Synthesis of a xylosylated rhamnose pentasaccharide - The repeating unit of the O-specific side chain of lipopolysaccharides from the reference strains for Stenotrophomonas maltophilia serogroup O18

Article abstract of DOI:10.1081/CAR-120003740

A xylosylated rhamnose pentasaccharide, α-L-Rhap-(1→3)-[β-L-Xylp-(1→ 2)-] [β-L-Xylp-(1→4)-]α-L-Rhap-(1→3)-L-Rhap, the repeating unit of the O-specific side chain of the lipopolysaccharides from the reference strains for Stenotrophomonas maltophilia serogroup O18, was synthesized by a highly regio- and stereoselective procedure. Thus coupling of methyl rhamnopyranoside (9) with 2,3,4-tri-O-acetyl-α-L-rhamnopyranosyl trichloroacetimidate (8) gave the (1→3)-linked disaccharide (10), and subsequent benzoylation and deacetylation afforded the disaccharide acceptor 12. Condensation of 12 with 8 yielded methyl 2,3,4-tri-O-acetyl-α-L-rhamnopyranosyl-(1→3)-α-L- rhamnopyranosyl-(1→3)-2,4-di-O-benzoyl-α-L-rhamnopyranoside (13). Coupling of 13 with 2,3,4-tri-O-benzoyl-α-L-xylopyranosyl trichloroacetimidate (4) followed by deprotection gave the target pentasaccharide (15).

Full text of DOI:10.1081/CAR-120003740

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SYNTHESIS OF A XYLOSYLATED RHAMNOSE
PENTASACCHARIDE—THE REPEATING UNIT OF THE O-
SPECIFIC SIDE CHAIN OF LIPOPOLYSACCHARIDES FROM
THE REFERENCE STRAINS FOR Stenotrophomonas
maltophilia SEROGROUP O18
Jianjun Zhang a & Fanzuo Kong a
a Research Center for Eco-Environmental Science , Academia Sinica , P.O. Box 2871, Beijing,
100085, China
Published online: 28 Oct 2011.
To cite this article: Jianjun Zhang & Fanzuo Kong (2002) SYNTHESIS OF A XYLOSYLATED RHAMNOSE PENTASACCHARIDE—THE
REPEATING UNIT OF THE O-SPECIFIC SIDE CHAIN OF LIPOPOLYSACCHARIDES FROM THE REFERENCE STRAINS FOR
Stenotrophomonas maltophilia SEROGROUP O18, Journal of Carbohydrate Chemistry, 21:1-2, 89-97, DOI: 10.1081/
CAR-120003740
To link to this article: http://dx.doi.org/10.1081/CAR-120003740
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J. CARBOHYDRATE CHEMISTRY, 21(1&2), 89–97 (2002)
SYNTHESIS OF A XYLOSYLATED RHAMNOSE
PENTASACCHARIDE—THE REPEATING UNIT
OF THE O-SPECIFIC SIDE CHAIN OF
LIPOPOLYSACCHARIDES FROM THE
REFERENCE STRAINS FOR
STENOTROPHOMONAS MALTOPHILIA
SEROGROUP O18
*
Jianjun Zhang and Fanzuo Kong
Research Center for Eco-Environmental Science, Academia Sinica,
P.O. Box 2871, Beijing 100085, China
ABSTRACT
A xylosylated rhamnose pentasaccharide, a-L-Rhap-(1!3)-[b-L-Xylp-(1!
2)-] [b-L-Xylp-(1!4)-]a-L-Rhap-(1!3)-L-Rhap, the repeating unit of the O-
specific side chain of the lipopolysaccharides from the reference strains for
Stenotrophomonas maltophilia serogroup O18, was synthesized by a highly
regio- and stereoselective procedure. Thus coupling of methyl rhamnopy-
ranoside (9) with 2,3,4-tri-O-acetyl-a-L-rhamnopyranosyl trichloro-
acetimidate (8) gave the (1!3)-linked disaccharide (10), and subsequent
benzoylation and deacetylation afforded the disaccharide acceptor 12. Con-
densation of 12 with 8 yielded methyl 2,3,4-tri-O-acetyl-a-L-rhamnopyr-
anosyl-(1!3)-a-L-rhamnopyranosyl-(1!3)-2,4-di-O-benzoyl-a-L-rhamno-
pyranoside (13). Coupling of 13 with 2,3,4-tri-O-benzoyl-a-L-xylopyranosyl
trichloroacetimidate (4) followed by deprotection gave the target pentasac-
charide (15).
