Dicyclohexylcarbodiimide → Nalpha-Benzyloxycarbonyl-O-benzyl-L-tyrosyl-L-tryptophyl-L-seryl-L-tyrosyl-D-leucyl-L-leucine methyl ester

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Reaction Steps

The above product, 2.0 g. of L-tryptophyl-L-seryl-L-tyrosyl-D-leucyl-L-leucine methyl ester, is dissolved in 70 ml. of dimethylformamide and cooled in an ice bath. Nα -Benzyloxycarbonyl-O-benzyl-L-tyrosine, 970 mg., 355 mg. of 1-hydroxybenztriazole and 545 mg. of dicyclohexylcarbodiimide are added. The reaction is stirred at ice bath temperature for several hours, then to room temperature and finally at room temperature for twenty-four hours. The mixture is filtered and the filtrate evaporated under reduced pressure. The residue is dissolved in 400 ml. of ethyl acetate, 20 ml. of water and 20 ml. of 0.5N hydrochloric acid. The ethyl acetate is separated, washed with saturated salt solution, with 0.5N sodium bicarbonate solution, again with saturated salt solution and is evaporated to a solid residue; 2.81 g.

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