Synthesis of Leonosides e and F derived from Leonurus japonicas Houtt

Article abstract of DOI:10.1016/j.carres.2013.07.012

Leonosides E and F, two natural phenylethanoid glycosides derived from Leonurus japonicas Houtt, which bear different trisaccharide moieties - one linear and one branched, were totally synthesized via a direct transglycosylation strategy. After trisaccharyl trichloroacetimidates 3 and 4 were prepared as glycosyl donors, they were coupled with the homovanillyl aglycon via silver triflate-promoted transglycosylation to successfully furnish the fully protected glycosides, which were globally deprotected to afford the target molecules in 6.77% and 10.08% overall yields for the longest linear synthetic sequence starting from 6 and 14.

Full text of DOI:10.1016/j.carres.2013.07.012

Carbohydrate Research 380 (2013) 174–180
Contents lists available at ScienceDirect
Carbohydrate Research
journal homepage: www.elsevier.com/locate/carres
Synthesis of Leonosides E and F derived from Leonurus japonicas
Houtt
Guofeng Gu a, , Yisheng Zhao a,b, Zhongwu Guo a,
⇑
⇑
a National Glycoengineering Research Center, Shandong University, Jinan 250010, PR China
b School of Pharmacy, Shandong University, Jinan 250012, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 15 July 2013
Received in revised form 25 July 2013
Accepted 27 July 2013
Available online 2 August 2013
Leonosides E and F, two natural phenylethanoid glycosides derived from Leonurus japonicas Houtt, which
bear different trisaccharide moieties—one linear and one branched, were totally synthesized via a direct
transglycosylation strategy. After trisaccharyl trichloroacetimidates 3 and 4 were prepared as glycosyl
donors, they were coupled with the homovanillyl aglycon via silver triflate-promoted transglycosylation
to successfully furnish the fully protected glycosides, which were globally deprotected to afford the target
molecules in 6.77% and 10.08% overall yields for the longest linear synthetic sequence starting from 6 and
14.
Keywords:
Phenylethanoid glycoside
Leonoside E
Ó 2013 Elsevier Ltd. All rights reserved.
Leonoside F
Transglycosylation
Carbohydrate
Total synthesis
1. Introduction
proved to exhibit anti-inflammatory, anti-platelet aggregation, and
cytotoxic activities.17–19 Recently, two phenylethanoid glycosides,
Many natural products are glycosylated with diversified sugar
chains which participate in a variety of biological functions.1–3
For instance, digoxin, a trisaccharyl glycoside isolated from the
plant Digitalis lanata, is now widely used in the treatment of vari-
ous heart conditions.4 OSW-1 is a cholestane glycoside isolated
from the bulbs of Ornithogalum saundersiae, which has exhibited
exceptionally potent cytotoxicities against various malignant tu-
mor cells.5,6 QS-21, a triterpene glycoside purified from the plant
Quillaja saponaria, is currently under clinical investigation as a vac-
cine adjuvant.7–9 Pharmaceutical Coramsine and Curaderm-BEC5
cream, whose primary ingredients are solasodine glycoalkaloids,
have been applied to the treatment of various cancers in clinic.10
Clearly, glycosylated natural products have valuable pharmacolog-
ical properties, thus they are attractive candidates for new drug
development and their synthetic and structure–activity relation-
ship studies have drawn significant attention.11–15
Leonoside E (1), 2-(3-methoxyl-4-hydroxyphenyl)-ethyl
nopyranosyl-(1?2)- -rhamnopyranosyl-(1?3)-b- -glucopyran-
oside, and Leonoside F (2), 2-(3-methoxyl-4-hydroxyphenyl)-ethyl
-rhamnopyranosyl-(1?3)-[b- -glucopyranosyl-(1?6)]-b-
glucopyranoside (Fig. 1), were isolated from the plant Leonurus
japonicas Houtt and characterized by Zhang and co-workers.20 In
vitro studies revealed that these phenylethanoid glycosides
a-L-arabi-
a-
L
D
a
-
L
D
D-
exhibited potent hepatoprotective activity against
amine-induced toxicity in HL-7702 cells at the concentration of
10 M. Being attracted by their peculiar oligosaccharide structures
D-galactos-
l
and potent bioactivity, we have performed the first total synthesis
of Leonoside E and Leonoside F.
2. Results and discussion
We planned to adopt a direct transglycosylation strategy
(Scheme 1) for the synthesis of the target phenylethanoid glyco-
sides. The key intermediates were trisaccharyl trichloroacetimi-
dates 3 and 4 that were used as glycosyl donors, and the
common glycosyl acceptor was 3-methoxyl-4-benzoxylphenyleth-
anol 5.21 Since all of the glycosidic linkages in 1 and 2 are trans, we
utilized acyl groups, including both acetyl and benzoyl groups,
for global hydroxyl group protection, to take advantage of the
neighboring group participation for stereoselective trans-
glycosylation.
The plants of the genus Leonurus have been widely used in China
as a traditional medicine to deal with menstrual disorder, treat
edema, and invigorate blood circulation.16 Phytochemical investiga-
tions of these plants have uncovered a wide range of bioactive
molecules, including phenylethanoid glycosides, labdane-type
diterpenoids, flavonoids, and cyclic peptides that have been
⇑
Corresponding authors. Tel.: +86 531 88363612; fax: +86 531 88363602.
E-mail addresses: guofenggu@sdu.edu.cn (G. Gu), zwguo@sdu.edu.cn (Z. Guo).
0008-6215/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.carres.2013.07.012

G. Gu et al. / Carbohydrate Research 380 (2013) 174–180
175
HO
HO
HO
O
O
HO
HO
OMe
OH
O
O
O
HO
O
HO
HO
O
OMe
OH
O
O
HO
HO
HO
O
O
O
HO
HO
HO
OH
OH
1
2
HO
Figure 1. The chemical structures of Leonoside E (1) and Leonoside F (2).
AcO
OH
O
AcO
BzO
BzO
BzO
O
O
AcO
O
O
O
CCl3
NH
O
BzO
1
2
and
AcO
BzO
O
BzO
O
O
AcO
O
O
CCl3
NH
OMe
AcO
AcO
AcO
BnO
OAc
AcO
OAc
4
3
5
Scheme 1. Retrosynthetic plan for Leonoside E (1) and Leonoside F (2).
AcO
O
O
O
O
O
O
AcO
AcO
O
O
AcO
SiPr
OH
OAc
AcO
OC(NH)CCl3
SiPr
O
O
O
AcO
O
8
O
O
10
O
O
O
BzO
BzO
BzO
O
d
BzO
O
BzO
BzO
O
BzO
O
O
O
O
b
c
RO
OH
AcO
AcO
AcO
AcO
AcO
6
R = H
7 R = Bz
OAc
OAc
12
OAc
a
AcO
11
9
AcO
AcO
O
e
O
OMe
OBn
O
AcO
5
O
g
BzO
1
3
BzO
O
O
f
AcO
AcO
OAc
13
Scheme 2. Reagents and conditions: (a) BzCl, pyridine, ꢀ15 °C, 75%; (b) TMSOTf, CH2Cl2, 0 °C, 65%; (c) NIS, TMSOTf, CH2Cl2, ꢀ10 °C, 67%; (d) 90% TFA; then Ac2O, pyridine, 71%
(two steps); (e) hydrazine acetate, DMF, 0 °C; then Cl3CCN, DBU, CH2Cl2, 0 °C, 57% (two steps); (f) AgOTf, 4 Å molecular sieves, CH2Cl2, ꢀ40 °C, 64%; (g) H2, Pd(OH)2/C, MeOH;
then 1 N NaOH, MeOH, 80% (two steps).
