Enzymatic synthesis of sitagliptin intermediate using a novel ω-transaminase

Enantiopure β-amino acids are essential precursors of various pharmaceuticals, agrochemicals and other industrially important chemicals. In this study, we selected sixteen potential ω-Transaminases (ω-TAs) by BLAST and phylogenetic tree analysis. These ω-TAs were cloned, purified and tested for their reactivity for the synthesis of model β-amino acid (R)-3-amino-4-(2,4,5-triflurophenyl) butanoic acid [3-ATfBA], a key precursor for sitagliptin. In an enzymatic cascade, lipase converted β-ketoester substrate to β-keto acid, which was subsequently aminated by the selected ω-TA to its corresponding β-amino acid. A potent enzyme from Ilumatobacter coccineus (ω-TAIC) was identified for the production of 3-ATfBA. The pH dependency of the product inhibition suggested that lowering the reaction pH to 7.0 can circumvent the inhibition of ω-TAIC by 3-ATfBA and about 92.3% conversion of 100 mM β-keto ester substrate could be achieved. The applicability of this enzymatic system was further evaluated at the scale of 140 mM, wherein 3-ATfBA was generated with excellent conversion (81.9%) and enantioselectivity (99% ee). Furthermore, ω-TAIC was successfully used for the synthesis of various β-amino acids from their corresponding β-keto ester substrates.