* Corresponding author. Fax: +86-10-62923563; E-mail: fzkong@mail.rcees.ac.cn
89
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90
ZHANG AND KONG
INTRODUCTION
It was reported[1] very recently that the O-specific side chains of lipopolysacchar-
ides from the reference strains for Stenotrophomonas maltophilia serogroups O4 and O18
are both xylosylated rhamnans consisting of D- and L-form doubly branched pentasac-
charide repeating units, respectively. The O4 polymer has a D-form, and the O18 polymer
has an L-form as shown below.
b-D-Xylp 1
#
2
!2Þ-a-D-Rhap-ð1!3Þ-a-D-Rhap-ð1! 3Þ-a-D-Rhap-ð1!
4
"
b-D-Xylp 1
O4 Polymer
b-L-Xylp 1
#
2
!2Þ-a-L-Rhap-ð1!3Þ-a-L-Rhap-ð1!3Þ-a-L-Rhap-ð1!
4
"
b-L-Xylp 1
O18 Polymer ðwith absence of some xylose units at 4 positionÞ
It is known that S. maltophilia species has potential for bioremediation and the
biological control of plant pathogens,[2,3] and has emerged as a multi-drug-resistant
opportunistic pathogen responsible for nosocomial infections.[4] For investigation of the
structure–bioactivity relationship of the oligosaccharide of O18 polymer, we report
herewith a concise and efficient synthesis of the O18 pentasaccharide repeating unit.
Although the pentasaccharide repeating unit is not very complex, its synthesis will
need orthogonal masking groups and multi-protection–deprotection steps if a traditional
stepwise method is used. Our previous work described highly regio- and stereoselective
syntheses of oligosaccharides using unprotected sugars via an orthoester formation–
rearrangement strategy.[5–7] Later on we found that high regio- and stereoselectivity were
achieved in a one-pot manner using glycosyl trichloroimidates as the donors and
unprotected sugars as the acceptors.[8,9] Based on these new findings we readily ac-
complished the synthesis of the title pentasaccharide.

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XYLOSYLATED RHAMNOSE PENTASACCHARIDE
RESULTS AND DISCUSSION
91
As outlined in the Scheme 1, L-xylose (1) was converted to perbenzoylated
xylopyranosyl trichloroacetimidate (4) through benzoylation with benzoyl chloride in
pyridine, selective 1-O-debenzoylation in ammonia-methanol, and subsequent trichlor-
oacetimidation with trichloroactonitrile in the presence of DBU or potassium carbonate.
2,3,4-Tri-O-acetyl-a-L-rhamnopyranosyl trichloroacetimidate (8) was obtained by acety-
lation of L-rhamnose (5), selective 1-O-deacetylation and trichloroacetimidation. Cou-
pling of the rhamnose donor 8 with the acceptor methyl a-L-rhamnopyranoside (9) in the
presence of catalytic TMSOTf selectively gave the (1!3)-linked disaccharide 10. Its
structure was confirmed by benzoylation to give methyl 2,3,4-tri-O-acetyl-a-L-rhamno-
pyranosyl-(1!3)-2,4-di-O-benzoyl-a-L-rhamnopyranoside (11, 66.2% for 2 steps) show-
ing characteristic signals at d 5.49 ppm (dd, J3,4 =J4,5 = 9.6 Hz) and d 5.42 ppm (dd,
J
1,2 = 1.8 Hz, J2,3 = 3.4 Hz) in its 1H NMR spectrum for H-4 and H-2, respectively. It was
Scheme 1. Synthesis of xylosylated rhamnose pentasaccharide.