The synthesis of Leonoside E (1), as depicted in Scheme 2, com-
menced with regioselective benzoylation of isopropyl 4-O-ben-
(1:1 ratio) in a 71% overall yield for two steps. Compound 12 was
converted into the trisaccharyl donor 3 in two steps (in a 57% over-
all yield), including (i) regioselective deacetylation of the anomeric
position by hydrazine acetate23 and (ii) trichloroacetimidation24 of
the free anomeric hydroxyl group by trichloroacetonitrile with
1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as the promoter. This
zoyl-1-thio-b-
pyridine to obtain 3,4-di-O-benzoyl-1-thio-b-
D
-galactopyranside 622 by benzoyl chloride in
D
-galactopyranside
7 in a good yield (75%). The downfield shift of the H-3 signal of 7
to d 5.51 ppm in its 1H NMR spectrum confirmed the correct regi-
oselectivity. Glycosylation of 7 by trichloroacetimidate 8 in anhy-
drous CH2Cl2 at 0 °C under the promotion of trimethylsilyl
reaction afforded primarily the
a-anomer. However, the transgly-
cosylation between 3 and 5 in the presence of TMSOTf failed unex-
pectedly. It was found that aglycon 5 was unstable under the acidic
condition involved. Thus, silver triflate (AgOTf) was used as a mild
alternative promoter for this reaction,25 which afforded the desired
trisaccharide glycoside 13 in a 64% yield. The coupling constant
(J1,2 = 8.0 Hz) of the glucosyl H-1 of 13 at d 4.40 ppm in its 1H
NMR spectrum indicated the b-linkage between the glucose
residue and the aglycon. Finally, global deprotection was achieved
in two steps including catalytic hydrogenolysis to remove the ben-
zyl protection under a H2 atmosphere in the presence of 10%
Pd(OH)2/C and full deacylation with 1 N aq sodium hydroxide in
methanol, to afford the target Leonoside E (1) in an overall yield
of 80%. The structure of 1 was fully characterized by 1H NMR, 13C
NMR, and ESI-HRMS spectra.
triflate (TMSOTf) gave
a-(1?2)-linked disaccharide 9 in a 65%
yield. The -linkage in 9 was assigned based on the coupling con-
a
stant (J1,2 = 7.2 Hz) of its arabinosyl H-1 signal at d 4.52 ppm in the
1H NMR spectrum. As the glucosyl residue in the trisaccharyl donor
3 has a glycosidic linkage at the 3-O-position, 1,2;5,6-di-O-isopyro-
pylidene-
a
-D
-glucofuranose (10),
a
commercially available
inexpensive glucofuranose derivative with a free 3-OH group,
was used as a glycosyl acceptor, which can be opened later to form
the desired pyranose, for coupling with 9. The reaction was
promoted by N-iodosuccinimide (NIS) in the presence of a catalytic
amount of TMSOTf to furnish the desired trisaccharide 11 in a good
yield (67%), together with 10% of the corresponding b anomer.
Trifluroacetic acid (TFA)-promoted cleavage of the isopropylidene
groups in 11 was followed by acetylation with acetic anhydride
Leonoside F (2) was prepared by a similar strategy, as shown in
Scheme 3. First, the reaction between 10 and trichloroacetimidate
in pyridine to generate trisaccahride 12 as an
a,b-mixture

176
G. Gu et al. / Carbohydrate Research 380 (2013) 174–180
BzO
O
BzO
BzO
BzO
BzO
BzO
BzO
BzO
BzO
O
NH
O
O
BzO
O
RO
O
O
CCl3
NH
Cl3C
BzO
HO
O
R'O
O
O
BzO
10
AcO
17
OAc
O
d
O
O
AcO
O
O
AcO
O
a
c
O
O
O
AcO
AcO
O
O
OAc
AcO
AcO
AcO
OAc
19
AcO
14
AcO
OAc
18
OAc
R,R' = C(CH3)2
16 R,R' = H,H
15
b
BzO
BzO
BzO
O
e
O
O
BzO
AcO
5
O
OMe
OBn
O
g
AcO
2
4
O
f
AcO
AcO
20
OAc
Scheme 3. Reagents and conditions: (a) TMSOTf, CH2Cl2, 0 °C, 83%; (b) 80% HOAc, 60 °C, 68%; (c) TMSOTf, CH2Cl2, 0 °C, 74%; (d) 90% TFA; then Ac2O, pyridine, 70% (two steps);
(e) hydrazine acetate, DMF, 0 °C; then Cl3CCN, DBU, CH2Cl2, 0 °C, 65% (two steps); (f) AgOTf, 4 Å molecular sieves, CH2Cl2, ꢀ40 °C, 68%; (g) H2, Pd(OH)2/C, MeOH; then 1 N
NaOH, MeOH, 78% (two steps).
14 under the promotion of TMSOTf gave
a-(1?3)-linked
3. Experimental section
3.1. General methods
disaccharide 15 in an 83% yield. The 5,6-O-isopropylidene group
in 15 was selectively cleaved with 80% HOAc at 60 °C to afford a
diol 16 that was directly employed as a glycosyl acceptor. Glycosyl-
ation of 16 with 1.1 equiv of trichloroacetimidate donor 17 in
anhydrous CH2Cl2 at 0 °C under the influence of TMSOTf was reg-
ioselective for the more reactive 6-OH group to produce b-
(1?6)-linked trisaccharide 18 in a 74% yield. The coupling constant
(J1,2 = 7.9 Hz) of the glucosyl H-1 of 18 at d 4.95 ppm in its 1H NMR
spectrum confirmed the b-configuration of the newly formed gly-
cosidic linkage. Treatment of 18 with 90% TFA to remove the iso-
propylidene group followed by acetylation of the product with
Optical rotations were determined at 20 °C with a Rudolph
Autopol I automatic polarimeter. 1H and 13C NMR spectra were re-
corded with a Bruker 400 spectrometer for solutions in CDCl3 and
CD3OD. Chemical shifts are given in ppm downfield from internal
Me4Si. High-resolution mass spectra were performed by positive-
mode electrospray ionization on a JEOL JMS-DX-303HF spectrome-
ter. Thin-layer chromatography (TLC) was performed on the silica
gel HF254 plate with detection by charring with 30% (v/v) H2SO4
in MeOH or by a UV detector. Column chromatography was con-
ducted by elution of a silica gel column with ethyl acetate–petro-
leum ether (bp 60–90 °C) as the eluents. Solutions were
concentrated at <60 °C under diminished pressure.
