For protein expression and screening, all transfer steps were performed using Hamilton liquid-handling robots. The ligated libraries were transformed into chemically compotent E. coli BL21 (DE3) cells. Freshly transformed clones were used to inoculate 150 μL of LB media supplement with 50 μg mL -1 kanamycin in Corning®Costar®96-well microtitre flat bottom plates, covered with a BreathEasy film and incubated overnight at 30 o C, 80% humidity at 850rpm. 20 μL of overnight culture was used to inoculate 480 μL TB medium supplemented with 50 μg mL -1 kanamycin in 96-deep well plates and further incubated under the same conditions until an OD600 of 0.6 was reached and IPTG was added to a final concentration of 0.1 mM to induce protein expression. Plates were further incubated under the same conditions overnight and cells were harvested by centrifugation at 4000 rpm for 20 min. The supernatant was discarded, and the pelleted cells were stored at -80 o C. For reference, each plate contained 6 clones of the parent template, 2 clones containing RFP in pET28B as positive and negative controls. The pelleted cells were resuspended in 400 μL lysis buffer (100 mM KPi, 1 mg mL -1 lysozyme, 0.5 mg mL -1 polymixin B and 10 μg mL -1 DNase I) incubated for 2h at 30 o C, 80 % humidity at 850 rpm. Cell debris was removed by centrifugation at 4000 rpm for 30 min. 55 μL clarified lysate was transferred to 96-well microtitre plates containing, 45 μL of reaction mix. Reactions were incubated overnight at 30 o C, 80 % humidity at 850 rpm and quenched by the addition of 100 μL AcN (0.1% HCl). Samples were further incubated for 30 min and precipitated proteins were removed by centrifugation at 4000 rpm for 40 min and quenched supernatants analysed by UPLC analysis. Conversion of individual mutants were normalized to the average of the 6 parent clones of that plate. Mutants that demonstrated increased activity were rescreened as purified proteins, that were produced and purified as described above, but starter cultures were inoculated from glycerol stocks prepared from the original overnight cultures. Chemical Synthesis Synthesis of 3,6-dibromopicolinaldehyde (11) A stirred solution of 2,5-dibromo-6-methylpyridine (8 g, 31.8 mmol) in THF (80 mL) was cooled to 0 o C. To this solution tert-butyl nitrite (4.33g, 41.9 mmol) was added, followed by the dropwise addition of potassium tert-butoxide (28 mL, 20 wt% sol. In THF, 47.7 mmol). The reaction was stirred for 4 h. The reaction mixture was diluted with THF (25 mL) and quenched with NH4Cl in water (6.38g, 119 mmol). The reaction mixture was distilled under vacuum to approximately 50 mL and the resulting slurry was filtered and washed with water (2 x 50 mL). The resulting compound was added portion wise to a stirred solution of glyoxylic acid (100 mL, 50 wt%) at 80 o C and stirred for 4 h. Synthesis of N-benzhydryl-1-(3,6-dibromopyridin-2-yl)methanimine (12) 3,6-dibromopicolinaldehyde (5.0 g, 18.9 mmol) in toluene (20 mL) was heated to 50 °C and benzhydrylamine (3.47 g, 18.9 mmol) was added in one portion and stirred for 16 h. Methanol (61 mL) was added, and the reaction mixture was distilled to a volume of approximately 25 mL. Methanol (40 mL) was added, and the reaction mixture was distilled to a volume of approximately 20 mL. The resulting slurry was filtered and rinsed with two portions of methanol (15 mL each) and dried under vacuum to afford the product. Yield m = 6.5 g, 15.1 mmol, 79.9 %. Synthesis of (R,E)-N-((3,6-dibromopyridin-2-yl)methylene)-2-methylpropane-2-sulfinamide (15) 3,6-Dibromopicolinaldehyde (1 g, 3.7 mmol) and (R)-2-methylpropane-2-sulfinamide (0.48 g, 3.9 mmol) were combined in Nmethyl-2-pyrrolidone (20 mL). To the reaction mixture was added Cs2CO3 (0.55 g, 4.1 mmol). The reaction mixture was stirred for 2 h then cooled to 0 °C. Water (20 mL) was added to the reaction mixture. The resulting suspension was stirred for 1 h, solids isolated by filtration, washed with water (5 x10 mL) and dried to provide the title compound. Yield m = 0.9 g, 2.4 mmol, 62.5 %. ) To a dried round bottom flask under an inert atmosphere, (R,E)-N-( Synthesis of (R)-1-(3,6-dibromopyridin-2-yl)-2-(3,5-difluorophenyl)ethan-1-amine (R-5a) To a stirred solution of (R)-N- General procedure (A) for synthesis of 2-phenyl-1-(pyridin-2-yl)ethan-1-one and derivatives To a solution of the corresponding 2-pyridinecarbonitrile (1 equiv) in dry Et2O at 0 o C under an inert atmosphere, either benzylmagnesium bromide or (3,5-difluorobenzyl)magnesium bromide was added dropwise (1.2 equiv, 1 M in THF).