Exploiting an aromatic aglycone as a reporter of glycosylation stereochemistry in the synthesis of 1,6-linked maltooligosaccharides

Article abstract of DOI:10.1016/j.tetasy.2004.11.047

Analysis of glycosylation stereoselectivity in the synthesis of branched maltooligosaccharides is hampered by poor spectral dispersion due to the repetitive nature of the saccharide chain and overlap of sugar H-1 signals with benzylic proton signals from

Full text of DOI:10.1016/j.tetasy.2004.11.047

Tetrahedron:
Asymmetry
Tetrahedron: Asymmetry 16 (2005) 477–485
Exploiting an aromatic aglycone as a reporter
of glycosylation stereochemistry in the synthesis of
1,6-linked maltooligosaccharides
Laurence Marmuse,a Sergey A. Nepogodieva and Robert A. Fielda,b,
*
aCentre for Carbohydrate Chemistry, School of Chemical Sciences and Pharmacy, University of East Anglia, Norwich NR4 7TJ, UK
bDepartment of Biological Chemistry, John Innes Centre, Norwich NR4 7UH, UK
Received 10 November 2004; accepted 19 November 2004
Abstract—Analysis of glycosylation stereoselectivity in the synthesis of branched maltooligosaccharides is hampered by poor spec-
tral dispersion due to the repetitive nature of the saccharide chain and overlap of sugar H-1 signals with benzylic proton signals from
the typically used benzyl ether protecting groups. A suitably protected p-methoxyphenyl maltoside acceptor, when coupled with
benzylated maltooligosaccharide donors, gives discrete aglycone 1H NMR signals that can be used to report on the stereoselectivity
of 1,6-glycosylation reactions.
ꢀ 2004 Elsevier Ltd. All rights reserved.
1. Introduction
OH
O
OH
α (1 4) bond
Starch is a ubiquitous biopolymer that is composed of
two distinct a-glucans, the linear a(1,4)-linked amylose
and the branched a-1,4(a-1,6)-linked amylopectin (Fig.
1).1 The ratio of these two glucans, and other compo-
nents,2 and their propensity to self-organise into precise
three dimensional, helical arrangements, are key fea-
tures in the generation, structure and properties of the
starch granule. The European Union starch trade has
been estimated at ca. 3.5 million tonnes annually, worth
ca. $1700 million, which reflects the broad range of
applications for which starch and its derivatives are used
(e.g., as a component of adhesives, seed coatings, talcum
powder, surfactants, viscosity modifiers and glazing
agents in food, absorbent personal health products, bio-
degradable filler).1 To date bulk chemical modification
processes have largely been used to generate novel
starch-based products.1 However, with recent advances
in genetic engineering, modified crop plants are increas-
ingly investigated as a means of producing of ÔdesignerÕ
starches.3 Such approaches would benefit enormously
from a better understanding of the structure, dynamics
and assembly of the starch granule,4 from a materials
science perspective, and also from a more detailed pic-
HO
HO
O
OH
O
HO
HO
O
O
HO
HO
O
Amylose
OH
O
OH
O
HO
HO
O
HO
α (1 6) bond
HO
HO
HO
O
O
HO
O
O
OH
O
HO
HO
O
OH
HO
4) bond
α (1
HO
O
O
HO
HO
Amylopectin
O
Figure 1. Representative partial structures of amylose and
amylopectin.
ture of the biochemical events necessary for amylose,
amylopectin, and hence ultimately starch granule forma-
tion.5 Recent studies6,7 have investigated the impact of
glycan structure and solvation on amylopectin branch
points and their propensity to initiate helix formation.
*
Corresponding author. Fax: +44 1603 592003; e-mail: r.a.field@
uea.ac.uk
0957-4166/$ - see front matter ꢀ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2004.11.047

478
L. Marmuse et al. / Tetrahedron: Asymmetry 16 (2005) 477–485
These reports illustrate that the numbers of sugar units
present in models under study has an impact on the con-
clusions reached; there is a need to move to large struc-
tures (perhaps >20 sugar residues) in order to obtain
physiologically relevant information. We, therefore, set
out to develop synthetic routes to complex linear and
branched maltooligosaccharides that could be used to
address issues relating to starch structure and
biosynthesis.
and a maltoside acceptor, relying on environment-in-
duced changes in chemical shift of the acceptor aromatic
aglycone protons as a read-out of a/b selectivity (Fig. 2).
2. Results and discussion
These studies required access to a suitably protected
maltoside acceptor possessing both an aglycone that
gives rise to distinct 1H NMR signals, along with a
free hydroxyl group at C-6 of the reducing terminal unit.
Appropriate maltosaccharide donors were also required;
these were accessed directly from commercial maltotri-
ose (trisaccharide), and through selective acetolysis of
protected b-cyclodextrin (heptasaccharide).
Stepwise enzymatic syntheses of maltooligosaccharides
using immobilised amylosucrase8 and glycogen phos-
phorylase9 have been reported, as have blockwise enzy-
matic syntheses of linear and branched maltodextrins
and hemithiomaltodextrins using cyclodextrin glucosyl-
transferase in conjunction with maltose derivatives
as donor substrates.10 In terms of chemical syntheses,
several effective, but technically complex, syntheses of
branched maltooligosaccharides, up to a nonasaccha-
ride, have been reported by Motawia et al.11 In order
to access even larger structures, we had in mind the
use of readily available cyclodextrins as precursors of
maltooligosaccharide building blocks (DP 6, 7, 8 from
a-, b- and c-CD, respectively). Similar approaches have
been used before to generate such building blocks for
synthetic chemistry12,13 and enzyme studies.9,14
2.1. Synthesis of the maltoside acceptor
Commercial maltose monohydrate 1 was acetylated with
acetic anhydride and iodine16 and, on treatment with
BF3–OEt2, was converted into the mixed a,b p-methoxy-
phenyl glycosides in a combined 69% yield (Scheme 1).
Fractional crystallisation from diethyl ether gave the
pure b-glycoside 2 in 41% isolated yield. Deacetylation
and subsequent benzylidenation under standard condi-
tions gave compound 3 in 65% yield over two steps.
Taking b-cyclodextrin as a starting material, coupling
two maltoheptasaccharide together, for instance, would
generate one new stereogenic centre in a molecule that
possesses no fewer than 70 stereogenic centres in total.
