An efficient approach towards the convergent synthesis of "fully-carbohydrate" mannodendrimers

Article abstract of DOI:10.1002/1521-3765(20021004)8:19<4412::AID-CHEM4412>3.0.CO;2-F

Glycosylation of sugar trityl ethers with sugar 1,2-O-(1-cyano)ethylidene derivatives (the trityl-cyanoethylidene condensation) has been applied to the synthesis of highly branched (dendritic) mannooligosaccharides incorporating a Manα1 → 3(Manα1 → 6)Man

Full text of DOI:10.1002/1521-3765(20021004)8:19<4412::AID-CHEM4412>3.0.CO;2-F

FULL PAPER
An Efficient Approach towards the Convergent Synthesis of
™Fully-Carbohydrate∫ Mannodendrimers
[a]
Leon V. Backinowsky,* Polina I. Abronina,[a] Alexander S. Shashkov,[a]
Alexey A. Grachev,[b] Nikolay K. Kochetkov,[a] Sergey A. Nepogodiev,[c] and
J. Fraser Stoddart[d]
Abstract: Glycosylation of sugar trityl
ethers with sugar 1,2-O-(1-cyano)ethyli-
dene derivatives (the trityl-cyanoethyli-
dene condensation) has been applied to
the synthesis of highly branched (den-
dritic) mannooligosaccharides incorpo-
lowed by O-acetylation.Glycosylation
of acetates of methyl 6-O-trityl-a-d-
mannopyranoside and methyl 3,6-di-O-
trityl-a-d-mannopyranoside with one
equivalent of the donor 1 gave rise to
the isomeric tetrasaccharide derivatives,
Mana1!3(Mana1!6)Mana1!6Man-
fashion, 6'- and 6''-O-trityl derivatives
of the branched trisaccharide Mana1 !
3(Mana1 ! 6)ManaOMe served as pre-
cursors for two isomeric mannohexa-
osides.The 3,6-di- O-trityl ether of Man-
aOMe and the 6',6''-di-O-trityl ether of
Mana1 ! 3(Mana1 ! 6)ManaX (X ˆ
OMe or SEt) were efficiently bis-glyco-
sylated with the donor 1 to give the
corresponding protected mannohepta-
oside and mannononaoside.The yields
of these glycosylations with the donor 1
ranged from 50 to 66%.Final depro-
tection of all the oligosaccharides was
straightforward and afforded the target
products in high yields.Both the acy-
lated and deprotected products were
characterized, and the intersaccharide
connectivities were elucidated by exten-
sive one- and two-dimensional NMR
spectroscopy.The described blockwise
convergent approach allows assembly of
a variety of 3,6-branched mannooligo-
saccharides.
rating
a
Mana1 ! 3(Mana1 ! 6)Man
structural motif.The convergent syn-
thetic strategy used to assemble these
oligosaccharides was based on the use of
glycosyl acceptors and/or a glycosyl
donor already bearing this structural
motif.The former were represented by
mono- and ditrityl ethers of ManaOMe,
Mana1 ! 3ManaOMe, and Mana1 !
3(Mana1 ! 6)ManaX, where X ˆ OMe
or SEt.The pivotal glycosyl donor was
the peracetylated 1,2-O-(1-cyano)ethyli-
dene-3,6-di-O-(a-d-mannopyranosyl)-
b-d-mannopyranose (1), prepared by
orthogonal Helferich glycosylation of
the known 1,2-O-(1-cyano)ethylidene-
b-d-mannopyranose with tetra-O-ace-
tyl-a-d-mannopyranosyl bromide fol-
aOMe
and
Mana1 ! 3(Mana1 !
6)Mana1 ! 3ManaOMe, respectively.
The latter derivative was further man-
nosylated at the remaining 6-O-trityl
acceptor site to give the protected pen-
tasaccharide
Mana1 ! 3(Mana1 !
6)Mana1 ! 3(Mana1 ! 6)ManaOMe.
The isomeric pentasaccharide, Mana1
! 3(Mana1 ! 6)Mana1 ! 6(Mana1 !
3)ManaOMe, was prepared by reaction
of 1 with the 6-O-trityl derivative of
(Mana1 ! 3)ManaOMe.In a similar
Keywords: carbohydrates ¥ glycosy-
lation ¥ NMR spectroscopy ¥ oligo-
saccharides ¥ synthetic methods
Introduction
[a] Prof.L.V.Backinowsky, Dr.P.I.Abronina, Dr.A.S.Shashkov,
Prof.N.K.Kochetkov
Carbohydrates, as the most prominent cell surface-exposed
structures, play the role of recognition molecules.The
message transferred through the sugar code is mainly
deciphered[1] in interactions of carbohydrates with proteins,
for example, lectins, enzymes, and antibodies.Numerous
investigations into relevant ligand receptor binding events
have revealed that the weak binding affinities characteristic of
low molecular weight carbohydrates are circumvented in
nature through the involvement of multivalent structures.
Polyvalent interactions are extremely abundant in biological
systems[2] and they often play a crucial role in the binding of
carbohydrate ligands to protein receptors.[3] To understand
the mechanisms of biological processes mediated by multi-
valent interactions and to exploit the effects of multivalency,
N.D.Zelinsky Institute of Organic Chemistry
Russian Academy of Sciences, Leninsky Prospect 47
117913 Moscow (Russian Federation)
Fax : (‡7)095-135-5328
E-mail: leon@ioc.ac.ru
[b] A.A.Grachev
Higher Chemical College, Russian Academy of Sciences
Miusskaya pl.9, 125190 Moscow (Russian Federation)
[c] Dr.S.A.Nepogodiev
School of Chemical Sciences, University of East Anglia
Norwich, NR4 7TJ (UK)
[d] Prof.J.F.Stoddart
Department of Chemistry and Biochemistry
University of California at Los Angeles
405 Hilgard Avenue, Los Angeles, CA 90095-1569 (USA)
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4412 4423
chemists have prepared[4] a variety of ligands with multiple
arrays of carbohydrate residues.Artificial multivalent struc-
tures can involve, inter alia, glycoside clusters of various
architectures,[5] resin-immobilized oligosaccharides,[6] self-as-
sembled carbohydrate-derivatized monolayers,[7] and diverse
neoglycopolymers.[8] For some of them, that is to say, for
polyvalent mannosides, thermodynamic aspects of binding to
concanavalin A have been evaluated.[9]
Man(α1 6)
Man(α1 3)
ManαOMe
Man(α1 6)
Man(α1 6)
Man(α1 3)
Man(α1 3)ManαOMe
Man(α1 6)
Man(α1 6)
Man(α1 3)
ManαOMe
Man(α1 3)
The family of synthetic multivalent carbohydrate structures
has recently been complemented by highly branched (den-
dritic) oligomers, the so-called glycodendrimers.[10] In addition
to carbohydrate-coated dendrimers bearing mono- or oligo-
saccharide terminal groups,[11] and carbohydrate-centered
dendrimers,[12] yet another group is emerging upon the scene,
namely ™fully-carbohydrate∫ glycodendrimers composed of
carbohydrates as building units and constituting the ™wedges∫
of the cascade molecules.[13] Further development of synthetic
methodologies for highly branched oligosaccharides is of
substantial interest to chemists and glycobiologists.
One of the most rational approaches to higher oligosac-
charides composed of repeating elements is blockwise syn-
thesis based on the use of the same oligosaccharide glycosyl
donor.Here, we describe a blockwise assembly of a number of
mannooligosaccharides (Scheme 1) incorporating one, two, or
three d-mannopyranose residues glycosylated at positions 3
and 6.The trisaccharide Man a1 ! 3(Mana1 ! 6)Man is a
typical branching fragment of mannan chains in N-glycopro-
teins and the synthesis of some oligosaccharides incorporating
this fragment has been reported.[14] Our approach to the
construction of branched oligosaccharides is based on a
common strategy employing Mana1 ! 3(Mana1 ! 6)Man as
Man(α1 6)
Man(α1 3)
Man(α1 6)
ManαOMe
Man(α1 3)
Man(α1 6)
Man(α1 3)
Man(α1 6)
Man(α1 6)
Man(α1 3)
ManαOMe
Man(α1 6)
Man(α1 6)
Man(α1 3)
ManαOMe
Man(α1 6)Man(α1 3)
Man(α1 6)
Man(α1 3)
Man(α1 6)
Man(α1 3)
Man(α1 6)
ManαOMe
Man(α1 3)
Man(α1 6)
Man(α1 3)
Man(α1 6)
Man(α1 3)
Man(α1 6)
Man(α1 6)
ManαX
Man(α1 6)Man(α1 3)
X = OMe or SEt
Scheme 1.Target branched-chain oligomannosides.
a key building block and trityl-cyanoethylidene condensa-
tion[15] as the method of glycosylation.The advantages of this
glycosylation technique have been demonstrated in the
syntheses of several complex, regular polysaccharides of
bacterial origin[16] and of regular cyclic oligosaccharides that
may be regarded as fully synthetic cyclodextrin analogues.[17]
Results and Discussion
Synthesis of the glycosyl donor 1: A convergent approach to
the synthesis of mannooligosaccharides incorporating 3,6-
branched fragments requires a highly efficient and readily
accessible donor based on a Mana1 ! 3(Mana1 ! 6)Man
trisaccharide.Several synthetic schemes have been elabora-
20]
ted[14b, 18
for the construction of protected derivatives of
branched mannooligosaccharides, including those that can act
as glycosyl donors.[21, 22] Compound 1 (Scheme 2) fulfils these
requirements since 1,2-O-cyanoethylidene derivatives of
saccharides are known[15] to be excellent 1,2-trans-glycosylat-
ing agents.In our synthesis of 1, we converted the known[23]
1,2-O-[1-(exo-cyano)ethylidene]-b-d-mannopyranose triace-
tate 2 into the triol 3 and glycosylated it selectively at
positions 3 and 6.
