Synthesis of an xylosylated rhamnose pentasaccharide, the repeating unit of the O-chain polysaccharide of the lipopolysaccharide of Xanthomonas campestris pv. begoniae GSPB 525

Article abstract of DOI:10.1016/S0008-6215(01)00330-5

A xylosylated rhamnose pentasaccharide, α-L-Rhap-(1→3)-[β-L-Xylp-(1→2)-]-α-L-Rhap- (1→3)-[β-L-Xylp-(1→4)]-L-Rhap, the repeating unit of the O-chain polysaccharide (OPS) of the lipopolysaccharides of Xanthomonas campestris pv. begoniae GSPB 525 was synthesized by a highly regio- and stereoselective way. Thus coupling of 1,2-O-ethylidene-β-L-rhamnopyranose (1) with 2,3,4-tri-O-benzoyl-α-L-rhamnopyranosyl trichloroacetimidate (2) to give (1→3)-linked disaccharide (3), subsequent benzoylation, deethylidenation, acetylation, 1-O-deacetylation, and trichloroacetimidation afforded the disaccharide donor 11. Condensation of 11 with 1 yielded 2,3,4-tri-O-benzoyl-α-L-rhamnopyranosyl-(1→3)-2-O-acetyl-4-O- benzoyl-α-L-rhamnopyranosyl-(1→3)-1,2-O-ethylidene-β-L- rhamnopyranose (12), and selective deacetylation of 12 yielded the trisaccharide diol acceptor 15. Coupling of 15 with 2,3,4-tri-O-benzoyl-α-L-xylopyranosyl trichloroacetimidate (16), followed by deprotection, gave the target pentasaccharide 19.

Full text of DOI:10.1016/S0008-6215(01)00330-5

Carbohydrate Research 337 (2002) 391–396
www.elsevier.com/locate/carres
Synthesis of an xylosylated rhamnose pentasaccharide, the
repeating unit of the O-chain polysaccharide of the
lipopolysaccharide of Xanthomonas campestris pv. begoniae GSPB
525
Jianjun Zhang, Fanzuo Kong*
Research Center for Eco-En6ironmental Sciences, Academia Sinica, PO Box 2871, Beijing 100085, PR China
Received 7 November 2001; accepted 11 December 2001
Abstract
A xylosylated rhamnose pentasaccharide, a-
repeating unit of the O-chain polysaccharide (OPS) of the lipopolysaccharides of Xanthomonas campestris pv. begoniae GSPB 525
was synthesized by a highly regio- and stereoselective way. Thus coupling of 1,2-O-ethylidene-b- -rhamnopyranose (1) with
2,3,4-tri-O-benzoyl-a- -rhamnopyranosyl trichloroacetimidate (2) to give (1“3)-linked disaccharide (3), subsequent benzoylation,
deethylidenation, acetylation, 1-O-deacetylation, and trichloroacetimidation afforded the disaccharide donor 11. Condensation of
11 with 1 yielded 2,3,4-tri-O-benzoyl-a- -rhamnopyranosyl-(1“3)-2-O-acetyl-4-O-benzoyl-a- -rhamnopyranosyl-(1“3)-1,2-O-
ethylidene-b- -rhamnopyranose (12), and selective deacetylation of 12 yielded the trisaccharide diol acceptor 15. Coupling of 15
with 2,3,4-tri-O-benzoyl-a- -xylopyranosyl trichloroacetimidate (16), followed by deprotection, gave the target pentasaccharide
L
-Rhap-(1“3)-[b-
L
-Xylp-(1“2)-]-a-
L
-Rhap-(1“3)-[b-
L-Xylp-(1“4)]-L-Rhap, the
L
L
L
L
L
L
19. © 2002 Elsevier Science Ltd. All rights reserved.
Keywords: Oligosaccharide; Rhamnose; Xylose
leaves. Several data indicate that the lipopolysaccha-
rides (LPSs) contribute to bacterial virulence.3 For in-
vestigation of structure–bioactivity relationships of
oligosaccharides, we report herewith a concise and effi-
cient synthesis of the OPS repeating unit.
1. Introduction
It was reported recently that the repeating unit of the
O-chain polysaccharide (OPS) of the lipopolysaccha-
rides of Xanthomonas campestris pv. begoniae GSPB
525 is an xylosylated rhamnan pentasaccharide as
shown below:1
Although the pentasaccharide-repeating unit is not
very complex, its synthesis will need orthogonal mask-
ing groups and multiprotection–deprotection steps if
the traditional stepwise method is used. A stepwise
synthesis of the hexasaccharide with (1“2)- and (1“
3)-linked rhamnotetraose as the backbone and two
glucosamine units as the side chains has been reported.4
Our previous work described highly regio- and stereo-
selective syntheses of oligosaccharides using unpro-
tected sugars via orthoester formation–rearrangement
strategy.5–7 Later on we found that high regio- and
stereoselectivity were achieved in a one-pot manner
using glycosyl trichloroacetimidates as the donors and
partly protected sugars as the acceptors.8,9 Based on
these new findings, we readily accomplished the synthe-
sis of the title pentasaccharide.
It was known that Xanthomonas are phytopathogens
and cause leaf spots by colonizing the intercellular leaf
space.2 X. Campestris pv. begoniae causes a disease
characterized by large water-soaked lesions on the
* Corresponding author. Fax: +86-10-62923563.
E-mail address: fzkong@mail.rcees.ac.cn (F. Kong).
0008-6215/02/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved.
