6-Chloro-9-(2-nitrophenylsulfonyl)-9H-purine

The title compound, C11H6ClN5O4S, crystallized with two independent molecules in the asymmetric unit. The benzene ring makes dihedral angles of 66.46 (8) and 85.77 (9)° with the mean plane of the purine ring in the two molecules. In the crystal, intermolecular π–π stacking interactions [centroid–centroid distance = 3.8968 (12) Å], C—Cl⋯π interactions [Cl⋯centroid = 3.2505 (10) Å, C—Cl⋯centroid = 161.56 (18)°] and non-classical C—H⋯O and C—H⋯N hydrogen bonds link the molecules.


Comment
Purine derivatives are of great importance owing to their wide-ranging biological properties (Scozzafava et al., 2001;Bakkestuen et al., 2005). As there are several kinds of tautomers in purine derivatives, it is difficult to determine their structures by NMR, MS or IR sepctroscopy. The title compound is one of the key intermediates in our synthetic investigations of antimicrobial agents. Here we determined the accurate structure of the title compound by X-ray analysis.
As shown in Fig. 1, the title compound crystallized with two independent molecules (A and B) in the asymmetric unit.
The conformation of the molecules is different. The benzene ring makes a dihedral angle of 66.46 (8)° with the mean plane of the purine ring in molecule A, while in molecule B this same angle is 85.77 (9)°.

Experimental
A mixture of 6-chloropurine (0.463 g, 3 mmol), 2-nitrobenzenesulfonyl chloride (1.33 g, 6 mmol), Triethylamine (0.607 g, 6 mmol), DMAP (0.037 g, 0.3 mmol), THF (10 ml) and DCM (10 ml) was stirred for 12 h at room temperiture. The solvent was removed under vacuum. The residue was extracted with ethyl acetate (50 ml) and water (50 ml). The organic layer was washed three times with 30 ml ammonia solution (5 N) and 30 ml brine, and then dried with anhydrous sodium sulfate. The product was isolated by column chromatography on silica gel. Yield 0.712 g (69.8%). Crystals, suitable for X-ray analysis, were obtained by slow evaporation from a solution of ethyl acetate.

Refinement
All H atoms were positioned geometrically and refined using a riding model, with C-H = 0.93 Å and U iso (H) = 1.2U eq (C).
As the centroid of the benzene ring holds partial positive charge and the chlorine atom at the purine ring holds partial negative charge, the chlorine atom in one molecular is likely to be close to the benzene ring of another molecular (see Comment section), leading to the nitro groups of two neighbouring molecules approaching one another. Hence, a short  Fig. 1. The molecular structure of the two independent molecules of the title compound, with displacement ellipsoids drawn at the 50% probability level.   (7) 0.0079 (7) 0.0159 (7) O6 0.0454 (9) 0.0379 (9) 0.0480 (9) −0.0064 (7) 0.0069 (7) −0.0073 (7)