(2R,3S,4R,5R)-5-(4-Amino-5-iodo-7H-pyrrolo[2,3-d]pyrimidin-7-yl)-4-fluoro-2-(hydroxymethyl)tetrahydrofuran-3-ol

The title compound, C11H12FIN4O3, is composed of a 7-carbapurine moiety connected via an N atom to 2-deoxy-2-fluoro-β-d-ribose. The conformation about the N-glycosydic bond is −anti with χ = −129.0 (11)°. The glycosydic N—C bond length is 1.435 (14) Å. The sugar ring adopts an Nconformation with an unsymmetrical twist O-endo-C-exo (oT4). The conformation around the C—C bond is +sc, with a torsion angle of 53.0 (12)°. In the crystal, molecules are linked by N—H⋯O hydrogen bonds, forming chains propagating along the a axis. These chains are linked via O—H⋯I and C—H⋯O hydrogen bonds, forming layers lying parallel to the c axis.

In our study, we report a fluorinated nucleoside (Fig. 1). The three-dimensional structure and the packing of the title compound is shown Fig. 2 and hydrogen bonds geometry are summarized in Table 1. The orientation of the base relative to the sugar of purine nucleosides is defined by the torsion angle χ (O1-C7-N4-C5),being in the title compound -anti, withχ= -129.0 (11)°. The phase angle of pseudorotation (P)is 67.6 (11)°, and the maximum amplitude of puckering (τ m ) is 39.5 (7)° (Saenger, 1983). The sugar ring adopts a D conformation (Evans & Boeyens, 1989), with an unsymmetrical twist O1-endo-C10-exo( o T 4 ). The packing of the title compound is stabilized by hydrogen bonds, leading to a twodimensional network ( Fig. 3 and Table 1). The nucleobases are arranged head-to-head in a staircase-like fashion, in a pattern propagated by the a axis of the unit cell.
After the solvent was removed in vacuo, the residue was purified by column chromatography on silicagel to give I as a white solids.
Synthesis of compound 2 1(220.0 mg, 0.354 mmol) was suspended in 30 mL saturated methanolic ammonia and the solution was heated in a sealed bottle at 403 K for 12 h. The solution was evaporated in vacuo. The residue was purified by column chromatography on silica gel to afford 2 as a white solids. Crystals of the title compound (2) were obtained by slow evaporation of methanol.

Refinement
H atoms bond to N were located in a difference map and refined with distance of N-H = 0.86 Å or O-H = 0.82 Å and U iso (H) = 1.2U eq (N). other H atoms attached to C were fixed geometrically and treated as riding with C-H = 0.96 Å (methyl) or 0.93 Å (aromatic) and with U iso (H) = 1.2U eq (aromatic) or U iso (H) = 1.5U eq (methyl).

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2sigma(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.