Chapter 25: Carbohydrates
a hemi-acetal an acetal
are true acetals in that the -
of a hemi-acetal has been substituted by an -
In the simplest case, the "
" maybe from a simple alcohol such as methanol or ethanol.
In this case, the -
is referred to as the
, the "non-sugar" part of the glycoside.
Alternatively, the "
" can be from another saccharide so joining two saccharide units together.
The following diagram shows two glycosides of glucose:
sucrose, a disaccharide
So the organic chemistry here, is just that of simple acetals and ketals (
The mechanism by which aldehydes or ketones are interconverted to acetals or ketals is catalysed with aqueous acid BUT not aqueous base.
Hence, glycosides can be hydrolysed with aqueous acid to give the component saccharides.
Other groups such as -
can also be used to substitute the -
group, such systems are referred to a
Dr. Ian Hunt
, Department of Chemistry, University of Calgary