Synthesis
Methyl 3(R)-benzoylaminobutyrate (100 g) was used as a raw material, mixed with concentrated hydrochloric acid (1000 mL) and anhydrous methanol (500 mL), and the reaction was carried out in a sealed reaction for 50 hours at 100 °C (external temperature). Upon completion of the reaction, the treatment procedure of Example 7 was followed to obtain 3(R)-aminobutyric acid methyl ester hydrochloride (III) as a yellow oil (63.2 g, 91% yield, ee value 99.3%).
Another ethyl 3(R)-benzoylaminobutyrate (100 g), concentrated hydrochloric acid (1000 mL) and ethanol (500 mL) were added to a thick-walled, pressure-resistant glass reactor and the reaction was carried out for 36 hours at 110 °C (external temperature). The reaction mixture was allowed to stand at room temperature and then cooled in an ice water bath for 3 h. The precipitated benzoic acid was removed by filtration (white flaky crystals, dry weight 50.5 g, recovery 98%, melting point 121-122°C, content 99.6%). The filtrate was washed three times with dichloromethane (500 mL x 3). The washed mixture was processed by distillation and the aqueous phase was evaporated under reduced pressure at 30°C. Toluene (100 mL) was added to remove residual water. Anhydrous ethanol (500 mL) and thionyl chloride (5 mL) were added to the residue, and the reaction was heated to reflux for 6 h. After evaporation under reduced pressure, a yellow oily substance, ethyl 3(R)-aminobutyrate hydrochloride (III) (65.6 g, 92% yield, ee value 99.4%) was obtained. The treated ethanol distillate can be used in the same step for the next batch of reaction.
