Immobilization of helical poly(phenylacetylene)s having l-phenylalanine ethyl ester pendants onto silica gel as chiral stationary phases for HPLC

Abstract

Novel one-handed helical copoly(phenylacetylene)s bearing a small amount of 3-(triethoxysilyl)propyl residues (CPAs 1–4) were synthesized, and efficiently chemically immobilized onto silica gel by the intermolecular polycondensation of the triethoxysilyl groups. Their chiral recognition abilities were evaluated as immobilized-type chiral stationary phases (CSPs) for high performance liquid chromatography (HPLC). These immobilized-type CSPs showed different chiral recognition abilities from the corresponding coated-type CSPs, which may be ascribed to the conformational change in the copoly(phenylacetylene)s during the immobilization process according to the diffuse reflectance circular dichroism (DRCD) measurement of the copolymer. In addition, the immobilized-type CSPs showed a universal solvent tolerability, for instance, CHCl3-containing eluents that cannot be used with the corresponding coated-type CSPs could now be used for the immobilized-type CSPs so that the chiral recognition of i-CSP-2 for the racemic 1-(9-anthyl)-2,2,2-trifluoroethanol (5) was improved with separation factors comparable or higher than those obtained on the popular polysaccharide-based CSPs. The intermolecular polycondensation of the triethoxysilyl groups of the copoly(phenylacetylene)s is a valuable immobilization method for poly(phenylacetylene)-based CSPs.