Enantiomer affinity pattern

Table 6.1. Enantiomer affinity pattern of selected chiral analytes towards native CyDs having different cavity size (Reproduced with permission from Ref. 56).

The opposite enantiomer affinity pattern of the antihistaminic drug brompheniramine (BrPh) towards j8-CyD and TM-j8-CyD provoked us to study the structure of the corresponding diastereomeric complexes in solution using ID-ROESY [61]. For the complexes of (+)-BrPh with both CyDs, unambiguous confirmation was obtained indicating the inclusion of the 4-bromophenyl moiety of the analyte in the cavity of the CyD. In addition, in the case of the (+)-BrPh complex with fS-CyD, a weak but positive NOE effect was also observed for the protons of the maleate counter anion when saturating the CyD protons H-3 and H-5 located inside the cavity. This observation may indicate the simultaneous inclusion of the 4-bromophenyl moiety and maleate counter anion in the cavity of -CyD but this contradicts simple geometric considerations and the assumption that the stoichiometry of the complex is 1 1. 

It is possible in chiral CE to adjust the enantiomer migration order without changing the affinity pattern of the analyte enantiomers towards a chiral selector. This is impossible in chromatographic techniques unless using a chiral selector as a CM PA [42]. 

The reversal of the affinity pattern of enantiomers towards a chiral selector is the most dramatic change that may take place due to any chemical or structural modification of a chiral selector. The screening of the affinity pattern of a wide range of chiral analytes towards CyD-type hosts using CE indicated that the affinity pattern... 

Table 6.2. Enantiomer afFin ity pattern of selected chiral ...

Another example when ROESY experiments may provide information about distinct differences between the structures of analyte-CyD complexes is the complex of chiral yS2-sympathomimetic agent clenbuterol (CL) with / -CyD and heptakis (2,3-di-0-acetyl)-yS-CyD (HAD-j8-CyD). Again it was noted from the CE experiments that the enantiomers of CL exhibit an opposite affinity pattern towards these two CyDs (Fig. 6.8) [60]. 

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