Chiral discrimination controlled by the solvent dielectric constant

Abstract

Chiroselective molecular recognition accompanied by a change in configuration of a target substrate has been studied. ( RS)-α-Amino-ε-caprolactam 1 was used as the target substrate to be resolved while N-tosyl-( S)-phenylalanine 2 was used as the chiral selector. The dielectric constant ( ε) of the solvent was found to have a profound effect on the chiroselective molecular recognition. The specific chiral selector ( S)- 2 not only recognized both enantiomers ( R)- and ( S)- 1 individually to be deposited as the less-soluble salt from the different solvent but also controlled the configuration and diastereomeric excess of the less-soluble diastereomeric salt by simple adjustment of the solvents dielectric constant. The chiroselective recognition mechanism was examined based on the crystal structures of the salts, ( S)- 1·( S)- 2·H 2O and ( R)- 1·( S)- 2, obtained from the resolution process.