PII: S0008-6215(01)00330-5

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J. Zhang, F. Kong / Carbohydrate Research 337 (2002) 391–396
methanol, and converted to the trichloroacetimidate
2. Results and discussion
with trichloroactonitrile in the presence of DBU or
potassium carbonate, to furnish the disaccharide donor
As outlined in Scheme 1, coupling of the 2,3,4-tri-O-
benzoyl-a-
L
-rhamnopyranosyl trichloroacetimidate (2)
-rhamnopyranose (1) in
2,3,4-tri-O-benzoyl-a-
L
-rhamnopyranosyl-(1“3)-2-O-
with the 1,2-O-ethylidene-b-
L
acetyl-4-O-benzoyl-a-
L-rhamnopyranosyl trichloroace-
the presence of a catalytic amount of TMSOTf selec-
tively gave (1“3)-linked disaccharide 3 (74.2%) as the
main product, together with a small amount of (1“4)-
linked disaccharide 4 (6.9%) and (1“3) (1“4)-linked
trisaccharide 5 (1.9%). Their structures were confirmed
by benzoylation or acetylation to give 2,3,4-tri-O-ben-
timidate (11). These four steps were performed continu-
ously without separation, giving 86.9% overall yield.
Condensation of the disaccharide donor 11 with accep-
tor 1 using TMSOTf as the catalyst selectively gave
2,3,4-tri-O-benzoyl-a-
acetyl-4-O-benzoyl-a-
O-ethylidene-b- -rhamnopyranose (12) (76.7%) as the
L
-rhamnopyranosyl-(1“3)-2-O-
L
-rhamnopyranosyl-(1“3)-1,2-
zoyl-a-
ethylidene-b-
istic signals at l 5.48 ppm (dd, J3,4=J4,5 9.5 Hz) for
H-4, or 2,3,4-tri-O-benzoyl-a- -rhamnopyranosyl-(1“
-rhamnopyranose
L
-rhamnopyranosyl-(1“3)-4-O-benzoyl-1,2-O-
L
L
-rhamnopyranose (6), showing character-
major product, together with 2,3,4-tri-O-benzoyl-a-
L
-
-
rhamnopyranosyl-(1“3)-2-O-acetyl-4-O-benzoyl-a-
L
L
rhamnopyranosyl-(1“4)-1,2-O-ethylidene-b-L-rhamno-
4)-3-O-acetyl-1,2-O-ethylidene-b-
L
pyranose (13) (3.2%) as the minor one. No pentasac-
charide was detected perhaps due to steric hindrance.
Because of the presence of the ethylidene group, an
attempt for selective deacetylation of 12 with 3%
CH3COCl–MeOH10 was not successful since a very
complex product was obtained. Later, we found that
the acetyl group can be selectively removed with 0.5 N
ammonia–methanol without affecting either the ethyli-
dene or the benzoyl group, giving 15 in 83% yield.
Coupling of the trisaccharide acceptor 15 with the
xylose donor 16 gave the pentasaccharide 17, and sub-
(7), showing characteristic signals at l 5.18 ppm (dd,
1
J2,3 4.0, J3,4 9.7 Hz) for H-3 in its H NMR spectrum.
It was determined that it was necessary to maintain the
temperature during addition of TMSOTf below
−20 °C to ensure the formation of the orthoester inter-
mediate. Otherwise, for example at room temperature,
the regioselectivity was poor. Compound
6 was
deethylidenated with 90% trifluroacetic acid (TFA), and
the product was acetylated with acetic anhydride in
pyridine, selectively 1-O-deacetylated with ammonia–
Scheme 1.

J. Zhang, F. Kong / Carbohydrate Research 337 (2002) 391–396
393
sequent deethyledenation and acetylation furnished
pentasaccharide 18 as its a isomer, only. Finally deac-
ylation of 18 in ammonia–methanol gave the target
pentasaccharide 19. Bioassay of the resultant pentasac-
charide is in progress.
In summary, a branched xylosylated rhamnan pen-
tasaccharide was synthesized in a highly regioselective
way with a simple procedure. Large-scale preparations
can be performed with this method.
ambient temperature. Then the mixture was neutralized
with triethylamine, and concentrated to dryness. Purifi-
cation of the residue by column chromatography (1:1
petroleum ether–EtOAc) gave 3 (4.81 g, 74.2%), and
2,3,4-tri-O-benzoyl-a-
O-ethylidene-b- -rhamnopyranose (4, 0.45 g, 6.9%),
and 2,3,4-tri-O-benzoyl-a- -rhamnopyranosyl-(1“3)-
[2,3,4-tri-O-benzoyl-a- -rhamnopyranosyl-(1“4)]-1,2-
O-ethylidene-b- -rhamnopyranose (5, 0.10 g, 1.9%) as
L
-rhamnopyranosyl-(1“4)-1,2-
L
L
L
L
foamy solids. For 3 (R isomer): [h]D +132.5° (c 1.0,
1
CHCl3); H NMR (400 MHz, CDCl3): l 8.08–7.27 (m,
3. Experimental
15 H, 3 Ph), 5.89 (dd, 1 H, J2,3 3.1, J3,4 9.9 Hz, H-3),
5.77 (dd, 1 H, J1,2 1.5, J2,3 3.1 Hz, H-2), 5.69 (dd, 1 H,
General methods.—Melting points were determined
with a Mel-Temp apparatus. Optical rotations were
determined with a Perkin–Elmer model 241-MC auto-
matic polarimeter at 20 °C for solutions in a 1-dm,
J3,4=J4,5 9.9 Hz, H-4), 5.35–5.23 (m, 2 H, H-1,
CH3CHO2), 5.26 (d, 1 H, J1,2 1.7 Hz, H-1), 4.53 (m, 1
H, H-5), 4.28 (dd, 1 H, J1,2 1.7, J2,3 3.2 Hz, H-2), 3.81
(dd, 1 H, J2,3 3.2, J3,4 9.7 Hz, H-3), 3.74 (dd, 1 H,
1
jacketed cell. H and 13C NMR spectra were recorded
J3,4=J4,5 9.7 Hz, H-4), 3.40 (m, 1 H, H-5), 1.56 (d, 3 H,
with Varian XL-400 and Varian XL-200 spectrometers,
for solutions in CDCl3 with tetramethylsilane (Me4Si)
as the internal standard. Chemical shifts are expressed
in ppm downfield from the internal Me4Si absorption.
