Synthesis of partially benzylated arabinofuranosides, NMR analysis, and application to oligosaccharide synthesis

Article abstract of DOI:10.1016/j.tetasy.2010.06.033

The preparation and NMR analysis of 2,3-di-O-benzyl arabinofuranosides have been described. In DMSO-d₆, the sugar adopts a conformation in which the hydroxyl groups are in an equatorial position; the equilibrium composition is determined by steric factors. In CDCl₃, the sugar adopts a conformation in which the intramolecular hydrogen bonding plays an important role in determining the equilibrium composition. The use of 2,3-di-O-benzyl arabinose in the synthesis of oligoarabinofuranosides enabled the synthesis of α- or β-linked furanosides.

Full text of DOI:10.1016/j.tetasy.2010.06.033

Tetrahedron: Asymmetry 21 (2010) 2167–2171
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Tetrahedron: Asymmetry
journal homepage: www.elsevier.com/locate/tetasy
Synthesis of partially benzylated arabinofuranosides, NMR analysis,
and application to oligosaccharide synthesis
*
Patrice G. J. Plaza, Gurdial Singh
Department of Chemistry, University of the West Indies, St. Augustine, West Indies, Trinidad and Tobago
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 9 June 2010
Accepted 24 June 2010
The preparation and NMR analysis of 2,3-di-O-benzyl arabinofuranosides have been described. In DMSO-
d6, the sugar adopts a conformation in which the hydroxyl groups are in an equatorial position; the equi-
librium composition is determined by steric factors. In CDCl3, the sugar adopts a conformation in which
the intramolecular hydrogen bonding plays an important role in determining the equilibrium composi-
tion. The use of 2,3-di-O-benzyl arabinose in the synthesis of oligoarabinofuranosides enabled the syn-
thesis of a- or b-linked furanosides.
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
the glycosyl intermediate species that is formed. This could also
be affected by the factors listed above.
Carbohydrate synthesis remains a contemporary topic of re-
search since a universal strategy for glycosylation remains elusive.1
The number of available strategies for the formation of glycosidic
linkages is constantly increasing, as improvements in the stereo-
specificity, efficiency, and general applicability of chemical glyco-
sylation are sought.2 Glycosylation strategies traditionally begin
with the protection of the anomeric center.
In contrast our research involved the synthesis of 1-O-unpro-
tected sugars for use as glycosyl acceptors in the preparation of
1,5-linked oligofuranosides having free anomeric centers. Another
anticipated advantage of such an approach is the ability to utilize
the leaving groups that are not necessarily stable under glycosyla-
tion conditions.
We hypothesized that the partially protected 2,3-pentoses
should furnish increased amounts of the furano form, which could
be reacted preferentially to provide access to oligofuranosides with
a free anomeric center. On the basis of this premise, we embarked
on an investigation that involved the synthesis of 1-O-unprotected
sugars for use as glycosyl acceptors in the preparation of 1,5-linked
oligofuranosides with free anomeric centers. While this approach
could potentially lead to the formation of several glycosylation
products, if successful, it would dramatically simplify the synthesis
of oligofuranosides and possibly have a general application in
glycosylation. Of particular interest to us is the preparation of oli-
goarabinofuranosides;3 highly antigenic structures found in myco-
bacteria including Mycobacterium tuberculosis,4 the causative agent
of the disease Tuberculosis, which results in millions of deaths
annually.
2. Results and discussion
2,3-Di-O-benzylated
D-arabinose was synthesized from the
commercially available
D-arabinose (Scheme 1). The methyl furan-
oside was selectively protected at the primary hydroxyl group
using trityl chloride followed by benzylation to give the fully
protected sugars. Removal of the trityl group and the anomeric
methyl group was accomplished in one step to yield the desired
compounds.
