The Stereoselective Deacylation of Long-chain Amino Acid Esters by Comicelles of N-Acyl-l-histidine and Various Cationic Surfactants

Abstract

Abstract The stereoselective deacylation of H–(CH2)\undersetn−1—CONHCH(R)CO2–C6H4NO2-p (R=CH3, CH(CH3)2, CH2CH(CH3)2, and C6H5CH2; n=2–16) with N-acyl-l-histidine (acyl=octanoyl, dodecanoyl, and hexadecanoyl) and cationic surfactants (CmH2m+1\overset+N(CH3)2R X; (R,X,m)=(CH3,Br,16), (C2H5,Br,16), (C6H5CH2,Cl,16), and (\overset*CH(CH3)C6H5,Br, 14–18) was examined with particular reference to the structural effects of surfactants, nucleophiles, and substrates on both the deacylation rates and the stereoselectivity. The cationic surfactant, R-(+)-C16H33\overset+N(CH3)2\overset*CH(CH3)C6H5 Br, which possesses the hydrophobic and chiral groups near the polar head, formed the stereoselectively most effective comicelles with N-dodecanoyl-l-histidine. The order of stereoselectivity observed in the deacylation of the amino acid esters including the identical acyl chain length (n), phenylalanine>leucine>alanine∼valine. suggested steric effects of the substituent bound to the asymmetric carbon atom of the substrate on the stereoselectivity. The highest stereoselectivity (enantiomer rate ratio=4.4 at 25 °C under pH 7.61) was observed in the deacylation of the N-decanoylphenylalanine p-nitrophenyl ester, involving an appropriately long acyl chain.