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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2016/02/10 23:17:10」(JST)

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In stereochemistry, epimer refers to one of a pair of stereoisomers. The two isomers differ in configuration at only one stereogenic center. All other stereocenters in the molecules, if any, are the same in each.

Doxorubicin and epirubicin are two epimers that are used as drugs.


Doxorubicin–epirubicin comparison

Examples

The sugars glucose and galactose are epimers. In glucose, the -OH group on the first carbon is in the axial position, the direction opposite the -OH group on carbon C-4. In galactose, the -OH group is oriented in the same direction, the equatorial position.^[1] In cyclical compounds like these, the -OH group on C-1 may lie in opposite directions as well. This structural difference distinguishes two anomers. The two molecules pictured are both epimers and anomers (as indicated by the α and β designation).


α-D-glucopyranose	β-D-glucopyranose

The stereoisomers α-D-glucopyranose and β-D-mannopyranose are epimers because they differ only in the stereochemistry at the C-2 position. The hydroxyl group in α-D-glucopyranose is equatorial (in the "plane" of the ring) while in β-D-mannopyranose the C-2 hydroxyl group is axial (up from the "plane" of the ring). These two molecules are epimers but, because not mirror images of each other, are also not enantiomers (enantiomers have the same name but differ in D and L classification). They are also not sugar anomers, since the wrong carbon is involved in the stereochemistry.


β-D-glucopyranose	β-D-mannopyranose

Other closely related compounds are epi-inositol and inositol and lipoxin and epilipoxin.


Epi-inositol	Inositol	Lipoxin	Epilipoxin

Epimerisation

Epimerisation is a chemical process where an epimer is transformed into its chiral counterpart. It can happen in condensed tannins depolymerisation reactions. Epimerisation can be spontaneous (generally a slow process), or catalyzed by enzymes, e.g. the epimerization between the sugars N-acetylglucosamine and N-acetylmannosamine, which is catalyzed by Renin-Binding Protein.

References

^ Structure of the glucose molecule

English Journal

High-level soluble expression of a bacterial N-acyl-d-glucosamine 2-epimerase in recombinant Escherichia coli.

Klermund L1, Riederer A2, Groher A3, Castiglione K4.
Protein expression and purification.Protein Expr Purif.2015 Jul;111:36-41. doi: 10.1016/j.pep.2015.03.009. Epub 2015 Mar 21.
N-Acyl-d-glucosamine 2-epimerase (AGE) is an important enzyme for the biocatalytic synthesis of N-acetylneuraminic acid (Neu5Ac). Due to the wide range of biological applications of Neu5Ac and its derivatives, there has been great interest in its large-scale synthesis. Thus, suitable strategies for
PMID 25804337
PMID 25906737

Novel cellobiose 2-epimerases for the production of epilactose from milk ultrafiltrate containing lactose.

Krewinkel M1, Kaiser J1, Merz M1, Rentschler E1, Kuschel B1, Hinrichs J2, Fischer L3.
Journal of dairy science.J Dairy Sci.2015 Jun;98(6):3665-78. doi: 10.3168/jds.2015-9411. Epub 2015 Apr 8.
A selected number of enzymes have recently been assigned to the emerging class of cellobiose 2-epimerases (CE). All CE convert lactose to the rare sugar epilactose, which is regarded as a new prebiotic. Within this study, the gene products of 2 potential CE genes originating from the mesophilic bact
PMID 25864053