Chiral calix[4]azacrowns for enantiomeric recognition of amino acid derivatives

Abstract

In this study the synthesis of novel chiral calix[4]azacrown derivatives has been reported. The enantioselectivity of chiral receptors was investigated by using UV–vis spectroscopy. All the chiral calix[4]arene derivatives exhibited certain chiral recognition toward the enantiomers of phenylalanine (Phe-OMe·HCl) and alanine methyl ester hydrochlorides (Ala-OMe·HCl). As a chiral receptor, the furfuryl-armed calix[4]azacrown ether 7 has the best enantiomeric discriminating ability for α-amino acid ester hydrochlorides (up to K L/ K D=2.08, ΔΔ G 0=−1.82 kJ mol −1) in CHCl 3. The enantiomeric recognition abilities for guests are also discussed from a thermodynamic point of view.