N-[4-methoxybenzenesulfonyl]-(D)-threonine (4.0 g, 13.84 mmol), 1-hydroxybenzotriazole (1.87 g, 13.84 mmol), 4-methylmorpholine (7.9 mL, 69.2 mmol), and O-t-butyl-hydroxylamine hydrochloride (5.22 g, 41.52 mmol) are dissolved in methylene chloride (100 mL). To this solution is added N-[dimethylaminopropyl]-N'-ethylcarbodiimide hydrochloride (3.45 g, 17.99 mmol), and the reaction is stirred overnight. The mixture is then diluted with water and extracted with methylene chloride. The combined organic extracts are washed with brine, dried (Na2SO4), and concentrated in vacuo. The crude product is purified by silica gel chromatography (ethyl acetate) to give N-(t-butyloxy)-2(R)-[[4-methoxybenzenesulfonyl]-amino]-3(R)-hydroxybutanamide.
