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 175 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 2 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 ethylacetate 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.
