An about 33% solution of HBr in acetic acid  (10 ml) is placed in a 250 ml round bottom flask and benzyloxycarbonyl-glycyl-l-phenylalanine benzyl ester  (4.46 g, 10 mmol) is added with swirling. The flask is closed with a cotton-filled drying tube and swirled to effect complete dissolution of the protected dipeptide. Vigorous evolution of CO2 takes place  and some evolution of heat can be observed . When the gas evolution ceases (about 20 minutes)  dry ether (200 ml) is added with swirling and the reaction mixture is stored in a refrigerator  for several hours. The precipitate is collected on a filter, washed with ether (50 ml) and dried over NaOH pellets in vacuo. Glycyl-l-phenylalanine benzyl ester hydrobromide (3.4 g, 87%) can be purified by recrystallization from ethanol-ether and it melts then at 193 °C; correct analytical values are obtained for N and Br.
KeywordsTrifluoroacetic Acid Hydrogen Fluoride Hydrobromic Acid Benzyl Ester Benzyl Ether
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