Synthesis of the α-D-GlcpA-(1 → 3)-α-L-Rhap-(1 → 2)-L-Rha trisaccharide isolated from the cell wall hydrolyzate of the green alga, Chlorella vulgaris

Article abstract of DOI:10.1016/S0008-6215(01)00196-3

The title trisaccharide was synthesized from 6-O-acetyl-2,3,4-tri-O-benzyl-α-D-glucopyranosyl chloride (10), ethyl 2,4-di-O-benzyl-1-thio- (5) and benzyl 3,4-di-O-benzyl-α-L-rhamnopyranoside (9). The disaccharide 11 obtained from compounds 5 and 10 was used as the glycosyl donor to glycosylate the rhamnopyranoside derivative 9 having free OH-2 using the NIS-AgOTf-mediated glycosylation methodology. Zemplen deacetylation of the trisaccharide 12 resulted in the 6″-OH derivative (13), which was selectively oxidized with CrO₃ to the uronic acid derivative 14. The benzyl groups were removed by catalytic hydrogenolysis to furnish the target trisaccharide (1).

Full text of DOI:10.1016/S0008-6215(01)00196-3

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Carbohydrate Research 334 (2001) 253–259
Synthesis of the
a-D
-GlcpA-(1“3)-a-
L-Rhap-(1“2)- -Rha trisaccharide
L
isolated from the cell wall hydrolyzate of the green alga,
Chlorella 6ulgaris
Ferenc Sajtos,a Ja´nos Hajko´,b Katalin E. Ko¨ve´r,c Andra´s Lipta´ka,b,*
aResearch Group for Carbohydrates of the Hungarian Academy of Sciences, PO Box 55,
H-4010 Debrecen, Hungary
bDepartment of Biochemistry, Uni6ersity of Debrecen, PO Box 55, H-4010 Debrecen, Hungary
cDepartment of Inorganic and Analytical Chemistry, Uni6ersity of Debrecen, PO Box 21,
H-4010 Debrecen, Hungary
Received 2 October 2000; received in revised form 18 June 2001; accepted 10 July 2001
Dedicated to Professor Peter Ko¨ll on the occasion of his 60th birthday
Abstract
The title trisaccharide was synthesized from 6-O-acetyl-2,3,4-tri-O-benzyl-a-
D
-glucopyranosyl chloride (10), ethyl
2,4-di-O-benzyl-1-thio- (5) and benzyl 3,4-di-O-benzyl-a- -rhamnopyranoside (9). The disaccharide 11 obtained from
L
compounds 5 and 10 was used as the glycosyl donor to glycosylate the rhamnopyranoside derivative 9 having free
OH-2 using the NIS–AgOTf-mediated glycosylation methodology. Zemple´n deacetylation of the trisaccharide 12
resulted in the 6%%-OH derivative (13), which was selectively oxidized with CrO3 to the uronic acid derivative 14. The
benzyl groups were removed by catalytic hydrogenolysis to furnish the target trisaccharide (1). © 2001 Elsevier
Science Ltd. All rights reserved.
Keywords: Chlorella 6ulgaris; Hydrogenolysis; Oligosaccharide synthesis; a-
(1“2)- -rhamnopyranose
D
-Glucopyranuronosyl-(1“3)-a-L-rhamnopyranosyl-
L
1. Introduction
were determined by chemical and modern
spectroscopic methods, involving positive- and
negative-ion FABMS, and 1D and 2D NMR
techniques. A search among the synthesized
oligosaccharides revealed that neither the
above disaccharide, nor the trisaccharide have
been prepared as yet. Among the glycopyran-
Japanese authors reported the isolation of
a-
D
-glucopyranuronosyl-(1“3)-
a-
L
-rhamnose1
and
D
-glucopyranuronosyl-(1“3)-a-
L
-
rhamnopyranosyl-(1“2)-a-
L
-rhamnose2 from
the acid hydrolyzate of the cell wall of the
uronosyl-
three disaccharides were synthesized: b-
copyranuronosyl-(1“4)-,3 b-
-galactopyran-
uronosyl-(1“4)-,3 and b-
-glucopyranuron-
osyl-(1“3)-
-rhamnose.4 All of these three
synthetic routes applied glycopyranuronosyl
L
-rhamnoses, only the following
green alga Chlorella 6ulgaris, whose structures
D
-glu-
D
D
* Corresponding author. Tel.: +36-52-512900x2256; fax:
+36-52-512913.
