General procedure for the synthesis of N-tert-butoxycarbonyl-O-benzyl-L-tryptophan from benzyl bromide and (S)-2-((tert-butoxycarbonyl)amino)-3-(1H-indol-3-yl)propanoic acid: to a solution of methyl (S)-2-((tert-butoxycarbonyl)amino)-3-(1H-indol-3-yl)propanoate (2 g, 6.57 mmol) in DMF (27 mL) K2CO3 (2.27 g, 16.5 mmol) and benzyl bromide (811 μL, 6.83 mmol) were added to it. The reaction mixture was stirred at room temperature for 12 hours. After completion of the reaction, the reaction was quenched with saturated aqueous NaHCO3 solution. The reaction mixture was diluted with EtOAc (10 mL) and washed with aqueous NH4Cl to separate the organic and aqueous layers. The aqueous layer was extracted with EtOAc (3 x 10 mL), the organic layers were combined, washed with brine (3 x 15 mL), dried over anhydrous Na2SO4, filtered and concentrated under reduced pressure. A white powdery product (2.1 g, 81% yield) was obtained by recrystallization from cyclohexane with a melting point of 140 °C. The spectral data of the product were in agreement with those reported in the literature.1H NMR (250 MHz, CDCl3): δ=8.00 (br s, 1H), 7.56 (d, J=8.3 Hz, 1H), 7.38-7.30 (m, 4H), 7.29-7.17 (m, 3H), 7.16-7.07 (m, 1H), 6.81 (s, 1H), and 5.09 (d, J=3.7Hz, 2H), 4.79-4.61 (m, 1H), 3.29 (d, J=5.3Hz, 2H), 1.43 (s, 9H).
![N-[(tert-Butoxy)carbonyl]-L-tryptophan](/CAS/GIF/13139-14-5.gif)