Mass spectra were recorded with a VG PLATFORM
mass spectrometer using the ESI mode. Thin-layer
chromatography (TLC) was performed on silica gel HF
with detection by charring with 30% (v/v) H2SO4 in
MeOH or by UV detection. Column chromatography
was conducted by elution of a column (8×100 mm,
16×240 mm, 18×300 mm, and 35×400 mm) of silica
gel (100–200 mesh) and EtOAc–petroleum ether (bp
60–90 °C) as the eluent. Analytical LC was performed
with a Gilson HPLC consisting of a pump (model 306),
stainless steel column packed with silica gel (Spherisorb
SiO2, 10×300 mm or 4.6×250 mm), differential re-
fractometer (132-RI detector), UV–Vis detector (model
118). EtOAc–petroleum ether (bp 60–90 °C) was used
as the eluent at a flow rate of 1–4 mL/min. Solutions
were concentrated at a temperature B60 °C under
diminished pressure.
J 4.8 Hz, CH3CHO2), 1.37 (d, 3 H, J5,6 6.2 Hz, H-6),
1.32 (d, 3 H, J5,6 6.4 Hz, H-6); 13C NMR (100 MHz,
CDCl3): l 165.9, 165.8, 165.7 (3 C, 3 COPh), 104.6 (1
C, CH3CHO2), 100.0, 96.5 (2 C, 2 C-1), 81.8, 79.8, 71.7,
71.0, 71.0, 70.9, 70.3, 67.4, 21.9, 17.9, 17.6. Anal. Calcd
for C35H36O12: C, 64.81; H, 5.59. Found: C, 64.93; H,
5.40. For 4 (R isomer): [h]D +105.5° (c 1.0, CHCl3);
1H NMR (400 MHz, CDCl3): l 8.10–7.25 (m, 15 H, 3
Ph), 5.78 (dd, 1 H, J2,3 3.2, J3,4 9.8 Hz, H-3), 5.75 (dd,
1 H, J1,2 1.6, J2,3 3.2 Hz, H-2), 5.69 (dd, 1 H, J3,4=J4,5
9.8 Hz, H-4), 5.60 (d, 1 H, J1,2 1.5 Hz, H-1), 5.30 (q, J
4.8 Hz, 1 H, CH3CHO2), 5.25 (d, 1 H, J1,2 2.3 Hz, H-1),
4.28 (m, 1 H, H-5), 4.26 (dd, 1 H, J1,2 2.3, J2,3 4.4 Hz,
H-2), 4.06 (dd, 1 H, J2,3 4.4, J3,4 8.9 Hz, H-3), 3.71 (dd,
1 H, J3,4=J4,5 8.9 Hz, H-4), 3.49 (m, 1 H, H-5), 1.51 (d,
3 H, J 4.9 Hz, CH3CHO2), 1.42 (d, 3 H, J5,6 6.2 Hz,
H-6), 1.37 (d, 3 H, J5,6 6.2 Hz, H-6); 13C NMR (100
MHz, CDCl3): l 165.8, 165.8, 165.7 (3 C, 3 COPh),
104.1 (1 C, CH3CHO2), 98.8, 96.5 (2 C, 2 C-1), 80.1,
80.0, 72.5, 71.7, 71.1, 70.1, 69.7, 67.7, 21.6, 18.5, 17.7.
Anal. Calcd for C35H36O12: C, 64.81; H, 5.59. Found:
C, 64.89; H, 5.67. For 5 (R isomer): [h]D +139.5° (c
All of the intermediates containing the ethylidene
group were composed of R and S isomers. These two
isomers had no apparent difference in reactivity, and
thus no separation was conducted in the synthesis.
However, for the convenience of identification by NMR
spectrometry, the predominant R isomer was isolated in
pure form in most of the cases.
1
1.0, CHCl3); H NMR (400 MHz, CDCl3): l 7.99–7.17
(m, 30 H, 6 Ph), 6.04–5.99 (m, 2 H, H-2, H-3), 5.90
(dd, 1 H, J2,3 3.1, J3,4 10.0 Hz, H-3), 5.81 (dd, 1 H, J1,2
1.8, J2,3 2.7 Hz, H-2), 5.76 (dd, 1 H, J3,4=J4,5 10.0 Hz,
H-4), 5.65 (dd, 1 H, J3,4=J4,5 9.8 Hz, H-4), 5.61 (d, 1
H, J1,2 1.5 Hz, H-1), 5.35 (d, 1 H, J1,2 0.9 Hz, H-1),
5.30–5.26 (m, 2 H), 4.59 (m, 1 H, H-5), 4.41 (dd, 1 H,
J1,2 2.5, J2,3 3.5 Hz, H-2), 4.30 (m, 1 H, H-5), 4.07 (dd,
1 H, J2,3 3.5, J3,4 9.1 Hz, H-3), 3.99 (dd, 1 H, J3,4=J4,5
9.1 Hz, H-4), 3.60 (m, 1 H, H-5), 1.57 (d, 3 H, J 4.9 Hz,
CH3CHO2), 1.49 (d, 3 H, J5,6 6.2 Hz, H-6), 1.38 (d, 3
H, J5,6 6.3 Hz, H-6), 1.26 (d, 3 H, J5,6 6.1 Hz, H-6); 13C
NMR (100 MHz, CDCl3): l 166.0, 165.9, 165.6, 165.5,
165.4, 165.0 (6 C, 6 COPh), 104.3 (1 C, CH3CHO2),
100.1, 99.5, 96.5 (3 C, 3 C-1), 82.5, 79.8, 72.3, 72.0,
71.7, 71.7, 70.5, 69.6, 69.4, 67.8, 67.6, 21.7, 19.0, 17.7,
Preparation of 2,3,4-tri-O-benzoyl-h-
osyl-(1“3)-1,2-O-ethylidene-i- -rhamnopyranose (3).
