To a solution of 1-methyl-6-(1,2,3,4-tetrahydro-1,7-naphthyridin-5-yl)-3,4-dihydroquinolin-2(1H)-one (intermediate A-5, 0.1 g, 0.341 mmol) in DCE (3 mL)/THF (1.5 mL) were added tert-butyl 2-oxoethylcarbamate (0.081 g, 0.511 mmol), acetic acid (0.02 g, 0.341 mmol) and the reaction mixture was stirred at room temperature for 10 min. Then, sodium triacetoxyborohydride (0.144 g, 0.682 mmol) was added and stirring was continued at room temperature over night. Then, the mixture was diluted with DCM, poured into aq NaHCO3 and extracted with DCM (2×25 mL). Combined organics were washed with brine, dried over Na2SO4, filtered and evaporated to dryness. The residue was purified by reverse phase HPLC on a Gemini-NX column, eluting with a 20 to 98% MeOH—H2O (0.05% TEA) gradient to give the title compound (0.036 g, 24%) as a white foam. MS: 437.2 (M+H+).
