Biology Reference
In-Depth Information
glycosylation using the glycosyl donor and acceptor derived from
glucose,
α
β
-isomers arise with respect to stereoselectivity of
the anomeric carbon, and four isomers are conceivable with respect
to regioselectivity owing to the four hydroxy groups in the acceptor.
Thus, the glycosylation using the two glucose substrates involves a
possibility for the production of eight isomers for the glucose dimer
(Fig. 1.4). The large numbers of isomers for the oligosaccharides
composed of glucose residues are theoretically calculated [25].
Among the multiple fashions of the glycosidic linkages, only one
kind of the linkage must be constructed to produce polysaccharides
with well-defined structure on the basis of the aforementioned two
important selectivities in the glycosylation.
For stereo- and regioselective construction of the glycosidic
linkage, a leaving group, protective groups, a catalyst, and a solvent
should appropriately be selected. Over the past century, the reaction
control in the glycosylation has been one of the main research
areas in the carbohydrate chemistry. Although many chemical
glycosylations using various glycosyl donors, acidic catalysts,
- and
OR
OR
OR'
O
O
catalyst
OR'
RO
RO
O
OR
RO
RO
O
(activator)
O
O
+
R'O
OR'
HO
OR'
RO
OR
OR
OR'
RO
+
R'O
OR'
X
O
solvent
O
β
-isomer
OR'
OR
R'O
OR'
OR'
glycosyl donor
glycosyl acceptor
α
-isomer
X: leaving group
R, R': protective group
Figure 1.3
Reaction manner of glycosylation.
1,6-linkage
OH
OH
1,4-linkage
O
O
HO
HO
HO
*
HO
OH
OH
OH
1,3-linkage
activated anomeric carbon
1,2-linkage
eight isomers
Figure 1.4
Eight isomers are produced by glycosylation of glucose donor
with glucose acceptor.