acetic anhydride in pyridine furnished 19 as an
a,b-mixture (3:2
ratio) in a 70% overall yield for two steps. As described above, reg-
ioselective deacetylation of the anomeric position of 19 by hydra-
zine acetate and trichloroacetimidation with trichloroacetonitrile
and DBU afforded the trisaccharyl donor 4 in a 65% overall yield
for two steps. Next, 4 was coupled with 5 in the presence of silver
triflate (0.5 equiv) to produce the fully protected form of Leonoside
F (20) in a 68% yield. The b-linkage between the glycan and the
aglycon was assigned based on the coupling constant
(J1,2 = 8.0 Hz) of the glucosyl H-1 of 20 at d 4.14 ppm in its 1H
NMR spectrum. Subsequently, 20 was hydrogenolized in methanol
under a H2 atmosphere with 10% Pd(OH)2/C as the catalyst, which
was followed by saponification with 1 N aq NaOH in methanol, to
give the target molecule 2 in an overall yield of 78% for two steps.
The spectrographic data for the synthetic 2 were all fulfilled by its
structure.
3.2. Isopropyl 3,4-di-O-benzoyl-1-thio-a-L-rhamnopyranoside
(7)
A solution of benzoyl chloride (0.8 mL, 6.88 mmol) in CH2Cl2
(5 mL) was added dropwise to a solution of isopropyl 4-O-ben-
zoyl-1-thio-a-L
-rhamnopyranoside 622 (2.0 g, 6.13 mmol) in anhy-
drous CH2Cl2 (40 mL) containing 5 mL of pyridine at ꢀ30 °C within
10 min. The reaction mixture was stirred for 1 h with the tempera-
ture slowly warmed up to 0 °C, at the end of which time TLC (3:1
petroleum ether–ethyl acetate) indicated the completion of the ben-
zoylation. The mixture was then diluted with CH2Cl2 (100 mL), and
washed with 1 M aq HCl, water, and brine. The organic layer was
dried over anhydrous Na2SO4 and then concentrated. The resulting
residue was purified by flash column chromatography (3:1 petro-
leum ether–ethyl acetate) to afford 7 (1.98 g, 75%) as a white foamy
In summary, two natural phenylethanoid glycosides, Leono-
side E (1) and Leonoside F (2), were synthesized by a highly
convergent and efficient strategy. The syntheses were high-
lighted with the construction of the trisaccharyl trichloroacetim-
solid. ½a 2D0
ꢁ
ꢀ72 (c 1, CHCl3); 1H NMR (400 MHz, CDCl3): d 1.32 (d, 3H, J
idate donors
3 and 4 first, followed by a tansglycosylation
6.2 Hz, H-6), 1.37 (d, 2 ꢂ 3H, J 6.7 Hz, –CH(CH3)2), 3.13 (m, 1H, –
CH(CH3)2), 4.38 (dd, 1H, J 1.4, 3.0 Hz, H-2), 4.50 (m, 1H, H-5), 5.41
(d, 1H, J 1.4, H-1), 5.51 (dd, 1H, J 3.0, 9.8 Hz, H-3), 5.60 (t, 1H, J
9.8 Hz, H-4), 7.34–7.93 (m, 10H, Ph); 13C NMR (100 MHz, CDCl3): d
17.4, 23.6, 23.8, 35.9, 67.2, 71.4, 71.9, 73.1, 83.7, 165.6, 165.9; ESI-
HRMS (positive mode): Calcd for (C23H26O6S+NH4+): 448.1788;
found m/z: 448.1800.
reaction under the influence of silver triflate to directly couple
them with the aglycon 5. The trisaccharide syntheses were
significantly facilitated by using a commercially available gluco-
furanose derivative 10 as one of the building blocks, which was
readily converted to glucopyranose later on through ring
opening and closing. This intermediate also enabled easily
protecting group manipulation and regioselective glycosylation
in the presence of more than one free hydroxyl groups in the
structure. Clearly, if revised glycans and aglycons were used
for the tansglycosylation reaction, the present synthetic strategy
could lead to a variety of Leonoside analogs or other phenyleth-
anoid glycosides rapidly for structure–activity relationship
studies and other biological applications.
3.3. Isopropyl 2,3,4-tri-O-acetyl-
3,4-di-O-benzoyl-1-thio- -rhamnopyranoside (9)
a-L-arabinopyranosyl-(1?2)-
a-L
To a solution of 7 (630 mg, 1.46 mmol) and 2,3,4-tri-O-acetyl-b-
-arabinopyranosyl trichloroacetimidate 8 (677 mg, 1.61 mmol) in
L
anhydrous CH2Cl2 (5 mL) at 0 °C was added TMSOTf (30 lL,

G. Gu et al. / Carbohydrate Research 380 (2013) 174–180
177
0.165 mmol) under N2 protection. After the reaction mixture was
stirred for 40 min, it was neutralized with triethylamine and con-
centrated, and the resulting residue was purified by flash column
chromatography (3:1 petroleum ether–ethyl acetate) to yield 9
3.6, 10.0 Hz, H-2Glu), 5.19 (br s, 2H, H-1Rha, H-4Ara), 5.24 (t, 1H, J
10.0 Hz, H-4Glu), 5.29 (dd, 1H, J 7.1, 9.6 Hz, H-2Ara), 5.38 (t, 1H, J
10.2 Hz, H-4Rha), 5.44 (dd, 1H, J 2.7, 10.2 Hz, H-3Rha), 6.34 (d, 1H,
J 3.6 Hz, H-1Glu), 7.35–7.96 (m, 10H, Ph); ESI-HRMS (positive
ion): Calcd for (C45H52O23+NH4+): 978.3238; found m/z: 978.3247.
(655 mg, 65%) as a white foamy solid. ½a D20
ꢁ
ꢀ3 (c 2, CHCl3); 1H
NMR (400 MHz, CDCl3): d 1.30 (d, 3H, J 6.2 Hz, H-6Rha), 1.35, 1.37
(2 d, 2 ꢂ 3H, J 6.6 Hz, –CH(CH3)2), 2.06, 2.15, 2.16 (3 s, 3 ꢂ 3H,
3CH3CO), 3.14 (m, 1H, –CH(CH3)2), 3.51 (dd, 1H, J 1.4, 13.0 Hz, H-
5aAra), 4.40 (dd, 1H, J 3.0, 13.0 Hz, H-5bAra), 4.37 (dd, 1H, J 1.8,
2.7 Hz, H-2Rha), 4.43 (m, 1H, H-5Rha), 4.52 (d, 1H, J 7.1 Hz, H-1Ara),
4.96 (dd, 1H, J 3.5, 9.6 Hz, H-3Ara), 5.20 (br s, 1H, H-4Ara), 5.35
(dd, 1H, J 7.1, 9.6 Hz, H-2Ara), 5.43 (t, 1H, J 10.0 Hz, H-4Rha), 5.49
(d, 1H, J 1.8 Hz, H-1Rha), 5.52 (dd, 1H, J 2.7, 10.0 Hz, H-3Rha), 7.35-
8.00 (m, 10H, Ph); 13C NMR (100 MHz, CDCl3): d 17.5, 20.7 (2C),
20.9, 23.7, 23.9, 36.4, 63.4, 67.2, 67.7, 69.0, 70.0, 72.0, 72.3, 78.2,
83.4, 102.1, 165.5, 165.7, 169.7, 170.2, 170.4; ESI-HRMS (positive
mode): Calcd for (C34H40O13S+NH4+): 706.2528; found m/z:
706.2537.