The pure 2,3-di-O-benzyl derivatives obtained after column
chromatography were analyzed using one dimensional and two-
dimensional NMR in two solvents; CDCl3 and DMSO-d6. The equi-
librium proportions of the various anomers in solution were deter-
mined by the integration of the anomeric proton NMR signals
(Table 1). Neither the acyclic aldehyde nor the hydrates could be
detected by natural abundance NMR.
A free anomeric center means that the sugar is able to muta-ro-
tate so that the factors governing the equilibrium composition
need to be thoroughly investigated. These include the reaction
temperature, the nature of the solvent employed, and the substit-
uents on the sugar.5 The success of the proposed strategy depends
on the selectivity of the attack of the primary hydroxyl group on
The 1H NMR spectrum of 2,3-di-O-benzyl arabinose in deuter-
ated chloroform showed the presence of four major anomers; the
a- and b-pyranoses and the a- and b-furanoses. Neither the acyclic
aldehyde nor the hydrate could be detected by natural abundance
NMR. The anomeric protons of the furanoses resonated at lower
fields than those of the pyranoses, with chemical shifts of 5.37
and 5.26 ppm for the
The anomeric signal for the b-furanose appeared as a doublet with
a- and b-anomers, respectively (Table 1).
* Corresponding author. Tel.: +1 868 662 2002/3538; fax: +1 868 645 3771.
E-mail address: gurdial.singh@sta.uwi.edu (G. Singh).
0957-4166/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2010.06.033

2168
P. G. J. Plaza, G. Singh / Tetrahedron: Asymmetry 21 (2010) 2167–2171
O
OH
OH
HO
TrO
MeOH, cat. H+
rt, 20h
NaH, BnBr, DMF
O
O
TrCl, py
OMe
OH
OMe
OH
0oC to rt, 4h
79-89%
rt, 18h
HO
82-87%,
HO
OH
HO
3
2
1 D-arabinose
OBn
HO
TrO
O
O
O
OH
OBn
HO
OMe
OBn
MeCN:H2O:TFA (4:3:1)
OH
OBn
BnO
95oC, 12h
72-83%
BnO
4
5
Scheme 1. Preparation of 2,3-di-O-benzyl arabinose.
Table 1
a
Chemical shift data for 2,3-di-O-benzyl-D-arabinose in CDCl3
5
a-Furanose
H-1, C-1
H-2, C-2
H-3, C-3
5.37
3.98
4.30
3.90
100.7
86.6
82.7
82.3
H-4, C-4
H-5a, 5b, C-5b
3.62, 3.70
62.5
b-Furanose
H-1, C-1
H-2, C-2
H-3, C-3
5.26
4.01
4.20
4.00
95.0
83.6
80.7
81.7
62.4
H-4, C-4
H-5a, 5b, C-5b
3.58, 3.69
a-Pyranose
H-1, C-1
H-2, C-2
H-3, C-3
4.60
3.60
3.55
3.91
96.6
79.4
78.8
65.8
64.2
H-4, C-4
H-5a, 5b, C-5b
3.41, 3.87
Figure 1. TOCSY spectrum of 2,3-di-O-benzyl-D-arabinose.
b-Pyranose
H-1, C-1
H-2, C-2
H-3, C-3
5.19
3.85
3.79
3.97
91.6
76.4
75.7
66.8
61.7
H-4, C-4
H-5a, 5b, C-5b
3.65, 3.87
a
All values are given as chemical shifts in ppm.
H-5a and H-5b unassigned.
b
3.50
4.00
4.50
5.00
5.50
6.00
6.50
7.00
a splitting of 4.1 Hz, while that of the
singlet.
a-furanose appeared as a
First order coupling between H-1 and H-2 in the b-furanose as
well as the
a- and b-pyranoses produced crosspeaks in the
1H–1H COSY spectrum and led to the identification of H-2 of these
anomers. The H-5a and H-5b protons of one of the furanose ano-
mers showed a strong coupling to each other and to H-4, which
in turn is coupled to H-3.
