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温度

0 °C

A solution of NaBH4 (262 mg, 6.92 mmol) in 4:1 THF:H2O (20 ml) was cooled to 0° C. To this mixture was slowly added a solution of the ester from step (38a) (4.61 mmol) in THF (12 ml). Gas was evolved. When gas evolution ceased, the mixture was quenched by the careful addition of saturated aqueous ammonium chloride. The resulting solution was stirred at 0° C. for an additional 15 min. EtOAc (200 ml) was added and the resulting mixture was washed with saturated aqueous NaCl. The organic layer was dried over MgSO4 and concentrated in vacuo. Purification by flash chromatography (silica, 0-10% MeOH/CHCl3) gave 2-tert-butoxycarbonylamino-4-hydroxy-butyric acid benzyl ester (350 mg, 25% for 2 steps) as a clear, colorless oil: 1H NMR (300 MHz, Methanol-D) δ 7.23-7.43 (m, 5 H), 5.06-5.25 (m, 2 H), 4.00-4.57 (m, 2 H), 3.54-3.69 (m, 1 H), 1.67-2.12 (m, 2 H), 1.29-1.50 (m, 9 H). LC-MS (Method A, retention time: 1.25 min).

1. customthe mixture was quenched by the careful addition of saturated aqueous ammonium chloride
2. additionEtOAc (200 ml) was added
3. washthe resulting mixture was washed with saturated aqueous NaCl
4. dry with materialThe organic layer was dried over MgSO4
5. concentrationconcentrated in vacuo
6. customPurification by flash chromatography (silica, 0-10% MeOH/CHCl3)