Two mmoles of aspartic acid and 4 mmoles of NaHCO3 were dissolved in 5 ml of water. A solution containing 1 mmol of 5-dibutylamino-naphthalene-1-sulfonyl chloride (Bansyl chloride, Purchased from TCI) in acetone was slowly added. More acetone was added until the solution was clear. The mixture was stirred overnight at room temperature and protected from light. Acetone was removed by flash evaporation and the remaining water solution was acidified to a of pH=4.5 to 5 by adding 2M citric acid. Then, NaCl was added until saturation and the solution was extracted with three portions of ethyl acetate (20 ml each). Extracts were combined, dried over MgSO4 and the solution was filtered. The solvent was removed and the residue was purified by liquid chromatography on a silica gel. A gradient of 0 to 5% methanol in dichloromethane was used as eluent. Fractions containing the desired product were combined and solvents removed. The residue was triturated in 1:1 ether: petroleum ether. The precipitate was filtered out and dried in vacuum overnight thus affording 5-dibutylamino-naphthalene-1-sulfonyl)-L-aspartic acid (NST705).
