Highly efficient synthesis and antitumor activity of monosaccharide saponins mimicking components of Chinese folk medicine Cordyceps sinensis

Article abstract of DOI:10.1080/10286020.2012.670220

Ergosterol 3-O-β-d-glucopyranoside (1a) and ergosterol 3-O-d-galactopyranoside (1b) were highly efficiently synthesized and evaluated for their inhibitory activities against two tumor cell lines. The structures of these compounds were extensively confirmed by ¹H, ¹³C NMR, IR, and HRMS. Compounds 1a and 1b exhibited interesting cytotoxic profiles. The antitumor activity of compound 1a was higher than that of 1b.

Full text of DOI:10.1080/10286020.2012.670220

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Highly efficient synthesis and antitumor
activity of monosaccharide saponins
mimicking components of Chinese folk
medicine Cordyceps sinensis
Zhen-Yuan Zhu a , Qiang Yao a , Yang Liu a , Chuan-Ling Si b , Jing
Chen a , Nian Liu a , Hong-Yu Lian a , Li-Na Ding a & Yong-Min Zhang
c
a Key Laboratory of Food Nutrition and Safety, Ministry of
Education, College of Food Science and Biotechnology, Tianjin
University of Science and Technology , Tianjin , 300457 , China
b Tianjin Key Laboratory of Pulp & Paper, College of Material
Science and Chemical Engineering, Tianjin University of Science
and Technology , Tianjin , 300457 , China
c Université Pierre et Marie Curie-Paris 6, Institut Parisien de
Chimie Moléculaire (UMR CNRS 7201) , 4 place Jussieu, 75005 ,
Paris , France
Published online: 20 Mar 2012.
To cite this article: Zhen-Yuan Zhu , Qiang Yao , Yang Liu , Chuan-Ling Si , Jing Chen , Nian Liu ,
Hong-Yu Lian , Li-Na Ding & Yong-Min Zhang (2012) Highly efficient synthesis and antitumor activity
of monosaccharide saponins mimicking components of Chinese folk medicine Cordyceps sinensis ,
Journal of Asian Natural Products Research, 14:5, 429-435, DOI: 10.1080/10286020.2012.670220
To link to this article: http://dx.doi.org/10.1080/10286020.2012.670220
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Journal of Asian Natural Products Research
Vol. 14, No. 5, May 2012, 429–435
Highly efficient synthesis and antitumor activity of monosaccharide
saponins mimicking components of Chinese folk medicine
Cordyceps sinensis
Zhen-Yuan Zhua*, Qiang Yaoa, Yang Liua, Chuan-Ling Sib, Jing Chena, Nian Liua,
Hong-Yu Liana, Li-Na Dinga and Yong-Min Zhangc
aKey Laboratory of Food Nutrition and Safety, Ministry of Education, College of Food Science and
Biotechnology, Tianjin University of Science and Technology, Tianjin 300457, China; Tianjin
Key Laboratory of Pulp & Paper, College of Material Science and Chemical Engineering,
b
c
Tianjin University of Science and Technology, Tianjin 300457, China; Universite Pierre
´
et Marie Curie-Paris 6, Institut Parisien de Chimie Moleculaire (UMR CNRS 7201),
´
4 place Jussieu, 75005 Paris, France
(Received 5 August 2011; final version received 23 February 2012)
Ergosterol 3-O-b-D-glucopyranoside (1a) and ergosterol 3-O-b-D-galactopyranoside
(1b) were highly efficiently synthesized and evaluated for their inhibitory activities
against two tumor cell lines. The structures of these compounds were extensively
confirmed by 1H, 13C NMR, IR, and HRMS. Compounds 1a and 1b exhibited interesting
cytotoxic profiles. The antitumor activity of compound 1a was higher than that of 1b.
Keywords: ergosterol; saponins; glycosylation; Cordyceps sinensis
1. Introduction
However, the precise action mechan-
isms of these saponins remain ambiguous
by modern standards. One reason is that
each saponin extract from an herbal plant
normally contains several dozens of sapo-
nin components. These components have
such similar structural patterns, and some
components exist in such tiny amounts,
that separation of each component is, if
not impossible, an extremely formidable
task. Chemical synthesis could provide a
realistic way to determine the availability
of homogeneous saponins, thus affording
new opportunities for understanding and
applying this important group of natural
products.