—1,2-O-Ethylidene-b- -rhamnopyranose (1, 1.90 g,
10.0 mmol) and 2,3,4-tri-O-benzoyl-a- -rhamnopyran-
L-rhamnopyran-
L
L
L
osyl trichloroacetimidate (2, 6.2 g, 10.0 mmol) were
dried together under high vacuum for 2 h, then dis-
solved in anhyd CH2Cl2 (40 mL). TMSOTf (90 mL, 0.5
mmol) was added dropwise at −25 °C with N2 protec-
tion. The reaction mixture was stirred for 3 h, during
which time the temperature was gradually raised to

394
J. Zhang, F. Kong / Carbohydrate Research 337 (2002) 391–396
17.6. Anal. Calcd for C62H58O19: C, 67.26; H, 5.28.
Found: C, 67.33; H, 5.25.
1.36 (d, 3 H, J5,6 6.3 Hz, H-6); 13C NMR (100 MHz,
CDCl3): l 170.9 (1 C, COCH3), 165.8, 165.6, 165.5 (3
C, 3 COPh), 104.3(1 C, CH3CHO2), 99.7, 96.4 (2 C, 2
C-1), 78.6, 77.6, 73.4, 71.6, 71.1, 70.2, 69.7, 67.8, 21.6,
21.0, 18.6, 17.6. Anal. Calcd for C37H38O13: C, 64.34;
H, 5.55. Found: C, 64.40; H, 5.41.
2,3,4-Tri-O-benzoyl-h-
O-benzoyl-1,2-O-ethylidene-i-
To a solution of 2,3,4-tri-O-benzoyl-a-
osyl-(1“3)-1,2-O-ethylidene-b- -rhamnopyranose (3,
L
-rhamnopyranosyl-(1“3)-4-
-rhamnopyranose (6).—
-rhamnopyran-
L
L
L
4.8 g, 7.4 mmol) in pyridine (20 mL) was added benzoyl
chloride (1.5 mL, 13 mmol) at 0 °C. The reaction
mixture was slowly raised to rt and stirred for 12 h, at
the end of which time TLC (4:1 petroleum ether–
EtOAc) indicated that the reaction was complete. Wa-
ter (100 mL) was added to the reaction mixture, and
stirring was continued for 30 min. The aqueous solu-
tion was extracted with CH2Cl2 (3×100 mL), the ex-
tract was washed with HCl (1 N) and satd aq NaHCO3,
and dried (Na2SO4). The solution was concentrated,
and purification of the residue by flash-column chro-
matography on a silica gel column (3:1 petroleum
ether–EtOAc) gave 6 (5.16 g, 92.6%) as a syrup. For R
2,3,4-Tri-O-benzoyl-h-
O-acetyl-4-O-benzoyl-h-
L
-rhamnopyranosyl-(1“3)-2-
L
-rhamnopyranosyl trichloro-
acetimidate (11).—Compound 6 (5.03 g, 6.69 mmol)
was dissolved in 90% TFA (70 mL) and stirred for 2 h,
at the end of which time the reaction mixture was
poured directly to toluene (250 mL) and concentrated.
Drying the residue under high vacuum gave 8 as a
white foamy solid in a quantitative yield. To the solu-
tion of compound 8 in pyridine (100 mL) was added
Ac2O (20.0 mL). The reaction mixture was stirred at rt
for 12 h, at the end of which time TLC (4:1 petroleum
ether–EtOAc) indicated that the reaction was complete.
The reaction mixture was concentrated to dryness, and
the residue was dissolved in CH2Cl2 (300 mL), washed
with water and satd aq NaHCO3, dried (Na2SO4), and
concentrated to give 9. Compound 9 was dissolved in a
1 M solution of ammonia–MeOH (200 mL) and stirred
for 6 h, at the end of which time TLC (3:1 petroleum
ether–EtOAc) indicated that the reaction was complete.
The solution was concentrated directly to give 10 as a
syrup. A mixture of 10, trichloroacetonitrile (4.2 mL,
20 mmol), and 1,8-diazabicyclo[5.4.0]undecene (DBU)
(0.50 mL, 4.04 mmol) in dry CH2Cl2 (50 mL) was
stirred under nitrogen for 3 h, and then concentrated.
