Cesium carbonate → tert-butyl 4-{3-[(3R)-3-{[(1S)-3-tert-butoxy-1-(5-{2-[4-(2-{[(4-methylphenyl)sulfonyl]oxy}ethoxy)phenyl]ethyl}pyridin-3-yl)-3-oxopropyl]carbamoyl}piperidin-1-yl]-3-oxopropyl}piperidine-1-carboxylate

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Tert-butyl 4-{3-[(3R)-3-{[(1S)-3-tert-butoxy-1-{5-[(4-hydroxyphenyl)ethyl]pyridin-3-yl}-3-oxopropyl]carbamoyl}piperidin-1-yl]-3-oxopropyl}piperidine-1-carboxylate (67 mg, 0.10 mmol) was dissolved in N,N-dimethylformamide (9.7 mL). Cesium carbonate (79 mg, 0.24 mmol) and ethane-1,2-diyl bis(4-methylbenzenesulfonate) (54 mg, 0.15 mmol) were added. The mixture was stirred at room temperature for 4 hours, quenched by addition of saturated aqueous ammonium chloride solution and extracted with ethyl acetate. The combined extracts were washed with brine and dried over sodium sulfate. The solution was concentrated under reduced pressure and the residue was purified by chromatography on silica gel (ethyl acetate in hexane 20% to 100% followed by dioxane in ethyl acetate 0 to 60%) to yield 64 mg of tert-butyl 4-{3-[(3R)-3-{[(1S)-3-tert-butoxy-1-(5-{2-[4-(2-{[(4-methylphenyl)sulfonyl]oxy}ethoxy)phenyl]ethyl}pyridin-3-yl)-3-oxopropyl]carbamoyl}piperidin-1-yl]-3-oxopropyl}piperidine-1-carboxylate.

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