Clearly the physical differences that one can anticipate
from diastereomers differing in only 1 of 70 stereogenic
centres does not leave one optimistic that chromato-
graphic separation of mixed anomers is going to be a
fruitful practice in the synthesis of increasingly large
structures. Robust coupling reactions that give essen-
tially complete control of anomeric stereochemistry
are, therefore, required. We considered thioglycosides
to be particularly suitable glycosyl donor building
blocks since they allow for protecting group manipul-
ation at a late stage and can be activated in a chemo-
selective fashion.15 Herein we report the assessment of
a model system that allows straightforward analysis of
the stereoselectivity of thioglycoside-based 1,6-glycosyl-
ation reactions between maltooligosaccharide donors
Selective tert-butyldimethylsilylation of the primary
alcohol in 3 gave silyl ether 4 in 85%, which was subse-
quently benzoylated under standard conditions to give
the crystalline, fully protected maltoside 5. Removal of
the silyl ether protecting group with TBAF led to malt-
ose derivative 6, with the required free hydroxyl group
at C-6, in 70% yield.
2.2. Synthesis of the maltotrioside and maltoheptaoside
donors
Acetylated maltotriose was prepared by treating malto-
triose with sodium acetate in acetic anhydride.17 With-
out purification, the resulting undecaacetate 7 (Scheme
2) was converted into peracetylated mixed anomeric
thiomethyl glycosides 8 (a:b ca. 1:1.5) in 90% yield by
treatment with iodine, dimethyldisulfide and hexameth-
yldisilane.18 In order to effect a-glycosylation later,
participating acetate groups in 8 were replaced with
BnO
O
OR
BnO
OBn
O
BnO
BnO
BnO
OR
OBn
O
OBn
BnO
O
BnO
BnO
BnO
O
OBn
O
O
OBn
OMe
BnO
BnO
β
O
O
O
Ph
O
α
OBn
OBn
H
O
O
O
Ph
H
H
H
O
O
H
H
O
O
BzO
BzO
BzO
O
O
O
BzO
BzO
O
OMe
O
O
BzO
BzO
BzO
H
H
R = Bn or R = benzylated α-maltotetraosyl
Figure 2. Potential differences in environment that might be encountered by the aromatic aglycone protons of a-1,6- and b-1,6-linked
maltooligosaccharyl-maltoside, and which may give rises to differences in aglycone 1H NMR signals.

L. Marmuse et al. / Tetrahedron: Asymmetry 16 (2005) 477–485
479
sidered a suitable starting material in which one glyco-
sidic bound can be selectively cleaved to give a linear
heptasaccharide. Initial studies investigated acetolysis
of per-O-benzylated b-cyclodextrin19 using the method
developed for per-O-acetylated b-cyclodextrin13 or for
thiolytic cleavage of per-O-methylated a/b-cyclodex-
trin.20 However, in the case of per-O-benzylated cyclo-
dextrin reaction conditions typically employed in such
processes gave mixed products arising from benzyl ether
cleavage.21 Resorting to acetolysis of per-O-acetylated
b-cyclodextrin with Ac2O and H2SO4,13 peracetylated
maltoheptaosides 11 were obtained in 46% yield
(Scheme 2). Following the procedure for the preparation
of benzylated thiomaltotriosides 10, reaction of 11 with
iodine, dimethyldisulfide and hexamethyldisilane gave
peracetylated heptasaccharide thioglycosides 12 (a:b
ca. 1:1.5) in 86% yield. Deacetylation of 12 with sodium
methoxide in methanol and subsequent benzylation with
sodium hydride, imidazole and tetraethylammonium
iodide in DMF12b gave the required heptasaccharide
donors 14 (72% from 12).
OH
O
HO
HO
OH
O
HO
O
HO
OH
OH
1
a
OAc
O
AcO
AcO
OAc
O
AcO
O
O
OMe
AcO
AcO
2
b
Ph
O
O
O
OR1
O
R2O
R2O
O
O
OMe
R2O
R2O
3 R1 = TBDMS, R2 = H
4 R1 = TBDMS, R2 = Bz
5 R1 = H, R2 = Bz
c
d
2.3. Glycosylation reactions: preparation of the branched
pentasaccharides 15 and nonasaccharides 16
Scheme 1. Reagents and conditions: (a) p-methoxyphenol, CH2Cl2,
BF3–OEt2, 41%; (b) (i) MeOH, NaOMe, (ii) benzaldehyde dimethyl-
acetal, DMF, p-toluenesulfonic acid, 65%; (c) tert-butyldimethylsilyl-
chloride, pyridine, 75%; (d) BzCl, pyridine, 83%; (e) Bu4NF, THF,
70%.
Our ultimate objective was to develop a set of glycosyl-
ation reaction conditions that would give high yields
and a-stereoselectivity with complex maltooligosaccha-
ride donors and acceptors. In initial reactions between
maltoside acceptor 6 and thiomaltotrioside donor 10,
diethyl ether-based solvent mixtures were employed be-
cause of the reported a-selectivity that they afford.22
Due to the limited solubility of acceptor 6 in neat diethyl
ether, glycosylation reactions were carried out in diethyl
ether–DCM 4:1, with NIS/TMSOTf23 as the promoter
at ꢀ60 ꢁC. Under such conditions, the branched penta-
saccharides 15 were obtained in 57% isolated yield
(Scheme 3). The 1H NMR spectrum of the mixture,
complicated by the presence of the benzylic protecting
group proton signals, did not easily allow confirmation
of the stereoselectivity of the glycosylation reaction.
However, mass spectrometry did confirm that coupling
OAc
O
n
AcO
AcO
OAc
O
AcO
OAc
O
O
a
AcO
AcO
O
AcO
n
AcO
OAc
SMe
7 n = 1
11 n = 5
OAc
O
AcO
AcO
OAc
AcO
O
OAc
O
O
AcO
b
AcO
O
AcO
AcO
8
9
n = 1, R = Ac
n = 1, R = H
12 n = 5, R = Ac
13 n = 5, R = H
14 n = 5, R = Bn
c
c
6
10 or 14
d
d
10 n = 1, R = Bn
Scheme 2. Reagents and conditions: (a) Me–S–S–Me, I2, Me3Si–
SiMe3, CH2Cl2, 8 90%, 12 86%; (b) MeOH, NaOMe, 9 92%, 13 94%;
(c) for 10: BnBr, NaH, Et4NI, DMF. For 14: BnBr, NaH, Et4NI,
imidazole, DMF, 10 85%, 14 80%.
a
OBn
O
n
BnO
BnO
OBn
O
BnO
OBn
O
O
BnO
BnO
O
BnO
non-participating benzyl ether protecting groups. After
removal of the acetate groups with sodium methoxide
in methanol, giving thiomethyl maltotrioside 9, treat-
ment with benzyl bromide in the presence of sodium
hydride and tetraethylammonium iodide in DMF11d
gave trisaccharide donor 10.