Saponins, glycosides of steroids or triter-
penes, exist widely in terrestrial plants and
usually in considerable amounts [1]. They
are constituents of many significant foods,
forage crops, and herbal medicinal plants,
such as Ginseng, Liquorice, Astragalus
mongholicus, Angelica sinensis, seven
leaves grass, Primula malacoides, Radix
ophiopogonis, Smilax glabra, Lilac pink,
Cordyceps sinensis, Lucid ganoderma,
and so on [2–4,5]. Saponins are of special
importance in traditional Chinese herbs,
and the list of those containing saponins as
active componentsis long. Saponin extracts
from these herbs have been used in China to
treat various human diseases with surpris-
ingly good precision.
C. sinensis Berk. Sacc (Clavicipitaceae)
is one of the rarest and most valued species in
traditional Chinese medicines. A number of
*Corresponding author. Email: zhyuanzhu@tust.edu.cn
ISSN 1028-6020 print/ISSN 1477-2213 online
q 2012 Taylor & Francis
http://dx.doi.org/10.1080/10286020.2012.670220
http://www.tandfonline.com

430
Z.-Y. Zhu et al.
and the enzyme is expensive. The enzyme on
H3C
CH3
the substrate specificity is strong. Relatively,
the chemical synthesis is indispensable.
The core of the formation of glycosidic
bond is an anomeric acetal synthesis,
because the dehydration directly generating
glycosidic bond is a violent reaction, so
the usual method is to use a leaving groups
at anomeric position (donor), which reacts
with an alcohol (accepter) to give, in the
presence of a promoter, the desired glycoside
(Scheme 1).
CH3
H3C
CH3
H3C
H
H
RO
1a:R=D-Glu
1b:R=D-Gal
Figure 1. Structures of compounds 1a and 1b.
bioactive constituents from Cordyceps
species have been reported. These include:
cordycepin and other antibacterial and
antitumor adenosine derivatives; ophicordin,
an antifungal agent; a polysaccharide, shown
to have antitumor activity; an immunopo-
tentiating galactomannan; and L-tryptophan.
Recently, ergosterol and only its 3-O-
glucopyranoside (compound 1a, in Figure 1)
were isolated and identified from the mycelia
of C. sinensis. The compound (1a) displayed
very good antitumor activity, but the content
of the mycelia was very low [6,7]. It is
valuable to develop an efficient way to
prepare this kind of saponins to promote
further studies, such as thorough pharmaco-
logical research and further structure–
activity relationship investigation. Herein,
we report the chemical synthesis of 1aand 1b
from commercially available ergosterol. The
preliminary antitumor activity of these
synthetic saponins was then investigated.
Knorr–Koenigs reaction is a classic
glycosylation, using a bromide as donor and
heavy metals as promoters, and the problem
of this reaction is that the promoting agents
are expensive and environment unfriendly.
The Schmidt method in 1980, so-called
imidate method, is the most valuable
glycosidic bond synthesis method, which
has advantage of good stability, easy
operation, high yield, good selectivity, etc.
In the reaction, because of the molecular
weight, ergosterol has the big ergosterol
skeleton stiffness, the glycosylation reaction
is difficult, so we chose trichloroacetimidate
as D-glucose and D-galactose 1-OH acti-
vation group, Trimethylsilyl trifluorometha-
nesulfonate (TMSOTf) as promoter. Acetyl
groups have been used as hydroxyl protec-
tion,butthereactionproductswerecomplex,
separationwasdifficultandreactionratewas
slow [10,11]. In this paper, we switch to
benzoyl for sugar ring hydroxyl protection
and thereaction, indican smoothly. Glycosyl
trichloroacetimidates 2a and 2b, as shown in
Figure 2, were readily prepared in good
yields from the corresponding 1-OH sugars
[12] (Scheme 2).
2. Results and discussion
For many methods, including the indican
enzyme synthesis and chemical synthesis
[8,9], enzymatic synthesis is of advantage,
such as mild reaction, good region-, and
stereoselectivity. However, it requires gly-
cosyltransferase and glycosidase-catalysed,
Promoter
(activition/coupling)
O
derivatization
O
PG
PG
OH
O
PG
LG
OR
HOR
(acceptor)
LG = leaving group
PG = protecting group or sugar unit
Scheme 1. Glycosylation reaction.

Journal of Asian Natural Products Research
431
OBz
OBz
OBz
NH
NH
O
O
BzO
BzO
O
O
CCl3
CCl3
BzO
OBz
OBz
2a
2b
Figure 2. Structures of 2a and 2b.
