Nα -Benzyloxycarbonyl-L-phenylalanine (4.95 g, 16.5 mmol) was dissolved in dichloromethane (70 ml) and the solution was cooled to 0° C. and stirred during the addition of pentafluorophenol (3.35 g, 18.2 mmol), followed by EDC (3.49 g, 18.2 mmol). The mixture was allowed to warm to room temperature, stirred for a further 1 hour then cooled back to 0° C. Aniline (3.85 g, 41.4 mmol) was added dropwise and the mixture was warmed to room temperature then stirred overnight. The solution was washed twice with 1M sodium carbonate, twice with 1M hydrochloric acid and finally with brine before drying over anhydrous magnesium sulphate. The solution was filtered and evaporated to a white solid which was recrystallised from ethyl acetate-hexane. Yield: 2.57 g (41%). 1H-NMR; δ (CDCl3), 7.87 (1H, brs), 7.43-7.03 (15H, br m), 5.62 (1H, m), 5.08 (2H, s), 4.59 (1H, s) and 3.15 (2H, s).
