m-Chloroperbenzoic acid → 5,11-Dihydro-11-ethyl-2-fluoro-5-methyl-8-{2-{(1-oxido-4-quinolinyl)oxy}-ethyl}-6H-dipyrido[3,2-b:2',3'-e] [l,4]diazepin-6-one

Solid mCPBA (457 mg, 2.12 mmol) was added to a solution of 5,11-dihydro-2-fluoro-11-ethyl-5-methyl-8-{2-(4-quinolinyloxy)ethyl}-6H-dipyrido[3,2-b:2′,3′-e][1,4]diazepin-6-one (470 mg, 1.06 mmol) in CH2Cl2 (10 mL). The mixture was stirred at room temperature for 13 h then was concentrated under reduced pressure. The residue was dissolved in CHCl3 (75 mL), the solution was successively washed with aqueous 10% Na2S2O3 (3×25 mL), aqueous saturated NaHCO3 (3×25 mL) and brine (25 mL), dried (MgSO4), filtered and concentrated under reduced pressure. The residue was purified by flash chromatography (CHCl3:MeOH, 19:1 to 9:1) to give the title compound (250 mg, 51% yield) as a white solid: MS (ESI) m/z 460 (MH)+.