3.6. 2,3,4-Tri-O-acetyl-
benzoyl- -rhamnopyranosyl-(1?3)-2,4,6-tri-O-acetyl-
glucopyranosyl trichloroacetimidate (3)
a-L-arabinopyranosyl-(1?2)-3,4-di-O-
a
-
L
D-
To a solution of 12 (336 mg, 0.35 mmol) in DMF (5 mL) was
added hydrazine acetate (64 mg, 0.70 mmol) at 0 °C. The reaction
mixture was stirred for 2 h under this condition, when TLC (2:1
petroleum ether–ethyl acetate) indicated the completion of the
reaction. The reaction mixture was diluted with EtOAc (40 mL),
and washed successively with water (30 mL) and brine (30 mL).
The organic phase was dried over anhydrous Na2SO4 and concen-
trated, and the residue was then subjected to silica gel column
chromatography (1:1 petroleum ether–EtOAc). The resultant prod-
uct was dissolved in anhydrous CH2Cl2 (5 mL), and then to the
solution was added trichloroacetonitrile (0.14 mL, 1.4 mmol) and
3.4. 2,3,4-Tri-O-acetyl-
benzoyl- -rhamnopyranosyl-(1?3)-1,2;5,6-di-O-isopropylidene-
-glucofuranose (11)
a-L-arabinopyranosyl-(1?2)-3,4-di-O-
a-L
a-
D
DBU (20 lL) at 0 °C. The mixture was stirred for 1.5 h and concen-
trated, and the residue was purified by flash column chromatogra-
To a solution of 9 (613 mg, 0.89 mmol) and 1,2;5,6-di-O-isopro-
pylidene- -glucofuranose 10 (232 mg, 0.89 mmol) in anhydrous
CH2Cl2 (8 mL) was added NIS (300 mg, 1.34 mmol) and a catalytic
amount of TMSOTf (18
phy (2:1 petroleum ether–ethyl acetate) to afford 3 (212 mg, 57%
a
-D
for two steps) as a white foamy solid. ½a D20
ꢁ
+65 (c 2, CHCl3); 1H
NMR (400 MHz, CDCl3): d 1.28 (d, 3H, J 6.2 Hz, H-6Rha), 2.05, 2.09,
2.10, 2.12, 2.17, 2.20 (6 s, 6 ꢂ 3H, 6CH3CO), 3.49 (dd, 1H, J 1.0,
13.0 Hz, H-5aAra), 3.91 (dd, 1H, J 3.0, 13.0 Hz, H-5bAra), 4.03 (m,
1H, H-5Rha), 4.09–4.18 (m, 2H, H-5,6aGlu), 4.22–4.30 (m, 2H, H-
2Rha, h-6bGlu), 4.33 (t, 1H, J 9.6 Hz, H-3Glu), 4.49 (d, 1H, J 7.0 Hz,
H-1Ara), 4.93 (dd, 1H, J 3.5, 9.6 Hz, H-3Ara), 5.16 (dd, 1H, J 3.6,
9.6 Hz, H-2Glu), 5.18–5.21 (m, 1H, H-4Ara), 5.23 (d, 1H, J 1.8 Hz, H-
1Rha), 5.28 (t, 1H, J 9.6 Hz, H-4Glu), 5.30 (dd, 1H, J 7.0, 9.6 Hz, H-
2Ara), 5.39 (t, 1H, J 10.0 Hz, H-4Rha), 5.46 (dd, 1H, J 2.8, 10.0 Hz,
H-3Rha), 6.57 (d, 1H, J 3.6 Hz, H-1Glu), 7.32–8.01 (m, 10H, Ph),
8.70 (s, 1H, NH); 13C NMR (100 MHz, CDCl3): d 17.6, 20.2, 20.7
(2C), 20.8, 20.9, 21.0, 61.5, 63.3, 67.6 (2C), 68.2, 68.9, 69.9, 70.5,
71.3, 71.4, 72.2, 75.4, 75.5, 90.8, 93.2, 100.3, 101.9, 160.7, 165.5
(2C), 169.3, 169.7, 169.8, 170.1, 170.2, 170.7; Anal. Calcd for C45-
H50Cl3NO22: C, 50.83; H, 4.74; N, 1.32. Found: C, 50.85; H, 4.48;
N, 1.40.
l
L, 0.1 mmol) at ꢀ10 °C under N2 protec-
tion. The reaction mixture was stirred for 40 min, at end of which
time TLC (2:1 petroleum ether–ethyl acetate) indicated the com-
plete disappearance of 9. The reaction mixture was neutralized
with triethylamine and concentrated, and the residue was purified
by flash column chromatography (2:1 petroleum ether–ethyl ace-
tate) to yield 11 (520 mg, 67%) as a white foamy solid. ½a D20
ꢀ4 (c
ꢁ
1, CHCl3); 1H NMR (400 MHz, CDCl3): d 1.25 (d, 3H, J 6.0 Hz, H-
6Rha), 1.34, 1.41, 1.52 (3 s, 4ꢂ3H, C(CH3)2), 2.06, 2.16, 2.20 (3 s,
3 ꢂ 3H, 3CH3CO), 3.52 (dd, 1H, J 1.2, 13.0 Hz, H-5aAra), 3.96-4.08
(m, 2H, H-6aGlu, H-5bAra), 4.15 (dd, 1H, J 3.2, 9.0 Hz, H-4Glu),
4.22–4.28 (m, 2H, H-5,6bGlu), 4.43-4.51 (m, 3H, H-2,5Rha, H-3Glu),
4.52-4.56 (m, 2H, H-1Ara, H-2Glu), 4.97 (dd, 1H, J 3.5, 9.6 Hz, H-
3Ara), 5.11 (d, 1H, J 1.2 Hz, H-1Rha), 5.20 (br s, 1H, H-4Ara), 5.34
(dd, 1H, J 7.1, 9.6 Hz, H-2Ara), 5.43 (t, 1H, J 10.0 Hz, H-4Rha), 5.57
(dd, 1H, J 3.0, 10.0 Hz, H-3Rha), 5.92 (d, 1H, J 3.6 Hz, H-1Glu),
7.32–8.00 (m, 10H, Ph); 13C NMR (100 MHz, CDCl3): d 17.2, 20.7,
20.8, 20.9, 25.4, 26.3, 26.8 (2C), 63.3, 67.0, 67.6, 68.3, 68.9, 70.0,
71.5, 71.8, 71.9, 75.9, 76.6, 81.1, 81.9, 96.4, 101.9, 105.3, 109.3,
112.0, 165.5, 165.7, 169.6, 170.2, 170.4; ESI-HRMS (positive ion):
Calcd for (C43H52O19+NH4+): 890.3441; found m/z: 890.3451.
