Enantiomers are mirror images of each other. These are otherwise called as D and L sugars; for example, D-fructose and L-fructose are enantiomers. If the OH group to the carbon atom lies on the right-hand side, then it is known as D series, as shown in Figure 2.3.

Most of the sugars in humans are D-sugars, except a few sugars that are of L-forms, such as L-fucose present in glycoproteins and L-iduronic acid found in glycosaminoglycans (GAGs).