Glycosylations directed by the armed-disarmed effect with acceptors containing a single ester group

Article abstract of DOI:10.1002/ejoc.200700347

A selective glycosylation reaction controlled by the armed-disarmed effect is described by the use of phenyl thioglycosides. The donor thioglycoside is fully protected with benzyl ethers while the acceptor thioglycoside contains benzyl ethers at position

Full text of DOI:10.1002/ejoc.200700347

FULL PAPER
DOI: 10.1002/ejoc.200700347
Glycosylations Directed by the Armed-Disarmed Effect with Acceptors
Containing a Single Ester Group
Thomas H. Schmidt[a] and Robert Madsen*[a]
Keywords: Carbohydrates / Glycosylation / Protecting groups / Tandem reactions / Armed-disarmed effect
A selective glycosylation reaction controlled by the armed-
corresponding 1,4-linked disaccharides in good yield. These
disarmed effect is described by the use of phenyl thioglycos- disaccharides can act as glycosyl donors for an additional
ides. The donor thioglycoside is fully protected with benzyl
ethers while the acceptor thioglycoside contains benzyl
ethers at position 2 and 3 and a strongly electron-with-
drawing pentafluorobenzoate ester group at position 6. The
coupling can be performed with galactose, glucose, man-
nose, and phthalimide-protected glucosamine to afford the
coupling reaction in the same pot if another acceptor and
more promoter are added. In this way, two consecutive
glycosylations can be achieved to afford trisaccharides in one
operation.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2007)
design selective coupling reactions between more reactive
thioglycosides (serving as donors) and less reactive thiogly-
cosides with a free hydroxy group (serving as acceptors).[6]
Selective coupling reactions can also be achieved by con-
trolling the reactivity of the leaving group in the glycosyl
donor. Several leaving groups can be activated under condi-
tions where others are completely stable, which makes it
possible for the glycosyl component to serve either as a do-
nor or as an acceptor depending on the promoter.[7] Thio-
glycosides are a special case because their reactivity de-
pends on the steric bulk and the electronic properties of
the aglycon, which makes it possible to perform a selective
coupling reaction between two different thioglycosides.[8]
In the original work on the armed-disarmed effect the
donor glycoside was fully protected with ether groups while
the acceptor was protected with ester groups at all positions
but one.[4] Most importantly, the 2-position in the acceptor
always contained an ester group and this electron-with-
drawing group close to the anomeric center plays a key role
in lowering the reactivity of the acceptor. However, in sub-
sequent coupling reactions this ester group will create a 1,2-
trans linkage due to neighboring group participation. In our
recent syntheses of pectic oligosaccharides we needed a
number of galactans with a 1,2-cis linkage,[9] and we de-
cided to investigate whether a single ester group at the 6-
position would be sufficient to disarm a glycosyl acceptor.
Indeed, we were able to show that coupling between 1 and
2 could be performed in 52% yield to give disaccharide 3
as a 6:1 α/β mixture[9b] (Scheme 1, PFBz = pentafluoroben-
zoyl). Disaccharide 3 was used in further coupling reactions
to afford the 1,2-cis linked galactans.
Introduction
The role of oligosaccharides in biological processes has
been studied intensively over the past two decades.[1] These
studies have created an increasing demand for synthetic oli-
gosaccharides and have stimulated research efforts directed
toward the development of more efficient syntheses. A large
number of glycosyl donors have been exploited[2] together
with a variety of glycosylation techniques and strategies.[3]
Although very powerful coupling methods have been devel-
oped, oligosaccharide synthesis is still plagued by multiple
protecting group manipulations which are often necessary
in order to control the regio- and diastereoselectivity in the
glycosylation reactions.
In 1988, Fraser-Reid and co-workers coined the term
“armed-disarmed effect” to describe the differences in reac-
tivity between glycosyl donors depending on their protect-
ing groups.[4] Ether-protected glycosyl donors are more re-
active (armed) than ester-protected donors (disarmed) and
a selective coupling can be achieved between an armed do-
nor and a disarmed counterpart if the latter contains a free
hydroxy group. The concept was initially established with
n-pentenyl glycosides and later demonstrated with other
glycosyl donors.[5] In 1999, the armed-disarmed principle
was further developed by Wong and co-workers who de-
scribed a “programmable one-pot synthesis” of smaller oli-
gosaccharides.[6] The reactivity of a large number of tolyl
thioglycosides was measured and these data were used to
[a] Center for Sustainable and Green Chemistry, Department of
Chemistry, Building 201, Technical University of Denmark,
2800 Lyngby, Denmark
Herein, this selective glycosylation reaction will be fur-
ther explored with a series of phenyl thioglycosides. Perben-
zylated phenyl thioglycosides will serve as donors and cou-
Fax: +45-4593-3968
E-mail: rm@kemi.dtu.dk
Eur. J. Org. Chem. 2007, 3935–3941
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3935

T. H. Schmidt, R. Madsen
FULL PAPER
(short “ether” in the sequel) as the solvent. Notably, when
the solvent was changed to dichloromethane, the yield in
the last coupling fell to 56%. In all cases, only the α-anomer
was observed at the new glycosidic linkage. However, some
anomerisation of the thiophenyl linkage took place in the
coupling with 7. It is known that thioglycosides can un-
dergo this epimerisation in the presence of an electrophile
to form the more stable α-anomer.[12] The anomeric config-
urations were determined from the JCH coupling constants
Scheme 1. Reagents and conditions: NIS, TESOTf, CH2Cl2,
–20 °C.[9b]
pled to the 4-position in phenyl thioglycosides which con-
tain a single ester group at position 6 and ether groups at
postion 2 and 3.
