To a solution of 1-(1,3-dimethoxypropan-2-yl)-6-iodo-4-oxo-1,4-dihydroquinoline-3-carboxylic acid (Intermediate 78, 500 mg, 1.12 mmol) and tert-butyl piperazine-1-carboxylate (312 mg, 1.67 mmol) in dichloromethane (50 mL) was added hydroxybenzotriazole (HOBT) (183 mg, 1.12 mmol) and N-methyl morpholine (484 mg, 4.79 mmol). The reaction mixture was stirred for 1 h at room temperature and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDCI HCl) (390. mg, 2.15 mmol) was added. The resulting reaction mixture was stirred for room temperature overnight. The reaction mixture was quenched with dilute hydrochloric acid (2N, 30 mL) and the layers were separated. The organic layer was washed with saturated sodium bicarbonate solution (40 mL), water (60 mL) and finally with brine successively and dried over anhydrous sodium sulphate, filtered, concentrated under vacuum to afford tert-butyl 4-{[1-(1,3-dimethoxypropan-2-yl)-6-iodo-4-oxo-1,4-dihydroquinolin-3-yl]carbonyl}piperazine-1-carboxylate 400 mg (57%) as thick oil.
