Enantioseparation of aminoglutethimide with cyclodextrins in capillary electrophoresis and studies of selector-selectand interactions using NMR spectroscopy and electrospray ionization mass spectrometry

The enantiomers of aminoglutethimide [2-(p-aminophenyl)-2-ethylglutarimide, AGT] can be resolved in CE using all of three most commonly used native cy clodextrins (CD): alpha-, beta-, and gamma -CDs. The migration order of the enantiomers was opposite using beta -CD compared to alpha- and gamma -CDs as chiral selectors. In order to examine some underlying mechanisms of the chiral recognition the interaction of AGT with the chiral selectors was stu died with one- and two-dimensional NMR spectroscopy and electrospray ioniza tion mass spectrometry (ESI-MS). The Job's and Scott's plots constructed ba sed on the complexation-induced chemical shifts (CICS) observed in NMR spec tra provided some preliminary information on the stoichiometry of the inter molecular complexes but did not seem to be absolutely reliable perhaps beca use the self-association of the analyte molecules and the formation of mult iple type selectand-selector complexes. Therefore, an attempt was made to c haracterize the complexes using ESI-MS. This technique provided information on the stoichiometry and relative affinity constants of selector-selectand complexes. The information on the structure of complexes in the solution w as obtained using one-dimensional rotating frame nuclear Overhauser enhance ment (1D-ROESY) NMR spectroscopic studies. Significant differences were obs erved between the structures of the AGT complexes with beta- and gamma -CD.