Results and Discussion
Thioglycosides are very useful glycosyl donors and have
been widely employed in oligosaccharide synthesis.[10]
Phenyl thioglycosides are easily prepared from the corre-
sponding peracetylated monosaccharides. Reaction with
thiophenol and boron trifluoride etherate in dichlorometh-
ane installs the thiophenyl group at the anomeric center in
high yield and with complete 1,2-trans selectivity directed
by the neighboring acetoxy group.[11] Subsequent deacety-
lation and protection then gives rise to a range of thioglyco-
sides which can serve as donors or acceptors in the selective
coupling reactions. A majority of the prepared compounds
turned out to be crystalline which further facilitated their
synthesis. It was decided to investigate thioglycosides de-
rived from -galactose, -glucose, -mannose, and phthal-
imide-protected -glucosamine. Galactose was chosen for
the exploratory studies because this monosaccharide was
also used in our earlier studies. Three galactosides 5–7 con-
taining different ester groups at the 6-position were pre-
pared and submitted to the coupling with the perbenzylated
galactoside 4 (Scheme 2). The glycosylation reaction re-
quires a strongly electrophilic promoter system, and it was
soon discovered that NIS/TESOTf gave the best results
while the weaker electrophiles DMTST and MeOTf reacted
sluggishly and gave lower yields. The glycosylations were
performed with 1.2 equiv. of the donor, 1.3 equiv. of NIS,
and 0.2 equiv. of TESOTf at –20 °C. Under these condi-
tions coupling between 4 and acetyl-protected 5 produced
the desired disaccharide 8 in 32% yield. The yield increased
to 43% when benzoyl-protected 6 was used in the coupling.
In both cases, smaller amounts of byproducts were ob-
served by TLC but were not further characterised. Fortu-
nately, when the ester group was changed to the more elec-
tron-withdrawing pentafluorobenzoyl group, the yield of
the cross-coupled product improved to 67%. This is in ac-
cordance with our earlier observations where the coupling
with the pentafluorobenzoyl group gave a significantly
higher yield than with the acetyl and the benzoyl group.[9b]
The three glycosylations were performed with diethyl ether Scheme 2. Reagents and conditions: NIS, TESOTf, Et2O, –20 °C.
3936 Eur. J. Org. Chem. 2007, 3935–3941
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© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Selective Glycosylations
FULL PAPER
of the anomeric carbons. For the α-anomers the JC–1,H–1
value was measured to about 170 Hz while the value for the
β-anomer was around 160 Hz.[13]
To further explore the use of a single ester group to dis-
arm the glycosyl acceptor, the selective coupling was also
studied with glucose, mannose and glucosamine
(Scheme 2). In these cases, only the pentafluorobenzoyl
group was employed for protection of the acceptor. With
glucose, the reaction between 11 and 12 furnished the disac-
charide 13 in 65% yield when ether was used as the solvent.
In dichloromethane the yield was only 42% while the coup-
ling in acetonitrile gave 33% yield. Surprisingly, a 1:1 α/β
mixture at the newly generated glycosidic linkage was ob-
tained in all three solvents even though ether is supposed
to favour the α-product and acetonitrile the β-product.[14]
In this case, no epimerisation was observed around the thi-
ophenyl linkage. With mannose, coupling between 14 and
15 gave disaccharide 16 in 68% yield when ether was used
as the solvent while the yield dropped to 57% in dichloro-
methane. With phthalimide-protected glucosamine, reac-
tion between 17 and 18 gave the chitibiose-derivative 19 in
56% yield with ether as the solvent and 45% yield with
dichloromethane as the solvent. These results clearly show
that the preferred solvent is ether which is known to de-
crease the rate of a glycosylation as compared to dichloro-
methane.[14]
Following the successful synthesis of several disaccha-
rides by the selective coupling it was decided to extend the
investigation to the synthesis of trisaccharides. First, it was
studied whether a disaccharide could serve as the donor.
Thus, dimannan 16 was converted into the corresponding
perbenzylated compound 20 (Scheme 3). Subsequent coup-
ling with acceptor 15 gave trimannan 21 in 60% yield. The
reaction was carried out in ether and other solvents were
not investigated in this case.
Another approach to trisaccharides would involve two
consecutive glycosylations with monosaccharides in the
same pot.[15] Therefore, monosaccharides 14 and 15 were
mixed in ether at –20 °C followed by addition of NIS and
TESOTf. After 35 min TLC showed the formation of disac-
charide 16 which was not isolated. Instead, monosaccharide
22 and more NIS were added and the mixture was stirred
at –20 °C for an additional 40 min. This resulted in triman-
nan 23 in 49% yield. It was also attempted to form the
trisaccharide by mixing the three monosaccharides 14, 15,
and 22 in the same flask followed by addition of excess
NIS/TESOTf. However, only a very small amount of tri-
mannan 23 was formed in this case while the main product
resulted from a coupling between 14 and 22. This disaccha-
ride was isolated in 55% yield which indicates that triben-
zoyl mannoside 22 is more reactive as an acceptor than
pentafluorobenzoyl mannoside 15.
Scheme 3. Reagents and conditions: NIS, TESOTf, Et2O, –20 °C.
sponding trigalactan increased to 61%. Again, it was at-
tempted to form the trisaccharide by reacting 4, 7, and 26
at the same time. However, this experiment gave the same
result as observed with mannose and the main product was
a disaccharide from coupling between 4 and 26. As a result,
the step-wise addition procedure is necessary in order to
achieve two glycosylations in the same pot.
Conclusions
In summary, we have further developed a selective glyco-
The same experiments were also performed with galac- sylation reaction based on the armed-disarmed effect. Two
tose. Monosaccharides 4 and 7 were reacted in ether for phenyl thioglycosides can be coupled in good yield when
10 min followed by addition of 24 and more NIS. This gave the reactivity of the acceptor is decreased by a single penta-
the trigalactan 25 in 52% yield with a 1,2-cis linkage at the fluorobenzoate ester at the 6-position. An additional glyco-
two new glycosidic bonds. When the tribenzoyl galactoside sylation reaction can be performed in the same pot if an-
26 was added to the reaction mixture the yield of the corre- other acceptor and more promoter are added to the reac-
Eur. J. Org. Chem. 2007, 3935–3941
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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3937

T. H. Schmidt, R. Madsen
Phenyl 2,3-Di-O-benzyl-6-O-pentafluorobenzoyl-1-thio-β- -galacto-
FULL PAPER
D
tion mixture. This method gives easy access to a number of
useful di- and trisaccharide building blocks for oligosaccha-
ride synthesis.