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92
ZHANG AND KONG
noted that the temperature during addition of TMSOTf had to be maintained below ꢀ20
°C to ensure formation of the orthoester intermediate, otherwise, for example at room
temperature, the regioselectivity was poor. Benzoylation with benzoyl chloride in
pyridine followed by deacetylation[10] furnished the disaccharide acceptor 12. Conden-
sation of the rhamnose donor 8 with the acceptor 12 promoted by catalytic TMSOTf
selectively gave the 3-linked trisaccharide 13. Acetylation of 13 gave 16, as confirmed
1
from the H NMR spectrum of 16. Coupling of the trisaccharide acceptor 13 with the
xylose donor 4 gave the pentasaccharide 14 and subsequent deacylation in ammonia–
methanol gave the target pentasaccharide 15. The bioassay of the resultant pentasac-
charide is in progress.
In summary, a branched xylosylated rhamnan pentasaccharide was synthesized in a
highly regioselective way with a straightforward procedure. It should be possible to carry
out large scale preparations of 15 employing this method.
EXPERIMENTAL
General Methods. Optical rotations were determined at 25 °C with a Perkin–
Elmer Model 241-Mc automatic polarimeter. Melting points were determined with a
‘‘Mel-Temp’’ apparatus. 1H NMR, 13C NMR, and 1H NMR HOMO COSY spectra were
recorded with Bruker ARX 400 spectrometers for solutions in CDCl3. Chemical shifts are
given in parts per million (ppm) downfield from internal Me4Si. Mass spectra were
recorded with a JMS-D300S mass spectrometer using a direct sample introduction
technique. Thin-layer chromatography (TLC) was performed on Silica Gel HF254 with
detection by charring with 30% (v/v) H2SO4 in MeOH or in some cases by UV detection.
Column chromatography was conducted by elution of a column (16ꢁ240, 18ꢁ300,
35ꢁ400 mm) of silica gel (100–200 mesh) with EtOAc-petroleum ether (60–90 °C) as
the eluent. Solutions were concentrated at <60 °C under diminished pressure. L-Xylose
and L-rhamnose were commercial products from Acros Organics.
2,3,4-Tri-O-benzoyl-a-L-xylopyranosyl trichloroacetimidate (4). To a solution
of L-xylose 1 (7.50 g, 50 mmol) in pyridine (100 mL) was added benzoyl chloride (35
mL, 300 mmol) at 0 °C. The reaction mixture was slowly warmed to room temperature
and stirred for 12 h, at the end of which time TLC (4:1 petroleum ether-EtOAc) indicated
that the reaction was complete. Water (300 mL) was added to the reaction mixture, and
stirring was continued for 30 min. The aq solution was extracted with CH2Cl2 (3ꢁ100
mL), the extract was washed with M HCl and saturated aq sodium bicarbonate, dried
(Na2SO4) and concentrated to give 2 (27.5 g, 97.2%) as a white solid. Compound 2 (17.0
g, 30.0 mmol) was dissolved in a 2 M solution of ammonia–methanol (200 mL) and
stirred for 14 h, at the end of which time TLC (3:1 petroleum ether-EtOAc) indicated that
the reaction was complete. The solution was concentrated, and purification of the residue
by flash column chromatography on a silica gel column (3:1 petroleum ether-EtOAc)
gave compound 3 (12.1 g, 87.3%) as a syrup. A mixture of 3 (9.2 g, 20 mmol),
trichloroacetonitrile (6.3 mL, 30 mmol), and 1,8-diazabicyclo[5.4.0]undecene (DBU)
(0.50 mL, 4.04 mmol) in dry dichloromethane (50 mL) was stirred under nitrogen for 5 h
and then concentrated in vacuo. The residue was purified by flash chromatography (4:1

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XYLOSYLATED RHAMNOSE PENTASACCHARIDE
93
petroleum ether-EtOAc) to give 4 (10.8 g, 89.1%); [a]D + 31.3° (c 1.5, CHCl3); lit.[11]
[a]D +33.1° (c 1.3, CHCl3).