The transformation of 2 into the triol 3 had previously been
accomplished by Et3N-[17] or NaOMe-catalyzed[24] methanol-
ysis.Here, we effected the deacetylation with NaOMe in a
MeOH/C5H5N mixture,[25] and the product 3 was then
subjected to glycosylation.Glycosylation of hydroxyl-con-
Chem. Eur. J. 2002, 8, No. 19
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L.V.Backinowsky et al.
FULL PAPER
The glycosyl acceptors 6 12: To construct the required
variety of branched oligosaccharides (Scheme 1), it was
necessary to synthesize a range of saccharide derivatives that
could serve as glycosyl acceptors for the trisaccharide donor 1
in the trityl-cyanoethylidene condensation.To this end, we
used the known trityl ethers 6[29] and 7[30] of methyl a-d-
mannopyranoside, as well as compounds 8 12[31] (Scheme 3).
In summary, the trityl ether 8 (Scheme 4) was prepared by
selective glycosylation of the primary secondary trityl ether
7 by 2,3,4,6-tetra-O-benzoyl-a-d-mannopyranosyl bromide at
Me
CN
Me
CN
O
O
AcO
AcO
AcO
HO
HO
HO
a
b
O
O
O
O
2
3
OAc
O
OAc
O
AcO
AcO
AcO
AcO
AcO
AcO
OAc
D
C
Me
CN
O
AcO
AcO
AcO
O
Me
O
O
O
CN
O
C
RO
A
O
O
O
O
O
A
AcO
AcO
AcO
B
O
O
AcO
B
OAc
4 R = H
AcO
AcO
O
c
OAc
1 R = Ac
5
Scheme 2.Synthesis of the trisaccharide glycosyl donor 1.Reagents and
conditions: a) NaOMe/MeOH/C5H5N, room temperature, 5 min;
b) 2,3,4,6-tetra-O-acetyl-a-d-mannopyranosyl bromide, Hg(CN)2, HgBr2,
MeCN, room temperature, 16 h (with 3.5 equiv of the glycosyl bromide the
product is 4, 62%; with 4 equiv of the glycosyl bromide, the products after
acetylation are 1, 46%, and 5, 16%); c) Ac2O/C5H5N, DMAP, 80%.
OAc
O
OBz
O
AcO
AcO
AcO
BzO
BzO
BzO
Br
Br
7
8
9
1. AgOTf, CH2Cl2
AgOTf, CH2Cl2
2. HCl/MeOH
3. TrCl/C5H5N
4. Ac2O/C5H5N
taining cyanoethylidene derivatives, which may be considered
as an example of orthogonal glycosylation,[26] has substantially
extended the potential of the trityl-cyanoethylidene conden-
sation.This reaction is usually performed with acylglycosyl
bromides under the conditions of the Helferich reaction[27] or
in the presence of silver trifluoromethanesulfonate (triflate)
in combination with 2,4,6-collidine.[17] To ensure selective
glycosylation of the triol 3, we employed a milder promoter,
namely, a mixture of Hg(CN)2 and HgBr2.The reaction of
triol 3 with 3.5 equivalents of 2,3,4,6-tetra-O-acetyl-a-d-
mannopyranosyl bromide resulted in the formation of trisac-
charide 4 (62% yield after chromatography).Acetylation of
this cyanoethylidene derivative afforded the crystalline fully
protected compound 1.When a somewhat larger amount of
the glycosyl bromide (4 equivalents) was used, a tetrasacchar-
ide 5 was obtained together with the trisaccharide 4.Since
both these saccharides exhibit nearly identical chromato-
graphic mobilities on silica gel, their separation was effected
by chromatography after acetylation.The yield of the target
compound 1 was 46%, while that of compound 5 was 16%.A
similar approach to the construction of oligosaccharides
incorporating 3,6-bis-glycosylated hexopyranose residues,
but requiring a larger number of steps, has been reported
previously.[28]
Scheme 4.Synthesis of the trityl ethers 8 and 9.
the secondary position.[32] This disaccharide 8 was further
glycosylated by 2,3,4,6-tetra-O-acetyl-a-d-mannopyranosyl
bromide to give a trisaccharide with differently protected
mannopyranosyl residues.Its de-O-acetylation by mild acid-
catalyzed methanolysis, which did not affect the O-benzoyl
groups,[33] followed by 6-O-tritylation (TrCl/C5H5N) and
O-acetylation, furnished the trisaccharide trityl ether 9.The
trisaccharide trityl ether 10, isomeric with compound 9, was
synthesized from 7 according to an analogous route, except
that the sequence of attachment of the O-acetylated and
O-benzoylated mannose units to the acceptor 7 was reversed.
The tetra-O-acetyl-a-d-mannopyranosyl residue was first
introduced[32a] at position 3 of the acceptor, and then the
resulting 6-O-trityl ether was subjected to AgOTf-promoted
mannosylation with 2,3,4,6-tetra-O-benzoyl-a-d-mannopyra-
nosyl bromide.The peracylated trisaccharide thus formed was
modified as outlined above (selective de-O-acetylation,
O-tritylation, and O-acetylation) to yield the target trityl
ether 10.Syntheses of the bis-trityl ethers 11 and 12 involved
bis-glycosylation of the ditrityl ether 7 (or its 1-SEt analogue),
complete deacylation of the peracylated trisaccharide deriv-
atives, tritylation of the primary OH groups, and per-O-
acetylation.
*
TrO
AcO
OAc
O
*
*
O
TrO
AcO
TrO
OAc
O
OAc
O
AcO
OMe
BzO
BzO
BzO
*
TrO
AcO
O
OBz
Syntheses of the oligosaccharides: Previous glycosylations by
cyanoethylidene derivatives of disaccharides[16c,d] and linear
tri-[16b] and tetrasaccharides[34] have shown that their efficien-
cies do not differ from those of monosaccharide derivatives.
One might expect the cyanoethylidene derivative of a
branched trisaccharide, such as compound 1, to also be an
efficient glycosyl donor.To verify this hypothesis, we carried
out a reaction of 1 with methyl 2,3,4-tri-O-acetyl-6-O-trityl-a-
d-mannopyranoside 6 as a glycosyl acceptor (Scheme 5).This
reaction was conducted under the standard conditions of
trityl-cyanoethylidene condensation,[15] and afforded the fully
protected tetrasaccharide derivative 13 in 56% yield.Thus,
the 1,2-O-cyanoethylidene derivative of a branched trisac-
OMe
OMe
6
7
8
*
*
TrO
OAc
O
BzO
BzO
BzO
TrO
AcO
OBz
O
OAc
O
AcO
AcO
AcO
O
O
O
OAc
O
OAc
O
OAc
O
AcO
AcO
AcO
O
O
O
OMe
OMe
BzO
BzO
BzO
AcO
AcO
X
AcO
AcO
O
OBz
O
OAc
O
*
TrO
*
TrO
OAc
9
10
11 X = OMe
12 X = SEt
Scheme 3.Building blocks containing trityl ethers that can serve as
glycosyl acceptors in reactions with the trisaccharide donor 1.The potential
sites of glycosylation are marked with asterisks.
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Fully-Carbohydrate Mannodendrimers
4412 4423
OR
RO
derivative 15, which was isolated in about 60% yield.The
tetrasaccharide 14 was used as a glycosyl acceptor for the
synthesis of a mannopentaoside under the conditions of the
Bredereck reaction.Condensation of 14 with 2,3,4,6-tetra-O-
benzoyl-a-d-mannopyranosyl bromide in the presence of
silver triflate and 2,4,6-collidine (Scheme 6) gave the pro-
tected pentaoside 16 in 47% yield.
The demonstrated effectiveness of the use of trisaccharide 1
as a glycosyl donor, in combination with 6-O- and 3,6-di-O-
trityl ethers of mannopyranose as glycosyl acceptors, served as
a basis for the blockwise synthesis of other branched
oligomannosides.The aforementioned glycosyl acceptors 8
12 were used for this purpose.The positions of the O-trityl
groups in compounds 8 12 dictate the sites for the introduc-
tion of the Mana1 ! 3(Mana1 ! 6)Man fragment.Thus,
condensation of the glycosyl donor 1 with the disaccharide
acceptor 8 under the standard conditions for the trityl-
cyanoethylidene condensation gave (Scheme 7) the peracy-
lated pentaoside 17 in 66% yield following chromatography.
O
RO
RO
1
6
D
OR
O
O
a
RO
B
O
RO
RO
RO
OR
O
C
O
O
OR
RO
RO
A
OMe
13 R = Ac
22 R = H
b
Scheme 5.Synthesis of the tetrasaccharide 13 (and 22).Reagents and
conditions: a) TrClO4 (10 mol%), CH2Cl2, room temperature, 16 h, 56%;
b) NaOMe/MeOH/C5H5N.
charide, such as compound 1, can indeed be used as a building
block for the construction of complex oligomannosides.
