2009_Book_FoodChemistry

292 4 Carbohydrates
trimethylchlorosilane, in pyridine as solvent, provides
a sugar derivative with all HO-groups silylated:
Monosaccharides form glycosides (cf. 4.2.4.5).
When this occurs between the lactol group of one
monosaccharide and any HO-group of a second
monosaccharide, a disaccharide results.
Compounds with up to about 10 monosaccharide
residues are designated as oligosaccharides.
When a glycosidic linkage is established only between
the lactol groups of two monosaccharides,
then a nonreducing disaccharide is formed, and
when one lactol group and one alcoholic HOgroup
are involved, a reducing disaccharide results.
The former is denoted as a glycosylglycoside,
the latter as a glycosylglycose, with additional
data for linkage direction and positions. Examples
are saccharose and maltose:
(4.112)
4.2.4.8 Cleavage of Glycols
Oxidative cleavage of vicinal dihydroxy groups
or hydroxy-amino groups of a sugar with lead
tetraacetate or periodate is of importance for
structural elucidation. Fructose, in a 5-membered
furanose form, consumes 3 moles of periodate
(splitting of each α-glycol group requires 1 mole
of oxidant) while, in a pyranose ring form, it
consumes 4 moles of periodate.
Saccharose consumes 3 moles (cf. Reaction
4.113) and maltose 4 moles of periodate.
The final conclusion as to sugar linkage positions
and ring structure is drawn from the periodate
consumption, the amount of formic acid produced
(in the case of saccharose, 1 mole; maltose,
2 moles) and the other carbonyl fragments which
are oxidized additionally by bromine to stable
carboxylic acids and then released by hydrolysis.
The glycol splitting reaction should be considered
an optional or complementary method to
the permethylation reaction applied in structural
elucidation of carbohydrates.
4.3 Oligosaccharides
4.3.1 Structure and Nomenclature
(4.113)
An abbreviated method of nomenclature is
to use a three letter designation or symbol for
a monosaccharide and suffix f or p for furanose or
pyranose. For example, saccharose and maltose