To a solution of 3-(benzyloxycarbonylamino)-3-methylbutanoic acid (described in international publication number WO 2008/083347 A1) (5.74 g, 22.9 mmol) in N,N-dimethylformamide (150 ml) was added N,N-carbonyldiimidazole (4.45 g, 27.4 mmol). The reaction mixture was stirred for 1 hour at room temperature. N,N-diisoproylethylamine (11.2 ml, 68.8 mmol) and N,N,N-trimethylethylenediamine (3.6 ml, 27.8 mmol) were added was added to the reaction mixture. The mixture was stirred for an additional 18 hours at room temperature. The reaction mixture was poured into water and was extracted with ethyl acetate. The organic layer was washed two more times with water and dried over sodium sulfate. The dried organic layer was filtered and concentrated in vacuo. The crude product was purified on silica gel column chromatography (0 to 10% methanol in dichloromethane) to give 2.08 g (27% yield) of benzyl 4-((2-(dimethylamino)ethyl)(methyl)amino)-2-methyl-4-oxobutan-2-ylcarbamate. 1H NMR (CDCl3) δ 7.34-7.26 (m, 5 H), 6.14 (s, 1 H), 5.04 (s, 2 H), 3.47 (t, J=5.3 Hz, 2 H), 3.02 (s, 3 H), 2.60 (s, 2 H), 2.59 (t, J=5.3 Hz, 2 H), 2.24 (s, 6 H), 1.46 (s, 6 H); MS (ESI+) calculated for C18H30N3O3: 335.23, Found: 336.2 (M+H+).