pyranoside (7): To an ice-cooled solution of phenyl 2,3-di-O-benzyl-
1-thio-β--galactopyranoside[17] (5.00 g, 11.0 mmol) and Et3N
(2.17 mL, 15.6 mmol) in CH2Cl2 (25 mL) was added pentafluo-
robenzoyl chloride (1.64 mL, 11.4 mmol) in a dropwise fashion
over 45 min. The mixture was stirred for 1 h at room temperature
and then washed with 0.1  HCl (2ϫ20 mL), dried (MgSO4), and
concentrated to afford a crystalline residue, which was recrystal-
lised from heptane/EtOAc to give 4.98 g (70%) of 7. Rf = 0.26
(heptane/EtOAc, 4:1). M.p. 152–153 °C. [α]2D0 = +5.0 (c = 1.0,
Experimental Section
General: CH2Cl2 was dried by distillation from CaH2 while diethyl
ether was dried by distillation from sodium/benzophenone. NIS
was recrystallised from dioxane/CCl4. Reactions were conducted
under nitrogen when anhydrous solvents were used. All reactions
were monitored by TLC using aluminium plates precoated with
silica gel 60. Compounds were visualized by dipping in a solution
of (NH4)6Mo7O24·4H2O (25 g/L) and Ce(SO4)2 (10 g/L) in 10%
aqueous H2SO4 followed by heating. Melting points are uncor-
rected. Flash column chromatography was performed with E.
Merck silica gel 60 (particle size 0.040–0.063 mm). Optical rota-
tions were measured with a Perkin–Elmer 241 polarimeter while IR
spectra were recorded with a Perkin–Elmer 1720 Infrared Fourier
Transform spectrometer. NMR spectra were recorded with a Var-
ian Mercury 300 instrument. Me4Si was used as the internal stan-
CHCl ). IR (KBr): ν = 3036, 1733, 1497, 1009, 746 cm–1. 1H NMR
˜
3
(300 MHz, CDCl3): δ = 7.56–7.21 (m, 15 H), 4.83 (d, J = 10.3 Hz,
1 H), 4.72 (d, J = 10.3 Hz, 1 H), 4.69–4.64 (m, 3 H), 4.61 (d, J =
9.7 Hz, 1 H), 4.54 (dd, J = 4.8, 11.6 Hz, 1 H) 4.02 (d, J = 3.0 Hz,
1 H), 3.75–3.71 (m, 2 H), 3.61 (dd, J = 3.2, 8.9 Hz, 1 H), 2.49 (br.
s, 1 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 158.83, 138.09,
137.48, 133.70, 132.05–127.61 (15 C), 88.01, 82.12, 76.96, 75.96,
75.40, 72.66, 66.84, 65.53 ppm. C33H27F5O6S (646.6): calcd. C
61.30, H 4.21, F 14.69, S 4.96; found C 61.08, H 4.13, F 14.78, S
4.74.
General Procedure for Glycosylation Reactions: A mixture of the
perbenzylated donor (0.93 mmol) and the ester-protected acceptor
(0.77 mmol) was dried azeotropically with toluene and stored un-
der high vacuum for 1 h. The mixture was dissolved in anhydrous
Et2O (15 mL) under a nitrogen atmosphere, cooled to –20 °C, fol-
lowed by addition of NIS (0.23 g, 1.02 mmol) and TESOTf
(0.04 mL, 0.18 mmol). The dark red solution was stirred at –20 °C
until TLC revealed full conversion of the donor (10–45 min). The
reaction was quenched with Et3N, diluted with CH2Cl2 (10 mL),
washed with 10% aqueous Na2S2O3 (2ϫ20 mL) and saturated
aqueous NaHCO3 (2ϫ20 mL). The organic phase was dried
(MgSO4) and concentrated and the residue purified by flash
chromatography.
1
dard in H NMR while CDCl3 (δ = 77.16 ppm) served as the in-
ternal standard in 13C NMR spectroscopy. Microanalyses were ob-
tained at the Microanalytical Laboratory, University of Vienna
while high-resolution mass spectra were recorded at the Depart-
ment of Physics and Chemistry, University of Southern Denmark.
The glycosyl donors 4, 11, 14, and 17 were prepared according to
literature procedures.[16]
Phenyl
6-O-Acetyl-2,3-di-O-benzyl-1-thio-β-D-galactopyranoside
(5): To an ice-cooled solution of phenyl 2,3-di-O-benzyl-1-thio-β--
galactopyranoside[17] (1.50 g, 3.31 mmol) in CH2Cl2 (12 mL) were
added Et3N (0.65 mL, 4.66 mmol) and Ac2O (0.33 mL,
3.49 mmol). The mixture was stirred at 5 °C for 18 h and then
washed with 0.1  HCl (2ϫ20 mL), dried (MgSO4), and concen-
trated to afford a crystalline residue, which was recrystallised from
heptane/EtOAc to give 1.39 g (85%) of 5. Rf = 0.17 (heptane/
Phenyl
2,3,4,6-Tetra-O-benzyl-α-
D-galactopyranosyl-(1Ǟ4)-6-O-
acetyl-2,3-di-O-benzyl-1-thio-β-D-galactopyranoside (8): The coup-
ling between 4 and 5 was performed according to the general pro-
cedure and stopped after 20 min to afford 32% yield of 8. Rf =
0.18 (heptane/EtOAc, 4:1). [α]2D0 = +8.1 (c = 1.0, CHCl3). IR (KBr):
EtOAc, 7:3). M.p. 135–137 °C (heptane/EtOAc). [α]2D0 = +8.1 (c =
1.0, CHCl ). IR (KBr): ν = 1717, 1275, 1090, 734 cm–1. H NMR
1
˜
3
ν = 3030, 1709, 1454, 1098, 698 cm–1. 1H NMR (300 MHz,
˜
(300 MHz, CDCl3): δ = 7.56–7.21 (m, 15 H), 4.85–4.70 (m, 4 H),
4.61 (d, J = 9.8 Hz, 1 H), 4.36–4.32 (m, 2 H), 3.98 (d, J = 3.2 Hz,
1 H), 3.73 (t, J = 9.2 Hz, 1 H), 3.64 (d, J = 5.6 Hz, 1 H), 3.58 (dd,
J = 3.2, 8.9 Hz, 1 H), 2.42 (br. s, 1 H), 2.06 (s, 3 H) ppm. 13C NMR
(75 MHz, CDCl3): δ = 170.94, 138.09, 137.53, 133.86, 131.95–
127.54 (15 C), 87.68, 82.30, 76.95, 75.88, 75.70, 72.45, 66.73, 63.51,
20.99 ppm. C28H30O6S (494.6): calcd. C 67.99, H 6.11, S 6.48;
found C 67.41, H 6.52, S 6.09.
