Triethylamine → L-Aspartic Acid

Compound 8 (1.0 g; 3.07 mmoles) was dissolved in dimethylformamide (7 ml). β-Hydroxy,β-methyl-aspartic acid (0.5 g; 3.07 mmoles) was added to the solution. Triethylamine (0.64 ml; 4.5 mmoles) was added to the stirred suspension. Stirring was continued for 2.5 hours, after which a clear solution was obtained. The solvent was then evaporated in vacuo. The residue was dissolved in water and the aqueous solution was subsequently extracted three times with ethyl acetate in order to remove the p-nitrophenol. Following acidification of the aqueous solution to pH 1-2 by addition of 5% (w/w) aqueous potassium bisulfate, the solution was extracted four times with dichloromethane-butanol-2 (3:2; v/v). The combined organic extracts were evaporated in vacuo to give compound 9 as a syrup. The product was purified by column chromatography on silica(R) ("Merck" 40-63 μm) using butanol-1-acetic acid-water (4:1:1; v/v) as the eluent. Fractions containing pure 9 were combined and evaporated in vacuo. The residue was dissolved in water upon which the product was isolated by lyophilization (450 mg; 42%).