N-Hydroxysulfosuccinimide Sodium Salt

Experimental procedure: 1 (1.0 mmol), is dissolved in dry DMF (2.5 mL), then N-oxysulfosuccinimide sodium salt (250 mg, 1.17 mmol) and DCC (375 mg, 1.8 mmol) are added and the mixture is left under stirring overnight, then cooled to 4 °C and stirred for 2 h. The precipitate formed is filtered off, and the solution is diluted with EtOAc (10 mL), cooled to 4 °C overnight, filtered, and diluted with dry Et₂O (200 mL). The mixture is kept at ambient temperature for 2-3 h and the desired compound is collected by filtration, washed with Et₂O and dried in vacuo to give 2. To a stirring solution of 2-aminoethyl-trimethylammonium chloride (3) (69 mg, 0.5 mmol) in the mixture of pyridine (1 mL), acetonitrile (1 mL), and water (1 mL), 2 (155 mg, 0.25 mmol) is added in one portion and the mixture is stirred for 6 h, then diluted with CHCl₃ (50 mL), washed with water (100 mL), brine (100 mL), dried over Na₂SO₄, and evaporated to dryness. The residue is dissolved in acetone (2 mL) and precipitated in Et₂O to give 4 as a white solid (95 mg, 70% from 2).