Oxalic acid dihydrate → HCID 70191891, compound

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Reaction Steps

(5S,1'S)-3-Phenylmethyl-5-(1'-tert-butoxycarbonylamino-2'-phenylethyl)-2-isoxazoline (3.69 g, 7.88 mmol) obtained in a manner similar to that described in Example 6 was dissolved in methanol (40 ml). To the solution, ammonium acetate (1.21 g, 15.8 mmol) and acetic acid (1.0 ml) were added. A 3% Pt-on-carbon catalyst (300 mg, 8.1% by weight based on substrate) was added thereto. The mixture was stirred for 24 hours in a hydrogen atmosphere at atmospheric pressure. The catalyst was removed by filtration under reduced pressure, and the filtrate was concentrated under reduced pressure. The resulting oil (6.56 g) was extracted with methylene chloride (50 ml) and an aqueous 10% NaOH (50 ml). The organic layer was washed with water, then dried over anhydrous magnesium sulfate. The desiccant was filtered off and the filtrate was concentrated under reduced pressure to give a foamy residue (4.0 g) containing (2S,3S,5S)-2-tert-butoxycarbonylamino-3-hydroxy-5-amino-1,6-diphenylhexane and (2S,3S,5R)-2-tert-butoxycarbonylamino-3-hydroxy-5-amino-1,6-diphenylhexane. Analysis by HPLC revealed that the ratio of (2S,3S,5S)-2-tert-butoxycarbonylamino-3-hydroxy-5-amino-1,6-diphenylhexane to (2S,3S,5R)-2-tert-butoxycarbonylamino-3-hydroxy-5-amino-1,6-diphenylhexane was 6:1. To the thus-obtained product, oxalic acid dihydrate (993 mg, 7.88 mmol) was added, and the resulting mixture was heated to dissolve in aqueous methanol (water content: 20 v/v%, 50 ml). When the mixture was dissolved, it was cooled and crystals precipitated were collected by filtration. The crystals were washed with aqueous methanol (water content: 20%, 10 ml×3, 3 ml×3) then dried under reduced pressure. The crude crystals (2.58 g) were confirmed, by HPLC, to contain (2S,3S,5S)-2-tert-butoxycarbonylamino-3-hydroxy-5-amino-1,6-diphenylhexane and (2S,3S,5R)-2-tert-butoxycarbonylamino-3-hydroxy-5-amino-1,6-diphenylhexane in the ratio of 97:3. The crude crystals were recrystallized from aqueous methanol (water ratio: 20 v/v%, 35 ml) in a manner similar to that as described above to give the desired compound as colorless crystals. Yield: 2.06 g (55%). This compound was identical to that obtained in Example 41. (2S,3S,5R)-2-tert-Butoxycarbonylamino-3-hydroxy-5-amino-1,6-diphenylhexane was not detected by HPLC.

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