Chiara Carboni, Hans G. T. Kierkels, Lucia Gardossi, Kamil Tamiola, Dick B. Janssen and Peter J. L. M. Quaedflieg

Tetrahedron Asymmetry: 2006; 17: 245–251 https://doi.org/10.1016/j.tetasy.2005.12.023 

Abstract:
We have demonstrated for the first time that D-glutamine (D-Gln) and D-glutamic acid (D-Glu) can be efficiently obtained in high ee (97% and 90%, respectively) by enzymatic kinetic resolution of D,L-Gln and D,L-Glu. This was achieved by enantioselective conversion of the L-enantiomers to their N-phenylacetyl derivatives in aqueous solution, using a mutant of penicillin-G acylase (PGA) from E. coli and phenylacetic acid methylester as the acyl donor. Kinetic modeling studies suggest that the high ee values obtained are both due to a strong enantiopreference for the L-amino acid in the deacylation step of the covalent enzyme intermediate, as well as to completeness of conversion that is transiently obtained as a result of the distinct preference of the mutant PGA for phenylacetic acid methylester over the N-phenylacetyl-L-amino acid product. For the other amino acids tested (Asn, Asp, and Ser), the highest ee values that were obtained for the remaining D-enantiomer are moderate (50–80%) because of lower enantioselectivity in the enzyme deacylation step and due to less complete conversion of the L-amino acid caused by competition for the active site between the acyl donor and the N-phenylacetyl-L-amino acid that is produced. The results demonstrate that the mutated PGA has great potential for the production of optically active D-amino acids by kinetic resolution.