A toyocamycin analogue with the sugar moiety in a syn conformation.

The title compound [systematic name: 4-amino-5-cyano-1-(beta-D-ribofuranosyl)-7H-pyrrolo[2,3-d]pyrimidine hemihydrate], C(12)H(13)N(5)O(4).0.5H(2)O, is a regioisomer of toyocamycin with the ribofuranosyl residue attached to the pyrimidine moiety of the heterocycle. This analogue exhibits a syn glycosylic bond conformation with a chi torsion angle of 57.51 (17) degrees. The ribofuranose moiety shows an envelope C2'-endo ((2)E) sugar conformation (S-type), with P = 161.6 (2) degrees and tau(m) = 41.3 (1) degrees. The conformation at the exocyclic C4'-C5' bond is +sc (gauche, gauche), with a gamma torsion angle of 54.4 (2) degrees. The crystal packing is stabilized by intermolecular O-H...O, N-H...N and O-H...N hydrogen bonds; water molecules, located on crystallographic twofold axes, participate in interactions. An intramolecular O-H...N hydrogen bond stabilizes the syn conformation of the nucleoside.