L-Tryptophyl-L-seryl-L-tyrosyl-D-phenylalanyl-L-leucine methyl ester (example 1, h), 1.6 g., is dissolved in 30 ml. of dimethylformamide and treated with 0.789 g., of Nα -p-methoxybenzyloxycarbonyl-O-benzyl-L-serine and cooled in an ice bath. 1-Hydroxybenzotriazole, 326 mg., and finally 500 mg., of dicyclohexylcarbodiimide are added and the reaction mixture stirred to room temperature overnight and for twenty-four additional hours. The reaction mixture is filtered and the solvent removed under reduced pressure. The residue is dissolved in 200 ml. of ethyl acetate and washed with 0.25 N hydrochloric acid, saturated sodium chloride solution, 5% sodium bicarbonate solution, and finally, saturated sodium chloride solution. The ethyl acetate solution is refrigerated for several days and a gelatinous precipitate separated. After triturating with ether for two hours, the above named product is separated and dried, 1.7 g.
