Enantioselective Separation of Amino Acids Using Chiral Polystyrene Microspheres Synthesized by a Post-Polymer Modification Approach.

The enantioselective separation of a racemic mixture of amino acids was achieved by chiral amino acid-modified polystyrene (PS) that was developed by a post-polymer modification approach. Styrene was polymerized using the reversible addition-fragmentation chain-transfer (RAFT) polymerization technique and further post-polymer modification was applied by Friedel-Crafts acylation reaction with chiral -phthaloyl-l-leucine acid chloride to obtain the protected PS-l-Leu. The chiral PS (protected PS-l-Leu) was assembled into microspheres using a surfactant and was used for carrying out the enantioselective separation of amino acid racemic mixtures by enantioselective adsorption followed by a simple filtration process. Compared to as-precipitated chiral PS (protected PS-l-Leu) powder, the protected PS-l-Leu microspheres exhibited a better enantioselective separation efficiency (ee %). Furthermore, the protected PS-l-Leu was deprotected to obtain the amine-functionalized deprotected PS-l-Leu chiral PS, which was also assembled into microspheres and used for carrying out enantioselective separation. Deprotected PS-l-Leu-functionalized chiral PS microspheres could achieve up to 81.6 ee % for the enantioselective separation of a racemic mixture of leucine. This is one of the first reports of the synthesis of amino acid-modified chiral PS microspheres and their application to the simple filtration-based enantioselective separation of native amino acids from their racemic mixtures.