[BH4-].[Na+].Br[CH:4]1[CH:9]2[CH:10]([OH:15])[CH:11]([OH:14])[CH:12]([OH:13])[C:5]1([CH2:17][OH:18])[O:6][C:7](=[O:16])[NH:8]2.C(O)(=O)C>O>[OH:15][CH:10]1[CH:11]([OH:14])[CH:12]([OH:13])[C:5]2([CH2:17][OH:18])[CH2:4][CH:9]1[NH:8][C:7](=[O:16])[O:6]2Sodium borohydride (55 g) is added by portions to a solution of 9-bromo-6,7,8-trihydroxy-1-hydroxymethyl-3-oxo-2-oxa-4-azabicyclo[3.3.1]nonane (100 g) in water (1.3 l) at 25°-30° C. with stirring. After stirring for 2 hours at the same temperature, the reaction mixture is adjusted to pH 6-7 with acetic acid and concentrated to about 800 ml under reduced pressure. The concentrate is chromatographed on a column of activated carbon (4.8 l), and the column is washed with water (5 l) and eluted with 50% aqueous methanol. The eluate is concentrated under reduced pressure. Methanol (350 ml) is added to the residue and refluxed for 10-20 minutes to remove a methanol soluble by-product. The mixture is allowed to stand in a refrigerator overnight, and the resulting crystals are collected by filtration, followed by washing with cold methanol and drying in a desiccator under reduced pressure to give 6,7,8-trihydroxy-1-hydroxymethyl-3-oxo-2-oxa-4-azabicyclo[3.3.1]nonane (64 g).
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