Molecular mechanism of dielectrically controlled optical resolution (DCR)

We have recently found the first example of dielectrically controlled optical resolution (DCR). By adjusting the dielectric constant of the solvent used in the resolution process, each optical isomer of (R,S)-alpha-amino-epsilon-caprolactam can be selectively obtained using N-tosyl-(S)-phenylalanine as a chiral selector. The molecular mechanism of DCR has been investigated by comparing the molecular and crystal structures of the optical selector, its target substrate and their diastereomeric salts. Strong hydrophobic interactions between the phenyl rings of the optical selector govern the molecular aggregation of the selectors and form a hydrophilic layer in which molecular recognition takes place. The recognition site in the hydrophilic layer can inherently identify both of the isomers. The dielectric constant of the solvent used in the discrimination process controls the intermolecular interaction which determines the isomer to be selected. The molecular mechanism of DCR disclosed in this study strongly suggests that DCR is not a specific but a general phenomenon. This method can be applicable to a large variety of optical resolution processes.