E-mail address: liptaka@tigris.klte.hu (A. Lipta´k).
L
0008-6215/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0008-6215(01)00196-3

254
F. Sajtos et al. / Carbohydrate Research 334 (2001) 253–259
Ring opening of the dioxolane-type benzyli-
dene acetals of pyranosides under hy-
drogenolytic conditions with various reagents
is well-documented.9 Since the direction of the
ring cleavage is determined by the stereochem-
istry at the acetal carbon atom,10,11 hy-
drogenolysis of an exo–endo mixture of
benzylidene acetals generally results in a mix-
ture of regioisomeric benzyl ethers. Indeed,
hydrogenolysis of 4 (1.2:1 exo–endo) gave the
two regioisomeric benzyl ethers 6 and 5 in
30.6 and 53.2% yield, respectively. The out-
come of this experiment clearly indicated that
isomerization of the benzylidene ring11 due to
the Lewis acid character of the reagent
applied.
donors and no glycopyranosyl“glycopyran-
uronosyl transformation was used.
In the present paper, the preparation of a
suitably protected a-
a- -rhamnopyranoside derivative in a glycosyl
donator form is reported, which was used
to glycosylate benzyl 3,4-di-O-benzyl-a-
D
-glucopyranosyl-(1“3)-
L
L
-
rhamnopyranoside. The CH2OH group of the
produced trisaccharide was oxidized to a car-
boxylic function, and then the molecule was
deprotected to the title trisaccharide (1).
For the synthesis of 5 and 6 alternative
reaction sequences are described via the re-
gioselective benzylation of ethyl 4-O-benzyl-1-
thio-a-
-rhamnopyranoside12 using phase-
L
transfer conditions6 (“5), or via a stannyli-
dene acetal12 (“6). However, the convenient
separation of the regioisomers 5 and 6 (Rf 0.30
and 0.14 in 8:2 hexane–EtOAc) makes hy-
drogenolysis of 4 superior to the previous
methods.
2. Results and discussion
Our synthetic strategy was based on the
protection of the hydroxyl functions with ben-
zyl ethers as ‘permanent’, and acetates as
‘temporary’ protecting blocking groups. In or-
der to avoid difficulties, oxidation to uronic
acid was planned at the trisaccharide level,
and thus the target structure 12 was synthe-
sized via a stepwise approach from the
monosaccharide building blocks 5, 9 and 10.
The synthetic schemes reported for the
preparation of the rhamnopyranosides 56 and
95 include the common intermediates 2–4 to
minimize the number of the synthetic steps.
Thus, treatment of ethyl 1-thio-a- -rhamno-
L
pyranoside7 (2) with a,a-dimethoxytoluene in
the presence of p-toluenesulfonic acid (TsOH)
in N,N-dimethylformamide (DMF) gave 3
with an 1.3:1 exo:endo ratio (inseparable mix-
For the synthesis of compound 9,5 the HO-
2 group of 6 was acetylated to give the glyco-
syl donor 7. Glycosylation of benzyl alcohol
with 7 in dichloromethane at room tempera-
ture in the presence of methyl trifluoro-
methanesulfonate (MeOTf)14 and powdered 4
1
ture) as indicated by H NMR analysis. Com-
pound 3 was benzylated using benzyl bromide
and NaH in DMF, affording 4 with a BnO-4
group, that could be hydrogenolyzed with the
LiAlH4–AlCl3 reagent8 in dichloromethane–
diethyl ether to furnish an easily separable
mixture of the 2,4-di-O-benzyl (5) and 3,4-di-
O-benzyl (6) derivatives.
