Facile synthesis of four natural triterpene saponins with important antitumor activity

Article abstract of DOI:10.1080/00397910903576602

The first synthesis of four natural triterpene saponins, which exhibit significant antitumor activities, was concisely achieved by adopting a stepwise glycosylation. The key intermediate 13 was afforded via Bu2SnO-mediated regioseletive benzoylation. Duri

Full text of DOI:10.1080/00397910903576602

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Facile Synthesis of Four Natural
Triterpene Saponins with Important
Antitumor Activity
Tiantian Guo a , Qingchao Liu a , Lei Zhang a , Peng Wang a & Yingxia
Li b
a School of Medicine and Pharmacy, Ocean University of China,
Qingdao, China
b School of Pharmacy, Fudan University, Shanghai, China
Version of record first published: 13 Jan 2011.
To cite this article: Tiantian Guo, Qingchao Liu, Lei Zhang, Peng Wang & Yingxia Li (2011):
Facile Synthesis of Four Natural Triterpene Saponins with Important Antitumor Activity, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry,
41:3, 357-371
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Synthetic Communications1, 41: 357–371, 2011
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397910903576602
FACILE SYNTHESIS OF FOUR NATURAL TRITERPENE
SAPONINS WITH IMPORTANT ANTITUMOR ACTIVITY
Tiantian Guo,1 Qingchao Liu,1 Lei Zhang,1 Peng Wang,1 and
Yingxia Li2
1School of Medicine and Pharmacy, Ocean University of China,
Qingdao, China
2School of Pharmacy, Fudan University, Shanghai, China
The first synthesis of four natural triterpene saponins, which exhibit significant antitumor
activities, was concisely achieved by adopting a stepwise glycosylation. The key inter-
mediate 13 was afforded via Bu2SnO-mediated regioseletive benzoylation. During the
preparation of the target compounds, it was found that the a-L-arabinopyranosyl unit in
intermediates 17 and 20 existed in the unusual 1C4 conformation, and after removing the
benzoyl groups, the a-L-arabinopyranosyl unit was normal in a typical 4C1 form.
Keywords: Antitumor activities; Bu2SnO-mediated regioseletive benzoylation; glycosylation; glycosyl
trichloroacetimidate; triterpene saponins
INTRODUCTION
Saponins are a large family of natural products that are composed of a sac-
charide attached to a triterpene or steroid. Triterpene saponins have been isolated
from a great number of terrestrial plants with great variety of structures and bioac-
tivities.[1] Among these triterpene saponins, quite a lot of compounds were found to
exhibit remarkable cytotoxicity or antiproliferative activities.[2] For example,
3-O-[O-b-D-glucopyranosyl-(1!2)-O-a-D-xylopyranosyl] oleanolic acid (1) and
3-O-[O-b-D-glucopyranosyl-(1!2)-O-a-L-arabinopyranosyl] oleanolic acid (2) iso-
lated from the rhizomes of Anemone flaccida show significant cytotoxic activity
in vitro against different tumor cell lines, of which the inhibitory rate against the
human leukemia cell line HL-60 was 76.1% at a concentration of 10 mg=mL.[3]
Besides, 3-O-[O-b-D-glucopyranosyl-(1!3)-O-a-L-rhamnopyranosyl-(1!2)-O-a-
L-arabinopyranosyl] oleanolic acid (3) isolated from the roots of Pulsatilla chinensis
also exhibits important cytotoxic activity against HL-60 human leukemia cell with
an IC50 value of 3.6 mg=mL.[4] Furthermore, 3-O-[O-b-D-glucopyranosyl-(1!3)-O-
a-L-rhamnopyranosyl-(1!2)-O-b-L-xylopyranosyl] oleanolic acid (4) isolated
from Dahurian patrinia root and rhizome of Patrinia scabiosaefolia is one of the
Received June 11, 2009.
Address correspondence to Yingxia Li, School of Pharmacy, Fudan University, Shanghai 201203,
China. E-mail: liyx417@fudan.edu.cn
357

358
T. GUO ET AL.
Figure 1. Structures of target compounds 1, 2, 3, and 4.
main bioactive fractions (Fig. 1).[5] Based on the bioactivity study of these triterpene
saponins, we were interested in conveniently preparing this kind of saponins to pro-
mote further structure–activity relationship (SAR) studies for development of desir-
able antitumor agents. Herein, we report the chemical synthesis of the four natural
triterpene saponins.
RESULTS AND DISCUSSION
Construction of the glycosidic linkage with the aglycone is critical in the
synthesis of saponins. For strategical consideration, saponins with one sugar moiety
are much easier synthetic targets than those with two or more sugar moieties.
Analyzing the structures of the target saponins 1, 2, 3 and 4, we find that they are
characterized by a 20-OH linear sugar chain on C-3 of oleanolic acid and 1,2-
trans-glycoside linkage between sugars and aglycone. It is known that a mixture of
a- and b-anomers would be obtained without a neighboring participating group at
C-2 of sugar donor, and the ortho ester formation or the acyl transfer with small
acyl protecting group (such as acetyl) at C-2 of sugar donor would be predominant
side reactions.[6] As a matter of fact, the use of 2-O-benzoyl-glycosyl donors was
an efficient approach to produce a unique 1,2-trans-glycoside linkage in saponin
synthesis.[6b,7] Consequently, stepwise glycosylation fashion, a strategy for saponin
synthesis, was adopted to construct the target molecules with the use of 2-O-benzoyl-
glycosyl tricholoacetimidates as donors.
Glycosyl trichloroacetimidates 5–7 that are involved in the synthesis were easily
afforded in satisfactory yields via reactions of corresponding sugar hemiacetals with
trichloroacetonitrile in the presence of 1,8-diazabicyclo-[5.4.0]undec-7-ene (DBU) in
CH2Cl2.[6] The key glycosylated intermediates 13 and 14[8] were prepared as shown in
Scheme 1. Glycosylation of benzyl ester 8[8] with glycosyl donors 5 in the presence of a
catalytic amount of trimethylsilyl trifluoromethanesulfonate (TMSOTf) was per-
formed to afford the desired 1,2-trans-glycosidic product 9 exclusively in an excellent
yield. Meanwhile, glycosylation of benzyl ester 8[6] with glycosyl donor 6 in the pres-
ence of a catalytic amount of TMSOTf was performed to provide the desired product
10 in a 96.5% yield. Removal of the benzoyl groups from the glycosyl residues of 9

FOUR NATURAL TRITERPENE SAPONINS
359
Scheme 1. Synthesis of the key intermediates 13 and 14. Reagents and conditions: (a) TMSOTf (0.1 equiv.),
ꢀ
˚
CH2Cl2, 4 A MS, 0 C to rt, 98.7% for 9, 95.6% for 10; (b) NaOMe, CH3OH-CH2Cl2 (v:v, 2:1), 100% for 11,
100% for 12; (c) Bu2SnO, toluene, reflux; BzCl (2.0 equiv.), 89.7%; (d) PPTs, DMP, rt, 92.5%.
and 10 with NaOMe in MeOH and CH2Cl2 provided the corresponding saponin deri-
vatives 11 and 12. Then we focused on the regioselective protection of 3,4-OHs of gly-
cosyl moieties in order to introduce the glucopyranosyl residue at 2-OH of
D-xylopyranosyl and L-arabinopyranosyl moieties. Selective protection of the equa-
torial 3,4-OHs of 11 was examined via organotin-mediated regioseletive benzoyla-
tion.[9] Thus, treatment of compound 11 with Bu2SnO in anhydrous toluene under
azeotropic conditions followed by 2.0 equiv. BzCl and a catalytic amount of dimethy-
laminopyridine (DMAP) at 0 ꢀC led to the expected 3,4-di-O-benzoylated product 13
1
in a satisfactory 89.7% yield. In the H NMR of 13, the H-30 and H-40 signals all
appeared downfield at d 5.57 and 5.27 ppm, which clearly proved the regioselectivity
of benzoylation. Selective protection of the 3,4-OHs of 12 was carried out with the use
of 2,2-dimethoxypropane (DMP) and pyridinium toluene-4-sulphonates (PPTs),
providing the isopropylidenated product 14 in an excellent 92.5% yield.[8a,10]
For target compounds 1 and 2, the next work was to introduce the glucopyr-
anosyl residue at 20-OH of compounds 13 and 14 (Scheme 2). Glycosylation of 13
and 14 with 2,3,4,6-tetra-O-benzoyl-D-glucopyranosyl trichloroacetimidate 7 under
the action of TMSOTf (0.1 equiv.) led to the desired products 15 and 16 in good
yields. After removal of isopropylidene of 16 with 80% HOAc,[7c,10] we found that

