The title compound, 9(R)-[6(R)-hydroxymethyl-1-oxa-4-thiacyclohexan-2-yl]-1
,9-dihydro-6H-purin-6-one-water (4/3), C10H12N4O3S .0.75H(2)O, crystallizes
in the triclinic space group P1 with four molecules in the asymmetric unit
and 0.75 waters of hydration per molecule. The structure was refined to an
R value of 0.072 for 3382 observed reflections. The four crystallographica
lly independent molecules are designated A, B, C and D. All four oxathiane
rings adopt the chair conformation and the purine bases are in an anti orie
ntation with respect to the sugar moieties. Molecules A and D and molecules
C and B are base paired by a single hydrogen bond of the type N-H . . .N.
These base pairs are again hydrogen bonded to their translated pairs in the
direction of a cell diagonal.