Separation of Diastereoisomers by Means of TLC
The isomers that differ only in configuration or conformation are recognized as stereoisomers that are divided into enantiomers and diastereoisomers. The con-formational isomers represent dynamic spatial arrangements, the stereoisomers being interconvertible by the simple torsion of substituted carbon atoms around a simple bond in the molecule. In enantiomers, the distances between the atoms nonbonded directly are rigorously identical, whereas in diastereoisomers there are always differences between these distances. Diastereoisomerism is caused by the differences in conformation or only in configuration at several sites in the molecule. The separation of diastereoisomeric compounds by thin layer chromatography on polar adsorbents such as silica gel and alumina is widely used. Separation of the enantiomers comprising the racemate is a common problem in stereochemical research as well as in the preparation of biologically active compounds, particularly, drugs. The chirality sense and optical activity of the enantiomers are determined by their absolute configuration.