A solution of 50.0 mg (0.14 mmol) 2-hydroxy-2-((S)-6-oxo-6,7-dihydro-5H-dibenzo[b,d]azepin-7-ylcarbamoyl)-pentanoic acid and 14.2 mg (0.15 mmol) 2,2-difluoropropylamine in 2.5 ml tetrahydrofuran were cooled to 0° C. and 20.2 mg (0.15 mmol) 1-hydroxy-benzotriazole hydrate, 39 μl (0.3 mmol) diisopropylethylamine and 28.6 mg (0.15 mmol) N-(3-dimethylaminopropyl)-N′-ethyl-carbodiimide hydrochloride were added. Stirring was continued overnight. Removal of the solvent by distillation and chromatography on silicagel with heptane/ethylacetate (gradient 90:10 to 50:50) yielded 30.0 mg (50%) (R/S)-N-(2,2-Difluoro-propyl)-2-hydroxy-N-((S)-6-oxo-6,7-dihydro-5H-dibenzo[b,d]azepin-7-yl)-2-propyl-malonamide: MS (m/e): 446.1 (M+H)+.