The residue was purified by flash chromatography (4:1
petroleum ether–EtOAc) to give 11 (5.3 g, 86.9% for
four steps) as a yellow syrup: [h]D +143.3° (c 1.1,
1
isomer: [h]D +162.0° (c 1.0, CHCl3); H NMR (400
MHz, CDCl3): l 8.09–7.20 (m, 20 H, 4 Ph), 5.83 (dd, 1
H, J2,3 3.5, J3,4 10.1 Hz, H-3), 5.60 (dd, 1 H, J3,4=J4,5
10.1 Hz, H-4), 5.48 (dd, 1 H, J3,4=J4,5 9.5 Hz, H-4),
5.40–5.38 (m, 2 H, H-2, CH3CHO2), 5.30 (d, 1 H, J1,2
2.1 Hz, H-1), 5.22 (d, 1 H, J1,2 1.5 Hz, H-1), 4.45 (m, 1
H, H-5), 4.34 (dd, 1 H, J1,2 2.1, J2,3 3.9 Hz, H-2), 5.18
(dd, 1 H, J3,4 3.9, J4,5 9.5 Hz, H-3), 3.64 (m, 1 H, H-5),
1.62 (d, 3 H, J 4.8 Hz, CH3CHO2), 1.33 (d, 3 H, J5,6 6.2
Hz, H-6), 1.29 (d, 3 H, J5,6 6.2 Hz, H-6); 13C NMR (100
MHz, CDCl3): l 166.0, 165.8, 165.1, 165.0 (4 C, 4
COPh), 105.0 (1 C, CH3CHO2), 99.6, 96.6 (2 C, 2 C-1),
79.6, 78.5, 72.4, 71.9, 71.0, 70.0, 69.5, 67.5, 21.9, 17.9,
17.6. Anal. Calcd for C42H40O13: C, 67.01; H, 5.36.
Found: C, 66.94; H, 5.28.
1
CHCl3); H NMR (400 MHz, CDCl3): l 8.78 (s, 1 H,
2,3,4-Tri-O-benzoyl-h-
O-acetyl-1,2-O-ethylidene-i-
To a solution of 2,3,4-tri-O-benzoyl-a-
osyl-(1“4)-1,2-O-ethylidene-b- -rhamnopyranose (4,
L
-rhamnopyranosyl-(1“4)-3-
-rhamnopyranose (7).—
-rhamnopyran-
NH), 8.09–7.25 (m, 20 H, 4 Ph), 6.32 (d, 1 H, J1,2 0.8
Hz, H-1), 5.66 (dd, 1 H, J2,3 3.2, J3,4 9.7 Hz, H-3),
5.61–5.54 (m, 3 H), 5.36 (dd, 1 H, J1,2 0.8, J2,3 3.2 Hz,
H-2), 5.19 (d, 1 H, J1,2 1.1 Hz, H-1), 4.52 (dd, 1 H, J2,3
3.2, J3,4 9.8 Hz, H-3), 4.27 (m, 1 H, H-5), 4.19 (m, 1 H,
H-5), 2.38 (s, 3 H, COCH3), 1.35 (d, 3 H, J5,6 6.2 Hz,
H-6), 1.26 (d, 3 H, J5,6 6.1 Hz, H-6). Anal. Calcd for
C44H40Cl3NO14: C, 57.86; H, 4.41. Found: C, 57.88; H,
4.50.
L
L
L
400 mg, 0.60 mmol) in pyridine (5 mL) was added
acetyl anhydride (1.0 mL, 1 mmol). The reaction mix-
ture was stirred at rt for 12 h, at the end of which time
TLC (3:1 petroleum ether–EtOAc) indicated that the
reaction was complete. The reaction mixture was con-
centrated, and purification of the residue by flash-
column chromatography on a silica gel column (3:1
petroleum ether–EtOAc) gave 7 (0.38 g, 92.0%) as a
2,3,4-Tri-O-benzoyl-h-
O - acetyl - 4 - O-benzoyl - h -
1,2-O-ethylidene-i- -rhamnopyranose (12).—2,3,4-Tri-
O-benzoyl-a- -rhamnopyranosyl-(1“3)-2-O-acetyl-4-
O-benzoyl-a- -rhamnopyranosyl trichloroacetimidate
(11, 4.8 g, 5.26 mmol) and 1,2-O-ethylidene-b-
L
-rhamnopyranosyl-(1“3)-2-
L
- rhamnopyranosyl - (1“3)-
L
1
syrup. For R isomer: [h]D +131.0° (c 1.1, CHCl3); H
L
NMR (400 MHz, CDCl3): l 8.09–7.25 (m, 15 H, 3 Ph),
5.74 (dd, 1 H, J2,3 3.1, J3,4 10.1 Hz, H-3), 5.69 (dd, 1 H,
L
L
-
J
3,4=J4,5 10.1 Hz, H-4), 5.58 (dd, 1 H, J1,2 1.9, J2,3 3.1
rhamnopyranose (1, 1.00 g, 5.26 mmol) were dried
together under high vacuum for 2 h, then dissolved in
anhyd CH2Cl2 (40 mL). TMSOTf (90 mL, 0.5 mmol)
was added dropwise at −25 °C with N2 protection.
The reaction mixture was stirred for 3 h, during which
time the temperature was gradually raised to ambient
temperature. Then the mixture was neutralized with
Hz, H-2), 5.29–5.28 (m, 2 H, H-1, H-1), 5.25 (q, 1 H,
J 4.8 Hz, CH3CHO2), 5.18 (dd, 1 H, J2,3 4.0, J3,4 9.7
Hz, H-3), 4.65 (dd, 1 H, J1,2 2.4, J2,3 4.0 Hz, H-2), 4.27
(m, 1 H, H-5), 3.92 (dd, 1 H, J3,4=J4,5 9.7 Hz, H-4),
3.62 (m, 1 H, H-5), 2.26 (s, 3 H, COCH3), 1.51 (d, 3 H,
J 4.9 Hz, CH3CHO2), 1.46 (d, 3 H, J5,6 6.1 Hz, H-6),

J. Zhang, F. Kong / Carbohydrate Research 337 (2002) 391–396
395
triethylamine, and concentrated to dryness. Purification
of the residue by column chromatography (1:1
petroleum ether–EtOAc) gave 12 (3.79 g, 76.7%) and
Hz, H-4), 4.95 (d, 1 H, J1,2 1.3 Hz, H-1), 4.43 (dd, 1 H,
J2,3 3.4, J3,4 9.0 Hz, H-3), 4.24 (m, 1 H, H-5), 4.20 (dd,
1 H, J1,2 2.2, J2,3 3.4 Hz, H-2), 4.13 (m, 1 H, H-5), 3.86
(dd, 1 H, J1,2 3.2, J3,4 9.8 Hz, H-3), 3.47 (m, 1 H, H-5),
2.31 (s, 3 H, COCH3), 2.08 (s, 3 H, COCH3), 1.56 (d, 3
H, J 4.7 Hz, CH3CHO2), 1.37 (d, 3 H, J5,6 6.2 Hz, H-6),
1.27 (d, 3 H, J5,6 6.3 Hz, H-6), 1.23 (d, 3 H, J5,6 6.2 Hz,
H-6); 13C NMR (100 MHz, CDCl3): l 170.7, 170.0 (2
C, 2 COCH3), 165.8, 165.8, 165.1, 164.9 (4 C, 4 COPh),
104.9(1 C, CH3CHO2), 100.1, 99.2, 96.4 (3 C, 3 C-1),
79.7, 79.0, 74.4, 73.1, 71.7, 71.7, 71.6, 70.6, 69.5, 69.3,
67.6, 67.5, 21.8, 21.2, 17.6, 17.6, 17.4. Anal. Calcd for
C52H54O19: C, 63.54; H, 5.54. Found: C, 63.28; H, 5.66.
