A solution of 6′-hydroxy-4,4-dimethyl-4,5-dihydro-3H-[1,3′]bipyridinyl-2,6-dione (468 mg, 2.00 mmol), 4-(tert-butyl-dimethyl-silanyloxy)-piperidine-1-carboxylic acid 5-benzoylamino-pyridin-2-yl ester (0.90 g, 2.00 mmol) and triethylamine (0.20 g, 2.00 mmol) in dimethylformamide (10 mL) was stirred at room temperature for 18 hours. The solvent was evaporated in vacuo. The residue was dissolved in ethyl acetate, filtered over a short pad of silicagel and washed with ethyl acetate. The solvent was evaporated in vacuo and the residue was dissolved in 1N HCl in ethyl acetate (10 mL, 10.0 mmol). After stirring for 1.5 hours at room temperature the solvent was evaporated in vacuo. The white solid was washed with a small amount of ethyl acetate and diethyl ether and dissolved in a few millilitres of dichloromethane and triethylamine (1 mL). Purification by flash column chromatography (SiO2, ethyl acetate:acetone 90:10) yielded the title compound (182 mg, 25% yield) as a white solid.
