Hydrochloric Acid → (4S)-4-hydroxy-4-(3-indolylmethyl)-2-hydroxyiminoglutaric acid

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Reaction Steps

Ammonium salt (44.7 g, 0.131 mol) of 4-hydroxy-4-(3-indolylmethyl)-2-hydroxyiminoglutaric acid was dissolved in 500 mL of water at 25° C., and subsequently the pH value of the aqueous solution was adjusted to 2 with 25.5 g of 36% hydrochloric acid. The acidic solution was subject to extraction with 1300 mL of ethyl acetate, and the ethyl acetate solution was washed with 200 mL of saturated aqueous NaCl solution. An aqueous solution (500 mL) of sodium carbonate (13.9 g, 0.131 mol) was added to the resulting ethyl acetate solution, and stirred to separate an alkali aqueous solution from ethyl acetate. The pH value of the resulting alkali aqueous solution was adjusted to 2 by adding 23.1 g of 36% hydrochloric acid. (R)-(+)-1-Phenylethylamine (6.99 g, 57.6 mmol) was dripped into the resulting acidic aqueous solution, and stirred at 25° C. for one hour. The yielded crystal was filtered, and dried under reduced pressure to yield 21.8 g (47.8 mmol) of (R)-(+)-1-phenylethylamine salt of (4S)-4-hydroxy-4-(3-indolylmethyl)-2-hydroxyiminoglutaric acid (yield: 72.7%, optical purity: 87.4%).

Provenance & Evidence