360
T. GUO ET AL.
Scheme 2. Synthesis ofꢀthe target compounds 1 and 2. Reagents and conditꢀions: (a) TMSOTf (0.1 equiv.),
˚
CH2Cl2, 4 A MS, ꢁ20 C, 89.7% for 15, 90.6% for 16; (b) 80% HOAc, 60 C, 89.8%; (c) H2, 10% Pd=C,
CH3OH-CH2Cl2 (v:v, 1:1), rt, then NaOCH3, CH3OH-CH2Cl2 (v:v, 2:1), rt, 81.5% for 1, 80.7% for 2.
1
0
0
0
0
the J1 -2 proton coupling constant of 17 was small (J1 -2 ¼ 3.6 Hz) in H NMR
spectra, which suggested that the arabinose ring may adopt the unusual 1C4
conformation rather than the typical C1 form. This phenomenon was consistent
4
with those reported in the literature.[7c,11] Removal of the 28-O-benzyl group in 15
and 17 by hydrogenolysis in the presence of Pd=C, followed by removal of the
benzoyl groups on the sugar residues with NaOMe in MeOH and CH2Cl2 afforded
the expected natural saponins 1 and 2 in satisfactory yields, in which the arabinosyl
moiety of 2 became normal in a typical 1C4 form. All the analytical data for
the synthesized triterpene saponins 1 and 2 are identical to those reported in the
literature.[5,12,13]

FOUR NATURAL TRITERPENE SAPONINS
361
Natural triterpene saponins 3 and 4 were further synthesized from the key
intermediates 13 and 14 (Scheme 3). Recently, we just synthesized three bidesmosi-
dic triterpene saponins in a one-pot strategy under the combined use of glycosyl
trichloroacetimidates and p-toluene 1-thioglycosides (STol) donors,[14] so we
decided to complete the synthesis of compounds 3 and 4 via the one-pot strategy.
As depicted in Scheme 3, coupling of p-toluene thioglycoside 9[14] with imidate 7
was completed within 45 min with the use of a catalytic amount of TMSOTf (0.2
equiv.) at ꢁ78 ꢀC, providing the desired disaccharide p-toluene thioglycoside donor,
Without purification, the reaction mixture was warmed to ꢁ10 ꢀC, and then sap-
onin acceptor 13 or 14 was added, followed by addition of N-iodosuccinimide
(NIS) (2.0 equiv.) and TMSOTf (0.5 equiv.), affording the fully protected saponin
18 or 19 in a satisfactory yield. By removing the isopropylidene of 18 with 80%
HOAc at 60 ꢀC, intermidiate 20 was achieved in 92.3% yield. Interestingly, the ara-
1
4
binosyl residue in 20 also adopted a C4 conformation instead of the typical C1
form. This conformational assignment was supported by a broad single peak of
Scheme 3. Synthesis of the target compounds 3 and 4. Reagents and conditions: (a) TMSOTf (0.2 equiv.),
ꢀ
ꢀ
˚
˚
CH2Cl2, 4 A MS, ꢁ78 C; (b) NIS (2.0 equiv.), TMSOTf (0.5 equiv.), CH2Cl2, 4 A MS, ꢁ10 C, 78.1% for
18 (two steps), 75.3% for 19 (two steps); (c) 80% HOAc, 60 ꢀC, 92.3%; (d) H2, 10% Pd=C, CH3OH-CH2Cl2
(v:v, 1:1), rt; then NaOCH3, CH3OH-CH2Cl2 (v:v, 2:1), rt, 79.5% for 3, 81.1% for 4.

362
T. GUO ET AL.
the H-10 signal of anabinosyl moiety of 20. This phenomenon was consistent with
those reported in the literature.[7c,11] Removal of the 28-O-benzyl group in 19 and
20 by hydrogenolysis in the presence of Pd=C, followed by removal of the benzoyl
groups on the sugar residues with NaOMe in MeOH and CH2Cl2, afforded the
expected natural saponins 4 and 3 in satisfactory yields, in which the arabinosyl
4
moiety of 3 returned to the normal C1 conformation, and this was supported by
comparison of the H-10 signal of anabinosyl moiety of compound 3 (J1 ,2 6.0 Hz)
0
0
0
0
to that of compound 20 (J1 ,2 br s). The physical data of 3 and 4 are in agreement
with the literature reported.[4,5]
In conclusion, the first synthesis of the natural triterpene saponins 1, 2, 3, and 4
was efficiently achieved. Further investigation on preparation and bioactivity evalu-
ation of their derivatives is currently under way in our research group.
EXPERIMENTAL
General Methods
Solvents were purified in the usual way. Thin-layer chromatography (TLC) was
performed on precoated Merck silica-gel 60 F254 plates. Flash column chromato-
graphy was performed on silica gel (200–300 mesh, Qingdao, China). Optical
rotations were determined with a Jasco P-1020 polarimeter. Melting points were
determined with a Yanaco apparatus and are uncorrected. NMR spectra were
recorded on a Jeol JNM-ECP 600-MHz spectrometer with Me4Si as the internal
standard, and chemical shifts are recorded in d value. Mass spectra were obtained
on a Q-TOF Global mass spectrometer.
Benzyl 3-O-2,3,4-Tri-O-benzoyl-b-D-xylopyranosyl Oleanolate (9)
Benzyl ester 8 (500 mg, 0.92 mmol), trichloroacetimidate 5 (0.67 g, 1.10 mmol),
˚
and powdered 4-A molecular sieves (0.80 g) were stirred for 40 min at rt in dry
CH2Cl2 (10 mL). TMSOTf (0.016 mL, 0.082 mmol) was added dropwise. The mix-
ture was stirred for 20 min, followed by addition of Et3N (0.20 mL) and filtration.
The filtrate was concentrated and purified by silica-gel column chromatography
(petroleum ether–EtOAc, 10:1, v:v) to afford 9 (0.88 g, 98.7%), Rf 0.38 (petroleum
25
ether–EtOAc, 6:1, v:v); ½aꢀD þ 29.6 (c 0.60, CHCl3); IR (KBr) n: 2945, 1727, 1451,
1
1252,1089, 1066, 1023, 707 cmꢁ1; H NMR (CDCl3) d: 7.31–7.98 (m, 20 H, Ph-H),
5.79 (t-like, J ¼ 8.4, 7.8 Hz, 1 H, H-30), 5.45 (dd, J ¼ 8.4, 6.6 Hz, 1 H, H-20), 5.28
(t, J ¼ 3.6 Hz, 1 H, H-12), 5.32 (m, 1 H, H-40), 5.10 (d, J ¼ 12.6 Hz, 1 H, PhCHH),
5.06 (d, J ¼ 12.6 Hz, 1 H, PhCHH), 4.84 (d, J ¼ 6.0 Hz, 1 H, H-10), 4.43 (dd,
J ¼ 12.0, 4.8 Hz, 1H, H-50-1), 3.63 (dd, J ¼ 12.0, 7.8 Hz, 1 H, H-50-2), 3.15 (dd,
J ¼ 11.4, 4.8 Hz, 1H, H-3), 2.89 (dd, J ¼ 14.4, 4.8 Hz, 1 H, H-18), 1.09, 0.92, 0.89,
0.87, 0.77, 0.65, 0.57 (s each, 3 H each, CH3 ꢂ 7); 13C NMR (CDCl3): d 177.6
(C-28), 165.7, 165.2, 165.1, 143.7 (C-13), 136.5, 133.5, 133.3, 133.2, 129.9, 129.8,
129.7, 129.5, 129.2, 128.5, 128.4, 128.3, 128.0, 127.8, 122.5 (C-12), 103.0 (C-10),
89.9 (C-3), 70.9, 70.1, 68.9, 66.0, 62.7, 55.5, 47.6, 46.8, 46.0, 41.7, 41.5, 39.3, 38.8,
38.5, 36.7, 33.9, 33.2, 32.6, 32.2, 30.8, 27.9, 27.7, 26.0, 23.7, 23.5, 23.2, 22.9, 18.2,

