4.1.8.4 Synthesis of N-acetyl-L-tryptophan (10b)
L-tryptophan (1.00 g, 4.95 mmol) was dissolved in a mixed solution of acetone (20 mL) and 2 N NaOH (15 mL). Acetyl chloride (0.821 mL, 9.90 mmol) was added slowly and dropwise at room temperature, while 2 N NaOH was added to maintain the pH of the reaction system greater than 10. The reaction mixture was stirred at room temperature for 1 hr. Upon completion of the reaction, the acetone was removed by vacuum evaporation and the remaining aqueous phase was acidified to acidity with 3 N HCl. The aqueous phase was extracted with ethyl acetate (3 × 50 mL) and the organic phase was combined. The organic phase was washed with saturated saline and dried over anhydrous Na2SO4. The organic phase was concentrated under reduced pressure to give N-acetyl-L-tryptophan 10b (0.96 g, 80% yield) as a colorless solid.ESI/MS m/z: 246.1 [M + H]+; 1H NMR (500 MHz, DMSO) δ 12.55 (s, 1H), 10.84 (s, 1H), 8.14 (d, J = 8.0 Hz, 1H), 7.52 (d, J = 8.0 Hz, 1H), 7.33 (d, J = 8.0 Hz, 1H), 7.13 (d, J = 2.0 Hz, 1H), 7.06 (dd, J = 11.0, 4.0 Hz, 1H), 6.98 (t, J = 7.5 Hz, 1H), 4.46 (td, J = 8.5, 5.0 Hz, 1H), 3.15 (dd, J = 14.5, 5.0 Hz, 1H), 2.98 (dd, J = 14.5, 8.5 Hz, 1H), 1.80 (s, 3H).
