Enantioseparation of selected chiral sulfoxides in high-performance liquid chromatography with polysaccharide-based chiral selectors in polar organic mobile phases with emphasis on enantiomer elution order.

The separation of the enantiomers of 17 chiral sulfoxides was studied on polysaccharide-based chiral columns in polar organic mobile phases. Enantiomer elution order (EEO) was the primary objective in this study. Two of the six chiral columns, especially those based on amylose tris(3,5-dimethylphenylcarbamate) and cellulose tris(4-chloro-3-methylphenylcarbamate) (Lux Cellulose-4) proved to be most successful in the separation of the enantiomers of the studied sulfoxides. Interesting examples of EEO reversal were observed depending on the chiral selector or the composition of the mobile phase. For instance, the R-(+) enantiomer of lansoprazole eluted before the S-(-) enantiomer on Lux Cellulose-1 in both methanol or ethanol as the mobile phase, while the elution order was opposite in the same eluents on amylose tris(3,5-dimethylphenylcarbamate) with the S-(-) enantiomer eluting before the R-(+) enantiomer. The R-(+) enantiomer of omeprazole eluted first on Lux Amylose-2 in methanol but it was second when acetonitrile was used as the mobile phase with the same chiral selector. Several other examples of reversal in EEO were observed in this study. An interesting example of the separation of four stereoisomers of phenaminophos sulfoxide containing chiral sulfur and phosphor atoms is also reported here.