Intermediate 22B (0.25 g, 0.55 mmol) was dissolved in DMF and EDCI (0.17 g, 0.87 mmol) was added, followed by HOBt (0.12 g, 0.87 mmol). The resulting mixture was stirred for 30 min and (Z)-N′-hydroxy-acetimidamide (0.06 g, 0.82 mmol) was added and the mixture was stirred overnight. The reaction mixture was diluted with water and extracted with EtOAc. The organic layer was washed successively with water, 2N Na2CO3 solution and brine, dried over anhydrous Na2SO4, filtered, and concentrated under reduced pressure. The residue was used in the next step without purification. LCMS (+ESI) m/z 1025.2 [2M+H]+.
