6-Amino-2-naphthalenesulfonic acid → 6-{[(Benzyloxy)carbonyl]amino}naphthalene-2-sulfonic acid

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Reaction Steps

To a suspension of 6-aminonaphthalene-2-sulfonic acid, sodium salt (3 g, 12.2 mmol) in 70 mL of water is added solid NaOH (1.01 g, 25 mmol) at room temperature. The mixture is stirred for 1 hour, and benzyl chloroformate (3.43 mL, 24 mmol) is then added. The resulting mixture is stirred over a period of 16 hours. The crude product is treated as in EXAMPLE 24, Part A to give 4.70 g of crude N-CBz-6-aminonaphthalene-2-sulfonic acid, sodium salt. A mixture of the sulfonic acid, sodium salt (2.3 g, 6.10 mmol) in 15 mL of thionyl chloride is heated at 80° C. for 5 hours. The mixture is allowed to cool to room temperature and concentrated in vacuo. The residue is diluted with EtOAc and washed successively with water (2×), saturated NaHCO3 solution and saturated NaCl. The organic layer is dried over anhydrous MgSO4, filtered and concentrated to give a solid. The crude product is triturated from 50% EtOAc/hexanes to afford the title compound (0.50 g, 1.33 mmol) as a beige solid.

Provenance & Evidence