Patent ID: 7585988

Claim:
A process for preparation of crystalline sodium or potassium (2S,3S)-3-[[(1S-1-isobutoxymethyl-3-methylbutyl]carbamoyl]oxirane-2-carboxylate, comprising the following steps (1) to (6): (1) hydrolyzing an ester of (2S,3S)-3-[[(1S)-1-isobutoxymethyl-3-methylbutyl]carbamoyl]oxirane-2-carboxylic acid, to obtain (2S,3S)-3-[[(1S)-1-isobutoxymethyl-3-methylbutyl]carbamoyl]oxirane-2-carboxylic acid, (2) causing the carboxylic acid obtained in the preceding step to react with an organic amine, to prepare a salt of (2S,3S)-3-[[(1S)-1-isobutoxymethyl-3-methylbutyl]carbamoyl]oxirane-2-carboxylic acid with the organic amine, (3) adding an acid to the salt obtained in the preceding step, to obtain (2S,3S)-3-[[(1S)-1-isobutoxymethyl-3-methylbutyl]carbamoyl]oxirane-2-carboxylic acid, (4) causing the carboxylic acid obtained in the preceding step react with a basic sodium or potassium compound in a mixed solvent of water and an aliphatic alcohol or acetone, to obtain a sodium or potassium salt, (5) recrystallizing the sodium or potassium salt obtained in the preceding step using an aliphatic alcohol, and (6) drying the product recrystallized in the preceding step under reduced pressure.