stereochemistry Stereochemistry, a subdiscipline of chemistry, involves the study of the relative spatial arrangement of atoms that form the structure of molecules and their manipulation. The study of stereochemistry focuses on the relationships between stereo ...

, an epimer is one of a pair of diastereomers. The two epimers have opposite configuration at only one stereogenic center out of at least two. All other stereogenic centers in the molecules are the same in each. Epimerization is the interconversion of one epimer to the other epimer. Doxorubicin and epirubicin are two epimers that are used as drugs.

Examples

The stereoisomers β-D- glucopyranose and β-D- mannopyranose are epimers because they differ only in the stereochemistry at the C-2 position. The hydroxy group in β-D-glucopyranose is equatorial (in the "plane" of the ring), while in β-D-mannopyranose the C-2 hydroxy group is

axial Axial may refer to: * one of the anatomical directions describing relationships in an animal body * In geometry: :* a geometric term of location :* an axis of rotation * In chemistry, referring to an axial bond * a type of modal frame, in music * ...

(up from the "plane" of the ring). These two molecules are epimers but, because they are not mirror images of each other, are not

enantiomer In chemistry, an enantiomer ( /ɪˈnænti.əmər, ɛ-, -oʊ-/ ''ih-NAN-tee-ə-mər''; from Ancient Greek ἐνάντιος ''(enántios)'' 'opposite', and μέρος ''(méros)'' 'part') – also called optical isomer, antipode, or optical ant ...

s. (Enantiomers have the same name, but differ in D and L classification.) They are also not sugar

anomers In carbohydrate chemistry, a pair of anomers () is a pair of near-identical stereoisomers that differ at only the anomeric carbon, the carbon that bears the aldehyde or ketone functional group in the sugar's open-chain form. However, in order ...

, since it is not the anomeric carbon involved in the stereochemistry. Similarly, β-D-glucopyranose and β-D- galactopyranose are epimers that differ at the C-4 position, with the former being equatorial and the latter being axial. In the case that the difference is the -OH groups on C-1, the anomeric carbon, such as in the case of α-D-glucopyranose and β-D-glucopyranose, the molecules are both epimers and anomers (as indicated by the α and β designation).Structure of the glucose molecule
/ref> Other closely related compounds are ''epi''-inositol and inositol and lipoxin and epilipoxin.

Epimerization

Epimerization is a chemical process where an epimer is converted to its diastereomeric counterpart. It can happen in condensed tannins depolymerization reactions. Epimerization can be spontaneous (generally a slow process), or catalysed by enzymes, e.g. the epimerization between the sugars ''N''-acetylglucosamine and ''N''-acetylmannosamine, which is catalysed by renin-binding protein. The penultimate step in Zhang & Trudell's classic epibatidine synthesis is an example of epimerization. Pharmaceutical examples include epimerization of the erythro isomers of

methylphenidate Methylphenidate, sold under the brand names Ritalin and Concerta among others, is the most widely prescribed central nervous system (CNS) stimulant medication used to treat attention deficit hyperactivity disorder (ADHD) and, to a lesser extent ...

to the pharmacologically preferred and lower-energy threo isomers, and undesired ''in vivo'' epimerization of

tesofensine Tesofensine (NS2330) is a serotonin–noradrenaline–dopamine reuptake inhibitor from the phenyltropane family of drugs, which is being developed for the treatment of obesity. Tesofensine was originally developed by a Danish biotechnology compa ...

to brasofensine.

References

{{Reflist Stereochemistry