(18-Crown-6)-2,3,11,12-tetracarboxylic acid as a chiral NMR solvating agent for determining the enantiomeric purity and absolute configuration of β-amino acids

(18-Crown-6)-2,3,11,12-tetracarboxylic acid is an excellent chiral NMR solvating agent for cyclic beta-amino acids and acyclic derivatives with aliphatic, aromatic, and heterocyclic aromatic moieties. The beta-amino acids are mixed with the crown ether in methanol-d(4) in either their neutral or protonated form. Substantial enantiomeric discrimination typically occurs for the resonances of the alpha-methylene and beta-methine hydrogen atoms. Resonances of the substituent group of the beta-amino acid often exhibit enantiomeric discrimination. The enantiomeric discrimination of the alpha-methylene and beta-methine resonances of specific groups of compounds shows consistent patterns that correlate with the absolute configuration. (C) 2009 Elsevier Ltd. All rights reserved.