A solution of 2-tert-butoxycarbonylamino-3-(1H-imidazol-4-yl)-propionic acid benzyl ester (6.062 g, 17.57 mmol) and triethylamine (3.57 g, 4.90 mL, 35.14 mmol) in CHCl3 (50 mL) was cooled to 0° C. under argon. Trityl chloride (4.9 g, 17.57 mmol) in CHCl3 was added and after 20 minutes the solution became opaque. The solution was stirred at 0° C. overnight, warmed to room temperature, washed with water and brine, dried over MgSO4 and filtered. The solvent was removed and the crude material was chromatographed (silica gel, 25% EA/PE, Rf 0.78 75% EA/PE) to afford the title compound as a viscous gum (7.58 g, 74%). ESMS 588 (M+H+) 1H NMR (500 MHz, CDCl3) δ 1.42 (9H, s), 2.98 (1H, dd, J=4.65, 14.53 Hz), 3.05 (1H, dd, J=5.05, 14.53 Hz), 4.58 (1H, m), 5.02 (2H, d, J=2.55 Hz), 6.06 (1H, d, J=8.25 Hz), 6.47 (1H, s), 7.09 (6H, m), 7.26 (4H, m), 7.29 (10H, m), 7.36 (1H, s). 13C NMR (CDCl3) δ 28.11, 29.87, 53.61, 66.37, 74.95, 79.12, 119.30, 127.78, 128.16, 129.48, 135.29, 136.23, 138.48, 142.01, 155.34, 171.44.
