943-80-6

949-99-5

943-80-6

A mixed solution of concentrated HNO3 (60%) and concentrated H2SO4 (1.4:1.1 v/v) was prepared and cooled to 10°C. A portion of the mixed solution (3.5 mL) was slowly added dropwise to a solution of L-phenylalanine (4.139 g, 25.1 mmol) in H2SO4 (98%, 12.5 mL) with stirring. The reaction mixture was kept stirred at 10 °C for 2.5 hours. Upon completion of the reaction, the pH of the reaction solution was adjusted with NH4OH to 5. The resulting light yellow precipitate was collected by filtration, washed sequentially with a small amount of water and CH3CN, and dried to give 4-nitro-L-phenylalanine as a yellow powder (4.748 g, 90% yield). 4-Nitro-L-phenylalanine (2.006 g, 9.54 mmol) was suspended in water (35 mL), 0.2 g of 5% palladium-barium sulfate catalyst was added, and the hydrogenation reaction was carried out for 3 h at room temperature. The reaction solution was filtered through a diatomaceous earth pad and the filtrate was concentrated to give a light brown residue. The residue was washed with CH3CN to give a light brown solid (1.460 g, 85% yield) which was used directly in the next step of the reaction. 4-Amino-L-phenylalanine derivative (0.060 g, 0.33 mmol) was dissolved in 6N HCl (4 mL) and aqueous sodium nitrate solution (0.030 g/0.5 mL) was slowly added at 0 °C. The reaction mixture was stirred at the same temperature for 40 min and then diluted with 6N HCl (0.25 mL). Subsequently, aqueous sodium azide solution (0.033 g/0.75 mL) was added at 0 °C. The reaction mixture was stirred at 0 °C for 5 min and then warmed up to room temperature to continue the reaction for 1 h. The reaction mixture was then concentrated and the reaction was carried out at room temperature. Upon completion of the reaction, the reaction solution was concentrated and the residue was reprecipitated by CH3CN to give a pure colorless amorphous solid (0.0435 g, 64% yield). The analytical and spectroscopic data of the product were in agreement with literature reports [10].