Reactions at Oxygen Atoms
2.1
153
⊡ Scheme 60
Examples of chemical phosphorylation with phosphorous (III) reagents
⊡ Scheme 61
Example of enzymatic phosphorylation
A non-specific bacterial acid phosphatase from Shigella flexneri (PhoN-Sf) has been screened
for regioselective phosphorylation of primary alcohol(s) of more than 20 different cyclic and
acyclic monosaccharides using pyrophosphate as the phosphate donor ( > Scheme 61) [368].
These studies have shown that PhoN-Sf is capable of phosphorylating a range of hexoses
(D-glucose epimers, glycosides, and C-2 derivatives), pentoses, heptoses, ketoses, and acyclic
carbohydrates.
3 Reactions at the Anomeric Hydroxyl
3.1 Alkylation Reactions
In general, reactions and conditions for the introduction of protecting groups in the anomeric hemiacetal group are the same as those mentioned previously for non-anomeric hydroxyl
groups. Probably, the only exception relates to the alkylation reaction since alkyl ethers of
the anomeric hydroxyl group, which are acetals rather than ethers, are normally formed under
Fischer glycosylation conditions using the alcohol as the aglycon [369]. This process involves
cleavage of the C-1–O-1 bond at the anomeric center and, therefore will not be treated here,
but it is the method of choice for the preparation of alkyl glycosides.
2.1
153
⊡ Scheme 60
Examples of chemical phosphorylation with phosphorous (III) reagents
⊡ Scheme 61
Example of enzymatic phosphorylation
A non-specific bacterial acid phosphatase from Shigella flexneri (PhoN-Sf) has been screened
for regioselective phosphorylation of primary alcohol(s) of more than 20 different cyclic and
acyclic monosaccharides using pyrophosphate as the phosphate donor ( > Scheme 61) [368].
These studies have shown that PhoN-Sf is capable of phosphorylating a range of hexoses
(D-glucose epimers, glycosides, and C-2 derivatives), pentoses, heptoses, ketoses, and acyclic
carbohydrates.
3 Reactions at the Anomeric Hydroxyl
3.1 Alkylation Reactions
In general, reactions and conditions for the introduction of protecting groups in the anomeric hemiacetal group are the same as those mentioned previously for non-anomeric hydroxyl
groups. Probably, the only exception relates to the alkylation reaction since alkyl ethers of
the anomeric hydroxyl group, which are acetals rather than ethers, are normally formed under
Fischer glycosylation conditions using the alcohol as the aglycon [369]. This process involves
cleavage of the C-1–O-1 bond at the anomeric center and, therefore will not be treated here,
but it is the method of choice for the preparation of alkyl glycosides.