BnO
O
Ph
O
O
O
BzO
BzO
O
O
O
OMe
BzO
BzO
15 n = 1
16 n = 5
For the preparation of benzylated thioheptasaccharide
donor 14, b-cyclodextrin (cyclomaltoheptaose) was con-
Scheme 3. Reagents and conditions: (a) NIS, TMSOTf, Et2O–CH2Cl2
(1:4), 15 57%, 16 36%.

480
L. Marmuse et al. / Tetrahedron: Asymmetry 16 (2005) 477–485
to give pentasaccharide products 15 had been achieved:
the observed spectrum of the [M+Na]+ ion
(C142H138O31Na, major peak m/z 2362.9) and the iso-
tope pattern for [M+Na]+ of this compound were an
excellent match.
To allow more detailed analysis of NMR data, the pure
a- and b-anomers 15a and 15b were isolated from the
above mixture by extensive, laborious column chroma-
tography on silica gel, giving isolated yields of 21% for
the pentasaccharide 15a and 6% for the pentasaccharide
15b. From preliminary synthetic reactions of the type
outlined, coupled with extensive chromatography, and
long-winded two-dimensional NMR experiments, it
was evident that anomeric 1H NMR signals for internal
b-linkages in maltooligosaccharides lie at ca. 4.6 ppm,
enveloped by both other sugar and benzylic proton sig-
Figure 4. Expansion of the methoxyphenyl region of 1H NMR spectra
(400 MHz, CDCl3) of pentasaccharides 15 (a,b mixture) and purified
anomers 15a and 15b.
1
nals, whilst anomeric H signals for a-linkages lie clear
of other signals at ca. 5.5–6.0 ppm. In contrast, ano-
meric 13C NMR signals for internal b-linkages in mal-
tooligosaccharides (ca. 105 ppm) are distinct from C-1
signals for internal a-linked sugars (ca. 96–98 ppm).
However, spectral overlap in the former case, and the
insensitivity of the technique in the latter, make direct
1H or 13C NMR quantitation of a/b mixtures by analy-
sis of sugar signals impractical.
Coupling of maltoside acceptor 6 with maltoheptaoside
donor 14 (Scheme 3) under similar conditions to those
used in the pentasaccharide synthesis gave a mixture
of anomeric nonasaccharides, 16, in 36% combined yield
(a:b ca. 3.7:1). Very careful chromatographic purifica-
tion afforded small quantities of pure 16a (16 mg, 4%
isolated yield). Although less distinct from other aro-
matic signals in this instance, due to the 22 benzyl pro-
1
On first inspection, the H NMR spectra for pure and
1
mixed anomers of pentasaccharide 15 look very similar
(Fig. 3, 15). On closer inspection, clear differences in
the aromatic region are evident. Two sets of peaks cor-
responding to the protons of the p-methoxyphenyl agly-
cone can be distinguished. These protons show chemical
shifts that are influenced by the stereochemistry of the
newly formed 1,6-linkage; in the case of the major com-
ponent of the mixture, the a-glycoside 15a, doublets
appear at 6.63 and 6.82 ppm, whereas for the minor
b-linked component 15b, doublets appear at 6.57 ppm
and 6.77 ppm (Fig. 4). Hence, the anomeric composition
of the mixture of pentasaccharides 15 can easily be
determined by integration of the p-methoxyphenyl agly-
cone proton signals.
tecting groups in 16, H NMR analysis illustrates that
aglycone 1H NMR signals (6.75/6.95 ppm for 16a;
6.68/6.88 ppm for 16b) can again be used to report on
the stereochemical composition of the mixed anomeric
products (Fig. 5).
Figure 5. Extracts of the aromatic region of 1H NMR spectra
(400 MHz, CDCl3) of nonasaccharides 16 (a,b mixture) and purified
anomer 16a.
3. Conclusion
In summary, judicious choice of a p-methoxyphenyl
acceptor aglycone provides, through 1H NMR spectros-
copy, direct access to information about glycosylation
stereoselectivity for 1,6-maltooligosaccharide couplings
that would otherwise be tortuous to analyse. Optimisa-
tion of maltooligosaccharide glycosylation reaction ste-
reochemistry using this reporter system is ongoing.
Figure 3. Extracts of 1H NMR spectra (400 MHz, CDCl3) of
pentasaccharides 15 (a,b mixture) obtained by glycosylation of 6 with
10 and purified anomers 15a and 15b.

L. Marmuse et al. / Tetrahedron: Asymmetry 16 (2005) 477–485
481
4. Experimental
4.1. General methods
(2 · 80 mL) and H2O (2 · 80 mL) and dried over
MgSO4. Concentration in vacuo and crystallisation
(diethyl ether) gave the title b-aryl glycoside (5.8 g,
41%); mp 130–132 ꢁC (diethyl ether); [a]D = +49.2 (c
1.0, CHCl3); dH (CDCl3): 2.01, 2.03, 2.04, 2.05, 2.06,
2.11 (2) (21H, 7 · s, 7 · Ac), 3.78 (4H, m, OMe, H-5a),
3.97 (1H, m, H-5b), 4.01 (2H, m, H-4b, H-6), 4.26
Reactions were carried out in dry solvents using septa
and syringes for addition of reagents. Anhydrous
DMF and Et2O were purchased from Aldrich, CH2Cl2
was distilled from CaH2, MeOH was distilled from
Mg(OMe)2, pyridine was distilled from P2O5 and stored
(2H, m, H-6,60), 4.49 (1H, dd, J5,6 2.9 Hz, J6,6
0
12.2 Hz, H-60), 4.87 (1H, dd, J1,2 3.9 Hz, H-2b), 4.99
(1H, d, J1,2 7.6 Hz, H-1a), 5.06 (2H, m, H-2a, H-4a),
5.32 (1H, t, J2,3 ꢁ J3,4 8.8 Hz, H-3a), 5.37 (1H, t,
J2,3 ꢁ J3,4 10.2 Hz, H-3b), 5.44 (1H, d, J1,2 3.9 Hz, H-
1b), 6.82 (2H, JAB 8.0 Hz, C6H4–OMe), 6.94 (2H, JAB
8.0 Hz, C6H4–OMe); dC (CDCl3): 20.7 (2), 20.8 (2),
20.9, 21.0, 21.1 (7 · CH3C@O), 55.8 (OMe), 61.7, 63.0
(C-6a, C-6b), 68.2, 68.7, 69.5, 70.2, 72.2, 72.4, 72.8,
75.5 (C-2a,b to C-5a,b), 95.7 (C-1b), 99.8 (C-1a),
114.7, 114.9, 116.1, 118.9 (Ar), 150.9, 155.9 (Ar quat.),
169.7, 169.9, 170.2, 170.5, 170.6, 170.7, 170.8
(CH3C@O); m/z (ES) 765.3 (70% [M+Na]+), (ES)
(Found: [M+NH4]+, 760.2659. C33H46O19N requires
760.2659).
