Diphenyl phosphoryl azide (323 μL, 1.5 mmol) was added to a stirred solution of Levofloxacin (361 mg, 1.0 mmol) and Et3N (280 μL, 2.0 mmol) in CH2Cl2 (10 mL) at 0° C. under an atmosphere of nitrogen. The mixture was stirred at 0° C. for 15 min, then allowed to warm to room temperature and stirred for 4 hr. Further aliquots of diphenyl phosphoryl azide (323 μL, 1.0 mmol) and Et3N (280 μL, 2.0 mmol) were added and the mixture was stirred at room temperature overnight. H2O (20 mL) and CH2Cl2 (15 mL) were added and the aqueous and organic layers were partitioned. The aqueous layer was extracted with CH2Cl2 (2×20 mL), and the combined organic layers were dried over Na2SO4, filtered and the solvent was removed under vacuum to leave a crude residue.
