Structure of 7-methyl-8-oxo-7,8-dihydroguanosine monohydrate.

2-Amino-7-methyl-9-(beta-D-ribofuranosyl)-1H,9H-purine-6,8-dione monohydrate, C11H15-N5O6.H2O, Mr = 331.29, orthorhombic, P212121, a = 6.9811 (6), b = 9.808 (2), c = 20.61 (2) A, V = 1411.1 (13) A3, Z = 4, Dx = 1.559 g cm-3, Cu Kalpha, lambda = 1.54178 A, mu = 10.825 cm-1, F(000) = 696, T = 295 K, R = 0.0296 for 2472 reflections (F greater than or equal to 4 sigma F). The sugar conformation and puckering parameters are 2E (C2'-endo), P = 161.8 degrees and tau m = 39.2 degrees. The side chain is gauche-gauche. The glycosidic torsion angle is 65.1 (2) degrees corresponding to the syn conformation which is stabilized by the O5'--H...N3 intramolecular hydrogen bond. The purine ring is nearly planar [r.m.s. deviation: 0.014 (2) A]; the dihedral angle between the pyrimidine and imidazole rings is 1.14 (8) degrees.