FOUR NATURAL TRITERPENE SAPONINS
363
17.0, 16.3, 15.2 HRESIMS calcd. for C63H74O10Na [M þ Na]þ 1013.5180; found
1013.5137.
Benzyl 3-O-b-D-Xylopyranosyl Oleanolate (11)
To a solution of 9 (0.50 g, 0.50 mmol) in dry CH2Cl2–MeOH (1:2, v:v, 20 mL),
NaOMe in a MeOH and CH2Cl2 solution (v:v, 2:1) was added. The mixture was stir-
red at rt for 5 h, neutralized with Dowex Hþ resin to pH 7, and then filtered. The
filtrate was concentrated, and the resulting residue was subjected to silica-gel column
chromatography (CHCl3-CH3OH, 15:1, v:v) to give 11 (397 mg, 100%) as a white
25
amorphous solid, Rf ¼ 0.58 (CHCl3-CH3OH, 10:1, v:v); ½aꢀD þ 23.2 (c 1.50, CHCl3);
1
IR (KBr) n: 3315, 2938, 1723, 1451, 1361, 1155, 1023, 960, 696 cmꢁ1; H NMR
(CDCl3) d: 7.28–7.34 (m, 5 H, Ph-H), 5.28 (t-like, J ¼ 3.3 Hz, 1 H, H-12), 5.10 (d,
J ¼ 12.1 Hz, 1 H, PhCHH), 5.05 (d, J ¼ 12.1 Hz, 1H, PhCHH), 4.49 (d, J ¼ 5.5 Hz,
1 H, H-10), 4.08 (dd, J ¼ 12.1, 4.4 Hz, 1 H, H-50-1), 3.75 (dd, J ¼ 11.0, 7.7 Hz, 1 H,
H-40), 3.63 (t-like, J ¼ 7.7, 6.6 Hz, 1 H, H-30), 3.52 (t-like, J ¼ 6.6, 5.5 Hz, 1 H,
H-20), 3.38 (dd, J ¼ 11.0, 6.6 Hz, 1 H, H-50-2), 3.16 (dd, J ¼ 11.0, 4.4 Hz, 1H, H-3),
2.89 (dd, J ¼ 13.2, 4.4 Hz, 1 H, H-18), 1.11, 0.98, 0.91, 0.89, 0.88, 0.80, 0.60 (s each,
3 H each, CH3 ꢂ 7); 13C NMR (CDCl3): d 177.5 (C-28), 143.5 (C-13), 136.4, 128.3,
128.2, 128.1, 128.0, 127.8, 122.2 (C-12), 102.5 (C-10), 87.9 (C-3), 72.9, 71.6, 68.0, 65.8,
65.6, 55.4, 47.6, 46.8, 46.0, 41.6, 41.5, 39.3, 38.8, 38.5, 36.7, 33.9, 33.2, 32.5, 32.2,
30.9, 27.9, 27.7, 26.0, 23.7, 23.5, 23.2, 22.7, 18.1, 17.0, 16.2, 15.2 HRESIMS calcd.
for C42H62O7Na [M þ Na]þ 701.4393; found 701.4387.
Benzyl 3-O-3,4-Di-O-benzoyl-b-D-xylopyranosyl Oleanolate (13)
Compound 11 (150 mg, 0.221 mmol) and dibutyltin oxide (55 mg,
0.221 mmol) were suspended in benzene (6 mL), and the mixture was stirred at
reflux overnight with the azeotropic removal of water (Dean–Stark trap). The
resulting hazy-to-clear solution was cooled under N2 in an ice-water bath and stir-
red, and then BzCl (45 mL, 2.05 eq) was added. After addition was complete, the
flask was removed from the bath and allowed to reach room temperature for
30 min. The reaction mixture was concentrated in vacuo. The solid residue was
purified by silica-gel column chromatography (petroleum ether–EtOAc, 1:8, v:v)
to give 13 (176 mg, 89.7%) as a white amorphous solid, Rf ¼ 0.32 (petroleum
25
ether–EtOAc, 1:6, v:v); ½aꢀD ꢁ 9.83 (c 2.04, CHCl3); IR (KBr) n: 3506, 2941,
1723, 1451, 1272, 1097, 1096, 1027, 707 cmꢁ1 1H NMR (CDCl3) d: 7.30–8.03
;
(m, 15 H, Ph-H), 5.57 (t-like, J ¼ 9.2, 8.7 Hz, 1 H, H-30), 5.27–5.31 (m, 2 H,
H-12, H-40), 5.10 (d, J ¼ 12.4 Hz, 1 H, PhCHH), 5.05 (d, J ¼ 12.4 Hz, 1 H,
PhCHH), 4.55 (d, J ¼ 6.9 Hz, 1 H, H-10), 4.31 (dd, J ¼ 11.9, 5.5 Hz, 1 H, H-50-1),
3.81 (t-like, J ¼ 6.9, 6.8 Hz, 1 H, H-20), 3.50 (dd, J ¼ 11.5, 9.2 Hz, 1 H, H-50-2),
3.22 (dd, J ¼ 11.5, 4.6 Hz, 1H, H-3), 2.91 (dd, J ¼ 13.7, 3.7 Hz, 1 H, H-18), 1.98
(dt, J ¼ 13.3, 4.1 Hz, 1 H, H-16), 1.12, 1.01, 0.92, 0.90, 0.90, 0.81, 0.60 (s each, 3
H each, CH3 ꢂ 7); 13C NMR (CDCl3): d 177.5 (C-28), 165.7, 165.2, 143.6 (C-13),
136.5, 133.4, 133.2, 129.9, 129.8, 129.5, 129.2, 128.4, 128.3, 127.9, 122.5 (C-12),
102.7 (C-10), 89.7 (C-3), 70.9, 70.1, 68.9, 63.4, 62.7, 55.6, 47.6, 46.7, 46.0, 41.7,

