Synthesis of β-D-Glcp-(1→2)-[β-D-Ribf-(1→3)-]α-L-Rhap- (1→3)-α-L-Rhap-(1→2)-α-L-Rhap, the repeating unit of the lipopolysaccharide of Acetobacter diazotrophicus PAL 5

Article abstract of DOI:10.1081/CAR-120016856

A pentasaccharide, the major repeating unit of the lipopolysaccharide (LPS) of the nitrogen fixing bacterium Acetobacter diazotrophicus PAL 5 was efficiently synthesized as its allyl glycoside using a regio- and stereoselective strategy. The key acceptor, allyl 3-O-acetyl-4-O-benzoyl-α-L-rhamnopyranoside (3), was prepared by selective 3-O-acetylation of allyl 4-O-benzoyl-α-L-rhamnopyranoside. Condensation of 3 with 2,3,4,6-tetra-O-benzoyl-α-D-glucopyranosyl trichloroacetimidate furnished the disaccharide 5. Deallylation and subsequent trichloroacetimidation of 5 afforded 2,3,4,6-tetra-O-benzoyl-β-D-glucopyranosyl-(1→2)-3-O-acetyl-4-O- benzoyl-α-L-rhamnopyranosyl trichloroacetimidate (10). Selective 3-O-glycosylation of allyl α-L-rhamnopyranoside (1) with 10 followed by benzoylation gave trisaccharide (12), which could be conveniently converted to a donor (14). Condensation of 14 with allyl 3,4-di-O-benzoyl-α-L-rhamnopyranoside (15) gave tetrasaccharide 16. Selective deacetylation of 16 gave the acceptor 17 which was ribosylated to furnish the protected pentasaccharide, and finally deprotection led to the title compound.

Full text of DOI:10.1081/CAR-120016856

Journal of Carbohydrate Chemistry
ISSN: 0732-8303 (Print) 1532-2327 (Online) Journal homepage: http://www.tandfonline.com/loi/lcar20
SYNTHESIS OF β-d-Glcp-(1→2)-[β-d-Ribf-(1→3)-]α-
l-Rhap-(1→3)-α-l-Rhap-(1→2)-α-l-Rhap, THE
REPEATING UNIT OF THE LIPOPOLYSACCHARIDE OF
Acetobacter diazotrophicus PAL 5
Jianjun Zhang & Fanzuo Kong
To cite this article: Jianjun Zhang & Fanzuo Kong (2002) SYNTHESIS OF β-d-Glcp-(1→2)-
[β-d-Ribf-(1→3)-]α-l-Rhap-(1→3)-α-l-Rhap-(1→2)-α-l-Rhap, THE REPEATING UNIT OF THE
LIPOPOLYSACCHARIDE OF Acetobacter diazotrophicus PAL 5, Journal of Carbohydrate
Chemistry, 21:6, 579-589
To link to this article: http://dx.doi.org/10.1081/CAR-120016856
Published online: 16 Aug 2006.
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JOURNAL OF CARBOHYDRATE CHEMISTRY
Vol. 21, No. 6, pp. 579–589, 2002
SYNTHESIS OF b-D-Glcp-(1 2)-[b-D-Ribf-(1 3)-]a-L-
!
!
Rhap-(1 3)-a-L-Rhap-(1 2)-a-L-Rhap, THE
!
!
REPEATING UNIT OF THE LIPOPOLYSACCHARIDE
OF ACETOBACTER DIAZOTROPHICUS PAL 5
*
Jianjun Zhang and Fanzuo Kong
Research Center for Eco-Environmental Sciences, Academia Sinica,
P.O. Box 2871, Beijing 100085, P.R. China
ABSTRACT
A pentasaccharide, the major repeating unit of the lipopolysaccharide (LPS)
of the nitrogen fixing bacterium Acetobacter diazotrophicus PAL 5 was
efficiently synthesized as its allyl glycoside using a regio- and stereo-
selective strategy. The key acceptor, allyl 3-O-acetyl-4-O-benzoyl-a-L-
rhamnopyranoside (3), was prepared by selective 3-O-acetylation of allyl
4-O-benzoyl-a-L-rhamnopyranoside. Condensation of 3 with 2,3,4,6-tetra-O-
benzoyl-a-D-glucopyranosyl trichloroacetimidate furnished the disaccharide
5. Deallylation and subsequent trichloroacetimidation of 5 afforded 2,3,4,6-
tetra-O-benzoyl-b-D-glucopyranosyl-(1 !2)-3-O-acetyl-4-O-benzoyl-a-L-
rhamnopyranosyl trichloroacetimidate (10). Selective 3-O-glycosylation of
allyl a-L-rhamnopyranoside (1) with 10 followed by benzoylation gave tri-
saccharide (12), which could be conveniently converted to a donor (14).
Condensation of 14 with allyl 3,4-di-O-benzoyl-a-L-rhamnopyranoside (15)
gave tetrasaccharide 16. Selective deacetylation of 16 gave the acceptor 17
which was ribosylated to furnish the protected pentasaccharide, and finally
deprotection led to the title compound.
Key Words: Regio- and stereoselective synthesis; Rhamnan;
Trichloroacetimidate
*
Corresponding author.
579
DOI: 10.1081/CAR-120016856
0732-8303 (Print); 1532-2327 (Online)
www.dekker.com
Copyright D 2002 by Marcel Dekker, Inc.

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580
ZHANG AND KONG
INTRODUCTION
The pentasaccharide, b-D-Glcp-(1 !2)-[b-D-Ribf-(1 !3)-]a-L-Rhap-(1 !3)-a-L-
Rhap-(1 !2)-a-L-Rhap, is the major repeating unit of the lipopolysaccharide (LPS)
of the nitrogen fixing bacterium Acetobacter diazotrophicus PAL 5 occurring in sugar
cane in Brazil and Australia.[1] Field experiments suggest that up to 80% of the N
incorporated into Brazilian sugar cane may be obtained from biological nitrogen fix-
ation (BNF). The involvement of the carbohydrate-rich molecules in establishing the
interaction between the BNF bacterium and the host has been reported.[2,3] These facts
are of interest from the viewpoints of the biological roles of carbohydrates.