The glycosylation of the ergosterol with
the donor 2a or 2b, achieved in the
conditions described below and promoted
by TMSOTf, gave the compound 3a in 90%
yield (3b in 93%). The stereochemistry of
the newly introduced linkage was deter-
mined to be b on the basis of the Glc
H-1, H-2 coupling constant (J1,2 ¼ 7.6 Hz)
and Gal H-1, H-2 coupling constant
(J1,2 ¼ 8.4 Hz) [13]. De-O-benzoylation
of compound 3a (3b) in methanol–
dichloromethane quantitatively afforded
the target product 1a (1b) (Scheme 3).
Figure 3. As clearly shown on the graphs,
against S180, inhibition rates of com-
pounds 1a and 1b reduced gradually with
decreasing concentrations, and the inhi-
bition rate of 1a was higher than that of 1b,
when in 24 h, the inhibition rate of 1a
achieved maximum of 90%. As for H22
cells, the inhibition rate of compound 1b
was higher than that of 1a, but no dose-
response relationship. In 48 h, compound
1b forwarded best inhibition rate of 60%
with the concentration of 50 mg/ml.
Growth inhibition due to compounds 1a
and 1b against S180, H22 from the
laboratory of Tianjin University of Science
and Technology was studied to compare
their antitumor activities. The inhibitory
effects of 1a and 1b were assessed by
measuring the number of viable cells
surviving after treatment with 12.5, 25,
50, 100, and 200 mg/ml of tested com-
pounds for 1–3 days by the colorimetric 3-
(4,5-dimethylthiazol-2-yl)-2,5-diphenylte-
trazolium bromide (MTT) assays. The
percent inhibition of the proliferation of
the two malignant cell lines is shown in
3. Experimental
3.1. General experimental procedures
Optical rotations were measured with
a JASCO P-1020 polarimeter (JASCO
International Co., Ltd, Tokyo, Japan). IR
(KBr disks) spectra were recorded by
Bruker Tensor 27 spectrometer (Bruker
1
Corporation, Ettlingen, Germany). H and
13C NMR spectra were taken on a Bruker
400/600 MHz spectrometer (Bruker Cor-
poration) with tetramethylsilane as and
internal standard, and chemical shifts
values were recorded. Mass spectra were
OH
OBz
O
a
O
OBz
OBz
HO
HO
BzO
BzO
OH
OBz
OH
OBz
HN
b
c
O
O
BzO
BzO
BzO
BzO
CCl3
OH
O
OBz
OBz
Scheme 2. Reagents and conditions: (a) BzCl (5.5eq), pyridine, CH2Cl2, 08C to rt, 16 h, 99.5%,
(b) methylamine (0.005 eq.), THF, rt, 3 h, 95%, and (c) CNCCl3 (8 eq.), DBU (0.1 eq.), CH2Cl2, rt,
3 h, 96%.

432
Z.-Y. Zhu et al.
CH3
CH3
H3C
H3C
H3C
CH3
CH3
H3C
H3C
H3C
H3C
O
H
H3C
NH
H
PO
H
a
H
+
O
O
O
HO
PO
CCl3
2a, 2b
3a, 3b
OH
CH3
CH3
H3C
H3C
H3C
O
1a glycosyl =
1b glycosyl =
HO
HO
O
H3C
H
OH
OH
H
b
OH
O
O
O
HO
O
HO
OH
1a, 1b
Scheme 3. Reagents and conditions: (a) TMSOTf (0.1 eq.), CH2Cl2, 08C to rt, 2.5 h, 95% for 3a,
93% for 3b and (b) NaOMe–MeOH, 98% for 1a, 96% for 1b.
(a) 100
90
(b)
100
90
80
70
60
50
40
30
20
10
0
1a
1b
1a
1b
80
70
60
50
40
30
20
10
0
200
100
50
25
12.5
200
100
50
25
12.5
Concentration (µg/ml)
Concentration (µg/ml)
(d) 70
60
(c) 100
1a
1b
1a
1b
80
60
40
20
0
50
40
30
20
10
0
200
100
50
25
12.5
200
100
50
25
12.5
Concentration (µg/ml)
Concentration (µg/ml)
Figure 3. Growth inhibition activities of compounds 1a and 1b on (A) S180 cell lines of 24 h, (B)
S180 cell lines of 48 h, (C) S180 cell lines of 72 h, and (D) H22 cell lines of 48 h. Each point
represents means of three independent experiments (SD % 7%).

