DL-leucine → Methyl DL-leucinate hydrochloride

2-Amino-4-methylpentanoic acid (5.0 g 38.2 mmol) was slowly added to saturated HCl/MeOH (50 mL). The mixture was stirred (RT, 5 h) then heated to reflux (16 h). After the reaction, the solvent was removed under reduced pressure. The residue was diluted with water (50 mL), then NaHCO3 was added to adjust to pH 7. The mixture was then extracted with DCM (3×50 mL), the combined organic layers were dried over MgSO4, concentrated under reduced pressure to afford methyl 2-amino-4-methylpentanoate as a colorless liquid (5.3 g, 96%). Mass calculated for C7H15NO2=145.20; found: [M+H]+=145.9. The product was used in next step without further purification.

1. temperaturethen heated
2. temperatureto reflux (16 h)