Inspection of the TOCSY spectrum (Fig. 1) reveals that this
strongly coupled system belongs to the
a-furanose isomer. The
H-2 resonance of this anomer is also visible having a small cros-
speak with the anomeric proton and is also involved in the spin
system associated with the remaining protons. The b-furanose
was also analyzed as H-1, H-2, H-3 and as being in the same spin
system, while H-2 and H-3 are also strongly associated with H-4,
H-5a, and H-5b (see Fig. 2).
7.50
ppm
7.50
7.00
6.50
6.00
5.50
5.00
4.50
4.00
3.50
ppm (t2)
Figure 2. COSY spectrum of 2,3-di-O-benzyl-D-arabinose in DMSO-d6.
Identification of the pyranose forms of the dibenzylated sugars
proved to be more difficult because of overlapping resonances evi-
dent even in the HMQC spectrum. The TOCSY spectrum revealed
the presence of small crosspeaks between H-1 and H-3 of both
mer. The remaining signals were assigned to either anomer on the
basis of the chemical shifts of the remaining protons; those at low-
er fields were assigned to the b-anomer.
The ratios of the four anomers were obtained by the integration
of the signals in the NMR spectrum (Table 2). The data suggested
the
tween H-1 and H-5a for the
overlapped with that of the H-5a resonance of the b-pyranose iso-
a
- and b-pyranoses. A small crosspeak was also observed be-
a-pyranose isomer; however the signal

P. G. J. Plaza, G. Singh / Tetrahedron: Asymmetry 21 (2010) 2167–2171
2169
Table 2
Next we investigated the effect of temperature on these com-
pounds by conducting variable temperature 1H NMR. In our exper-
iments with 2,3-di-O-benzyl arabinose in DMSO-d6, the proportion
of furanoses increased when the mixture was heated (Fig. 3). At
higher temperatures, the signals due to the hydroxyl protons be-
came less and lesser visible in the spectra because of the disruption
in hydrogen bonding, which allows free rotation of the sugar and
population of the furanose configuration.
% Pyranose and furanose forms of 2,3-di-O-benzyl-D-arabinose in CDCl3 and DMSO-d6
CDCl3
DMSO-d6
a
-Furanose
b-Furanose
-Pyranose
b-Pyranose
26
21
26
27
49.5
10.5
24.2
15.8
a
A at equilibrium room temperature; B at 60 °C; C at 90 °C; and D
at room temperature after heating to 120 °C.
that the free energies of the pyranoses are comparable to those of
the furanoses.
From our results, the benzyl substitution at the 2- and 3-posi-
tions resulted in an increase in the proportion of the furanose at
In DMSO-d6, the proportion of the various anomers presented
equilibrium. The a-furanose appeared to be the most favored con-
equilibrium changes. The a-furanose was the most abundant rep-
formation, hence we proceeded to investigate the preparation of
linear oligoarabinofuranosides using the partially benzylated arab-
inose acceptor. We decided to conduct our chemistry using dichlo-
romethane as the reaction medium primarily as it would be easier
to isolate the products formed; furthermore it would test the pre-
mise that the equilibrium mixture could be driven to allow the
resenting 49.5% of the mixture, while the b-furanose which ac-
counted for 10.5% was the least abundant (Table 2). It should be
noted that integrating the signals of the hydroxyl protons yields
different ratios than those obtained by integrating the signals of
the anomeric protons themselves. The overall effect was an in-
crease in the percentage of pyranose in the solution, particularly
the a
-pyranose. A comparison of the peak heights in 13C NMR data
furanose component to react exclusively. 2,3-Di-O-benzyl-D-arabi-
nose was reacted with the corresponding propane-1,3-diyl phos-
led to the identification of the carbons of the furanose anomers.
