O-(3,4-Dihydro-4-oxo-1,2,3-benzotriazin-3-yl)-N,N,N',N'-tetramethyluronium Tetrafluoroborate

Experimental procedure:
To a stirred solution of 1 (60 mg, 0.133 mmol), DIEA (19.4 mg, 0.15 mmol) in anhydrous DMF (0.5 mL) is added TDBTU (51.1 mg, 0.145 mmol), and the reaction mixture is stirred at room temperature for 2 h. A solution of spermine (5.6 mg, 0.028 mmol) and DIEA (0.074 g, 0.57 mmol) in anhydrous DMF (0.2 mL) is then added dropwise and the resulting solution stirred at 55 °C for 6 h. The mixture is then concentrated under reduced pressure, and the resulting solid is dissolved in CH₃OH (2 mL). Subsequent precipitation, by addition to an aqueous solution that is saturated with NaHCO₃, and preparative thin-layer chromatography (SiO₂, CHCl₃:CH₃OH = 15:1) affords 2 (42.9 mg, 79%).