Direct HPLC enantioseparation of chemopreventive chiral isothiocyanates sulforaphane and iberin on immobilized amylose-based chiral stationary phases under normal-phase, polar organic and aqueous conditions
Sulforaphane and iberin are promising chemopreventive chiral phytochemicals. The chirality of these organic
isothiocyanates is due to the presence of a stereogenic sulfur atom. Investigations of the effectiveness of single
enantiomers as chemoprotective agents highlight the key role played by sulfur chirality on biological activity.
The predominant native (R)-enantiomer is active whereas the (S)-counterpart is inactive or poorly active.
Here, we provide an enantioselective method for the direct and complete resolution of both chiral sulfoxides
by high-performance liquid chromatography on immobilized amylose-derived chiral stationary phases. A set of
five different columns was investigated utilizing normal-phase, polar organic and aqueous conditions. The effect
of the composition of mobile phase on enantioselectivity and retention was carefully evaluated.
U-shape retention maps, which are indicative of a double and competitive hydrophilic interaction liquid
chromatography and reversed-phase liquid chromatography retention mechanism, were established by recording
the retention factors of the enantiomers of sulforaphane on the Chiralpak IA-3 and Chiralpak IG-3 chiral
stationary phases varying progressively the water content in the water-acetonitrile mobile phases.