Stereoregular poly(phenylacetylene) derivatives bearing L‐leucine ethyl ester pendants, poly‐1 and poly‐2a, were, respectively, synthesized by the polymerization of N‐(4‐ethynylphenylcarbamoyl)‐L‐leucine ethyl ester (1) and N‐(4‐ethynylphenyl‐carbonyl)‐L‐leucine ethyl ester (2) using Rh(nbd)BPh4 as a catalyst, while stereoirregular poly‐2b was synthesized by solid‐state thermal polymerization of 2. Their chiral recognition abilities for nine racemates were evaluated as chiral stationary phases (CSPs) for high‐performance liquid chromatography (HPLC) after coating them on silica gel. Both poly‐1 and poly‐2a with a helical conformation showed their characteristic recognition depending on coating solvents and the linkage groups between poly(phenylacetylene) and L‐leucine ethyl ester pendants. Poly‐2a with a shorter amide linkage showed higher chiral recognition than poly‐1 with a longer urea linkage. Coating solvents played an important role in the chiral recognition of both poly‐1 and poly‐2a due to the different conformation of the polymer main chains induced by the solvents. A few racemates were effectively resolved on the poly‐2a coated with a MeOH/CHCl3 (3/7, v/v) mixture. The separation factors for these racemates were comparable to those obtained on the very popular CSPs derived from polysaccharide phenylcarbamates. Stereoirregular poly‐2b exhibited much lower chiral recognition than the corresponding stereoregular, helical poly‐2a, suggesting that the regular structure of poly(phenylacetylene) main chains is essential to attain high chiral recognition.
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Zhang et al. (2013) studied this question.
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