In
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
diastereomers.
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 and
epirubicin are two epimers that are used as drugs.
Examples
The stereoisomers β-
D-
glucopyranose
Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, using ...
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, since it is not the
anomeric carbon
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 fo ...
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.
They ...
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 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
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 stimu ...
.
References
{{Reflist
Stereochemistry