Crystal structure of 6,7-dihydroxy-6,7-dihydro-3H-imidazo[1,2-a]purin-9(5H)-one

In the crystal of the title purine derivative, molecules are linked by O—H⋯N, N—H⋯O and N—H⋯N hydrogen bonds, forming a three-dimensional framework.


Chemical context
Purine are essential ingredients of various compounds, for example two of the five bases in nucleic acids, adenine and guanine, are purines. Purine derivatives have been developed as inhibitors of cyclin-dependent kinase (Sausville, 2002), and as antiparasitic (Braga et al., 2007;Yadav et al., 2004), antitumor (Prekupec et al., 2003;Trá vníček et al., 2001), antiradical (Klanicová et al., 2010) and antiviral (Manikowski et al., 2005) drugs. The synthesis and the cancerostatic and antiviral activities of the title compound were reported on many years ago (Shapiro et al., 1969). Its crystal structure has not been reported to date, and as the conformation of a biologically active molecule is crucial to its activity we undertook the structure analysis of the title compound, which we report on herein.

Structural commentary
The molecular structure of title compound is depicted in Fig. 1. The C1-O1 bond length of 1.220 (2) Å shows typical doublebond character, and is coplanar with the purine moiety for their aromatic nature. The non-aromatic five-membered ring (N1/C7/C6/N5/C2) adopts a twisted conformation on the C6-C7 bond. The two hydroxyl groups lie on opposite sides of the ISSN 2056-9890 ring mean plane with an O2-C7-C6-O3 torsion angle of 114.8 (2) .

Database survey
A search of the Cambridge Structural Database (CSD, Version 5.37, update May 2016; Groom et al., 2016) for 1,9dihydro-6H-6-one as substructure, gave 61 hits. Many of these compounds concern guanine and guaninium and some metal complexes, but none involve a fused third ring. The structure of the title compound has not been reported previously.

Figure 2
A view along the c axis of the crystal packing of the title compound. The hydrogen bonds are shown as dashed lines (see Table 1).

Figure 3
A view along the b axis of the crystal packing of the title compound. The hydrogen bonds are shown as dashed lines (see Table 1).

Figure 1
The molecular structure of the title compound, with atom labelling. Displacement ellipsoids are drawn at the 50% probability level.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2 (Agilent, 2012); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008) and PLATON (Spek, 2009); software used to prepare material for publication: SHELXTL (Sheldrick, 2008) and PLATON (Spek, 2009). 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.