Rhamnans with a long backbone consisting of a-(1 !2) and a-(1 !3) linked
L-rhamnose units to which are attached various kinds of side chains are widely dis-
tributed in nature. These target compounds are structurally very similar, but the syn-
thetic approaches used are quite different. A stepwise synthesis of the hexasaccahride
with rhamnotetraose as the backbone and two glucosamine units as the side chains has
been reported.[4] Our previous work described highly regio- and stereoselective syn-
theses of oligosaccharides via orthoester formation-rearrangement strategy using gly-
cosyl trichloroacetimidates as the donors and lightly protected sugars as the acceptors
were achieved in a one-pot manner.[5–7] As part of our ongoing research project on the
synthesis of rhamnans, we present herein the synthesis of the well-defined ribosylated
glucorhamnan pentasaccharide.
RESULTS AND DISCUSSION
As outlined in Scheme 1, allyl a-L-rhamnopyranoside was converted to allyl 4-O-
benzoyl-a-L-rhamnopyranoside (2) through 2,3-O-isopropylidenation with 2,2-di-
methoxypropane in DMF in the presence of catalytic TsOH, 4-O-benzoylation with
benzoyl chloride in pyridine, and deisopropylidenation with 90% acetic acid. These
three steps were performed continuously without separation, giving 85.3% overall
yield. Subsequent acetylation of 2 with 1.05 equiv of acetyl chloride in pyridine-
dichloromethane selectively gave allyl 3-O-acetyl-4-O-benzoyl-a-L-rhamnopyranoside
1
(3) as the only product in 91.5% yield. Its structure was confirmed by its H NMR
spectrum which showed a characteristic upfield signal at d 4.11 ppm (dd, J1,2 =1.6 Hz,
J
2,3 =3.2 Hz) for H-2. Coupling of the glucose donor 4 with the acceptor 3 in the
presence of catalytic TMSOTf furnished the (1 !2)-linked disaccharide 5. The 3-O-
acetyl group of the disaccharide 5 was successfully removed without affecting any of
the benzoyl groups in CH3COCl-methanol[8] (3%) to give the desired acceptor 6 in
84.5% yield. Thus coupling of 6 with 2,3,4-tri-O-acetyl-a-D-ribofuranosyl trichlor-
oacetimidate[9] (7) gave trisaccharide 8 in satisfactory yield (79.5%). However, perhaps
because of the presence of peracetylated ribofuranosyl group, an attempt to deallylate 8
with PdCl2 was not successful and gave a very complex product. Later on, we tried to
first construct the glucorhamnose tetrasaccharide acceptor 17, and then successively
made the target pentasaccharide. Thus, deallylation of 5 with PdCl2, followed by tri-
chloroacetimidation[10] with CCl3CN in the presence of DBU or K2CO3 gave the
disaccharide donor 10. Coupling of the donor 10 with the acceptor allyl a-L-rham-
nopyranoside (1) in the presence of catalytic TMSOTf selectively gave the (1 !3)-
linked trisaccharide 11. Benzoylation of 11 gave allyl 2,3,4,6-tetra-O-benzoyl-b-D-

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ACETOBACTER DIAZOTROPHICUS PAL 5 SYNTHESIS
581
1) 2,2-dimethoxypropane,
D MF, TsOH
2) BzCl, Pyridine
OAll
OAll
OAll
O
O
O
H3C
HO
H3C
BzO
H3C
BzO
CH3COCl,
Pyridine
AcO
3) 90% HOAc
HO
HO
OH
OH
OH
2
3
1
OAll
AcO
O
OAll
BzO
O
H3C
O
PdCl2
OBz
OBz
BzO
H3C
BzO
7
C
OC(NH)CCl
3
O
RO
3,
TMSOTf
BzO
BzO
BzO
AcO OAc
O
O
O
AcO
O
BzO
TMSOTf
O
OBz
OBz
OR
4 R = C(NH)CCl
O
D
E
BzO
BzO
BzO
3
5 R=Ac
6 R=H
OAc
AcO
8
3% CH3CO C l /C H 3OH
OAll
OR
1
O
H3C
BzO
A
O
H3C
OAll
BzO
O
R2O
OR
H3C
O
O
OR
2
O
H3C
BzO
B
BzO
O
H3C
O
H3C
BzO
BzO
15
OH
O
BzO
PdCl2
1
OBz
AcO
AcO
O
O
5
H3C
O
C
O
O
TMSOTf
TMSOTf
BzO
BzO
BzO
BzO
BzO
BzO
BzO
RO
O
BzO
BzO
O
BzO
BzO
BzO
D
11 R1 = All,
12R1 = All,
13 R1 = H,
R2= H
BzCl, Pyr.
BzO
CCl3CN ,
DBU
9 R = H
R2= Bz
R2= Bz
10 R = C(NH)CCl
3
PdCl2
16 R = Ac
S1/AQ2
3% CH3CO C l /C H 3OH
17 R = H
CCl3CN , D BU
14 R1 = C(NH)CCl3, R2= Bz
OAll
OAll
O
H3C
HO
O
H3C
BzO
A
BzO
HO
O
O
BzO
O
O
H3C
HO
O
H3C
BzO
OC(NH)CCl3
OBz
B
O
BzO
O
satd NH3/MeOH
OH
O
18
OBz
O
H3C
HO
17
O
H3C
BzO
C
TMSOTf
O
OH
OBz
OBz
O
HO
O
HO
OH
OH
BzO
O
BzO
O
O
O
D
E
OBz
HO OH
20
BzO
OBz
19
Scheme 1. Synthesis of the target pentasaccharide.
glucopyranosyl-(1 !2)-3-O-acetyl-4-O-benzoy-a-L-rhamnopyranosyl-(1 !3)-2,4-di-O-
1
benzoy-a-L-rhamnopyranoside (12, 68.1% for 2 steps). The H NMR spectrum of 12
showed characteristic upfield signals at d 4.45 ppm (dd, J2,3 =3.0 Hz, J3,4 =9.8 Hz) for
H-3 and d 3.75 ppm (dd, J1,2 = 1.3 Hz, J2,3 =3.2 Hz) for H-2 respectively. It was noted
that the temperature during addition of TMSOTf had to be maintained below ꢀ 20°C

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582
ZHANG AND KONG
to ensure formation of the orthoester intermediate, otherwise, for example at room
temperature, the regioselectivity was poor. Condensation of the rhamnose donor 14,
readily prepared from 12 through deallylation and trichloroacetimidation, with the
acceptor 15 furnished the tetrasaccharide 16. Subsequent selective deacetylation of
16 with CH3COCl-methanol (3%) afforded the tetrasaccharide acceptor, allyl 2,3,4,6-
tetra-O-benzoyl-b-D-glucopyranosyl-(1 !2)-4-O-benzoyl-a-L-rhamnopyranosyl-(1 !3)-
2,4-di-O-benzoyl-a-L-rhamnopyranosyl-(1 !2)-3,4-di-O-benzoyl-a-L-rhamnopyranoside
(17). Coupling of the tetrasaccharide 17 with 2,3,4-tri-O-benzoyl-a-D-ribofuranosyl
trichloroacetimidate[9] (18) proceeded smoothly in dichloromethane in the presence
of TMSOTf, giving the pentasaccharide (19). The structure of 19 was specified by
its 1H, 13C NMR, and 1H–1H COSY NMR spectra. Deacylation of 19 in am-
monium-saturated methanol gave the target pentasaccharide 20. The bioassay of 20
is in progress.
