Diisopropyl {[(R)-2-(2-amino-6-chloro-9H-purin-9-yl)-1-methylethoxy]methyl}phosphonate

In the title compound, C15H25ClN5O4P, the r.m.s. deviation for the purine ring system is 0.0165 Å. The coordination about the P atom is a distorted tetrahedron [O=P—O angles = 116.70 (6) and 109.87 (6)°]. In the crystal, molecules are linked by N—H⋯O hydrogen bonds, generating a three-dimensional network.

Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: FK2051).
In (I), all bonds lengths and angles are normal (Allen et al., 1987). Molecules are stacked along the a axis, and linked into a zigzag sheet propagating along the c axis by intermolecular N-H···O hydrogen bonds ( Figure 2 and Table 2).

Experimental
The title compound was synthesized according to the procedure of Kuo-Long Yu et al. (1992). Colourless single crystals (m.p. 404-406 K) were obtained by slow evaporation of a solution in absolute ethanol.

Refinement
The H atoms linked to the C atoms were fixed geometrically and treated as riding with C-H = 0.95 Å (aromatic), 0.98Å (ethyl), 0.99 Å (methylene) with U iso (H) =1.2-1.5Ueq(C). H atoms of the amino group were located in a difference Fourier map and also refined riding with N-H = 0.89 Å.

Figure 2
The crystal packing of (I) with hydrogen bonds drawn as dashed lines.  Superposition of the molecular conformations of the title compound (red) and its F-substituent (blue, Baszczyňski et al.,  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.