Acetals Derived from Carbohydrate Carbonyl Groups

Acetals Derived from Carbohydrate Carbonyl Groups 

The formation and chemistry of dithioacetals of sugars have been reviewed. 4,6-Dichloro-4,6-dideoxy-D-gaIactose reacted with cyclohexanone ethylene acetal in the presence of an acid catalyst to give the acyclic derivative (48), which was converted into the corresponding 5-ulose. Treatment with base converted (48) into the 5,6-anhydro-derivative, which was hydrolysed to give the L-idose diacetal (49), presumably by way of a4,5-anhydro-D-glucose derivative. 

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Acetals Derived from Carbohydrate Carbonyl Groups... 

The OH unit derived from the carbonyl group, formed by cycliza-tion to a furanose or a pyranose, is attached to the so-called anomeric carbon. An aldose will cyclize to form a stable hemi-acetal structure a furanose or a pyranose. A ketose will cyclize to form a stable hemiketal structure a furanose or a pyranose. The Haworth projection is an older representation for carbohydrates that is based on a planar pyranose or furanose ring. Cyclization of an aldose or a ketose to a furanose or pyranose is accompanied by mutarotation at the anomeric carbon. Mutarotation is the change in optical rotation of a pure furanose or pyranose derivative to that resulting from a mixture of isomers at the anomeric carbon. 

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