Diisopropylethylamine → tert-butyl 4-(3-(3-(3-methoxy-4-((6-methoxypyridin-3-yl)methoxy)benzyl)-3H-imidazo[4,5-b]pyridin-6-yl)-1,2,4-oxadiazol-5-yl)piperidine-1-carboxylate

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To a stirred solution of N′-hydroxy-3-(3-methoxy-4-((6-methoxypyridin-3-yl)methoxy)benzyl)-3H-imidazo[4,5-b]pyridine-6-carboximidamide (0.38 g, 0.75 mmol) in N,N-dimethylformamide (10 mL) was added 1-(tert-butoxycarbonyl)piperidine-4-carboxylic acid (0.21 g, 0.92 mmol), 1-[bis(dimethylamino)methylene]-1H-1,2,3-triazolo[4,5-b]pyridinium 3-oxid hexafluorophosphate (0.35 g, 0.92 mmol) and N,N-diisopropylethylamine (0.19 g, 1.50 mmol). The reaction mixture was stirred at room temperature. After 1 h, the mixture was diluted with ethyl acetate and brine. The organic phase was separated, dried over magnesium sulfate, filtered, and concentrated. The residue was dissolved in 1,4-dioxane (20 mL) and heated to 85° C. After 16 h, the reaction mixture was allowed to cool to room temperature and was concentrated. The crude product was purified by silica gel chromatography (2% methanol/dichloromethane elute) to provide 0.14 g (25%) of tert-butyl 4-(3-(3-(3-methoxy-4-((6-methoxypyridin-3-yl)methoxy)benzyl)-3H-imidazo[4,5-b]pyridin-6-yl)-1,2,4-oxadiazol-5-yl)piperidine-1-carboxylate as a yellow solid.

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