Journal of Asian Natural Products Research
433
obtained on a Q-TOF Global mass spec- 3.3.1. Ergosterol-3-O-(2,3,4,6-tetra-O-
trometer (Waters Company, Miford, MA,
USA). Solvents were purified in the usual
way. Thin-layer chromatography was
performed on precoated Merck silica gel
60 F254 plates (Merck Corporation, Darm-
stadt, Germany). Flash column chromatog-
raphy was carried out using silica gel (200–
300 mesh, Qingdao Marine Chemical
Group Co., Qingdao, China).
benzoyl-b-D-glucopyranoside) (3a)
To a stirring solution of 2,3,4,6-tetra-O-
benzoyl-D-glucosyltrichloroacetimidate
(2a, 0.37 g, 0.5 mmol) in 15 ml of dry
˚
CH2Cl2 was added 4 A molecular sieves
(1.5 g) followed by ergosterol (0.22 g,
0.55 mmol) as a solid powder. It was
stirred for 0.5h at 08C, and then TMSOTf
(8.5ml, 0.05mmol) was added under Ar
protection. The mixture was continuously
stirred at 08C for 1 h and rt for another 0.5 h,
then neutralized with Et3N. The yellow
solution was diluted with CH2Cl2 and
filtered to remove the molecular sieves.
The organic layer was concentrated under
reduced pressure to give a yellow syrup,
which was purified by column chromatog-
raphy (EtOAc–petroleum ether, 10:1,
V:V) to afford compound 3a (462.9 mg,
0.475mmol, 95%) as a white power with Rf
0.55 (EtOAc–petroleum ether, 1:4, V:V).
3.2. Malignant cell inhibition studies
The inhibitory effects of 1a and 1b on the
growth of S180 and H22 cancer cells were
assessed by measuring the number of viable
cells surviving after treatment with 12.5, 25,
50, 100, and 200 mg/ml of tested com-
pounds for 1–3 days by the colorimetric
MTT assays. First, the anticancer effects of
these trimethyl-S180 and H22 malignant
cell lines were obtained from the Tianjin
University of Science and Technology. The
cell lines were maintained in a medium
consisting of RPMI 1640/FCS 10% at 378C
in an atmosphere of 5% CO2. Malignant cell
lines, 106 cells/ml in 96-well round bottom
plates (Costar Corporation, Cambridge,
MA, USA), were cultured with various
concentrations of 1a and 1b in a 5% CO2-air
humidified atmosphere at 378C. After 16,
40, and 64h of culture, MTT (3-(4,5-
dimethylthiazol-2-yl)-2,5-diphenyltetrazo-
lium bromide) was added to each well. MTT
uptake was measured after 6 h of incubation
using a scintillation counter. The inhibitory
effect of each compound on cell prolifer-
ation was calculated using Equation (1).
25
½aꢀD þ 6.45 (c ¼ 0.1, CH2Cl2); IR (KBr)
n
max cm21: 2958, 1737, 1491, 1092, 709; 1H
NMR (CDCl3) d (ppm): 8.05–7.28 (m, 20H,
ArH), 5.94 (t, J ¼ 9.6 Hz, 1H, H-30), 5.66 (t,
J ¼ 9.6 Hz, 1H, H-40), 5.54 (dd, J ¼ 9.6,
7.6 Hz, 1H, H-20), 5.36 (d, J ¼ 2.8 Hz, 1H,
H-6), 5.23 (dd, J ¼ 6.8, 3.6Hz, 1H, H-23),
5.13 (dd, J ¼ 10.0, 1.2 Hz, 1H, H-22), 5.00
(d, J ¼ 7.6 Hz, 1H, H-10), 4.64 (dd,
J ¼ 12.4, 3.6 Hz, 1H, H-60), 4.56 (dd,
J ¼ 10.0, 6.0 Hz, 1H, H-60), 4.22–4.18 (m,
1H, H-50), 3.71–3.63 (m, 1H, H-3), 1.15 (d,
J ¼ 6.0 Hz, 3H, CH3-21), 1.07 (d,
J ¼ 6.4 Hz, 3H, CH3-27), 0.95 (d,
J ¼ 7.2Hz, 3H, CH3-25), 0.91 (s, 3H,
Control group ðcpmÞ 2 Experimental group ðcpmÞ
Control group ðcpmÞ
Inhibition percent ð%Þ
¼
£ 100:
ð1Þ
3.3. Synthesis of 1a and 1b
CH3-19), 0.86 (t, J ¼ 6.4 Hz, 3H, CH3-28),
0.63 (s, 3H, CH3-18). HRESIMS m/z:
All reactions were carried out under argon
atmosphere in flame-dried glassware
unless otherwise stated.