2,3,4-tri-O-benzoyl-a-
acetyl-4-O-benzoyl-a-
O-ethylidene-b- -rhamnopyranose (13, 0.158 g, 3.2%).
L
-rhamnopyranosyl-(1“3)-2-O-
L
-rhamnopyranosyl-(1“4)-1,2-
L
1
For 12 (R isomer): [h]D +117.3° (c 1.1, CHCl3); H
NMR (400 MHz, CDCl3): l 8.09–7.21 (m, 20 H, 4 Ph),
5.60 (dd, 1 H, J2,3 3.3, J3,4 10.0 Hz, H-3), 5.58 (dd, 1 H,
J
3,4=J4,5 9.8 Hz, H-4), 5.47–5.45 (m, 2 H, H-2, H-4),
5.31–5.29 (m, 2 H, H-2, CH3CHO2), 5.13 (d, 1 H, J1,2
1.4 Hz, H-1), 5.12 (d, 1 H, J1,2 2.1 Hz, H-1), 5.09 (d,
J1,2 1.2 Hz, 1 H, H-1), 4.81 (dd, 1 H, J2,3 3.3, J3,4 9.6
Hz, H-3), 4.29–4.20 (m, 3 H, H-2, H-5, H-5), 3.77 (dd,
1 H, J2,3 4.0, J3,4 9.2 Hz, H-3), 3.68 (dd, 1 H, J3,4=J4,5
9.2 Hz, H-4), 3.37 (m, 1 H, H-5), 2.32 (s, 3 H, COCH3),
1.54 (d, 3 H, J 4.8 Hz, CH3CHO2), 1.37 (d, 3 H, J5,6 6.4
Hz, H-6), 1.32 (d, 3 H, J5,6 6.2 Hz, H-6), 1.27 (d, 3 H,
J5,6 6.3 Hz, H-6); 13C NMR (100 MHz, CDCl3): l 170.8
(1 C, COCH3), 165.8, 165.7, 165.1, 164.9 (4 C, 4
COPh), 104.6 (1 C, CH3CHO2), 100.0, 99.0, 96.4 (3 C,
3 C-1), 81.1, 79.8, 74.8, 73.1, 71.7, 71.4, 71.3, 70.9, 70.7,
69.2, 67.7, 67.5, 21.8, 17.7, 17.6, 17.6. Anal. Calcd for
C50H52O18: C, 63.82; H, 5.57. Found: C, 63.71; H, 5.50.
For 13 (R isomer): [h]D +99.2° (c 1.1, CHCl3); 1H
NMR (400 MHz, CDCl3): l 8.06–7.20 (m, 20 H, 4 Ph),
5.65 (dd, 1 H, J2,3 3.2, J3,4 9.8 Hz, H-3), 5.55 (dd, 1 H,
2,3,4-Tri-O-benzoyl-h-
O-benzoyl-h- -rhamnopyranosyl-(1“3)-1,2-O-ethyli-
dene-i- -rhamnopyranose (15).—Ammonia was bub-
L
-rhamnopyranosyl-(1“3)-4-
L
L
bled in to a solution of 2:1 THF–MeOH (120 mL) until
concentration of the solution reached 1.5 M. Com-
pound 12 (3.20 g, 0.34 mmol) was dissolved in THF (40
mL), the solution was mixed with the ammonia solu-
tion (20 mL), and the mixture was stirred for 24 h. TLC
(3:1 petroleum ether–EtOAc) indicated that more than
half of the starting material had reacted. The solution
was concentrated, and purification of the residue by
column chromatography on a silica gel column (1:1
petroleum ether–EtOAc) gave compound 15 (1.7 g,
80.2%, corrected yield, 0.98 g 12 was recovered) as a
syrup: [h]D +85.2° (c 1.1, CHCl3); 1H NMR (400
MHz, CDCl3): l 8.06–7.20 (m, 20 H, 4 Ph), 5.76 (dd, 1
H, J2,3 3.0, J3,4 9.7 Hz, H-3), 5.61 (dd, 1 H, J3,4=J4,5
9.8 Hz, H-4), 5.47–5.42 (m, 3 H, H-1, H-2, H-4), 5.30
(q, 1 H, J 4.8 Hz, CH3CHO2), 5.26 (d, 1 H, J1,2 1.1 Hz,
H-1), 5.23 (d, 1 H, J1,2 0.9 Hz, H-1), 4.36–4.25 (m, 3
H), 4.16–4.06 (m, 2 H), 3.91 (dd, 1 H, J1,2 1.1, J2,3 3.1
Hz, H-2), 3.65 (dd, 1 H, J3,4=J4,5 9.1 Hz, H-4), 3.41
(m, 1 H, H-5), 1.51 (d, 3 H, J 4.8 Hz, CH3CHO2), 1.39
(d, 3 H, J5,6 6.3 Hz, H-6), 1.35 (d, 3 H, J5,6 6.2 Hz,
H-6), 1.32 (d, 3 H, J5,6 6.0 Hz, H-6); 13C NMR (100
MHz, CDCl3); l 165.8, 165.7, 165.3, 165.0 (4 C, 4
COPh), 104.3 (1 C, CH3CHO2), 100.8, 98.7, 96.5 (3 C,
3 C-1), 80.1, 79.8, 73.1, 73.0, 71.7, 71.0, 70.8, 69.9, 69.5,
67.8, 67.7, 21.7, 18.4, 17.7, 17.6. Anal. Calcd for
C48H50O17: C, 64.13; H, 5.61. Found: C, 64.24; H, 5.68.