In summary, a very concise and efficient synthesis of allyl b-D-glucopyranosyl-
(1 !2)-[b-D-ribofuranosyl-(1 !3)-]a-L-rhamnopyranosyl-(1 !3)-a-L-rhamnopyranosyl-
(1 !2)-a-L-rhamnopyranoside was achieved through a regio- and stereoselective
process. In terms of the simplicity and efficiency, this method can be used for con-
struction of higher oligosaccharides with similar structures.
EXPERIMENTAL
General methods. Melting points were determined with a ‘Mel-Temp’ ap-
paratus. Optical rotations were determined with a Perkin-Elmer model 241-MC auto-
1
matic polarimeter for solutions in a 1-dm, jacketed cell. H and 13C NMR spectra were
recorded with Varian XL-400 and Varian XL-200 spectrometers, for solutions in CDCl3
with tetramethylsilane (Me4Si) as the internal standard or in D2O with acetone 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 spec-
trometer using the ESI mode. Thin-layer chromatography (TLC) was performed on
silica gel HF, detection being affected by charring with 30% (v/v) sulfuric acid in
methanol or sometimes by UV detection. Column chromatography was conducted by
elution of a column (16 ꢁ 240, 18ꢁ 300, 35 ꢁ 400 mm) of silica gel (100–200 mesh)
with EtOAc–petroleum ether (60–90°C) as the eluent. Analytical LC was performed
with a Gilson HPLC consisting of a pump (model 306), stainless steel packed with
silica gel (Spherisorb SiO2, 10ꢁ 300 mm or 4.6 ꢁ 250 mm), differential refractometer
(132-RI Detector), UV/VIS detector (model 118), and EtOAc/petroleum ether (bp 60–
90°C) was used as the eluent at a flow rate of 1–4 mL/min. Solutions were concen-
trated at a temperature <60°C under diminished pressure.
Allyl 4-O-benzoyl-a-L-rhamnopyranoside (2). To a solution of allyl a-L-rham-
nopyranoside (1) (2.04 g, 10 mmol) in DMF (10 mL) containing p-toluenesulfonic acid
monohydrate (38 mg, 0.2 mmol) was added 2,2-dimethoxypropane (2.5 mL, 20 mmol)
and the mixture was stirred for 12 h, at the end of which time TLC (3/1 petroleum
ether/ethyl acetate) indicated that the reaction was complete. Then the reaction mix-
ture was added dropwise to a solution of pyridine (20 mL) containing benzoyl chloride
(4.7 mL, 40 mmol). After stirring for 24 h at room temperature, the mixture was diluted

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ACETOBACTER DIAZOTROPHICUS PAL 5 SYNTHESIS
583
with dichloromethane, washed with 1 N hydrochloric acid, water, and satd aq solution of
sodium bicarbonate subsequently. The organic layer was combined, dried, and con-
centrated to a residue. The residue was dissolved in 90% acetic acid and refluxed for 1 h.
The solution was concentrated, and purification of the residue by flash column chro-
matography on a silica gel column (1:1 petroleum ether–EtOAc) gave compound 2
(2.63 g, 85.4%) as a syrup; [a]D ꢀ 71.3° (c 1.3, CHCl3); 1H NMR (CDCl3): d 8.06–7.42
(m, 5 H, Bz-H), 5.93 (m, 1 H, OCH2CHCH2), 5.32–5.21 (m, 2 H, OCH2CHCH2), 5.07
(dd, 1 H, J3,4 = J4,5 =9.9 Hz, H-4), 4.92 (d, 1 H, J1,2 =0.8 Hz, H-1), 4.24–3.98 (m, 5 H),
3.07–2.90 (bs, 2 H, 2 OH), 1.24 (d, J5,6 =6.4 Hz, 3 H, H-6).
Anal. Calcd for C16H.20O6: C, 62.32; H, 6.54. Found: C, 64.49; H, 6.76.
Allyl 3-O-Acetyl-4-O-benzoyl-a-L-rhamnopyranoside (3). A solution of
acetyl chloride (0.8 mL, 11 mmol) in anhyd dichloromethane (10 mL) was added
dropwise to a solution of allyl 4-O-benzoyl-a-L-rhamnopyranoside (2, 3.08 g, 10 mmol)
in anhyd dichloromethane (100 mL) containing 5 mL pyridine at 0°C within 10 min,
and the mixture was stirred at room temperature for 2 h, at the end of which time TLC
(3/1 petroleum ether/ethyl acetate) indicated that the reaction was complete. The
mixture was washed with 1 N hydrochloric acid, water, and satd aq solution of sodium
bicarbonate subsequently. The organic layer was combined, dried, and concentrated to a
residue. Purification of the residue on a silica gel column with 3:1 petroleum ether–
ethyl acetate as the eluent gave 3 (3.20 g, 91.5%) as a syrup; [a]D ꢀ 53.2° (c 1.0,
1
CHCl3); H NMR (CDCl3): d 8.06–7.42 (m, 5 H, Bz-H), 5.93 (m, 1 H, OCH2CHCH2),
5.48 (dd, 1 H, J2,3 =3.2 Hz, J3,4 = 9.8 Hz, H-3), 5.37 (dd, 1 H, J3,4 = J4,5 =9.8 Hz, H-4),
5.36–5.23 (m, 2 H, OCH2CHCH2), 4.90 (d, 1 H, J1,2 = 1.6 Hz, H-1), 4.24 (m, 1 H,
OCH2CHCH2), 4.11 (dd, 1 H, J1,2 =1.6 Hz, J2,3 =3.2 Hz, H-2), 4.07–4.01 (m, 2 H, H-5,
OCH2CHCH2), 1.99 (s, 3 H, CH3CO), 1.25 (d, J5,6 = 6.3 Hz, 3 H, H-6).
