Enantiomeric separations by use of calixarene electrokinetic chromatography

Chiral acylcalix[4]arene amino acid derivatives have been synthesized and used as pseudostationary phases in capillary electrophoresis (CE). Use of these calix[4]arene (CX4) derivatives with electrokinetic capillary chromatography (4-EKC) resulted in enantioseparation of three binaphthyl derivatives at pH values above 7. The structures of the CX4 derivatives, i.e., (N-L-alaninoacyl)calix-[4]arene (CX4-L-Ala) and (N-L- valinoacyl)calix[4]arene (CX4-L-Val), and the buffer pH were found to be important factors in chiral separation. When CX4-L-Ala was used as a pseudostationary phase in the CE buffer, baseline resolution was achieved for 1,1\u27-bi-2-naphthol (BINOL) and 1,1\u27-binaphthyl-2,2\u27-dismine (BNA). The addition of sodium dodecyl sulfate (SDS) to the CX4-L-Ala solution resulted in baseline resolution of the enantiomers of 1,1\u27-binaphthyldiyl hydrogen phosphate (BNHP). In contrast, chiral separations of BNHP, BINOL, and BNA were successfully achieved in a single run with use of CX4-L-Val as a chiral selector in the absence of SDS. The utility of these new chiral selectors for chiral separation in CE is compared and discussed in detail