3.7. 3-Methoxyl-4-benzoxylphenylethyl 2,3,4-tri-O-acetyl-
arabinopyranosyl-(1?2)-3,4-di-O-benzoyl- -rhamnopyranosyl-
(1?3)-2,4,6-tri-O-acetyl-b- -glucopyranoside (13)
a-L-
a-L
D
To a solution of 3 (75 mg, 0.07 mmol) and 3-methoxyl-4-ben-
zoxylphenylethanol 5 (18 mg, 0.07 mmol) in anhydrous CH2Cl2
0
3.5. 2,3,4-Tri-O-acetyl-
O-benzoyl- -rhamnopyranosyl-(1?3)-1,2,4,6-tetra-O-acetyl-
-glucopyranose (12)
a
-
L
-arabinopyranosyl-(1?2)-3,4-di-
(3 mL) was added 4AÅ molecular sieves (50 mg). The reaction mix-
ture was stirred at rt for 30 min under a N2 atmosphere, and then
cooled to ꢀ40 °C. Silver triflate (10 mg, 0.04 mmol) was added in
the dark. The reaction mixture was stirred for 2 h while it was
slowly warmed up to 0 °C, neutralized with triethylamine, and
concentrated. Purification of the resulting residue on a silica gel
column using 3:2 petroleum ether–EtOAc as the eluents gave 13
a
-L
D
A solution of 11 (472 mg, 0.54 mmol) in 90% aq TFA (10 mL) was
stirred at rt for 1 h. The reaction mixture was then co-evaporated
with toluene (2 ꢂ 30 mL), and the resulting residue was dissolved
into pyridine (5 mL) and acetic anhydride (3 mL). The reaction mix-
ture was stirred overnight at rt, and then concentrated under
diminished pressure. The resulting residue was purified by flash
column chromatography (2:1 petroleum ether–ethyl acetate) to
(52 mg, 64%) as a white foamy solid. ½a D20
ꢁ
+24 (c 0.5, CHCl3); 1H
NMR (400 MHz, CDCl3): d 1.24 (d, 3H, J 6.2 Hz, H-6Rha), 1.93, 2.05,
2.10, 2.11, 2.13, 2.18 (6 s, 6 ꢂ 3H, 6CH3CO), 2.82 (t, 2H, J 6.6 Hz, –
OCH2CH2–), 3.48 (dd, 1H, J 1.2, 13.0 Hz, H-5aAra), 3.56–3.65 (m,
2H, H-5Glu, –OCH2CH2–), 3.90 (s, 3H, –OCH3), 3.89–3.95 (m, 2H,
yield 12 (369 mg,
a
/b isomer ꢃ 1:1, 71%) as a white foamy solid.
½
a 2D0
ꢁ
+36 (c 1.5, CHCl3); 1H NMR (400 MHz, CDCl3) for
a
isomer: d
H-3Glu, H-5bAra), 4.00 (m, 1H, H-5Rha), 4.08–4.18 (m, 3H, H-6aGlu
,
1.28 (d, 1H, J 6.2 Hz, H-6Rha), 2.06, 2.09, 2.12, 2.13, 2.15, 2.18,
2.21 (7 s, 7 ꢂ 3H, 7CH3CO), 3.48 (dd, 1H, J 1.2, 12.1 Hz, H-5aAra),
3.90 (dd, 1H, J 3.0, 12.1 Hz, H-5bAra), 3.98–4.12 (m, 3H, H-5Rha, H-
5,6aGlu), 4.22–4.28 (m, 3H, H-2Rha, H-3,6bGlu), 4.50 (d, 1H, J
7.1 Hz, H-1Ara), 4.93 (dd, 1H, J 3.5, 9.6 Hz, H-3Ara), 5.13 (dd, 1H, J
H-2Rha, –OCH2CH2–), 4.25 (dd, 1H, J 4.8, 12.3 Hz, H-6bGlu), 4.40
(d, 1H, J 8.0 Hz, H-1Glu), 4.46 (d, 1H, J 7.2 Hz, H-1Ara), 4.92 (dd,
1H, J 3.5, 9.6 Hz, H-3Ara), 5.05 (d, 1H, J 1.7 Hz, H-1Rha), 5.08 (dd,
1H, J 8.0, 9.6 Hz, H-2Glu), 5.13 (s, 2H, -OCH2Ph), 5.15 (t, 1H, J
9.6 Hz, H-4Glu), 5.19 (m, 1H, H-4Ara), 5.28 (dd, 1H, J 7.2, 9.6 Hz, H-

178
G. Gu et al. / Carbohydrate Research 380 (2013) 174–180
2Ara), 5.35 (t, 1H, J 10.0 Hz, H-4Rha), 5.41 (dd, 1H, J 2.8, 10.0 Hz, H-
3Rha), 6.66 (dd, 1H, J 1.8, 8.2 Hz, Ph), 6.76 (d, 1H, J 1.8 Hz, Ph), 6.80
(d, 1H, J 8.2 Hz, Ph), 7.26–7.97 (m, 10H, Ph); 13C NMR (100 MHz,
CDCl3): d 17.5, 20.4, 20.7, 20.8, 20.9 (2C), 21.1, 35.6, 56.0, 62.1,
63.3, 67.5, 67.6, 68.9, 69.3, 70.0, 70.7, 71.1, 71.3 (2C), 72.1, 72.5,
75.6, 78.7, 100.2, 100.9, 101.9, 113.1, 114.1, 120.7, 146.6, 149.4,
165.4, 165.5, 169.2, 169.4, 169.7, 170.2 (2C), 170.8; ESI-HRMS (po-
sitive ion): Calcd for (C59H66O24+NH4+): 1176.4282; found m/z:
1176.4284.
solid. ½a 2D0
ꢁ
ꢀ51 (c 1, CHCl3); 1H NMR (400 MHz, CDCl3): d 1.21 (d,
3H, J 6.2 Hz, H-6Rha), 1.31, 1.49 (2 s, 2 ꢂ 3H, C(CH3)2), 1.99, 2.04,
2.16 (3 s, 3 ꢂ 3H, 3CH3CO), 3.79 (dd, 1H, J 5.2, 11.2 Hz, H-6aGlu),
3.92 (dd, 1H, J 3.2, 11.2 Hz, H-6bGlu), 3.95–4.00 (m, 1H, H-5Glu),
4.16–4.25 (m, 2H, H-4Glu, H-5Rha), 4.37 (d, 1H, J 3.0 Hz, H-3Glu),
4.52 (d, 1H, J 3.7 Hz, H-2Glu), 4.92 (d, 1H, J 1.4 Hz, H-1Rha), 5.07 (t,
1H, J 9.8 Hz, H-4Rha), 5.20 (dd, 1H, J 1.2, 3.4 Hz, H-2Rha), 5.23 (dd,
1H, J 3.4, 9.8 Hz, H-3Rha), 5.91 (d, 1H, J 3.7 Hz, H-1Glu); 13C NMR
(100 MHz, CDCl3): d 17.2, 20.7, 20.8, 20.9, 26.1, 26.5, 64.2, 67.1,
68.1, 69.0, 70.0, 70.7, 78.0, 79.2, 81.6, 95.3, 104.9, 111.8, 170.0,
170.1, 170.3; ESI-HRMS (positive ion): Calcd for (C21H32O13+NH4+):
510.2181; found m/z: 510.2180.
