GENERAL STEPS: To a stirred suspension of (S)-2-(((benzyloxy)carbonyl)amino)-3-(1H-indol-3-yl)propanoic acid (2.45 g, 7.2 mmol) in 10 mL of anhydrous dichloromethane, 4-dimethylaminopyridine (DMAP, 88 mg, 0.72 mmol) and benzyl alcohol (1.28 g, 11.8 mmol) were added. A 5 mL solution of N,N'-dicyclohexylcarbodiimide (DCC, 1.48 g, 7.2 mmol) in dichloromethane was slowly added at 0 °C. The reaction was carried out at 0 °C with the addition of N,N'-dicyclohexylcarbodiimide (DCC, 1.48 g, 7.2 mmol). The reaction mixture was slowly warmed to room temperature and stirred overnight. The white precipitate was removed by filtration and the solvent was subsequently removed by distillation under reduced pressure to afford the colorless oily product Cbz-L-tryptophan benzyl ester (3 g, 98%). The product had a rotativity of [α]D20 = +50 (c = 1.0, CHCl3, 365 nm). Thin layer chromatography (TLC) showed Rf = 0.29 (ethyl acetate:hexane = 1:2).1H NMR (400 MHz, CDCl3) δ: 8.26 (br, 1H), 7.56 (d, J = 8.0 Hz, 1H), 7.41-7.33 (m, 9H), 7.26-7.20 (m, 3H), 7.12 (t, J = 8.0 Hz , 1H), 6.76 (d, J = 2.0 Hz, 1H), 5.47 (d, J = 8.0 Hz, 1H), 5.18-5.10 (m, 4H), 4.82 (q, J = 8.0 Hz, 1H), 3.34 (d, J = 5.1 Hz, 2H).13C NMR (100 MHz, CDCl3) δ: 171.8, 155.8 , 136.1, 136.0, 135.1, 128.5, 128.4, 128.3, 128.0, 127.5, 127.4, 126.9, 122.9, 122.0, 119.5, 118.5, 111.2, 109.4, 67.1, 66.8, 54.6, 27.8.Fourier transform infrared (FTIR) spectroscopy ( FTIR, pure sample) showed absorption peaks located at 3395, 3343, 1742, 1458, 1377, 721 cm-1. High resolution mass spectrometry (HRMS, ESI) calculated value of C20H20O4N2 [M + H]+ was 429.1814 and measured value was 429.1821.
