Molecular mechanism of DCR phenomenon observed in (RS)-1-cyclohexylethylamine–mandelic acid resolution system

A bug in enantiomer separation: double salt formation – diastereomeric and double salt structures of 1-cyclohexylethylammonium 2- and 4-chloromandelate

The number of crystal structures of diastereomeric salt pairs and especially of double salts is limited in the literature.

Molecular Mechanisms of Dielectrically Controlled Resolution (DCR)

It is widely believed that the chiral discrimination process is solely dependent on the stereochemistryof the relevant molecules. However, through systematic studies on several resolution systems with popularchiral selectors, we have discovered a new fact that triggers modification of this prevailing conceptof chiral resolution. The studies have demonstrated that one enantiomer of a chiral selector can recognizeboth enantiomers of a target molecule in different solvent systems with different dielectric constants.The phenomenon was termed dielectrically controlled resolution (DCR). Since DCR was observed in differentresolution systems and was not too specific to a particular system, DCR was expected to widely occurin various resolution systems. We have investigated the molecular mechanism underlying this interestingphenomenon based on X-ray analysis of the relevant diastereomeric salts. The disclosed mechanism clearlyindicates that a chiral selector can inherently recognize both enantiomers of a target moleculeand only the dielectric property of the solvent employed in the resolution process governs the selectionof the enantiomer.