N,N,N′,N′-Tetra methyl azodicarboxamide (TMAD) (118 mg) and tri-n-butyl phosphine (0.17 ml) were added to a THF solution (5 ml) of N-[3-(1-ethyl-3,3,5-trimethyl-2,4-dioxo-2,3,4,5-tetrahydro-1H-benzo[b][1,4]diazepin-7-yloxy)propyl]-2-nitrobenzenesulfonamide (231 mg) and 2-(2-hydroxyethyl)-7-methyl-2H-isoquinolin-1-one (93 mg), and stirred at room temperature overnight. Water was added to the reaction mixture, and extraction with dichloromethane was performed. The organic layer was dried over anhydrous sodium sulfate, and concentrated under reduced pressure. The residue was purified by silica gel column chromatography (ethyl acetate:methanol=20:1→10:1) The purified product was concentrated to dryness under reduced pressure to thereby obtain 205 mg (yield: 65%) of N-(3-(1-ethyl-3,3,5-trimethyl-2,4-dioxo-2,3,4,5-tetrahydro-1H-benzo[b][1,4]diazepin-7-yloxy)propyl)-N-(2-(7-methyl-1-oxo-1H-isoquinolin-2-yl)ethyl)-2-nitrobenzenesulfonamide as a white amorphous solid.