The HMQC, COSY, and TOCSY spectra were once again used to as-
sign the data (Table 3).
phate donor in the presence of catalytic TMSOTf (Scheme 2).6
This mainly gave the b-linked disaccharide 7 (b:a; 4:1) in 51% yield
as an inseparable mixture. In order to further characterize and
establish the structure of the disaccharide 7, we subjected the ano-
meric mixture to an acetylation reaction that resulted in the for-
Table 3
mation of the corresponding acetates 8, with the
a-stereoisomer
a
Chemical shift data for 2,3-di-O-benzyl arabinose 5 in DMSO-d6
being the major product. For 7, the anomeric protons at the b-link-
age resonated at 4.74 and 4.98 ppm with coupling constants of 3.7
and 3.1 Hz, respectively. The anomeric protons at the terminal res-
OH-1
a
6.45
(J = 4.35 Hz)
-Furanose
b-Furanose
6.40
(J = 6.26 Hz)
a
6.80
(J = 6.72 Hz)
-Pyranose
b-Pyranose
6.27
(J = 4.32 Hz)
idue resonated further downfield at 5.35 and 5.32 ppm for the
a-
H-1, C-1
H-2, C-2
H-3, C-3
H-4, C-4
H-5, H-
50, C-
5.24
3.84
3.76
4.05
3.49–
3.60
100.1 5.27
94.6 4.40
97.4
5.13
91.1
and b-anomers, respectively.
Disaccharide 7 was then converted into its propane-1,3-diyl-
phosphate sugar 9, which was somewhat labile, and coupled with
88.8
83.6
81.9
61.7
3.88
3.74
4.04
3.49–
3.60
84.0 3.47b
82.6
81.6 3.86
63.7 3.47,
3.75
79.9.3 3.68b
80.4
76.5
75.9
65.0
65.9
65.8
62.6
3.97
3.40,
3.68
another equivalent of 2,3-di-O-benzyl-D-arabinose in the presence
of TMSOTf to give trisaccharide 10 in 65% isolated yield along with
the recovery, (ca. 20%), of arabinofuranosides 7 formed as a result
of the hydrolysis of phosphate 9. We were unable to separate the
two anomeric trisaccharides 10 by column chromatography or by
5
a
All values are given as chemical shifts in ppm.
Overlap of signals.
b
A
B
C
D
ppm (f1)
6.50
6.00
5.50
Figure 3. Partial spectra of 2,3-di-O-benzyl arabinose in DMSO-d6.

2170
P. G. J. Plaza, G. Singh / Tetrahedron: Asymmetry 21 (2010) 2167–2171
O
O
HO
BnO
+
BnO
P
OH
OBn
O
O
O
O
OH
OBn
O
O
O
TMSOTf
-78oC to rt
O
OBn
OH
OR
OBn
BnO
BnO
OBn
BnO
OBn
30min, 51%
BnO
5
6
7 R=H
Ac2O, py, 98%
BnO
8 R=OAc, (α:β = 19:1)
Cl
O
O
P
BnO
O
O
O
O
O
O
O
O
O
P
TMSOTf
O
O
O
O
-78oC to rt
30min, 65%
BnO
OBn
BnO
BnO
OBn
N-MeIm,
CH2Cl2, 1h
OH
OBn
BnO
OBn
OBn
BnO
9
10
Scheme 2. Preparation of oligoarabinofuranosides from the reducing end.
HPLC. In their 13C NMR spectra, chemical shifts for anomeric car-
bons, for the pair of trisaccharides, were observed at 100.2,
106.5, 101.1 and 100.2, 105.6 and 96.1 ppm. These data and an
additional spectroscopy enabled the assignment of the central
(9.3 g, 33.3 mmol) was added and the mixture was stirred at rt
overnight. The reaction mixture was then poured into an ice-water
mixture and allowed to warm up to room temperature. The mix-
ture was then extracted with chloroform (3 ꢀ 50 mL). The organic
layers were then combined and washed using saturated aqueous
ammonium chloride (2 ꢀ 50 mL) and water (2 ꢀ 50 mL). The or-
ganic layer was then dried (Na2SO4) and the solvents were re-
moved in vacuo. The resulting residue was purified via column
chromatography (CHCl3 followed by CHCl3/MeOH; 9:1). The trity-
lated methyl glycoside was then benzylated under standard benzy-
lation conditions. Deprotection of the trityl and methyl groups was
carried out by refluxing in a solution of CH3CN/H2O/TFA (4:3:1;
1:20 w/v) at 95 °C, 12 h. The solvent was then removed in vacuo
and the residue was neutralized using saturated aqueous NaHCO3
(20 mL) and solid NaHCO3. The mixture was then extracted using
EtOAc (2 ꢀ 20 mL). The organic layers were combined and dried
(Na2SO4) and the solvent was removed under reduced pressure.
