1963-21-9

24424-99-5

28334-73-8

General procedure: under stirring conditions, (2S)-2-(2-aminoacetamido)-3-methylbutanoic acid (1 mmol) was slowly added to a solution of ethanol (1 mL) containing guanidine hydrochloride (15 mmol) and di-tert-butyl dicarbonate (2.5-3 mmol), and the reaction temperature was maintained at 35-40°C. The reaction mixture was stirred continuously until a clarified solution was formed. Subsequently, the ethanol was removed by evaporation under vacuum. The residue was washed sequentially with distilled water (2 mL) and hexane or petroleum ether (2 mL) to obtain nearly pure (S)-2-(2-((tert-butoxycarbonyl)amino)acetylamino)-3-methylbutyric acid. The crude product can be recrystallized if further improvement of product purity is required.