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 stereois ...

, an epimer is one of a pair of

diastereomer In stereochemistry, diastereomers (sometimes called diastereoisomers) are a type of stereoisomer. Diastereomers are defined as non-mirror image, non-identical stereoisomers. Hence, they occur when two or more stereoisomers of a compound have dif ...

s. 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.

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and

epirubicin Epirubicin is an anthracycline drug used for chemotherapy. It can be used in combination with other medications to treat breast cancer in patients who have had surgery to remove the tumor. It is marketed by Pfizer under the trade name Ellence in ...

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 (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, 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 Inositol, or more precisely ''myo''-inositol, is a carbocyclic sugar that is abundant in the brain and other mammalian tissues; it mediates cell signal transduction in response to a variety of hormones, neurotransmitters, and growth factors and ...

and

lipoxin A lipoxin (LX or Lx), an acronym for lipoxygenase interaction product, is a bioactive autacoid metabolite of arachidonic acid made by various cell types. They are categorized as nonclassic eicosanoids and members of the specialized pro-resolvin ...

and epilipoxin.

Epimerization

Epimerization is a chemical process where an epimer is converted to its diastereomeric counterpart. It can happen in

condensed tannins depolymerization Condensed tannins (proanthocyanidins, polyflavonoid tannins, catechol-type tannins, pyrocatecollic type tannins, non-hydrolyzable tannins or flavolans) are polymers formed by the condensation of flavans. They do not contain sugar residues. The ...

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 Epibatidine is a chlorinated alkaloid that is secreted by the Ecuadoran frog '' Epipedobates anthonyi'' and poison dart frogs from the Ameerega genus. It was discovered by John W. Daly in 1974, but its structure was not fully elucidated until ...

synthesis is an example of epimerization. Pharmaceutical examples include epimerization of the erythro isomers of

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

brasofensine Brasofensine (NS-2214, BMS-204756) is a phenyltropane that had been under development by Bristol-Myers Squibb for the treatment of Parkinson's and Alzheimer's diseases. In animal models of Parkinson's disease, brasofensine was effective in stim ...

References

{{Reflist Stereochemistry