Principles of Biochemistry (2+1)

3.2.1.1.2.2 D&L Isomerism

The designation of a sugar isomer as the D form or of its mirror image as the L form is determined by its spatial relationship to the parent compound of the carbohydrate family, the three carbon sugar glyceraldehydes.

 

The orientation of the -H and -OH groups around the carbon atom adjacent to the terminal primary alcohol carbon determines whether the sugar belongs to the D or L series. When the -OH group on this carbon is on the right, the sugar is a member of the D series; when it is on the left, it is a member of the L series. Most of the monosaccharide occurring in nature is of the D configuration.

 

The structure of D and L Glyceraldehyde and D and L glucose are given below: