CBZ-d-Methionine (5.4 g, 20 mmol), N-hydroxybenzotriazole H2O (HOBt, 3.0 g, 20 mmol), 2-(1H-benzotriazole-1-yl)-1,1,3,3-tetramethyluronium hexafluorophosphate (HBTU, 7.7 g, 20 mmol), 4-(dimethylamino)-pyridine (DMAP, ˜0.020 g, ˜0.16 mmol) and triethylamine (2.8 ml, 20 mmol) were added to a solution of 4-chloroaniline (1.3 g, 10 mmol) in THF. The non-homogeneous solution was stirred at room temperature for 24 hours. The solvent was then removed and the residue taken into ethyl acetate (˜200 ml) and washed sequentially with NaHCO3 (3×100 ml), 10% citric acid (3×100 ml), water (3×100 ml) and saturated NaCl (1×75 ml). The organic layer was then dried with sodium sulfate, filtered, and concentrated to yield (2R)-N-(4-chlorophenyl)-4-methylthio-2-[(phenylmethoxy)carbonylamino]butanamide (M+1=393.26)