,
A molecular sieves afforded the expected ben-
zyl rhamnopyranoside 815 (85.7%), and subse-
quent Zemple´n deacetyla-tion (NaOMe in
MeOH) yielded compound 9.5

F. Sajtos et al. / Carbohydrate Research 334 (2001) 253–259
255
3. Experimental
For the synthesis of 11, 6-O-acetyl-2,3,4-tri-
O-benzyl-a-
-glucopyranosyl chloride16 (10)
D
was coupled with 56 in dichloromethane–tolu-
ene in the presence of silver trifluoromethane-
sulfonate (AgOTf)17 as the promoter,
furnishing the desired disaccharide with a
complete a-stereoselectivity in an isolated
yield of 59.4, and 21.8 of the starting 5 was
recovered. The configuration of the glycosidic
General.—All moisture-sensitive reactions
were performed under an Ar atmosphere us-
ing oven-dried glassware. Solvents were dried
over standard drying agents. Organic solu-
tions were concentrated under reduced pres-
sure at 40 °C (bath). Column chromatography
was performed on Kieselgel 60 (0.063–0.2
mm, Merck). TLC was carried out on
Kieselgel 60 F254 (Merck) plates. Compounds
were visualized by spraying with 50% aq
H2SO4 followed by heating. Melting points
(uncorrected) were determined on a Kofler
hot-stage apparatus. Optical rotations were
measured with a Perkin–Elmer 241 polarime-
ter at rt, using a 10-cm (1-mL) cell. NMR
spectra were recorded with a Bruker WP-200
SY (1H, 200.13 MHz; 13C, 50.31 MHz) or a
Bruker Avance DRX 500 (1H, 500.13 MHz;
13C, 125.76 MHz) spectrometer for solutions
in CDCl3 (internal Me4Si) or in D2O (internal
DSS). Proton chemical shifts (l) are given in
ppm relative to the signal for internal Me4Si
(CDCl3) or DSS (D2O). Carbon chemical
shifts were referenced to the solvent signal.
1
linkage was confirmed by the JC-1,H-1 coupling
constant (167.1 Hz).18 Attempts to obtain
higher yield of the disaccharide 11 failed, how-
ever the formation of the corresponding b-
linked disaccharide was not detected at all.
The thioglycosyl donor 11 was activated with
N-iodosuccinimide (NIS–AgOTf)19 and cou-
pled to acceptor 9 to produce the trisaccharide
1
12 exclusively. The large value of the JC-1,H-1
coupling constant (171.1 Hz) assigned for the
newly formed glycosidic bond was in full
agreement with the expected a-rhamnosidic
linkage.
Removal of the primary acetyl function
(12“13), followed by Jones oxidation (CrO3–
H2SO4)20 in acetone, led to the uronic acid 14.
Deprotection of the trisaccharide 14 upon re-
ductive cleavage of the benzyl groups
(Pd(OH)2–C/H2) in tert-butanol and water
containing acetic acid (pH 4–5) gave, after
purification on Toyopearl HW-40F, the target
trisaccharide 1 in a yield of 44.3%. The struc-
Ethyl 2,3-O-benzylidene-1-thio-h- -rhamno-
L
pyranoside (3).—To a solution of 2 (5.0 g,
24.0 mmol) in a,a-dimethoxytoluene (25 mL)
were added p-toluenesulfonic acid (456 mg,
2.40 mmol) and DMF (5 mL). The mixture
was stirred overnight at rt, then diluted with
toluene (200 mL), washed with satd NaHCO3
(2×30 mL) and water (3×30 mL), dried,
filtered, and concentrated. Column chro-
matography (3:1 hexane–EtOAc) of the
residue yielded 3 (1.3:1 exo:endo, 4.7 g,
ture (86% in an a- -rhamnopyranosidic form)
L
1
of 1 was confirmed by H and 13C NMR
spectroscopic methods. The NMR data were
in full accordance with the data published
recently.1
1
66.1%); [h]D −156.0° (c 0.71, CHCl3); H
NMR (200 MHz, CDCl3): l 7.55–7.32 (m, 5
H, Ph), 6.15 (s, 0.57 H, PhCHexo), 5.91 (s, 0.43
H, PhCHendo), 5.66 (s, 0.43 H, Hendo-1), 5.56
(s, 0.57 H, Hexo-1), 1.38–1.21 (m, 6 H, CCH3
13
and SCH2CH3); C NMR (50 MHz, CDCl3):
l 138.5 and 137.0 (2 Cquat.), 129.5-126.0 (Ph),
104.0 and 102.9 (2 PhCH), 79.6 and 79.4 (2
C-1), 78.0 and 75.6 (C-2,3), 72.5 (C-4), 66.0
and 65.7 (2 C-5), 24.5 (SCH2CH3), 17.2 (C-6),
14.6 (SCH2CH3). Anal. Calcd for C15H20O4S:
C, 60.79; H, 6.80. Found: C, 61.03; H, 6.82.
