Structure of 3-isoinosine.

3-beta-D-Ribofuranosylhypoxanthine, 3-beta-D-ribofuranosyl-1,6-dihydro-3H-purin-6-one, C10H12-N4O5, Mr = 268.23, monoclinic, P2(1), a = 6.503 (1), b = 24.007 (6), c = 7.392 (2) A, beta = 106.53 (2) degrees, V = 1106.3 (9) A3, Z = 4, Dx = 1.610 g cm-3, lambda(Mo K alpha) = 0.71073 A, mu = 1.23 cm-1, F(000) = 560, T = 299 K, R = 0.048 and wR = 0.043 for 1602 observed reflections. There are two crystallographically independent molecules in the structure; in both of them the 6-oxo, 7H tautomer is the predominant form. The bond lengths and angles of the two molecules are almost identical and the hypoxanthine moiety is almost planar. The torsional angles of the glycosidic linkage O(4')-C(1')-N(3)-C(4) are -159.3 and -148.8 degrees, both in the anti range. The sugar puckers are 4T3 (C4'-exo/C3'-endo), with P = 46.35 degrees and tau m = 42.30 degrees, and 2E (C2'-endo), with P = 157.24 degrees and tau m = 41.32 degrees. All N and O atoms except N(3) and O(4') participate in a three-dimensional hydrogen-bonding system.