Enantioseparation on optically active stereoregular polyphenylacetylene derivatives as chiral stationary phases for HPLC

Optically active (R)-(+)-4-(1-(1-naphthyl)ethylcarbamoyloxy)phenylacetylene (1) and (R,R)-(+)-3,5-bis(1-phenylethylcarbampyloxy) (2) were prepared and polymerized with a rhodium catalyst in the presence of silica gel having a phenylacetylene residue on surface to obtain chiral stationary phases (CSPs 1 and 2, respectively), for enantioseparation of racemates by high-performance liquid chromatography. The homopolymer of 1 (poly-1) which was not immobilized on silica gel was soluble in tetrahydrofuran and its structure, molecular weight and chiroptical properties were examined. Poly-1 showed an intense induced CD in the UV-visible region which may be due to a predominant one-handed helical conformation of the main chain. On the other hand, homopolymer of 2 was not soluble in common organic solvents. Copolymers of 2 with achiral phenylacetylenes bearing a siloxy group were soluble in THF. However, they showed a weak induced CD. Several racemates such as Troger base and spiropyran derivatives were resolved on CSPs 1 and 2, and CSP-1 showed relatively higher chiral recognition ability. The results suggest that the poly-1 is among the useful polymeric CSPs and the predominant one-handed helical sense may play an important role for the enantioseparation. Enantiomers of some racemates were eluted in reversed elution order on the two CSPs, indicating that the chiral discrimination mechanism of the CSPs may be different.