364
T. GUO ET AL.
41.6, 39.3, 38.8, 38.5, 36.8, 33.9, 33.2, 32.6, 32.2, 30.8, 27.8, 27.7, 26.0, 23.7, 23.5,
23.2, 22.8, 18.2, 17.0, 16.4, 15.1 HRESIMS calcd. for C56H71O9 [M þ H]þ
887.5098; found 887.5068.
Benzyl 3-O-2,3,4-Tri-O-benzoyl-a-L-arabinopyranosyl Oleanolate (10)
Benzyl ester 8 (500 mg, 0.92 mmol), trichloroacetimidate 6 (0.67 g, 1.10 mmol),
˚
and powdered 4-A molecular sieves (0.80 g) were stirred for 40 min at rt in dry
CH2Cl2 (10 mL). TMSOTf (0.016 mL, 0.082 mmol) was added dropwise. The mix-
ture was stirred for 20 min, followed by addition of Et3N (0.20 mL) and filtration.
The filtrate was concentrated and purified by silica-gel column chromatography (pet-
roleum ether–EtOAc, 10:1, v:v) to afford 10 (0.85 g, 95.6%). Rf 0.40 (petroleum
25
ether–EtOAc, 6:1, v:v); ½aꢂD þ 33.6 (c 0.60, CHCl3); IR (KBr) n: 2951, 1729, 1451,
1
1260, 1088, 1055, 1031, 707 cmꢁ1; H NMR (CDCl3) d: 7.26–8.07 (m, 20 H, Ph-
H), 5.76 (dd, J ¼ 8.5, 6.5 Hz, 1 H, H-20), 5.67 (m, 1 H, H-40), 5.59 (dd, J ¼ 9.2,
3.7 Hz, 1 H, H-20), 5.28 (t, J ¼ 3.6 Hz, 1 H, H-12), 5.08 (d, J ¼ 12.5 Hz, 1 H, PhCHH),
5.04 (d, J ¼ 12.5 Hz, 1 H, PhCHH), 4.78 (d, J ¼ 6.2 Hz, 1 H, H-10), 4.33 (dd, J ¼ 12.8,
3.7 Hz, 1 H, H-50-1), 3.87 (m, 1 H, H-50-2), 3.16 (dd, J ¼ 11.3, 4.4 Hz, 1 H, H-3), 2.90
(dd, J ¼ 11.4, 3.7 Hz, 1 H, H-18), 1.09, 0.91, 0.89, 0.86, 0.78, 0.65, 0.57 (s each, 3 H
each, CH3 ꢃ 7); 13C NMR (CDCl3): d 177.5 (C-28), 165.8, 165.5, 165.1, 143.6 (C-13),
136.5, 133.4, 133.3, 133.2, 129.9, 129.8, 129.7, 129.5, 129.0, 128.5, 128.4, 128.2, 128.0,
127.7, 122.6 (C-12), 103.2 (C-10), 90.0 (C-3), 70.8, 70.2, 68.7, 66.0, 62.6, 55.5, 47.5,
46.8, 45.9, 41.6, 41.5, 39.2, 38.8, 38.4, 36.7, 33.9, 33.1, 32.6, 32.2, 30.7, 27.9, 27.7,
25.9, 23.6, 23.5, 23.1, 22.9, 18.1, 17.0, 16.1, 15.2; ESI-MS (m=z): 1013.5 [M þ Na]þ.
Benzyl 3-O-[2-O-(2,3,4,6-Tetra-O-benzoyl-b-D-glucopyranosyl)-3,4-di-
O-benzoyl-b-D-xylopyranosyl] Oleanolate (15)
Compound 13 (140 mg, 0.158 mmol), trichloroacetimidate
7 (140 mg,
˚
0.19 mmol), and powdered 4-A molecular sieves (0.20 g) in dry CH2Cl2 (5 mL) were
stirred for 40 min at room temperature, and then TMSOTf (0.005 mL, 0.032 mmol)
was added dropwise. The mixture was stirred for 10 min, followed by addition of
Et3N and filtration. The filtrate was concentrated and purified by a silica–gel column
chromatography (petroleum ether–EtOAc, 6:1, v:v) to afford 15 (208 mg, 89.7%),
25
Rf ¼ 0.38 (petroleum ether–EtOAc, 1:4, v:v); ½aꢂD ꢁ 1.28 (c 1.45, CHCl3); IR (KBr)
1
n: 2953, 1731, 1599, 1455, 1264, 1097, 1062, 1027, 707 cmꢁ1; H NMR (CDCl3): d
7.23–8.02 (m, 35 H, Ph-H), 5.68 (t, J ¼ 9.4 Hz, 1 H, H-300), 5.64 (t, J ¼ 9.4 Hz, 1 H,
H-400), 5.54 (t, J ¼ 7.7 Hz, 1 H, H-30), 5.48 (dd, J ¼ 9.4, 7.7 Hz, 1 H, H-20’), 5.28 (t,
J ¼ 3.3 Hz, 1 H, H-12), 5.12–5.16 (m, 2 H, H-100, H-40), 5.10 (dd, J ¼ 12.7 Hz, 1H,
PhCHH), 5.06 (dd, J ¼ 12.6 Hz, 1 H, PhCHH), 4.76 (d, J ¼ 5.5 Hz, 1 H, H-10),
4.62 (dd, J ¼ 12.5, 3.3 Hz, 1 H, H-600-1), 4.45 (dd, J ¼ 12.1, 5.0 Hz, 1 H, H-600-2),
4.26 (dd, J ¼ 12.1, 5.0 Hz, 1 H, H-50-1), 4.10–4.12 (m, 2 H, H-20, H-500), 3.49 (dd,
J ¼ 12.1, 7.7 Hz, 1 H, H-50-2), 3.12 (dd, J ¼ 11.5, 4.4 Hz, 1 H, H-3), 2.89 (dd,
J ¼ 14.9, 4.4 Hz, 1 H, H-18), 1.12, 1.04, 0.92, 0.90, 0.80, 0.72, 0.58 (s each, 3 H each,
CH3 ꢃ 7); 13C NMR (CDCl3): d 177.6 (C-28), 166.3, 165.7, 165.2, 165.1, 143.8
(C-13), 136.5, 133.6, 133.5, 133.4, 133.3, 133.2, 129.9, 129.8, 129.7, 128.5, 128.4,

