Synthesis of stryphnoside A, a triterpene saponin isolated from the pericarps of Stryphnodendron fissuratum

Article abstract of DOI:10.1016/j.carres.2011.06.006

Stryphnoside A, α-L-rhamnopyranosyl 3β-O-[α-L- arabinopyranosyl-(1→4)-β-D-xylopyranosyl-(1→2) -β-Dglucopyranosyl]- 2α-hydroxyolean-12-en-28-oate, has been synthesized in 11 steps in 15% overall yield starting from the naturally abundant oleanolic acid. Co

Full text of DOI:10.1016/j.carres.2011.06.006

Carbohydrate Research 346 (2011) 1786–1791
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Carbohydrate Research
journal homepage: www.elsevier.com/locate/carres
Synthesis of stryphnoside A, a triterpene saponin isolated from the pericarps
of Stryphnodendron fissuratum
Xun Lv a,b, Shouyi Yu a,b, Jing Wang a, Yuguo Du a,b,
⇑
a State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
b College of Chemistry and Chemical Engineering, Graduate University of Chinese Academy of Sciences, Beijing 100049, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 9 April 2011
Received in revised form 3 June 2011
Accepted 6 June 2011
Available online 12 June 2011
Stryphnoside A,
glucopyranosyl]-2
starting from the naturally abundant oleanolic acid. Condensation of a partially protected glucopyranosyl
donor and 2 ,3b-dihydroxyolean-12-en-28-oic acid derivative using inverse glycosylation procedure has
significantly simplified the target saponin synthesis. Stryphnoside A exhibited weak cytotoxic activities
against tumor cells HeLa, A549, and HepG2 with IC50 at mM level.
Ó 2011 Elsevier Ltd. All rights reserved.
a
-
a
L
-rhamnopyranosyl 3b-O-[
-hydroxyolean-12-en-28-oate, has been synthesized in 11 steps in 15% overall yield
a-L-arabinopyranosyl-(1?4)-b-D-xylopyranosyl-(1?2)-b-D-
a
Keywords:
Stryphnosides
Glycosylation
Saponins
Natural products
Cytotoxicity
1. Introduction
obtain b glycosylation product, and at the same time facilitate the
continuous C-2 glycosylation.11,12 Herein, we report the total syn-
Saponins, as an important family of natural products, are widely
distributed in terrestrial plants and some lower marine animals.
The diversity of structures, the challenges of isolation and purifica-
tion, the broad spectrum of biological and pharmacological activities
have driven chemists to the research field of saponins.1–5 Stryphno-
sideA (1, Fig. 1) was originally isolatedfromthe pericarps ofstryphno-
dendron fissuratum, part of the stryphnodendron family where species
have long been used as medicinal plants for the treatment of hemor-
rhages, wounds, and diarrhea in Brazil.6 Interestingly, it was also sug-
gested that the fruit of this Brazilian plant could cause bovine death.7
On the basis of spectroscopic analysis and hydrolytic reactions, the
thesis of stryphnoside A applying this methodology.
2. Results and discussion
There are two challenges in stryphnoside A synthesis, namely,
b-D-glucopyranosylation on C-3 of 2a,3b-dihydroxyolean-12-en-
28-oic acid derivative, and the following C-20 sugar chain elonga-
tion on glucose residue. To provide a suitable aglycon acceptor,
2a-hydroxy-3-oxoolean-12-en-28-oic acid benzyl ester (2) was
prepared from the natural oleanolic acid according to a published
method (Scheme 1).13
chemical structure of stryphnoside A was elucidated as
pyranosyl 3b-O-[ -arabinopyranosyl-(1?4)-b- -xylopyranosyl-(1
?2)-b- -glucopyranosyl]-2
-hydroxyolean-12-en-28-oate (1).8 The
structural complexity, especially having a C-2 hydroxyl group and
a-L-rhamno-
Acetylation of 2 with Ac2O in pyridine (?3a), followed by
NaBH4 reduction, afforded benzyl-2a-acetyl-3b-hydroxyolean-
12-en-28-oic acid (4a) in 78% yield. Glycosylation of 4a and
a-L
D
D
a
a
C-3b/C-28 diglycosides on oleanolic acid derivative, has hindered
the chemical synthesis, and the successful examples are rarely re-
ported.9,10 Curious about the toxic activities of stryphnoside A, as well
as an intention to explore a practical synthetic strategy for the struc-
ture-related compounds, we launched a project toward the total syn-
thesis of stryphnoside A.
O
HO
O
C
HO
HO
O
O
HO
HO
In our previous research, we found that a thioglycoside having a
C-2 unprotected hydroxyl group could be a good glycosyl donor to
HO
O
H3C
HO
O
O
O
O
HO
HO
HO
HO
OH
1
⇑
Corresponding author. Tel./fax: +86 10 62849126.
E-mail addresses: duyuguo@rcees.ac.cn, duyuguo@mail.rcees.ac.cn (Y. Du).
