Analysis of pD-dependent complexation of N-benzyloxycarbonylaminophosphonic acids by α-cyclodextrin. enantiodifferentiation of phosphonic acid pKa values

Abstract

The influence of aqueous solution pD on stereoselective complexation of N-benzyloxycarbonylaminophosphonic acids with α-cyclodextrin was investigated by means of nuclear magnetic resonance spectroscopy. The highest enantiodiscrimination was achieved at pD close to the pKa of less acidic hydroxyl group of the phosphonic moiety of analytes (6.5-7.5). This effect results from the stereoselective differentiation of pKa (up to 0.28 pD unit) upon complexation with applied chemical shift reagent. Moreover, analysis of 2D-ROESY spectra proved that the host-guest inclusion mode is strongly influenced by pD. © 2007 Wiley-Liss, Inc.