The crystal structure of guanosine dihydrate and inosine dihydrate

Crystals of the dihydrates of guanosine (C_(10)H_(13)N_5O_5) and inosine (C_(10)H_(12)N_4O_5) are nearly isostructural. They are monoclinic, space group P2_1, with cell dimensions ɑ = 17·518, b = 11 ·502, c = 6·658 Å, β = 98·17° (guanosine) and ɑ = 17·573, b =11·278, c=6-654 Å, β = 98·23° (inosine). There are two nucleoside and four water molecules per asymmetric unit. Data were collected on an automated diffractometer; the structures were solved by Patterson and trial-and-error methods and refined to R indices of about 0·035. The structure features hydrogen bonding between purine bases to form ribbons parallel to b and parallel stacking of purine bases along c; the separation between adjacent rings within stack is 3·3 Å. The conformations about the glycosidic C-N bond and the puckerings of the sugar rings arc quite different for the two molecules in the asymmetric unit.