The “smart” amine donors o‐xylylenediamine and cadaverine were employed for the rapid screening of a large ketone library and subsequent preparative‐scale synthesis of selected compounds using a commercially available amine transaminase, ATA256. The methodology enables both screening and preparative‐scale biotransformations to be performed with a single enzyme and simplifies the generation of sp3‐rich small‐molecule libraries.
The development of effective high‐throughput screening assays has contributed greatly to the wealth of designer enzymes available, by enabling rapid identification of desired variants from large mutant libraries. Here, we report a general and operationally simple end‐point assay for transaminases that enables the screening of both amine donors and acceptors in liquid phase. The spectrophotometric‐based screen exploits the amine donor 2‐aminoethylaniline (2‐AEA) and relies on reaction of in situ generated indole with Ehrlich's reagent. The assay has also been adapted to allow screening in the reverse direction by addition of indole and subsequent spectrophotometric analysis. Importantly, the screen provides qualitative information on the enantio‐preference of the individual biocatalysts. To increase the assay throughput, an engineered expression strain (E. coli BL21(DE3) ΔtnaA) lacking tryptophanase activity, was generated to enable reliable and direct evaluation of individual colonies arrayed on agar plates.
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