Influence of stereoregularity and linkage groups on chiral recognition of poly(phenylacetylene) derivatives bearing L‐leucine ethyl ester pendants as chiral stationary phases for HPLC

Abstract

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)BPh 4 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/CHCl 3 (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.

Helical Polymers Showing Inverse Helicity and Synergistic Effect in Chiral Catalysis: Catalytic Functionality Determining Enantioconfiguration and Helical Frameworks Providing Asymmetric Microenvironment

“…Since the fascinating chirality is derived from helical conformations, the chiral amplification effect can render the polymers with considerable optical activity. The optically active helical polymers have found significant applications in chiral recognition, chiral resolution, etc. More interestingly, helical polymers functionalized with pendant catalytic groups can be utilized as mimetic enzymes to catalyze asymmetric reactions efficiently.…”

Synthesis of Optically Active Poly(diphenylacetylene)s Using Polymer Reactions and an Evaluation of Their Chiral Recognition Abilities as Chiral Stationary Phases for HPLC

“…Optically active poly(phenylacetylene)s with a preferred-handed helicity have been prepared [16] and some of these systems have been reported to exhibit good chiral recognition abilities as CSPs for HPLC because of their preferred-handed helical conformation [17][18][19][20][21][22][23][24][25][26]. However, very few optically active poly(diphenylacetylene)s have been prepared to date, which has limited research towards evaluating the scope and efficiency of the chiral recognition abilities of these materials [27][28][29][30][31][32][33][34][35].…”

Influence of Helical Structure on Chiral Recognition of Poly(phenylacetylene)s Bearing Phenylcarbamate Residues of L‐Phenylglycinol and Amide Linage as Pendants

“…Many kinds of synthetic polymers have also been prepared as the CSPs for HPLC, and some of them exhibit excellent chiral recognition abilities . Among these synthetic polymers, the helical poly(phenylacetylene) derivatives with stereoregular structures showed high chiral recognition abilities as CSPs . The poly(phenylacetylene)s possess dynamic helical conformations, and the change of the helical pitch and inversion of the helicity can be achieved by changing their functional pendants or applying external stimuli, such as temperature and solvents.…”

“…Previously, we synthesized a series of poly(phenylacetylene) derivatives having helical conformations to use as the CSPs for HPLC, which include those bearing L ‐phenylglycinol and its phenylcarbamate residues as pendants, and discussed the influence of different L‐amino acid derivatives on the helical structures of the stereoregular main chains and chiral recognition abilities, etc . In this study, based on our previous studies, four poly(phenylacetylene) derivatives ( PPA-1 , PPA-2 , PPA-3 , PPA-4 ) bearing the phenylcarbamate residues of L ‐phenylglycinol and an amide linkage as pendants were prepared to use as the CSPs for HPLC.…”