Configuration of the ketoses

Ketoses have the keto group in the 2-position with one less chiral carbon compared to aldoses. So, ketoses have a half number of stereoisomers compared to aldoses with same number of carbon atoms. For example, aldopentose has three chiral centers with eight stereoisomers, while ketopentose has two chiral centers with four stereoisomers. The configuration of D-2 ketones is illustrated by the following examples. Dihydroxyacetone may not be a sugar, but it is included as the ketose analog of glyceraldehyde.

Configuration of the Ketoses

Epimers are stereoisomers that differ in configuration of only one asymmetric carbon of enantiomers or diastereomers. Example, D-glucose and D-mannose are C-2 epimers and D-glucose and D-talose are C-3 epimers. D-fructose and D-tagatose are C-4 epimers of ketohexoses.