˚
over 4 A molecular sieves. Cation-exchange resins were
washed with water and dry MeOH before use. TLC
was performed on precoated aluminium plates (Silica
Gel 60 F254, Merck). Spots were visualised by exposure
to UV light or by immersion into 5% ethanolic H2SO4
followed by heating to 150 ꢁC. Solutions of reaction
products were dried over MgSO4 and solvents were
evaporated under reduced pressure at 25–40 ꢁC. Column
chromatography was performed on silica gel (40–70 lm,
BDH–Merck). Melting points were determined using a
Gallenkamp melting point apparatus and are uncor-
rected. Optical rotations were measured at 25 ꢁC using
a Perkin–Elmer 141 polarimeter. 1H and 13C NMR
spectra were recorded at 24 ꢁC with a Varian Gemini
2000 spectrometer at 300 and 75 MHz, respectively, or
with a Varian Unity Plus spectrometer at 400 and
100 MHz, respectively, using TMS (for solution in
CDCl3) or MeOH (d 49.9, for solutions in D2O) as inter-
nal standards. Resonance assignments were made with
the aid of COSY and HSQC experiments. In cases where
spectral dispersion was poor, only selected diagnostic
NMR data are given; other spectral features were in ac-
cord with the proposed structures. Due to the repetitive
sequence of the saccharides being analysed, in places
attributing a given signal to an individual sugar residue
is not possible and assignments given should be taken as
tentative. Sugar residues are referred to alphabetically
from the reducing terminus as a, b etc.; the second chain
introduced through a 1,6-linkage, is referred to as a0, b0,
etc. Accurate electrospray ionisation mass spectra (ESI-
MS) were obtained using positive ionisation mode on
Finnigan MAT 900 XLT mass spectrometer. For com-
pounds with molecular masses >1000 low resolution
ESI-MS were obtained on the same instrument or
low resolution MALDI-TOF MS were obtained on
Applied Biosystems Voyager mass spectrometer and
experimental data were matched to theoretical isotope
patterns.
4.3. p-Methoxyphenyl 4-O-(4,6-O-benzylidene-a-D-
glucopyranosyl)-b-D-glucopyranoside, 3
b-Aryl glycoside 2 (2.94 g, 3.88 mmol) was dissolved in
dry MeOH (30 mL), sodium methoxide solution (8 mL
of 0.2 M solution in methanol) was added and the mix-
ture was stirred at room temperature until the reaction
was complete, as judged by TLC. Amberlite IR-120
(H+) ion exchange resin was added to neutralise the mix-
ture, followed by concentration in vacuo. The resulting
residue was dissolved in DMF (20 mL) and benzalde-
hyde dimethyl acetal (1.16 mL, 7.76 mmol) and p-tolu-
enesulfonic acid monohydrate (50 mg) were added.
The mixture was stirred at room temperature for 12 h,
neutralised with triethylamine, concentrated in vacuo
and the resulting residue was subjected to column chro-
matography (acetone–CH2Cl2, 7:3) to give the title com-
25
D
pound (1.3 g, 65%); ½aꢂ = +27.0 (c 0.9, MeOH); dH
(CD3OD): 3.91–4.22 (15H, m, H-2a,b, H-3a,b, H-4a,b,
H-5a,b, H-6a,b, OMe), 4.79 (1H, d, J1,2 7.7 Hz, H-1a),
4.86 (1H, s, CH–Ph), 5.22 (1H, d, J1,2 3.7 Hz, H-1b),
6.83 (2H, d, JAB 9.2 Hz, C6H4–OMe), 7.05 (2H, d, JAB
9.2 Hz, C6H4–OMe), 7.31–7.50 (9H, m, Ar); dC
(CDCl3): 55.7 (OMe), 61.2, 63.8 (C-6a, C-6b), 68.7,
70.9, 73.1, 73.3, 74.8, 76.0, 79.8, 80.7 (C-2a,b to
C-5a,b), 101.8, 102.0 (C-1a, C-1b), 102.2 (CH2Ph),
114.8–155.7 (Ar); m/z (ES) 559.1 (100% [M+Na]+),
(ES) (Found: [M+NH4]+, 554.2230. C26H36O12N
requires 554.2232).
4.2. p-Methoxyphenyl 2,3,6-tri-O-acetyl-4-O-(2,3,4,6-
tetra-O-acetyl-a-D-glucopyranosyl)-b-D-glucopyr-
anoside, 2
Maltose octaacetate 1 (13 g, 19 mmol) was prepared by
reaction of maltose monohydrate (6.9 g, 19 mmol) with
acetic anhydride (70 mL) in the presence of iodine
(500 mg) using a literature procedure.16 The peracetate
obtained in this way was dissolved in dry CH2Cl2
(100 mL), p-methoxyphenol (10.85 g, 87 mmol) was
added, the mixture was cooled on an ice bath and
BF3–OEt2 (13 mL, 54.6 mmol) was added dropwise.
The mixture was stirred for 12 h at room temperature,
diluted with CH2Cl2 (150 mL), washed successively
with H2O (2 · 80 mL), saturated NaHCO3 solution
4.4. p-Methoxyphenyl 4-O-(4,6-O-benzylidene-a-D-
glucopyranosyl)-6-O-tert-butyldimethylsilyl-b-D-gluco-
pyranoside, 4
To a solution of benzylidene-protected maltoside 3
(1.33 g, 2.47 mmol) in dry pyridine (5 mL) was added
tert-butyldimethylsilyl chloride (632 mg, 4.19 mmol).
After stirring overnight, the mixture was concentrated
in vacuo and co-evaporated with toluene (three times).

