Naproxen-derived segmented and sidechain-modified polysiloxanes as chiral stationary phases

Abstract

The preparation of a series of polysiloxane-based chiral stationary phases (CSPs) derived from ( S)-naproxen diallyl amide is described. Two types of chiral polysiloxanes have been synthesized. Segmented polymers were obtained by double hydrosilation of the diallyl amide with difunctional oligomethylhydrosiloxanes. The latter are obtained by a linear homologation strategy, thus allowing systematic variation of the spacing of the chiral selectors along the polymer chain. This spacing clearly affects chromatographic behavior, for increased spacing decreases retention even when the total amount of chiral selector present is unaltered. Alternatively, chiral polysiloxanes were prepared by adding, through hydrosilylation, the diallyl amide as pendent sidechains to a polymethyl-hydrosiloxane. The resulting polymers were coated on silica gel, packed into HPLC columns and evaluated using normal and reversed-phase conditions. Comparison of the performance of both types of chiral polysiloxane-based CSPs shows them to afford less retention and comparable or higher enantioselectivity than does the corresponding brush-type CSP.