Prepd by sodium amalgam reduction of an acid soln of the γ-lactone of d-gulonic acid: Fischer, Stahel, Ber. 24, 532 (1891); van Ekenstein, Blanksma, Rec. Trav. Chim. 27, 3 (1908). Alternate synthesis: Meyer zu Reckendorf, Angew. Chem. Int. Ed. 6, 177 (1967); idem, Methods Carbohydr. Chem. 6, 129 (1972); R. Kster et al., Angew. Chem. Int. Ed. 19, 547 (1980).