To a solution of [1-methyl-2-oxo-ethyl]-carbamic acid benzyl ester (12.3 g, 69 mmol) and norvaline methylester hydrochloride (11.6 g, 69 mmol) in MeOH (300 mL) is added diisopropyl ethyl amine (9.4 g, 73 mmol) and 2 drops of acetic acid. After 10 min., ZnCl2 (9.46 g, 69 mmol) and sodium cyanoborohydride (8.72 g, 14 mmol) is added. The solution is stirred at ambient for 16 h. The solution is then concentrated. The residue is dissolved in EtOAc and 1N KHSO4. The organic layer is washed with 1N KHSO4, H2O, and sat. NaCl. The organic layer is dried over MgSO4, filtered and concentrated. The crude product is purified by column chromatograghy eluting with a gradient of 20% EtOAc/hexane to 40% EtOAc/hexanes. The title compound (8.6 gm, 26.6 mmol) is obtained as a foam. MS (ion spray) m/z 323, (M+H).
