Esterolytic action of imidazol-containing polymers

Abstract

N-Methacryloyl-L-histidine and N-methacryloyl-L-histidine methyl ester were synthesized and polymerized to obtain polymeric catalysts with different functions. In the presence of each of these polymers the solvolytic reactions of p-nitrophenyl acetate(PNPA), 3-nitro-4-acetoxybenzoic acid(NABA), 3-acetoxy-N-trimethylanilinium iodide(ANTI) and 3-nitro-4-decanoyloxybenzoic acid(NDBA) were performed. The ionic substrates, NABA and ANTI, were solvolyzed at anomalous rate by polymeric catalyst, indicating that electrostatic effects are operative in the catalysis by polymers. Furthermore, in the solvolysis of hydrophobic substrate NDBA, polymeric catalysts exhibited highly enhanced activities compared with the low molecular weight analogs implying that hydrophobic interaction can be the most important contribution to the high catalytic activity of imidazole-containing polymers. And solvolytic reactions of N-carbomethoxy-D- and L-phenylalanine p-nitrophenyl ester(D-NCP and L-NCP) by poly(N-methacryloyl-L-histidine) and poly(N-methacryloyl-L-histidine methyl ester) were carried out. However no significant difference between the solvolytic rates of two enantiomeric substrates were observed. When polymers with increased hydrophobicity were prepared by copolymerizing N-methacryloyl-L-histidine and its methyl ester with dodecyl methacrylate, and were subjected to catalyze the solvolyses of optically active esters, the enantio-selectivity became more pronounced as hydrophobic character of polymer catalysts were enhanced. Also interesting to note is that catalyst polymers contain histidine of L-configuration and it matches with L-phenylalanine-based substrates. And to further explore the role of hydrophobic interaction in the enantioselective solvolyses of optically active activated esters by optically active imidazole-containing polymers, solvolytic reactions of N-carbobenzoxy-D- and L-phenylalanine p-nitrophenyl ester by optically active imidazole-containing polymers were p...