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), 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; it is then poured into aqueous ammonium chloride solution and extracted with ethyl acetate. The organic phase is then dried over magnesium sulphate, and then filtered and evaporated to dryness. The crude product thereby obtained is then purified by chromatography over silica gel (dichloromethane/methanol gradient). The product is obtained in the form of a foam.
