Asymmetric synthesis of l-tert-leucine and l-3-hydroxyadamantylglycine using branched chain aminotransferase

l-Tert-leucine (Tle) and l-3-hydroxyadamantylglycine of (HAG) are important intermediates for a variety of pharmaceutical classes. They were asymmetrically produced from corresponding keto acids using branched-chain aminotransferase (BCAT) with l-glutamate (Glu) as an amino donor. For the production of l-Tle and l-HAG, BCAT from Enterobacter sp. TL3 (BCATen) and BCAT from Escherichia coli K12 (ilvE, newly named as BCATes) were used, respectively. In our current study, we characterized the basic properties of BCATen and BCATes such as substrate specificity, enantioselectivity, and kinetic parameters. The activities of BCATen and BCATes were inhibited severely by α-ketoglutarate which is a deaminated product of l-Glu. In the presence of 10 mM α-ketoglutarate, both enzymes activities were reduced up to 80%. In order to overcome product inhibition by α-ketoglutarate and the problem of equilibrium of the transamination reaction, coupling reactions were carried out with l-glutamate dehydrogenase (GDH)/formate dehydrogenase (FDH) and AspAT. The coupling reaction dramatically increased the yields of both target compounds. 135 mM of l-Tle (>99% ee) was produced from 150 mM corresponding keto acid in BCATen/GDH/FDH coupling reaction with 90% conversion. In addition, 90.5 mM l-HAG (>99% ee) was produced from 100 mM corresponding keto acid in BCATes/AspAT coupling reaction using recombinant whole-cells.