To a solution of methyl N-(tert-butoxycarbonyl)-L-alanyl-L-threoninate (9.00 g, 29.6 mmol) in dichloromethane (90 mL) was added Dess-Martin periodinane (15.1 g, 35.5 mmol) at room temperature. After being stirred for 70 min, saturated aqueous sodium thiosulfate solution was added, then the reaction mixture was stirred for 15 min. The mixture was poured into saturated aqueous sodium bicarbonate, and the mixture was extracted with ethyl acetate. The organic layer was washed with saturated brine, dried over sodium sulfate, filtrated and concentrated in vacuo. The residue was purified by silica gel column chromatography (hexane:ethyl acetate=3:1 to 1:1) to give methyl (2S)-2-{[N-(tert-butoxycarbonyl)-L-alanyl]amino}-3-oxobutanoate. MS (APCI): m/z 303 (M+H).