Figure 1. Chemical structure of stryphnoside A.
0008-6215/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.carres.2011.06.006

X. Lv et al. / Carbohydrate Research 346 (2011) 1786–1791
1787
COOH
ref. 12
COOBn
d
COOBn
RO
O
RO
HO
HO
2 R = H
oleanolic acid
a
4a
4b
4c
R = Ac
R = Bn
R = MOM
3a R = Ac
3b R = Bn
3c R = MOM
b
c
OR
O
RO
+
SEt
RO
COOBn
e
R2O
O
OH
R1O
R1O
R1O
O
5a
5b
5c
R = Ac
R = Bn
R = Bz
OH
1
6a
6c
6e
6b
6d
6f
R
= R2 = Ac,
R
1 = Bn, R2 = Ac
1
1
R
= Ac, R2 = Bn,
R
= R2 = Bn
1
R
= Ac, R2 = MOM,
R
1 = Bn, R2 = MOM,
1 = Bz, R2 = MOM
6g
R
Scheme 1. Regents and conditions: (a) Ac2O, Pyr, rt, 6 h, 96%; (b) BnOC(NH)CCl3, TfOH, CH2Cl2, 0 °C, 91%; (c) iPr2EtN, CH3OCH2Cl, CH2Cl2, 0 °C?rt, 4 h, 88%; (d) NaBH4, THF/
EtOH; ꢀ20 °C, 48 h, 78% for 4a; rt, 20 h, 84% for 4b; rt, 16 h, 82% for 4c; (e) NIS, TMSOTf, CH2Cl2, ꢀ42 °C, 30 min, 36–87%.
ethyl 3,4,6-tri-O-acetyl-b-
D
-thioglucopyranoside (5a)14 in the
arabinose residue appeared at 4.50 ppm (J 5.5 Hz), while a multiple
peak at d 3.85 ppm corresponding to H-4 of xylose, confirming the
right structure of 11. Coupling of 11 and 6f in dry CH2Cl2 at low tem-
perature (ꢀ50 °C) was carried out smoothly in the presence of co-cat-
alyst NIS/TMSOTf, providing the desired saponin derivative 12 in a
good yield of 79%. Selective removal of MOM group20 from 12 with
catalytic amount of p-toluenesulfonic acid (?13, 86%), followed by
H2 hydrogenation over Pd(OH)2/C (?14, 91%) and acetylation with
presence of N-iodosuccinimide (NIS) and trimethylsilyl trifluoro-
methanesulfonate (TMSOTf) at ꢀ42 °C in CH2Cl2 gave messy
products. However, the same reaction proceeded smoothly with
‘inverse procedure’,15 that is, donor 5a and NIS in dry CH2Cl2
was added into a pre-cooled mixture of acceptor 4a and TMSOTf
in CH2Cl2, generating a major component in 66% yield, which
was carefully identified as the
a-anomer (d 5.07 ppm, J 3.9 Hz,
H-1). Surprised by this observation, we then studied the stereo
outcomes of this reaction using different protecting groups on
both glycosyl donor and acceptor. The results were summarized
Ac2O-pyridine in CH2Cl2, afforded 3b-O-[2,3,4-tri-O-acetyl-
nopyranosyl-(1?4)-2,3-di-O-acetyl-b- -xylopyranosyl-(1?2)-3,4,6
-tri-O-acetyl-b- -glucopyranosyl]-2 -hydroxyloleanolic acid (15) in
a yield of 70% over three steps. It was interesting that 2 -OH of olean-
a-L-arabi-
D
D
a
in Table 1. We found that coupling reaction between 2
a
-meth-
a
oxylmethylated (MOM) oleanolic acid derivative 4c and benzy-
lated thioglycoside 5b16 gave the best b-selectivity and good
yield under our conditions (entry 6, 6f).
olic acid derivative 15 could not be acetylated under the current
acetylation conditions. Condensation of acid 15 and 2,3,4-tri-O-acet-
yl-a-L
-rhamnopyranosyl trichloroacetimidate (16)21 in dry CH2Cl2 at
With compound 6f in hand, we started a formal convergent total
synthesisofstryphnosideA(Scheme 2). Zinc chloride promotedintra-
molecular rearrangement of the thio ortho ester 717 gave ethyl 2-O-
ꢀ78 °C using TMSOTf-catalyzed inverse procedure obtained acety-
lated stryphnoside A derivatives 17 (79%). Global deacetylation of
17 with catalytic amount of sodium methoxide in CH2Cl2–MeOH
co-solvent finished the total synthesis of stryphnoside A (1). Remark-
ably, this complex natural saponin was prepared convergently in 11
steps and in 15% overall yield. The characteristic data (1H, 13C NMR,
MS, and optical rotation) of the synthetic compound 1 were identical
to those reported for the natural product.8
acetyl-b-
TMSOTf catalyzed regioselective18 glycosylation of diol 8 and 2,3,4-
tri-O-acetyl-
-arabinopyranosyl trichloroacetimidate (9)19 was ap-
D-thioxylopyranoside (8) in an excellent yield of 92%.