Anal. Calcd for C18H.22O7: C, 61.70; H, 6.33. Found: C, 61.86; H, 6.30.
Allyl 2,3,4,6-Tetra-O-benzoyl-b-D-glucopyranosyl-(1 2)-3-O-acetyl-4-O-ben-
!
zoyl-a-L-rhamnopyranoside (5). 2,3,4,6-Tetra-O-benzoyl-a-D-glucopyranosyl trichlo-
roacetimidate (4) (3.70 g, 5 mmol) and allyl 3-O-acetyl-4-O-benzoyl-a-L-rhamnopyra-
noside (3) (1.75 g, 5 mmol) were dried together under high vacuum for 2 h, then
dissolved in anhyd CH2Cl2 (20 mL). TMSOTf (45 mL, 0.05 equiv) was added dropwise
at ꢀ 10°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 by column
chromatography (3:1 petroleum ether–EtOAc) gave 5 (3.92 g, 84.5%) as a foamy solid;
1
[a]D ꢀ 5.8° (c 0.5, CHCl3); H NMR (400 MHz, CDCl3): d 8.15–7.43 (m, 25 H, 5
PhH), 5.96 (dd, 1 H, J2,3 =J3,4 = 9.8 Hz, H-3’), 5.80 (m, 1 H, OCH2CHCH2), 5.66 (dd, 1
H, J3,4 = J4,5 =9.8 Hz, H-4’), 5.61 (dd, 1 H, J1,2 =7.8 Hz, J2,3 =9.8 Hz, H-2’), 5.38 (dd, 1
H, J2,3 =3.2 Hz, J3,4 =9.7 Hz, H-3), 5.39–5.21 (m, 3 H, H-4, OCH2CHCH2), 5.04 (d, 1
H, J1,2 =1.4 Hz, H-1), 4.88 (d, 1 H, J1,2 = 7.8 Hz, H-1’), 4.60–4.46 (m, 2 H, H-6’),
4.15–3.88 (m, 5 H, H-2, H-5, H-5’, OCH2CHCH2), 1.26 (s, 3 H, COCH3), 1.22 (d, 3 H,
J
5,6 = 6.4 Hz, H-6); 13C NMR (100 MHz, CDCl3): d 170.2 (COCH3), 165.9, 165.8,
165.1, 164.9, 164.8 (5 C, 5 COPh), 117.4 (OCH2CHCH2), 102.8, 98.1 (2 C, C-1, 1’),
78.3, 72.4, 72.2, 71.9, 71.8, 70.4, 69.5, 68.2, 66.7, 63.0, 19.7, 16.5.
Anal. Calcd for C52H48O16: C, 67.23; H, 5.21. Found: C, 67.09; H, 5.40.

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584
ZHANG AND KONG
Allyl 2,3,4,6-Tetra-O-benzoyl-b-D-glucopyranosyl-(1 2)-4-O-benzoyl-a-L-
!
rhamnopyranoside (6). To a solution of 5 (1.86 g, 2 mmol) in anhyd MeOH
(50 mL) was added CH3COCl (1.5 mL) at 0°C. The solution was stoppered 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 con-
centrated to dryness. The residue was passed through a short silica gel column to give 6
1
(1.69 g, 94.9%) as a white solid; [a]D + 18.5° (c 1.0, CHCl3); H NMR (400 MHz,
CDCl3): d 8.03–7.27 (m, 25 H, 5 PhH), 5.95 (dd, 1 H, J2,3 = J3,4 =9.6 Hz, H-3’), 5.80
(m, 1 H, OCH2CHCH2), 5.70–5.63 (m, 2 H, H-2’, H-4’), 5.25–5.13 (m, 3 H, H-1’,
OCH2CHCH2), 5.04 (d, 1 H, J1,2 =0.8 Hz, H-1), 4.90 (dd, 1 H, J3,4 = J4,5 =9.8 Hz, H-4),
4.67–4.50 (m, 2 H, H-6’), 4.20 (m, 1 H, H-5), 4.10 (m, 1 H, OCH2CHCH2), 4.03 (dd, 1
H, J1,2 =0.8 Hz, J2,3 = 3.1 Hz, H-2), 4.00 (dd, 1 H, J2,3 =3.1 Hz, J3,4 =9.8 Hz, H-3),
3.92–3.84 (m, 2 H, H-5’, OCH2CHCH2), 1.21 (d, 3 H, J5,6 =6.3 Hz, H-6); 13C NMR
(100 MHz, CDCl3): d 166.5, 166.0, 165.7, 165.2, 165.1 (5 C, 5 COPh), 117.1
(OCH2CHCH2), 102.9, 98.1 (2 C, C-1, 1’), 80.3, 75.4, 72.6, 72.3, 72.1, 70.0, 69.5, 68.1,
66.0, 63.1, 17.4.
Anal. Calcd for C50H46O15: C, 67.71; H, 5.23. Found: C, 67.53; H, 5.42.
Allyl 2,3,4-Tri-O-acetyl-b-D-ribofuranosyl-(1 3)-[2,3,4,6-tetra-O-benzoyl-b-
!
D-glucopyranosyl-(1 2)]-a-L-rhamnopyranoside (8). 2,3,4-Tri-O-acetyl-a-D-ribo-
!
furanosyl trichloroacetimidate (7, 421 mg, 1.0 mmol) and allyl 2,3,4,6-tetra-O-ben-
zoyl-b-D-glucopyranosyl-(1 !2)-4-O-benzoyl-a-L-rhamnopyranoside (6, 886 mg, 1.0
mmol) were dried together under high vacuum for 2 h, then dissolved in anhyd CH2Cl2
(10 mL). TMSOTf (18 mL, 0.10 mmol) was added dropwise at ꢀ 20°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 chro-
matography (1:1 petroleum ether–EtOAc) gave 8 (910 mg, 79.5%) as a foamy solid.
