epimerisation

Epimerisation is a type of stereoisomerization where two enantiomers or diastereomers interconvert. Specifically, it involves the inversion of configuration at a single stereogenic center in a molecule. This process results in the formation of a new stereoisomer, which is an epimer. Epimers are stereoisomers that differ in configuration at only one chiral center.

This phenomenon is common in carbohydrate chemistry. For example, glucose and galactose are epimers, differing only in the configuration at the C-4 carbon. The interconversion between these epimers can occur under certain chemical conditions, such as in basic or acidic solutions. In biological systems, epimerisation is often catalyzed by enzymes called epimerases. These enzymes play crucial roles in various metabolic pathways, including the interconversion of sugars and the synthesis of cell wall components.

The mechanism of epimerisation typically involves the transient formation of a planar intermediate, such as a carbocation or an enolate. This planar intermediate can then be reprotonated from either face, leading to the inversion of stereochemistry at the affected carbon. Understanding epimerisation is important for controlling the stereochemical outcome of chemical reactions and for comprehending biological processes.