General procedure for the synthesis of 2-amino-2-(3-nitrophenyl)acetic acid from 2-amino-2-phenylacetic acid: 2-amino-2-phenylacetic acid (33 mmol, 5 g) was cooled to 0 °C and slowly added to a mixture of concentrated sulfuric acid (98% w/w, 5 mL) and fuming nitric acid (90% w/w, 5 mL). The reaction mixture was stirred at 0 °C for 1 h, followed by continued stirring at room temperature for 30 min. Upon completion of the reaction, hydrolysis was carried out with cold water (60 mL). The pH of the reaction solution was adjusted to neutral by dropwise addition of 10 M ammonia. The resulting mixture was stirred at 4 °C for 10 h. 2-Amino-2-(3-nitrophenyl)acetic acid was isolated by filtration. The product was washed with cold water to give a yellow powdery solid. Yield: 64%. 1H-NMR (DMSO, 200 MHz): δ= 8.27 (s, 1H, H-4), 8.10 (d, J = 8.1 Hz, 1H, H-6), 7.83 (d, J = 7.9 Hz, 1H, H-8), 7.64 (t, J = 7.9 Hz, 1H, H-7), 4.51 (s, 1H, H-2). Elemental analysis: calculated values for C8H8N2O4: C, 48.98; H, 4.11; N, 14.28. measured values: C, 48.92; H, 4.19; N, 14.31.
