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In the crystal structure of 1,3-bis(4,6-diiso­propyl­sulfanyl-1H-pyrazolo­[3,4-d]­pyrimidin-1-yl)­propane, C25H36N8S4, the pairs of pyrazolo­[3,4-d]­pyrimidine rings in the mol­ecule stack as a result of intramolecular π–π interactions between the heterocyclic rings. The crystal packing also exhibits an intermolecular C—H...π interaction between one methyl group of an iso­propyl group and a pyrazolo­[3,4-d]­pyrimidine ring.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270103016676/de1217sup1.cif
Contains datablocks global, III

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270103016676/de1217IIIsup2.hkl
Contains datablock III

CCDC reference: 221084

Comment top

Interactions between aromatic moieties are known to play an important role in chemistry (Desiraju & Steiner, 1999; Hunter et al., 2001; Tsuzuki et al., 2002), stabilization of DNA/RNA structures (Hobza & Sponer, 1999), crystal engineering (Desiraju, 1995) and drug development (Meyer et al. 2003). Use of a polymethylene and especially a trimethylene linker for demonstrating intramolecular stacking was pioneered by Browne et al. (1968) and early work has been reviewed by Leonard (1979). In 1995, we reported the first synthesis (Avasthi et al., 1995) and crystal structure determination (Biswas et al., 1995) of a trimethylene-linker molecule, (I), based on the pyrazolo[3,4-d]pyrimidine core, which is isomeric with the biologically important purine system. The crystal structure exhibits an unusual intramolecular stacking (U-motif) and intermolecular stacking. The robustness of the U-motif in (I) has been further demonstrated by the crystal structure determination of the ethyl analog, (II) (Avasthi, Rawat et al., 2001) and other related propylene-linker compounds (Maulik et al.,1998; Avasthi, Aswal & Maulik, 2001; Avasthi, Tewari et al., 2002). Interestingly, no intramolecular stacking is observed when the trimethylene linker is replaced by an ethylene (Avasthi, Rawat et al., 2001) or tetramethylene linker (Maulik et al., 2000; Avasthi, Farooq et al., 2002). We report here the structure of 1,3-bis(4,6-di-isopropylthio-1H-pyrazolo[3,4-d] pyrimidin-1-yl)propane, (III). The conformation of (III) is shown in Fig. 1. The asymmetric unit contains only half of the molecule, which is related to the other half by the crystallographic symmetry operation (1 − x, y, 0.5 − z). The molecule is folded at the centre of the bridge [C8—C9—C8A = 113.9 (2)°] as a result of intramolecular stacking between the pyrazolo[3,4-d]pyrimidine rings. For comparison, the corresponding angles in (I) and (II) are 114.1 (2) and 113.5 (2)°, respectively. In (III), as in (I) and (II), the two pyrazolo[3,4-d]pyrimidine rings are positioned in such a way that only part of the pyrimidinyl rings overlap (Fig. 1). The overlapping six-membered rings are separated by an average distance (the mean value of the distances of all the atoms in one ring from the least-squares plane through the atoms in the other ring) of 3.555 Å [3.4 and 3.37 Å in (I) and (II), respectively], thus confirming the presence of an intramolecular ππ interaction. The pyrazolo[3,4-d]pyrimidine rings in (III), like those in (I) and (II), are nearly planar [maximum deviation = −0.036 (1) Å] and the angle between the least-squares planes is 21.96 (4)° [13.2 (1)° in (I) and ? in (II)]. It appears that because of the bulkiness of the isopropyl group, compared with the methyl/ethyl groups, the average intramolecular distance (3.555 Å) and angle between the least-squares planes [21.96 (4)°] have increased appreciably. However, the most striking effect of the presence of the isopropyl group instead of the methyl/ethyl groups found in (I) and (II) is seen in the packing diagram of (III) (Fig. 2). Molecule (III) does not exhibit intermolecular stacking due to the ππ interaction, but instead contains an intermolecular C—H···π interaction (Fig. 2) between one methyl group of the isopropyl group and the adjacent C3' atom of the pyrazolo[3,4-d]pyrimidine group [H···C3': 3.14 Å]. In conclusion, the replacement of the methyl or ethyl group in (I) or (II) by a bulky isopropyl group does not seriously affect the robustness of the U-motif formed by intramolecular stacking due to the aromatic ππ interaction. However, the parallel mode of intermolecular stacking seen in (I) and (II) is not present in (III) but is replaced by a C—H···π interaction.

Experimental top

Compound (III) was prepared using the method described by Avasthi et al. (1995), by stirring a mixture of 4,6-diisopropylthio- 1H-pyrazolo[3,4-d]pyrimidine and 1,3-dibromopropane in dimethylformamide in the presence of anhydrous potassium carbonate. Diffraction quality crystals were prepared from a solution of methanol and butanol by slow evaporation at room temperature.