997.4836
[M þ Na]þ
(calcd
for
C62H70O10Na, 997.4867).

434
Z.-Y. Zhu et al.
3033, 2871, 1728, 1602, 1492, 1315, 708; 1H
3.3.2. Ergosterol-3-O-(b-D-
glucopyranoside) (1a)
NMR (CDCl3) d (ppm): 8.15–7.25 (m, 20H,
ArH), 5.85–5.78 (m, 1H, H-40), 5.65–5.61
(m, 1H, H-20), 5.47 (dd, J ¼ 5.2, 1.6 Hz, 1H,
H-30), 5.37 (d, J ¼ 2.8 Hz, 1H, H-6), 5.23
(dd, J ¼ 12.4, 2.0 Hz, 1H, H-23), 5.13 (dd,
J ¼ 15.4, 8.8 Hz, 1H, H-22), 4.97 (d,
J ¼ 8.4 Hz, 1H, H-10), 4.71 (dd, J ¼ 11.2,
7.2 Hz, 1H, H-60), 4.47 (dd, J ¼ 11.2, 6.4 Hz,
1H, H-60), 4.37 (t, J ¼ 5.6 Hz, 1H, H-50),
3.74–3.63 (m, 1H, H-3), 1.28 (d, J ¼ 4.4 Hz,
3H, CH3-21), 1.07 (d, J ¼ 6.4 Hz, 3H,
CH3-27), 1.04 (s, 3H, CH3-19), 0.95 (d,
J ¼ 6.8 Hz, 3H, CH3-25), 0.86(t, J ¼ 6.8 Hz,
3H, CH3-28), 0.64 (s, 3H, CH3-18). HRE-
SIMS m/z: 997.4823 [M þ Na]þ (calcd for
C62H70O10Na, 997.4867).
Compound 3a (1 g, 1.03 mmol) was dis-
solved in MeOH–CH2Cl2 (1:1, 40 ml), and
then 40 mg NaOMe was added. After stirred
at rt for 3 h, the solution was neutralized with
ion-exchange resin (Hþ), and then filtered
and concentrated. The white residue was
purified by column chromatography
(CHCl3–MeOH 10:1 ! 6:1) to afford the
white solid 1a (0.57 g, 1.01 mol, 98.0%) with
the Rf 0.48 (CHCl3–MeOH, 6:1, V:V).
25
½aꢀD þ 12.2 (c ¼ 0.1, CH2Cl2); IR (KBr)
nmax cm21: 3385, 2956, 2871, 1457, 1369,
1
1027, 970; H NMR (DMSO-d6) d (ppm):
5.54 (d, J ¼ 4.8 Hz, 1H, H-6), 5.36–5.17 (m,
3H, H-7, 22, 23), 4.26 (d, J ¼ 7.8 Hz, 1H, H-
10), 3.61–3.56 (m, 1H, H-60), 3.45–3.43 (m,
2H, H-3, H-60), 3.16–3.03 (m, 3H, H-30, 40,
50), 2.40–2.91 (m, 1H, H-20), 1.02 (d,
J ¼ 6.6 Hz, 3H, CH3-21), 0.91 (t,
J ¼ 3.6 Hz, 3H, CH3-27), 0.89 (t,
J ¼ 6.6 Hz, 3H, CH3-25), 0.82 (t,
J ¼ 7.2 Hz, 3H, CH3-28), 0.62 (s, 3H, CH3-
19), 0.58 (s, 3H, CH3-18); 13C NMR
(DMSO-d6) d (ppm): 146.8 (C-8), 140.8
(C-5), 136.7 (C-22), 132.0 (C-23), 119.7
(C-6), 116.6 (C-7), 101.3 (C-10), 77.2 (C-50),
76.2 (C-30), 73.9 (C-20), 70.5 (C-40), 61.6
(C-60), 55.5 (C-17), 54.3 (C-14), 46.0 (C-9),
42.8 (C-13), 42.6 (C-24), 40.1 (C-20),
38.4 (C-12), 38.2 (C-4), 37.4 (C-1),
32.9 (C-25), 30.1 (C-2), 28.4 (C-10), 27.9
(C-16), 21.5 (C-15), 21.4 (C-26), 20.3
(C-11), 20.2 (C-21), 19.9 (C-27), 17.8
(C-28), 16.3 (C-19), 12.3 (C-18). HRESIMS
m/z: 581.3789 [M þ Na]þ (calcd for
C34H54O6Na, 581.3818).