CDCl3): δ = 7.51–7.19 (m, 35 H), 5.72 (d, J = 5.2 Hz, 1 H), 4.91
(d, J = 11.2 Hz, 1 H), 4.86–4.00 (m, 20 H), 3.89 (dd, J = 2.5,
10.2 Hz, 1 H), 3.72 (dd, J = 2.6, 9.9 Hz, 1 H), 3.52 (t, J = 7.9 Hz,
1 H), 3.23 (dd, J = 4.8, 8.2 Hz, 1 H), 1.91 (s, 3 H) ppm. 13C NMR
(75 MHz, CDCl3): δ = 170.51, 138.95, 138.81, 138.66, 138.31,
138.08, 138.00, 134.35, 131.74–127.10 (35 C), 100.55 (d, J =
171.1 Hz), 86.90 (d, J = 158.9 Hz), 79.47, 77.95, 76.27, 75.74, 75.22,
74.91, 74.58, 74.17, 73.28, 73.00, 72.51, 72.43, 69.82, 69.61, 67.90,
62.49, 20.88 ppm. C62H64O11S (1017.3): calcd. C 73.21, H 6.34, S
3.15; found C 72.81, H 6.37, S 2.47.
Phenyl 6-O-Benzoyl-2,3-di-O-benzyl-1-thio-β-
D-galactopyranoside
(6): Phenyl
2,3-di-O-benzyl-1-thio-β--galactopyranoside[17]
(1.50 g, 3.31 mmol) was treated with BzCl (0.40 mL, 3.44 mmol) as
described above to give the crude product as a solid, which was
recrystallised from heptane/EtOAc to furnish 1.69 g (92%) of 6.
Rf = 0.28 (heptane/EtOAc, 7:3). M.p. 161–164 °C (heptane/EtOAc)
(ref.[18] M.p. 151.5–152 °C). [α]2D0 = –1.7 (c = 1.0, CHCl3) [ref.[18]
Phenyl
2,3,4,6-Tetra-O-benzyl-α-D-galactopyranosyl-(1Ǟ4)-6-O-
benzoyl-2,3-di-O-benzyl-1-thio-β-
D-galactopyranoside (9): The coup-
ling between 4 and 6 was performed according to the general pro-
cedure and stopped after 20 min to afford 43% yield of 9. Rf =
0.24 (heptane/EtOAc, 4:1). [α]2D0 = –1.7 (c = 1.0, CHCl3). IR (KBr):
[α]2D0 = –3.8 (c = 1.1, CHCl )]. IR (KBr): ν = 1709, 1285, 1119, 738
˜
3
cm–1. H NMR (300 MHz, CDCl3): δ = 8.04–7.09 (m, 20 H), 4.81 ν = 3030, 1709, 1453, 1097, 697 cm–1. 1H NMR (300 MHz,
1
˜
(d, J = 10.3 Hz, 1 H), 4.70 (d, J = 10.3 Hz, 1 H), 4.67–4.65 (m, 2
CDCl3): δ = 8.00–7.07 (m, 40 H), 5.03 (d, J = 3.5 Hz, 1 H), 4.93
H), 4.60 (d, J = 9.8 Hz, 1 H), 4.57–4.48 (m, 2 H), 4.04 (d, J = (d, J = 11.7 Hz, 1 H), 4.92 (d, J = 11.7 Hz, 1 H), 4.81–4.52 (m, 12
3.2 Hz, 1 H), 3.80–3.73 (m, 2 H), 3.61 (dd, J = 3.2, 8.9 Hz, 1 H), H), 4.35 (dd, J = 5.2, 8.4 Hz, 1 H), 4.17–4.11 (m, 4 H), 4.04 (dd,
2.54 (br. s, 1 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 166.47, J = 2.4, 9.9 Hz, 1 H), 3.81–3.70 (m, 2 H), 3.57–3.46 (m, 2 H), 3.27
138.11, 137.57, 134.16, 133.31, 131.65–127.40 (20 C), 87.98, 82.30,
77.14, 75.96, 75.88, 72.59, 67.00, 64.10 ppm. C33H32O6S (556.7):
calcd. C 71.20, H 5.79, S 5.76; found C 70.93, H 5.91, S 5.48.
(dd, J = 4.8, 8.3 Hz, 1 H) ppm. 13C NMR (75 MHz, CDCl3): δ =
166.13, 138.87, 138.78, 138.47, 138.29, 138.26, 137.96, 134.04,
133.30, 131.66–127.33 (40 C), 100.80 (d, J = 171.0 Hz), 87.53 (d, J
3938
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© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2007, 3935–3941

Selective Glycosylations
FULL PAPER
= 159.2 Hz), 82.60, 79.38, 76.60, 76.17, 75.98, 75.66, 75.31, 74.97,
74.36, 74.25, 73.30, 72.60, 72.12, 69.56, 67.98, 62.79 ppm.
C67H66O11S (1079.3): calcd. C 74.56, H 6.16, S 2.97; found C 74.64,
H 6.65, S 2.76.
71.73, 68.86, 68.27, 65.73, 65.70, 64.48, 64.45 ppm. C67H61F5O11S
(1169.3): calcd. C 68.82, H 5.26, F 8.12, S 2.74; found C 68.98, H
5.28, F 8.09, S 2.61.
Phenyl 2,3-Di-O-benzyl-6-O-pentafluorobenzoyl-1-thio-α-D-manno-
Phenyl
2,3,4,6-Tetra-O-benzyl-α-
D-galactopyranosyl-(1Ǟ4)-2,3-
pyranoside (15): Phenyl 2,3-di-O-benzyl-1-thio-α--mannopyrano-
side[20] (3.00 g, 6.63 mmol) was treated with pentafluorobenzoyl
chloride (1.01 mL, 7.01 mmol) as described above for 7. The crude
product was purified by flash chromatography (heptane/EtOAc,
4:1) to give 2.98 g (70 %) of 15 as a solid. Rf = 0.26 (heptane/
di-O-benzyl-6-O-pentafluorobenzoyl-1-thio-α/β-
D
-galactopyranoside
(10α and 10β): The coupling between 4 and 7 was performed ac-
cording to the general procedure and stopped after 45 min to give
67% yield of 10 as a 4:3 α/β mixture.
