630 mg (2.374 mmol) of N-(tert-butoxycarbonyl)-2-phenyl-D-alanine were dissolved in 20 mL of dry DMF and O-(benzotriazol-1-yl)-1,1,3,3-tetramethyluronium tetrafluoborate (TBTU, 1.37 g, 4.27 mmol), morpholine (0.412 mL, 4.73 mmol) and diisopropylethylamine (1.63 mL, 9.5 mol) were added. The mixture was stirred at room temperature for 1 hour, then the solvent was removed and the residue dissolved with dichloromethane. The solution was washed with saturated NaHCO3, brine, water and dried over Na2SO4. 700 mg of the title compound were recovered (88% yield).
