Biomedical Engineering Reference
In-Depth Information
OAc
AcO
OAc
O
OBz
HO
O
HO
OAc
OMe
AcO
BnO
AcO
3. NIS
1. TMSOTf
N
3
O
O
SPh
O
AcO
O
Ph
52%
2.
OBz
HO
OBz
O
O
NH
O
Ph
SPh
HO
PhS
OBz
OAc
AcO
CCl
3
PhS
O
OBz
H
+
HO
OAc
AcO
O
OAc
OAc
AcO
AcO
O
O
O
Ph
Ph
O
OM
e
O
O
BnO
OBz
AcO
AcO
S
N
3
O
PhS
O
Ph
Ph
Deprotection
steps
ROH
SPh
OH
HO
OH
O
OH
OH
HO
O
O
O
HO
OMe
O
HO
OH
NHAc
SCHEME 12.28
Boons's participation method.
trisaccharide in 52% yield. Upon deprotection, this compound led to the Galili
trisaccharide, which has been identified as an epitope that can trigger acute rejections
in xenotransplantations [91]. Such compounds have invoked renewed interest due to
the discovery of a naturally occurring human antibody bearing a nonreducing end
a
-
D
-GalNAcpOR sequence [92]. Very recently,
the Boons group used this method in the solid-supported synthesis of
-
D
-Galp-(1
!
3)-
-
D
-Galp-(1
!
4)-
b
b
-glucans [93].
a
12.5.
-SIALIC ACID GLYCOSIDES
a
Sialic acids are a family of acidic ketoses that are found at the nonreducing end of
numerous glycoconjugates. They are recognized as ligands for numerous proteins and
are very widespread in various bioconjugates, including glycolipids, glycopeptides,
gangliosides, and oligosaccharides, rendering them attractive targets from both
synthetic and biological points of view [94]. In general, the
-sialosides with their
equatorial glycosidic bond to a ketose sugar devoid of participating functionality
present another class of highly challenging glycosidic bonds and whose synthesis has
been reviewed numerous times [95].
a
12.5.1. Synthesis of
-Sialyl Derivatives and Gangliosides
Gangliosides are known to be involved in vital processes, such as immune or nervous
system, as the molecules responsible for cell-cell and cell-ligand interactions, and
the sialyl residue, mostly
N
-acetylneuraminic acid, is of crucial importance in
these interactions with proteins. The sialyl Lewis
X
moiety (sLe
X
, Scheme 12.29) is
a
OH
CO
2
H
OH
OH
OH
OH
HO
O
OH
O
O
O
O
AcHN
OH
O
HO
NHAc
O
OH
sLe
X
HO
OH
SCHEME 12.29
Sialyl Lewis X ganglioside.
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