482
L. Marmuse et al. / Tetrahedron: Asymmetry 16 (2005) 477–485
Chromatography of the resulting residue (CH2Cl2–
MeOH, 12:1) gave the title compound (1.39 g, 85%);
½aꢂ = +30.7 (c 1.1, CHCl3); dH (CDCl3): 0.02 (6H, s,
chromatography (CH2Cl2–ethyl acetate, 1:0–95:5) gave
the title compound (936 mg, 70%) as white foam;
½aꢂ = +77 (c 1.0, CHCl3); dH (CDCl3): 3.73 (3H, s,
25
D
25
D
OMe), 3.80–3.88 (3H, m, H-4b, H-5a/b, H-6), 4.04–
SiMe2), 0.87 (9H, s, t-Bu), 3.29–4.18 (12H, m, H-2 to
H-6), 3.70 (3H, s, OMe), 4.65 (1H, d, J1,2 7.7 Hz, H-
1a), 4.99 (1H, d, J1,2 3.5 Hz, H-1b), 5.42 (1H, s, CH–
Ph), 6.70 (2H, d, JAB 9.1 Hz, C6H4–OMe), 6.98 (2H,
d, JAB 9.1 Hz, C6H4–OMe), 7.25–7.48 (5H, m, Ar); dC
(CDCl3): ꢀ5.4, ꢀ5.3 (Me2CSiCMe3) 18.2 (Me2CSiCMe3),
25.8 (Me2CSit-Bu), 55.4 (OMe), 62.5, 63.6 (C-6a, C-6b),
68.7, 70.8, 73.2, 73.4, 75.5, 76.1, 80.52, 80.7 (C-2a,b
to C-5a,b), 101.6 (C-1a), 101.8 (CH–Ph), 102.1 (C-1b),
114.3–137.8 (Ar), 151.2, 155.2 (Ar quat. from C6H4–
OMe); m/z (CI) 668.4 (45% [M+NH3]), 544.3 (100,
[Mꢀ124.1]), (ES) (Found: [M+NH4]+, 668.3101.
C32H50O12SiN requires 668.3097).
4.14 (3H, m, H-5a/b, 2 · H-6), 4.46 (1H, dd, J5,6
0
4.7 Hz, J6,6 10.1 Hz, H-6), 4.53 (1H, t, J3,4 ꢁ J4,5
9.3 Hz, H-4a), 5.19–5.23 (2H, m, H-1a, H-2b), 5.49
(1H, dd, J1,2 7.8 Hz, J2,3 9.5 Hz, H-2a), 5.53 (1H, s,
CH–Ph), 5.67 (1H, d, J1,2 4.2 Hz, H-1b), 5.75 (1H, t,
J2,3, J3,4 9.5 Hz, H-3a), 5.92 (1H, t, J2,3 ꢁ J3,4 9.5 Hz,
H-3b), 6.77 (2H, d, JAB 9.1 Hz, C6H4–OMe), 6.89 (2H,
d, JAB 9.1 Hz, C6H4–OMe), 7.25–7.86 (25H, m, Ar);
dC (CDCl3): 55.5 (OMe), 61.5, 63.8 (C-6a, C-6b), 68.5,
69.4, 71.2 (2), 72.2, 74.9, 75.0, 78.9 (C-2a,b to C-5a,b),
97.1 (C-1b), 100.2 (C-1a), 101.4 (CH–Ph), 114.6–136.8
(Ar), 151.0, 155.7 (Ar quat. from C6H4–OMe), 165.0,
165.3, 165.6, 165.7 (C@O); m/z (ES) 975.4 (100%,
[M+Na+]), (ES) (Found: [M+NH4]+, 970.3286
C54H52O16N requires 970.3281).
4.5. p-Methoxyphenyl 2,3-di-O-benzoyl-6-O-tert-butyl-
dimethylsilyl-4-O-(2,3-di-O-benzoyl-4,6-O-benzylidene-
a-D-glucopyranosyl)-b-D-glucopyranoside, 5
4.7. Methyl (2,3,4,6-tetra-O-acetyl-a-D-glucopyranosyl)-
(1!4)-(2,3,6-tri-O-acetyl-a-D-glucopyranosyl)-(1!4)-1-
thio-2,3,6-tri-O-acetyl-a,b-D-glucopyranoside 8
Silylated benzylidene maltoside 4 (1.40 g, 2.15 mmol)
was dissolved in dry pyridine (20 mL), cooled on an
ice bath and benzoyl chloride (2 mL, 17.2 mmol) was
added. After 2 days the mixture was diluted with
DCM (200 mL), washed successively with 1 M HCl
(3 · 60 mL) and saturated NaHCO3 solution
(3 · 60 mL) and dried over MgSO4. Concentration in
vacuo gave a residue which was subjected to column
chromatography (toluene–ethyl acetate, 10:1) and crys-
tallised from ethanol to give small crystals of the title
Maltotriose undecaacetate 7 was prepared according to
the procedure described by Wolfrom and Thompson.17
Acetic anhydride (20 mL) and NaOAc (2 g) were heated
to reflux and maltotriose (2.05 g, 4.06 mmol) was care-
fully added and the mixture was refluxed for a further
hour. The reaction mixture was cooled and the solvent
was co-evaporated with toluene. The resulting residue
was dissolved in CH2Cl2 (150 mL) and successively
washed with H2O (3 · 50 mL), saturated NaHCO3 solu-
tion (3 · 50 mL) and H2O (3 · 50 mL) and dried over
MgSO4. This material was used directly in the next step
without characterisation. The title compound was pre-
pared according to the procedure described by Kartha
and Field.18 Crude maltotriose undecaacetate 7 (3.71 g,
3.83 mmol) was dissolved in dry CH2Cl2 (40 mL), di-
methyldisulfide (190 lL, 2.10 mmol) and hexamethyldi-
silane (430 lL, 2.10 mmol) were added, followed by I2
(970 mg, 3.83 mmol). The mixture was stirred at room
temperature for 5 h, diluted with CH2Cl2 (200 mL),
washed with NaS2O3 solution (3 · 70 mL) and H2O
(2 · 80 mL) and dried over MgSO4. Concentration in va-
cuo and column chromatography (toluene–ethyl acetate,
9:1–1:1) gave the title compound as a white foam (3.50 g,
86%); a:b ca. 1:1.5; dH (CDCl3): 4.26 (d, J1,2 10.9 Hz, H-
1ab), 5.28 (d, J1,2 3.9 Hz, H-1b or H-1c), 5.41 (d, J1,2
4.1 Hz, H-1b or H-1c), 5.43 (d, J1,2 5.5 Hz, H-1aa); dC
(CDCl3): 11.3, 12.3 (SMe, a/b), 82.5 (2, C-1aa, C-1ab),
95.6, 95.8 (C-1b, C-1c).