The next step in studying the reactivity of compound 1 as a
glycosyl donor was an investigation of its reactions with the
ditrityl ether 7, which can be selectively monoglycosylated at
position 3[31, 32] or bis-glycosylated at positions 3 and 6[31] with
monosaccharide glycosyl donors.Here (Scheme 6), glycosy-
lation of compound 7 with one equivalent of the glycosyl
OR1
O
R1O
R1O
E
R1O
OR
O
RO
OR1
O
1
8
O
b
RO
G
R1O
R1O
1
7
C
O
a
OR
O
O
R1O
OR1
O
O
D
RO
R1O
C
O
R1O
O
O
a
R1O
A
OR1
R2O
O
RO
RO
E
O
OMe
O
OR
OR
B
R2O
R2O
RO
OAc
O
OR
O
OR2
TrO
AcO
OAc
AcO
RO
O
O
RO
AcO
RO
RO
A
A
C
D
O
O
AcO
17 R1 = Ac, R2 = Bz
25 R1 = R2 = H
OMe
OMe
O
O
B
b
B
AcO
RO
O
OAc
O
OR
O
O
Scheme 7.Synthesis of the pentaoside 17 (and 25).Reagents and
conditions: a) TrClO4 (10 mol%), CH2Cl2, room temperature, 16 h, 66%;
b) NaOMe/MeOH/C5H5N.
AcO
AcO
AcO
RO
RO
RO
D
F
O
OAc
O
15 R = Ac
23 R = H
d
OR
14
OBz
O
OR2
O
Under similar conditions, glycosylation of the trityl ethers 9
and 10 with equivalent amounts of the cyanoethylidene
derivative 1 (Scheme 8) yielded the fully protected hexaosides
18 (58%) and 19 (60%).The bis-trityl ethers 11 and 12
BzO
R2O
R2O
R2O
BzO
C
BzO
OR1
OR1
O
R1O
R1O
R1O
Br
O
R1O
O
A
D
O
c
O
underwent bis-glycosylation with the donor
1 to give
OMe
B
R1O
O
OR1
O
(Scheme 9) nonaosides 20 (50%) and 21 (54%), respectively.
The formation of the nonaoside 21 demonstrates the stability
of thioglycosides under the conditions of the trityl-cyano-
ethylidene condensation and represents yet another example
of orthogonal glycosylation.The structures of all the oligo-
saccharides obtained followed unambiguously from the
manner of their synthesis and were confirmed by 1H and
13C NMR spectroscopy and mass spectrometry.
R1O
E
R1O
R1O
O
OR1
16 R1 = Ac, R2 = Bz
24 R1 = R2 = H
d
Scheme 6.Synthesis of the tetrasaccharide 14, heptasaccharide 15 (and
23), and pentasaccharide 16 (and 24).Reagents and conditions: a) 1 (1 mol
equiv), TrClO4 (10 mol%), CH2Cl2, room temperature, 16 h, 55%; b) 1
(2 mol equivalents), TrClO4 (10 mol%), CH2Cl2, room temperature, 16 h,
60%; c) 2,3,4,6-tetra-O-benzoyl-a-d-mannopyranosyl bromide (4 equiv),
AgOTf/2,4,6-collidine, CH2Cl2, room temperature, 10 min (47%);
d) NaOMe/MeOH/C5H5N.
All peracylated oligosaccharides were deprotected (Zem-
¬
plen) to give the unprotected tetraoside 22 (Scheme 5), the
∫symmetrical∫ heptaoside 23, the known[35] isomeric penta-
osides 24 (Scheme 6) and 25 (Scheme 7), the isomeric hexa-
osides 26 and 27 (Scheme 8), and the nonaosides 28 and 29
(Scheme 9) in virtually quantitative yields.The 1H and
13C NMR spectra of these oligosaccharides corroborate their
structures.
donor 1 gave the tetrasaccharide derivative 14 in 55% yield.
Owing to the lower reactivity of primary trityl ethers as
compared with their secondary counterparts, the 6-O-trityl
group remained unchanged in the molecule.The use of a
twofold molar excess of the donor 1 for the glycosylation of
the acceptor 7 led to the formation of the heptasaccharide
NMR spectroscopy: The branched mannooligosaccharides,
both protected and unprotected, were characterized by means
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L.V.Backinowsky et al.
FULL PAPER
residue, and 2) to establish intersaccharide connectivities.
The spin-spin coupling constants of vicinal protons available
from 1D 1H NMR spectra had values indicative of a-d-
mannopyranose residues (J1,2 ꢀ 1.5 2.0 Hz; J2,3 ꢀ 3.0
OR1
O
R1O
R1O
R1O
9
F
OR1
O
O
R1O
D
O
a
R1O
OR1
O
O
3.5 Hz), but their utility in making signal assignments was
E
R1O
R1O
R1O
O
[36]
C
R1O
OR1
limited.Correlation spectroscopy (COSY),
relayed coher-
ence transfer spectroscopy (COSYRCT),[37] and total corre-
lation spectroscopy (TOCSY)[38] were used for identifying
groups of protons belonging to separate mannopyranosidic
residues.
OR1
O
O
R1O
A
18 R1 = Ac, R2 = Bz
26 R1 = R2 = H
O
b
R2O
OMe
B
R2O
R2O
O
OR2
Assignments of the 1H NMR spectra of the protected
pentasaccharides 16 and 17 and hexasaccharides 18 and 19
were facilitated by the fact that the signals of the protons of
the monosaccharide residues bearing O-benzoyl groups are
shifted downfield compared to those of the other protons.In
this respect, the 1H NMR spectrum of compound 19 (Figure 1)
is noteworthy as all the signals of the protons of residue C are
distinguishable, even in the 1D spectrum.The chemical shifts
of the protons of the other monosaccharide residues in this
oligosaccharide proved to be sufficiently different to permit
their assignments using a combination of 2D 1H NMR spectra.
The relationships between sets of signals belonging to
glycosidically linked residues (in this work designated as A, B,
C, and so on, as shown in the schemes) were established using
either the 1D NOE technique in a difference mode with pre-
irradiation of the anomeric protons and/or rotating-frame
Overhauser enhancement spectroscopy (ROESY).[39] For
instance, the glycoside residues (residues A) were unequiv-
ocally identified from the H-1A/OMe correlations in the
ROESY spectra.Analysis of the ROESY spectra of the
deprotected oligosaccharides revealed, as expected, the
presence of H-1'/H-6 and H-1'/H-3 cross-peaks for the
Man1 ! 6Man and Man1 ! 3Man fragments, respectively.
For the Man1 ! 3Man fragment, H-1'/H-2 and H-1'/H-4
cross-peaks were also observed, probably as a result of spin
diffusion and/or spatial transfer.[40] Heteronuclear multiple
quantum coherence (HMQC)[41] spectroscopy proved to be
useful for the unambiguous identification of anomeric protons
1
OR2
O
R2O
R2O
C
R2O
OR1
O
O
R1O
A
O
R1O
OR1
O
R1O
R1O
R1O
a
B
OMe
R1O
O
OR1
E
O
O
D
R1O
O
OR1
O
R1O
R1O
R1O
19 R1 = Ac, R2 = Bz
27 R1 = R2 = H
F
10
O
b
OR1
Scheme 8.Synthesis of the isomeric hexaosides 18 and 19 (and 26 and 27).
Reagents and conditions: a) TrClO4 (10 mol%), CH2Cl2, room temper-
ature, 16 h, 58% (18) and 60% (19); b) NaOMe/MeOH.
OR
RO
O
RO
RO
I
1
11
OR
O
O
RO
E
a
O
RO
RO
RO
OR
O
G
O
RO
RO
O
OR
C
20 X =OMe, R = Ac
28 X =OMe, R = H
b
b
OR
O
O
RO
A
O
21 X =SEt, R = Ac
29 X =SEt, R = H
RO
RO
B
X
OR
O
RO
RO
RO
O
OR
F
O
O
D
a
RO
O
OR
O
RO
RO
RO
1
H
1
12
in H NMR spectra from the characteristic, low-field reso-
O
OR
nances of the anomeric carbon atoms.For instance, the high-
field chemical shift (dC ˆ 86.3 ppm) of the anomeric carbon
atom of residue A bearing the ethylthio group in the
nonaoside 29 allowed us to identify (dH ˆ 5.44 ppm) the
anomeric proton in this residue using the HMQC procedure
(Figure 2).In this way, an independent and comprehensive
proof of the relative positions of each residue in an
oligosaccharide framework was obtained for all the synthe-
sized compounds.
Scheme 9.Synthesis of the nonaosides 20 and 21 (and 28 and 29).Reagents
and conditions: a) TrClO4 (10 mol%), CH2Cl2, room temperature, 16 h,
50% (20) and 54% (21); b) NaOMe/MeOH/C5H5N.
of 1D- and 2D NMR spectroscopy.For most of the new
compounds, all peaks in the 1H and 13C NMR spectra could be
assigned to such an extent that it was possible 1) to delineate
the spin system for each individual a-d-mannopyranose
Figure 1.The ™carbohydrate region∫ of the 1H NMR spectrum (500 MHz, CDCl3, 208C) of the hexasaccharide derivative 19 showing the assignments of all
the resonances.The designation of the monosaccharide residues ( A F) in 19 is shown in Scheme 8.
4416
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Chem. Eur. J. 2002, 8, No. 19

Fully-Carbohydrate Mannodendrimers
4412 4423
Table 1.Types of a-d-mannopyranose residues that can be identified within the
structures of the synthesized mannooligosaccharides.[a]
Residues
terminal
Protected
Deprotected
Ac4Man(1 ! 3)
(11) Man(1 ! 3)
(13)
(13)
Ac4Man(1 ! 6)
Bz4Man(1 ! 3)
Bz4Man(1 ! 6)
(10) Man(1 ! 6)
(2)
(2)
6-monosubstituted ! 6)Ac3Man(1 ! 3)
! 6)Ac3Man(1 ! 6)
(3) ! 6)Man(1 ! 3)
(3) ! 6)Man(1 ! 6)
(3) ! 3,6)Man(1 ! 3)
(9) ! 3,6)Man(1 ! 6)
(3)
(3)
(2)
(9)
3,6-disubstituted ! 3,6)Ac2Man(1 ! 3)
! 3,6)Ac2Man(1 ! 6)
−reducing×
! 3,6)Ac2Man(1 ! OMe (6) ! 3,6)Man(1 ! OMe (6)
Figure 2.The anomeric region of the 2D-transformed data matrix from an
HMQC experiment conducted on the nonasaccharide 29 (100 MHz, D2O,
258C).The assignment A/B/C/D/E/F/G/H/I of the d-mannopyranose
residues is illustrated in Scheme 9.
