Enantioselective recognition of sodium carboxylates by an 1,8-diaminoanthracene based ion pair receptor containing amino acid units

Abstract

An anthracene based ion pair receptor containing two amino acid units supported by cation and anion binding domains has been synthesized and shown to exhibit enhanced anion binding affinities in the presence of sodium cations. The receptor’s ability to recognize enantiomers was studied using chiral carboxylates derived from 2-phenylbutyric acid, mandelic acid, and three Boc-protected amino acids. Sodium cation coordination does not influence chiral recognition but does affect the strength of anion binding. The greatest enhancement of anion binding in the presence of sodium cations was found for halides, and the highest enantiodiscrimination was found for Boc-N-tryptophan. Comparative anion and salt binding studies revealed that the simultaneous action of multiple binding domains in the structure of receptor 1 is responsible for its stronger salt association and better enantioselectivity than in the case of mono-supported receptor 2.