In rounds 1-2 variants were evaluated in the deamination direction using mono-brominated amine 8a as the substrate (note that the parent template had no activity towards 8a) (Figure and Supplementary Table ). A single F125G mutation installed during round 1 gave low levels of activity towards amine 8a, which was further improved in round 2. Pleasingly, the L59A mutation installed during round 2 also gave rise to our first activity towards deamination of the target di-brominated substrate 5a, which was then used as the substrate for the round 3 of engineering. For the fourth and final round of engineering, assays were performed in the synthesis direction using ketone 5 as the substrate. Here, isopropyl amine (iPA) was selected as the amine donor due to its low cost and previous implementation in industrial scale processes involving engineered aminotransferases. With a suitable aminotransferase in hand, we carried out a series of biotransformations to assess enzyme activity and selectivity under a range of substrate, enzyme and iPA concentrations. Using substrate 5 (2.5 mM) and iPA (500 mM) as the amine donor, our engineered aminotransferase affords the target product (S)-5 with 90% conversion and >99% e.e.) using 4 mol% enzyme (Figure and Table . At higher substrate loadings (5 mM), reasonable conversions of 70% and 50% can be achieved using 2 mol% and 1 mol% of enzyme, respectively.