Enantioselective catalysis of deacylation of p-nitrophenyl N-acylphenyl-alanates by mixed micelles composed of Nα-hexadecanoyl-L-histidine and a cationic surfactant

Abstract

The deacylation of p-nitrophenyl N-acyl-L- and -D-phenylalanates (acyl = acetyl, decanoyl, and hexadecanoyl) with the co-micellar system composed of N^α-hexadecanoyl-L-histidine and octadecyltrimethylammonium chloride was investigated for the 20–35 °C range in CH₃CN–H₂O (3 : 97 v/v). The enantioselective properties of the co-micellar system effective for the deacylation of such substrates were investigated in the light of substrate-binding properties, activation parameters, and kinetic salt and organic co-solvent effects. Kinetic enantioselectivity is exclusively favoured for the L-substrates, even though the binding constants for the D-isomers are greater than those for the corresponding L-isomers in most cases. The highest enantioselectivity in terms of the apparent second-orde rate ratio (k_{a, obs}^L/k_{a, obs}^D) is 4.7 as observed for the deacylation of p-nitrophenyl N-decanoyl-L- and -D-phenylalanate at 20 °C and pH 7.6.