a-L
plied in dry methylene dichloride at ꢀ42 °C with inverse procedure
(?10), followed by acetylation with acetic anhydride in pyridine, fur-
nished disaccharide donor ethyl 2,3,4-tri-O-acetyl-
a
-
L
-arabinopyr-
The cytotoxic activities of synthetic compound 1 on tumor cells
HeLa, A549, and HepG2, as well as two normal cell lines (HL7702
and H9C2), were evaluated following the standard MTT assay.22
As shown in Table 2, stryphnoside A (1) inhibited tumor cell
growth with IC50 ranging from 3.2 to 4.8 mM, while the corre-
anosyl-(1?4)-2,3-di-O-acetyl-b- -thioxylopyranoside (11) in 73%
D
isolated yield over two steps. Based on 2D NMR spectrum, H-1 of
sponding positive control showed inhibition at lM scale. Interest-
ingly, compound 1 exhibited a lower cytotoxicity to the normal
Table 1
Synthesis of the key intermediate 6
cells HL7702 and H9C2.
Entry
Donor
Acceptor
Product
Yielda (%)
a:b
In conclusion, the natural product stryphnoside A has been
chemically synthesized in 11 steps in 15% overall yield starting
from the natural abundant oleanolic acid and monosaccharides.
Applying a partially protected glucopyranosyl donor, combining
with inverse glycosylation procedure, has significantly simplified
the target saponin synthesis. The approach described here should
be valuable for structure-related8,13,23–26 molecule design, synthe-
sis, and bioactivity screening.
1
2
3
4
5
6
7
5a
5b
5a
5b
5a
5b
5c
4a
4a
4b
4b
4c
4c
4c
6a
6b
6c
6d
6e
6f
73
70
52
60
36
87
62
66:7
61:9
26:26
30:30
5:31
9:78
10:52
6g
a
Isolated total yield.

1788
X. Lv et al. / Carbohydrate Research 346 (2011) 1786–1791
OAc
O
O
a
b
HO
HO
HO
HO
O
O
SEt
O
AcO
SEt
RO
O
9
OAc
O
AcO
AcO
8
SEt
7
10
11
R = H
R = Ac
c
AcO
AcO
O
d
6f
AcO
9
OC(NH)CCl3
COOR3
R2O
O
R1O
R1O
O
OAc
R1O
O
O
O
AcO
O
AcO
AcO
AcO
1
R
= R3 = Bn, R2 = MOM
= R3 = Bn, R2 = H
= R2 = R3 = H
12
13
14
15
e
c
1
R
f
1
R
OC(NH)CCl3
1
R
= Ac, R2 = R3 = H
H3C
AcO
O
AcO
16
g
16
OAc
O
HO
O
C
RO
RO
O
O
OR
RO
RO
O
H3C
O
O
O
O
RO
RO
RO
RO
RO
OR
17 R = Ac
1 R = H
h
Scheme 2. Complete the total synthesis of stryphnoside A (1). Reagents and conditions: (a) ZnCl2, CH2Cl2, ꢀ78 °C, 92%; (b) TMSOTf, CH2Cl2, ꢀ15 °C, then 9; (c) Ac2O, Py; for
11, 73% from 8; for 15, 81% from 13; (d) NIS, TMSOTf, CH2Cl2, ꢀ50 °C, 79%; (e) TsOH, CH3OH, 86%; (f) Pd(OH)2/C, H2; (g) TMSOTf, CH2Cl2, ꢀ78 °C, then 16, 79%; (g) CH3ONa,
CH3OH–CH2Cl2, 91%.
Table 2
a
dropwise chloromethyl methyl ether (0.44 mL, 6.0 mmol) at 0 °C.
Cytotoxicity of compound 1 on tumor cells and normal cells (IC50
)
The mixture was stirred at 0 °C for 1 h and at rt for 3 h, then
quenched by addition of water and extracted with ether
(30 mL ꢁ 3). The combined organic layer was washed successively
with cold 0.2 N HCl, satd NaHCO3 solution, and water, then dried
over Na2SO4, and concentrated under diminished pressure. The
residue was purified by silica gel chromatography (30:1 petroleum
ether–EtOAc) to give 3c (532 mg, 88%): ½a2D5 +311 (c 2.3, CHCl3); 1H
NMR (400 MHz, CDCl3): d 7.35–7.30 (m, 5H, PhH), 5.28 (t, 1H, J
3.5 Hz, H-12), 5.10, 5.06 (2d, 2H, 12.5 Hz, PhCH2), 4.70 (s, 2H,
CH3OCH2), 4.54 (dd, 1H, J 6.0, 12.8 Hz, H-2), 3.38 (s, 3H, CH3OCH2),
2.22 (dd, 1H, J 3.8, 4.3 Hz, H-18), 2.01–0.55 (m, 41H). 13C NMR
(100 MHz, CDCl3): d 213.1, 177.3, 143.9, 136.4, 128.4, 128.0,
127.9, 121.9, 95.4, 65.9, 56.9, 55.6, 48.7, 47.4, 47.3, 46.6, 45.8,
41.7, 41.3, 39.3, 37.8, 33.8, 33.3, 32.3, 30.7, 27.5, 26.0, 25.8, 23.6,
22.9, 21.6, 19.2, 16.7, 16.1. Anal. Calcd for C39H56O5: C, 77.44; H,
9.33. Found: C, 77.62; H, 9.42.
Entry
Hela
A549
HepG
HL7702
H9C2
Compound 1 (mM)
Cisplatin (
3.6
26.1
4.8
>30.0
3.2
10.0
>6.0
n.d.