[a] Values in parentheses represent the numbers of similar residues.
The signals of the carbon atoms were assigned by means of
HMQC and the attached proton test (APT) technique,[42]
taking into account the characteristic downfield shifts, that
is, the a-glycosylation effects,[43] for C-3 and/or C-6 bearing a
carbohydrate substituent as compared with those of the
corresponding non-glycosylated carbon atoms.Thus, the fact
that the C-3 atoms of the 3-substituted residues, as well as the
C-6 atoms, can be reliably identified in the 13C NMR spectra
of deprotected glycosides 22 29 allowed us to use the HMQC
and APT techniques to assign the H-3 and H-6 signals in the
1H NMR spectra of these oligosaccharides.The chemical
shifts of all other carbon atoms were determined from the
assigned signals for the protons.
The chemical shifts of the anomeric H and C atoms of the
methyl pentaosides 24 and 25 are consistent with those reported
1
in the literature.[35] The JC1,H1 coupling constants (GATED
spectrum) determined for compound 22 are in the range 171
173 Hz, an observation that establishes a-configurations for the
glycosidic linkages in all of the monosaccharide residues.[44]
The assignment of all 13C signals of the heptasaccharide 15 was
not possible because of the similarities of the chemical shifts of
the protons for similar structural units (for example, D and E, F
and G).However, the structurally significant resonances, that is
to say, those of the anomeric carbons, the C-6 atoms, and the
low-field resonances of the C-3 atoms of the units A, B, and C,
could be assigned.Our interpretations of the NMR spectro-
scopic data for the protected mannooligosaccharides based on
the described methodology are summarized in the tables in the
Experimental Section.The interpreted NMR spectra allowed us
to summarize the characteristic spectroscopic features of the
branched oligosaccharides studied.The structural elements
incorporated into the newly synthesized oligosaccharides can
be grouped according to the type of substitution on an a-d-
mannopyranose residue (Table 1).As expected, the NMR
spectra of similar mannopyranose residues are nearly identical,
whereas different types of residues give rise to noticeable
differences.Thus, a comparison of the NMR spectroscopic
characteristics of the different structural elements revealed
features typical of the protected and deprotected 3,6-branched
mannooligosaccharides.To this end, the chemical shifts of the
analogous atoms present in similar mannopyranose residues
were averaged and the resulting mean chemical shifts are
schematically depicted in Figures 3 and 4.
Figure 3.A schematic representation of 1H NMR spectroscopic data for
some typical a-d-mannopyranose residues incorporated into a) protected
and b) deprotected 3,6-branched mannooligosaccharides.Chemical shifts
are depicted as vertical lines and their values are calculated as the means of
d values for the analogous signals in similar residues selected from Tables 2
and 4.
Chem. Eur. J. 2002, 8, No. 19
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4417

L.V.Backinowsky et al.
FULL PAPER
1
The H NMR spectra of the deprotected oligosaccharides
(Figure 3b) also display several linkage type dependent
chemical shifts.Upfield shifts on going from the (1 ! 3)- to
the (1 ! 6)-linkage are observed for the anomeric protons
(Dd ˆ À0.19 to À0.22 ppm) and H-5 atoms (Dd ˆ À0.08 to
À0.10 ppm). The resonances of the H-2 atoms are somewhat
more downfield shifted in the (1 ! 3)-linked residues as
compared with the (1 ! 6)-linked ones (Dd ˆ À0.07 to
À0.14 ppm).
The 13C NMR spectra seem to be more sensitive to the type
of residue within the 3,6-branched mannooligosaccharide
structures than the 1H NMR spectra.The a-glycosylation
effects are well defined (Figure 4a), corresponding to
‡5.8 ppm (C-3) and ‡3.3 ppm (C-6) for the (1 ! 6)-linked
units and ‡6.4 ppm (C-3) and ‡3.9 ppm (C-6) for the (1 ! 3)-
linked ones.These characteristic shift differences have
successfully been employed in the interpretation of the
13C NMR spectra of the synthesized protected oligosacchar-
ides.The resonances of C-1, C-2, and C-5 of the (1 ! 6)-linked
units are somewhat upfield shifted compared with the (1 ! 3)-
linked ones, these shifts being largest for anomeric carbon
atoms and ranging from À1.4 to À1.6 ppm.
The 13C NMR spectroscopic pattern of the monosaccharide
units of deprotected oligosaccharides (Figure 4b) is very
similar to that of the protected oligosaccharides.Thus, the
resonances of the anomeric carbon atoms involved in 1 ! 3
linkages are shifted downfield by 2.6 3.2 ppm compared with
those involved in 1 ! 6 linkages.The a-glycosylation effects
are ‡7.1 to ‡7.6 ppm for C-3 and ‡5.5 to ‡4.9 ppm for C-6.
No remarkable b-glycosylation effect is observed for C-4 in
branching monosaccharide units.The resonances of C-4 in
these units are shifted upfield by 1.1 1.2 ppm compared to
those observed in non-substituted (terminal) or 6-substituted
monosaccharide residues.
Thus, NMR spectroscopy can be used with confidence for
the characterization of these oligosaccharides containing
similar structural elements.It is also possible to determine
both the total number of anomeric H and C atoms and the
ratio of the low-field (1 ! 3 bond) to the high-field (1 ! 6
bond) signals, which gives an indication of the degree of
branching in the newly synthesized oligosaccharides.
Figure 4.A schematic representation of 13C NMR spectroscopic data for
some typical a-d-mannopyranose residues incorporated into a) protected
and b) deprotected 3,6-branched mannooligosaccharides.Chemical shifts
are depicted as vertical lines and their values are calculated as the means of
d values for the analogous signals in similar residues selected from Tables 3
and 5.
Conclusion
The results reported herein concerning the synthesis of highly
branched mannooligosaccharides (5-mers, 6-mers, a 7-mer,
and a 9-mer) demonstrate the efficiency of the blockwise
synthetic approach and hence one may anticipate its success-
ful application in the synthesis of more complex dendritic
carbohydrate structures.Triphenylmethylium perchlorate
catalyzed condensation of tritylated oligosaccharides (glyco-
syl acceptors) with a branched cyanoethylidene derivative
(glycosyl donor) has enabled the stereospecific and regiospe-
cific introduction of Mana1 ! 3(Mana1a ! 6)Man frag-
ment(s) at the site(s) of tritylation on the acceptors.In the
case of ditrityl ethers, two trisaccharide fragments can be
introduced simultaneously or, if the acceptor bears both
primary and secondary O-trityl groups, regioselectively at the
Figure 3a shows the mean 1H NMR parameters for the
protected oligosaccharides.The chemical shifts for H-3 and/or
H-6a and H-6b are shifted upfield upon O-3 and O-6
glycosylation.The effect of the linkage type manifests itself
most distinctly and systematically in the chemical shift
differences for H-2 (Dd ˆ ‡0.20 to ‡0.23 ppm) and H-1
(Dd ˆ À0.17 to À0.18 ppm, except at the branching points) of
the glycosylating residues on going from the (1 ! 3)- to the
(1 ! 6)-linkage.The chemical shifts of H-1 of the glycoside
residues have an average value of d ˆ 4.69 ppm, while the
chemical shifts of the other protons of these residues depend
on the type of acyl protecting groups on the attached residues,
and have therefore not been averaged.
4418
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Chem. Eur. J. 2002, 8, No. 19

Fully-Carbohydrate Mannodendrimers
4412 4423
Table 2.Chemical shifts ( d values) of the mannopyranosidic protons in the 1H NMR
spectra (CDCl3, 258C) of protected mannooligosaccharides 1, 4, 5, and 13 21.
secondary position.The branched oligosaccharides obtained
may be regarded as first and second generation glycoden-
drons.