compound (1.72 g, 75%); mp 176–178 ꢁC (ethanol);
25
½aꢂ = +60.1 (c 1.0, CHCl3); dH (CDCl3): 0.12 (3H, s,
D
SiMe2), 0.16 (3H, s, SiMe2), 0.96 (9H, s, t-Bu), 3.73–
3.87 (6H, m, OMe, H-4b, H-5b, H-6a), 4.11–4.15 (3H,
m, H-5a, H-6b, H-60b ), 4.39–4.45 (2H, m, H-4a, H-
60a), 5.15 (1H, d, J1,2 7.7 Hz, H-1a), 5.19 (1H, dd, J1,2
3.9 Hz, J2,3 9.9 Hz, H-2b), 5.46 (1H, dd, J1,2J2,3
9.4 Hz, H-2a), 5.52 (1H, s, CH-Ph), 5.64 (1H, d, J1,2
H-1b), 5.72 (1H, t, J2,3, J3,4 9.4 Hz H-3a), 5.92 (1H, t,
J2,3, J3,4 9.9 Hz, H-3b), 6.75 (2H, d, JAB 8.9 Hz,
C6H4–OMe), 6.92 (2H, d, JAB 8.9 Hz, C6H4–OMe),
7.24–7.85 (25H, m, Ar); dC (CDCl3): ꢀ5.05, ꢀ5.0
(Me2CSit-Bu), 18.5 (Me2CSit-Bu), 26.0 (Me2CSit-Bu),
55.5 (OMe), 62.2, 63.8 (C-6a, C-6b), 68.6, 69.3, 71.4,
71.5, 72.1, 75.1, 75.5, 79.2 (C-2a,b to C-5a,b), 96.7 (C-
1b), 100.3 (C-1a), 101.6 (CH–Ph), 114.4–136.8 (Ar),
151.2, 155.2 (Ar quat. from C6H4–OMe), 164.9, 165.2,
165.4, 165.5 (C@O); m/z (ES) 1089.6 [M+Na]+.
4.6. p-Methoxyphenyl 2,3-di-O-benzoyl-4-O-(2,3-di-O-
benzoyl-4,6-O-benzylidene-a-D-glucopyranosyl)-b-D-
glucopyranoside, 6
4.8. Methyl a-D-glucopyranosyl-(1!4)-glucopyranosyl-
(1!4)-1-thio-a,b-D-glucopyranoside, 9
To a solution of fully protected silyl maltoside 5 (1.5 g,
1.40 mmol) in dry THF (10 mL) was added dropwise
Bu4NF (2.8 mmol, 2.8 mL of a 1 M solution in THF).
The mixture was stirred at room temperature for 1 h
and the solvent was removed in vacuo. The resulting res-
idue was dissolved in DCM (100 mL), washed with H2O
(30 mL), saturated NaHCO3 solution (3 · 30 mL) and
H2O (3 · 30 mL). Concentration in vacuo and column
Fully acetylated methyl thiomaltotrioside 8 (3.43 g,
3.37 mmol) was dissolved in dry MeOH (30 mL) con-
taining a catalytic amount of sodium methoxide and
the mixture was stirred at room temperature until the
reaction was complete, as judged by TLC. Amberlite
IR-120 (H+) ion exchange resin was added to neutralise
the mixture, followed by concentration in vacuo to give

L. Marmuse et al. / Tetrahedron: Asymmetry 16 (2005) 477–485
483
the title compound (1.66 g, 92%); a:b ca. 1:1.5;
4.11. Methyl (2,3,4,6-tetra-O-acetyl-a-D-glucopyranosyl)-
(1!4)-{(2,3,6-tri-O-acetyl-a-D-glucopyranosyl)-(1!4)}5-
2,3,6-tri-O-acetyl-1-thio-a,b-D-glucopyranoside 12
25
D
½aꢂ = +149.0 (c 0.6, MeOH); dH (CD3OD): 2.05, 2.17
(SMe, a/b), 4.27 (d, J1,2 9.7 Hz, H-1ab), 5.14–5.17 (m,
H-1b/c,a/b), 5.20 (d, J1,2 4.5 Hz, H-1aa); dC (CD3OD):
12.0, 12.7 (SMe, a/b), 87.1, 87.9 (C-1aa, C-1ab), 102.5,
102.6, 102.7, 102.8 (C-1b/c,a/b); m/z (ES) 557.3 (50%,
[M+Na]+), (ES) (Found: [M+NH4]+, 552.1957
C19H38O15N requires 552.1957).
Per-O-acetylmaltoheptaose 11 (1.00 g, 0.47 mmol) was
dissolved in dry CH2Cl2 (5 mL), dimethyldisulfide
(23 lL, 0.26 mmol) and hexamethyldisilane (52 lL,
0.26 mmol) were added, followed by I2 (0.47 mmol,
120 mg) and the mixed was stirred at room temperature
for 8 h. The reaction was then diluted with CH2Cl2
(150 mL) and washed with NaS2O3 solution
(3 · 50 mL) and H2O (2 · 50 mL) and dried over
MgSO4. Concentration in vacuo and column chroma-
4.9. Methyl (2,3,4,6)-tetra-O-benzyl-a-D-glucopyranos-
yl)-(1!4)-(2,3,6-tri-O-benzyl-a-D-glucopyranosyl)-
(1!4)-1-thio-2,3,6-tri-O-benzyl-a/b-D-glucopyranoside
Deprotected trisaccharide 9 (1.6 g, 2.95 mmol) was dis-
solved in dry DMF (35 mL), NaH (88.8 mmol, 4.0 g of
a 60% w/v suspension in mineral oil) was added slowly
to the reaction and stirred at room temperature for half
an hour. The mixture was then cooled on an ice bath
and BnBr (10.5 mL, 88.8 mmol) was added, followed
by Et4NI (50 mg). The stirred mixture was allowed to
slowly warm to room temperature over 5 h and excess
NaH was decomposed by dropwise addition of MeOH
(50 mL). The resulting solution was concentrated in
vacuo, diluted with CH2Cl2 (200 mL), washed with
H2O (3 · 70 mL) and dried with MgSO4. The crude
product was purified by column chromatography
tography (hexane–ethyl acetate, 4:1) gave the title com-
25
D
pound as a yellowish solid (850 mg, 86%); ½aꢂ = +145.0
(c 1.1, CHCl3); dH (CDCl3): 5.28–5.42 (7 · H-1); dC
(CDCl3): 11.2, 12.2 (SMe, a/b), 82.4 (C-1aa,b), 95.7
(6) (C-1b-g); m/z (MALDI-TOF) 2113.5 (100%
[M+Li]+).
