tert-Butyl (S)-6-(4-(2-((tert-butoxycarbonyl)amino)-3-oxo-3-(piperidin-1-yl)propyl)phenyl)hexanoate (Compound SP426) (5.65 g, 11.24 mmol) was dissolved in DCM (30.0 ml), trifluoroacetic acid (15.0 ml, 195 mmol) was added and the mixture was stirred for 30 minutes at room temperature, after which the reaction solution was concentrated under reduced pressure. The resulting residue was dissolved in dioxane (40 ml) and a 10% aqueous sodium carbonate solution (80 ml), N-(9-fluorenylmethoxycarbonyloxy)-succinimide (3.68 g, 10.90 mmol) was added and the mixture was stirred at room temperature for 1 hour. The reaction solution was washed with diethyl ether, made acidic by adding a 5 N aqueous HCl solution and then extracted with ethyl acetate. The ethyl acetate layer was dried over anhydrous Na2SO4, filtered and concentrated under reduced pressure to afford the title compound SP427 (6.39 g, 100%).