>6.0
n.d.
l
M)
a
Values are means of three independent experiments.
3. Experimental
3.1. General methods
Optical rotations were determined at 25 °C with a Perkin-Elmer
Model 241-Mc automatic polarimeter. 1H NMR and 13C NMR were
recorded with a Bruker ARX 400 spectrometer for solutions in
CDCl3 or CD3OD. Chemical shifts are given in ppm downfield from
internal Me4Si. Mass spectra were measured using a MALDITOF-
MS with
a-cyano-4-hydroxycinnamic acid (CCA) as matrix. Thin-
layer chromatography (TLC) was performed on silica gel HF254 with
detection by charring with 30% (v/v) H2SO4 in MeOH or in some
cases by UV detection. Column chromatography was conducted
by elution of a column of silica gel (100–200 mesh) with EtOAc–
petroleum ether (60–90 °C) as the eluent, or a column of Bio-Gel
P2 with water as the eluent. Solutions were concentrated at
<50 °C under reduced pressure.
3.3. Benzyl-2
oic acid (4c)
a-O-methoxymethyl-3b-hydroxyolean-12-en-28-
To a solution of 3c (605 mg, 1.0 mol) in THF (20 mL) and eth-
anol (4 mL) was added NaBH4 (45 mg, 1.2 mmol) at 0 °C. After the
mixture was stirred at 0 °C for 12 h, 1 N HCl (10 mL) was added
dropwise, and the mixture was extracted with EtOAc
(50 mL ꢁ 3). The organic layer was washed with saturated NaH-
CO3 (30 mL ꢁ 3) and brine (30 mL ꢁ 3), dried over Na2SO4, fil-
tered, and concentrated. The residue was purified by silica gel
chromatography (30:1 petroleum ether–EtOAc) to give 4c as a
3.2. Benzyl-2a-O-methoxymethyl-3-oxoolean-12-en-28-oic acid
(3c)
To a stirred mixture of 2 (561 mg, 1.0 mmol) and N,N-diisopro-
pylethylamine (0.52 mL, 3.0 mmol) in CH2Cl2 (30 mL) was added

X. Lv et al. / Carbohydrate Research 346 (2011) 1786–1791
1789
syrup (498 mg, 82%): ½aD25 +129 (c 1.3, CHCl3); 1H NMR (400 MHz,
CDCl3): d 7.34–7.30 (m, 5H, PhH), 5.28 (t, 1H, J 3.5 Hz, H-12), 5.10,
separated and dried over Na2SO4 and concentrated. The syrup
was treated with Ac2O (3 mL) in pyridine (3 mL) for 2 h, then con-
centrated to dryness. The residue was purified by silica gel col-
umn chromatography (2:1 petroleum ether–EtOAc) to give
disaccharide 11 as a white foam (392 mg, 73%): ½a2D5 ꢀ159 (c 1,
CHCl3); 1H NMR (400 MHz, CDCl3): d 5.23–5.21 (m, 1H, H-4’),
5.20 (t, 1H, J 8.8 Hz, H-3’), 5.04–5.02 (m, 2H, H-3, H-2’), 4.92 (t,
1H, J 9.2 Hz, H-2), 4.50 (d, 1H, J 5.5 Hz, H-1’), 4.47 (d, 1H, J
9.2 Hz, H-1), 4.01 (dd, 1H, J 12.4, 5.0 Hz, H-5a’), 3.98 (dd, 1H, J
6.5, 11.6 Hz, H-5a), 3.86–3.84 (m, 1H, H-4), 3.61 (dd, 1H, J 12.4,
2.4 Hz, H-5b’), 3.34 (dd, 1H, J 3.2, 11.6 Hz, H-5b), 2.67–2.64 (m,
2H, SCH2CH3), 2.10–2.03 (5s, 15H, 5Ac), 1.26 (t, 3H, SCH2CH3).
