Formate → (R)-propyl 2-(7-amino-6,7,8,9-tetrahydropyrido[1,2-a]indol-10-yl)acetate

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Sodium phosphate, dibasic (3.8 equiv.) and sodium formate (266 equiv.) were added to a solution of D-Alanine (38 equiv.) in water. The pH was measured as 7.6. Nicotinamide Adenine Dinucleotide (0.04 equiv.), Pyridoxal-5-phosphate (0.11 equiv.), Lactate dehydrogenase (1 equiv.), Formate dehydrogenase (1 equiv.), and Amine-Transaminase-117 (1 equiv.) were added under stirring and slowly dissolved. The measured pH was 7.3. The mixture was aged at 22° C. for 1 h. The flask was flushed with nitrogen and propyl (7-oxo-6,7,8,9-tetrahydropyrido[1,2-α]indol-10-yl)acetate from Step 5 was added as a DMSO (0.06 M) solution. The reaction was adjusted to pH 7.2 and aged at 30° C. overnight under nitrogen atmosphere. Upon completion of the reaction as determined by HPLC, the pH of the reaction was adjusted to pH 4.0 with 6 N HCl and Celite (20 g per L) was added. After stirring for 1 hr the reaction was filtered through a Celite bed and the filter cake was washed twice with 0.1 N HCl. The combined aqueous filtrate was extracted with 1 volume of MTBE. The organic layer did not contain amine and was discarded. The aqueous layer was diluted with an equal volume of MTBE and the pH of the mixture was adjusted to pH 9.5 using 5N NaOH. The two phases were separated and the aqueous layer was extracted with MTBE. The spent aqueous layer had no detectable amine and was discarded. The combined organic layers were washed with dilute sodium carbonate and dried over Na2SO4. Evaporation of the volatiles afforded the crude title compound (80%). The ee was determined as 99% by SFC assay. The SFC conditions are ADH column (250×4.6 mm, 5 um), isocratic 20% MeOH, 25 mM iso-proply amine/CO2, 2 ml/min, 35° C., 200 bar, 215 nm, 15 min. Under these conditions the desired R-amine has an 8.99 min retention time (S-amine; 5.82 min)

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