Compound[a]
H-1
H-2
H-3
H-4
H-5
H-6a
H-6b
1
4
5
A
B
C
A
B
C
A
B
C
D
A
B
C
D
A
B
C
D
A
B
C
D
E
F
G
A
B
C
D
E
A
B
C
D
E
A
B
C
D
E
F
A
B
C
D
E
F
A
B
C
D
E
F
G
H
I
A
B
C
D
E
F
5.46
4.95
4.74
5.42
5.09
4.84
5.49
5.07
5.14
4.89
4.65
4.86
4.97
4.79
4.73
4.86
4.94
4.88
4.64
4.92
4.84
4.94
4.96
4.88
4.82
4.73
4.99
5.14
4.99
4.90
4.71
5.30
4.89
5.03
4.85
4.69
5.32
4.82[c]
4.93
5.05
4.84[c]
4.73
5.00
5.14
4.91
5.07
4.85
4.67
4.97
4.81
4.90
4.93
5.06
5.05
4.83
4.84
5.26
4.96
4.78
4.86
4.93
5.06
5.04
4.84
4.83
4.63
5.08
5.19
4.64
5.40
5.26
4.73
5.30
5.20
5.26
5.20
5.24
5.02
5.22
5.15
4.93
5.04
5.35
5.13
4.98
5.23
5.04
5.03
5.33
5.25
5.21
5.04
5.71
5.08
5.37
5.41
5.47
5.29
5.08
5.30
5.43
5.48
5.28
5.32
5.09
5.29
5.21
5.07
5.71
5.33
5.08
5.30
5.16
5.02
5.23
5.32
5.31
5.09
5.09
5.29
5.29
5.26
5.02
5.21
5.33
5.31
5.07
5.07
5.28
5.27
3.96
5.27
5.26
3.80
5.36
5.28
3.98
5.30
5.24
5.29
5.32
4.15
5.16
5.30
4.10
3.96
5.17
5.36
4.14
3.95
4.13
5.19
5.17
5.33[b]
5.28
4.24
4.01
5.90
5.19
5.38
4.33
5.78
4.23
5.23
5.33
4.35
5.76
5.36
4.23
5.24
5.33
4.20
5.24
5.91
4.24
5.23
5.31
4.12
5.20
5.32
4.22
4.22
5.23
5.23
5.30
5.30
4.13
5.18
5.27
4.25
4.21
5.21
5.22
5.31
5.31
5.16
5.28
5.26
3.96
5.36
5.28
3.91
5.29
5.27
5.32
5.30
5.22
5.26
5.25
5.15
5.18
5.22
5.27
5.20
5.20
5.26
5.25
5.25
5.27[b]
5.26
5.27
5.23
6.11
5.27
5.29
5.43
6.10
5.30
5.32
5.32
5.29[b]
6.10
5.42
5.30[b]
5.31[b]
5.30[b]
5.30
5.37
6.11
5.32
5.30
5.31
5.16
5.37
5.42
5.30
5.29
5.30
5.30
5.30
5.30
5.17
5.34
5.42
5.28
5.27
5.28
5.29
5.28
5.28
3.61
4.17
4.00
3.46
4.27
4.06
3.66
4.21
3.97
4.04
3.90
3.78
4.05
4.05
3.79
3.94
3.90
4.05
3.80
3.94
3.84
3.93
4.03
4.03
4.07
3.96
3.99
4.52
3.96
4.07
3.85
4.62
3.95
4.12
4.09
3.88
4.62
4.06
3.86
4.11
4.10
3.97
4.00
4.55
3.84
4.11
4.10
3.83
3.97
4.00
3.83
3.85
4.09
4.09
4.09
4.09
4.27
3.95
3.96
3.82
3.82
4.09
4.09
4.08
4.08
3.52
4.08
4.00
3.73
4.14
4.12
3.82
4.12
4.11
4.08
3.56
3.48
4.05
4.05
3.12
3.54
4.00
4.10
3.50
3.53
3.51
3.99
4.03
4.08
4.10
3.66
3.57
4.46
4.04
4.12
3.56
4.45
3.53
4.15
4.15
3.50
4.51
3.65
3.53
4.06
4.13
3.66
3.58
4.47
3.56
4.11
4.13
3.49
3.57
3.62
3.54
3.53
4.10
4.10
4.14
4.14
3.45
3.52
3.62
3.54
3.51
4.10
4.10
4.12
4.13
3.72
4.32
4.27
3.97
4.36
4.27
3.90
4.33
4.29
4.27
3.72
3.72
4.25
4.23
3.19
3.71
4.28
4.29
3.74
3.71
3.74
4.30
4.25
4.29
4.26
3.93
3.75
4.70
4.31
4.31
3.82
4.63
3.79
4.28
4.29
3.82
4.67
3.83
3.80
4.30
4.27
3.97
3.78
4.70
3.78
4.30
4.30
3.78
3.76
3.80
3.77
3.77
4.29
4.29
4.28
4.28
3.79
3.76
3.77
3.76
3.76
4.27
4.29
4.28
4.27
Experimental Section
General information and techniques: Triphenylmethylium perchlorate
(TrClO4) was prepared according to the published procedure[45] and
reprecipitated from a solution in nitromethane with dry diethyl ether;[46]
silver trifluoromethanesulfonate (AgOTf) was prepared as described
elsewhere.[47] Pyridine was distilled from KOH.Dichloromethane and
acetonitrile were distilled from P2O5 and CaH2, nitromethane from CaH2,
and all were stored over 3 ä molecular sieves.The solvents used in the
trityl-cyanoethylidene condensation (benzene and dichloromethane) were
degassed and distilled over CaH2 in a high-vacuum system.Solutions were
concentrated at about 408C on a rotary evaporator.Glycosylations of the
trityl ethers 6 12 with the cyanoethylidene derivative 1 were carried out by
applying vacuum techniques.[15] Column chromatography was carried out
using Silpearl silica gel (Sklarny Kavalier, Czech Republic).Thin-layer
chromatography (TLC) was carried out on Merck DC-Alufolien Kieselgel
13
14
15
60F254.Spots were visualized by spraying with 25%
H 2SO4 and
subsequent heating at about 1508C.Tritylated compounds gave a bright-
yellow coloration immediately after spraying or on gentle heating.Melting
points were determined on a Kofler hot stage.Optical rotations were
measured using a JASCO DIP-360 polarimeter at about 208C in chloro-
form (protected oligosaccharides) or water (deacylated oligosaccharides).
Fast atom bombardment mass spectra were obtained with a Kratos
MS80RF instrument using a krypton primary atom beam at 8 eVand trans-
indol-3-ylacrylic acid or 3-nitrobenzyl alcohol matrices.Time-of-flight mass
spectrometry with matrix-assisted laser-desorption ionization was carried
16
17
18
1
out on a Vision 2000 instrument. H and 13C NMR spectra were recorded
on Bruker WM-250, AM-300, and DRX-500 instruments with samples in
CDCl3 (protected oligosaccharides, Me4Si as the internal standard) and
D2O (deacylated oligosaccharides, acetone as the internal standard, dH
2.225 ppm, dC ˆ 31.45 ppm). 2D NMR spectra were obtained using stand-
ard Bruker software for Aspect 2000 and 3000 spectrometers (APT, COSY,
COSYRCT, ROESY, HMQC).NMR data for compounds 1, 4, 5, 13 29
are listed in Tables 2 5.
ˆ
1,2-O-[1-(exo-Cyano)ethylidene]-3,6-di-O-(2,3,4,6-tetra-O-acetyl-a-d-
mannopyranosyl)-b-d-mannopyranose (4): A mixture of 1,2-O-[1-(exo-
cyano)ethylidene]-b-d-mannopyranose[25] (3; 1.95 g, 8.44 mmol), Hg(CN)2
(7.60 g, 30.0 mmol), and HgBr2 (1.08 g, 3.00 mmol) was dried in vacuo (oil
pump) for 2 h.MeCN (10 mL) was added, and then a solution of 2,3,4,6-
tetra-O-acetyl-a-d-mannopyranosyl bromide[24] (12.33 g, 30.0 mmol) in
MeCN (15 mL) was added dropwise with stirring over a period of about
1 h.Stirring was continued for about 16 h at ambient temperature.The
reaction mixture was then concentrated, the residue was partitioned
between CHCl3 and aqueous NaI (about 100 mL of each), and the organic
layer was washed with water and concentrated.Column chromatography
(PhMe/EtOAc, 1:1) afforded the product 4 (4.7 g, 62%), [a]D ˆ ‡35.4 (c ˆ
0.88); elemental analysis calcd (%) for C37H49NO24 (891.8): C 49.83, H 5.53,
N 1.57; found: C 49.92, H 5.62, N 1.50.
19
20
4-O-Acetyl-1,2-O-[1-(exo-cyano)ethylidene]-3,6-di-O-(2,3,4,6-tetra-O-
acetyl-a-d-mannopyranosyl)-b-d-mannopyranose (1) and 1,2-O-[1-(exo-
cyano)ethylidene]-3,4,6-tri-O-(2,3,4,6-tetra-O-acetyl-a-d-mannopyrano-
syl)-b-d-mannopyranose (5): a) The monohydroxy derivative 4 (1.0 g) was
acetylated with Ac2O (2 mL) in C5H5N (1 mL) in the presence of a catalytic
amount of DMAP at about 208C for 16 h.After cooling, several drops of
H2O were added to the mixture, which was then diluted with CHCl3.The
resulting solution was successively washed with H2O, dilute aqueous HCl,
and aqueous NaHCO3, and concentrated.Crystallization of the residue
from MeOH gave the title compound 1 (0.84 g, 80%); m.p. 154 1598C;
[a]D ˆ ‡27.3 (c ˆ 0.9); elemental analysis calcd (%) for C39H51NO25 (933.8):
C 50.16, H 5.50, N 1.50; found: C 50.31, H 5.17, N 1.25.
21
G
H
I
b) Glycosylation of 3 (3.85 g, 16.7 mmol) with 2,3,4,6-tetra-O-acetyl-a-d-
mannopyranosyl bromide (27.4 g, 66.8 mmol) in the presence of Hg(CN)2
(16.9 g, 66.8 mmol) and HgBr2 (2.11 g, 5.85 mmol) in MeCN (20 mL) was
carried out as described above.Column chromatography gave a fraction
[a] The rows correspond to individual a-d-mannopyranose residues designated as A, B,
C, etc.(see schemes).[b,c] Assignment within the group of signals may be interchanged.
Chem. Eur. J. 2002, 8, No. 19
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4419

L.V.Backinowsky et al.
FULL PAPER
Table 3.Chemical shifts ( d values) of the mannopyranosidic carbons in the 13C NMR
spectra (CDCl3, 2588C) of protected mannooligosaccharides 1, 4, 5, and 13 21.
Table 4.Chemical shifts ( d values) of the mannopyranosidic protons in the
1H NMR spectra (D2O, 25 8C) of deprotected mannooligosaccharides 22
29.