EtOAc, 4:1). M.p. 116–118 °C (heptane/EtOAc). [α]2D0 = +40.4 (c =
For 10α: Rf = 0.15 (heptane/EtOAc, 17:3). 1H NMR (300 MHz,
CDCl3): δ = 7.34–7.04 (m, 35 H), 5.64 (d, J = 6.8 Hz, 1 H), 4.83–
4.45 (m, 13 H), 4.34 (t, J = 5.9 Hz, 1 H), 4.23 (dd, J = 3.9, 7.1 Hz,
1 H), 4.13–3.93 (m, 6 H), 3.81 (dd, J = 2.4, 10.3 Hz, 1 H), 3.63
(dd, J = 2.6, 9.8 Hz, 1 H), 3.45 (t, J = 8.6 Hz, 1 H), 3.18 (dd, J =
3.7, 7.2 Hz, 1 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 138.94,
138.78, 138.64, 138.29, 138.11, 137.98, 134.37, 131.21–126.85 (35
C), 100.75 (JC,H = 170.4 Hz), 86.79 (JC,H = 170.2 Hz), 79.57, 77.77,
76.43, 76.22, 75.18, 75.02, 74.56, 74.53, 73.38, 73.16, 72.66, 72.44,
69.78, 69.65, 67.98, 64.45 ppm. HRMS: calcd. for C67H65F5NO11S
[M + NH4]+ 1186.4194; found 1186.4185.
For 10β: Rf = 0.18 (heptane/EtOAc, 17:3). [α]2D0 = +34.6 (c = 1.0,
CHCl3). 1H NMR (300 MHz, CDCl3): δ = 7.50–7.02 (m, 35 H),
4.85–4.79 (m, 2 H), 4.69–4.29 (m, 12 H), 4.17 (dd, J = 5.1, 8.4 Hz,
1 H), 4.08–3.87 (m, 6 H), 3.63 (t, J = 9.4 Hz, 1 H), 3.55 (t, J =
6.2 Hz, 1 H), 3.42 (t, J = 8.6 Hz, 1 H), 3.36 (dd, J = 1.9, 9.2 Hz, 1
H), 3.18 (dd, J = 5.3, 7.9 Hz, 1 H) ppm. 13C NMR (75 MHz,
CDCl3): δ = 138.90, 138.77, 138.53, 138.28, 138.28, 138.00, 133.67,
1
1.0, CHCl ). IR (KBr): ν = 3069, 1742, 1497, 1010, 838 cm–1. H
˜
3
NMR (300 MHz, CDCl3): δ = 7.45–7.23 (m, 15 H), 5.68 (d, J =
1.7 Hz, 1 H), 4.75–4.50 (m, 6 H), 4.42 (ddd, J = 2.4, 5.3, 9.4 Hz, 1
H), 4.15 (t, J = 9.6 Hz, 1 H), 4.08 (dd, J = 1.7, 2.9 Hz, 1 H), 3.73
(dd, J = 2.9, 9.4 Hz, 1 H), 2.61 (br. s, 1 H) ppm. 13C NMR
(75 MHz, CDCl3): δ = 159.12, 137.64, 137.58, 134.08, 131.32–
127.62 (15 C), 85.79, 79.54, 75.37, 72.12, 71.78, 71.25, 66.64, 65.79
ppm. C33H27F5O6S (646.6): calcd. C 61.30, H 4.21, F 14.69, S 4.96;
found C 61.25, H 4.29, F 14.59, S 4.86.
Phenyl 2,3,4,6-Tetra-O-benzyl-α-
O-benzyl-6-O-pentafluorobenzoyl-1-thio-α-
D
-mannopyranosyl-(1Ǟ4)-2,3-di-
-mannopyranoside (16):
D
The coupling between 14 and 15 was performed according to the
general procedure and stopped after 35 min to afford 68% yield of
16. Rf = 0.25 (heptane/EtOAc, 17:3). [α]2D0 = +60.9 (c = 1.0, CHCl3).
IR (KBr): ν = 3063, 1740, 1498, 1104, 738 cm–1 1H NMR
.
˜
(300 MHz, CDCl3): δ = 7.30–7.02 (m, 35 H), 5.47 (d, J = 1.6 Hz,
1 H), 5.17 (d, J = 1.8 Hz, 1 H), 4.71 (d, J = 10.7 Hz, 1 H), 4.48–
4.31 (m, 10 H), 4.24–4.16 (m, 4 H), 4.07 (t, J = 9.3 Hz, 1 H), 3.94
(t, J = 9.2 Hz, 1 H), 3.88–3.84 (m, 1 H), 3.77 (dd, J = 1.7, 9.3 Hz,
1 H), 3.71–3.52 (m, 5 H) ppm. 13C NMR (75 MHz, CDCl3): δ =
138.78, 138.78, 138.57, 138.51, 137.70, 137.70, 134.01, 131.33–
127.30 (35 C), 100.83 (JC,H = 171.0 Hz), 85.41 (JC,H = 169.0 Hz),
79.80, 79.79, 75.79, 75.79, 75.29, 75.17, 74.67, 73.33, 73.26, 72.21,
132.11–127.40 (35 C), 100.75 (JC,H = 171.0 Hz), 87.58 (JC,H
=
160.4 Hz), 82.29, 80.59, 79.43, 79.41, 76.39, 75.92, 75.68, 75.00,
74.48, 74.39, 73.38, 72.60, 72.19, 69.75, 68.10, 64.55 ppm. HRMS:
calcd. for C67H65F5NO11S [M + NH4]+ 1186.4194; found
1186.4186.
Phenyl 2,3-Di-O-benzyl-6-O-pentafluorobenzoyl-1-thio-β-D-gluco-
72.10, 71.99, 71.42, 70.34, 68.91, 65.84 ppm. C67H61F5O11
S
pyranoside (12): Phenyl 2,3-di-O-benzyl-1-thio-β--glucopyrano-
side[19] (10.6 g, 23.4 mmol) was treated with pentafluorobenzoyl
chloride (3.6 mL, 25.0 mmol) as described above for 7. The crude
product was crystallised from heptane/EtOAc to afford 14.2 g
(94%) of 12. Rf = 0.26 (heptane/EtOAc, 4:1). M.p. 119–120 °C
(1169.3): calcd. C 68.82, H 5.26, S 2.74; found C 68.62, H 5.44, S
2.56.