FOUR NATURAL TRITERPENE SAPONINS
365
128.3, 128.2, 122.6 (C-12), 103.4 (C-10), 101.3 (C-100), 89.9 (C-3), 76.5, 73.3, 73.1,
72.1, 70.0, 69.8, 66.0, 63.3, 61.5, 55.5, 47.6, 46.9, 46.0, 41.8, 41.5, 39.4, 39.3, 38.5,
36.7, 34.0, 33.2, 32.7, 32.6, 30.8, 27.9, 26.0, 23.8, 23.5, 23.2, 22.8, 18.2, 17.0, 16.4,
15.4, 14.2; HRMALDIMS calcd. for C90H96O18 [M þ Na]þ 1487.6596; found
1487.6590.
3-O-[2-O-b-D-Glucopyranosyl-(1!2)-a-L-xylopyranosyl]
Oleanolic Acid (1)
A mixture of 15 (100 mg, 0.07 mmol) and 10% Pd-C (50 mg) in CH2Cl2-MeOH
(1:1, v:v, 10 mL) in the presence of AcOH (two drops) was stirred under 1 atm of H2
for 4 h. The reaction mixture was then filtered, and the filtrate was concentrated to
dryness to give a white solid. The solid was dissolved in MeOH-CH2Cl2 (2:1, v:v,
10 mL), and then NaOMe (50 mg) was added. After stirring at rt for 8 h, the solution
was neutralized with ion-exchange resin (Hþ), filtered, and concentrated. The residue
was purified by column chromatography on silica gel (CHCl3-MeOH, 6:1, v:v) to give
1 (43 mg, 81.5% two steps) as a white solid, Rf ¼ 0.41 (CHCl3-MeOH, 4:1, v:v);
25
½aꢂD þ 31.2 (c 0.15, CH3OH), lit.[10] þ 29.1 (c 0.11, CH3OH); IR (KBr) n: 3405,
1
2941, 1696, 1599, 1454, 1361, 1077, 1034 cmꢁ1; H NMR (C5D5N): d 5.46 (s, 1 H,
H-12), 5.36 (d, J ¼ 7.8 Hz, 1 H, H-100), 4.81 (d, J ¼ 7.0 Hz, 1 H, H-10), 4.76 (dd,
J ¼ 12.7, 5.0 Hz, 1 H, H-50-1), 4.73 (dd, J ¼ 12.4, 1.7 Hz, 1 H, H-600-1), 4.53 (dd,
J ¼ 12.1, 6.0 Hz, 1H, H-600-2), 4.47 (t-like, J ¼ 8.1, 7.4 Hz, 1 H, H-20), 4.32 (t,
J ¼ 9.3 Hz, 1 H, H-300), 3.95 (dd, J ¼ 12.4, 2.7 Hz, 1 H, H-50-2), 3.86 (t, J ¼ 8.8 Hz, 1
H, H-400), 3.75–3.82 (m, 4 H, H-200, H-30, H-40, H-500), 3.30 (dd, J ¼ 12.1, 4.4 Hz, 1
H, H-3), 3.28 (dd, J ¼ 13.7, 3.7 Hz, 1 H, H-18), 1.26, 1.25, 1.08, 0.99, 0.97, 0.94,
0.93 (s each, 3 H each, CH3 ꢃ 7); 13C NMR (C5D5N) d: 180.2 (C-28), 144.9 (C-13),
122.6 (C-12), 105.9 (C-10), 105.7 (C-100), 88.7 (C-3), 83.1, 78.3, 78.0, 77.9, 77.0, 71.6,
71.0, 66.5, 62.7, 55.7, 48.1, 46.5, 46.3, 42.0, 41.8, 39.8, 39.3, 38.7, 37.1, 34.1, 33.1,
33.0, 28.5, 28.2, 26.7, 26.2, 23.7, 23.6, 23.5, 18.5, 17.4, 16.9, 15.5; HRESIMS calcd.
for C41H65O12 [M þ H]þ 749.4476; found 749.4481.
Benzyl 3-O-[2-O-(2,3,4,6-Tetra-O-benzoyl-b-D-glucopyranosyl)-
3,4-O-isopropylidene-a-L-arabinopyranosyl] Oleanolate (16)
Compound 14 (140 mg, 0.194 mmol), trichloroacetimidate
7 (172 mg,
˚
0.234 mmol), and powdered 4-A molecular sieves (0.20 g) in dry CH2Cl2 (5 mL) were
stirred for 40 min at room temperature, and then TMSOTf (0.007 mL, 0.04 mmol)
was added dropwise. The mixture was stirred for 10 min, followed by addition of
Et3N and filtration. The filtrate was concentrated and purified by silica-gel column
chromatography (petroleum ether–EtOAc, 6:1, v:v) to afford 16 (228 mg, 90.6%),
25
Rf ¼ 0.31 (petroleum ether–EtOAc, 4:1, v:v); ½aꢂD þ 32.7 (c 1.40, CHCl3); IR (KBr)
1
n: 2945, 1731, 1455, 1260, 1097, 711 cmꢁ1; H NMR (CDCl3): d 7.27–8.04 (m, 25
H, Ph-H), 5.90 (t, J ¼ 9.6 Hz, 1 H, H-300), 5.71 (t, J ¼ 9.9 Hz, 1 H, H-400), 5.50
(dd, J ¼ 9.3, 7.7 Hz, 1 H, H-200), 5.30 (d, J ¼ 7.7 Hz, 1 H, H-100), 5.26 (t, J ¼ 3.3 Hz,
1 H, H-12), 5.10 (dd, J ¼ 12.7 Hz, 1 H, PhCHH), 5.05 (dd, J ¼ 12.6 Hz, 1 H,
PhCHH), 4.58 (dd, J ¼ 12.7, 3.3 Hz, 1 H, H-600-1), 4.45 (dd, J ¼ 12.1, 4.4 Hz, 1 H,

366
T. GUO ET AL.
H-600-2), 4.35 (d, J ¼ 6.6 Hz, 1 H, H-10), 4.10–4.14 (m, 2 H, H-40, H-500), 3.89–3.93 (m,
2 H, H-30, H-50-1), 3.87 (dd, J ¼ 8.2, 6.6 Hz, 1 H, H-20), 3.67 (dd, J ¼ 12.6, 4.4 Hz, 1
H, H-50-2), 2.99 (dd, J ¼ 11.5, 4.9 Hz, 1 H, H-3), 2.89 (dd, J ¼ 13.7, 3.8 Hz, 1 H,
H-18), 1.50, 1.24 (s each, 3 H each, O-C(CH3)2-O), 1.10, 0.95, 0.91, 0.89, 0.79,
0.71, 0.56 (s each, 3H each, CH3 ꢃ 7); 13C NMR (CDCl3): d 177.6 (C-28), 166.3,
165.3, 163.5, 143.9 (C-13), 136.6, 133.7, 133.4, 130.0, 129.9, 128.6, 128.5, 128.2,
122.6 (C-12), 110.3 (O-C(CH3)2-O), 101.7 (C-10), 101.6 (C-100), 90.2 (C-3), 72.9,
72.6, 72.2, 70.2, 69.6, 66.1, 65.0, 63.3, 60.5, 55.3, 47.7, 46.9, 46.1, 41.9, 41.5, 39.4,
39.1, 38.5, 36.8, 34.0, 33.3, 32.8, 32.6, 31.1, 30.9, 28.1, 27.8, 26.1, 25.7, 23.8, 23.6,
23.2, 18.3, 17.0, 16.6, 15.4 HRMALDIMS calcd. for C79H92O16 [M þ Na]þ
1319.6384, found 1319.6387.
Benzyl 3-O-[2-O-(2,3,4,6-Tetra-O-benzoyl-b-D-glucopyranosyl)-a-
L-arabinopyranosyl] Oleanolate (17)
A mixture of 16 (200 mg, 0.15 mmol) in 80% HOAc (2 mL) was stirred at 60 ꢀC
for 2 h, concentrated, and redissolved in CH2Cl2 (10 mL). The organic layer was suc-
cessively washed with sat. NaHCO3 and brine, dried over anhydrous Na2SO4, and
then concentrated in vacuo. The residue was purified by silica-gel column chromato-
graphy (petroleum ether–EtOAc, 5:1, v:v) to afford 17 (169 mg, 89.8%), Rf ¼ 0.34
25
(petroleum ether–EtOAc, 3:1, v:v); ½aꢂD þ22.8 (c 1.65, CHCl3); IR (KBr) n: 3410,
1
2945, 1727, 1451, 1264, 1089, 704 cmꢁ1; H NMR (CDCl3): d 7.28–8.01 (m, 25 H,
Ph-H), 5.89 (t, J ¼ 9.9 Hz, 1 H, H-300), 5.68 (t, J ¼ 9.9 Hz, 1 H, H-400), 5.54 (dd,
J ¼ 9.9, 7.7 Hz, 1 H, H-200), 5.28 (t, J ¼ 3.6 Hz, 1 H, H-12), 5.10 (d, J ¼ 7.7 Hz, 1H,
H-100), 5.08 (d, J ¼ 12.7 Hz, 1 H, PhCHH), 5.03 (d, J ¼ 12.6 Hz, 1 H, PhCHH),
4.79 (d, J ¼ 2.7 Hz, 1 H, H-10), 4.58 (dd, J ¼ 12.1, 3.3 Hz, 1 H, H-600-1), 4.46 (dd,
J ¼ 12.7, 5.5 Hz, 1 H, H-600-2), 4.18 (ddd, J ¼ 9.9, 5.5, 3.2 Hz, 1H, H-500), 3.96 (t,
J ¼ 3.6 Hz, 1 H, H-20), 3.67–3.71 (m, 2 H, H-30, H-40), 3.62 (dd, J ¼ 11.6, 8.2 Hz,
1 H, H-50-1), 3.50 (dd, J ¼ 11.5, 4.4 Hz, 1 H, H-50-2), 3.05 (dd, J ¼ 11.6, 4.4 Hz, 1
H, H-3), 2.90 (dd, J ¼ 13.7, 4.4 Hz, 1 H, H-18), 1.12, 0.92, 0.90, 0.86, 0.83, 0.72,
0.58 (s each, 3H each, CH3 ꢃ 7); 13C NMR (CDCl3): d 177.7 (C-28), 166.3, 166.0,
165.4, 165.3, 143.9 (C-13), 136.6, 133.7, 133.5, 133.4, 130.1, 129.9, 128.6, 128.2,
122.6 (C-12), 101.7 (C-10), 101.6 (C-100), 90.2 (C-3), 73.0, 72.7, 72.2, 70.2, 69.7,
66.1, 64.8, 63.3, 60.5, 55.3, 47.7, 46.9, 46.1, 41.9, 41.6, 39.5, 39.1, 38.5, 36.8, 34.1,
33.3, 32.8, 32.6, 30.9, 29.9, 28.2, 27.8, 26.1, 25.7, 23.9, 23.6, 23.3, 18.3, 17.1, 16.6,
15.4 HRMALDIMS calcd. for C79H92O16 [M þNa]þ 1279.6071; found 1279.6069.
3-O-[2-O-b-D-Glucopyranosyl-(1!2)-a-L-arabinopyranosyl] Oleanolic
Acid (2)
A mixture of 17 (120 mg, 0.10 mmol) and 10% Pd-C (60 mg) in CH2Cl2-MeOH
(1:1, v:v, 12 mL) in the presence of AcOH (two drops) was stirred under 1 atm of H2
for 4 h. The reaction mixture was then filtered, and the filtrate was concentrated to
dryness to give a white solid. The solid was dissolved in MeOH-CH2Cl2 (2:1, v:v,
12 mL), and then NaOMe (60 mg) was added. After stirring at rt for 8 h, the solution
was neutralized with ion-exchange resin (Hþ), then filtered and concentrated. The