The residue obtained was purified via column chromatography
using CHCl3/MeOH (95:5); a light yellow oil, mmax (film)/cmꢁ1
3402, 3032, 2920, 1959, 1880, 1816, 1642, 1454, 1357, 1213, and
1082. 1H NMR (400 MHz) CDCl3 dH (ppm): shared resonances:
7.2–7.4 (10H, m, aromatic protons), 4.5–4.8 (4H, benzylic protons),
3.28 (1H, br s; hydroxyl proton), 1.5–2.9 (7H; hydroxyl protons);
arabinofuranoside residue as being a-linked.
3. Conclusion
In conclusion, we have investigated the equilibria present in
2,3-di-O-benzylated pentose sugars. We have successfully demon-
strated that the furanose component of the equilibrium mixture
could be selectively utilized for the synthesis that enabled the
establishment of a procedure for the iterative synthesis of oligoara-
binofuranosides from the reducing end using propane-1,3-diyl
phosphate as the leaving group. The preparation of a longer chain,
stereoregular oligoarabinofuranosides is currently underway.
4. Experimental
All chemicals used were of reagent or HPLC grade and used as
supplied without prior purification unless otherwise stated. The
solvents DCM and diethyl ether were dried over calcium hydride
for 24 h, distilled, and stored over 4 Å molecular sieves. Flash
column chromatography was carried out using forced flow of the
indicated solvent on Merck (230–400 mesh) silica gel. TLC was per-
formed using pre-coated Silica Gel 60 F254 plates; compounds were
visualized using acidic ammonium molybdate solution (ammo-
nium molybdate(VI) tetrahydrate (25 g) in 1 M H2SO4 (500 ml)).
Anhydrous reactions were performed under argon in an oven dried
apparatus; anhydrous transfers were done with standard syringe
techniques.
a-furanose: 5.37 (1H, d, J = 0.8 Hz, H-1), 4.30 (1H, H-4), 3.98 (1H,
H-2), 3.90 (1H, H-3), 3.70 (1H, H-5b), 3.62 (1H, H-5a); b-furanose:
5.26 (1H, d, J = 4.3 Hz, H-1), 4.20 (1H, H-3), 4.01 (1H, H-2), 4.00
(1H, H-4), 3.69 (1H, H-5b), 3.58 (1H, H-5a);
a-pyranose: 4.60 (1H,
H-1), 3.91 (1H, H-4), 3.87 (1H, H-5b), 3.60 (1H, H-2), 3.55 (1H, H-
3), 3.41 (1H, H-5a); b-pyranose: 5.19 (1H, d, J = 3.2 Hz, H-1), 3.97
(1H, H-4), 3.85 (1H, H-3), 3.87 (1H, H-5a), 3.79 (1H, H-2), 3.65
(1H, H-5b); 13C (100 MHz) CDCl3 dC (ppm): shared resonances:
138.2, 137.8, 137.8, 137.6, 137.4, 137.2, 137.0, 128.6, 128.4,
128.3, 128.2, 128.0, 127.9, 127.8, 127.75, 127.7, 127.6, 127.5 (aro-
matic-C), 74.2, 73.3, 72.8, 72.44, 72.39, 72.3, 72.2, 71.8 (benzylic-
The 1H, 13C, and 31P NMR spectra were recorded on Bruker
400 MHz spectrometers in the deuterated solvent states. For ease
of interpretation protons are expressed as multiples of 1. Refer to
the main text for equilibrium ratios. IR spectra were recorded on
a Perkin Elmer Spectrum RXI FT-IR spectrometer. High resolution
mass data were obtained using a Bruker Daltonics micrOTof-Q
instrument in the electron spray ionization mode.
