Diastereoisomerization

Diastereoisomerization is a type of stereoisomerization that involves the conversion of one diastereomer into another. Diastereomers are stereoisomers that are not mirror images of each other. This means they have the same connectivity of atoms but differ in the spatial arrangement of at least two stereocenters, and they are not enantiomers. Diastereoisomerization typically occurs through chemical reactions that temporarily break and reform bonds, altering the configuration at one or more stereocenters while leaving others unchanged.

A common mechanism for diastereoisomerization involves epimerization, where only one stereocenter in a molecule inverts its configuration. This can happen under specific conditions, such as in the presence of an acid or base catalyst, or through radical or photochemical processes. For instance, sugars can undergo epimerization at various positions, leading to the formation of different sugars that are diastereomers of the original.

The interconversion between diastereomers is distinct from enantiomerization, which involves the conversion of a chiral molecule into its non-superimposable mirror image (enantiomer). Diastereoisomers have different physical and chemical properties, such as melting points, boiling points, solubilities, and reactivity, which allows for their separation by techniques like chromatography or fractional crystallization. In contrast, enantiomers have identical physical properties (except for their interaction with plane-polarized light) and can only be separated by chiral resolution methods. The term diastereoisomerization specifically refers to the process by which one diastereomeric form is transformed into another.