A solution of hydroxybenzotriazole (0.54 g; 4 mmoles) in tetrahydrofuran (30 ml) and, subsequently, a solution of dicyclohexylcarbodiimide (0.825 g; 4 mmoles) in methylene chloride (15 ml) were added, at 0° C. under stirring to a mixture of (2S)-3-phenylcarbonylthio-2-phenylmethylpropionic acid (1.2 g; 4 mmoles), 4-(2-thiazolyl)-L-phenylalanine methyl ester dihydrochloride (1.34 g; 4 mmoles), prepared as described in example 4, triethylamine (1.11 ml; 8 mmoles) in tetrahydrofuran (20 ml) and methylene chloride (30 ml).