FOUR NATURAL TRITERPENE SAPONINS
367
residue was purified by column chromatography on silica gel (CHCl3-MeOH, 6:1,
v:v) to give 2 (58 mg, 80.7% two steps) as a white solid, Rf ¼ 0.39 (CHCl3-MeOH,
25
4:1, v:v); ½aꢂD þ23.5 (c 1.21, pyridine), lit.[10] þ 20.1 (c 1.00, pyridine); IR (KBr) n:
1
3393, 2941, 1696, 1451, 1385, 1073, 645 cmꢁ1; H NMR (C5D5N): d 5.45 (s, 1 H,
H-12), 5.10 (d, J ¼ 7.8 Hz, 1 H, H-100), 4.89 (d, J ¼ 5.0 Hz, 1 H, H-10), 4.74 (dd,
J ¼ 7.7, 5.0 Hz, 1 H, H-20), 4.57–4.65 (m, 3 H, H-40, H-50-1, H-600-1), 4.50 (dd,
J ¼ 7.7, 3.3 Hz, 1 H, H-30), 4.43 (dd, J ¼ 12.1, 5.5 Hz, 1 H, H-600-2), 4.26–4.32 (m,
4 H, H-300, H-400, H-500, H-50-2), 3.83 (dd, J ¼ 9.4, 7.7 Hz, 1 H, H-200), 3.31 (dd,
J ¼ 11.7, 4.4 Hz, 1 H, H-3), 3.29 (dd, J ¼ 13.7, 3.7 Hz, 1 H, H-18), 1.27, 1.25, 1.06,
1.00, 0.98, 0.95, 0.91 (s each, 3 H each, CH3 ꢃ 7); 13C NMR (C5D5N): d 180.3
(C-28), 144.9 (C-13), 122.6 (C-12), 105.0 (C-10), 105.5 (C-100), 88.9 (C-3), 82.9,
78.2, 78.1, 77.5, 77.0, 71.6, 71.1, 66.3, 62.6, 55.5, 48.0, 46.7, 46.3, 42.1, 41.9, 39.8,
39.4, 38.5, 36.9, 34.3, 33.2, 32.9, 28.5, 28.1, 26.6, 26.2, 23.7, 23.6, 23.1, 18.3, 17.5,
16.7, 15.5 HRESIMS calcd. for C41H65O12 749.4476; found 749.4498.
Typical Procedure for the One-Pot Synthesis of Triterpene
Saponins 18–19
˚
A solution of p-toluene thioglycoside 9 (45 mg, 0.11 mmol) and 4-A MS (80 mg)
in CH2Cl2 (5 mL) was stirred at room temperature under argon for 30 min, and then
cooled to ꢁ78 ꢀC. At this temperature, a solution of TMSOTf (0.2 equiv.) in dry
CH2Cl2 was injected, and after 10 min trichloacetimidate 7 (280 mg, 0.23 mmol, 2.1
equiv.) in dry CH2Cl2 was added. The resulting mixture was stirred for an additional
30 min and then warmed up to ꢁ10 ꢀC. A solution of saponin acceptor 13 or 14
(0.11 mmol, 1.0 equiv.) in CH2Cl2 (2 mL) was added to the mixture, followed by
NIS (50 mg, 0.11 mmol, 2.0 equiv.). After being stirred for 1 h, the reaction mixture
was quenched with Et3N and then filtered through a pad of celite. The filtrate was
concentrated. The residue was purified by silica-gel column chromatography (3:1,
petroleum ether–EtOAc) to give the fully protected saponin 18 or 19 as a white solid.
The amounts of the reactants and the yields of the saponin products were calculated
based on saponin accepter 13 or 14.
Benzyl 3-O-[2,3,4,6-Tetra-O-benzoyl-b-D-glucopyranosyl-
(1!3)-2,4-di-O-acetyl-a-L-rhamnopyranosyl-(1!2)-3,4-O-
isopropylidene-a-L-arabinopyranosyl] Oleanolate (18)
23
Yield, 78.1%; ½aꢂD þ 36.4 (c 2.56, CHCl3); Rf 0.40 (2:1, petroleum ether–
EtOAc); IR (KBr) nmax 2945, 1731, 1599, 1451, 1369, 1256, 1093, 1069, 1023,
707 cmꢁ1
;
1H NMR (CDCl3): d 7.27–8.04 (m, 25 H, Ph-H), 5.89 (t, J ¼ 10.1,
9.6 Hz, 1 H, H-3000), 5.66 (t, J ¼ 10.1, 9.7 Hz, 1 H, H-4000), 5.48 (dd, J ¼ 10.1, 7.8 Hz,
1 H, H-2000), 5.34 (dd, J ¼ 3.2, 1.9 Hz, 1 H, H-200), 5.30 (s, 1 H, H-100), 5.29 (t,
J ¼ 3.2 Hz, 1 H, H-12), 5.10 (d, J ¼ 12.4 Hz, 1 H, PhCHH), 5.06 (d, J ¼ 12.3 Hz, 1
H, PhCHH), 5.01 (t-like, J ¼ 10.1, 9.6 Hz, 1 H, H-400), 4.87 (d, J ¼ 7.8 Hz, 1 H,
H-1000), 4.55 (dd, J ¼ 12.4, 3.7 Hz, 1 H, H-6000-1), 4.50 (dd, J ¼ 12.4, 4.6 Hz, 1 H,
H-6000-2), 4.12 (d, J ¼ 6.0 Hz, 1 H, H-10), 4.14–4.18 (m, 2 H, H-3000, H-40), 4.08–4.11
(m, 2 H, H-30, H-5000), 4.05 (m, 1 H, H-50-1), 3.94 (dq, J ¼ 9.6, 5.9 Hz, 1 H, H-500),
3.66–3.69 (m, 2 H, H-20, H-50-2), 2.97 (dd, J ¼ 11.5, 4.1 Hz, 1 H, H-3), 2.91 (dd,