The exo-isomer 3 was crystallized from dry

256
F. Sajtos et al. / Carbohydrate Research 334 (2001) 253–259
previously reported;6 13C NMR (50 MHz,
CDCl3): l 138.5 and 137.5 (2 Cquat.), 128.5–
127.6 (2 Ph), 82.5 (C-1), 81.0 and 80.2 (C-2,4),
74.9 and 72.3 (2 PhCH2), 72.1 (C-3), 67.6
(C-5), 25.1 (SCH2CH3), 17.9 (C-6), 14.9
(SC2CH3).
Compound 6 had [h]D −140.7° (c 0.60,
CHCl3), lit. [h]D −152.4° (c 1.00, CHCl3);13
1H and 13C NMR shifts were in full accor-
dance with the data described previously.13
Ethyl 2-O-acetyl-3,4-di-O-benzyl-1-thio-h-
EtOH (10 mL); mp 114–116 °C; [h]D −142.9°
(c 0.36, CHCl3).
Ethyl 4-O-benzyl-2,3-O-benzylidene-1-thio-
h- -rhamnopyranoside (4).—To a stirred solu-
L
tion of 3 (1.2:1 exo:endo, 4.39 g, 14.81 mmol)
in dry DMF (20 mL) was added NaH (0.71 g,
29.62 mmol) at 0 °C. After 30 min, BnBr (2.60
mL, 22.22 mmol) was added, and the mixture
was stirred overnight at rt. The excess of the
reagent was decomposed by subsequent addi-
tion of MeOH and water. The mixture was
then diluted with toluene (600 mL), and
washed with water (4×100 mL). The organic
layer was dried, and concentrated. The residue
was purified by column chromatography (19:1
hexane–EtOAc) to obtain 4 (5.1 g, 89.1%).
Crystallization from abs EtOH (10 mL) re-
sulted in 3.0 g of 4 (5:1 exo:endo); mp 47–
48 °C; 1H NMR (200 MHz, CDCl3): l
7.52–7.21 (m, 10 H, 2 Ph), 6.07 (s, 0.83 H,
PhCHexo), 5.91 (s, 0.17 H, PhCHendo), 5.65 (s,
0.17 H, Hendo-1), 5.55 (s, 0.83 H, Hexo-1), 4.96
and 4.72 (2 d, 1.66 H, PhCH2exo), 4.83 and
4.53 (2 d, 0.34 H, PhCH2endo), 2.77–2.41 (m, 2
H, SCH2CH3), 1.37–1.21 (m, 6 H, CCH3 and
SCH2CH3); 13C NMR (50 MHz, CDCl3): l
138.6 and 138.0 (2 Cquat.), 129.2–126.2 (2 Ph),
103.8 and 102.9 (2 PhCH), 79.8 (C-1), 79.4,
78.0 and 76.6 (C-2,3,4), 73.0 (PhCH2), 65.0
(C-5), 24.4 (SCH2CH3), 17.8 (C-6), 14.6
(SCH2CH3). Anal. Calcd for C22H26O4S: C,
68.37; H, 6.78. Found: C, 68.59; H, 6.76.
