A solution of 27.9 g (75 mmol) 3-(4-benzyloxy-phenyl)-2-tert-butoxycarbonylamino-propionic acid, (Bachem Inc., Torrance, Calif. 90505) 16.5 mL (150 mmol) 4-methylmorpholine, and 28.5 g (75 mmol) O-Benzotriazol-1-yl-N,N,N′,N′-bis(tetramethylene)uronium hexafluorophosphate in 110 mL dry DMF was stirred in an ice-bath for 30 minutes. Next, 10.7 mL (75 mmol) of 1-(2-aminoethyl)piperidine (Aldrich, Milwaukee, Wis.) was added, and the resulting solution was warmed to 25° C. and stirred 60 minutes. The mixture was poured into 200 mL ethyl acetate, and washed sequentially with 200 mL each of 2.5% aqueous HCl solution, brine, saturated aqueous sodium bicarbonate solution, and finally twice with brine. The mixture was then dried over anhydrous sodium sulfate and concentrated at reduced pressure to give 33.7 g (94%) of (S)-[2-(4-benzyloxy-phenyl)-1-(2-piperidin-1-yl-ethylcarbamoyl)-ethyl]-carbamic acid tert-butyl ester as a pale amber solid; mp 54-61° C.
