Solvent-dependent enantioselective interaction of some bis-allylamide chiral selectors studied by NMR

A series of chiral selectors, all of them bis-allylamides of C(2)-symmetric dicarboxylic acids, were studied by NMR in different solvents in an attempt to affect the equilibria between free selector and the diastereomeric complexes formed by its interaction with the (+)- and (-)-forms of O,O'-dibenzoyltartaric acid (DBTA). The results show that by changing the polarity of the solvent the equilibria are displaced, as observed from changing chemical shift differences. Phase-sensitive (1)H[(1)H]-NOESY experiments revealed different interactions between the chiral selector and the analyte enantiomers. The individual equilibrium constants were determined by separate studies of the equilibria between the selector and the respective enantiomers of the chiral DBTA probe.