4.12. Methyl a-D-glucopyranosyl-(1!4)-{a-D-glucopyr-
anosyl-(1!4)}5-1-thio-a,b-D-glucopyranoside 13
Acetylated methyl thiomaltoheptoside 12 (850 mg,
0.40 mmol) was dissolved in dry MeOH (10 mL) con-
taining a catalytic amount of sodium methoxide and
the mixture was stirred at room temperature until the
reaction was complete, as judged by TLC. H2O (5 mL)
was added, followed by Dowex AG-50 (H+) resin to
neutralise the mixture. Concentration in vacuo gave
the title compound (446 mg, 94%) as a solid; a:b ca.
1:2; dH (D2O): 1.93, 2.02 (3H, s, SMe a/b), 4.27 (d,
J1,2 9.9 Hz, H-1b), 5.14 (d, J1,2 4.1 Hz, H-1a), 5.21 (m,
H-1b-g); dC (D2O): 11.4, 12.2 (SMe a/b), 85.5 (C-1aa),
86.3 (C-1ab), 99.6–99.8 (C-1b-g); m/z (ES) 1205.5
(100% [M+Na]+), (ES) (Found: [M+NH4]+, 1200.4081.
C43H78O35SN requires 1200.4070).
(hexane–ethyl acetate, 9:1–7:3) to give the title com-
25
D
pound (3.63 g, 85%) as white solid; ½aꢂ = +67.2 (c
1.06, CHCl3); dH (CDCl3): 5.34 (d, J1,2 5.3 Hz, H-1aa),
5.54 (d, J1,2 3.5 Hz, H-1b/c,a/b), 5.56 (d, J1,2 3.5 Hz,
H-1b/c,a/b), 5.65 (d, J1,2 3.5 Hz, H-1b/c,a/b), 5.66 (d,
J1,2 3.8 Hz, H-1b/c,a/b), 5.68 (d, J1,2 3.5 Hz, H-1b/c,a/
b); dC (CDCl3): 12.2, 12.6 (SMe, a/b), 84.2 (C-1aa), 85.0
(C-1ab), 96.5, 96.8, 96.9, 97.0 (C-1b/c,a/b); m/z (ES)
1453.0 (20% [M+NH4]+), 180.9 (100, [Mꢀ1272.1]).
4.10. Tricosa-O-acetylmaltoheptaose, 11
The title compound was prepared according to the pro-
cedure described by Sakairi et al.13 Peracetylated b-
cyclodextrin (20 g, 9.91 mmol) was dissolved in solution
of Ac2O–H2SO4, (50:1, 120 mL). The mixture was
heated at ꢁ60 ꢁC for 20 h, poured into ice water
(200 mL) containing sodium acetate (12 g) and the
mixture was stirred overnight. Organic material was
extracted with CH2Cl2 (3 · 100 mL), washed with brine
(2 · 100 mL), saturated NaHCO3 solution (2 · 100 mL),
and water (1 · 100 mL) and dried over MgSO4. Concen-
tration in vacuo and purified by column chromato-
graphy (ethyl acetate–hexane, 9:1–1:0) gave the title
4.13. Methyl (2,3,4,6-tetra-O-benzyl-a-D-glucopyranosyl)-
(1!4)-{2,3,6-tri-O-benzyl-a-D-glucopyranosyl)-(1!4)}5-
2,3,6-tri-O-benzyl-1-thio-a,b-D-glucopyranoside 14
Methyl thiomaltoheptaoside 13 (446 mg, 0.37 mmol)
was dissolved in dry DMF (25 mL), NaH (33 mmol,
1.32 g of a 60% w/v suspension in mineral oil) was added
slowly to the reaction and mixed at room temperature
for half an hour. The mixture was then cooled on an
ice bath and BnBr (2.95 mL, 24.8 mmol) was added,
followed by Et4NI (12 mg) and imidazole (5 mg). The
stirred mixture was allowed to slowly warm to room
temperature over 20 h and excess NaH was decomposed
by dropwise addition of MeOH (10 mL). The resulting
solution was concentrated in vacuo, diluted with
CH2Cl2 (100 mL), washed with H2O (2 · 50 mL) and
dried with MgSO4. The crude product was purified by
column chromatography (toluene–ethyl acetate, 10:0–
compound as white solid (9.76 g, 46%); a:b ca. 8:1;
25
D
½aꢂ = +162.0 (c 1.15, CHCl3); dH (CDCl3): 4.85 (1H,
dd, J1,2 3.6 Hz, J2,3 10.1 Hz, H-2), 4.95 (1H, dd, J1,2
3.1 Hz, J2,3 10.1 Hz, H-2aa), 5.08 (1H, t, J3,4 ꢁ J4,5
9.5 Hz, H-4g), 5.52 (1H, t, J2,3 ꢁ J3,4 9.3 Hz, H-3aa),
5.76 (0.11H, J1,2 ꢁ 9 Hz, H-1ab), 6.24 (1H, d, J1,2
3.6 Hz, H-1aa) dC (CDCl3): 20.2–20.8 (CH3C@O),
61.3, 62.08, 62.3, 67.8, 68.3, 68.8, 69.0, 69.2, 69.7, 69.9,
70.1, 70.3, 70.4, 71.5, 71.6, 72.1, 72.3, 73.2, 76.7 (C-2
to C-6), 88.8 (C-1aa), 95.6, 95.6, 95.8 (C-1), 169.0,
169.5, 169.6, 169.8, 169.9, 170.4, 170.5 (2), 170.6,
170.7, 170.8 (CH3C@O); m/z (ES) 2141 (33%,
[M+Na]+).
9:1) to give the title compound as gum (943 mg, 80%);
25
D
a:b ca. 1:1.5; ½aꢂ = +69 (c 1.00, CHCl3); dH (CDCl3):
2.04 (s, SMea), 2.23 (s, SMeb), 5.33 (d, J1,2 5.3 Hz, H-
1aa), 5.52–5.70 (H-1a, H-1b-g); dC (CDCl3): 12.5
(SMe), 85.0 (C-1aa), 86.4 (C-1ab), 96.4–97.0 (C-1b-g);
m/z (MALDI-TOF): 3172.4 (100%, [M+Li]+).

