General procedure for the synthesis of N-Boc-D-tryptophan from Boc-D-tryptophan: a) Synthesis of compound 22; Compound 1 (Boc-D-tryptophan, 10.0 g, 33 mmol) was dissolved in THF (50 mL), cooled to 0 °C under nitrogen atmosphere, and then BH3/THF solution was slowly added dropwise. The reaction mixture was gradually warmed to room temperature and stirred continuously for 16 hours. Upon completion of the reaction, the reaction was quenched with aqueous potassium carbonate and subsequently extracted with ethyl acetate (100 mL x 3). The organic phases were combined, washed with brine (50 mL), dried over anhydrous sodium sulfate and concentrated under reduced pressure. Purification by column chromatography (petroleum ether/ethyl acetate=4:1) afforded the product 22 (N-Boc-D-chromanol) as a white solid (5.72 g, 60% yield).1H NMR (400 MHz, CDCl3): δ1.46 (s, 9H), 3.02 (d, J=6.8 Hz, 2H), 3.80-3.55 (m, 2H). 4.10-3.95 (m, 1H), 4.86 (br s, 1H), 7.07 (s, 1H), 7.16 (t, J=7.2Hz, 1H), 7.23 (t, J=7.2Hz, 1H), 7.39 (d, J=8.4Hz, 1H), 7.68 (d, J=7.6Hz, 1H), 8.20 (s, 1H).
![N-[(tert-Butoxy)carbonyl]-D-tryptophan](/CAS/GIF/5241-64-5.gif)
