292 4 Carbohydrates
trimethylchlorosilane, in pyridine as solvent, pro-
vides a sugar derivative with all HO-groups sily-
lated:
(4.112)4.2.4.8 CleavageofGlycols
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 eachα-glycol group requires 1 mole
of oxidant) while, in a pyranose ring form, it
consumes 4 moles of periodate.
Saccharose consumes 3 moles (cf. Reac-
tion 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 pro-
duced (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 consid-
ered an optional or complementary method to
the permethylation reaction applied in structural
elucidation of carbohydrates.
4.3 Oligosaccharides
4.3.1 StructureandNomenclature
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 monosaccha-
ride residues are designated as oligosaccharides.
When a glycosidic linkage is established only be-
tween the lactol groups of two monosaccharides,
then anonreducing disaccharideis formed, and
when one lactol group and one alcoholic HO-
group are involved, areducing disaccharidere-
sults. The former is denoted as a glycosylglyco-
side, the latter as a glycosylglycose, with addit-
ional data for linkage direction and positions. Ex-
amples are saccharose and maltose:(4.113)An abbreviated method of nomenclature is
to use a three letter designation or symbol for
a monosaccharide and suffixforpfor furanose or
pyranose. For example, saccharose and maltose