Biphasic enantioselective partitioning studies using small-molecule chiral selectors

Enantioselective partitioning of racemic N-3,5-(dinitrobenzoyl)leucine or racemic naproxen was studied using a two-component chiral phase transfer approach. A combination of an achiral ion-pairing reagent and a chiral complexing agent (selector) is necessary to effect enantioselective partitioning between an aqueous bicarbonate solution and a nonpolar organic solvent. In these biphasic resolutions, the interplay between the ion-pairing reagent and the selector is essential for maximizing enantioselectivities. Furthermore, the lipophilicity of the ion-pairing reagent, the concentration of the ion-pairing reagent and selector, and the polarity of the organic solvent all exert a considerable influence on the biphasic process. In this manuscript, we conduct optimization studies through analysis of solvent, concentration and ion-pairing effects. Conclusions concerning the mechanistic rationale behind enantioselective partitioning are given.