600 μL of a 0.15M solution in NMP of 5-hydantoin acetic acid was mixed with 98 mg of polystyrene-bound carbodiimide resin (loading 1.28 mmol/g). 340 μL of a 0.3M solution of HOBT in NMP was added to the mixture and vortexed for 10 minutes before 200 μL of a 0.3M solution in NMP of 2-(4′-fluoro-biphenyl-4-yl)-propylamine was added. The reaction mixture was vortexed overnight at room temperature in a sealed vessel. Resin was removed by filtration and the solution was evaporated to dryness. The product was purified on semi prep-HPLC C18-column (H2O:CH3CN, 0.1% TFA buffer, gradient 10% to 95% CH3CN, 10 min).