Ethyl 2,4-di-O-benzyl- (5) and ethyl 3,4-di-
L
-rhamnopyranoside (7).—Compound 6 (980
mg, 2.52 mmol) was treated with 1:1 pyri-
dine–Ac2O (10 mL) for 5 h. The mixture was
concentrated and co-evaporated with toluene
(3×10 mL). Column chromatography (15:1
hexane–EtOAc) of the residue furnished 7
(1.02 g, 94.0%); [h]D −77.6° (c 0.84, CHCl3),
lit. (
CHCl3);21 1H NMR shifts were in full accor-
dance with the data reported previously;21 13
D
enantiomer) [h]D +61° (c 2.1,
C
NMR (50 MHz CDCl3): l 170.3 (CꢀO), 138.4
and 137.7 (2 Cquat.), 128.4–127.7 (2 Ph), 82.3
(C-1), 80.3 and 78.3 (C-3,4), 75.4 and 71.8 (2
PhCH2), 70.8 (C-2), 68.3 (C-5), 25.5
(SCH2CH3).
Benzyl
2-O-acetyl-3,4-di-O-benzyl-h- -
L
rhamnopyranoside (8).—To a solution of 7
(770 mg, 1.79 mmol) in dry CH2Cl2 (15 mL)
,
were added 4 A powdered molecular sieves (4
g) and benzyl alcohol (278 mL, 2.68 mmol),
and the mixture was stirred under Ar
overnight. After the addition of MeOTf (810
mL, 7.15 mmol) at 0 °C, the mixture was
stirred for 24 h at rt. Triethylamine (800 mL)
was added, and the mixture was filtered
through Celite, then the cake was washed with
CH2Cl2 (3×10 mL). The combined filtrates
were washed with water (3×20 mL), dried
and concentrated. The product was purified
by column chromatography (3:1 hexane–
EtOAc) to obtain pure 8 (730 mg, 85.7%); [h]D
−19.6° (c 0.55, CHCl3), lit. [h]D −25.0° (c
2.0, CHCl3);15 1H NMR shifts were in full
accordance with the data reported previ-
ously;15 13C NMR (50 MHz, CDCl3): l 170.3
(CꢀO), 138.4, 138.0 and 136.9 (3 Cquat.),
128.4–127.7 (3 Ph), 97.0 (C-1), 80.0 and 78.1
(C-3,4), 75.4, 71.8 and 69.2 (3 PhCH2), 69.0
(C-2), 67.9 (C-5), 21.1 (CH3CO), 17.9 (C-6).
O-benzyl-1-thio-h- -rhamnopyranoside (6).—
L
A mixture of LiAlH4 (857 mg, 22.59 mmol)
and AlCl3 (2.54 g, 19.06 mmol) in Et2O (20
mL) was heated to 35 °C. Then, a solution of
4 (2.73 g, 7.06 mmol) in dry 1:1 CH2Cl2 –Et2O
(70 mL) was added dropwise, and the mixture
was stirred for 15 min at reflux temperature.
The excess of LiAlH4 was decomposed with
EtOAc (10 mL), and Al(OH)3 was precipi-
tated by the addition of water (15 mL). After
dilution with EtOAc, the organic layer was
decanted, washed with water (3×25 mL),
dried, and concentrated. Column chromatog-
raphy (4:1 hexane–EtOAc) of the residue gave
5 (1.46 g, 53.2%) and 6 (0.84 g, 30.6%).
Compound 5 had [h]D −92.1° (c 0.60,
CHCl3), lit. [h]D −91.3° (c 0.64, CHCl3);6 1H
NMR shifts were in agreement with those

F. Sajtos et al. / Carbohydrate Research 334 (2001) 253–259
257
(C-6), 14.9 (SCH2CH3). Anal. Calcd for
C51H58O10S: C, 70.97; H, 6.77. Found: C,
71.23; H, 6.79.