J3,4=J4,5 9.8 Hz, H-4), 5.47 (dd, 1 H, J3,4=J4,5 9.9 Hz,
H-4), 5.43–5.42 (m, 2 H, H-1, CH3CHO2), 5.35 (d, J1,2
1.9 Hz, H-1), 5.32 (dd, 1 H, J1,2 1.5, J2,3 3.2 Hz, H-2),
5.20–5.17 (m, 2 H, H-1, H-2), 4.37–4.21 (m, 3 H),
4.04–3.99 (m, 2 H), 3.48 (m, 1 H, H-5), 2.33 (s, 3H,
COCH3), 1.48 (d, 3 H, J 4.9 Hz, CH3CHO2), 1.34–1.25
(m, 9 H); 13C NMR (100 MHz, CDCl3): l 170.6 (1 C,
COCH3), 165.9, 165.7, 165.1, 164.9 (4 C, 4 COPh),
102.5 (1 C, CH3CHO2), 99.0, 96.5, 91.8 (3 C, 3 C-1),
79.1, 78.3, 74.1, 73.5, 71.6, 71.5, 70.7, 69.3, 67.6, 67.7,
67.5, 64.2, 21.2, 18.2, 17.7, 17.6. Anal. Calcd for
C50H52O18: C, 63.82; H, 5.57. Found: C, 63.88; H, 5.61.
2,3,4-Tri-O-benzoyl-h-
O-acetyl-4-O-benzoyl-h-
L
-rhamnopyranosyl-(1“3)-2-
-rhamnopyranosyl-(1“3)-4-
L
O-acetyl-1,2-O-ethylidene-i- -rhamnopyranose (14).—
L
To a solution of 12 (100 mg, 0.11 mmol) in pyridine (5
mL) was added Ac2O (1.0 mL, 1 mmol). The reaction
mixture was stirred at rt for 12 h, at the end of which
time TLC (3:1 petroleum ether–EtOAc) indicated that
the reaction was complete. The reaction mixture was
concentrated, purification of the residue by flash-
column chromatography on a silica gel column (3:1
petroleum ether–EtOAc) gave 14 (92 mg, 85.0%) as a
2,3,4-Tri-O-benzoyl-h-
[2,3,4-tri-O-benzoyl-i- -xylopyranosyl-(1“2)]-4-O-
benzoyl-h- -rhamnopyranosyl-(1“3)-[2,3,4-tri-O-ben-
zoyl-i- -xylopyranosyl-(1“4)]-1,2-O-ethylidene-i-
rhamnopyranose (17).—2,3,4-Tri-O-benzoyl-a- -xylo-
pyranosyl trichloroacetimidate (16, 1.94 g, 3.20 mmol)
and 2,3,4-tri-O-benzoyl-a- -rhamnopyranosyl-(1“3)-
4-O-benzoyl-a- -rhamnopyranosyl-(1“3)-1,2-O-ethyl-
idene-b- -rhamnopyranose (15, 1.20 g, 1.34 mmol) were
L
-rhamnopyranosyl-(1“3)-
L
L
L
L-
L
L
1
syrup. For R isomer: [h]D +111.8° (c 1.1, CHCl3); H
L
NMR (400 MHz, CDCl3): l 8.08–7.20 (m, 20 H, 4 Ph),
5.66 (dd, 1 H, J2,3 3.2, J3,4 9.7 Hz, H-3), 5.57 (dd, 1 H,
L
dried together under high vacuum for 2 h, then dis-
solved in anhyd CH2Cl2 (50 mL). TMSOTf (58 mL, 0.32
mmol) was added dropwise at −20 °C with N2 protec-
tion. The reaction mixture was stirred for 2 h, during
J3,4=J4,5 9.8 Hz, H-4), 5.45 (dd, 1 H, J3,4=J4,5 9.7 Hz,
H-4), 5.33–5.30 (m, 2 H, H-2, CH3CHO2), 5.22–5.16
(m, 3 H, H-2, H-1, H-1), 5.13 (dd, 1 H, J3,4=J4,5 9.0

396
J. Zhang, F. Kong / Carbohydrate Research 337 (2002) 391–396
which time the temperature was gradually raised to
ambient temperature. Then the mixture was neutralized
with triethylamine, and concentrated to dryness. Purifi-
cation of the residue by column chromatography (3:1
petroleum ether–EtOAc) gave 17 (1.93 g, 80.7%) as a
syrup: [h]D +98.3° (c 1.0, CHCl3); 1H NMR (400
MHz, CDCl3): l 8.10–6.78 (m, 50 H, 10 Ph), 6.08–5.82
(m, 2 H), 5.75–5.61 (m, 3 H), 5.53–5.29 (m, 6 H),
5.22–4.94 (m, 4 H), 4.68–4.46 (m, 3 H), 4.42–4.23 (m,
3 H), 4.11–4.02 (m, 2 H), 3.91–3.83 (m, 1 H), 3.68–
3.31 (m, 3 H), 1.52–0.94 (m, 12 H). Anal. Calcd for
C100H90O31 C, 67.18; H, 5.07. Found: C, 67.02; H, 5.13.