Phenyl 3-O-Benzyl-2-deoxy-6-O-pentafluorobenzoyl-2-phthalimido-
1-thio-β-D-glucopyranoside (18): Phenyl 3-O-benzyl-2-deoxy-2-
phthalimido-1-thio-β--glucopyranoside[21] (5.00 g, 10.2 mmol)
was treated with pentafluorobenzoyl chloride (1.55 mL, 10.8 mmol)
as described above for 7. The crude product was purified by flash
chromatography (heptane/EtOAc, 7:3) to afford 5.09 g (73%) of 18
as a solid. Rf = 0.23 (heptane/EtOAc, 7:3). M.p. 149–151 °C (hep-
(heptane/EtOAc). [α]2D0 = –32.3 (c = 1.0, CHCl ). IR (KBr): ν =
˜
3
3031, 1734, 1494, 1008, 741 cm–1. H NMR (300 MHz, CDCl3): δ
1
= 7.55–7.20 (m, 15 H), 4.96 (d, J = 11.5 Hz, 1 H), 4.95 (d, J =
11.2 Hz, 1 H), 4.74 (d, J = 8.3 Hz, 1 H), 4.72–4.66 (m, 3 H), 4.57
(dd, J = 4.1, 12.5 Hz, 1 H), 3.57–3.49 (m, 4 H), 2.38 (s, 1 H) ppm.
13C NMR (75 MHz, CDCl3): δ = 138.11, 137.73, 133.29, 132.13–
127.74 (15 C), 87.88, 85.82, 80.48, 76.91, 75.58, 75.45, 69.59, 65.40
ppm. C33H27F5O6S (646.6): calcd. C 61.30, H 4.21, F 14.69, S 4.96;
found C 61.12, H 4.13, F 14.52, S 4.74.
tane/EtOAc). [α]2D0 = +40.4 (c = 1.0, CHCl ). IR (KBr): ν = 3063,
˜
3
1751, 1764, 1715, 1389, 1087, 719 cm–1 1H NMR (300 MHz,
.
CDCl3): δ = 7.83–7.70 (m, 4 H), 7.34–6.95 (m, 10 H), 5.55 (d, J =
10.0 Hz, 1 H), 4.76–4.62 (m, 3 H), 4.51 (d, J = 12.1 Hz, 1 H), 4.32–
4.19 (m, 2 H), 3.79 (ddd, J = 2.2, 4.9, 9.9 Hz, 1 H), 3.69 (dd, J =
7.9, 9.9 Hz, 1 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 168.41,
167.36, 137.79, 134.29–123.56 (17 C), 83.76, 80.23, 77.38, 74.94,
71.50, 65.39, 54.42 ppm. C34H24F5NO7S (685.6): calcd. C 59.56, H
3.53, F 13.86, N 2.04, S 4.68; found C 59.69, H 3.59, F 13.83, N
2.08, S 4.64.
Phenyl 2,3,4,6-Tetra-O-benzyl-
benzyl-6-O-pentafluorobenzoyl-1-thio-β-
D
-glucopyranosyl-(1Ǟ4)-2,3-di-O-
-glucopyranoside (13): The
D
coupling between 11 and 12 was performed according to the gene-
ral procedure and stopped after 10 min to give 65% yield of 13 as
a 1:1 α/β mixture which could not be separated. Rf = 0.18 (heptane/
1
EtOAc, 9:1). IR (KBr): ν = 3063, 1742, 1498, 1071, 737 cm–1. H
˜
NMR (300 MHz, CDCl3): δ = 7.53–7.10 (m, 70 H), 5.43 (d, J =
Phenyl 3,4,6-Tri-O-benzyl-2-deoxy-2-phthalimido-β-D-glucopyranos-
3.7 Hz, 1 H), 5.14 (d, J = 11.2 Hz, 1 H), 4.98 (d, J = 11.7 Hz, 1 H), yl-(1Ǟ4)-3-O-benzyl-2-deoxy-6-O-pentafluorobenzoyl-2-phthal-
4.91–4.34 (m, 29 H), 3.98–3.39 (m, 20 H) ppm. 13C NMR (75 MHz,
imido-1-thio-β- -glucopyranoside (19): The coupling between 17
D
CDCl3): δ = 138.95, 138.95, 138.76, 138.57, 138.51, 138.36, 138.26, and 18 was performed according to the general procedure and
138.08, 138.08, 138.08, 137.83, 137.79, 133.26, 133.06, 132.69– stopped after 15 min to afford 56% yield of 19. Rf = 0.12 (heptane/
126.59 (70 C), 102.91 (JC,H = 159.8 Hz), 98.57 (JC,H = 169.6 Hz), EtOAc, 17:3). [α]2D0 = +25.4 (c = 1.0, CHCl ). IR (KBr): ν = 3062,
˜
3
87.51 (JC,H = 160.1 Hz, 2 C), 86.02, 85.08, 84.54, 82.84, 81.93, 1777, 1744, 1716, 1387, 1084, 721 cm–1. 1H NMR (300 MHz,
80.81, 80.18, 79.20, 77.90, 77.70, 76.93, 76.56, 75.94, 75.84, 75.71,
75.63, 75.58, 75.48, 75.33, 75.23, 75.12, 74.79, 73.63, 73.58, 73.36,
CDCl3): δ = 8.03–7.53 (m, 8 H), 7.40–6.74 (m, 25 H), 5.35 (d, J =
9.9 Hz, 1 H), 5.33 (d, J = 7.9 Hz, 1 H), 4.91 (d, J = 13.0 Hz, 1 H),
Eur. J. Org. Chem. 2007, 3935–3941
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
3939

T. H. Schmidt, R. Madsen
EtOAc, 7:3). [α]2D0 = +7.1 (c = 1.0, CHCl ). IR (KBr): ν = 3064,
FULL PAPER
4.81–4.10 (m, 12 H), 4.02 (dd, J = 8.6, 9.4 Hz, 1 H), 3.93–3.70 (m,
4 H), 3.58–3.54 (m, 2 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 1727, 1498, 1070, 712 cm–1. 1H NMR (300 MHz, CDCl3): δ = 8.06–
167.89 (2 C), 167.73 (2 C), 138.51, 138.13, 137.97, 137.94, 133.05– 6.81 (m, 45 H), 5.78 (dd, J = 3.3, 9.6 Hz, 1 H), 5.57 (dd, J = 1.8,
123.36 (38 C), 97.73 (JC,H = 160.6 Hz), 83.54 (JC,H = 159.2 Hz), 3.2 Hz, 1 H), 4.92 (dd, J = 1.9, 11.9 Hz, 1 H), 4.88 (d, J = 1.8 Hz,
˜
3
80.27, 79.53, 78.97, 78.24, 75.19, 75.08, 75.03, 74.95, 73.40, 71.47,
68.22, 64.11, 56.63, 54.69 ppm. C69H55F5N2O13S (1247.3): calcd. C
66.45, H 4.44, F 7.62, N 2.25, S 2.57; found C 66.39, H 4.62, F
7.88, N 2.20, S 2.46.