2,3,4-Tri-O-acetyl-a-L-rhamnopyranosyl trichloroacetimidate (8). To a solu-
tion of rhamnose 5 (8.2 g, 50 mmol) in pyridine (100 mL) was added Ac2O (28.3 mL, 300
mmol) at 0 °C. The reaction mixture was slowly warmed to room temperature and stirred
for 12 h. 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 saturated aq sodium bicarbonate, dried (Na2SO4) and
concentrated to give 6 (16.1 g, 97.0%). Compound 6 (10.0 g, 30.0 mmol) was dissolved
in 1 M solution of ammonia–methanol (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, and purification of the residue by flash column chromatog-
raphy on a silica gel column (3:1 petroleum ether-EtOAc) gave compound 7 (8.10 g,
93.1%) as a syrup. A mixture of 7 (5.80 g, 20.0 mmol), trichloroacetonitrile (6.3 mL, 30
mmol), and 1,8-diazabicyclo[5.4.0]undecene (DBU) (0.50 mL, 4.04 mmol) in dry
dichloromethane (50 mL) was stirred under nitrogen for 5 h and then concentrated in
vacuo. The residue was purified by flash chromatography (4:1 petroleum ether-EtOAc) to
give 8 (7.60 g, 87.5%) as a yellow syrup; [a]D ꢀ 54.5° (c 1.1, CHCl3); lit.[12] [a]D ꢀ 52°
(c 1.0, CHCl3).
!
Methyl 2,3,4-Tri-O-acetyl-a-L-rhamnopyranosyl-(1 3)-2,4-di-O-benzoyl-a-L-
rhamnopyranoside (11). 2,3,4-Tri-O-acetyl-a-L-rhamnopyranosyl trichloroacetimi-
date[8] (4.35 g, 10.0 mmol) and methyl a-L-rhamnopyranoside (9) (1.78 g, 10.0 mmol)
were dried together under high vacuum for 2 h, then dissolved in anhydrous CH2Cl2 (40
mL). TMSOTf (30 mL, 0.1 equiv) was added dropwise at ꢀ25 °C with N2 protection. The
reaction mixture was stirred for 3 h, during which time the temperature was gradually
warmed to ambient temperature. Then the mixture was neutralized with triethylamine and
concentrated to dryness to afford the crude methyl 2,3,4-tri-O-acetyl-a-L-rhamnopyr-
anosyl-(1!3)-a-L-rhamnopyranoside (10). To the solution of crude 10 in pyridine (20
mL), benzoyl chloride (3.5 mL, 30 mmol) was added dropwise, and the mixture was
stirred overnight at room temperature. TLC (3:1 petroleum ether-EtOAc) indicated that
the reaction was complete. Ice water was added, and the mixture was diluted with di-
chloromethane, washed with M HCl, water, and saturated aq sodium bicarbonate subse-
quently. The organic layer was combined, dried, and concentrated. Purification by col-
umn chromatography (3:1 petroleum ether-EtOAc) gave 11 (4.29 g , 66.2% for 2 steps) as
a syrup. [a]D + 37.1° (c 1.0, CHCl3); 1H NMR (400 MHz, CDCl3): d 8.15ꢀ7.43 (m, 10 H,
2 PhH), 5.49 (dd, 1 H, J3,4 =J4,5 =9.6 Hz, H-4A), 5.42 (dd, 1 H, J1,2 = 1.8 Hz, J2,3 =3.4 Hz,
H-2A), 5.05 (dd, 1 H, J2,3 = 3.2 Hz, J3,4 =9.8 Hz, H-3B), 4.89ꢀ4.81 (m, 4 H, H-1A, H-1B,
H-2B, H-4B), 4.37 (dd, 1 H, J2,3 =3.4 Hz, J3,4 =9.6 Hz, H-3A), 4.03ꢀ3.82 (m, 2 H, H-5A,
5B), 3.45 (s, 3 H, OCH3), 1.89 (s, 3 H, COCH3), 1.88 (s, 3 H, COCH3), 1.82 (s, 3 H,
COCH3), 1.32 (d, 3 H, J5,6 = 6.3 Hz, H-6A/H-6B), 1.05 (d, 3 H, J5,6 =6.3 Hz, H-6A/H-6B);
13C NMR (100 MHz, CDCl3): d 169.5, 168.9, 168.7 (3 C, 3 COCH3), 165.7, 165.0 (2 C, 2
COPh), 98.7, 97.8 (2 C, C-1A, 1B), 72.9, 71.7, 70.5, 69.3, 68.0, 66.7, 66.1 54.8 (9 C, C-2A,
2B, 3A, 3B, 4A, 4B, 5A, 5B, OCH3), 20.2, 20.1, 20.0, 17.2, 16.7 (5 C, C-6A, 6B, 3 COCH3).