164.7, 164.6, 164.5 (10 C, 10 COPh), 99.8, 99.4, 98.1,
97.7, 90.6 (5 C, 5 C-1), 79.3, 76.9, 75.1, 74.2, 73.4, 72.3,
71.4, 70.4, 70.3, 69.8, 69.4, 68.1, 66.7, 63.0, 61.2, 21.1,
19.6, 18.1, 18.0, 17.4. Anal. Calcd for C102H92O33: C,
66.37; H, 5.02. Found: C, 66.30; H, 5.21.
h -
(1“2)]h -
nosyl-(1“4)]-h-
L
- Rhamnopyranosyl - (1“3) - [i -
- rhamnopyranosyl - (1“3) - [i -
-rhamnopyranose (19).—Pentasaccha-
L
- xylopyranosyl-
L
L
- xylopyra-
L
ride 18 (800 mg, 0.43 mmol) was dissolved in a satd
ammonia solution in MeOH (10 mL). After 96 h at rt,
the reaction mixture was concentrated, and the residue
was purified by chromatography on Sephadex LH-20
(MeOH) to afford 19 as a foamy solid (256 mg, 82.5%):
[h]D −21.7° (c 1.0, CHCl3); 1H NMR (400 MHz,
CDCl3): l 5.34 (d, 1 H, J1,2 1.6 Hz, H-1), 5.25 (d, 1 H,
J1,2 1.5 Hz, H-1), 5.04 (d, 1 H, J1,2 1.5 Hz, H-1), 4.87
2,3,4-Tri-O-benzoyl-h-
[2,3,4-tri-O-benzoyl-i- -xylopyranosyl-(1“2)]-4-O-
benzoyl-h- -rhamnopyranosyl-(1“3)-1,2-di-O-acetyl-
[2,3,4-tri-O-benzoyl-i- -xylopyranosyl-(1“4)]-h-
L
-rhamnopyranosyl-(1“3)-
L
L
L
L-
(d, 1 H, J1,2 6.1 Hz, H-1), 4.75 (d, 1 H, J1,2 J3,4=J4,5
rhamnopyranose (18).—Compound 17 (1.00 g, 0.56
mmol) was dissolved in 90% TFA (20 mL) and stirred
for 2 h, at the end of which time the reaction mixture
was poured directly to toluene (100 mL), and then the
mixture was concentrated. Drying the residue under
high vacuum gave a white foamy solid, which was
dissolved in pyridine (10 mL), and then Ac2O (2.0 mL)
was added. The reaction mixture was stirred for 12 h at
rt, at the end of which time TLC (2:1 petroleum
ether–EtOAc) indicated that the reaction was complete.
The reaction mixture was concentrated to dryness, and
the residue was dissolved in CH2Cl2 (300 mL), washed
with water and satd aq NaHCO3, dried (Na2SO4), and
concentrated. The residue was purified by flash chro-
matography (2:1 petroleum ether–EtOAc) to give 18
6.2 Hz, H-1); 13C NMR (100 MHz, CDCl3): l 103.9,
102.5, 101.4, 99.9, 93.7 (5 C, C-1); MS (m/z) Calcd for
C28H48O21: 720.66 [M]+. Found: 743.69 [M+Na]+.
Acknowledgements
This work was supported by The Chinese Academy
of Sciences (Projects KJ952J1510 and RCEES9904) and
by The National Natural Science Foundation of China
(Projects 29802009, 30070185 and 39970864).
References
1
(0.97 g, 94.2%) as a syrup: [h]D +93.5.0°; H NMR
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(400 MHz, CDCl3): l 8.13–6.78 (m, 50 H, 10 Ph), 6.08
(dd, 1 H, J 9.5 Hz), 5.95 (dd, 1 H, J2,3 3.3, J3,4 9.8 Hz,
H-3), 5.87 (dd, 1 H, J 10.0 Hz), 5.73–5.57 (m, 7 H),
5.39 (dd, 1 H, J1,2 1.2, J2,3 3.1 Hz, H-2), 5.34 (d, 1 H,
J1,2 0.9 Hz, H-1), 5.27 (d, 1 H, J1,2 1.2 Hz, H-1), 5.20
(dd, 1 H, J1,2 1.0, J2,3 3.3 Hz, H-2), 4.90 (dd, 1 H, J2,3
3.2, J3,4 9.6 Hz, H-3), 4.84 (d, 1 H, J1,2 7.3 Hz, H-1),
4.74 (dd, 1 H, J1,2 0.9, J2,3 3.1 Hz, H-2), 4.68 (m, 1 H,
H-5), 4.41–4.35 (m, 3 H), 4.27 (dd, 1 H, J2,3 3.4, J3,4 9.9
Hz, H-3), 3.94 (m, 1 H, H-5), 3.80 (m, 1 H, H-5),
3.60–3.54 (m, 2 H), 2.17 (s, 3 H, COCH3), 1.53 (d, 3 H,
J5,6 6.2 Hz, H-6), 1.27 (s, 3 H, COCH3), 1.22 (d, 3 H,
J5,6 6.4 Hz, H-6), 1.07 (d, 3 H, J5,6 6.4 Hz, H-6); 13C
NMR (100 MHz, CDCl3): l 169.8, 168.6 (2 C, 2
COCH3), 166.4, 165.8, 165.6, 165.5, 165.4, 165.1, 165.1,