368
T. GUO ET AL.
J ¼ 13.7, 4.1 Hz, 1 H, H-18), 2.09, 2.04 (s each, 3 H each, CH3CO ꢃ 2), 1.58, 1.31 (s
each, 3 H each, O-(CH3)2-O), 1.05 (d, J ¼ 6.0 Hz, 3 H, H-600), 1.14, 0.98, 0.93, 0.91,
0.88, 0.76, 0.62 (s each, 3 H each, CH3 ꢃ 7); 13C NMR (CDCl3): d 177.6 (C-28),
170.4, 169.4, 166.0, 164.8, 143.8 (C-13), 136.6, 133.1, 133.0, 129.3, 128.5, 128.4,
122.6 (C-12), 110.3 (O-(CH3)2C-O), 103.4 (C-10), 102.0 (C-1000), 94.6 (C-100), 88.9
(C-3), 78.1, 75.6, 74.3, 74.0, 73.5, 72.0, 69.6, 66.0, 63.1, 60.5, 55.9, 53.5, 46.9, 46.0,
41.5, 41.3, 39.4, 39.2, 36.8, 33.2, 27.8, 26.2, 26.0, 23.8, 21.1, 17.4, 16.5, 15.4;
HRMALDI-MS: m=z calcd. for [M þ Na]þ C89H106O22: 1549.7084; found:
1549.7068.
Benzyl 3-O-[2,3,4,6-Tetra-O-benzoyl-b-D-glucopyranosyl-
(1!3)-2,4-di-O-acetyl-a-L-rhamnopyranosyl-(1!2)-3,4-O-
isopropylidene-b-D-xylopyranosyl] Oleanolate (19)
23
Yield, 75.3%; ½aꢂD þ 15.9 (c 1.85, CHCl3); Rf 0.36 (2:1, petroleum ether–
1
EtOAc); IR (KBr) nmax 2945, 1735, 1451, 1268, 1093, 707 cmꢁ1; H NMR (CDCl3):
d 7.27–8.07 (m, 35 H, Ph-H), 5.58 (t-like, J ¼ 7.7, 7.2 Hz, 1 H, H-30), 5.51 (t-like,
J ¼ 9.9, 9.4 Hz, 1 H, H-4000), 5.38 (dd, J ¼ 9.9, 8.3 Hz, 1 H, H-2000), 5.29 (t, J ¼ 3.8 Hz,
1 H, H-12), 5.11–5.14 (m, 2 H, H-200, H-40), 5.10 (d, J ¼ 12.7 Hz, 1 H, PhCHH), 5.06
(d, J ¼ 12.6 Hz, 1 H, PhCHH), 5.04 (s, 1 H, H-100), 4.96 (t, J ¼ 9.9 Hz, 1 H, H-400),
4.66 (d, J ¼ 5.5 Hz, 1 H, H-10), 4.38 (d, J ¼ 8.2 Hz, 1 H, H-1000), 4.32–4.37 (m, 2 H,
H-50-1, H-6000-1), 4.27 (dd, J ¼ 12.1, 3.3 Hz, 1 H, H-6000-2), 3.93–3.98 (m, 2 H,
H-300, H-500), 3.89 (dd, J ¼ 7.1, 5.5 Hz, 1 H, H-20), 3.53 (dd, J ¼ 12.1, 7.7 Hz, 1 H,
H-50-2), 3.41 (m, 1 H, H-5000), 3.12 (dd, J ¼ 11.6, 4.4 Hz, 1 H, H-3), 2.91 (dd,
J ¼ 14.9, 4.9 Hz, 1 H, H-18), 1.85, 1.85 (s each, 3 H each, CH3CO ꢃ 2), 1.05 (d,
J ¼ 6.1 Hz, 3 H, H-600), 1.12, 0.93, 0.92, 0.90, 0.87, 0.71, 0.60 (s each, 3 H each,
CH3 ꢃ 7); 13C NMR (CDCl3): d 177.7 (C-28), 170.1, 169.7, 166.2, 166.1, 165.7,
165.6, 164.9, 164.8, 143.9 (C-13), 136.6, 133.6, 133.5, 133.4, 133.3, 133.2, 133.0,
129.9, 129.8, 128.7, 128.6, 128.5, 122.7 (C-12), 103.6 (C-10), 101.1 (C-1000), 97.7
(C-100), 89.2 (C-3), 76.5, 75.4, 72.9, 72.0, 71.9, 70.2, 70.0, 69.0, 67.1, 66.1, 62.6,
55.9, 47.8, 47.0, 46.1, 41.9, 41.6, 39.5, 39.3, 38.9, 36.9, 34.1, 33.3, 32.9, 32.6, 30.9,
29.9, 28.1, 27.8, 26.2, 26.1, 23.8, 23.6, 20.8, 20.3, 18.4, 17.5, 17.1, 16.4, 15.6.
HRMALDI-MS: m=z calcd. for [M þ Na]þ C100H110O24: 1717.7242; found:
1717.7279.
Benzyl 3-O-[2,3,4,6-Tetra-O-benzoyl-b-D-glucopyranosyl-
(1!3)-2,4-di-O-acetyl-a-L-rhamnopyranosyl-(1!2)-a-
L-arabinopyranosyl] Oleanolate (20)
A mixture of 19 (100 mg, 0.07 mmol) in 80% HOAc (2 mL) was stirred at 60 ꢀC
for 2 h, concentrated, and redissolved in CH2Cl2 (10 mL). The organic layer was suc-
cessively washed with saturated. NaHCO3 and brine, dried over anhydrous Na2SO4,
and then concentrated in vacuo. The residue was purified by silica-gel column chro-
matography (petroleum ether–EtOAc, 5:1, v:v) to afford 20 (90 mg, 92.3%), Rf ¼ 0.29
23
(petroleum ether–EtOAc, 2:1, v:v); ½aꢂD þ 21.8 (c 3.25, CHCl3); IR (KBr) nmax 2934,
1
1727, 1451, 1377, 1260, 1085, 704 cmꢁ1; H NMR (CDCl3): d 7.27–8.05 (m, 25 H,
Ph-H), 5.89 (t, J ¼ 9.9, 9.3 Hz, 1 H, H-3000), 5.72 (t, J ¼ 9.8, 9.4 Hz, 1 H, H-4000),