C);
(C-5); b-furanose: 95.0 (C-1), 83.6 (C-2), 81.7 (C-4), 80.7 (C-3),
62.4 (C-5); -pyranose: 96.6 (C-1), 79.4 (C-3), 78.8 (C-2), 65.9 (C-
a-furanose: 101.0 (C-1), 86.6 (C-2), 82.7 (C-4), 82.3 (C-3), 62.5
a
4), 64.2 (C-5); b-pyranose: 91.6 (C-1), 76.4 (C-3), 75.7 (C-2), 66.8
(C-4), 61.7 (C-5).
1H NMR (400 MHz) DMSO-d6 dH (ppm): shared resonances: 7.2–
7.4 (10H, m, aromatic protons), 4.4–4.8 (4H, benzylic protons + 1H;
4.1. 2,3-Di-O-benzyl-D-arabinose 5
hydroxyl protons, OH-5); a-furanose: 6.45 (1H, d, J = 4.4 Hz; OH-1),
At first, -arabinose (5.0 g, 33.3 mmol) was suspended in meth-
D
5.25 (1H, d, J = 1.7 Hz, H-1), 4.05 (1H, H-4), 3.84 (1H, H-2), 3.76 (1H,
H-3), 3.49–3.60 (2H, H-5a, H-5b); b-furanose: 6.40 (1H, d, J = 6.3 Hz;
OH-1), 5.27 (1H, d, J = 4.3 Hz, H-1), 4.04 (1H, H-4), 3.88 (1H, H-2),
anol, after which p-TSA (290 mg, 1.5 mmol) was added and the
mixture stirred at 40 °C for 20 h. The solvent was removed in vacuo
and the crude product dissolved in pyridine (50 mL). Trityl chloride

P. G. J. Plaza, G. Singh / Tetrahedron: Asymmetry 21 (2010) 2167–2171
2171
3.74 (1H, H-3), 3.49–3.60 (2H, H-5a, H-5b);
a
-pyranose: 6.80 (1H, d,
(2 ꢀ 5 mL) and dried (Na2SO4). The resulting residue was purified
using flash column chromatography with petroleum ether/diethyl
ether 1:5 as the eluent to give phosphate 19.
The chromatographed product (80 mg, 0.094 mmol) was dis-
solved in dry CH2Cl2 (10 mL) and cooled to ꢁ78 °C under an argon
atmosphere. Next, TMSOTf (0.025 mL, 0.14 mmol) was added and
J = 6.7 Hz; OH-1), 4.40 (1H, d, J = 6.8 Hz, H-1), 3.86 (1H, H-4), 3.47
(2H, H-2, H-3), 3.47 (1H, H-5a), 3.75 (1H, H-5b); b-pyranose: 6.27
(1H, d, J = 4.3 Hz; OH-1), 5.13 (1H, d, J = 2.7 Hz, H-1), 3.97 (1H, H-
4), 3.68 (2H, H-2, H-3), 3.40 (1H, H-5a), 3.68 (1H, H-5b); 13C
(100 MHz) DMSO-d6 dC (ppm): shared resonances: 137.7, 128.5,
128.4, 128.2, 128.0, 128.0, 127.8, 127.7, 127.6 (aromatic-C), 73.8,
the mixture was stirred for 2 min. 2,3-Di-O-benzyl-D-arabinose
71.7, 71.1, 70.9 (2C), 70.8, 70.3, 70.2 (benzylic-C);
100.1 (C-1), 88.8 (C-2), 83.6 (C-3), 81.9 (C-4), 61.7 (C-5); b-fura-
nose: 94.6 (C-1), 84.0 (C-2), 82.6 (C-3), 81.6 (C-4), 63.7 (C-5);
pyranose: 97.4 (C-1), 80.4 (C-3), 79.9 (C-2), 65.8 (C-4), 62.6 (C-5);
b-pyranose: 91.1 (C-1), 76.5 (C-2), 75.9 (C-3), 65.0 (C-4), 65.9 (C-
5). m/z found (M+) 330.1513; C19H22O5 requires 330.1467.