Anal. Calcd for C33H38O14: C, 60.17; H, 5.82. Found: C, 60.24; H, 6.01.

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94
ZHANG AND KONG
Methyl a-L-Rhamnopyranosyl-(1 3)-2,4-di-O-benzoyl-a-L-rhamnopyrano-
!
side (12). To a solution of 11 (658 mg, 1.00 mmol) in anhydrous MeOH (50 mL)
was added acetyl chloride (1.5 mL) at 0 °C. The solution was sealed in a flask and
stirred at room temperature until TLC (3:1 petroleum ether-EtOAc) showed that the
starting material disappeared. The solution was neutralized with Et3N, then concentrated
to dryness. The residue was passed through a short silica gel column to give 12 (510
1
mg, 95.9%) as a white solid; [a]D +42.1° (c 1.0, CHCl3); H NMR (400 MHz, CDCl3):
d 8.11ꢀ7.44 (m, 10 H, 2 PhH), 5.47ꢀ5.42 (m, 2 H, H-4A, H-2A), 4.89 (d, 1 H, J1,2 = 1.6
Hz, H-1B), 4.81 (d, 1 H, J1,2 =1.5 Hz, H-1A), 4.36 (dd, 1 H, J2,3 =3.3 Hz, J3,4 =9.7 Hz,
H-3A), 4.14ꢀ3.65 (m, 2 H, H-5A, 5B), 3.57 (dd, J1,2 = 1.6 Hz, J2,3 = 3.2 Hz, H-2B), 3.48
(dd, 1 H, J2,3 =3.2 Hz, J3,4 =9.8 Hz, H-3B), 3.45 (s, 3 H, OCH3), 3.28 (dd, J3,4 =J4,5 = 9.8
Hz, H-4B), 2.00ꢀ1.90 (br, 3 H, 3OH), 1.29 (d, 3 H, J5,6 = 6.3 Hz, H-6A/H-6B), 1.21 (d, 3
H, J5,6 = 6.3 Hz, H-6A/H-6B); 13C NMR (100 MHz, CDCl3): d 165.5, 165.4 (2 C, 2
COPh), 101.2, 98.0 (2 C, C-1A, 1B), 74.3, 73.3, 72.3, 71.8, 70.7, 70.2, 68.5, 66.1, 54.8
(9 C, C-2A, 2B, 3A, 3B, 4A, 4B, 5A, 5B, OCH3), 17.1, 16.7 (2 C, C-6A, 6B).
Anal. Calcd for C27H32O11: C, 60.89; H, 6.06. Found: C, 60.77; H, 6.12.
!
Methyl 2,3,4-Tri-O-acetyl-a-L-rhamnopyranosyl-(1 3)-a-L-rhamnopyrano-
!