1 H), 4.79 (d, J = 10.7 Hz, 1 H), 4.73 (d, J = 11.9 Hz, 1 H), 4.65–
4.31 (m, 9 H), 4.31–4.25 (m, 3 H), 4.21–3.96 (m, 6 H), 3.87 (d, J
= 4.5 Hz, 1 H), 3.85 (dd, J = 2.8, 9.4 Hz, 1 H), 3.78–3.69 (m, 5 H),
3.58 (dd, J = 3.7, 12.3 Hz, 1 H), 3.51 (t, J = 2.4 Hz, 1 H), 3.47 (s,
3 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 165.94, 165.36, 165.23,
138.84, 138.74, 138.52, 138.50, 137.82, 137.76, 133.82, 133.64,
133.29, 129.78–126.94 (45 C), 100.76 (JC,H = 171.0 Hz), 100.67
(JC,H = 171.0 Hz), 98.49 (JC,H = 170.1 Hz), 79.94, 79.25, 75.79,
75.15, 74.92, 74.73, 74.64, 73.98, 73.32, 73.19, 72.76, 72.70, 72.56,
72.16, 71.37, 71.16, 70.46, 69.60, 68.80, 65.98, 62.97, 55.58 ppm.
HRMS: calcd. for C89H85F5NO20 [M + NH4]+ 1582.5580; found
1582.5534.
Phenyl
2,3,4,6-Tetra-O-benzyl-α-
D-mannopyranosyl-(1Ǟ4)-2,3,6-
tri-O-benzyl-1-thio-α-
D-mannopyranoside (20): To a solution of 16
(0.86 g, 0.74 mmol) in MeOH (25 mL) was added sodium (70 mg,
3.0 mmol) and the mixture was heated to 50 °C for 20 min. The
reaction was cooled to room temperature and quenched with Am-
berlite IR-120 (H+) ion-exchange resin (10 mL). The mixture was
stirred for 10 min, filtered and concentrated. The residue was puri-
fied by flash chromatography (heptane/EtOAc, 7:3) to give 0.72 g
(0.74 mmol) of a syrup (Rf = 0.20, heptane/EtOAc, 7:3). To an ice-
cooled solution of this in DMF (9 mL) were added Bu4NI (20 mg,
0.06 mmol), NaH (50 mg of a 50% oil dispersion, 1.0 mmol) and
BnBr (0.17 mL, 1.4 mmol). The reaction was stirred at room tem-
perature for 16 h and then quenched with AcOH. The mixture was
diluted with Et2O (20 mL), washed with water (2ϫ25 mL), dried
(MgSO4), evaporated to dryness, and purified by flash chromatog-
raphy (heptane/EtOAc, 4:1) to afford 0.61 g (78%) of 20 as a syrup.
Rf = 0.23 (heptane/EtOAc, 3:1). [α]2D0 = +41.8 (c = 1.0, CHCl3). 1H
NMR (300 MHz, CDCl3): δ = 7.51–7.15 (m, 40 H), 5.59 (d, J =
1.7 Hz, 1 H), 5.32 (d, J = 1.8 Hz, 1 H), 4.86 (d, J = 10.8 Hz, 1 H),
4.68–4.31 (m, 13 H), 4.13 (t, J = 9.3 Hz, 1 H), 4.01–3.65 (m, 10
H), 3.58 (dd, J = 1.7, 10.7 Hz, 1 H) ppm. 13C NMR (75 MHz,
CDCl3): δ = 138.82, 138.80, 138.71, 138.67, 138.57, 137.88, 137.81,
134.18, 132.11–127.35 (40 C), 100.21 (d, J = 170.2 Hz), 85.48 (d, J
= 170.8 Hz), 80.20, 79.96, 75.83, 75.34, 75.17, 75.03, 74.87, 73.50,
73.15, 73.10, 72.22, 72.16, 72.02, 71.78, 71.21, 70.15, 69.38 ppm.
C67H68O10S (1065.3): calcd. C 75.54, H 6.43, S 3.01; found C 75.82,
H 6.76, S 2.56.
Benzyl 2,3,4,6-Tetra-O-benzyl-α-
O-benzyl-6-O-pentafluorobenzoyl-α-
2,3,6-tri-O-benzyl-β- -galactopyranoside (25): The glycosylation be-
D
-galactopyranosyl-(1Ǟ4)-2,3-di-
D
-galactopyranosyl-(1Ǟ4)-
D
tween 4 and 7 was carried out in accordance with the general pro-
cedure. A solution of 24[23] (1.1 equiv.) in Et2O and more NIS
(1.5 equiv.) were added after 10 min and the mixture was stirred at
–20 °C for an additional 10 min. The reaction was worked up as
described above to afford 52% yield of 25. Rf = 0.08 (heptane/
EtOAc, 17:3). [α]2D0 = +39.4 (c = 1.0, CHCl ). IR (KBr): ν = 3061,
˜
3
1741, 1498, 1098, 697 cm–1. 1H NMR (300 MHz, CDCl3): δ = 7.44–
7.14 (m, 50 H), 5.09 (d, J = 3.0 Hz, 1 H), 4.97–4.51 (m, 18 H),
4.43–4.29 (m, 6 H), 4.12–3.87 (m, 10 H), 3.68–3.48 (m, 4 H), 3.55
(dd, J = 2.7, 9.9 Hz, 1 H), 3.16 (dd, J = 4.6, 8.0 Hz, 1 H) ppm. 13
C
NMR (75 MHz, CDCl3): δ = 138.90, 138.84, 138.84, 138.80,
138.68, 138.59, 138.34, 138.22, 138.17, 137.75, 128.58–127.28 (50
C), 102.96 (JC,H = 160.9 Hz), 100.63 (JC,H = 169.6 Hz), 100.20
(JC,H = 169.6 Hz), 79.91, 79.72, 79.34, 77.50, 76.32, 76.05, 75.33,
75.22, 75.17, 75.02, 74.44, 74.33, 73.62, 73.44, 73.24, 73.24 72.49,
72.35, 72.29, 71.17, 71.13, 69.51, 68.89, 68.10, 67.69 ppm. HRMS:
calcd. for C95H95F5NO17 [M + NH4]+ 1616.6516; found 1616.6487.
