Under a nitrogen atmosphere 0.99 g (16.0 mmol) methylboric acid, 15.5 mL 2 M Na2CO3 solution and 1.02 g (1.40 mmol) Pd(dppf)Cl2 were added to a solution of 8.40 g (14.5 mmol) methyl(S)-2-(4-amino-3-bromo-5-chloro-benzyl)-4-oxo-4-[4-(2-oxo-1,2,4,5-tetrahydro-1,3-benzodiazepin-3-yl)-piperidin-1-yl]-butanoate in 50 mL 1,4-dioxane and 3 mL MeOH and the reaction mixture was refluxed overnight. The reaction solution was filtered while hot and the filtrate was combined with EtOAc. The organic phase was washed several times with semisaturated NaHCO3 solution and dried over Na2SO4. It was filtered through activated charcoal and evaporated down i.vac. The residue was taken up in a little DCM and purified by chromatography (silica gel, gradient DCM to DCM/MeOH/NH3 90:10:1). The fractions containing the product were combined, evaporated down i.vac., triturated with DIPE, suction filtered and dried.