Computing details top

Data collection: XSCANS (Siemens, 1996); cell refinement: XSCANS; data reduction: XSCANS; program(s) used to solve structure: SHELXTL (Bruker, 1997); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.

Figures top
[Figure 1] Fig. 1. Displacememt ellipsoid plot (30% probability), showing the molecular structure of (III) and the atomic labelling scheme.
[Figure 2] Fig. 2. Crystal-packing diagram of (III), showing the intermolecular C—H···π-stacking interactions (dashed lines) between the pyrazolo[3,4-d]pyrimidine rings.
1,3-bis(4,6-diisopropylsulfanyl-1H-pyrazolo[3,4-d]pyrimidin-1-yl)propane top
Crystal data top
C25H36N8S4F(000) = 1224
Mr = 576.90Dx = 1.235 Mg m3
Monoclinic, C2/cMelting point: 358 K
Hall symbol: -C 2ycMo Kα radiation, λ = 0.71073 Å
a = 21.044 (2) ÅCell parameters from 44 reflections
b = 8.814 (1) Åθ = 3.9–12.5°
c = 18.953 (2) ŵ = 0.34 mm1
β = 118.07 (1)°T = 293 K
V = 3101.9 (6) Å3Rectangular, colourless
Z = 40.30 × 0.28 × 0.20 mm
Data collection top
Bruker P4
diffractometer
Rint = 0.020
Radiation source: fine-focus sealed tubeθmax = 25.0°, θmin = 2.2°
Graphite monochromatorh = 241
θ–2θ scansk = 110
3403 measured reflectionsl = 2022
2738 independent reflections3 standard reflections every 97 reflections
2352 reflections with I > 2σ(I) intensity decay: none
Refinement top
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.035H-atom parameters constrained
wR(F2) = 0.094 w = 1/[σ2(Fo2) + (0.0402P)2 + 1.8299P]
where P = (Fo2 + 2Fc2)/3
S = 1.03(Δ/σ)max = 0.001
2738 reflectionsΔρmax = 0.22 e Å3
173 parametersΔρmin = 0.21 e Å3
0 restraintsExtinction correction: SHELXL97, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: structure-invariant direct methodsExtinction coefficient: 0.0045 (3)
Crystal data top
C25H36N8S4V = 3101.9 (6) Å3
Mr = 576.90Z = 4
Monoclinic, C2/cMo Kα radiation
a = 21.044 (2) ŵ = 0.34 mm1
b = 8.814 (1) ÅT = 293 K
c = 18.953 (2) Å0.30 × 0.28 × 0.20 mm
β = 118.07 (1)°
Data collection top
Bruker P4
diffractometer
Rint = 0.020
3403 measured reflections3 standard reflections every 97 reflections
2738 independent reflections intensity decay: none
2352 reflections with I > 2σ(I)
Refinement top
R[F2 > 2σ(F2)] = 0.0350 restraints
wR(F2) = 0.094H-atom parameters constrained
S = 1.03Δρmax = 0.22 e Å3
2738 reflectionsΔρmin = 0.21 e Å3
173 parameters
Special details top