3.3.4. Ergosterol-3-O-(b-D-
galactopyranoside) (1b)
The similar procedure for the preparation
of 1a was adopted, and thus 3b (1 g,
1.03 mmol) produced 1b (552.1 mg,
0.99 mol, 96.0%) as a white solid with
Rf 0.46 (CHCl3 –MeOH, 6:1, V:V).
25
½aꢀD þ 20.3 (c ¼ 0.1, CH2Cl2); IR (KBr)
n
max cm21: 3415, 2957, 2872, 1458, 1370,
1
1093, 1077, 802; H NMR (DMSO-d6) d
(ppm): 5.49 (d, J ¼ 5.4 Hz, 1H, H-6),
5.36–5.18 (m, 3H, H-7, 22, 23), 4.22 (d,
J ¼ 7.2 Hz, 1H, H-10), 3.50–3.57 (m, 1H,
H-40), 3.48–3.42 (m, 1H, H-60), 3.37–3.31
(m, 2H, H-60, H-3), 3.28–3.23 (m, 3H, H-
20, 30, 50), 1.02 (d, J ¼ 6.6 Hz, 3H, CH3-
21), 0.90 (t, J ¼ 3.6 Hz, 3H, CH3-27), 0.83
(t, J ¼ 4.2 Hz, 3H, CH3-25), 0.82 (t,
J ¼ 8.4 Hz, 3H, CH3-28), 0.61 (s, 3H,
CH3-19), 0.53 (s, 3H, CH3-18); 13C NMR
(DMSO-d6) d (ppm): 140.9 (C-8), 140.2
(C-5), 136.8 (C-23), 131.9 (C-22), 119.7
(C-6), 116.6 (C-7), 102.0 (C-10), 76.1 (C-
50), 75.5 (C-30), 73.9 (C-20), 71.1 (C-40),
68.6 (C-3), 60.9 (C-60), 55.5 (C-17), 54.4
(C-14), 46.0 (C-9), 42.8 (C-13), 42.5 (C-
24), 40.1 (C-20), 38.8 (C-12), 38.2 (C-4),
37.5 (C-1), 32.9 (C-25), 30.1 (C-2), 28.4
(C-10), 23.0 (C-16), 21.4 (C-15), 21.0 (C-
26), 20.2 (C-11), 20.1 (C-21), 19.9 (C-27),
3.3.3. Ergosterol-3-O-(2,3,4,6-tetra-O-
benzoyl-b-D-galactopyranoside) (3b)
The similar procedure for the preparation of
3a was adopted. Thus, ergosterol (0.22 g,
0.55 mmol) and 2b (0.37 g, 0.5 mmol)
produced 3b (453 mg, 0.465 mol, 93.0%) as
a white solid with Rf 0.41 (EtOAc–
25
petroleum ether, 1:4, V:V). ½aꢀD 2 9.5
(c ¼ 0.1, CH2Cl2); IR (KBr) nmax cm21
:

Journal of Asian Natural Products Research
435
Applications (CRC Press, New York,
2001), pp. 163–169.
[2] H. Kurt and M. Andrew, Saponins (Cam-
bridge University Press, New York,
1995).
17.8 (C-28), 16.4 (C-19), 12.3 (C-18).
HRESIMS m/z: 581.3793 [M þ Na]þ
(calcd for C34H54O6Na, 581.3818).
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Acknowledgments
This work was financially supported by
Program for Changjiang Scholars and Innova-
tive Research Team in University (IRT1166),
National Agricultural Innovation Project (No.
2011GB2A100009), Natural Science Foun-
dation of Tianjin City (No. 09JCZDJC21800),
the Foundation of Tianjin Educational Com-
mittee (No. 20090604), the Scientific and
Technical Supporting Programs of Science
and Technology Commission Foundation of
Tianjin (No. 08ZCGHHZ00800), National
Natural Science Foundation of China (NSFC,
No. 31000279), and Recruited faculty research
start-up foundation in Tianjin University of
Science and Technology (No. 0200060).
[12] F. Qu, Y.X. Li, and Y.C. Zhang, Chin.
J. Org. Chem. 23, 249 (2003).
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