Enzymatic preparation of 5-hydroxy-l-proline, N-Cbz-5-hydroxy-l-proline, and N-boc-5-hydroxy-l-proline from (α-N-protected)-l-ornithine using a transaminase or an amine oxidase

N-Cbz-4,5-dehydro-l-prolineamide or N-Boc-4,5-dehydro-l-prolineamide are alternative key intermediates for the synthesis of saxagliptin, a dipeptidyl peptidase IV (DPP4) inhibitor recently approved for treatment of type 2 diabetes mellitus. An efficient biocatalytic method was developed for conversion of l-ornithine, N-α-benzyloxycarbonyl (Cbz)-l-ornthine, and N-α-tert-butoxycarbonyl (Boc)-l-ornithine to 5-hydroxy-l-proline, N-Cbz-5-hydroxy-l-proline, and N-Boc-5-hydroxy-l-proline, respectively. Rec. Escherichia coli expressing lysine-ɛ-aminotransferase and rec Pichia pastoris expressing l-ornithine oxidase were used for these conversions. N-Cbz-5-hydroxy-l-proline, and N-Boc-5-hydroxy-l-proline were chemically converted to key intermediates N-Cbz-4,5-dehydro-l-prolineamide and N-Boc-4,5-dehydro-l-prolineamide, respectively.