1
[a]D +9.3° (c 0.5, CHCl3); H NMR (400 MHz, CDCl3): d 8.17–7.28 (m, 25 H, 5
PhH), 5.95 (dd, 1 H, J3,4 =J4,5 =9.7 Hz, H-4C), 5.83 (m, 1 H, OCH2CHCH2), 5.69 (dd,
1 H, J3,4 =J4,5 = 9.7 Hz, H-4D), 5.60 (dd, 1 H, J2,3 = 9.6 Hz, J3,4 =9.7 Hz, H-3D), 5.36 (d,
1 H, J2,3 =3.7 Hz, H-2E), 5.26 (m, 1 H, OCH2CHCH2), 5.21 (d, 1 H, J1,2 = 7.7 Hz,
H-1D), 5.16–5.08 (m, 3 H, H-1C, H-2D, OCH2CHCH2), 4.96–4.92 (m, 2 H, H-1E,
H-3E), 4.66–4.67 (m, 2 H, H-6D), 4.30–3.70 (m, 8 H), 2.09 (s, 3 H, COCH3), 2.04 (s, 3
H, COCH3), 1.40 (s, 3 H, COCH3), 1.08 (d, 3 H, J5,6 =6.3 Hz, H-6C); 13C NMR (100
MHz, CDCl3): d 170.4, 169.8, 169.6 (3 C, 3 COCH3), 166.0, 165.8, 165.3, 165.3,
165.1, 165.0 (5 C, 5 COPh), 116.9 (OCH2CHCH2), 102.0, 98.4, 97.6 (3 C, C-1C, 1D,
1E), 78.3, 73.9, 72.6, 72.1, 72.0, 71.9, 70.0, 69.8, 68.0, 67.2, 66.8, 65.0, 63.1, 62.1,
20.9, 20.8, 20.6, 17.5.
Anal. Calcd for C61H60O22: C, 63.98; H, 5.28. Found: C, 63.95; H, 5.51.
2,3,4,6-Tetra-O-benzoyl-b-D-glucopyranosyl-(1 2)-3-O-acetyl-4-O-benzoyl-
!
a-L-rhamnopyranosyl trichloroacetimidate (10). To a solution of allyl 2,3,4,6-tetra-
O-benzoyl-b-D-glucopyranosyl-(1 !2)-3-O-acetyl-4-O-benzoyl-a-L-rhamnopyranoside
(5, 928 mg, 1 mmol) in 90% acetic acid (10 mL) containing sodium acetate (293 mg,
3 mmol) was added PdCl2 (89 mg, 0.5 mmol), and the mixture was stirred for 12 h,

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ACETOBACTER DIAZOTROPHICUS PAL 5 SYNTHESIS
585
at the end of which time TLC (2:1 petroleum ether–EtOAc) indicated that the reaction
was complete. The mixture was diluted with dichloromethane (30 mL), washed with
water and satd aq sodium bicarbonate. The organic layer was concentrated, and the
residue was passed through a short silica gel column with 2:1 petroleum ether–EtOAc
as the eluent to give crude 2,3,4,6-tetra-O-benzoyl-b-D-glucopyranosyl-(1 !2)-3-O-ace-
tyl-4-O-benzoyl-a,b-L-rhamnopyranose (9, 844 mg, 95.0%). Compound 9 was dissolved
in dichloromethane (10 mL), and CCl3CN (0.2 mL, 2 mmol) and DBU (27 mL, 0.18
mmol) were added. The reaction mixture was stirred for 2 h, at the end of which time
TLC (3:1 petroleum ether–ethyl acetate) indicated that the reaction was complete.
Concentration of the reaction mixture followed by purification on a silica gel column
with 3:1 petroleum ether–EtOAc as the eluent, furnished the disaccharide donor 10
1
(876 mg, 89.4%) as a foamy solid; [a]D ꢀ 11.6° (c 1.1, CHCl3); H NMR (400 MHz,
CDCl3): d 8.42 (s, 1 H, CNHCCl3), 8.17–7.28 (m, 25 H, 5 PhH), 6.52 (d, 1 H, J1,2 =1.6
Hz, H-1), 5.99 (dd, 1 H, J2,3 = J3,4 =9.7 Hz, H-3’), 5.70–5.59 (m, 2 H, H-4’, H-2’), 5.37
(dd, 1 H, J3,4 = J4,5 =9.8 Hz, H-4), 4.93 (d, 1 H, J1,2 = 7.7 Hz, H-1’), 4.63–4.53 (m, 2 H,
H-3, H-6’), 4.32 (dd, 1 H, J1,2 =1.6 Hz, J2,3 =3.1 Hz, H-2), 4.24–4.12 (m, 2 H,
H-5, H-6’), 1.30 (d, 3 H, J5,6 = 6.4 Hz, H-6), 1.22 (s, 3 H, COCH3).
Anal. Calcd for C51H44Cl3NO16: C, 59.28; H, 4.29. Found: C, 59.50; H, 4.44.
Allyl 2,3,4,6-Tetra-O-benzoyl-b-D-glucopyranosyl-(1 2)-3-O-acetyl-4-O-ben-
!
zoyl-a-L-rhamnopyranosyl-(1 3)-2,4-di-O-benzoyl-a-L-rhamnopyranoside (12).
!
2,3,4,6-Tetra-O-benzoyl-b-D-glucopyranosyl-(1 !2)-3-O-acetyl-4-O-benzoyl-a-L-rham-
nopyranosyl trichloroacetimidate (10, 1.03 g, 1 mmol) and allyl a-L-rhamnopyranoside
(1, 204 mg, 1 mmol) were dried together under high vacuum for 2 h, then dissolved in
anhyd CH2Cl2 (40 mL). TMSOTf (18 mL, 0.1 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 under reduced pressure to
afford the crude allyl 2,3,4,6-tetra-O-benzoyl-b-D-glucopyranosyl-(1 !2)-3-O-acetyl-4-
O-benzoyl-a-L-rhamnopyranosyl-(1 !3)-a-L-rhamnopyranoside (11). To the solution of
crude 11 in pyridine (20 mL) was added benzoyl chloride (3.5 mL, 30 mmol) 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 dichloromethane, washed with 1 N hydrochloric acid, water, and satd
aq sodium bicarbonate. The organic layer was combined, dried, and concentrated.
