Chiral recognition by cyclodextrins: the interaction of naringin with β-cyclodextrin
Complex formation between naringin, 1, the bitter component of grapefruit, and β-cyclodextrin has been studied by 1H NMR spectroscopy. Differential binding of the diastereoisomers of 1 to a polymer supported β-cyclodextrin column allowed partial separation of the isomers and a full assignment of the 1H NMR spectrum of the mixture to be made. In aqueous solution, one diastereoisomer binds to β-cyclodextrin approximately 1.7 times more strongly than the other. The interaction occurs by inclusion of the aromatic ring B, but substantial chemical shift changes are also observed for certain protons in the disaccharide unit of 1. Comparison of NMR data for the inclusion complex of the aglycone naringenin, 2, suggests that the disaccharide unit is an important factor in the chiral recognition of 1 by β-cyclodextrin.