Boc-L-prolinol

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-ε-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.

D-proline and N-boc-5-hydroxy-L-proline are key chiral intermediates in the production of eletriptan and saxagliptin, respectively. An efficient proline racemase-proline dehydrogenase cascade was developed for the enantioselective production of D-proline. It included the racemization of L-proline to DL-proline and the enantioselective dehydrogenation of L-proline in DL-proline. The racemization of L-proline to DL-proline used an engineered proline racemase (ProR). L-proline up to 1000 g/L could be racemized to DL-proline with 1 g/L of wet Escherichia coli cells expressing ProR within 48 h. The efficient dehydrogenation of L-proline in DL-proline was achieved using whole cells of proline dehydrogenase-producing Pseudomonas pseudoalcaligenes XW-40. Moreover, using a cell-recycling strategy, D-proline was obtained in 45.7% yield with an enantiomeric excess of 99.6%. N-boc-5-hydroxy-L-proline was also synthesized from L-glutamate semialdehyde, a dehydrogenated product of L-proline, in a 16.7% yield. The developed proline racemase-proline dehydrogenase cascade exhibits great potential and economic competitiveness for manufacturing D-proline and N-boc-5-hydroxy-L-proline from L-proline.

l-Proline is the only, out of 20 essential, amino acid that contains a cyclized substituted α-amino group (is formally an imino acid), which restricts its conformational shape. The synthesis of well-defined homo- and copolymers of l-proline has been plagued either by the low purity of the monomer or the inability of most initiating species to polymerize the corresponding N-carboxy anhydride (NCA) because they require a hydrogen on the 3-N position of the five-member ring of the NCA, which is missing. Herein, highly pure l-proline NCA was synthesized by using the Boc-protected, rather than the free amino acid. The protection of the amine group as well as the efficient purification method utilized resulted in the synthesis of highly pure l-proline NCA. The high purity of the monomer and the use of an amino initiator, which does not require the presence of the 3-N hydrogen, led for the first time to well-defined poly(l-proline) (PLP) homopolymers, poly(ethylene oxide)-b-poly(l-proline), and poly(l-proline)-b-poly(ethylene oxide)-b-poly(l-proline) hybrids, along with poly(γ-benzyl-l-glutamate)-b-poly(l-proline) and poly(Boc-l-lysine)-b-poly(l-proline) copolypeptides. The combined characterization (NMR, FTIR, and MS) that results for the l-proline NCA revealed its high purity. In addition, all synthesized polymers exhibit high molecular and compositional homogeneity.