Phenyl
tri-O-benzyl-α-
fluorobenzoyl-1-thio-α-
2,3,4,6-Tetra-O-benzyl-α-
-mannopyranosyl-(1Ǟ4)-2,3-di-O-benzyl-6-O-penta-
-mannopyranoside (21): The coupling be-
D-mannopyranosyl-(1Ǟ4)-2,3,6-
Methyl 2,3,4,6-Tetra-O-benzyl-α-
O-benzyl-6-O-pentafluorobenzoyl-α-
2,3,6-tri-O-benzoyl-α- -galactopyranoside (27): The glycosylation
D-galactopyranosyl-(1Ǟ4)-2,3-di-
D
D
-galactopyranosyl-(1Ǟ4)-
D
D
tween 20 and 15 was performed according to the general procedure
and stopped after 25 min to afford 60% yield of 21. Rf = 0.17
between 4 and 7 was carried out in accordance with the general
procedure. A solution of 26[22] (1.1 equiv.) in Et2O and more NIS
(1.5 equiv.) were added after 10 min and the mixture was stirred at
–20 °C for an additional 10 min. The reaction was worked up as
described above to afford 61% yield of 27. Rf = 0.12 (heptane/
(heptane/EtOAc, 4:1). [α]2D0 = +37.9 (c = 1.0, CHCl ). IR (KBr): ν
˜
3
= 3030, 1741, 1498, 1052, 738 cm–1. H NMR (300 MHz, CDCl3):
1
δ = 7.44–7.13 (m, 50 H), 5.62 (d, J = 1.6 Hz, 1 H), 5.30 (d, J =
1.7 Hz, 1 H), 5.29 (d, J = 1.7 Hz, 1 H), 4.81 (dd, J = 3.0, 11.2 Hz,
1 H), 4.68 (dd, J = 4.6, 12.0 Hz, 1 H), 4.63–4.02 (m, 21 H), 3.98
(d, J = 9.6 Hz, 1 H), 3.85–3.60 (m, 11 H) 3.46 (dd, J = 1.6, 10.8 Hz,
1 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 139.07, 138.99, 138.96,
138.86, 138.70, 138.68, 138.43, 137.78, 137.73, 134.11, 131.38–
127.29 (50 C), 100.65 (JC,H = 170.7 Hz), 100.11 (JC,H = 169.6 Hz),
85.35 (JC,H = 170.2 Hz), 80.30, 79.93, 75.85, 75.58, 75.27, 74.95,
74.90, 74.44, 74.41, 73.58, 73.39, 73.04, 72.18, 72.14, 72.14, 72.11,
71.40, 70.67, 70.13, 70.10, 69.19, 65.98, 65.95, 65.91 ppm.
C94H89F5O16S (1601.8): calcd. C 70.49, H 5.60, S 2.00; found C
69.99, H 5.81, S 1.85.
EtOAc, 4:1). [α]2D0 = +82.3 (c = 1.0, CHCl ). IR (KBr): ν = 3031,
˜
3
1724, 1452, 1099, 713 cm–1. 1H NMR (300 MHz, CDCl3): δ = 8.09–
7.12 (m, 45 H), 5.64–5.60 (m, 2 H), 5.19 (d, J = 3.1 Hz, 1 H), 4.96
(d, J = 3.2 Hz, 1 H), 4.91–4.00 (m, 25 H) 3.92 (dd, J = 3.2, 10.2 Hz,
1 H), 3.80 (dd, J = 2.6, 10.2 Hz, 1 H), 3.52 (t, J = 8.7 Hz, 1 H),
3.41 (s, 3 H), 3.23 (dd, J = 4.6, 8.1 Hz, 1 H) ppm. 13C NMR
(75 MHz, CDCl3): δ = 166.27, 166.19, 166.06, 138.95, 138.75,
138.65, 138.29, 138.25, 138.12, 133.35, 133.33, 133.30, 129.96–
127.37 (45 C), 100.50 (JC,H = 169.6 Hz), 97.49 (JC,H = 169.6 Hz),
97.49 (JC,H = 171.0 Hz), 79.46, 77.47, 76.64, 75.95, 75.02, 74.70,
74.44, 74.19, 73.93, 73.31, 72.86, 72.23, 70.81, 69.65, 69.14, 68.58,
67.77, 67.74, 63.85, 63.40, 63.38, 55.50 ppm. HRMS: calcd. for
C89H85F5NO20 [M + NH4]+ 1582.5580; found 1582.5549.
Methyl 2,3,4,6-Tetra-O-benzyl-α-
O-benzyl-6-O-pentafluorobenzoyl-α-
2,3,6-tri-O-benzoyl-α- -mannopyranoside (23): The glycosylation
D
-mannopyranosyl-(1Ǟ4)-2,3-di-
D
-mannopyranosyl-(1Ǟ4)-
D
between 14 and 15 was carried out in accordance with the general
procedure. A solution of 22[22] (1.1 equiv.) in Et2O and more NIS
(1.5 equiv.) were added after 35 min and the mixture was stirred at
–20 °C for an additional 40 min. The reaction was worked up as
described above to afford 49% yield of 23. Rf = 0.28 (heptane/
Acknowledgments
Financial support from the Lundbeck Foundation is gratefully ac-
knowledged. We thank Karen Margrethe Juul, Martin Hansen,
3940
www.eurjoc.org
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2007, 3935–3941

Selective Glycosylations
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Palle Pedersen and Kenneth Rasmussen for performing the prelimi-
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Green Chemistry is sponsored by the Danish National Research
Foundation.
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Received: April 19, 2007
Published Online: June 25, 2007
Eur. J. Org. Chem. 2007, 3935–3941
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
3941