In a mixture of 10 ml of water and 50 ml of chloroform were suspended 3.79 g of methyl phenylalanyltyrosinate hydrochloride and 0.53 g of sodium carbonate. To the mixture was added dropwise 1.75 g of 4-methoxybenzoylchloride in parallel with 10 ml of sodium carbonate solution (0.75 g), while stirring and cooling with ice. The mixture was stirred for two hours and the chloroform layer was collected. The layer was washed with 5% hydrochloric acid and water, dried and concentrated to dryness. The residue was crystallized from ethyl acetate to give 3.9 g of methyl N-(4-methoxybenzoyl)-phenylalanyltyrosinate with a mp. 195°-197° C in a yield of 82%. Analysis, calculated for C27H28O6N2C 68.05, H 5.92, N 5.88, found C 68.42, H 6.08, N 5.74.
