Benzyl-[(1R)-2-amino-1-benzylethyl]carbamate (described in J. Med. Chem., 2010, p 106; 200 mg, 0.71 mmol) and N—BOC-D-alanine (134 mg, 0.71 mmol) were added to a stirred solution of 1-(3-dimethylaminopropyl)-3-ethyl-carbodiimide hydrochloride salt (163 mg, 0.85 mmol), 1-hydroxybenzotriazole monohydrate (115 mg, 0.75 mmol) and N-methylmorpholine (72 mg, 0.71 mmol) in DMF (3 mL) at room temperature under a nitrogen atmosphere. After 16 h the mixture was treated with 8 mL of ethyl acetate (creating a suspension) and washed with 12 mL of a 10% aqueous citric acid solution, 12 mL of water, 12 mL of a 3% aqueous solution of sodium bicarbonate, and another 10 mL of a saturated aqueous brine solution. The organic layer was dried over sodium sulfate and evaporated under reduced pressure to give 338 mg (93%) of a white foam of the title compound, which was used with no further purification.