484
L. Marmuse et al. / Tetrahedron: Asymmetry 16 (2005) 477–485
4.14. p-Methoxyphenyl (2,3,4,6-tetra-O-benzyl-a-D-gluco-
pyranosyl)-(1!4)-(2,3,6-tri-O-benzyl-a-D-glucopyranos-
yl)-(1!4)-2,3,6-tri-O-benzyl-D-glucopyranosyl)-(1!6)-
[(2,3-di-O-benzoyl-4,6-O-benzylidene-a,b-D-glucopyranos-
yl)-(1!4)-2,3-di-O-benzoyl-b-D-glucopyranoside 15
and H2O (2 · 40 mL) and dried over MgSO4. The crude
product was purified by two rounds of column chroma-
tography (hexane–ethyl acetate, 7:3) to give the title
compound as a white foam (162 mg, 36%); a:b ca.
3.7:1; dC (CDCl3): 55.5 (OMe), 96.2, 96.3, 97.0, 97.5
(C-1b, C-1a0-g0), 100.6 (C-1a), 101.3 (CH–Ph), 114.7,
119.0 (C6H4–OMe) 151.3, 155.8 (ArC, quat. from
C6H4–OMe); m/z (MALDI) 4092.9 (100%, [M+Na]+).
Further purification by column chromatography
(CH2Cl2–ethyl acetate, 99:1) afforded the pure a anomer
16a (16 mg, 4%) as a white solid; dH (CDCl3): 5.14 (1H,
d, J1,2 7.7 Hz, H-1a), 5.23 (1H, dd, J1,2 3.7 Hz, J2,3
10.8 Hz, H-2a0), 5.40 (1H, s, CH–Ph), 5.45 (1H, dd,
J1,2, J2,3 9.5 Hz, H-2a), 5.73 (1H, t, H-3), 5.94 (1H, t,
J2,3, J3,4 9.5 Hz, H-3a0), 6.75 (2H, d, JAB 9.0 Hz,
C6H4–OMe), 6.93 (2H, d, JAB, C6H4–OMe).
Glycosyl donor 10 (430 mg, 0.29 mmol) and glycosyl
acceptor 6 (200 mg, 0.21 mmol) were dissolved in dry
˚
Et2O–DCM (4:1) containing activated 4 A molecular
sieves (300 mg) and stirred for 90 min. The reaction mix-
ture was cooled to ꢀ60 ꢁC, and N-iodosuccinimide
(94 mg, 0.42 mmol) and TMSOTf (7.6 lL, 0.042 mmol,
10 mol% with respect to NIS) were added to the solu-
tion. The reaction was allowed to warm to ice bath tem-
perature and stirred for 8 h. The mixture was then
filtered through Celite, the filtrate was diluted with
CH2Cl2 (100 mL) and washed successively with NaS2O3
solution (3 · 30 mL), saturated NaHCO3 solution
(2 · 40 mL) and H2O (2 · 40 mL) and dried over
MgSO4. The crude product was purified by column
chromatography (hexane–ethyl acetate, 6:4) to give the
title compound as a white foam (283 mg, 57%), a:b ca.
3.5:1. Further purification with (CH2Cl2–ethyl acetate,
99:1) afforded the pure a anomer (107 mg, 21%) along
Acknowledgements
These studies were supported by the Weston Founda-
tion and the EPSRC. We thank Dr. Alan Haines
(UEA) for helpful discussions and the EPSRC Mass
Spectrometry Service Centre, University of Wales,
Swansea, for invaluable support.
with the pure b-anomer 15b (31 mg, 6%); Compound
25
D
15a: ½aꢂ = +66.8 (c 0.96, CHCl3); dH (CDCl3): 3.26–
4.17 (29H, m, OMe, sugar-H), 4.56–4.28 (19H, m, Ar,
H-6), 5.04 (1H, d, JAB 12 Hz, Ar), 5.07 (1H, d, J1,2
8.3 Hz, H-1a), 5.14–5.18 (2H, m, H-1a0, H-2a0), 5.32
(1H, s, CH–Ph), 5.39 (1H, t, J1,2, J2,3 8.3 Hz, H-2a),
5.58 (3H, m, H-1b, H-1b0-c0), 5.66 (1H, t, J2,3, J3,4
8.3 Hz, H-3a), 5.86 (1H, t, J2,3 ꢁ J3,4 9.9 Hz, H-3a0),
6.67 (2H, d, JAB 8.3 Hz, C6H4–OMe), 6.86 (2H, d, JAB
8.3 Hz, C6H4–OMe), 6.97–7.78 (75H, m, H-Ar); dC
(75 MHz, CDCl3): 55.4 (OMe), 96.3, 96.8, 97.3, 97.5
(C-1b, C-1a0-c0), 100.5 (C-1a), 101.2 (CH–Ph), 114.6,
118.9 (C6H4–OMe), 151.2, 155.7 (ArC, quat. from
C6H4–OMe); m/z (MALDI-TOF) 2362.9 ([M+Na]+);
Compound 15b: (31 mg, 6%); dH (CDCl3): 6.60 (2H, d,
JAB 12.0 Hz, C6H4–OMe), 6.81 (2H, d, JAB 12.0 Hz,
C6H4–OMe), 7.03–7.79 (H-Ar); dC (CDCl3): 104.5 (C-
1a0b), 101.4 (CH–Ph), 100.1 (C-1a), 96.8 (·2), 96.3 (C-
1b, C-1b0, C-1c0), 114.6, 118.7 (C6H4–OMe), 151.2,
155.7 (ArC, quat. from C6H4–OMe).
References
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4.15. p-Methoxyphenyl (2,3,4,6-tetra-O-benzyl-a-D-gluco-
pyranosyl)-(1!4)-{(2,3,6-tri-O-benzyl-a-D-glucopyranosyl)-
(1!4)}5-(2,3,6-tri-O-benzyl-D-glucopyranosyl)-(1!6)-
[(2,3-di-O-benzoyl-4,6-O-benzylidene-a,b-D-glucopyranos-
yl)-(1!4)-2,3-di-O-benzoyl-b-D-glucopyranoside 16
´
7. Corzana, F.; Motawia, M. S.; Herve du Penhoat, C.; van
den Berg, F.; Blennow, A.; Perez, S.; Engelsen, S. B.
J. Am. Chem. Soc. 2004, 126, 13144–13155.
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Glycosyl donor 14 (460 mg, 0.145 mmol) and glycosyl
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´
´
´
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