11.5 Acylation and Alkylation of Monosaccharides
The –OH group of monosaccharide reacts with acetic anhydride or acetyl chloride to form esters. Similarly, ether can be prepared using methyl iodide/silver oxide. The nucleophilic character of –OH group is relatively poor, so silver oxide is used to increase the leaving tendency of the iodide ion in the SN2 reaction (Scheme 1).
Scheme 1
11.6 Glycosides
Glycosides are cyclic acetal form of sugars and the bond between the anomeric carbon and the alkoxy oxygen is called a glycosidic bond. They are prepared by the acid-catalyzed reaction of an alcohol with a pyranose or furanose.
Naming of glycosides is done by replacing the “ e ” of the sugar with “ ide ”. Example, a glycoside of glucose is glucoside and if pyranose or furanose name is used, the acetal is called pyranoside or furanoside. Both α - and β -glycoside obtained from the reaction of a single anomer with an alcohol (Scheme 2).
Scheme 2