3.8. Leonoside E (1)
To a solution of 13 (38 mg, 0.033 mmol) in MeOH (5 mL) was
added 10% Pd(OH)2/C (10 mg), and the resulting suspension was
stirred under H2 atmosphere at rt overnight. The solid materials
were filtrated off, and the solution was concentrated. The resulting
product was then re-dissolved in MeOH (5 mL), to which was
added 1 N aq NaOH dropwise until pH 10 was reached. The reac-
tion mixture was stirred at rt for 3 h, and then neutralized with
Amberlite IR 120 (H+). The reaction solution was filtered off and
concentrated. The resulting residue was purified by flash column
chromatography (3:1 CH2Cl2–MeOH) to afford 1 (16 mg, 80%) as
3.11. 2,3,4-Tri-O-acetyl-
tetra-O-benzoyl-b- -glucopyranosyl-(1?6)]-1,2-O-isopropylidene-
-glucofuranose (18)
a-L-rhamnopyranosyl-(1?3)-[2,3,4,6-
D
a-D
To a solution of 16 (350 mg, 0.71 mmol) and 2,3,4,6-tetra-O-
benzoyl- -glucopyranosyl trichloroacetimidate 17 (580 mg,
0.78 mmol) in anhydrous CH2Cl2 (10 mL) at 0 °C was added
TMSOTf (14 L, 0.08 mmol) under N2 protection. The reaction mix-
a
-D
l
ture was stirred for 1 h, neutralized by triethylamine, and then
concentrated. The resulting residue was purified by flash column
chromatography (1:1 petroleum ether–ethyl acetate) to yield 18
a white solid. ½a D20
ꢁ
ꢀ19 (c 0.12, CH3OH); 1H NMR (400 MHz, CD3-
OD): d 1.25 (d, 3H, J 6.2 Hz, H-6Rha), 2.86 (br t, 2H, J 7.0 Hz, –OCH2-
CH2–), 3.27–3.34 (m, 2H), 3.35 (t, 1H, J 9.7 Hz), 3.41 (t, 1H, J 9.6 Hz),
3.48 (t, 1H, J 8.8 Hz), 3.53 (dd, 1H, J 3.5, 9.3 Hz), 3.56 (dd, 1H, J 1.2,
10.7 Hz), 3.65 (dd, 1H, J 7.2, 9.2 Hz), 3.69 (dd, 1H, J 5.4, 11.9 Hz),
3.72–3.80 (m, 3H), 3.86 (s, 3H, –OCH3), 3.86–3.91 (m, 2H), 3.95–
4.02 (m, 2H), 4.07 (m, 1H, –OCH2CH2–), 4.32 (d, 1H, J 7.9 Hz, H-
1Glu), 4.37 (d, 1H, J 7.2 Hz, H-1Ara), 5.46 (d, 1H, J 1.3 Hz, H-1Rha),
6.70 (m, 2H), 6.87 (s, 1H); 13C NMR (100 MHz, CD3OD): d 16.5,
35.4, 55.0, 61.3, 65.8, 68.4, 68.6, 68.8, 70.6, 70.8, 71.5, 73.0 (2C),
74.1, 76.5, 81.1, 83.5, 100.3, 102.8, 106.0, 112.4, 114.7, 121.0,
130.2, 144.5, 147.4; ESI-HRMS (positive ion): Calcd for (C26H40-
O16+Na+): 631.2209; found m/z: 631.2211.
(563 mg, 74%) as a white foamy solid. ½a D20
ꢁ
ꢀ10 (c 0.5, CHCl3); 1H
NMR (400 MHz, CDCl3): d 1.13 (d, 3H, J = 6.2 Hz, H-6Rha), 1.26,
1.30 (2 s, 2 ꢂ 3H, C(CH3)2), 1.97, 2.01, 2.15 (3 s, 3 ꢂ 3H, 3CH3CO),
3.92 (dd, 1H, J 4.8, 10.6 Hz, H-6aGlu), 3.92 (m, 1H, H-5Glu), 4.07–
4.15 (m, 2H, H-6bGlu, H-5Glu), 4.17–4.25 (m, 2H, H-4Glu, H-5Rha),
4.31 (d, 1H, J 3.5 Hz, H-3Glu), 4.44 (dd, 1H, J 4.6, 12.2 Hz, H-6aGlu),
4.45 (d, 1H, J 3.6 Hz, H-2Glu), 4.74 (dd, 1H, J 3.0, 12.2 Hz, H-6bGlu),
4.88 (s, 1H, H-1Rha), 4.95 (d, 1H, J 7.9 Hz, H-1Glu), 5.07 (t, 1H, J
9.8 Hz, H-4Rha), 5.17–5.23 (m, 2H, H-2,3Rha), 5.53 (dd, 1H, J 7.9,
9.7 Hz, H-2Glu), 5.70 (t, 1H, J 9.7 Hz, H-4Glu), 5.82 (d, 1H, J 3.6 Hz,
H-1Glu), 5.90 (t, 1H, J 9.7 Hz, H-3Glu), 7.35-8.06 (m, 20H, Ph); 13C
NMR (100 MHz, CDCl3): d 17.1, 20.6, 20.7, 20.9, 26.2, 26.6, 62.7,
66.7, 67.0, 69.1, 69.4, 70.1, 70.6, 72.1, 72.3, 72.4, 72.9, 77.4, 78.9,
81.5, 95.2, 101.4, 105.0, 111.9, 165.1, 165.2, 165.7, 166.0, 169.8,
169.9, 170.1; ESI-HRMS (positive ion): Calcd for (C55H58O22+NH4+):
1088.3758; found m/z: 1088.3762.
