Monoclinic polymorph of 3,7-dimethyl-1-(5-oxohex­yl)-3,7-dihydro-1H-purine-2,6-dione

Dmitrijs Stepanovs; Anatoly Mishnev

doi:10.1107/S1600536811040232

. 2011 Oct 5;67(Pt 11):o2851. doi: 10.1107/S1600536811040232

Monoclinic polymorph of 3,7-dimethyl-1-(5-oxohexyl)-3,7-dihydro-1H-purine-2,6-dione

Dmitrijs Stepanovs ^a, Anatoly Mishnev ^a,^*

PMCID: PMC3247589 PMID: 22219894

Abstract

The structure of the title compound, pentoxifylline, C₁₃H₁₈N₄O₃, has been previously characterized as a triclinic polymorph [Pavelčík et al. (1989 ▶). Acta Cryst. C45, 836–837]. We have discovered the monoclinic form. There are no strong hydrogen bonds in the crystal structure, rather, moderate C—H⋯O hydrogen bonds are present, which serve to stabilize the three-dimensional architecture.

Related literature

For general background to pentoxifylline, see Dettelbach & Aviado (1985 ▶). For the structure and the nature of the hydrogen bonding in the triclinic polymorph, see: Pavelčík et al. (1989 ▶); Gilli (2002 ▶).

Experimental

Crystal data

C₁₃H₁₈N₄O₃
M _r = 278.31
Monoclinic,
a = 9.743 (6) Å
b = 17.410 (8) Å
c = 7.956 (3) Å
β = 90.89 (2)°
V = 1349.4 (12) Å³
Z = 4
Mo Kα radiation
μ = 0.10 mm⁻¹
T = 190 K
0.40 × 0.30 × 0.05 mm

Data collection

Nonius KappaCCD diffractometer
5073 measured reflections
3103 independent reflections
1817 reflections with I > 2σ(I)
R _int = 0.053

Refinement

R[F ² > 2σ(F ²)] = 0.066
wR(F ²) = 0.163
S = 1.01
3065 reflections
184 parameters
H-atom parameters constrained
Δρ_max = 0.24 e Å⁻³
Δρ_min = −0.20 e Å⁻³

Data collection: KappaCCD Server Software (Nonius, 1997 ▶); cell refinement: HKL SCALEPACK (Otwinovski & Minor, 1997 ▶); data reduction: HKL DENZO (Otwinovski & Minor, 1997 ▶) and SCALEPACK; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: ORTEP-3 (Farrugia, 1997 ▶); software used to prepare material for publication: SHELXL97.

Supplementary Material

Crystal structure: contains datablock(s) I, global. DOI: 10.1107/S1600536811040232/tk2793sup1.cif

e-67-o2851-sup1.cif^{(18.2KB, cif)}

Structure factors: contains datablock(s) I. DOI: 10.1107/S1600536811040232/tk2793Isup2.hkl

e-67-o2851-Isup2.hkl^{(150.4KB, hkl)}

Supplementary material file. DOI: 10.1107/S1600536811040232/tk2793Isup3.cml

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C2—H2⋯O18ⁱ	0.93	2.39	3.206 (4)	147
C15—H15B⋯O19ⁱⁱ	0.96	2.60	3.439 (4)	147
C16—H16A⋯O18ⁱ	0.96	2.55	3.395 (4)	148

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Symmetry codes: (i) Inline graphic ; (ii) .

Acknowledgments

This work was supported by the European Regional Development Fund (No. 2DP/ 2.1.1.1.0/10/APIA/VIAA/066).

supplementary crystallographic information

Comment

The background to pentoxifylline has been summarized (Dettelbach & Aviado, 1985). The polymorph structure II differs from the known form I Pavelčík et al., 1989; Gilli, 2002) in their molecular conformation and the packing of the molecules in the lattice. The bond lengths of forms I and II are close to their standard values, but torsion angle N7—C10—C11—C12 (75.6 (3)° for I and 175.8 (2)° for II) and some bond angles significantly differ: N7—C10—C11 (114.2 (2)° for I and 111.9 (2)° for II), C10—C11—C12 (115.4 (2)° for I and 115.4 (2)° for II), C11—C12—C13 (111.0 (2)° for I and 114.1 (2)° for II). In the crystal structure of II, the molecules are connected by means of C—H···O hydrogen bonds, Table 1.

Experimental

Title compound was obtained by recrystallization of Trental tablets, produced by Sanofi-Aventis Deutschland GmbH. Crystals were grown by slow evaporation from dichloromethane at temperature range 308–315 K.