Utility of crown ethers derived from methyl beta-D-galactopyranoside and their lanthanide couples as chiral NMR discriminating agents

Two chiral crown ethers derived from methyl beta -D-galactopyranoside are e xamined as chiral NMR discriminating agents for protonated primary amines. amino alcohols. and amino acids. In combination, the solubility and use of the two crown ethers span a range of common NMR solvents including chlorofo rm. acetonitrile. and methanol. which are compatible with the solubilities of various protonated amines. Enantiomeric discrimination is observed in th e spectra of most substrates in the presence of the crown ethers. In severa l cases. the enantiomeric discrimination is larger than observed with previ ously reported chiral crown ethers. The crown ether V contains a beta -diol unit capable of forming a chelate bond with lanthanide(III) ions. Adding y tterbium(III)nitrate to NMR samples in acetonitrile containing V causes sub stantial enhancements in the enantiodiscrimination in the spectra of severa l substrates. (C) 2001 Elsevier Science Ltd. All rights reserved.