Epimer

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In chemistry , epimers are special stereoisomers with at least two stereocenters which differ in configuration at only one stereocenter , with the exception of the last asymmetric one. All other stereocenters in the molecules, if any, are the same. The anomer is a special case of the epimer in which the configuration at the anomeric carbon atom changes ( mutarotation ).

In the nomenclature , the prefix “epi-” is added to one of the epimeric pairs , for example for quinine and epi- quinine . If the pairs are enantiomers , the prefix “ent-” is used.

Examples

The sugars glucose and mannose are epimers. For example, β- D - glucopyranose and β- D - mannopyranose differ because they only have a different stereochemical configuration at the C-2 position. The hydroxy group of β- D -glucopyranose is in the equatorial position (in the “plane” of the ring), while the C-2 hydroxy group of β- D -annopyranose is in the axial position (out of the “plane” of the ring). However, since the images are not mirrored, these are not enantiomers, but epimers:

Beta-D-glucopyranose.svg Beta-D-mannopyranose.svg
β- D -glucopyranose
[contains five stereocenters,
including one anomeric
center (right)]

β- D -mannopyranose
[contains five stereocenters,
including one anomeric
center (right)]

Likewise, D - erythrose and D - threose are epimers. Also cis -Dekalon and trans -Dekalon are epimers, the latter is more stable:

Cis-Decalone Structural Formula V1.svg Trans-Decalone Structural Formula V1.svg
cis -decalone
(contains two stereocenters)

trans -decalone
(contains two stereocenters)

Doxorubicin and Epirubicin are two closely related drugs and epimers:

Doxorubicin – epirubicin comparison.svg
Comparison of doxorubicin and epirubicin

Other such compounds are epi- inositol and inositol :

Epi-inositol.svg Myo-inositol.svg
epi -inositol
(contains six stereocenters)
Inositol
(contains six stereocenters)

Other epimers are lipoxin and epi- lipoxin:

Lipoxin B4.svg 15-epi-lipoxin B4.svg
Lipoxin epi lipoxin

Testosterone and 17- epi -testosterone are also epimers:

Testosterone.svg Epitestosterone.png
Testosterone
(contains six stereocenters)
17- epi -testosterone
(contains six stereocenters)

Epimerization

Epimerization is a chemical process in which an epimer is converted into its chiral counterpart. An example of this would be the condensed tannins - depolymerization . Epimerization can be spontaneous (generally a slow process) or catalyzed by enzymes . The latter happens during the epimerization between the sugar N -acetylglucosamine and N -acetylmannosamine , which is catalyzed by RENBP , a renin- binding protein.

Individual evidence

  1. Joachim Buddrus, Bernd Schmidt: Fundamentals of organic chemistry. 5th edition, de Gruyter Verlag, Berlin 2015, ISBN 978-3-11-030559-3 , pp. 760–761.