Enantioselective hydrolysis of α‐amino acid esters catalysed by polymeric copper and nickel complexes

Abstract

It is known, that metal complexes are effective catalysts for the hydrolysis of a-amino acid esters. In several cases enantioselectivity, i. e. a difference in the hydrolysis rate of enantiomeric esters, has been observed when optically active metal complexes were used as catalysts. The hydrolysis Of D-and L-histidine methyl esters (HisOMe) in the presence of the complexes Ni(L-or n-His) and CU(L-or D-His) at different pH and temperatures has been examined'.2), and kinetic enantioselectivity was observed in the nickel containing system. The hydrolysis rate in the presence of complexes with opposite configurations of His and HisOMe was approximately 40% higher than that found in the presence of complexes with identical ligand configurations. Leach and Angeli-ci3) have studied the enantioselective hydrolysis of Leu, Phe, and Ser methyl esters in the presence of N-carboxymethyl-L-valinato copper(I1) with the result that the rate of hydrolysis of D-leucine methyl ester and D-phenylalanine methyl ester in mixed ligand complexes is higher than that of the L-enantiomers. Katagawa et showed the occurrence ofenantioselectivity in the hydrolysis of the methyl esters of alanine, proline, and valine in the presence of nickel complexes with an optically active tetraamine ligand. Finally other authors5.') reported that poly(L-1ysine)-copper(I1) complexes exhibit an asymmetrically-selective catalysis on the hydrolysis of phenylalanine esters at pH 7. It was supposed that enantioselective effects were due to different stabilities of diastereomeric complexes formed by the aminoester enantiomers and the catalyst. However, only homogeneous catalysts have been used for enantioselective hydrolysis of amino acid esters prior to our work. Results and DiscussionThe present work was undertaken to study the hydrolysis of a number of amino acid methyl esters in the presence of polystyrene type asymmetric catalysts containing groupings of S-(2-aminoethyl)-L-cysteine (polymer l), S-(carboxymethy1)-L-cysteine (polymer 2), and N-carboxymethyl-L-valine (polymer 3), coordinated with copper or nickel ions.These same catalysts were used previously in the ligand-exchange chromatography of race-mates7-" and showed significant thermodynamic enantioselective effects in mixed sorption complexes of stationary ligands and amino acid enantiomers. The hydrolysis of a-amino acid esters in

Polymer-Supported Quenching Reagents for Parallel Purification

“…Contrary to polymer-supported synthesis, it is advantageous to have as high a loading of functionality as possible in PSQ. Hence the polyamine resin 1 is prepared by heating Merrifield resin with tris(2-aminoethyl)amine (400 mol %) in DMF (65 °C, 6 h) . The starting loading of chloromethyl groups affects the amount of amine cross-linking that occurs in this reaction.…”