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 F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
S10.72652 (3)0.09840 (6)0.38944 (3)0.06254 (18)
S20.49839 (3)0.06907 (5)0.10838 (3)0.05883 (17)
N10.58349 (8)0.55675 (16)0.26696 (8)0.0488 (4)
N20.63817 (8)0.59195 (18)0.34150 (9)0.0598 (4)
C30.67177 (10)0.4644 (2)0.37210 (11)0.0581 (5)
H30.71150.45570.42250.070*
C3'0.64020 (9)0.34162 (19)0.31913 (10)0.0455 (4)
C40.65180 (9)0.18612 (19)0.31228 (10)0.0463 (4)
N50.60762 (8)0.11002 (16)0.24719 (8)0.0492 (3)
C60.55244 (9)0.18830 (19)0.18806 (10)0.0455 (4)
N70.53710 (7)0.33438 (15)0.18501 (8)0.0451 (3)
C7'0.58319 (9)0.40652 (18)0.25234 (10)0.0428 (4)
C80.53726 (10)0.67407 (19)0.21351 (10)0.0515 (4)
H8A0.50120.62690.16490.062*
H8B0.56600.74080.19910.062*
C90.50000.7674 (3)0.25000.0518 (6)
H9A0.46470.83230.20900.062*0.50
H9B0.53530.83230.29100.062*0.50
C100.73466 (11)0.0806 (2)0.34705 (13)0.0635 (5)
H100.68830.13360.32450.076*
C110.75587 (17)0.0575 (4)0.28210 (18)0.1069 (10)
H11A0.80250.01080.30440.160*
H11B0.72120.00680.24130.160*
H11C0.75740.15380.25930.160*
C120.79013 (14)0.1723 (3)0.41677 (17)0.0990 (9)
H12A0.79560.27020.39810.149*
H12B0.77430.18470.45640.149*
H12C0.83550.12000.43990.149*
C130.43175 (10)0.1936 (2)0.03455 (11)0.0566 (5)
H130.41080.25730.06070.068*
C140.37376 (12)0.0888 (3)0.02454 (14)0.0809 (7)
H14A0.33580.14830.06480.121*
H14B0.35470.02800.00320.121*
H14C0.39420.02400.04930.121*
C150.46332 (14)0.2940 (3)0.00501 (12)0.0800 (7)
H15A0.48350.23240.03130.120*
H15B0.50040.35620.03460.120*
H15C0.42630.35760.04370.120*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
S10.0607 (3)0.0567 (3)0.0556 (3)0.0120 (2)0.0153 (2)0.0014 (2)
S20.0729 (3)0.0385 (3)0.0514 (3)0.0020 (2)0.0178 (2)0.00528 (19)
N10.0520 (8)0.0393 (7)0.0509 (8)0.0004 (6)0.0207 (7)0.0064 (6)
N20.0563 (9)0.0511 (9)0.0588 (9)0.0033 (7)0.0161 (7)0.0131 (7)
C30.0498 (10)0.0570 (11)0.0550 (10)0.0009 (9)0.0143 (8)0.0099 (9)
C3'0.0435 (9)0.0466 (9)0.0473 (9)0.0011 (7)0.0221 (7)0.0032 (7)
C40.0483 (9)0.0455 (9)0.0480 (9)0.0027 (7)0.0252 (8)0.0026 (7)
N50.0555 (8)0.0411 (8)0.0499 (8)0.0026 (6)0.0239 (7)0.0012 (6)
C60.0526 (9)0.0407 (9)0.0454 (9)0.0009 (7)0.0247 (8)0.0019 (7)
N70.0516 (8)0.0396 (7)0.0439 (7)0.0002 (6)0.0222 (6)0.0037 (6)
C7'0.0463 (9)0.0401 (9)0.0472 (9)0.0001 (7)0.0264 (7)0.0028 (7)
C80.0636 (11)0.0397 (9)0.0524 (9)0.0006 (8)0.0284 (9)0.0023 (7)
C90.0653 (15)0.0307 (11)0.0596 (14)0.0000.0295 (12)0.000
C100.0591 (11)0.0446 (10)0.0789 (13)0.0041 (8)0.0260 (10)0.0026 (9)
C110.124 (2)0.108 (2)0.114 (2)0.0314 (18)0.077 (2)0.0018 (17)
C120.0900 (17)0.0618 (15)0.114 (2)0.0219 (13)0.0219 (15)0.0168 (14)
C130.0592 (11)0.0537 (11)0.0518 (10)0.0087 (9)0.0219 (9)0.0087 (8)
C140.0557 (12)0.0914 (17)0.0770 (14)0.0003 (11)0.0157 (11)0.0204 (13)
C150.1148 (18)0.0601 (13)0.0571 (12)0.0002 (13)0.0338 (12)0.0050 (10)
Geometric parameters (Å, º) top
S1—C61.7497 (17)C13—C141.520 (3)
S1—C131.8117 (19)C13—H130.9800
S2—C41.7452 (17)C9—C8i1.509 (2)
S2—C101.815 (2)C9—H9A0.9700
N5—C41.325 (2)C9—H9B0.9700
N5—C61.362 (2)C10—C111.508 (3)
N7—C61.322 (2)C10—C121.520 (3)
N7—C7'1.345 (2)C10—H100.9800
C7'—N11.352 (2)C14—H14A0.9600
C7'—C3'1.393 (2)C14—H14B0.9600
N1—N21.373 (2)C14—H14C0.9600