Compound[a]
C-1
C-2
C-3
C-4
C-5
C-6
Compound[a]
H-1
H-2
H-3
H-4
H-5
H-6a
H-6b
1
4
5
A
B
C
A
B
C
A
B
C
D
A
B
C
D
A
B
C
D
A
B
C
D
E
F
G
A
B
C
D
E
A
B
C
D
E
A
B
C
D
E
F
A
B
C
D
E
F
A
B
C
D
E
F
G
H
I
A
B
C
D
E
F
100.1
97.6
97.3
97.0
100.5
97.6
97.3
100.5
99.0
97.8
98.4
97.2
99.0
97.4
98.1
99.0
98.8
97.5
98.3
99.1
97.2
98.9[b]
99.1[b]
976.
69.6
69.2
78.8
79.9
69.2
69.3
78.8
69.4
69.4
69.2
69.4
70.6
69.8
69.2
71.2
70.8
69.6
69.1
71.1
70.8
70.6
698.
68.4
69.0
80.0
81.1
69.2
69.0
80.0
68.6
68.3
68.9
68.9
74.8
68.3
68.0
75.2
74.7
68.3
69.1
75.0
75.0
75.4
n.d.
65.7
65.7
72.8
64.8
65.5
66.3
72.8
65.8
66.2
66.0
65.9[b]
65.8[b]
65.9[b]
65.6
68.0
67.4
65.5
65.9
n. d.
n. d.
n. d.
69.4
68.4
74.5
74.1
69.4
68.4
74.5
69.5
69.7
68.6
69.2
69.3
68.6
69.3
70.2
69.6
69.3
68.4
n. d.
n. d.
n. d.
62.2
62.1
67.1
66.1
62.6
62.2
67.1
62.2
62.7
62.1
65.8
66.6
62.0
62.3
62.5
66.2
62.2[b]
61.9[b]
66.2[b]
66.0
66.6[b]
22
A
B
C
D
A
B
C
D
E
F
G
A
B
C
D
E
A
B
C
D
E
A
B
C
D
E
F
A
B
C
D
E
F
A
B
C
D
E
F
4.76
4.88
5.13
4.91
4.73
5.07
4.87
5.13
5.15
4.89
4.91
4.80
5.21
4.97
5.25
4.98
4.72
5.09
4.87
5.13
4.90
4.72
5.10
4.89
4.87
5.11
4.90
4.78
5.07
4.92
4.85
5.11
4.92
4.79
5.08
4.91
4.87
4.89
5.12
5.13
4.92
4.92
5.44
5.13
4.94
4.91
4.94
5.24
5.18
4.97
4.97
3.94
4.14
4.06
3.98
4.09
4.23
4.14
4.07
4.07
3.98
3.98
4.05
4.33
4.06
4.15
4.07
4.07
4.06
4.12
4.05
3.96
4.07
4.06
3.99
4.12
4.06
3.98
4.07
4.06
3.98
4.13
4.06
3.98
4.08
4.08
4.00
4.13
4.12
4.07
4.07
3.98
3.98
4.23
4.13
4.03
4.22
4.18
4.12
4.12
4.04
4.04
3.93
3.91
3.87
3.84
3.83
4.01
3.93
3.89
3.89
3.83
3.83
3.78
4.08
3.91
3.96
3.92
3.83
3.87
3.91
3.87
3.82
3.85
3.86
3.82
3.98
3.86
3.82
3.83
3.87
3.83
3.87
3.88
3.83
3.83
3.88
3.84
3.88
3.91
3.89
3.88
3.83
3.84
3.89
3.93
3.88
4.01
3.98
3.94
3.94
3.89
3.89
3.74
3.89
3.67
3.66
3.90
3.86
3.87
3.66
3.67
3.67
3.67
3.86
3.94
3.73
3.72
3.74
3.88[b]
3.64
3.90[b]
3.64
3.64
3.85
3.67
3.71
3.85
3.67
3.67
3.85
3.72
3.68
3.88
3.68
3.68
3.83
3.72
3.73
3.88
3.88
3.68
3.69
3.68
3.68
3.95
3.74
3.77
3.93
3.94
3.73
3.73
3.72
3.72
3.75
3.77
3.78
3.70
3.75
3.96
3.88
3.79
3.77
3.68
3.68
3.75
4.04
3.76
3.87
3.76
3.78
3.76
3.86
3.76
3.67
3.77
3.75
3.82
3.87
3.77
3.67
3.77
3.93
3.70
3.87
3.78
3.70
3.77
3.93
3.83
3.95
3.95
3.77
3.77
3.68
3.68
4.28
3.97
3.86
3.93
3.92
3.82
3.83
3.76
3.76
3.79
3.78
3.76
3.78
3.75
3.76
3.78
3.75
3.77
3.77
3.77
3.69
3.81
3.84
3.87
3.84
3.74
3.75
3.78
3.75
3.75
3.75
3.76
3.79
3.78
3.76
3.76
3.77
3.79
3.78
3.80
3.78
3.78
3.77
3.79
3.83
3.81
3.80
3.77
3.77
3.81
3.81
3.79
3.83
3.86
3.84
3.83
3.82
3.83
3.82
3.82
3.95
3.97
3.86
3.89
3.97
3.98
3.98
3.90
3.90
3.88
3.88
3.98
4.05
3.96
3.96
3.96
3.97
3.86
3.95
3.85
3.89
3.95
3.87
3.91
3.94
3.87
3.87
3.97
3.93
3.89
3.96
3.90
3.89
3.96
3.93
3.95
4.00
3.97
3.90
3.90
3.95
3.95
4.03
3.98
3.94
4.03
4.03
3.96
3.93
3.94
3.94
23
13
14
15
24
25
26
n.d.
n.d.
621.
621.
623.
623.
698.
692.
690.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
68.2
67.4
66.6
65.6
66.0
68.1
66.6
68.1
65.8
66.0
68.9
66.6
65.6
68.1
n.d.
n.d.
n.d.
976.
16
17
18
98.3
99.1[b]
97.3
98.9[b]
97.5
98.6
98.7
97.4
99.1
97.5
98.4
98.7
97.6
97.4
99.1
97.6
98.2
99.3
97.3
97.6
98.8
97.6
98.2
99.3
97.7
97.7
97.5
99.1[c]
98.9[c]
97.7
97.6
81.3
99.1
97.6
97.7
97.5
98.8
99.1
97.6
97.6
71.1
70.8
70.2
69.6
69.1[c]
70.8
70.8
70.8
69.9
69.4
70.8
70.7
69.5
70.7
69.8
69.4
70.9
69.9
70.3
70.5
69.9
69.3
70.9
69.9
69.7
70.7[b]
70.6[b]
69.9
69.9
69.4
69.4
72.4
69.9
69.4
70.5
70.6
69.8
69.7
69.4
69.4
74.6
75.0
69.9
68.4
69.2[c]
74.2
69.2
74.9
68.5
69.1
73.9
69.2
69.3
75.0
68.5
69.1
75.4
68.6
69.9
74.9
68.6
69.0
75.3
68.5
69.3
75.0
75.0
68.6
68.6
69.1
69.1
75.4
68.5
69.0[b]
74.9
74.9
68.5
68.5
69.0[b]
69.2[b]
69.4
66.7
66.3
62.7
62.0
62.3
66.3
62.8
66.7
62.1
62.4
66.8
62.9
65.7
67.2
62.1
62.4
66.8
65.9
62.8
66.8
61.9
62.3
67.1
66.0
65.6
66.8
66.8
62.0[e]
62.1[e]
62.4
62.4
66.9
66.1
65.5
66.8
66.8
62.1[d]
62.0[d]
62.4[d]
62.4[d]
69.8
68.8
69.4
68.5
69.5
69.6
69.5
69.4
68.7
69.5
69.6
69.7
69.5
69.4
68.7
69.3
70.2
68.9
69.3
69.3
68.6
69.4
70.2
69.7
69.4
69.4
69.3
69.3
69.1
69.1
69.9
70.3
69.6
69.4
69.4
69.4
69.4
68.6
68.6
27
28
65.8[b]
65.9[b]
68.1
65.6
66.7
G
H
I
A
B
C
D
E
F
19
20
29
68.1
65.9[b]
65.6[b]
68.4
65.6
65.7
68.2
68.1
66.0[d]
66.0[d]
65.8[d]
65.8[d]
68.5
65.5
65.6
68.1
68.0
65.9[c]
65.9[c]
65.7[c]
65.7[c]
G
H
I
[a] The rows correspond to individual a-d-mannopyranose residues
designated as A, B, C, etc.(see schemes).[b] Assignment within the group
of signals may be interchanged
21
(10.1 g) with a mobility like that of the trisaccharide derivative 4, and this
fraction was acetylated.Crystallization from MeOH gave the trisaccharide
cyanoethylidene derivative 1 (7.2 g, 46%). Column chromatography of the
mother liquor afforded 5 (3.3 g; 16%) as an amorphous solid, [a]D ˆ ‡41
(c ˆ 2.9); elemental analysis calcd (%) for C51H67NO33 (1221.1): C 50.12, H
5.53, N 1.15; found: C 50.37, H 5.67, N 1.05.
G
H
I
Methyl 2,3,4-tri-O-acetyl-6-O-[2,4-di-O-acetyl-3,6-di-O-(2,3,4,6-tetra-O-
acetyl-a-d-mannopyranosyl)-a-d-mannopyranosyl]-a-d-mannopyranoside
(13): A solution of methyl 2,3,4-tri-O-acetyl-6-O-trityl-a-d-mannopyrano-
side (6) (0.145 g, 0.26 mmol) and the cyanoethylidene derivative 1 (0.241 g,
[a] The rows correspond to individual a-d-mannopyranose residues designated as
A, B, C, etc.(see schemes).[b,c,d,e] Assignment within the group of signals may be
interchanged.n.d. ˆ not determined.
