Epimers, Epimerisation, Anomers, Mutarotation, Mechanism of Mutarotation

Epimers

What are Epimers?

Epimer in stereochemistry specifies one of a pair of stereoisomers.  At the stereogenic centre, two isomers present in the molecule differ, while the rest remains identical. A molecule may contain numerous stereocenters leading to several stereoisomers.

Epimers

Stereoisomers are isomeric molecules that possess the same constitution and molecular formula, but they vary in three-dimensional orientations of their atoms in space.

Epimers – Example

Below, stereoisomers illustrate the D and L configurations of glucose. Here, glucose is referred the D and L on the basis of last chiral carbon atom.

Glucose involves the formation of glycogen, starch, glucose, oligosaccharides and polysaccharides. Due to the presence of carbon in glucose molecule it may exhibit stereoisomerism, that is enantiomers and diastereomers.

Epimerization

What is Epimerisation/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.

Epimerization

The penultimate step in Zhang & Trudell's classic epibatidine synthesis is an example of epimerization. Pharmaceutical examples include epimerization of the erythro isomers of methylphenidate to the pharmacologically preferred and lower-energy threo isomers, and undesired in vivo epimerization of tesofensine to brasofensine.

Anomers

Anomers are cyclic monosaccharides which differ from one another in the configuration of C-1 or C-2 carbon.

A pair of anomers, which differ only at the carbon bearing the aldehyde or ketone functional group in the sugar's open-chain form, are two nearly identical stereoisomers in the study of carbohydrates. Since the anomeric carbon is planar and achiral in open-chain form, anomers can only occur when the sugar is in its cyclic form. In a cyclic saccharide, an anomer is an epimer at the hemiacetal/hemiketal carbon, to put it more precisely. The process of changing one anomer into another is known as anomerization. Various anomers have different physical characteristics, melting points, and particular rotations, as is normal for stereoisomeric substances.

The process of changing one anomer into another is known as anomerization. Anomerization, also known as mutarotation, happens easily in solution and is catalysed by acid and base in the case of reducing sugars. This reversible process often results in an anomeric combination where the two separate anomers eventually approach equilibrium.

Anomers

• Cyclic monosaccharides known as anomers differ from one another by the orientation of their C-1 or C-2 carbons.
• For aldoses, it is C-1 and C-2 for ketoses.
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Example

The following are two examples of glucose's cyclic hemiacetal form:

Example of anomers are α-D -Glucose, and β-D -glucose, because the position of a hydroxyl group at carbon 1(C1) is different.

Summary:-

What are Anomers?

Cyclic monosaccharides known as anomers differ from one another depending on whether they include C-1 or C-2 carbons.

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