Benzyl 3,4-di-O-benzyl-h- -rhamnopyran-
L
oside (9).—To a solution of 8 (730 mg, 1.53
mmol) in dry MeOH (20 mL) was added
NaOMe (pH 9–10). The mixture was kept at
rt overnight, and neutralized with Amberlite
IR-120 (H+) resin. Then, the resin was filtered
off, and the filtrate was concentrated and co-
evaporated with dry CH2Cl2 (2×10 mL). The
residue was purified by column chromatogra-
phy (7:3 hexane–EtOAc) to give pure 9 (630
mg, 94.8%); [h]D −52.4° (c 0.63, CHCl3), lit.
Benzyl (6-O-acetyl-2,3,4-tri-O-benzyl-h-
D
-
-
glucopyranosyl)-(1“3)-(2,4-di-O-benzyl-h-
L
rhamnopyranosyl)-(1“2)-3,4-di-O-benzyl-h-
-rhamnopyranoside (12).—A mixture of 11
(672 mg, 0.78 mmol), 9 (282 mg, 0.65 mmol)
and 4 A molecular sieves (beads) was stirred
L
,
for 30 min in dry CH2Cl2 (15 mL) under Ar.
The mixture was cooled to −20 °C and sub-
sequently a solution of NIS (219 mg, 0.97
mmol) in 3:2 dry MeCN–dry CH2Cl2 (5 mL)
and AgOTf (25 mg, 97.30 mmol) in dry tolu-
ene (1 mL) were added and the reaction mix-
ture was stirred for 10 min. The reaction was
quenched by Et3N (50 mL), diluted with
CH2Cl2 (40 mL), and filtered. The filtrate was
washed with 10% aq Na2S2O3 (2×20 mL),
satd NaHCO3 (20 mL) and water (20 mL),
dried and concentrated. The residue was
purified by column chromatography (3:1 hex-
ane–EtOAc) to give pure 12 (525 mg, 65.5%);
13
[h]D −58° (c 0.6, CHCl3);5 1H and C NMR
shifts were in agreement with those previously
published.22
Ethyl
(6-O-acetyl-2,3,4-tri-O-benzyl-h- -
D
glucopyranosyl) - (1“3) - 2,4 - di - O - benzyl - 1-
thio-h- -rhamnopyranoside (11).—To a solu-
L
tion of 1015 (1.2 g, 2.35 mmol) and 5 (540 mg,
1.39 mmol) in dry CH2Cl2 (20 mL) was added
,
4 A powdered molecular sieves (2 g), and the
mixture was stirred under Ar for 30 min. The
mixture was cooled to −40 °C, then a solu-
tion of AgOTf (890 mg, 3.48 mmol) in dry
toluene (20 mL) was added dropwise and the
mixture was stirred for 30 min at −40 °C.
After the addition of pyridine (1 mL) and
CH2Cl2 (150 mL), the mixture was filtered
through Celite. The filtrate was washed with
10% aq Na2S2O3 (2×30 mL), satd NaHCO3
(20 mL) and water (20 mL), dried, and evapo-
rated. The product was purified by column
chromatography (3:1 hexane–EtOAc) giving
pure 11 (713 mg, 59.4%), and 118 mg (21.8%)