13C NMR (100 MHz, CDCl3): d 170.7, 170.4, 170.3, 169.7, 100.0,
84.4, 78.0, 74.4, 74.1, 70.7, 70.4, 69.8, 69.0, 68.0, 67.2, 62.1,
24.9, 21.4, 21.2, 15.5. Anal. Calcd for C22H32O13S: C, 49.25; H,
6.01. Found: C, 49.36; H, 5.90.
5.04 (2d, 2H, 12.5 Hz, PhCH2), 4.73, 4.69 (2d, 2H,
J 6.8 Hz,
CH3OCH2), 3.54–3.52 (m, 1H, H-2), 3.40 (s, 3H, CH3OCH2), 3.07
(d, 1H, J 9.4 Hz, H-3), 2.92 (dd, 1H, J 3.8, 4.3 Hz, H-18), 1.12,
1.06, 0.93, 0.92, 0.90, 0.83, 0.59 (7s, 7 ꢁ 3H, 7CH3). 13C NMR
(100 MHz, CDCl3): d 177.4, 143.8, 136.4, 128.4, 128.0, 127.9,
122.2, 96.6, 81.3, 78.6, 65.9, 55.6, 54.9, 47.5, 46.7, 45.8, 44.5,
41.7, 41.3, 39.3, 39.1, 38.1, 33.8, 33.1, 32.6, 32.3, 30.7, 28.8,
27.5, 25.9, 23.6, 23.5, 23.0, 18.1, 17.0, 16.8, 16.5. Anal. Calcd for
C39H58O5: C, 77.19; H, 9.63. Found: C, 77.04; H, 9.72.
3.4. Benzyl-3b-O-(3,4,6-tri-O-benzyl-b-
D-glucopyranosyl)-2a-O-
methoxymethylolean-12-en-28-oic acid (6f)
To a solution of 4c (61 mg, 0.10 mmol) containing 4 Å molecu-
lar sieves in anhyd CH2Cl2 (5 mL) was added TMSOTf (0.9 L,
l
0.050 mmol) under N2 atmosphere at ꢀ42 °C. After stirring for
10 min, a solution of 5b (55 mg, 0.11 mmol) and NIS (37 mg,
0.16 mmol) in CH2Cl2 (5 mL) was added dropwise. The mixture
was stirred under these conditions for 20 min, quenched by
Et3N, diluted with CH2Cl2, and washed with aq Na2S2O3. The or-
ganic layer was dried over Na2SO4 and concentrated. The residue
was purified by silica gel column chromatography (3:1 petroleum
ether–EtOAc) to give compound 6f as a white foam (81 mg, 78%):
3.7. Benzyl-3b-O-[2,3,4-tri-O-acetyl-
(1?4)-2,3-di-O-acetyl-b- -xylopyranosyl-(1?2)-3,4,6-tri-O-
benzyl-b- -glucopyranosyl]-2 -O-methoxymethylolean-12-en-
28-oic acid (12)
a-L-arabinopyranosyl-
D
D
a
To
0.24 mmol), NIS (81 mg, 0.36 mmol), and 4 Å molecular sieves in
anhyd CH2Cl2 (10 mL) was added TMSOTf (2.2 L, 0.012 mmol) un-
a mixture of 6f (208 mg, 0.20 mmol), 11 (129 mg,
l
½
a2D5 +97 (c 1.1, CHCl3); 1H NMR (400 MHz, CDCl3): d 7.36–7.20 (m,
der N2 protection at ꢀ50 °C. The mixture was stirred at these con-
ditions for 40 min, quenched by Et3N, diluted with CH2Cl2 (30 mL),
and washed with aq Na2S2O3. The organic layer was dried over
Na2SO4 and concentrated. The residue was purified by silica gel
column chromatography (2:1 petroleum ether–EtOAc) to give
compound 12 as a white foamy solid (239 mg, 79%): ½a2D5 +92 (c
0.9, CHCl3); 1H NMR (400 MHz, CDCl3): d 7.41–7.20 (m, 20H,
5PhH), 5.30 (t, 1H, J 3.5 Hz, H-12), 5.22 (d, 2H, 1.5 Hz), 5.13–5.00
(m, 6H), 4.91–4.79 (m, 4H), 4.74 (d, 1H, J 10.0 Hz), 4.63–4.54 (m,
4H), 4.47 (d, 1H, J 3.2 Hz), 4.41 (d, 1H, J 7.6 Hz), 3.99–3.96 (m,
2H), 3.80–3.58 (m, 8H), 3.38 (d, 1H, J 7.7 Hz), 3.29 (s, 3H), 3.11 (t,