Purification of the crude product by column chromatography (3:1 petroleum ether–
EtOAc) gave 12 (810 mg, 68.1% for 2 steps) as a syrup: [a]D +42.6° (c 1.0, CHCl3);
1H NMR (400 MHz, CDCl3): d 8.15–7.27 (m, 35 H, 7 PhH), 5.95 (m, 1 H,
OCH2CHCH2), 5.71 (dd, 1 H, J2,3 =J3,4 =9.6 Hz, H-3@), 5.56–5.46 (m, 2 H, H-4@,
H-2@), 5.44 (dd, 1 H, J1,2 =1.5 Hz, J2,3 = 3.1 Hz, H-2), 5.42–5.25 (m, 3 H, H-4,
OCH2CHCH2), 5.13 (dd, 1 H, J2,3 = 3.2 Hz, J3,4 = 9.6 Hz, H-3’), 5.11 (d, 1 H, J1,2 =1.5
Hz, H-1/H-1’), 5.06 (d, 1 H, J1,2 =1.0 Hz, H-1/H-1’), 5.05 (dd, 1 H, J3,4 = J4,5 =9.6 Hz,
H-4’), 4.48 (d, 1 H, J1,2 =7.7 Hz, H-1@), 4.45 (dd, 1 H, J2,3 =3.0 Hz, J3,4 =9.8 Hz, H-3),
4.37–4.08 (m, 5 H, H-5/H-5’, H-6@, OCH2CHCH2), 3.76 (m, 1 H, H-5/H-5’), 3.75 (dd, 1
H, J1,2 =1.3 Hz, J2,3 =3.2 Hz, H-2’), 3.54 (m, 1 H, H-5@), 1.29 (d, 3 H, J5,6 =6.2 Hz, H-6/
H-6’), 1.16 (s, 3 H, COCH3), 1.01 (d, 3 H, J5,6 =6.2 Hz, H-6/H-6’); 13C NMR (100

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586
ZHANG AND KONG
MHz, CDCl3): d 168.9 (COCH3), 165.7, 165.6, 165.4, 165.0 164.6, 164.4, 164.3 (7 C, 7
COPh), 117.5 (OCH2CHCH2), 101.6, 100.5, 96.2 (3 C, C-1, 1’, 1@), 77.2, 76.0, 73.0,
72.3, 72.1, 71.6, 71.4, 71.1, 69.7, 69.0, 68.3, 68.2, 67.0, 66.1, 19.2, 17.2, 16.7.
Anal. Calcd for C72H66O22: C, 67.38; H, 5.18. Found: C, 67.46; H, 5.03.
2,3,4,6-Tetra-O-benzoyl-b-D-glucopyranosyl-(1 2)-3-O-acetyl-4-O-benzoyl-
!
a-L-rhamnopyranosyl-(1 3)-2,4-di-O-benzoyl-a-L-rhamnopyranosyl trichloroace-
!
timidate (14). To a solution 12 (1.2 g, 1 mmol) in 90% acetic acid (10 mL) con-
taining sodium acetate (293 mg, 3 mmol) was added PdCl2 (89 mg, 0.5 mmol), and the
mixture was stirred for 12 h, at the end of which time TLC (2:1 petroleum ether–
EtOAc) indicated that the reaction was complete. The mixture was diluted with di-
chloromethane (30 mL), washed with water and satd aq sodium bicarbonate. The
organic layer was concentrated, and the residue was passed through a short silica gel
column with 2:1 petroleum ether–EtOAc as the eluent to give crude 2,3,4,6-tetra-O-
benzoyl-b-D-glucopyranosyl-(1 !2)-3-O-acetyl-4-O-benzoyl-a-L-rhamnopyranosyl-
(1 !3)-2,4-di-O-benzoyl-a,b-L-rhamnopyranose (13, 1.05 g, 91.3%). Compound 13 was
dissolved in dichloromethane (10 mL), and CCl3CN (0.2 mL, 2 mmol) and DBU (27
mL, 0.18 mmol) were added. The reaction mixture was stirred for 2 h, at the end of
which time TLC (3:1 petroleum ether–ethyl acetate) indicated that the reaction was
complete. Concentration of the reaction mixture followed by purification on a silica gel
column with 3:1 petroleum ether–EtOAc as the eluent, furnished the trisaccharide
1
donor 14 (1.01 g, 86.0%) as a foamy solid: [a]D + 37.8° (c 1.1, CHCl3); H NMR (400
MHz, CDCl3): d 8.80 (s, 1 H, CNHCCl3), 8.19–7.27 (m, 35 H, 7 PhH), 6.47 (d, 1 H,
J
J
1,2 =1.9 Hz, H-1), 5.75 (dd, 1 H, J2,3 =J3,4 = 9.7 Hz, H-3@), 5.66 (dd, 1 H, J1,2 = 1.9 Hz,
2,3 =3.3 Hz, H-2), 5.61 (dd, 1 H, J3,4 = J4,5 =9.7 Hz, H-4@), 5.51 (dd, 1 H, J3,4 = J4,5
=
9.8 Hz, H-4), 5.40 (dd, 1 H, J1,2 = 7.7 Hz, J2,3 =9.7 Hz, H-2@), 5.20 (d, 1 H, J1,2 =1.6
Hz, H-1’), 5.18 (dd, 1 H, J2,3 = 3.2 Hz, J3,4 =9.6 Hz, H-3’), 5.08 (dd, 1 H, J3,4 =J4,5 =9.6
Hz, H-4’), 4.60 (d, 1 H, J1,2 = 7.7 Hz, H-1@), 4.54 (dd, 1 H, J2,3 =3.3 Hz, J3,4 = 9.8 Hz,
H-3), 4.30–4.24 (m, 2 H, H-5@, H-6@), 4.04–3.91 (m, 2 H, H-5/H-5’, H-6@), 3.86 (dd, 1
H, J1,2 = 1.6 Hz, J2,3 =3.2 Hz, H-2’), 3.61 (m, 1 H, H-5/H-5’), 1.43 (d, 3 H, J5,6 = 6.3 Hz,
H-6/H-6’), 1.25 (s, 3 H, COCH3), 1.02 (d, 3 H, J5,6 = 6.4 Hz, H-6/H-6’).
Anal. Calcd for C71H62Cl3NO22: C, 61.45; H, 4.50. Found: C, 61.26; H, 4.41.
Allyl 2,3,4,6-Tetra-O-benzoyl-b-D-glucopyranosyl-(1 2)-3-O-acetyl-4-O-ben-
!
zoyl-a-L-rhamnopyranosyl-(1 3)-2,4-di-O-benzoyl-a-L-rhamnopyranosyl-(1 2)-
!
