Synthesis and chiral recognition of amylose derivatives bearing regioselective phenylcarbamate substituents at 2,6- and 3-positions for high-performance liquid chromatography

Eighteen novel amylose derivatives bearing different phenylcarbamate substituents at 2,6- and 3-positions of a glucose ring were synthesized through the regioselective protection at 2- and 6-positions using a bulky trialkylsilyl chloride. Their chiral recognition abilities were then evaluated as the chiral stationary phases (CSPs) for high-performance liquid chromatography (HPLC) after coating them on the surface of macroporous silica gel. The chiral recognition abilities of these CSPs intricately depended on the nature, position and number of the substituents on the phenyl moieties. The introduction of substituents at meta-position of aromatic moieties at 2- and 6-positions of glucose unit was more attractive than other positions to improve the chiral recognition ability of these amylose derivatives. Each CSP seems to possess its own characteristic resolving power, and those based on amylose 3-(3,5-dichlorophenylcarbamate) showed comparatively better chiral recognition than others. For some racemates, the amylose derivatives with different phenylcarbamate substituents at 2,6- and 3-positions exhibited higher enantioselectivity than the amylose tris(3,5-dimethylphenylcarbamate), which is commercially available as Chiralpak AD, one of the most powerful CSPs. The structures of the obtained amylose derivatives were also investigated by circular dichroism spectroscopy.