2H), 2.92 (dd, 1H, J 3.8, 4.3 Hz), 2.67–2.65 (m, 2H, SCH2CH3),
2.12–2.04 (5s, 5 ꢁ 3H, 5Ac), 1.12, 1.07, 0.96, 0.93, 0.91, 0.88, 0.60
(7s, 7 ꢁ 3H, 7CH3). 13C NMR (100 MHz, CDCl3): d 178.0, 170.8,
170.7, 170.5, 170.0, 169.7, 144.3, 138.9, 138.6, 138.4, 137.0,
129.4, 129.0, 128.9, 128.8, 128.6, 128.5, 128.4, 128.3, 128.2,
128.1, 122.9, 103.9, 100.5, 100.4, 98.6, 93.0, 86.8, 79.1, 77.9, 76.2,
76.0, 75.4, 75.2, 74.5, 74.0, 73.8, 72.6, 70.0, 69.8, 69.5, 67.4, 66.5,
63.5, 62.4, 55.7, 48.2, 47.3, 46.4, 42.3, 41.9, 41.6, 39.9, 38.3, 34.4,
33.7, 33.2, 33.0, 31.3, 30.3, 30.2, 28.7, 28.1, 26.4, 24.2, 24.1, 23.6,
20H, 5PhH), 5.29 (t, 1H, J 3.5 Hz, H-12), 5.10, 5.07 (2d, 2H,
J 12.5 Hz, PhCH2), 4.95–4.81 (m, 4H, 2PhCH2), 4.61–4.55 (m,
4H), 4.48 (d, 1H, 7.2 Hz, H-10), 3.77–3.68 (m, 3H), 3.61–3.56 (m,
3H), 3.46–3.44 (m, 1H, H-20), 3.30 (s, 3H, CH3OCH2), 3.24 (d, 1H,
J 9.5 Hz, H-3), 2.92 (dd, 1H, J 3.8, 4.3 Hz, H-18), 2.54 (d, 1H,
J 1.6 Hz), 1.11, 1.08, 0.96, 0.93, 0.91, 0.87, 0.59 (7s, 7 ꢁ 3H,
7CH3). 13C NMR (100 MHz, CDCl3): d 177.4, 143.7, 138.7, 138.4,
138.2, 136.4, 128.4, 128.3, 128.0, 127.9, 127.5, 122.3, 104.0,
97.6, 90.3, 84.9, 75.6, 75.2, 75.1, 74.9, 74.1, 73.4, 69.1, 65.9,
55.2, 54.9, 47.6, 46.3, 45.8, 41.7, 41.3, 40.7, 39.2, 39.1, 37.7,
33.8, 33.1, 32.6, 32.3, 30.7, 28.7, 27.5, 25.8, 23.6, 23.5, 23.0,
18.1, 18.0, 16.8, 16.5. Anal. Calcd for C66H86O10: C, 76.27; H,
8.34. Found: C, 76.14; H, 8.50.
3.5. Ethyl 2-O-acetyl-1-thio-b-D-xylopyranoside (8)
To a solution of carefully dried 7 (2.4 g, 10.0 mmol) in dry CH2Cl2
(100 mL) was added zinc chloride (1 M in ether, 0.5 mL, 0.50 mmol)
at ꢀ78 °C. The mixture was stirred at these conditions for 30 min,
warmed up to 0 °C in 30 min, then quenched with saturated aqueous
NaHCO3 (50 mL). The organic layer was separated, the water phase
was extracted with CH2Cl2 (20 mL ꢁ 3), and the combined organic
phase was dried over Na2SO4 and concentrated to dryness. The syrup
was purified by silica gel column chromatography (2:1 petroleum
ether–EtOAc) to give 8 as a white amorphous solid (2.2 g, 92%):
21.5, 21.3, 21.2, 18.7, 17.9, 17.4, 17.2. Anal. Calcd for C86H112O23
C, 68.23; H, 7.46. Found: C, 67.98; H, 7.60.
:
3.8. Benzyl-3b-O-[2,3,4-tri-O-acetyl-
(1?4)-2,3-di-O-acetyl-b- -xylopyranosyl-(1?2)-3,4,6-tri-O-
-glucopyranosyl]-2 -hydroxyolean-12-en-28-oic acid
a-L-arabinopyranosyl-
D
benzyl-b-
D
a
½
a2D5 +135 (c 2.3, CHCl3); 1H NMR (400 MHz, CDCl3): d 4.76 (t, 1H, J
(13)
9.1 Hz, H-2), 4.40 (d, 1H, J 9.4 Hz, H-1), 4.09–4.07 (m, 1H, H-4),
3.74–3.53 (m, 4H), 3.27 (t, 1H, J 10.1 Hz, H-3), 2.68–2.66 (m, 2H,
SCH2CH3), 2.13 (s, 3H, Ac), 1.25 (t, 3H, SCH2CH3). Anal. Calcd for
C9H16O5S: C, 45.75; H, 6.83. Found: C, 45.61; H, 6.94.
