To a solution of NaBO3.4H2O (1.5 g, 3.9 mmol) in H2O (18.2 g) was charged isopropylamine (1.16 g, 19.6 mmol) dropwise at 20° C. After the mixture was stirred for 30 min, the pH was adjusted to 10.2-10.3 by 6N HCl. PLP (0.042 g, 0.27 mmol) and ATA-412 (1.0 g) was charged to the solution at 20° C. After the above mixture was stirred for 1 h, a solution of 45 (2 g, 4.7 mmoL) in DMSO (10 mL) was added slowly at 20° C. The solution was heated to 55° C. and stirred for 24 h. After the reaction was complete, the reaction was quenched by isopropyl alcohol (10 mL), and then partitioned with water and IPAc. The organic solution was dried over Na2SO4 and concentrated. The crude residual was further purified by flash chromatography on silica gel (5-20% EtOAc/PE) to give 46 (1.45 g, 85% yield). 1H NMR (DMSO-d6, 400 MHz): δ 7.95-7.78 (m, 1H), 6.95 (m, 1H), 3.01 (t, 1H), 1.36 (s, 9H), 1.17-1.10 (br, 4H), 1.12 (m, 3H); MS (ESI) m/e [M+H]+: 359.15.
