To a solution of 5 g of (3S)-2-[(benzyloxy)carbonyl]-1,2,3,4-tetrahydro-3-isoquinolinecarboxylic acid (16 mmol) in 160 mL of dichloromethane there are added 1.5 mL of morpholine (17.6 mmol) and then 9 mL of N,N,N-triethylamine (64 mmol), 3.3 g of 1-ethyl-3-(3′-dimethylaminopropyl)-carbodiimide (EDC) (19.2 mmol) and 2.6 g of hydroxybenzotriazole (HOBT) (19.2 mmol). The reaction mixture is stirred at ambient temperature overnight and is then poured onto a solution of ammonium chloride and extracted with ethyl acetate. The organic phase is subsequently dried over magnesium sulphate and then filtered and evaporated to dryness. The crude product so obtained is then purified by chromatography over silica gel (dichloromethane/methanol gradient). The product is obtained in the form of a foam.