a
-furanose:
(30 mg, 0.09 mmol) was then added to the reaction mixture which
was stirred for 30 min at room temperature. The reaction mixture
was quenched with saturated aqueous NaHCO3 (5 mL). The organ-
ic layer was then washed with saturated aqueous NaHCO3 (5 mL)
and water (5 mL), dried (Na2SO4), and evaporated under reduced
pressure. The resulting residue was purified via column chroma-
tography using petroleum ether/diethyl ether 2:1 to give the title
compound (61 mg, 65%). NMR data: 1H NMR (400 MHz) CDCl3
dH (ppm): 7.15–7.51 (35H, aromatic-H), 5.39 (0.5H, d, J = 6.4 Hz,
a
-
4.2. 20,30,50-Tri-O-benzyl-
benzyl- ,b- -arabinofuranoses 7
D-arabinofuranosyl-(a,b1–5)-2,3-di-O-
a
D
H-1a
, 5.31 (0.5H, dd, J = 4.5, 10.2 Hz, H-1b, 5.09 (0.5H, H-10b),
2,3,5-Tri-O-benzyl-1-O-propane-1,3-diyl phosphoryl-
D
-arabi-
5.08 (0.5H, H-10a), 4.86 (1H, d, J = 12.1 Hz; benzylic-H), 4.80 (1H,
d, J = 4.1 Hz, H-100), 4.73 (1H), 4.36–4.71 (14H; 13 benzylic-H + 1
ring-H), 4.14–4.25 (2H), 3.97–4.12 (4H), 3.76–3.94 (3H), 3.51–
3.65 (4H), 3.47 (1H, dd, J = 5.1, 10.0 Hz); 13C NMR (100 MHz) CDCl3
dC (ppm): 137.4–138.6 (satd aromatic-C), 127.6–128.5 (aromatic-
nofuranoside 66c (0.57 g, 1.05 mmol) was dissolved in dry CH2Cl2
(10 mL) and cooled to ꢁ78 °C under an argon atmosphere. Next,
TMSOTf (0.04 mL) was added and the mixture was stirred for
2 min. Then 2,3-di-O-benzyl-D-arabinose (0.31 g, 0.95 mmol) was
added to the reaction mixture which was stirred for 30 min at
room temperature. The reaction mixture was quenched with satu-
rated aqueous NaHCO3 (5 mL). The organic layer was then washed
with saturated aqueous NaHCO3 (5 mL) and water (5 mL), dried
(Na2SO4), and evaporated under reduced pressure. The resulting
residue was purified via column chromatography using 50:50
petroleum ether/diethyl ether to give the title compound (0.68 g,
C), 106.5 (C-10a), 105.6 (C-10b), 101.0 (C-1 ), 100.2 (C-100a,b),
a
96.1 (C-1b), 88.2, 87.1, 86.6, 84.3 (2C), 84.1, 83.5, 82.7, 82.4, 82.0,
81.8, 81.6, 80.8 (2C), 80.5 (2C), 80.3, 80.1 (ring-C), 73.4, 72.8,
71.8–72.3 (benzylic-C), 71.8, 70.1, 69.6, 67.6, 67.1, 66.7 (C-5, 5a,
5b), m/z found (M++Na) 1068.4090; C64H68NaO13 requires
1068.4588.
