9H-9-fluorenylmethyl N-(2-aminoethyl)carbamate hydrochloride (Compound 14; 5.00 g, 153.7 mmol) and L-(+)-tartaric acid (Compound 15; 5.89 g, 39.2 mmol) were dissolved by the addition of N,N-dimethylformamide (300 ml) and triethylamine (5.46 ml, 39.2 mmol). Next, 1-hydroxybenzotriazol hydrate (2.52 g, 16.5 mmol) was added, a solution of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (3.16 g, 16.5 mmol) in N,N-dimethylformamide (200 ml) was added drop by drop, and this was followed by overnight stirring at room temperature. This was concentrated under reduced pressure, the residue obtained was dissolved in ethyl acetate, and the organic phase was washed with a 2N aqueous solution of citric acid. Next, reverse extraction was conducted using aqueous sodium hydrogen carbonate, after which the water phase obtained was washed with ethyl acetate. Under ice cooling, the water phase was rendered acidic with a 2N aqueous solution of citric acid, after which it was extracted with ethyl acetate. The organic phase was washed with saturated brine, after which it was dried with sodium sulfate. After the solid was filtered and concentrated under reduced pressure, crystallization from methanol-diethyl ether was conducted to yield the desired N-[2-(9H-fluoren-9-ylmethoxycarbonylamino)-ethyl]-2,3-dihydroxy-succinamic acid (2.72 g, 42%).
