1.88 g of L-Tryptophan in the form of the hydrochloride is introduced into 25 ml of anhydrous methylene chloride and 2.14 ml of triethylamine, 3.1 g of BOP then 2.217 g of the product obtained in Stage 4 above, dissolved in 25 ml of anhydrous methylene chloride, are added. The solution is agitated for 2 hours at ambient temperature, then the solvent is evaporated off, the product obtained in the form of a yellow oil, is then purified by chromatography on silica, with chloroform-ethyl acetate: 85-15 as eluant. After evaporation of the solvent and washing, a yellow gum is obtained. In this way 2.69 g of expected product is obtained (mixture of two diastereoisomers).
