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

Two chiral crown ethers derived from methyl beta -D-galactopyranoside are examined 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 chloroform. acetonitrile. and methanol. which are compatible with the solubilities of various protonated amines. Enantiomeric discrimination is observed in the spectra of most substrates in the presence of the crown ethers. In several cases. the enantiomeric discrimination is larger than observed with previously reported chiral crown ethers. The crown ether V contains a beta -diol unit capable of forming a chelate bond with lanthanide(III) ions. Adding ytterbium(III)nitrate to NMR samples in acetonitrile containing V causes substantial enhancements in the enantiodiscrimination in the spectra of several substrates. (C) 2001 Elsevier Science Ltd. All rights reserved.