FOUR NATURAL TRITERPENE SAPONINS
369
5.52 (dd, J ¼ 9.9, 7.7 Hz, 1 H, H-2000), 5.31 (br s, 1 H, H-300), 5.30 (t, J ¼ 3.8 Hz, 1 H,
H-12), 5.12 (d, J ¼ 12.7 Hz, 1 H, PhCHH), 5.08 (d, J ¼ 12.7 Hz, 1 H, PhCHH), 5.05
(br s, 1 H, H-10), 5.02 (s, 1 H, H-200), 4.99 (d, J ¼ 7.7 Hz, 1 H, H-1000), 4.69 (d,
J ¼ 1.7 Hz, 1 H, H-100), 4.62 (dd, J ¼ 12.7, 1.7 Hz, 1 H, H-6000-1), 4.49 (dd, J ¼ 12.7,
2.8 Hz, 1 H, H-6000-2), 4.15 (m, 1 H, H-5000), 4.12 (dd, J ¼ 9.9, 3.8 Hz, 1 H, H-30),
3.92 (m, 1 H, H-40), 3.82–3.85 (m, 3 H, H-400, H-500, H-50-1), 3.77 (t, J ¼ 3.9,
2.6 Hz, 1 H, H-20), 3.61 (dd, J ¼ 12.1, 4.4 Hz, 1 H, H-50-2), 3.10 (dd, J ¼ 11.5,
3.8 Hz, 1 H, H-3), 2.91 (dd, J ¼ 14.3, 4.4 Hz, 1 H, H-18), 2.06, 2.05 (s each, 3 H each,
CH3CO ꢃ 2), 1.08 (d, J ¼ 6.0 Hz, 3 H, H-600), 1.12, 0.94, 0.93, 0.91, 0.89, 0.79, 0.61 (s
each, 3 H each, CH3 ꢃ 7); 13C NMR (CDCl3): d 177.5 (C-28), 170.4, 169.5, 165.9,
165.1, 164.8, 143.8 (C-13), 136.5, 133.5, 133.4, 133.2, 129.9, 129.8, 128.6, 128.5,
128.4, 128.3, 128.1, 128.0, 122.5 (C-12), 101.9 (C-100), 101.7 (C-1000), 98.0 (C-100),
90.4 (C-3), 76.2, 75.9, 72.9, 72.1, 72.0, 71.7, 70.4, 69.3, 67.0, 66.0, 65.4, 62.7, 55.5,
47.7, 46.8, 46.0, 41.8, 41.5, 39.4, 39.2, 38.6, 36.8, 33.9, 33.2, 32.7, 32.5, 30.8, 29.8,
28.2, 27.7, 25.9, 25.8, 23.7, 23.5, 23.1, 21.0, 18.3, 17.4, 16.9, 16.5, 15.4
HRMALDI-MS: m=z calcd for [M þ Na]þ C86H102O22: 1509.6772; found:
1509.6755.
Typical Procedure for Removal of the Protecting Groups of
Triterpene Saponins 3–4
A mixture of 19 or 20 (0.03 mmol) and 10% Pd-C (30 mg) in CH2Cl2-MeOH
(v:v=1:1, 8 mL) in the presence of AcOH (two drops) was stirred under 1 atm of
H2 for 4 h. The reaction mixture was then filtered and the filtrate, was concentrated
to dryness to give a white solid. The solid was dissolved in MeOH-CH2Cl2 (v:v = 2:1,
8 mL), and then NaOMe (40 mg) was added. After stirring at rt for 8 h, the solution
was neutralized with ion-exchange resin (Hþ), filtered, and concentrated. The residue
was purified by column chromatography on silica gel (3:1, CHCl3–MeOH) to give
triterpene saponins as a white solid.
3-O-[O-b-D-Glucopyranosyl-(1!3)-O-a-L-rhamnopyranosyl-(1!2)-a-
L-arabinopyranosyl] Oleanolic Acid (3)
Mp 229–231 ꢀC; ½aꢂD25ꢁ1.0 (c 0.65, MeOH); Rf 0.27 (2:1, CHCl3–MeOH); IR
1
(KBr) nmax 3393, 2945, 1692, 1455, 1389, 1054 cmꢁ1; H NMR (C5D5N): d 6.19 (br
s, 1 H, H-100), 5.45 (d, J ¼ 7.3 Hz, 1 H, H-1000), 5.48 (t, J ¼ 3.6 Hz, 1 H, H-12), 5.03
(br s, 1 H, H-200), 4.86 (d, J ¼ 6.0 Hz, 1 H, H-10), 4.83 (dd, J ¼ 9.0, 3.2 Hz, 1 H,
H-300), 4.65 (dq, J ¼ 9.6, 5.9 Hz, 1 H, H-500), 4.49–4.55 (m, 3 H, H-20, H-400, H-6000-
1), 4.37 (dd, J ¼ 11.9, 5.0 Hz, 1 H, H-6000-2), 4.32 (t, J ¼ 10.1, 3.8 Hz, 1 H, H-50-1),
4.27–4.30 (m, 3 H, H-30, H-3000, H-4000), 4.24 (dd, J ¼ 7.8, 3.7 Hz, 1 H, H-40), 4.14 (t,
J ¼ 9.1, 7.8 Hz, 1 H, H-2000), 3.98 (m, 1 H, H-5000), 3.83 (dd, J ¼ 12.4, 2.3 Hz, 1 H,
H-50-2), 3.29–3.33 (m, 2 H, H-3, H-18), 1.56 (d, J ¼ 5.9 Hz, 3 H, H-600), 1.35, 1.33,
1.15, 1.03, 0.99, 0.98, 0.85 (s each, 3 H each, CH3 ꢃ 7); 13C NMR (C5D5N): d 180.8
(C-28), 145.1 (C-13), 123.8 (C-12), 107.0 (C-1000), 105.7 (C-10), 102.0 (C-100), 89.1
(C-3), 83.5 (C-300), 78.9, 78.8, 76.2, 74.7, 73.3, 71.9, 71.8, 70.1, 69.7, 66.0, 62.8, 56.3,
48.4, 47.1, 46.8, 42.5, 42.3, 40.1, 39.9, 39.2, 37.4, 34.6, 33.7, 31.3, 28.5, 27.0, 26.5,

370
T. GUO ET AL.
24.1, 18.9, 17.7, 17.5, 15.9 ESI-HRMS: m=z calcd. for C47H75O16 [M ꢁ Hþ]: 895.5055;
found: 895.5072.
3-O-[O-b-D-Glucopyranosyl-(1!3)-O-a-L-rhamnopyranosyl-(1!2)-b-
D-xylopyranosyl] Oleanolic Acid (4)
25
Mp 235–237 ꢀC; ½aꢂD 3.67 (c 0.45, MeOH); Rf 0.30 (2:1, CHCl3–MeOH); IR
1
(KBr) nmax 3381, 2941, 1696, 1455, 1042 cmꢁ1; H NMR (C5D5N): d 6.51 (br s, 1
H, H-100), 5.53 (d, J ¼ 7.3 Hz, 1 H, H-1000), 5.48 (t, J ¼ 3.2 Hz, 1 H, H-12), 5.09 (br
s, 1 H, H-200), 4.89 (d, J ¼ 6.8 Hz, 1 H, H-10), 4.80 (m, 1 H, H-500), 4.56 (t, J ¼ 9.1 Hz,
Hz, 1 H, H-30), 4.51 (d, J ¼ 11.5 Hz, 1 H, H-50-1), 4.41 (m, 1 H, H-300), 4.28–4.35 (m,
3 H, H-40, H-4000, H-6000-1), 4.13–4.22 (m, 5 H, H-20, H-3000, H-400, H-50-2, H-6000-2),
4.00 (br s, 1 H, H-2000), 3.72 (m, 1 H, H-5000), 3.30–3.35 (m, 2 H, H-3, H-18), 1.67
(d, J ¼ 5.5 Hz, 3 H, H-600), 1.42, 1.32, 1.23, 1.02, 0.99, 0.98, 0.85 (s each, 3 H each,
CH3 ꢃ 7); 13C NMR (C5D5N): d 180.8 (C-28), 145.3 (C-13), 122.9 (C-12), 107.3
(C-1000), 106.8 (C-10), 102.1 (C-100), 89.1 (C-3), 83.8 (C-300), 79.9, 79.1, 79.0, 77.8,
76.4, 73.5, 72.1, 71.9, 70.3, 67.5, 62.9, 56.6, 48.5, 47.2, 42.6, 42.5, 40.2, 40.1, 39.4,
37.5, 33.8, 31.4, 28.8, 28.7, 27.4, 26.7, 24.3, 19.1, 19.0, 17.9, 17.8, 16.1; ESI-HRMS:
m=z calcd. for C47H75O16 [M ꢁ Hþ]: 895.5055; found: 895.5076.
ACKNOWLEDGMENT
This work is supported by the National Basic Research Program of China
(30701046).
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