syl-(1 3)-2,4-di-O-benzoyl-a-L-rhamnopyranoside (13). 2,3,4-Tri-O-acetyl-a-L-
rhamnopyranosyl trichloroacetimidate (8) (435 mg, 1.00 mmol) and methyl a-L-
rhamnopyranosyl-(1!3)-2,4-di-O-benzoyl-a-L-rhamnopyranoside (12) (532 mg, 1.00
mmol) were dried together under high vacuum for 2 h, then dissolved in anhydrous
CH2Cl2 (40 mL). TMSOTf (18 mL, 0.10 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 warmed to ambient temperature. Then the mixture was neutralized with
triethylamine and concentrated to dryness. Purification of the residue by column
chromatography (1:1 petroleum ether-EtOAc) gave 13 (547 mg, 68.0%) as a foamy
1
solid. [a]D + 11.5° (c 1.0, CHCl3); H NMR (400 MHz, CDCl3): d 8.12ꢀ7.44 (m, 10 H,
2 PhH), 5.48ꢀ5.43 (m, 2 H, H-4A, H-2A), 5.20 (dd, 1 H, J1,2 =1.5 Hz, J2,3 =3.4 Hz, H-
2C), 5.11 (dd, 1 H, J2,3 = 3.4 Hz, J3,4 = 9.7 Hz, H-3C), 4.93 (dd, 1 H, J3,4 =J4,5 = 9.7 Hz,
H-4C), 4.91ꢀ4.83 (m, 3 H, H-1A, 1B, 1C), 5.37 (dd, 1 H, J2,3 = 3.2 Hz, J3,4 = 9.8 Hz, H-
3A), 4.02ꢀ3.67 (m, 3 H, H-5A, 5B, 5C), 3.60ꢀ3.55 (m, 2 H, H-2B, 3B), 3.48 (dd, 1 H,
J
3,4 =J4,5 = 9.7 Hz, H-4B), 3.45 (s, 3 H, OCH3), 2.10 (s, 3 H, COCH3), 2.00 (s, 3 H,
COCH3), 1.94 (s, 3 H, COCH3), 1.30 (d, 3 H, J5,6 = 6.3 Hz, H-6A/H-6B/6C), 1.22 (d, 3
H, J5,6 =6.1 Hz, H-6A/H-6B/6C), 0.85 (d, 3 H, J5,6 = 6.2 Hz, H-6A/H-6B/6C); 13C NMR
(100 MHz, CDCl3): d 169.7, 169.6, 169.5 (3 C, 3 COCH3), 165.5, 165.1 (2 C, 2 COPh),
100.9, 98.2, 98.0 (3 C, C-1A, 1B, 1C), 77.9, 74.5, 73.2, 71.8, 71.5, 70.3, 70.3, 69.0, 68.7,
68.6, 66.4, 66.1, 54.8 (13 C, C-2A, 2B, 2C 3A, 3B, 3C, 4A, 4B, 4C, 5A, 5B, 5C, OCH3),
20.4, 20.3, 20.2, 17.2, 16.9, 16.5 (6 C, C-6A, 6B, 6C, COCH3, COCH3, COCH3).
Anal. Calcd for C39H48O18: C, 58.20; H, 6.01. Found: C, 58.03; H, 6.08.
!
Methyl 2,3,4-Tri-O-acetyl-a-L-rhamnopyranosyl-(1 3)-[2,3,4-tri-O-benzoyl-
!
!
b-L-xylopyranosyl-(1 2)][2,3,4-tri-O-benzoyl-b-L-xylopyranosyl-(1 4)]-a-L-rham-
!
nopyranosyl-(1 3)-2,4-di-O-benzoyl-a-L-rhamnopyranoside (14). 2,3,4-Tri-O-ben-
zoyl-a-L-xylopyranosyl trichloroacetimidate (4) (606 mg, 1.00 mmol) and methyl 2,3,
4-tri-O-acetyl-a-L-rhamnopyranosyl-(1!3)-a-L-rhamnopyranosyl-(1!3)-2,4-di-O-ben-
zoyl-a-L-rhamnopyranoside (13) (402 mg, 0.50 mmol) were dried together under high

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XYLOSYLATED RHAMNOSE PENTASACCHARIDE
95
vacuum for 2 h, then dissolved in anhydrous CH2Cl2 (10 mL). TMSOTf (9.0 mL, 0.05
mmol) was added dropwise at ꢀ20 °C with N2 protection. The reaction mixture was
stirred for 2 h, during which time the temperature was gradually warmed to ambient
temperature. Then the mixture was neutralized with triethylamine and concentrated to
dryness. Purification of the residue by column chromatography (3:1 petroleum ether–
