Enantiodifferentiation of alpha-hydroxyalkanephosphonic acids in 31P NMR with application of alpha-cyclodextrin as chiral discriminating agent.

Alpha-cyclodextrin was shown to be convenient chemical shift reagent for determination of the enantiomeric composition of alpha-hydroxyphosphonic acids by means of 31P NMR. The developed methodology appeared to be reliable, repetitive, easy to perform and simple for interpretation. Enantiomeric discrimination in the 31P NMR spectra for 12 of 13 studied hydroxyphosphonates was achieved, with baseline separation of resonances obtained for eight compounds. In those cases, the chemical nonequivalence values ranged from 0.069 to 0.313 ppm. The studies showed that enantioselectivity is strongly influenced by the solution pD and the optimal condition was found at pD 2 or 10 depending on the guest structure. On the basis of the ROESY spectra the complexation modes of selected hydroxyphosphonates with alpha-cyclodextrin was postulated. Copyright 2009 Wiley-Liss, Inc.