4420
¹ 2002 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
0947-6539/02/0819-4420 $ 20.00+.50/0
Chem. Eur. J. 2002, 8, No. 19

Fully-Carbohydrate Mannodendrimers
4412 4423
Table 5.Chemical shifts ( d values) of the mannopyranosidic carbons in the
with CH2Cl2, washed with water, and concentrated.Column chromatog-
raphy (PhH/EtOAc, 1:1) afforded the tetrasaccharide 13 (0.171 g, 56%);
[a]D ˆ ‡47.9 (c ˆ 0.86); elemental analysis calcd (%) for C51H70O34
(1227.0): C 49.92, H 5.75; found: C 49.89, H 5.76.
13C NMR spectra (D2O, 25 8C) of deprotected mannooligosaccharides 22
29.
Compound[a]
C-1
C-2
C-3
C-4
C-5
C-6
Methyl 2,4-di-O-acetyl-3-O-[2,4-di-O-acetyl-3,6-di-O-(2,3,4,6-tetra-O-ace-
tyl-a-d-mannopyranosyl)-a-d-mannopyranosyl]-6-O-trityl-a-d-mannopyr-
anoside (14): Glycosylation of methyl 2,4-di-O-acetyl-3,6-di-O-trityl-a-d-
mannopyranoside (7; 0.199 g, 0.260 mmol) with 1 (0.244 g, 0.260 mmol) in
the presence of TrClO4 (8.9 mg, 0.026 mmol) in CH2Cl2 (2 mL), as
described for the preparation of 13, followed by column chromatography
22
A
B
C
D
A
B
C
D
E
F
G
A
B
C
D
E
A
B
C
D
E
A
B
C
D
E
F
A
B
C
D
E
F
A
B
C
D
E
F
100.7
100.9
103.5
100.7
102.1
103.5
100.5
103.4
103.3
100.8
100.5
101.8
103.3
100.4
103.2
100.2
101.9
103.2
100.3
103.1
100.2
102.2
103.4
100.7
100.6
103.4
100.7
102.2
104.1
100.5
101.1
103.7
100.7
102.2
103.8
100.8
101.2
100.8
103.5
103.5
100.8
100.8
86.3
69.6
70.9
71.5
71.4
70.8
70.8
70.8
71.2
71.2
71.2
71.2
70.8
70.8
71.2
71.2
71.2
71.2
71.7
71.2
71.7
71.6
70.9
71.4
71.4
70.9
71.4
71.4
71.3
71.0
71.3
70.8
71.3
71.3
71.2
71.5
71.5
71.0
71.0
71.5
71.5
71.5
71.5
73.9
71.5
71.5
71.1
71.1
71.6
71.6
71.5
71.5
70.7
79.8
71.8
72.0
80.0
79.5
79.5
71.6
71.6
71.8
71.8
80.1
79.6
71.9
71.5
71.8
80.2
72.2
80.0
72.0
72.0
79.8
71.8
72.0
79.8
71.8
72.0
81.0
71.9
71.9
79.9
71.9
71.9
80.8
73.1
72.5
80.0
79.9
72.1
72.1
72.0
72.0
81.4
72.4
72.5
80.0
80.1
72.4
72.4
72.1
72.1
66.3
67.2
68.2
68.2
66.7
67.0
67.0
68.0
68.0
68.0
68.0
66.6
67.0
68.0
68.0
67.9
67.5
68.4
67.4
68.4
68.4
67.2
68.2
68.2
67.1
68.2
68.2
66.7
68.0
68.0
67.0
68.0
68.0
67.1
68.3
68.3
67.4
67.4
68.3
68.3
68.3
68.3
67.4
68.3
68.3
67.3
67.3
68.3
68.3
68.3
68.3
70.5[b]
71.0[b]
74.6
74.1
71.9
73.0
72.1
74.5
74.4
73.8
73.8
72.0
73.0
73.9
74.6
73.8
72.6
74.9
72.5
74.9
74.3
72.4
74.6
72.5
72.4
74.6
74.0
72.0
73.0
74.0
72.0
74.7
74.0
72.0
72.3
72.3
72.1
72.1
74.7
74.7
74.1
74.1
72.6
73.5
72.4
72.0
72.0
74.9
74.9
74.2
74.2
65.1[c]
67.1[c]
62.4
62.4
67.0
66.5
66.6
62.1
62.1
62.3
62.1
66.3
66.8
62.1
62.1
62.3
67.0
62.6
67.0
62.6
62.6
66.9
62.3
67.1
66.7
62.3
62.3
66.4
68.0
62.3
66.4
62.3
62.3
66.9[b]
67.9
67.4[b]
67.0[b]
67.0[b]
62.5
62.5
62.5
62.5
66.7
67.3
67.3
66.8
66.8
62.5
62.5
62.5
62.5
23
(PhMe/EtOAc, 1:2) afforded the tetraoside 15 (0.202 g, 55%); [a]D
ˆ
‡35.9 (c ˆ 1.7); elemental analysis calcd (%) for C68H82O32 (1410.6): C
57.90, H 5.86; found: C 57.90, H 5.55.
Methyl 2,4-di-O-acetyl-3,6-di-O-[2,4-di-O-acetyl-3,6-di-O-(2,3,4,6-tetra-O-
acetyl-a-d-mannopyranosyl)-a-d-mannopyranosyl]-a-d-mannopyranoside
(15): Glycosylation of 7 (0.114 g, 0.150 mmol) with 1 (0.280 g, 0.300 mmol)
in the presence of TrClO4 (10 mg, 0.03 mmol) in CH2Cl2 (2 mL), as
described above, followed by column chromatography (PhMe/EtOAc, 1:2)
afforded the heptaoside 15 (0.195 g; 59%); [a]D ˆ ‡50.3 (c ˆ 1.4); ele-
mental analysis calcd (%) for C87H118O58 (2091): C 49.93, H 5.59; found: C
24
25
26
‡
50.09, H 5.80; MALDI-TOF MS: m/z: 2117 and 2133 (calcd for [M‡Na]
‡
and [M‡K] m/z: 2114 and 2130, respectively).
Methyl 2,4-di-O-acetyl-3-O-[2,4-di-O-acetyl-3,6-di-O-(2,3,4,6-tetra-O-ace-
tyl-a-d-mannopyranosyl)-a-d-mannopyranosyl]-6-O-(2,3,4,6-tetra-O-ben-
zoyl-a-d-mannopyranosyl)-a-d-mannopyranoside (16): A mixture of the
trityl ether 14 (0.42 g, 0.23 mmol), AgOTf (0.23 g, 0.89 mmol), and 2,4,6-
collidine (0.01 mL, 0.09 mmol) in PhH was freeze-dried. A solution of
2,3,4,6-tetra-O-benzoyl-a-d-mannopyranosyl bromide (0.583 g, 0.89 mmol;
pre-dried by lyophilization of PhH) in CH2Cl2 (5 mL) was added dropwise
with stirring at 08C under argon to a solution of the above mixture in
CH2Cl2 (5 mL).A bright yellow coloration typical of the triphenylmethy-
lium cation appeared immediately.After 10 min, a drop of C 5H5N was
added (discoloration was observed), the solution was diluted with CHCl3,
and the precipitate was filtered off.The filtrate was washed with 1 m
aqueous Na2S2O3 and water, and then concentrated.Column chromatog-
raphy of the residue (PhH/EtOAc, 1:1) gave the pentaoside 16 (0.244 g;
47%); [a]D ˆ ‡20.3 (c ˆ 2.2); elemental analysis calcd (%) for C83H94O42
(1763.6): C 56.53, H 5.37; found: C 56.20, H 5.45.
27
28
Methyl 2,4-di-O-acetyl-6-O-[2,4-di-O-acetyl-3,6-di-O-(2,3,4,6-tetra-O-ace-
tyl-a-d-mannopyranosyl)-a-d-mannopyranosyl]-3-O-(2,3,4,6-tetra-O-ben-
zoyl-a-d-mannopyranosyl)-a-d-mannopyranoside (17): Glycosylation of
methyl 2,4-di-O-acetyl-3-O-(2,3,4,6-tetra-O-benzoyl-a-d-mannopyrano-
G
H
I
A
B
C
D
E
F
syl)-6-O-trityl-a-d-mannopyranoside (8; 0.30 g, 0.27 mmol) with
1
(0.257 g, 0.27 mmol) in CH2Cl2 (2 mL) in the presence of TrClO4 (9 mg,
0.027 mmol), as described above, followed by column chromatography
29
(PhH/EtOAc, 1:1), afforded the pentaoside 17 (0.315 g; 66%); [a]D
ˆ
104.2
100.8
101.5
100.8
103.8
103.9
100.8
100.8
‡21.2 (c ˆ 2.4); elemental analysis calcd (%) for C83H94O42 (1763.6): C
‡
56.53, H 5.37; found: C 56.19, H 5.48; FAB MS: m/z: 1785 [M‡Na À H] .
Methyl 2,4-di-O-acetyl-3-O-(2,3,4,6-tetra-O-benzoyl-a-d-mannopyrano-
syl)-6-O-{2,3,4-tri-O-acetyl-6-O-[2,4-di-O-acetyl-3,6-di-O-(2,3,4,6-tetra-O-
acetyl-a-d-mannopyranosyl)-a-d-mannopyranosyl]-a-d-mannopyrano-
syl}-a-d-mannopyranoside (18): Glycosylation of methyl 2,4-di-O-acetyl-3-
O-(2,3,4,6-tetra-O-benzoyl-a-d-mannopyranosyl)-6-O-(2,3,4-tri-O-acetyl-
G
H
I
6-O-trityl-a-d-mannopyranosyl)-a-d-mannopyranoside
(9;
0.175 g,
0.126 mmol) with compound 1 (0.117 g, 0.126 mmol) in CH2Cl2 (2 mL) in
the presence of TrClO4 (4 mg, 0.0126 mmol), as described above, followed
by column chromatography (PhH/EtOAc, 1:1), afforded the hexaoside 18
(0.150 g; 58%); [a]D ˆ ‡87.1 (c ˆ 1.0); C95H110O50 (2051.9): elemental
analysis calcd C 55.61, H 5.40; found: C 55.45, H 5.36; FAB MS: m/z:
[a] The rows correspond to individual a-d-mannopyranose residues
designated as A, B, C, etc.(see schemes).[b,c] Assignment within the
group of signals may be interchanged.