ethyl acetate) gave 14 (520 mg, 82.3%) as a syrup; [a]D + 44.5° (c 1.0, CHCl3); 1H NMR
(400 MHz, CDCl3): d 8.13ꢀ7.35 (m, 40 H, 8 PhH), 5.67 (dd, 1 H, J2,3 = J3,4 =9.9 Hz,
H-3D/H-3E), 5.47 (dd, 1 H, J1,2 =1.7 Hz, J2,3 =3.1 Hz, H-2C), 5.40ꢀ5.21 (m, 7 H, H-2D,
H-2E, H-3C, H-3D/H-3E, H-4A, H-4D, H-4E), 5.14 (dd, 1 H, J1,2 = 1.6 Hz, J2,3 = 3.3 Hz,
H-2A), 4.99 (dd, 1 H, J3,4 = J4,5 =9.7 Hz, H-4C), 4.98 (d, 1 H, J1,2 =1.7 Hz, H-1C), 4.73 (d, 1
H, J1,2 =1.6 Hz, H-1A), 4.67 (d, 1 H, J1,2 =1.7 Hz, H-1B), 4.65 (d, 1 H, J1,2 =6.0 Hz, H-1D/H-
1E), 4.13ꢀ4.06 (m, 2H, 1 H-5D, 1 H-5E), 4.08 (dd, 1 H, J2,3 = 3.3 Hz, J3,4 =9.8 Hz, H-3A),
4.00ꢀ3.85 (m, 2 H, H-5A, H-5C), 3.81 (d, 1 H, J1,2 =5.9 Hz, H-1D/H-1E), 3.62 (dd, 1 H,
J
2,3 = 3.1 Hz, J3,4 =9.6 Hz, H-3B), 3.49ꢀ3.39 (m, 7 H, H-2B, H-4B, H-5B, 1 H-5D/H-5E,
OCH3), 2.91 (q, 1 H, J=7.8 Hz, H-5D/H-5E), 2.16 (s, 3 H, COCH3), 2.03 (s, 3 H,
COCH3), 1.94 (s, 3 H, COCH3), 1.26 (d, 3 H, J5,6 = 6.1 Hz, H-6A), 0.90 (d, 3 H, J5,6 =6.3
Hz, H-6C), 0.80 (d, 3 H, J5,6 =6.4 Hz, H-6B); 13C NMR (100 MHz, CDCl3): d 169.7,
169.3, 169.2 (3 C, 3 COCH3), 165.2, 164.8, 164.5, 164.4, 164.3 (8 C, some signals
overlapped 8 COPh), 101.3, 99.2, 99.0, 98.7, 98.1 (5 C, C-1A, 1B, 1C, 1D, 1E), 80.4, 77.6
(2 C, C-3A, C-3B), 74.3, 73.7, 73.6, 72.0, 71.5, 71.2, 71.1, 70.5, 70.0, 69.2, 68.9, 68.8,
67.9, 65.9, 65.8, 62.0, 60.9, 59.9 (18 C, C-2A–E, 3C–E, 4A–E, 5A–E), 54.7 (1 C, OCH3),
20.5, 20.4, 20.3, 17.1, 16.6, 16.5 (6 C, C-6A, 6B, 6C, 3 COCH3).
Anal. Calcd for C91H88O32: C, 64.53; H, 5.24. Found: C, 64.70; H, 5.15.
!
!
Methyl a-L-Rhamnopyranosyl-(1 3)-[b-L-xylopyranosyl-(1 2)][b-L-xylopy-
!
!
ranosyl-(1 4)]-a-L-rhamnopyranosyl-(1 3)-a-L-rhamnopyranoside (15). Penta-
asaccharide 14 (500 mg, 0.30 mmol) was dissolved in a saturated solution of ammonia
in MeOH (10 mL). After 96 h at room temperature, the reaction mixture was concentrated
and the residue was purified by chromatography on Sephadex LH-20 (MeOH) to afford
15 as a foamy solid (190 mg, 86.3%); [a]D ꢀ18.2° (c 1.0, CHCl3); 1H NMR (400 MHz,
CDCl3): d 5.15 (d, 1 H, J1,2 =1.5 Hz, H-1), 5.08 (d, 1 H, J1,2 =1.6 Hz, H-1), 4.60 (d, 1 H,
J
1,2 = 1.5 Hz, H-1), 4.38 (d, 1 H, J1,2 =6.1 Hz, H-1), 4.32 (d, 1 H, J1,2 =6.0 Hz, H-1), 3.44
(s, 3 H, OCH3), 1.41 (d, 3 H, J5,6 = 6.1 Hz, H-6), 1.32 (d, 3 H, J5,6 =6.2 Hz, H-6), 1.28 (d,
3 H, J5,6 = 6.0 Hz, H-6); 13C NMR (100 MHz, CDCl3): d 104.7, 103.3, 101.2, 101.2, 100.3
(5C, C-1), 81.2, 78.6, 77.3, 76.8, 76.5, 74.2, 73.2, 72.7, 71.9, 70.9, 70.7, 70.6, 69.9, 68.7,
68.6, 68.4, 65.6, 65.5 (some signals overlapped), 53.8 (1 C, OCH3), 16.9, 16.6, 16.5 (3 C,
C-6A–C); MS (m/z) Calcd for C29H50O21: 734.69 [M]+. Found: 757.71 [M +Na]+.
