In
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 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 (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 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 and epilipoxin.
Epimerization
Epimerization is a chemical process where an epimer is converted to its diastereomeric counterpart.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