‡
2074 [M‡Na À H] .
0.26 mmol) in PhH (2 mL) was placed in one limb of a tuning fork-shaped
tube,[15] and a solution of TrClO4 (0.009 g, 0.026 mmol) in dry MeNO2
(0.2 mL) was placed in the other. The tube was connected to a vacuum line
((3 4) Â 10À3 Torr) and the solutions were freeze-dried.PhH (2 mL) was
then distilled into the limb containing the reagents, the resulting solution
was freeze-dried once more, and the residue was dried at 30 408C for
about 30 min.CH 2Cl2 (2 mL) was then distilled into the tube, the solutions
of the reagents and the catalyst were mixed, and the mixture was left
overnight at about 208C.A drop of C 5H5N was then added to the bright
yellow solution, whereupon it became colorless.The solution was diluted
Methyl 2,4-di-O-acetyl-6-O-(2,3,4,6-tetra-O-benzoyl-a-d-mannopyrano-
syl)-3-O-{2,3,4-tri-O-acetyl-6-O-[2,4-di-O-acetyl-3,6-di-O-(2,3,4,6-tetra-O-
acetyl-a-d-mannopyranosyl)-a-d-mannopyranosyl]-a-d-mannopyrano-
syl}-a-d-mannopyranoside (19): The hexaoside 19 was synthesized by
condensation of methyl 2,4-di-O-acetyl-6-O-(2,3,4,6-tetra-O-benzoyl-a-d-
mannopyranosyl)-3-O-(2,3,4-tri-O-acetyl-6-O-trityl-a-d-mannopyrano-
syl)-a-d-mannopyranoside (10; 0.257 g, 0.198 mmol) with
1 (0.185 g,
0.198 mmol) in CH2Cl2 (2 mL) in the presence of TrClO4 (6.8 mg,
0.02 mmol), as described above. Column chromatography (PhH/EtOAc,
Chem. Eur. J. 2002, 8, No. 19
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L.V.Backinowsky et al.
FULL PAPER
1:3) yielded 19 (0.20 g; 60%); [a]D ˆ ‡29.4 (c ˆ 2.4); elemental analysis
Carbohydrates in Chemistry and Biology (Eds.: B.Ernst, G.W.Hart, P.
Sinay»), Wiley-VCH, Weinheim, 2000, pp.863 914.
calcd (%) for C95H110O50 (2051.9): C 55.61, H 5.40; found: C 55.45, H 5.36.
[4] For recent reviews, see: a) K.L. Kiessling, J.E. Gestwicki, L.E.
Strong, Curr. Opin. Chem. Biol. 2000, 4, 696 703; b) C.R.Bertozzi,
L.L.Kiessling, Science 2001, 291, 2357 2364.
[5] a) Y.C. Lee, R.T. Lee, Acc. Chem. Res. 1995, 28, 321 327; b) M.
Dubber, T.K.Lindhorst, Synthesis 2001, 327 330; c) P.I.Kitov, J.M.
Sadowska, G.Mulvey, G.D.Armstrong, H.Ling, N.S.Pannu, R.J.
Read, D.R.Bundle, Nature 2000, 403, 669 672; d) E.Fan, Z.Zhang,
Methyl 2,4-di-O-acetyl-3,6-di-O-{2,3,4-tri-O-acetyl-6-O-[2,4-di-O-acetyl-
3,6-di-O-(2,3,4,6-tetra-O-acetyl-a-d-mannopyranosyl)-a-d-mannopyrano-
syl]-a-d-mannopyranosyl}-a-d-mannopyranoside (20): The nonaoside 20
was synthesized by the condensation of methyl 2,4-di-O-acetyl-3,6-di-O-
(2,3,4-tri-O-acetyl-6-O-trityl-a-d-mannopyranosyl)-a-d-mannopyranoside
(11; 0.201 g, 0.15 mmol) with the cyanoethylidene derivative 1 (0.280 g,
0.3 mmol) in CH2Cl2 (2 mL) in the presence of TrClO4 (10 mg, 0.03 mmol),
as described above.Column chromatography (PhH/EtOAc, 1:3) yielded 20
(0.20 g; 50%); [a]D ˆ ‡54.3 (c ˆ 2.4); elemental analysis calcd (%) for
C111H150O74 (2668.4): C 49.96, H 5.67; found: C 50.17, H 5.86; FAB MS: m/z:
2690 [M‡Na À H] .
Ethyl 2,4-di-O-acetyl-3,6-di-O-{2,3,4-tri-O-acetyl-6-O-[2,4-di-O-acetyl-3,6-
di-O-(2,3,4,6-tetra-O-acetyl-a-d-mannopyranosyl)-a-d-mannopyranosyl]-
a-d-mannopyranosyl}-1-thio-a-d-mannopyranoside (21): Glycosylation of
W.E.Minke, Z.Hou, C.L.M.J.Verlinde, W.G.J.Hol,
J. Am. Chem.
Soc. 2000, 122, 2663 2664; e) WB. .Turnbull, AR. .Pease, JF..
¬
Stoddart, ChemBiochem 2000, 1, 70 74; f) R.Roy, F.Herna ndez-
¬
Mateo, F.Santoyo-Gonza lez, J. Org. Chem. 2000, 65, 8743 8746; g) P.
‡
Langer, S.J.Ince, S.V.Ley, J. Chem. Soc. Perkin Trans. 1 1998, 3913
3915; h) D.A. Fulton, J.F. Stoddart, Biocongugate Chem. 2001, 12,
¬
655 672; i) I.Baussanne, J.M.Benito, C.O.Mellet, J.M.G.Ferna
n-
dez, J.Defaye, ChemBiochem 2001, 2, 777 783; j) J.J.Lundquist, E.J.
Toone, Chem. Rev. 2002, 102, 555 578.
ethyl
2,4-di-O-acetyl-3,6-di-O-(2,3,4-tri-O-acetyl-6-O-trityl-a-d-manno-
pyranosyl)-1-thio-a-d-mannopyranoside (12; 0.548 g, 0.4 mmol) was per-
formed with the cyanoethylidene derivative 1 (0.821 g, 0.88 mmol) in the
presence of TrClO4 (27 mg, 0.08 mmol) in CH2Cl2 (7 8 mL), as described
above.Conventional work-up and column chromatography (PhH/EtOAc,
1:4 ! 1:19) afforded the nonaoside 21; yield 0.58 g (54%); [a]D ˆ ‡65.1
[6] R.Liang, J.Loebach, N.Horan, M.Ge, C.Thompson, L.Yan, D.
Kahne. Proc. Natl. Acad. Sci. USA 1997, 94, 10554 10559.
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Proc. Natl.
Acad. Sci. USA 1999, 96, 11782 11786.
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Neoglycoconjugates: Preparation and Applications (Eds.: Y. C. Lee,
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in Carbohydrate Chemistry (Ed.: G.-J. Boons), Blackie Academic,
‡
(c ˆ 2.4); C112H152O73S (2698.4); FAB MS: found: m/z: 2721 [M‡Na] .
Methyl
6-O-(3,6-di-O-a-d-mannopyranosyl-a-d-mannopyranosyl)-a-d-
mannopyranoside (22): Methanolic NaOMe solution (0.5m, 0.1 mL) was
added to a solution of the acetate 13 (120 mg) in MeOH (2 mL) and C5H5N
(1 mL), and the reaction mixture was allowed to stand overnight at about
London, 1998, pp.243 321; c) N.V.Bovin, H-.J.Gabius,
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Rev. 1995, 24, 413 421; d) S.-K. Choi, M. Mammen, G. M. Whitesides,
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Synthesis 1999, 1515 1519.
‡
208C.It was then neutralized with cation-exchange resin KU-2 (H ) that
had been pre-washed with MeOH, the resin was filtered off, and the filtrate
was concentrated to give the methyl tetraoside 22 in virtually quantitative
yield.
[9] a) D.A. Mann, M. Kanai, D.J.Maly, L.L.Kiessling,
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Soc. 1998, 120, 10575 10582; b) SM. .Dimick, S.C.Powell, S.A.
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Table 6.Optical rotations for oligosaccharides 22 29.
Oligosaccharide 22
23
24
25
26
27
28
29
[a]D
‡ 70.3 ‡ 127.2 ‡ 95.7 ‡ 87.5 ‡ 31.9 ‡ 31.4 ‡ 74.9 ‡ 98.0
(c, H2O)
(2.3) (0.4) (1.3) (0.4) (1.7) (0.8) (0.8) (1.4)
Deprotected oligosaccharides 23 29: These compounds were prepared
from the corresponding acylated derivatives 15 21.In a typical experi-
ment, 0.5m methanolic NaOMe (0.1 mL) was added to a solution of
compound 19 (100 mg) in a mixture of dry MeOH (1 mL) and dry C5H5N
(1 mL), and the solution was left overnight at about 208C.It was then
diluted with H2O and the mixture was neutralized with cation-exchange
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Carbohydr. Res. 1998, 310, 35 41;
¬
¬
b) J.J.GarcÌa-Lo pez, F.Santoyo-Gonza lez, A.Vargas-Berenguel, J.J.
¬
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Received: November 28, 2001
Revised: May 13, 2002 [F3709]
Chem. Eur. J. 2002, 8, No. 19
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4423