!
Methyl 2,3,4-Tri-O-acetyl-a-L-rhamnopyranosyl-(1 3)-2,4-di-O-acetyl-a-L-
!
rhamnopyranosyl-(1 3)-2,4-di-O-benzoyl-a-L-rhamnopyranoside (16). Acetyla-
tion of 13 (80 mg, 0.5 mmol) with acetic anhydride (1 mL) in pyridine (5 mL) at room
temperature for 10 h gave compound 15 in a quantitative yield as a foamy solid; [a]D +
23.6° (c 1.0, CHCl3); 1H NMR (400 MHz, CDCl3): d 8.10ꢀ7.45 (m, 10 H, 2 PhH), 5.47
(dd, 1 H, J3,4 =J4,5 =9.8 Hz, H-4A), 5.43 (dd, 1 H, J1,2 =1.8 Hz, J2,3 = 3.4 Hz, H-2A), 5.00
(dd, 1 H, J2,3 = 3.3 Hz, J3,4 =9.9 Hz, H-3C), 4.93 (dd, 1 H, J1,2 =1.6 Hz, J2,3 =3.3 Hz, H-
2C), 4.91 (dd, 1 H, J3,4 =J4,5 =9.9 Hz, H-4C), 4.90 (d, J1,2 = 1.5 Hz, H-1B), 4.88 (dd, 1 H,
J
3,4 = J4,5 =9.7 Hz, H-4B), 4.85 (d, J1,2 =1.6 Hz, H-1C), 4.82 (dd, 1 H, J1,2 = 1.5 Hz,

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ZHANG AND KONG
J2,3 =3.1 Hz, H-2B), 4.60 (d, J1,2 =1.8 Hz, H-1A), 4.35 (dd, 1 H, J2,3 =3.4 Hz, J3,4 =9.8 Hz,
H-3A), 3.99 (m, 1 H, H-5A), 3.84 (dd, 1 H, J2,3 = 3.1 Hz, J3,4 =9.7 Hz, H-3B), 3.71 (m, 1 H,
5C), 3.57 (m, 1 H, H-5B), 3.44 (s, 3 H, OCH3), 2.11 (s, 3 H, COCH3), 1.99 (s, 3 H,
COCH3), 1.98 (s, 3 H, COCH3), 1.96 (s, 3 H, COCH3), 1.92 (s, 3 H, COCH3), 1.30 (d, 3
H, J5,6 = 6.2 Hz, 6C), 1.00 (d, 3 H, J5,6 =6.1 Hz, H-6A), 0.75 (d, 3 H, J5,6 =6.4 Hz, 6C); 13
C
NMR (100 MHz, CDCl3): d 169.6, 169.5, 169.4, 169.3, 169.1 (5 C, 5 COCH3), 165.5,
165.3 (2 C, 2 COPh), 98.6, 98.0, 97.8 (3 C, C-1A, 1B, 1C), 75.4, 73.6, 72.7, 71.6, 71.6,
70.7, 70.3, 69.6, 68.0, 67.1, 66.4, 66.1, 54.8 (13 C, C-2A, 2B, 2C 3A, 3B, 3C, 4A, 4B, 4C, 5A,
5B, 5C, OCH3), 20.4, 20.3, 20.2, 17.2, 16.8, 16.3 (8 C, some signals overlapped C-6A, 6B,
6C, 5 COCH3).
Anal. Calcd for C43H52O20: C, 58.10; H, 5.90. Found: C, 57.96; H, 6.11.
ACKNOWLEDGMENTS
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).
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Received September 17, 2001
Accepted January 2, 2002