9-Benzyl-6-benzylsulfanyl-9H-purin-2-amine

In the title compound, C19H17N5S, the dihedral angles between the purine ring system (r.m.s. deviation = 0.009 Å) and the S-bound and methylene-bound phenyl rings are 74.67 (8) and 71.28 (7)°, respectively. In the crystal, inversion dimers linked by pairs of N—H⋯N hydrogen bonds generate R 2 2(8) loops. C—H⋯N interactions link the dimers into (100) sheets.


Introduction
Thiopurine and its analogues possess a broad pharmacological activity for example as a cytotoxic agent (Nguyen et al., 2009) and in the treatment of lupus nephritis (Hadda et al., 2009). As part of our studies in this area, we report the synthesis and structure of the title compound.

Experimental
The method to synthesize the title compound was modified from a few papers (Banh et al., 2011;Salvatore et al., 2002;Salvatore et al., 2005). 2-amino-9H-purine-6-thiol (0.598 mmol) was mixed with cesium carbonate (0.598 mmol) in 3.5 ml of dimethylformamide and then stirred vigorously for 15 minutes. Another mixture containing benzyl bromide (1.315 mmol), tetrabutylammonium iodide (0.598 mmol) in 3.5 ml of DMF was added to the first mixture and the stirring was continued at room temperature for six hours. The reaction progress was monitored by TLC using n-hexane:ethyl acetate (0.5:3.5) as a solvent. After the product being formed, the reaction mixture was diluted with 70 mL of water and then extracted using 3 × 70 ml of ethyl acetate. The organic phase was collected, washed with 3× 70 ml of water and then dried over anhydrous magnesium sulfate. This organic phase was then evaporated in vacuo and the crude product was recrystallized from a hot methanol to afford the title compound as colourless blocks.

Refinement
N bound H atoms were located from difference Fourier maps and freely refined. The remaining H atoms were positioned geometrically and refined using a riding model with with C-H = 0.95-0.99 Å and U iso (H) = 1.2U eq (C).

Results and discussion
The purin ring is almost planar with the maximum deviation of 0.014 (2)Å at atom C11. It makes a dihedral angle of 71.28 and 74.67 (8)° with the two benzene rings, C1-C6 and C14-C19, respectively and these two benzene rings make a dihedral angle of 76.04)10)° with each other (Fig. 1).
In the crytsal structure, two dimers involving N5-H1N5···N3 i and C7-H7B···N3 ii are observed. These two dimers formed stacked molecules down the b-axis. Intermolecular interactions of C8-H8A···N2 iii further expand the molecules into infinite layers parallel to the bc-plane (Fig. 2).  The asymmetric unit of the title compound, showing 50% probability displacement ellipsoids.

Figure 2
The crystal packing of (I). Dashed lines indicate hydrogen bonds. H atoms not involved in the hydrogen bond interactions have been omitted for clarity.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 > σ(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.