51%). NMR data:
a
-linked disaccharide: 1H NMR (400 MHz) CDCl3
Acknowledgment
dH (ppm): 7.15–7.51 (50H, aromatic-H), 5.37 (1H, d, J = 7.6 Hz, H-
1
a
), 5.29 (1H, dd, J = 4.5, 10.7 Hz, H-1b, 5.07 (1H, H-10b, 5.06 (1H,
We thank The University of the West Indies for a scholarship
(P.G.J.P.).
d, J = 0.76 Hz, H-10a), 4.34–4.65 (20H, benzylic-H), 4.23 (2H, m),
4.20 (2H, dd, J = 5.4, 10.7 Hz), 4.01–4.12 (7H), 3.91 (1H, dd,
J = 3.0, 6.8 Hz), 3.83 (1H, dd, J = 5.6, 10.9 Hz), 3.79–3.83 (2H),
3.53–3.66 (4H), 3.51 (1H, dd, J = 5.8, 10.1 Hz), 3.45 (1H, dd,
References
J = 5.1, 10.1 Hz), 3.11 (1H, d, J = 7.7 Hz; OH-1a
); 13C NMR
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Tetrahedron 1996, 52, 1095–1121; (c) Demchenko, A. V. Lett. Org. Chem. 2005, 2,
580–589.
(100 MHz) CDCl3 dC (ppm): 137.4–138.6 (satd aromatic-C),
127.6–128.5 (aromatic-C), 106.5 (C-10a), 105.6 (C-10b), 101.0 (C-
2. Recent examples include: (a) Gudmundsdottir, A. V.; Nitz, M. Org. Lett. 2008, 10,
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1a), 96.1 (C-1b), 88.2, 87.1, 86.6, 84.1, 83.5, 82.7, 82.5, 81.9, 81.7,
81.6, 80.8, 80.2 (ring-C), 71.8–73.8 (benzylic-C), 70.8, 69.6, 67.1,
66.7 (C-5, 50). b-Linked disaccharide: 1H NMR (400 MHz) CDCl3 dH
(ppm): 7.11–7.45 (50H), 5.35 (1H, d, J = 7.2 Hz, H-1a), 5.32 (1H,
dd, J = 3.9, 11.7 Hz, H-1b), 4.98 (1H, d, J = 3.1 Hz), 4.74 (1H, d,
J = 3.6 Hz), 4.32–4.72 (20H), 3.89–4.26 (11H), 3.71–3.88 (2H),
3.73 (1H, dd, J = 5.3, 10.9 Hz), 3.43–3.67 (6H), 3.29 (1H, dd,
J = 2.4, 11.2 Hz), 3.13 (1H, d, J = 7.7 Hz; OH-1
(100 MHz) CDCl3 dC (ppm): 137.3–138.2 (satd aromatic-C),
127.7–128.5 (aromatic-C), 101.2 (C- ,b), 101.0 (C-1 ), 96.3 (C-
1b), 86.5, 84.3 (2C), 84.1, 83.6 (2C), 83.3, 82.9, 80.8 (2C), 80.3
(2C), 71.8–73.4 (benzylic-C + 1C), 68.4 (2C), 67.3. m/z found
(M++Na) 755.3512; C45H48NaO9 requires 755.3196.
a
); 13C NMR
a
a
4.3. 20,30,50-Tri-O-benzyl-
benzyl- -arabinofuranosyl-2,3-di-O-benzyl-
ofuranoses 10
D
-arabinofuranosyl-b1-5)-20,30-di-O-
a
-D
a
,b- -arabin-
D
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At first, disaccharide 7 (100 mg, 0.14 mmol) was dissolved in
dry CH2Cl2 and cooled to 0 °C under an argon atmosphere. Next,
propane-1,3-diyldioxyphosphoryl chloride7 (64 mg, 0.41 mmol)
was added, followed by 1-methylimidazole (0.04 mL, 0.55 mmol).
The mixture was allowed to warm up to room temperature and
stirred for 1 h. The reaction was then quenched with saturated
NaHCO3 (5 mL) and the organic layer washed with water
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