of 5 was also collected; [h]D +5.6° (c 1.60,
CHCl3); 1H NMR (500 MHz, CDCl3): l
7.38–7.09 (m, 25 H, 5 Ph), 5.35 (d, 1 H, J1,2
1.8 Hz, H-1), 5.22 (d, 1 H, J1%,2% 3.5 Hz, H-1%),
5.05–4.60 (m, 10 H, 5 PhCH2), 4.26–4.11 (m,
4 H, H-5,5%,6%a,6%b), 4.21 (t, 1 H, J3%,4% 9.4 Hz,
H-3%), 4.13 (dd, 1 H, J3,4 9.2 Hz, H-3), 4.09
(dd, 1 H, J2,3 2.8 Hz, H-2), 3.78 (t, 1 H, J4,5
9.2 Hz, H-4), 3.70 (dd, 1 H, J2%,3% 9.4 Hz, H-2%),
3.59 (t, 1 H, J4%,5% 9.2, H-4%), 2.63 (m, 2 H,
SCH2CH3), 1.99 (s, 3 H, Ac), 1.35 (d, 3 H, J5,6
5.0 Hz, CCH3), 1.20 (t, 3 H, SCH2CH3); 13C
NMR (125 MHz, CDCl3): l 170.6 (CꢀO),
138.3–137.8 (5 Cquat.), 128.3–127.6 (5 Ph),
93.9 (JC1%,H1% 167.1 Hz, C-1%), 82.0 (C-1), 81.8
(C-3%), 79.9 (C-4), 79.3 (C-2%), 77.5 (C-4%), 76.7
(C-2), 75.9 (C-3), 68.9 and 68.5 (C-5,5%), 62.9
(C-6%), 25.3 (SCH2CH3), 20.8 (CH3CO), 17.8
1
[h]D +17.9° (c 0.43, CHCl3); H NMR (500
MHz, CDCl3): l 7.35–7.10 (m, 40 H, 8 Ph),
5.22 (d, 1 H, J1%%,2%% 3.5 Hz, H-1%%), 5.20 (d, 1 H,
J1%,2% 2.2 Hz, H-1%), 5.04–4.50 (m, 16 H, 8
PhCH2), 4.78 (d, 1 H, J1,2 2.5 Hz, H-1), 4.30–
4.15 (m, 3 H, H-5%%,6%%a,6%%b), 4.20 (t, 1 H, J2%%,3%%
9.4 Hz, H-3%%), 4.18 (dd, 1 H, J3%,4% 9.0 Hz,
H-3%), 4.15 (dd, 1 H, J2,3 2.9 Hz, H-2), 4.05 (t,
1 H, J2%,3% 2.6 Hz, H-2%), 3.97 (dd, 1 H, J3,4 9.4
Hz, H-3), 3.79 (m, 2 H, H-5,5%), 3.70 (t, 1 H,
J4%,5% 9.0 Hz, H-4%), 3.66 (dd, 1 H, J2%%,3%% 9.7 Hz,
H-2%%), 3.61 (t, 1 H, J4%%,5%% 9.4 Hz, H-4%%), 3.51 (t,
1 H, J4,5 9.4 Hz, H-4), 1.94 (s, 3 H, Ac), 1.30
(d, 3 H, J5,6 6.2 Hz, CCH3), 1.24 (d, 3 H, J5%,6%
6.5 Hz, CCH3%); 13C NMR (125 MHz, CDCl3):
l 170.5 (CꢀO), 138.5–137.3 (8 Cquat.), 128.3–
127.3 (8 Ph), 99.5 (JC-1%,H-1% 171.1 Hz, C-1%),
98.0 (C-1), 94.4 (C-1%%), 82.0 (C-3%%), 80.7 (C-4),
80.0 (C-4%), 79.8 (C-3), 79.2 (C-2%%), 77.4 (C-
4%%), 75.4 (C-3%), 75.3 (C-2%), 74.3 (C-2), 68.9
(C-5%%), 68.5 and 68.1 (C-5,5%), 62.8 (C-6%%), 20.8
(CH3CO), 17.9 (C-6,6%). Anal. Calcd for
C76H82O15: C, 73.89; H, 6.69. Found: C, 74.13;
H, 6.67.
Benzyl (2,3,4-tri-O-benzyl-h-
uronosyl) - (1“3) - (2,4 - di - O - benzyl - h -
rhamnopyranosyl)-(1“2)-3,4-di-O-benzyl-h-
-rhamnopyranoside (14).—To a solution of
D
-glucopyran-
L
-
L

258
F. Sajtos et al. / Carbohydrate Research 334 (2001) 253–259
Anal. Calcd for C18H30O15: C, 44.45; H, 6.22.
Found: C, 44.31; H, 6.23.
