Enantioselective Liquid-Solid Extraction (ELSE)--An Unexplored, Fast, and Precise Analytical Method

A novel method of evaluating the enantioselectivity of chiral receptors is investigated. It involves extraction of an ionic guest in racemic form from an ion-exchange resin to the organic solvent, where it is bound by a chiral receptor. The enantioselectivity of the examined receptor is determined simply by measuring the enantiomeric excess of the extracted guest. We show that the concept is viable for neutral receptors binding chiral organic anions extracted into acetonitile. This method was determined to be more accurate and far less time-consuming than the classical titrations. Multiple racemic guests can be applied to a resin in a single experiment, giving the method a very high throughput.