Peptide deformylase as biocatalyst for the synthesis of enantiomerically pure amino acid derivatives

Peptide deformylases (PDFs) catalyze the removal of the N-terminal formyl group from nascent polypeptides. In spite of the vast amount of literature on PDF, no information whatsoever is available on its use in organic synthesis. To be able to explore the potential of E. coli PDF (EcPDF) in biocatalytic applications, a simple and efficient purification procedure was developed. This method, which was based on one affinity chromatographic step, furnished about 200 mg of pure EcPDF from 1 L of E. coli culture. The enzyme combined a good activity (tof ≥5 s⁻¹) with an almost complete enantioselectivity (E ratio >500) in the resolution of N-formylated α- and β-amino acids, α-amino acid amides and α-aminonitriles. N-Formyl derivatives of non-functionalized amines and β-amino alcohols were hydrolyzed with low to moderate activity and enantioselectivity. EcPDF was also successfully applied in the enantioselective formylation of α-aminonitriles, yielding, e.g. (S)-N-formyl-phenylalanine nitrile with >99.5% ee. The enzyme also proved very suitable for the mild and selective deprotection of N-formyl peptides as was shown for N-formyl-Leu-Tle-NHCH₃. This deprotection increased the diastereomeric excess of the dipeptide, which was unsatisfactory because of racemization of the N-terminal amino acid in the chemical peptide coupling step.