The two, epimeric α-hydroxyamidoximes 5 and 6 - and some derivatives thereof, particularly oxadiazoles 16 and 17 - have been stereospecifically prepared from the keto sugar 1. Compound 5 was found to exist in two polymorphous crystalline forms (α and β) depending on the crystallization solvent. Both forms are orthorhombic, space group P2₁2₁2₁ (α-form : α = 10.408(3), b = 10.559(2), c = 14.144(2) Ȧ; β-form : a = 7.890(1), b = 10.305(2), c = 19.064(4) Ȧ). The calculation of pseudorotation parameters showed that each polymorph is associated with a slightly different conformation of the dioxolane rings. The O-acetyl derivative 11 of 6 adopts a different conformation of the furanose ring. In the three structures, a network of hydrogen bonds exists. The amidoxime 5 forms a cupric complex [Cu(5)₂] whose ESR spictrum proved its square structure.