It is said that two carbohydrates are enantiomers if they are mirror images that are unmatched by one another. One example of the enantiomer is the D and L isomers of glucose. A second type of isomer seen in carbohydrates is diastereoisomers.
In stereochemistry, an epimer is one of a pair of stereoisomers. The two isomers differ in configuration to a single stereogenic center. All the other stereocenters in the molecules, if any, are the same in each.
Doxorubicin and epirubicin are two epimers that are used as drugs.
Glucose and galactose sugars are epimers. In glucose, the -OH on the first carbon is in the axial position, the opposite direction to the -OH on carbon C-4. In galactose, the -OH group is oriented in the same direction, the equatorial position. [1] In cyclic compounds such as this, the -OH group on C-1 can also stand in opposite directions. This structural difference distinguishes two anomers. The two molecules presented are both epimers and anomers (indicated by the names α and β).
The β-D-glucopyranose and β-D-manopyranose stereoisomers are epimers because they differ only by stereochemistry at the C-2 position. The hydroxyl group in the? -D-glucopyranose is axial (from the ring plane), while in β-D-manopyranose the C-2 hydroxyl group is equatorial (in the “plane” of the ring). These two molecules are epimers, but because they are not mirrors, they are not enantiomers (the enantiomers have the same name but differ in D and L). They are also not anomer of sugar, because the wrong carbon is involved in stereochemistry.