3.9. 2,3,4-Tri-O-acetyl-
a-L-rhamnopyranosyl-(1?3)-1,2;5,6-di-
O-isopropylidene- -glucofuranose (15)
a-D
To a solution of 2,3,4-tri-O-acetyl-a-L-rhamnopyranosyl trichlo-
roacetimidate 14 (736 mg, 1.69 mmol) and 10 (400 mg,
1.54 mmol) in anhydrous CH2Cl2 (8 mL) at 0 °C was added TMSOTf
(31 lL, 0.17 mmol) under N2 protection. The reaction mixture was
stirred for 1 h, then neutralized with Et3N, and concentrated. The
resulting residue was purified by flash column chromatography
(2:1 petroleum ether–ethyl acetate) to yield 15 (679 mg, 83%) as
3.12. 2,3,4-Tri-O-acetyl-
tetra-O-benzoyl-b- -glucopyranosyl-(1?6)]-1,2,4-tri-O-acetyl-
-glucopyranose (19)
a-L-rhamnopyranosyl-(1?3)-[2,3,4,6-
D
D
After a solution of 18 (493 mg, 0.46 mmol) in 90% aq TFA
a white foamy solid. ½a D20
ꢁ
ꢀ58 (c 0.5, CHCl3); 1H NMR (400 MHz,
(10 mL) was stirred at rt for 1 h, the reaction mixture was co-evap-
orated with toluene (2 ꢂ 30 mL). The resulting residue was dis-
solved in pyridine (5 mL) and acetic anhydride (3 mL), and the
mixture was stirred at rt overnight and then concentrated. The
resulting residue was purified by flash column chromatography
CDCl3): d 1.19 (d, 3H, J 6.2 Hz, H-6Rha), 1.31, 1.35, 1.40, 1.50 (4 s,
4 ꢂ 3H, C(CH3)2), 2.03, 2.17 (3 s, 3 ꢂ 3H, 3CH3CO), 3.95 (dd, 1H, J
5.9, 8.5 Hz, H-6aGlu), 4.10 (dd, 1H, J 3.3, 9.0 Hz, H-4Glu), 4.19 (dd,
1H, J 6.1, 8.5 Hz, H-6bGlu), 4.26–4.36 (m, 3H, H-3,5Glu, H-5Rha),
4.50 (d, 1H, J 3.7 Hz, H-2Glu), 4.91 (d, 1H, J 1.2 Hz, H-1Rha), 5.08 (t,
1H, J 9.8 Hz, H-4Rha), 5.20 (dd, 1H, J 1.2, 3.4 Hz, H-2Rha), 5.23 (dd,
1H, J 3.4, 9.8 Hz, H-3Rha), 5.91 (d, 1H, J 3.7 Hz, H-1Glu); 13C NMR
(100 MHz, CDCl3): d 17.0, 20.6, 20.7, 20.8, 25.9, 26.4, 64.0, 66.9,
68.0, 69.0, 69.9, 70.6, 77.6, 79.0, 81.4, 95.0, 104.9, 111.6, 169.9
(2C), 170.1; ESI-HRMS (positive ion): Calcd for (C24H36O13+NH4+):
550.2494; found m/z:550.2491.
(2:1 petroleum ether–ethyl acetate) to yield 19 (373 mg,
a
/b iso-
mer ꢃ 3:2, 70%) as a white foamy solid. ½a D20
ꢁ
+18 (c 1, CHCl3); 1H
NMR (400 MHz, CDCl3): d 1.11 (d, 1.2H, J 6.2 Hz, H-6Rha of b iso-
mer), 1.13 (d, 1.8H, J 6.2 Hz, H-6Rha of
a isomer), 1.89 (s, 1.8H),
1.95 (s, 3H), 1.99 (s, 1.2H), 2.04 (s, 2.4H), 2.05 (s, 1.8H), 2.06 (s,
3.6H), 2.11 (s, 1.2H), 2.13 (s, 3H), 3.60-3.73 (m, 1.8H), 3.75-3.91
(m, 1H), 3.85-3.96 (m, 2.2H), 4.09-4.18 (m, 1H), 4.45–4.51 (m,
0
0
1H, H-6aGlu ), 4.60–4.66 (m, 1H, H-6bGlu ), 4.71 (d, 0.4H, J 1.3 Hz,
3.10. 2,3,4-Tri-O-acetyl-
a-L-rhamnopyranosyl-(1?3)-1,2-O-
H-1Rha of b isomer), 4.79 (d, 0.6H, J 1.8 Hz, H-1Rha of
a
isomer),
isopropylidene- -glucofuranose (16)
a
-D
0
4.81–5.07 (m, 5.4H, H-1Glu , H-2,3,4Glu, H-3,4Rha, H-2Rha of b iso-
mer), 5.11 (dd, 0.6H, J 1.8, 2.6 Hz, H-2Rha of
a isomer), 5.46–5.54
A solution of 15 (602 mg, 1.13 mmol) in 80% aq acetic acid
(15 mL) was stirred at 60 °C for 2 h. The reaction mixture was co-
evaporated with toluene (2 ꢂ 20 mL) to dryness. Purification of
the resulting residue on a silica gel column using 1:1 petroleum
ether–EtOAc as the eluents gave 16 (378 mg, 68%) as a white foamy
0
0
(m, 1.4H, H-1 of b isomer and H-2Glu ), 5.64 (t, 0.4H, J 9.6 Hz, H-4Glu
0
of b isomer), 5.67 (t, 0.6H, J 9.6 Hz, H-4Glu of
a isomer), 5.88 (t,
0
0
0.4H, J 9.6 Hz, H-3Glu of b isomer), 5.89 (t, 0.6H, J 9.6 Hz, H-3Glu
of
a a isomer), 7.26–
isomer), 6.14 (d, 0.6H, J 3.6 Hz, H-1Glu of

G. Gu et al. / Carbohydrate Research 380 (2013) 174–180
179
8.02 (m, 20H, Ph); ESI-HRMS (positive ion): Calcd for (C58H60O25+-
NH4+): 1174.3762; found m/z: 1174.3765.
Ph), 6.68 (d, 1H, J 1.8 Hz, Ph), 6.79 (d, 1H, J 8.2 Hz, Ph), 7.24–8.06
(m, 25H, Ph); 13C NMR (100 MHz, CDCl3): d 17.2, 20.5, 20.6, 20.8,
20.9, 21.0, 35.4, 56.0, 63.0, 65.3, 67.4, 68.8, 69.5, 69.8, 70.2, 70.3,
70.6, 71.1, 71.5, 71.9, 72.3, 72.8, 73.6, 81.2, 99.4, 100.5, 101.3,
113.2, 114.3, 120.7, 146.4, 149.5, 165.0, 165.2, 165.7, 166.1,
169.3, 169.5, 169.8, 170.0, 170.1; ESI-HRMS (positive ion): Calcd
for (C72H74O26+NH4+): 1372.4807; found m/z: 1372.4840.
3.13. 2,3,4-Tri-O-acetyl-
tetra-O-benzoyl-b- -glucopyranosyl-(1?6)]-2,4-di-O-acetyl-
glucopyranosyl trichloroacetimidate (4)
a-L-rhamnopyranosyl-(1?3)-[2,3,4,6-
D
D-
To a solution of 19 (350 mg, 0.30 mmol) in DMF (5 mL) at 0 °C
was added hydrazine acetate (55 mg, 0.60 mmol). The reaction
mixture was stirred at 0 °C for 2 h, when TLC (2:1 petroleum
ether–ethyl acetate) indicated the completion of the reaction.
