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In the title compound [systematic name: 7-(2-de­oxy-β-D-erythro-pentofuranos­yl)-2-fluoro-7H-pyrrolo[2,3-d]pyrimidin-2-amine], C11H13FN4O3, the conformation of the N-glycosylic bond is between anti and high-anti [χ = −110.2 (3)°]. The 2′-deoxy­ribofuranosyl unit adopts the N-type sugar pucker (4T3), with P = 40.3° and τm = 39.2°. The orientation of the exocyclic C4′—C5′ bond is −ap (trans), with a torsion angle γ = −168.39 (18)°. The nucleobases are arranged head-to-head. The crystal structure is stabilized by four inter­molecular hydrogen bonds of types N—H...N, N—H...O and O—H...O.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270106053704/fa3053sup1.cif
Contains datablocks I, global

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270106053704/fa3053Isup2.hkl
Contains datablock I

CCDC reference: 638318

Comment top

Halogen-substituted analogues of nucleic acid components have become established as antiviral, antitumour and antifungal agents (Pankiewicz, 2000). An interesting family of this class of compounds is the haloadenine nucleosides, e.g. fludarabine, (Ia), cladribine (2-chloro-2'-deoxyadenosine), (IIa), clofarabine, (IIb), and 2'-deoxy-2-fluoroadenosine, (Ib) (Montgomery & Hewson, 1969; Montgomery, 1982; Bryson & Sorkin, 1993; Hassan et al., 2000). They are resistant to adenosine deaminase and effective in the treatment of indolent lymphoid malignancies, including chronic lymphocytic leukemia, hairy-cell leukemia, low-grade non-Hodgkin's lymphoma and acute myeloid leukaemia. Fludarabine and cladribine are used for the treatment of chronic lymphocytic leukaemia. However, the dose limitation of such drugs is imposed by cleavage resulting from rapid dephosphorylation, leading to a toxic 2-haloadenine with no anticancer activity (Struck et al., 1982). The introduction of fluorine at the 2'-position as in (IIb) confers resistance to phosphorolytic cleavage, which leads to lower toxicity (Montgomery et al., 1992).

As 7-deazapurine (pyrrolo[2,3-d]pyrimidine) nucleosides show resistance to the deamination caused by adenosine deaminase and cleavage by mammalian purine nucleoside phosphorylase, we became interested in 7-deaza-2-fluoroadenine nucleosides (purine numbering is used throughout the manuscript; IUPAC-IUB Joint Comission on Biochemical Nomenclature, 1983). Thus, 2'-deoxy-2-fluorotubercidin, (III), was prepared and its activity and base-pairing properties were studied (Peng et al., 2006). Similar to 2-haloadenine nucleosides (Montgomery & Hewson, 1970; Ramzaeva & Seela, 1994), (III) is a convertible nucleoside, allowing the attachment of functional groups to DNA for structural studies (Peng et al., 2006). The single-crystal X-ray analysis of compound (III) is described here.

The three-dimensional structure of (III) is shown in Fig. 1 and the selected geometric parameters are summarized in Table 1. The space group (P212121) is identical to that of the parent compound (IV) (Zabel et al., 1987) and the related compound (IIa) (Koellner et al., 1998).

The orientation of the base relative to the sugar (syn/anti) of purine nucleosides is defined by the torsion angle χ (O4'—C1'—N9—C4). For the `purine' 2'-deoxyribonucleosides, the preferred conformation around the N-glycosyl bond is usually in the anti range (Saenger, 1989; Sato, 1984). In the crystalline state of (III), the torsion angle of the glycosyl bond is between anti and high-anti with χ = -110.2 (3)°. This conformation is close to that of the parent compound 2'-deoxytubercidin, (IV) (χ = -104.4°; Zabel et al., 1987), but different from that of (IIa), which shows a syn conformation of the N-glycosylic bond [χ = 72.9 (3)°; Koellner et al., 1998)]. The glycosyl bond length (N9—C1') in (III) is 1.451 (3) Å, which is almost identical to those in (IV) [1.449 (2) Å] and (IIa) [1.458 (3) Å].

