stereochemistry Stereochemistry, a subdiscipline of chemistry, studies the spatial arrangement of atoms that form the structure of molecules and their manipulation. The study of stereochemistry focuses on the relationships between stereoisomers, which are defined ...

, 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 di ...

s. The two epimers have opposite

configuration Configuration or configurations may refer to: Computing * Computer configuration or system configuration * Configuration file, a software file used to configure the initial settings for a computer program * Configurator, also known as choice board ...

at only one

stereogenic center In stereochemistry, a stereocenter of a molecule is an atom (center), axis or plane that is the focus of stereoisomerism; that is, when having at least three different groups bound to the stereocenter, interchanging any two different groups cr ...

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 Doxorubicin, sold under the brand name Adriamycin among others, is a chemotherapy medication used to treat cancer. This includes breast cancer, bladder cancer, Kaposi's sarcoma, lymphoma, and acute lymphocytic leukemia. It is often used toge ...

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 Glucose is a sugar with the molecular formula , which is often abbreviated as Glc. It is overall the most abundant monosaccharide, a subcategory of carbohydrates. It is mainly made by plants and most algae during photosynthesis from water and ...

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 (Help:IPA/English, /ɪˈnænti.əmər, ɛ-, -oʊ-/ Help:Pronunciation respelling key, ''ih-NAN-tee-ə-mər''), also known as an optical isomer, antipode, or optical antipode, is one of a pair of molecular entities whi ...

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

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 In biochemistry, medicine, and related sciences, inositol generally refers to ''myo''-inositol (formerly ''meso''-inositol), the most important stereoisomer of the chemical compound cyclohexane-1,2,3,4,5,6-hexol. Its elemental formula, formula is ...

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-resolvi ...

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 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 u ...

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 a central nervous system (CNS) stimulant used in the treatment of attention deficit hyperactivity disorder (ADHD) and narcolepsy. It may be taken Oral adm ...

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, serotonin–noradrenaline–dopamine reuptake inhibitor from the phenyltropane family of drugs, which is being developed for the treatment of obesity. Tesofensine was ...

to brasofensine.

References

{{Reflist Stereochemistry