Thioacetic acid S—((S)-6-amino-6-phenylcarbamoyl-hexyl) ester-trifluoroacetate (1.03 mmol), DIPEA (3.08 mmol) and PyBOP (1.03 mmol) were added to a solution of (3R*,4S*)-2-oxo-4-phenyl-pyrrolidine-3-carboxylic acid in DCM/DMF: 5/9. The resulting reaction mixture was stirred at RT overnight. After removal of the solvent under reduced pressure, the resulting solid was poured into water and extracted twice with AcOEt. The organic layer was then washed with NaHCO3, water and brine before being dried over Na2SO4 and concentrated under reduced pressure to yield an oil. The latter was partially purified by silica gel chromatography and then subjected to HPLC purification.
