Triethylamine → Nepsilon-Benzyloxycarbonyl-Nalpha-(tert-butoxycarbonyl)-L-lysyl-L-phenylalanyl-L-leucine ethyl ester

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To a mixture of 1.68 g (4 mmol) of L-phenylalanyl-L-leucine ethyl ester trifluoroacetate, 0.56 mL (4 mmol) of triethylamine and 32 mL of chloroform were added at 0° C., first 1.52 g (4 mmol) of Nε -benzyloxycarbonyl-Nα -(tert-butoxycarbonyl)-L-lysine, and the 0.83 g (4 mmol) of dicyclohexylcarbodiimide, each being added in a single portion. The reaction mixture was warmed gradually to room temperature and then stirred overnight at that temperature. The precipitate which formed was removed by filtration. The filtrate was evaporated in vacuo and the residue was chromatographed on silica gel using 3:1 methylene chloride/ethyl acetate as eluent to give 2.48 g (92.7%) of the title compound as a white solid melting at 135°-136° C. after crystallization from a mixture of ethyl acetate and isopropyl ether. The product has the structural formula: ##STR110## as further confirmed by NMR, IR and elemental analyses.

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