The first example of a crystalline pyrazolidinedione nucleoside has been synthesized from the reaction of 2-deoxy-d-ribose with 4, 4-dimethylpyrazolidine-3, 5-dione and characterized by X-ray crystallography as a single α-pyranoside diastereomer [IUPAC name: 1-(2-deoxy-α- d-erythro-pentopyranosyl) 1 (R), 2 (R)-4, 4-dimethylpyrazolidine-3, 5-dione, C10H16N2O5]. Although the pyrazolidinedione ring is essentially planar, the two hydrazidic N atoms are ...