Biocatalytic Cascade for Synthesis of Sitagliptin Intermediate Employing Coupled Transaminase

Transaminases (TAs) are employed in synthesizing various enantiopure β-amino acids, key precursors for various pharmaceuticals. Sitagliptin, an oral hyperglycemic drug, is a well-known example. Herein, we developed the coupled enzyme cascade to synthesize the sitagliptin intermediate by fusing two different TAs to regenerate the amino donor. In a cascade system, ethyl 3-oxo-4-(2,4,5-trifluorophenyl) butanoate (1) was converted by esterase from Pseudomonas stutzeri (EstPS) to respective β-keto acid (2) which was subsequently converted by first TA to sitagliptin intermediate (3) using ( S )-α-MBA as an amino donor and the acetophenone formed in the reaction was recycled by the second TA to ( S )-α-MBA. A single whole-cell system was established by the co-expression of esterase and TA fusion protein. The whole-cell biotransformation reaction was performed with varying substrate concentrations from 50–200 mM. The excellent conversion of the product was achieved, ranging from 62-to 100% at the expense of only 25 mM ( S )-α-MBA. Notably, our designed system with fusion protein can produce ∼5-fold higher product at the expense of 0.5 equivalent ( S )-α-MBA. Finally, a preparative scale reaction was performed with 98% conversion.