1: L-aspartic acid γ-fluorenylmethyl ester hydrochloride With sodium carbonate 2: di-tert-butyl dicarbonate

sodium carbonate in tetrahydrofuran; water 1) 0 deg C, 15 min (pH 9.5) 2) 25 deg C, 2 h;

1: 85 percent / 1-ethyl-3-<3-(dimethylamino)propyl>carbodiimide methyl iodide, 4-(N,N-dimethylamino)-pyridine / dimethylformamide / 1) 0 to 5 deg C, 6 h, 2) r.t., overnight 2: 1) 30percent HBr, acetic acid, 2) conc. HCl / 1) r.t., 4 h, 2) Et2O 3: 71 percent / triethylamine / dimethylformamide; CH2Cl2 / 5 h / 0 - 5 °C View Scheme

in 1,4-dioxane; water

1: 1) 30percent HBr, acetic acid, 2) conc. HCl / 1) r.t., 4 h, 2) Et2O 2: 71 percent / triethylamine / dimethylformamide; CH2Cl2 / 5 h / 0 - 5 °C View Scheme