- D-glucopyranoside (1)
Yellow amorphous powder, Rf-values: 0.73 (S1), 0.77 (S2). Negative ESI-MS: m/z 755.3[M-H]−,
593.46 [M-H- deoxycaffeoyl]−, 575.30 [M-H- deoxycaffeoyl-H2O]−, 461.0 [M-H-deoxycaffeoyl
apioside]−, 299.4 [aglycone-H]– , 179.1 [caffeiate]−. 1H- and 13C-NMR: see Table 1.
3.5. Measurement of potential cytotoxicity by SRB assay
Potential cytotoxicity of the methanol extract of W. sinensis leaves and the isolated compounds 1,
6, 7 and doxorubicin as positive control and transformed cells as a negative control were tested at the
National Cancer Institute, Egypt, using the method of Skehan et al. [47]. Cells were plated in a
96-well plate (104 cells/well) for 24 h before treatment to allow the attachment of cells to the wall of
the plate. Different concentrations of the materials under investigation (0, 1, 2.5, 5 and 10 μg/mL)
were added to the cell monolayer. Triplicate wells were prepared for each individual dose and they
were incubated for 48 h at 37 °C in 5% CO2. After 48 h cells were fixed, washed and stained with
sulforhodamine B stain. Excess stain was washed with acetic acid and attached stain was recovered
with Tris-EDTA buffer and the color intensity was measured in an ELISA reader. The average of the
transformed cells was recorded. The survival curve of the tumor cell line was plotted for each
tested fraction.
3.6. Antioxidant activity
This activity was investigated in vitro for the investigated methanol extract and compounds 1, 6
and 7 using 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radicals, according to the method of Peiwu et al.
[48]. In a disposable cuvette a methanolic solution of DPPH (2.95 mL) was added to samples of
methanol extract and investigated compounds (50 µL in MeOH) at different concentrations
(2–100 mg mL−1) for luteolin and (20–100 mg mL−1) for methanol extract and compounds 1 and 6.
The absorbance was measured at 517 nm at regular intervals of 15 s for 5 min. Ascorbic acid was
used as standard (0.1 M) as described by Govindarajan et al. [49].
4. Conclusions
There is a real need to identify new compounds with potential anticancer activity, so experiments
exploring the anticancer potential of compounds from plants used in traditional medicines for the
treatment of many cancer diseases are required for the isolation and development of new anticancer
compounds. The compounds discussed in the present study have only been tested in a limited screen
against Hep-G2 tumor cell line; therefore, further anticancer experiments on these compounds against
other cell lines are required to explore their anticancer activities in greater detail.

Molecules 2011, 16
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Sample Availability: Samples of the compounds 6–9 are available from the authors.
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