6.81 g (36 mmol) of BOC-sarcosine were dissolved in 30 ml of N,N-dimethylformamide and treated portionwise with 6.5 g (40 mmol) of 1,1'-carbonyldiimidazole. After completion of the CO2 evolution the solution was stirred at 40° for 30'. Then, 9.04 g (15 mmol) of (S)-7-fluoro-12,12a-dihydro-9-oxo-9H,11H-azeto[2,1-c]imidazo[1,5-a][1,4]benzodiazepine-1-carboxamidoxime were added and the mixture was stirred at 90° overnight. By evaporation of the solution and chromatography of the residue on 450 g of silica gel while eluting with methylene chloride/methanol 19/1 there were obtained 8.81 g (65%) of (S)-7-fluoro-12,12a-dihydro-1-[5-(N-BOC-N-methylaminomethyl)-1,2,4-oxadiazol-3-yl]-9H,11H-azeto[2,1-c]imidazo[1,5-a][1,4]benzodiazepin-9-one, which was used in the next step without further purification.