12 (519 mg, 0.42 mmol) in dry MeOH (10 mL)
and dry CH2Cl2 (2 mL) was added a catalytic
amount of NaOMe. The mixture was stirred
for 4 h, then neutralized with Amberlite IR-
120 (H+) resin. The resin was filtered off, and
the filtrate was concentrated to give 13 (488
mg, 97.4%), which was dissolved in acetone
(10 mL), then a solution of CrO3 (410 mg,
4.10 mmol) in aq 3 M H2SO4 (2 mL) was
added dropwise. The mixture was stirred for
30 min at rt, diluted with CH2Cl2 (100 mL),
washed with cold water (3×20 mL), dried,
and concentrated. The residue was purified by
column chromatography (7:3 hexane–ace-
tone) to yield 14 (288 mg, 58.2%); [h]D +2.3°
Acknowledgements
This work was supported by the Hungarian
Scientific Research Fund (OTKA: F 19447, D
29185 to J. Hajko´ and T 029089, T 034515 to
K.E. Ko¨ve´r). We are grateful for DRX 500
purchase grants (OMFB: MEC-93-0098,
Phare Accord: H-9112-0198, OTKA: A084).
The generous support (to J. Hajko´) from the
Bolyai Research Scholarship is also
acknowledged.
1
(c 0.92, CHCl3); H NMR (500 MHz, CDCl3):
l 7.36–7.08 (m, 40 H, 8 Ph), 5.25 (d, 1 H,
J1%%,2%% 3.1 Hz, H-1%%), 5.16 (d, 1 H, J1%,2% 2.4 Hz,
H-1%), 4.99–4.45 (m, 16 H, 8 PhCH2), 4.81 (d,
1 H, J1,2 1.7 Hz, H-1), 4.19 (dd, 1 H, J3%,4% 8.3
Hz, H-3%), 4.14 (t, 1 H, J3%%,4%% 9.4 Hz, H-3%%),
4.11 (dd, 1 H, J2,3 2.9 Hz, H-2), 4.02 (t, 1 H,
J2%,3% 2.7 Hz, H-2%), 3.94 (dd, 1 H, J3,4 9.4 Hz,
H-3), 3.77 (t, 1 H, J4%%,5%% 9.4 Hz, H-4%%), 3.79–
3.73 (m, 2 H, H-5,5%), 3.75 (d, 1 H, H-5%%), 3.66
(t, 1 H, J4%,5% 8.3 Hz, H-4%), 3.64 (dd, 1 H, J2%%,3%%
9.4 Hz, H-2%%), 3.49 (t, 1 H, J4,5 9.4 Hz, H-4),
1.28 (d, 3 H, J5,6 6.1 Hz, CCH3), 1.19 (d, 3 H,
J5%,6% 6.6 Hz, CCH3%); 13C NMR (125 MHz,
CDCl3): l 171.9 (CꢀO), 138.5–137.3 (8 Cquat.),
128.4–127.4 (8 Ph), 99.7 (C-1%), 98.1 (C-1),
95.2 (C-1%%), 81.4 (C-3%%), 80.7 (C-4), 80.6 (C-
4%), 80.0 (C-3), 79.5 (C-4%%), 78.6 (C-2%%), 76.3
(C-3%), 75.8 (C-2%), 75.6-72.4 (8 PhCH2), 74.5
(C-2), 69.8 (C-5%%), 68.4 and 68.2 (C-5,5%), 18.0
(C-6,6%). Anal. Calcd for C74H78O15: C, 73.61;
H, 6.51. Found: C, 73.88; H, 6.53.
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h-
D
-Glucopyranuronosyl-(1“3)-h-
L
-rham-
nopyranosyl-(1“2)-
L
-rhamnopyranose (1).—
To a solution of 14 (160 mg, 0.13 mmol) in
tert-butanol (25 mL) and water (5 mL) was
added AcOH dropwise until pH 5–6, and
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was filtered through Celite, and concentrated.
The crude product was purified by gel filtra-
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44.3%); mp 165–174, lit. 166–176 °C;2 [h]D
+12.1° (c 0.32, water, equil), lit. [h]D +46° (c
0.3, water).2 The 1H and 13C NMR data found
for 1 are consistent with those reported.2

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