Benzyl Bromide → (s)-2-Benzyloxy-4-benzyloxycarbonylaminobutyric acid

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Reaktionsschritte

(S)-4-Benzyloxycarbonylamino-2-hydroxybutyric acid (5.25 g, 20.7 mmol) synthesized according to the report of Kawaguchi et al. (Journal of Antibiotics, Vol. 25, pp. 695-708 (1972)) was dissolved in 60 mL of N,N-dimethylformamide. Barium oxide (15.9 g, 103.7 mmol) was added under an ice bath. After the elapse of 2 min from the addition of barium oxide, barium hydroxide octahydrate (13.4 g, 42.5 mmol) was added thereto under an ice bath. After 10 min, benzyl bromide (7.5 mL, 63.1 mmol) was added thereto under an ice bath. After 5 min, the reaction solution was returned to room temperature and was vigorously stirred. After 1.5 hr, the completion of the reaction was confirmed by TLC (developing solvent system=chloroform:ethyl acetate:acetic acid=10:5:1), and water (0.5 mL) was added thereto under an ice bath. The mixture was diluted with chloroform (165 ml), and 4 N HCl (70 mL) was added thereto. Further, water (25 mL) was added followed by separation. The water layer was extracted with chloroform (50 mL). The organic layer and the extracted organic layer were combined and were washed with a saturated aqueous NaCl solution. The washed solution was dried over magnesium sulfate. The solvent was removed by distillation under the reduced pressure, and the residue was purified by column chromatography on silica gel (silica gel 60, neutral spheres, 160 g) (chloroform: ethyl acetate=4:1→chloroform:methanol=10:1→chloroform:methanol acetic acid=10:1:0.1 (600 mL)) to give (S)-2-benzyloxy-4-benzyloxycarbonylaminobutyrylic acid (2.86 g, 8.34 mmol).

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