An 'easy-on, easy-off' protecting group for the enzymatic resolution of (±)-1-phenylethylamine in an aqueous medium

A new approach has been developed for the biocatalytic resolution of (+/-)-1-phenylethylamine in 100% aqueous medium based on two integrated enzymatic steps: protection and deprotection of the reactive amine enantiomer catalyzed by the same enzyme-penicillin acylase from Alcaligenes faecalis. An 'easy-on, easy-off' protecting group has been introduced using (R)-phenyl-glycine amide as the acyl donor. (R)-Phenylglycyl-substituted (R)-1-phenylethylamine was poorly soluble and precipitated at enzymatic acylation in an alkaline medium (pH 10-11), driving the synthesis towards high yields. Conversely at pH <7.5, its solubility was continuously increasing, which rendered the subsequent deacylation by the same enzyme highly efficient. In contrast to the resolutions, which employ one biocatalytic step, the new approach made it possible to exploit two sequential enantioselective enzymatic reactions implementing a double enantioselectivity control. Effective enzymatic resolution of (+/-)-1-phenylethylamine in an aqueous medium was performed with (R)-phenyl-glycine amide as an acyl donor using the suggested approach. (C) 2004 Elsevier Ltd. All rights reserved.