A novel Janus-type AT nucleoside with benzoyl protecting groups forming a pleated-sheet structure.

The title compound, 5-amino-8-(2,3,5-tri-O-benzoyl-β-D-ribofuranosyl)pyrimido[4,5-d]pyrimidine-2,4(3H,8H)-dione methanol monosolvate, C(32)H(25)N(5)O(9)·CH(4)O, which crystallized slowly from methanol, exhibits an anti conformation with a glycosyl-bond torsion angle of χ=-141.28 (17)°. The furanose moiety adopts an N-type sugar puckering ((3)T(4)). The corresponding pseudorotation phase angle and maximum amplitude are P=24.5 (2)° and τ(m)=38.3 (2)°, respectively. In the solid state, one methanol molecule acts as a bridge joining adjacent nucleoside molecules head-to-head, leading to a pleated-ribbon supramolecular structure, with the base moieties located in the centre of the ribbon and the sugar residues protruding to the outside of the layers, as in a DNA helix. The pleated-ribbon supramolecular structure is tethered together into a two-dimensional infinite pleated-sheet structure through aromatic stacking between the nucleobase planes and the benzene rings of the benzoyl protecting groups on the 5'-OH group of furanose.