!
3,4-di-O-benzoyl-a-L-rhamnopyranoside (16). Compound 14 (693 mg, 0.5 mmol)
and allyl 3,4-di-O-benzoyl-a-L-rhamnopyranoside (15, 206 mg, 0.5 mmol) were dried
together under high vacuum for 2 h, then dissolved in anhyd CH2Cl2 (40 mL). TMSOTf
(18 mL, 0.1 mmoL) was added dropwise at ꢀ 5°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 triethylamine, and con-
centrated. Purification of the residue by column chromatography (2:1 petroleum ether–
EtOAc) gave 16 (684 mg, 83.6%) as a syrup: [a]D +71.2° (c 0.5, CHCl3); 1H NMR (400
MHz, CDCl3): d 8.10–7.25 (m, 45 H, 9 PhH), 5.90 (m, 1 H, OCH2CHCH2), 5.77 (dd, 1
H, J2,3 = 3.0 Hz, J3,4 =9.8 Hz, H-3A), 5.73 (dd, 1 H, J2,3 =J3,4 = 9.7 Hz, H-3D), 5.67 (dd, 1
H, J1,2 = 1.5 Hz, J2,3 =3.1 Hz, H-2B), 5.60 (dd, 1 H, J3,4 = J4,5 =9.8 Hz, H-4A), 5.50–5.28
(m, 5 H, H-2D, H-4B, H-4D, OCH2CHCH2), 5.25 (d, 1 H, J1,2 = 1.6 Hz, H-1C), 5.23 (dd, 1

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ACETOBACTER DIAZOTROPHICUS PAL 5 SYNTHESIS
587
H, J2,3 = 3.1 Hz, J3,4 = 9.7 Hz, H-3C), 5.14 (d, 1 H, J1,2 =1.5 Hz, H-1B), 5.11 (dd, 1 H,
3,4 = J4,5 =9.7 Hz, H-4C), 5.03 (d, 1 H, J1,2 = 1.3 Hz, H-1A), 4.64 (d, 1 H, J1,2 =7.7 Hz,
H-1D), 4.61 (dd, 1 H, J2,3 =3.1 Hz, J3,4 =9.8 Hz, H-3B), 4.31 (dd, 1 H, J1,2 =1.3 Hz,
2,3 = 3.0 Hz, H-2A), 4.30–4.07 (m, 6 H), 3.92 (m, 1 H, H-5C), 3.90 (dd, 1 H, J1,2 =1.6
J
J
Hz, J2,3 = 3.1 Hz, H-2C), 3.60 (m, 1 H, H-5A), 1.32 (d, 3 H, J5,6 = 6.2 Hz), 1.28 (s, 3 H,
COCH3), 1.26 (d, 3 H, J5,6 =6.4 Hz), 1.07 (d, 3 H, J5,6 = 6.2 Hz); 13C NMR (100 MHz,
CDCl3): d 168.8 (COCH3), 165.5, 165.4, 165.3, 165.1, 165.0, 164.9, 164.6, 164.5,
164.3 (9 C, 9 COPh), 117.3 (OCH2CHCH2), 101.3, 99.8, 99.1, 97.3 (4 C, C-1A, 1B, 1C,
1D), 73.8, 73.1, 72.2, 71.7, 71.6, 71.6, 71.5, 71.5, 71.4, 70.7, 69.8, 69.3, 67.9, 67.8,
67.3, 67.0, 66.6, 62.4 (18 C, C-2A, 2B,2C, 2D, 3A, 3B, 3C, 3D, 4A, 4B, 4C, 4D, 5A, 5B, 5C,
5D, 6D, OCH2CHCH2), 19.4, 17.2, 17.2, 16.8 (4 C, C-6A, 6B, 6C, COCH3).
Anal. Calcd for C92H84O28: C, 67.47; H, 5.17. Found: C, 67.54; H, 5.33.
Allyl 2,3,4,6-Tetra-O-benzoyl-b-D-glucopyranosyl-(1 2)-4-O-benzoyl-a-L-
!
rhamnopyranosyl-(1 3)-2,4-di-O-benzoyl-a-L-rhamnopyranosyl-(1 2)-3,4-di-O-
!
!
benzoyl-a-L-rhamnopyranoside (17). To a solution of 16 (654 mg, 0.4 mmol) in
anhyd MeOH (50 mL) was added acetyl chloride (1.5 mL) at 0°C. The solution was
stoppered 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 17 (603 mg, 94.6%) as a white solid: [a]D +75.5° (c 1.0, CHCl3);
1H NMR (400 MHz, CDCl3): d 8.11–7.32 (m, 45 H, 9 PhH), 5.91 (m, 1 H,
OCH2CHCH2), 5.79 (dd, 1 H, J2,3 =3.0 Hz, J3,4 = 9.8 Hz, H-3A), 5.68 (dd, 1 H, J1,2 =0.8
Hz, J2,3 =3.1 Hz, H-2B), 5.67 (dd, 1 H, J2,3 =J3,4 =9.6 Hz, H-3D), 5.62 (dd, 1 H, J3,4
4,5 = 9.8 Hz, H-4A), 5.53 (dd, 1 H, J3,4 = J4,5 =9.6 Hz, H-4D), 5.48 (dd, 1 H, J3,4 =J4,5
=
=
J
9.7 Hz, H-4B), 5.45 (dd, 1 H, J1,2 =7.7 Hz, J2,3 = 9.6 Hz, H-2D), 5.40–5.26 (m, 2 H,
OCH2CHCH2), 5.22 (d, 1 H, J1,2 = 0.8 Hz, H-1B), 5.13 (d, 1 H, J1,2 =1.6 Hz, H-1C),
5.03 (d, 1 H, J1,2 =1.6 Hz, H-1A), 4.80 (dd, 1 H, J3,4 = J4,5 =9.9 Hz, H-4C), 4.66 (d, 1 H,
J
1,2 = 7.7 Hz, H-1D), 4.58 (dd, 1 H, J2,3 =3.1 Hz, J3,4 =9.7 Hz, H-3B), 4.32–4.11 (m, 7
H), 3.92 (m, 1 H), 3.78–3.74 (m, 2 H), 3.45 (m, 1 H), 1.33 (d, 3 H, J5,6 =6.4 Hz), 1.27
(d, 3 H, J5,6 =6.4 Hz), 1.10 (d, 3 H, J5,6 = 6.3 Hz); 13C NMR (100 MHz, CDCl3): d
165.9, 165.5, 165.4, 165.3, 165.3, 165.1, 165.0, 164.9, 164.8, 164.5 (9 C, 9 COPh),
117.5 (OCH2CHCH2), 102.0, 99.5, 99.1, 97.3 (4 C, C-1A, 1B, 1C, 1D), 79.3, 73.8, 73.1,
72.1, 71.7, 71.6, 71.6, 71.5, 71.5, 71.4, 70.7, 69.8, 69.2, 68.9, 67.8, 66.9, 66.6, 62.3 (18
C, C-2A, 2B,2C, 2D, 3A, 3B, 3C, 3D, 4A, 4B, 4C, 4D, 5A, 5B, 5C, 5D, 6D, OCH2CHCH2),
17.2, 17.1, 16.8 (3 C, C-6A, 6B, 6C).