A
mixture of 12 (151 mg, 0.10 mmol) and TsOH (76 mg,
0.40 mmol) in MeOH (15 mL) was stirred at rt for 4 h, then
quenched with Et3N and concentrated. The residue was purified
by silica gel column chromatography (2:1 petroleum ether–EtOAc)
to give 13 as a foamy solid (126 mg, 86%): ½a2D5 +20 (c 2.7, CHCl3);
1H NMR (400 MHz, CDCl3): d 7.38–7.22 (m, 20H, 5PhH), 5.26 (t,
1H, J 3.5 Hz, H-12), 5.18 (m, 1H), 5.08–4.94 (m, 6H), 4.87–4.82
(m, 2H), 4.74 (t, 2H, J 11.2 Hz), 4.57–4.52 (m, 2H), 4.45–4.42 (m,
2H), 4.28 (d, 1H, J 7.8 Hz), 3.95–3.87 (m, 2H), 3.80–3.70 (m, 3H),
3.64–3.54 (m, 5H), 3.48–3.46 (m, 1H), 3.11 (t, 1H, J 11.4 Hz), 2.88
(d, 1H, J 9.2 Hz), 2.07–1.98 (5s, 15H, 5 Ac), 1.07, 1.05, 0.91, 0.88,
0.86, 0.85, 0.57 (7s, 7 ꢁ 3H, 7CH3). 13C NMR (100 MHz, CDCl3): d
178.1, 170.8, 170.7, 170.5, 169.9, 169.7, 144.2, 138.5, 138.3,
3.6. Ethyl 2,3,4–tri-O-acetyl-a-L-arabinopyranosyl-(1?4)-2,3-di-
O-acetyl-1-thio-b- -xylopyranoside (11)
D
To a pre-cooled mixture of 8 (236 mg, 1.0 mmol) and 4 Å
molecular sieves in anhyd CH2Cl2 (20 mL) was added TMSOTf
(18
l
L, 0.10 mmol) under N2 atmosphere at ꢀ15 °C. After stirring
at these conditions for 10 min, a solution of 9 (463 mg, 1.1 mmol)
in CH2Cl2 (20 mL) was added dropwise. The mixture was stirred
for another 30 min, quenched by Et3N. The organic layer was

1790
X. Lv et al. / Carbohydrate Research 346 (2011) 1786–1791
138.2, 137.0, 129.4, 129.1, 129.0, 128.9, 128.5, 128.4, 128.2, 122.9,
104.0, 101.0, 100.4, 97.5, 86.2, 78.6, 76.4, 76.1, 75.6, 75.3, 74.3,
73.9, 72.6, 69.9, 69.8, 69.1, 67.3, 67.0, 66.5, 63.8, 62.3, 56.1, 48.2,
47.3, 46.9, 46.4, 42.2, 41.9, 41.1, 39.9, 38.1, 34.5, 33.7, 33.2, 33.0,
31.3, 30.3, 29.9, 28.6, 28.2, 26.8, 24.2, 24.0, 23.6, 21.5, 21.4, 21.3,
21.2, 20.1, 18.8, 17.8, 17.5, 17.7. MALDITOF–MS: calcd for
170.3, 170.2, 169.7, 144.2, 123.4, 103.8, 101.8, 100.2, 98.3, 90.7,
77.0, 75.5, 73.8, 72.2, 72.1, 70.9, 69.9, 69.6, 69.5, 69.3, 69.1,
67.3, 66.8, 63.9, 62.3, 62.2, 56.1, 48.1, 47.8, 46.8, 46.2, 42.4,
42.2, 41.2, 39.9, 38.1, 34.3, 33.6, 33.2, 33.1, 31.3, 30.3, 28.4,
28.0, 26.4, 24.0 (2C), 23.5, 21.8, 21.5, 21.4, 21.3, 21.2, 21.1, 21.0,
18.8, 18.1, 17.7, 17.5, 17.1. MALDITOF-MS: calcd for C74H106O32:
C
56H84O22: 1468.7 [M]+; found, 1491.9 [M+Na]+, 1507.9 [M+K]+.
1506.7 [M]+; found, 1529.7 [M+Na]+. Anal. Calcd for C74H106O32
C, 58.95; H, 7.09. Found: C, 59.18; H, 6.97.
:
Anal. Calcd for C84H108O22: C, 68.64; H, 7.41. Found: C, 68.82; H,
7.54.
3.11.
b- -xylopyranosyl-(1?2)-b-
-12-en-28-oate (1)
a
-
L
-Rhamnopyranosyl 3b-O-[
a
-
L
-arabinopyranosyl-(1?4)-
-hydroxyolean
3.9. 3b-O-[2,3,4-Tri-O-acetyl-
di-O-acetyl-b- -xylopyranosyl-(1?2)-3,4,6-tri-O-acetyl-b-
glucopyranosyl]-2 -hydroxyolean-12-en-28-oic acid (15)
a
-
L
-arabinopyranosyl-(1?4)-2,3-
D
D
-glucopyranosyl]-2a
D
D-
a
To a stirred solution of 17 (60 mg, 0.04 mmol) in MeOH/CH2Cl2
(v/v, 1:1, 10 mL) was added 1 M NaOMe until pH 10 was reached.
