Methyl (S)-2-((tert-butoxycarbonyl)amino)-3-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)propionate (67.0 g, 165 mmol) was used as a raw material and dissolved in acetone (700 mL). To this solution, sodium periodate (71.0 g, 330 mmol), ammonium acetate (25.0 g, 330 mmol) and water (300 mL) were added sequentially and the reaction was stirred for 55 hours at room temperature. After completion of the reaction, the reaction mixture was filtered and the filtrate was concentrated under reduced pressure and extracted by adding ethyl acetate. The organic phase was washed sequentially with water and saturated aqueous sodium chloride solution and dried over anhydrous sodium sulfate. The solvent was removed under reduced pressure and the resulting solid was washed with a mixed solvent of petroleum ether/ethyl acetate (1:10, v/v) and dried to afford the target product (S)-(4-(2-((tert-butoxycarbonyl)amino)-3-methoxy-3-oxopropyl)phenylboronic acid (29 g, 55% yield).1H NMR (CDCl3, 400 MHz) δ: 7.71-7.56 (m 2H), 7.25-7.16 (m, 2H), 4.39-4.37 (m, 1H), 3.71 (s, 3H), 3.14-3.10 (m, 1H), 2.96-2.90 (m, 1H), 1.40 (s, 9H). MS (ESI) m/z 224 (M + H - Boc)+.
