L-Valine benzyl ester hydrochloride

72-18-4

100-51-6

2462-34-2

The general procedure for the synthesis of (S)-benzyl (S)-2-amino-3-methylbutyrate hydrochloride from L-valine and benzyl alcohol was as follows: 11.5 g (0.1 mol) of L-valine, 30 mL of ethylene dichloride, and 16.2 g (0.1 mol) of FeCl3 were added to a 250 mL three-neck flask. Hydrogen chloride gas was passed at a rate of 1.25 mL/s and the reaction was carried out for 0.5 h at room temperature. A total of 2250 mL (0.1 mol) of HCl was passed. subsequently, 11.66 g (0.108 mol) of benzyl alcohol (molar ratio of L-valine to benzyl alcohol 1:1.08) was added and the reaction was continued by passing HCl at a rate of 0.05 mL/s for 3 h. The reaction was carried out under reflux conditions. The aqueous dichloroethane solution was removed by azeotropic distillation under reflux conditions while anhydrous dichloroethane was replenished at the same rate to maintain the reaction volume. A total of 120 mL of the azeotrope was distilled and passed through 540 mL (0.024 mol) HCl. Upon completion of the reaction, the reaction solution was filtered while still hot to remove the catalyst FeCl3, and the filtrate was recycled. The filtrate was cooled to room temperature and the remaining dichloroethane was removed by vacuum distillation (10 mmHg, 40°C). The product was recrystallized at -10°C and the resulting solid was washed with 20 mL of pre-cooled dichloroethane (0°C), filtered and the filter cake was dried at 40°C for 5 h to give 18.20 g of (S)-benzyl (S)-2-amino-3-methylbutanoate hydrochloride in 75.3% yield. The 120 mL mixture obtained by azeotropic distillation was dehydrated with anhydrous sodium sulfate (5 g of anhydrous sodium sulfate per 100 mL of dichloromethane) to obtain 118 mL of anhydrous dichloroethane, which was available for recycling in Step 2. The retained filtrate was concentrated to 20 mL by rotary evaporation (10 mmHg, 40°C) and used as the mother liquor for the next batch of the reaction.