Potassium Carbonate → HCID 23663550, compound

The (2S,3S)-3-[[(1S)-1-isobutoxymethyl-3-methylbutyl]carbamoyl]oxirane-2-carboxylic acid (4.83 g) prepared in Example 6 or 7 was dissolved in acetone (23 mL), and potassium carbonate (1.11 g) dissolved in water (4.5 mL) was slowly added. The solution was stirred at room temperature until the deposited inorganic salt was dissolved. While the solution was heated at 50° C. in a bath, acetone (100 mL) was dropped and a seed crystal was placed in the solution, and then the solution was stirred for 30 minutes. Acetone (94 mL) was again dropped, and the solution was stirred for 1 hour while the temperature was kept. While gradually cooled to room temperature, the solution was stirred overnight. The precipitated crystalline product was collected by filtration, washed with a mixture of 2% water-acetone (20 mL), dried in air to obtain white solid potassium (2S,3S)-3-[[(1S)-1-isobutoxymethyl-3-methylbutyl]carbamoyl]oxirane-2-carboxylate (4.28 g, 81.7%). The NMR data of the solid product were the same as those in Example 11.