The mixture was stirred at rt for 3 h at pH 9, then neutralized with
Dowex-50 (H+) ion exchange resin, filtered, and the filtrate was
concentrated. The residue was purified by a Bio-Gel P2 column
using H2O as eluent, and the desired fractions were combined
and freeze dried to afford 1 as an amorphous solid (38 mg, 91%):
To a solution of 13 (180 mg, 0.12 mmol) in EtOAc/ethanol
(60 mL, v/v 1:1) at rt was added Pd(OH)2/C (60 mg). The suspen-
sion was stirred under hydrogen pressure (3 atm) for 0.5 h and
then filtered. The filtrate was concentrated, and the residue was
purified by silica gel column chromatography (EtOAc) to afford
14 as a foamy solid. MALDITOF-MS: calcd for C56H84O22: 1108.5
[M]+; found, 1131.8 [M+Na]+, 1147.8 [M+K]+. To the above inter-
mediate 14 (112 mg, 0.10 mmol) in CH2Cl2 (20 mL) was added pyr-
idine (5 mL) and Ac2O (3 mL) at rt. The solution was stirred at rt for
18 h and concentrated to dryness with the help of toluene. The res-
idue was purified by silica gel chromatography (1:1 petroleum
ether–EtOAc) to afford 15 as a foamy solid (120 mg, 81%): ½aD25
+35 (c 1.1, CHCl3); 1H NMR (400 MHz, CDCl3): d 5.27 (t, 1H, J
3.5 Hz), 5.20–5.18 (m, 2H), 5.07–4.97 (m, 3H), 4.91 (t, 1H, J
9.7 Hz), 4.78 (t, 1H, J 8.2 Hz), 4.59 (d, 1H, J 8.0 Hz), 4.67 (d, 1H, J
5.3 Hz), 4.43 (d, 1H, J 7.7 Hz), 4.18–4.10 (m, 2H), 3.98–3.92 (m,
2H), 3.87–3.72 (m, 4H), 3.57 (dd, 1H, J 10.3, 2.0 Hz), 3.23 (t, 1H, J
11.4 Hz), 2.92 (d, 1H, J 9.2 Hz), 2.80 (dd, 1H, J 10.1, 3.5 Hz), 2.06–
1.98 (m, 24H, 8Ac), 1.11, 1.05, 0.97, 0.92, 0.89, 0.87, 0.74 (7s,
7 ꢁ 3H, 7CH3). 13C NMR (100 MHz, CDCl3): d 183.5, 171.2, 170.7
(2C), 170.6, 170.5, 170.3, 170.2, 169.7, 144.0, 123.1, 103.8, 101.8,
100.1, 98.3, 77.0, 75.5, 73.8, 72.2, 72.1, 69.9, 69.8, 69.2, 67.3,
66.9, 63.7, 62.3, 61.0, 56.0, 48.2, 47.0, 46.8, 46.4, 41.6, 41.2, 39.9,
38.1, 34.4, 33.6, 33.2, 33.0, 31.3, 30.9, 28.4, 28.1, 26.5, 24.1, 24.0,
23.5, 21.5, 21.4, 21.3, 21.2, 21.1, 18.8, 17.5, 17.4, 17.1. MALDI-
½
a2D5 ꢀ55 (c 0.4, CH3OH); Selected 1H NMR (400 MHz, CD3OD): d
6.01 (d, 1H, J 1.8 Hz, H-1Rha), 5.29 (br s, 1H, H-12), 4.60 (d, 1H, J
7.6 Hz, H-1Xyl), 4.39 (d, 1H, J 7.4 Hz, H-1Glc), 4.24 (d, 1H, J 6.9 Hz,
H-1Ara), 3.88–3.21 (m, 21H), 2.98 (d, 1H, J 8.8 Hz), 2.92 (dd, 1H, J
10.6, 3.5 Hz, H-18), 1.24 (d, 3H, J 6.1 Hz, H-6Rha), 1.18, 1.12, 1.02,
0.97, 0.93, 0.90, 0.80 (7s, 7 ꢁ 3H, 7CH3). 13C NMR (100 MHz, CDCl3):
d 176.3, 144.1, 123.4, 104.9, 103.8, 103.0, 95.6, 94.1, 81.6, 77.7, 77.2
(2C), 75.3, 75.0, 73.3 (2C), 72.6 (2C), 71.6, 71.2, 70.6, 70.2, 68.9,
67.1, 66.5, 63.9, 61.4, 55.9, 48.8 (2C), 47.5, 46.7, 45.1, 40.9, 39.9,
37.9, 33.9, 33.2, 33.0, 32.6, 30.8, 27.4 (2C), 25.6, 23.8, 23.2, 23.1,
18.5, 17.4, 17.3, 16.8, 16.3. MALDITOF-MS: calcd for C62H90O25
:
1044.6 [M]+; found, 1067.9 [M+Na]+. Anal. Calcd for C52H84O21: C,
59.75; H, 8.10. Found: C, 59.49; H, 8.19.
Acknowledgments
This work was supported in partial by NNSF of China (projects
20872172, 20732001, 20921063, and 20890112). We would like
to thank Dr. Jianjun Zhang of CAU for providing compounds 9
and 16 as the starting materials.
TOF–MS: calcd for
C62H90O25:
1234.6 [M]+; found, 1257.6
[M+Na]+. Anal. Calcd for C62H90O25: C, 60.28; H, 7.34. Found: C,
60.43; H, 7.30.
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