Isophthalaldehyde → Di-tert-butyl (((((1,3-phenylenebis(methylene))bis(azanediyl))bis(propane-3,1-diyl))bis(azanediyl))bis(propane-3,1-diyl))dicarbamate

Isophthalaldehyde (1.07 g, 7.99 mmol) and MeOH (50 mL) were added to a round-bottom flask. To the solution was added tert-butyl (3-((3-aminopropyl)amino)propyl)carbamate (3.69 g, 16.0 mmol) and the reaction mixture was stirred for 24 h. Sodium borohydride (1.21 g, 32.0 mmol) was added portionwise and stirred for 1 h. The reaction mixture was concentrated under reduced pressure, and aq. NaOH (10%, 150 mL) and EtOAc (150 mL) were added. The layers were separated, and the aqueous layer was extracted with EtOAc (150 mL). The organic layers were combined, dried over Na2SO4, filtered, and concentrated under reduced pressure to afford the desired product as a clear oil. The intermediate was carried forward without further purification.