9 g of Nα -benzyloxycarbonyl-L-lysine, 5.6 g of tert.-butyloxycarbonylglycine, 3.2 g of triethylamine, 4.9 g of 1-hydroxybenzotriazole and 7.9 g of N,N'-dicyclohexylcarbodiimide are stirred in 100 ml of THF/DMF (7:3) for 1 hour at 0° C. and over night at ambient temperature. After the urea has been filtered off the mixture is concentrated by evaporation, the residue is taken up in ethyl acetate, extracted with saturated KHSO4 solution, washed with water, dried over MgSO4 and concentrated by evaporation in vacuo. The residue is chromatographed over silica gel with methylene chloride/ethyl acetate/methanol (10:1:1). 12.5 g (100% of theory) are obtained in the form of a colourless oil.