Anal. Calcd for C90H82O27: C, 67.74; H, 5.18. Found: C, 67.63; H, 5.26.
Allyl 2,3,4-Tri-O-benzoyl-b-D-ribofuranosyl-(1 3)-[2,3,4,6-tetra-O-benzoyl-
!
b-D-glucopyranosyl-(1 2)-]4-O-benzoyl-a-L-rhamnopyranosyl-(1 3)-2,4-di-O-
!
!
benzoyl-a-L-rhamnopyranosyl-(1 2)-3,4-di-O-benzoyl-a-L-rhamnopyranoside
!
(19). 2,3,4-Tri-O-benzoyl-a-D-ribofuranosyl trichloroacetimidate (18, 243 mg, 0.4
mmol) and 17 (590 mg, 0.37 mmol) were dried together under high vacuum for 2 h,
then dissolved in anhyd CH2Cl2 (40 mL). TMSOTf (18 mL, 0.10 mmol) was added
dropwise at ꢀ 10°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

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588
ZHANG AND KONG
of the residue by column chromatography (1:1 petroleum ether–EtOAc) gave 19 (536
1
mg, 71.1%) as a foamy solid: [a]D + 37.1° (c 1.0, CHCl3); H NMR (400 MHz, CDCl3):
d 8.10–7.19 (m, 60 H, 12 PhH), 6.00 (dd, 1 H, J2,3 = J3,4 =9.5 Hz, H-3D), 5.94 (m, 1 H,
OCH2CHCH2), 5.78 (dd, 1 H, J2,3 = 3.2 Hz, J3,4 =9.8 Hz, H-3A), 5.67 (dd, 1 H, J1,2 =1.7
Hz, J2,3 = 3.3 Hz, H-2B), 5.61–5.52 (m, 3 H, H-4A, H-4B, H-4D), 5.47–5.43 (m, 2 H,
H-2D, H-4E), 5.37 (m, 1 H, OCH2CHCH2), 5.35 (d, 1 H, J1,2 =7.7 Hz, H-1D), 5.26 (m,
1 H, OCH2CHCH2), 5.22–5.21(m, 2 H, H-1C, H-1E), 5.15 (dd, 1 H, J3,4 =J4,5 =9.8
Hz, H-4C), 5.12 (d, 1 H, J1,2 = 1.5 Hz, H-1B), 5.00 (d, 1 H, J1,2 =1.5 Hz, H-1A), 4.95 (dd,
1 H, J2,3 = J3,4 =4.0 Hz, H-3E), 4.84 (d, 1 H, J2,3 =4.0 Hz, H-2E), 4.61 (dd, 1 H, J2,3 =3.4
Hz, J3,4 =9.9 Hz, H-3B), 4.32–4.06 (m, 10 H), 3.82 (m, 1 H), 3.54–3.39 (m, 2 H), 1.33
(d, 3 H, J5,6 =6.3 Hz), 1.29 (d, 3 H, J5,6 =6.4 Hz), 0.75 (d, 3 H, J5,6 = 6.3 Hz); 13C NMR
(100 MHz, CDCl3): d 165.6, 165.4, 165.3, 165.1, 165.0, 164.9, 164.9, 164.9, 164.8,
164.5, 164.3, 163.9 (12 C, 12 COPh), 117.5 (OCH2CHCH2), 100.0 (1 C, C-1A/B/C
J
,
C1-H1 =173 Hz), 99.5 (1 C, C-1E, JC1-H1 =162 Hz), 99.1 (2 C, C-1A/B/C, JC1-H1 = 171
Hz), 97.2 (1 C, C-1D, JC1-H1 = 164 Hz), 17.2, 17.2, 16.5 (3 C, C-6A, 6B, 6C).
Anal. Calcd for C116H102O34: C, 68.29; H, 5.09. Found: C, 68.41; H, 5.03.
Allyl b-D-Ribofuranosyl-(1 3)-[b-D-glucopyranosyl-(1 2)]-a-L-rhamnopy-
!
!
ranosyl-(1 3)-a-L-rhamnopyranosyl-(1 2)-a-L-rhamnopyranoside (20). Penta-
!
!
saccharide 19 (500 mg, 0.25 mmol) was dissolved in a saturated solution of ammonia
in MeOH (10 mL). After 4 days at rt, the reaction mixture was concentrated and the
residue was purified by chromatography on Sephadex LH-20 (MeOH) to afford 20 as a
1
foamy solid (151 mg, 77.8%); [a]D ꢀ 46.1° (c 1.0, D2O); H NMR (400 MHz, D2O): d
5.95 (m, 1 H, OCH2CHCH2), 5.43 (s, 1 H, H-1), 5.41–5.30 (m, 2 H, OCH2CHCH2),
5.05 (d, 1 H, J1,2 5.1 Hz, H-1), 4.94 (s, 2 H, H-1), 4.62 (d, 1 H, J1,2 10.3 Hz, H-1); 13C
NMR (100 MHz, D2O): d 105.8, 104.8, 104.4, 102.9, 101.9 (5C, C-1); MS (m/z) Calcd
for C32H54O22: 790.31 [M] + . Found: 813.52[M+Na] + .
ACKNOWLEDGMENTS
This work was supported by The Chinese Academy of Sciences (KZCX3-J-08)
and by The National Natural Science Foundation of China (Projects 30070185 and
39970864).
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Received June 17, 2002
Accepted August 29, 2002