A mixture of N-methyl-phenethyl-amine (2.2 mL, 15.3 mmol), 2-tert-butoxycarbonylamino-3-methyl-butyric acid (3.33 g, 15.3 mmol), HBTU (8.7 g, 22.95 mmol), DIPEA (6.1 mL, 33.7 mmol) and DMF (75 mL) was stirred at room temperature for 14 hours. To the resulting mixture was added sodium bicarbonate (400 mL) and the desired product was extracted with ethyl acetate (400 mL×2). The combined organic layers were washed with water, dried over MgSO4 and concentrated under reduced pressure to yield an oil. The oil was purified by column chromatography (50% EtOAc/heptane) to yield a residue.
