Barbiturates into enantiomers

The same procedure has been applied for resolution of mephenytoin and some barbiturates into enantiomers (26). 

Zukowski, J. Sybilska, D. Bojarski, J. Szejtli, J. Resolution of chiral barbiturates into enantiomers by reversed-phase high-performance hquid chromatography using methylated P-cyclodextrins. J. Chromatogr. 1988,463 (3), 381-390. 

Figure 9 shows the examples of separations of racemic mixtures of methylphenobarbital and mephenytoin performed under optimal conditions available (37). It has been found that ( -CD complexation resuTts in a distinct enantioselectivity in the case of mephenytoin and barbiturates which have a chiral center in the pyrimidine ring. The resolution of barbiturate enantiomers is due to the different stabilities of their diastereo-isomeric -CD complexes, while the separation of mephenytoin enantiomers results from the difference in their adsorption on the RP phase. The latter case should be considered further. It has been already suggested (18) that the adsorption of CD complexes in which guest molecules are entirely immersed in the CD cavity is low on RP phases. The distinct adsorption arises from the part of the molecule which is outside the cavity. Taking into account this fact and the remarkable difference in the adsorption of -CD mephenytoin diastereoisomers one may conclude that a significant difference must exist between immersion of mephenytoin enantiomers in the -CD cavity. 

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