The reaction mixture was diluted with EtOAc (50 mL), and washed
successively with water (30 mL) and brine (30 mL). The organic
phase was dried over anhydrous Na2SO4 and concentrated, and
the residue was subjected to silica gel column chromatography
(1:1 petroleum ether–EtOAc). The product above was dissolved
in anhydrous CH2Cl2 (5 mL), and to the solution was added trichlo-
3.15. Leonoside F (2)
To a solution of 20 (33 mg, 0.024 mmol) in MeOH (4 mL) was
added 10% Pd(OH)2/C (8 mg), and the resulting suspension was
stirred under H2 atmosphere at rt overnight. The solid materials
were filtrated off, and the solution was concentrated. The resultant
product was re-dissolved in MeOH (5 mL), to which was added 1 N
aq NaOH dropwise until pH 10 was reached. The reaction mixture
was stirred at rt for 3 h and neutralized with Amberlite IR 120 (H+).
The reaction solution was filtered and concentrated. The resulting
residue was purified by flash column chromatography (3:1 CH2Cl2–
roacetonitrile (0.2 mL, 2.0 mmol) and DBU (20 lL) at 0 °C. The mix-
ture was stirred for 2 h and concentrated. The resulting residue
was purified by flash column chromatography (2:1 petroleum
ether–ethyl acetate) to afford 4 (248 mg, 65% for two steps) as a
MeOH) to afford 2 (12 mg, 78%) as a white solid. ½a D20
ꢀ39 (c 0.1,
ꢁ
CH3OH); 1H NMR (400 MHz, CD3OD): d 1.26 (d, 3H, J 6.2 Hz, H-
6Rha), 2.86 (br t, 2H, J 7.2 Hz, –OCH2CH2ꢀ), 3.23 (t, 1H, J 8.4 Hz),
3.26–3.38 (m, 4H), 3.41 (t, 1H, J 9.6 Hz), 3.45–3.52 (m, 3H), 3.68
(dd, 1H, J 5.4, 12.0 Hz), 3.72 (dd, 1H, J 3.4, 9.6 Hz, H-3Rha), 3.77
(m, 1H), 3.82 (dd, 1H, J 4.6, 11.5 Hz, H-6), 3.86 (s, 3H, –OCH3),
3.88 (dd, 1H, J 2.0, 12.0 Hz, H-6), 3.95 (dd, 1H, J 1.4, 3.3 Hz, H-
white foamy solid. ½a D20
ꢁ
+21 (c 1, CHCl3); 1H NMR (400 MHz,
CDCl3): d 1.14 (d, 3H, J 6.2 Hz, H-6Rha), 1.96, 2.06, 2.13 (3 s,
5 ꢂ 3H, 5CH3CO), 3.68 (dd, 1H, J 6.5, 11.6 Hz, H-6aGlu), 3.79 (m,
1H, H-5Glu), 3.92 (br d, 1H, J 11.6 Hz, H-6bGlu), 3.98–4.08 (m, 2H,
0
H-3,5Glu ), 4.15 (m, 1H, H-5Rha), 4.49 (dd, 1H, J 5.2, 12.1 Hz, H-
0
0
6aGlu ), 4.64 (dd, 1H, J 2.4, 12.1 Hz, H-6bGlu ), 4.81-4.85 (br s, 2H,
2Rha), 3.98–4.10 (m, 2H), 4.17 (dd, 1H, J 1.1, 10.9 Hz, H-6), 4.33
0
H-2Glu, H-1Rha), 4.90 (t, 1H, J 9.8 Hz, H-4Glu), 4.95 (d, 1H, J 7.8 Hz,
(d, 1H, J 7.9 Hz, H-1Glu), 4.38 (d, 1H, J 7.7 Hz, H-1Glu ), 5.18 (d, 1H,
0
H-1Glu ), 5.02 (t, 1H, J 10.0 Hz, H-4Rha), 5.07 (dd, 1H, J 3.0, 10.0 Hz,
J 1.4 Hz, H-1Rha), 6.67–6.73 (m, 2H), 6.87 (br s, 1H); 13C NMR
(100 MHz, CD3OD): d 16.5, 35.3, 55.1, 61.4, 68.4, 68.6 (2C), 70.2,
70.8, 70.9, 71.0, 72.6, 73.7, 74.3, 75.6, 76.6 (2C), 82.8, 101.3,
102.9, 103.5, 112.4, 114.7, 121.0, 130.2, 144.6, 147.5; ESI-HRMS
(positive ion): Calcd for (C27H42O17+Na+): 661.2314; found m/z:
661.2313.
0
H-3Rha), 5.13 (br s, 1H, H-2Rha), 5.49 (dd, 1H, J 7.8, 9.6 Hz, H-2Glu ),
0
0
5.64 (t, 1H, J 9.6 Hz, H-4Glu ), 5.86 (t, 1H, J 9.6 Hz, H-3Glu ), 6.36 (d,
1H, J 3.1 Hz, H-1Glu), 7.32-8.05 (m, 20H, Ph), 8.40 (s, 1H, NH); 13C
NMR (100 MHz, CDCl3): d 17.3, 20.3, 20.7, 20.8, 20.9, 21.0, 63.0,
65.6, 67.4, 68.2, 69.3, 69.6, 69.7, 70.5, 71.3, 71.7, 71.8, 72.3, 72.8,
77.8, 91.0, 92.7, 99.5, 100.7, 160.4, 165.1, 165.2, 165.8, 166.1,
169.6, 169.7, 170.0 (2C), 170.1; Anal. Calcd for C58H58Cl3NO24: C,
55.31; H, 4.64; N, 1.11. Found: C, 55.24; H, 4.81; N, 1.02.
Acknowledgements
This work was supported by grants from the National Basic Re-
search Program of China (973 Program, No. 2012CB822102), the
National Major Scientific and Technological Special Project for Sig-
nificant New Drugs Development (No. 2012ZX09502001-005) and
NNSF of China (Project 21002060).
3.14. 3-Methoxyl-4-benzoxylphenylethyl 2,3,4-tri-O-acetyl-
rhamnopyranosyl-(1?3)-[2,3,4,6-tetra-O-benzoyl-b-
glucopyranosyl-(1?6)]-2,4-di-O-acetyl-b-D-glucopyranoside
(20)
a
D
-
L
-
-
To
a solution of 4 (82 mg, 0.065 mmol) and 0 5 (16 mg,
Supplementary data
0.062 mmol) in anhydrous CH2Cl2 (5 mL) was added 4ÅA molecular
sieves (60 mg). The reaction mixture was stirred at rt for 30 min
under a N2 atmosphere, and then cooled to ꢀ40 °C. Silver triflate
(11 mg, 0.04 mmol) was added in the dark. The reaction mixture
was stirred for 2 h while it was slowly warmed up to 0 °C, then
neutralized with triethylamine and concentrated. Purification of
the resulting residue on a silica gel column using 3:2 petroleum
ether–EtOAc as the eluents afforded 20 (57 mg, 68%) as a white
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.carres.2013.07.
012.
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