tert-Butyl hydroperoxide → Phosphoric acid mono-(2-{[7-(4-bromo-2-chlorophenylamino)-8-chloro-imidazo[1,2-a]pyridine-6-carbonyl]-aminooxy}-ethyl) ester

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7-(4-bromo-2-chlorophenylamino)-8-chloroimidazo[1,2-a]pyridine-6-carboxylic acid (2-hydroxyethoxy)-amide (33a) (100 mg, 0.234 mmol), tetrazole (23 mg, 0.327 mmol) and di-tert-butyl diisopropylphosphoramidite (0.096 mL, 0.304 mmol) were dissolved/suspended in 30 mL of anhydrous DMF under an atmosphere of dry N2. The reaction mixture was stirred for about 3 hours, after which time the reaction was cooled to −78° C. and tert-butyl hydrogen peroxide (0.100 mL of 70% solution in water) was added. The cooling bath was then taken away and the reaction was slowly warmed up to room temperature and reacted over night. The reaction mixture was then partitioned between a solution of ethyl ether/ethyl acetate (5:1) and saturated aqueous NaHCO3. The organic layer was saved and successively washed with 10% aqueous sodium sulfite, 3 times with water and finally with brine. The resulting organic layer was dried over MgSO4, filtered and concentrated under vacuum. The residue was dissolved in 3 mL of a solution of TFA/DCM (2:1) under an atmosphere of dry N2. The reaction was stirred at room temperature for about 2 hours after which time it was concentrated under vacuum and the resulting residue was stirred in methanol for about 1 hour. The off-white solid was collected via suction filtration, washed with methanol followed by ethyl ether and then air-dried to give the desired compound (74).

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