To a round bottom flask was added (R)-2-(benzyloxycarbonylamino)-3-mercapto-3-methylbutanoic acid (4.68 g, 16.52 mmol), HOBT (2.53 g, 16.52 mmol), EDC (3.17 g, 16.52 mmol), DCM (50 mL), TEA (2.302 mL, 16.52 mmol) and 4,4-diethoxybutan-1-amine (2.66 g, 16.52 mmol). The reaction was stirred at rt overnight. The reaction was diluted with DCM (150 mL). The organics was washed with water (2×150 mL), saturated aqueous NaCl (100 mL). The organic layer was separated, dried over MgSO4, filtered and concentrated to give (R)-benzyl 1-(4,4-diethoxybutylamino)-3-mercapto-3-methyl-1-oxobutan-2-ylcarbamate (6.90 gm, 16.2 mmol, 98% yield) as an oil.