N1—C81.454 (2)C15—H15A0.9600
N2—C31.309 (2)C15—H15B0.9600
C4—C3'1.409 (2)C15—H15C0.9600
C3'—C31.412 (2)C12—H12A0.9600
C8—C91.509 (2)C12—H12B0.9600
C8—H8A0.9700C12—H12C0.9600
C8—H8B0.9700C11—H11A0.9600
C3—H30.9300C11—H11B0.9600
C13—C151.501 (3)C11—H11C0.9600
C6—S1—C13104.79 (9)C8i—C9—H9A108.8
C4—S2—C10104.48 (9)C8—C9—H9A108.8
C4—N5—C6117.56 (15)C8i—C9—H9B108.8
C6—N7—C7'111.54 (14)C8—C9—H9B108.8
N7—C6—N5128.69 (16)H9A—C9—H9B107.7
N7—C6—S1120.07 (13)C11—C10—C12112.3 (2)
N5—C6—S1111.24 (12)C11—C10—S2111.65 (16)
N7—C7'—N1126.11 (15)C12—C10—S2105.75 (16)
N7—C7'—C3'126.58 (15)C11—C10—H10109.0
N1—C7'—C3'107.29 (15)C12—C10—H10109.0
C7'—N1—N2110.66 (14)S2—C10—H10109.0
C7'—N1—C8128.07 (15)C13—C14—H14A109.5
N2—N1—C8121.20 (14)C13—C14—H14B109.5
C3—N2—N1106.16 (14)H14A—C14—H14B109.5
N5—C4—C3'120.14 (16)C13—C14—H14C109.5
N5—C4—S2121.10 (13)H14A—C14—H14C109.5
C3'—C4—S2118.73 (13)H14B—C14—H14C109.5
C7'—C3'—C4115.37 (15)C13—C15—H15A109.5
C7'—C3'—C3104.30 (15)C13—C15—H15B109.5
C4—C3'—C3140.13 (17)H15A—C15—H15B109.5
N1—C8—C9112.99 (13)C13—C15—H15C109.5
N1—C8—H8A109.0H15A—C15—H15C109.5
C9—C8—H8A109.0H15B—C15—H15C109.5
N1—C8—H8B109.0C10—C12—H12A109.5
C9—C8—H8B109.0C10—C12—H12B109.5
H8A—C8—H8B107.8H12A—C12—H12B109.5
N2—C3—C3'111.58 (16)C10—C12—H12C109.5
N2—C3—H3124.2H12A—C12—H12C109.5
C3'—C3—H3124.2H12B—C12—H12C109.5
C15—C13—C14112.36 (18)C10—C11—H11A109.5
C15—C13—S1112.32 (15)C10—C11—H11B109.5
C14—C13—S1105.22 (15)H11A—C11—H11B109.5
C15—C13—H13108.9C10—C11—H11C109.5
C14—C13—H13108.9H11A—C11—H11C109.5
S1—C13—H13108.9H11B—C11—H11C109.5
C8i—C9—C8113.9 (2)
C7'—N1—N2—C30.7 (2)S2—C6—N7—C7'178.21 (11)
C8—N1—N2—C3176.34 (16)C6—N7—C7'—N1177.79 (16)
N1—N2—C3—C3'0.3 (2)C6—N7—C7'—C3'0.8 (2)
N2—C3—C3'—C7'0.2 (2)N2—N1—C7'—N7179.63 (15)
N2—C3—C3'—C4174.1 (2)C8—N1—C7'—N72.8 (3)
C7'—C3'—C4—N53.4 (2)N2—N1—C7'—C3'0.82 (19)
C3—C3'—C4—N5177.3 (2)C8—N1—C7'—C3'175.97 (15)
C7'—C3'—C4—S1174.67 (12)C4—C3'—C7'—N73.4 (2)
C3—C3'—C4—S10.8 (3)C3—C3'—C7'—N7179.39 (16)
C10—S1—C4—N512.30 (16)C4—C3'—C7'—N1175.37 (15)
C10—S1—C4—C3'165.77 (14)C3—C3'—C7'—N10.59 (18)
C3'—C4—N5—C61.0 (2)C7'—N1—C8—C9126.74 (18)
S1—C4—N5—C6177.00 (12)N2—N1—C8—C956.8 (2)
C4—N5—C6—N72.1 (3)N1—C8—C9—C8i49.76 (11)
C4—N5—C6—S2178.28 (12)C4—S1—C10—C1167.79 (19)
C13—S2—C6—N72.52 (16)C4—S1—C10—C12169.71 (15)
C13—S2—C6—N5177.16 (12)C6—S2—C13—C1571.75 (15)
N5—C6—N7—C7'2.2 (2)C6—S2—C13—C14165.75 (14)
Symmetry code: (i) x+1, y, z+1/2.

Experimental details

Crystal data
Chemical formulaC25H36N8S4
Mr576.90
Crystal system, space groupMonoclinic, C2/c
Temperature (K)293
a, b, c (Å)21.044 (2), 8.814 (1), 18.953 (2)
β (°) 118.07 (1)
V3)3101.9 (6)
Z4
Radiation typeMo Kα
µ (mm1)0.34
Crystal size (mm)0.30 × 0.28 × 0.20
Data collection
DiffractometerBruker P4
diffractometer
Absorption correction
No. of measured, independent and
observed [I > 2σ(I)] reflections
3403, 2738, 2352
Rint0.020
(sin θ/λ)max1)0.595
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.035, 0.094, 1.03
No. of reflections2738
No. of parameters173
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å3)0.22, 0.21

Computer programs: XSCANS (Siemens, 1996), XSCANS, SHELXTL (Bruker, 1997), SHELXTL.

 

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