For (III), the phase angle of pseudorotation (P) is 40.3° and the maximum amplitude of puckering (τm) is 39.2°. This indicates that the sugar ring of (III) adopts an N conformation, with an unsymmetrical twist C3'-endo-C4'-exo (4T3) (Saenger, 1989). In the cases of (IV) and (IIa), the sugar ring conformation is S with P = 186.6 (2)° (3T2) for (IV) (Zabel et al., 1987) and 178.3° for (IIa) (Koellner et al., 1998). The conformation around the C4'—C5' bond of (III) is -ap (gauche, trans) with a torsion angle γ (C3'—C4'—C5'—O5') of -168.39 (18)°, whereas in (IV) and (IIa), the C4'—C5' bond shows a +ap (gauche, trans) conformation with γ = 179.6 (2)° for (IV) and 178.0 (2)° for (IIa).

The base moiety of compound (III) is essentially planar. The N3—C2 [1.305 (3) Å] and C2—N1 [1.315 (3) Å] bond lengths in (III) are shorter than those in (IV) (N3—C2 = 1.335 Å and C2—N1 = 1.333 Å). This might be caused by the strong electron-withdrawing effect of the 2-fluoro atom (pKa < 1.5) (Peng et al., 2006).

The structure of (III) is stabilized by hydrogen bonds leading to a three-dimensional network (Fig. 2 and Table 2). All four H atoms bonded to heteroatoms take part in the formation of the three-dimensional network (Table 2). The nucleobases are arranged head-to-head in a staircase-like fashion, in a pattern propagated by the a axis of the unit cell. Successive bases are nearly parallel with an interplanar spacing of approximately 3.894 Å, and are slipped in such a way that the C—F bond of the base at (x, y, z) projects on to the five-membered ring of the base at (1 + x, y, z). Thus, the average base pair distance is in the range of that of B-DNA (3.5 Å).

Related literature top

For related literature, see: Bryson & Sorkin (1993); Flack (1983); Flack & Bernardinelli (2000); Hassan et al. (2000); IUPAC-IUB (1983); Koellner et al. (1998); Montgomery (1982); Montgomery & Hewson (1969, 1970); Montgomery et al. (1992); Pankiewicz (2000); Peng et al. (2006); Ramzaeva & Seela (1994); Saenger (1989); Sato (1984); Struck et al. (1982); Zabel et al. (1987).

Experimental top

Compound (III) was synthesized as described by Peng et al. (2006) and crystallized from MeOH (m.p. 476 K). For the diffraction experiment, a single-crystal was fixed at the top of a Lindemann capillary with epoxy resin.

Refinement top

In the absence of suitable anomalous scattering, Friedel equivalents could not be used to determine the absolute structure. Refinement of the Flack (1983) parameter led to an inconclusive value (Flack & Bernardinelli, 2000) [0.1 (13)]. Therefore, Friedel equivalents (440) were merged before the final refinement. The known configuration of the parent molecule was used to define the enantiomer employed in the refined model. All H atoms were found in a difference Fourier synthesis. In order to maximize the data/parameter ratio, H atoms were placed in geometrically idealized positions [C—H = 0.93–0.98 Å and N—H 0.86 Å (AFIX 93)] and constrained to ride on their parent atoms [Uiso(H) = 1.2Ueq(C,N)]. The OH groups were refined as rigid groups allowed to rotate but not tip [AFIX 147; O—H = 0.82 Å and Uiso(H) = 1.5Ueq(O)].

Computing details top

Data collection: XSCANS (Siemens, 1996); cell refinement: XSCANS; data reduction: SHELXTL (Sheldrick, 1997); program(s) used to solve structure: SHELXTL; program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL and PLATON (Spek, 1999).

Figures top
[Figure 1]
[Figure 2]
Fig. 1.

Perspective view of (III), showing the atomic numbering. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as spheres of arbitrary size.

Fig. 2.

Packing of (III), showing the intermolecular hydrogen-bonding network (projection parallel to the a axis).
7-(2-deoxy-β-D-erythro-pentofuranosyl)- 2-fluoro-7H-pyrrolo[2,3-d]pyrimidin-2-amine top
Crystal data top
C11H13FN4O3F(000) = 560
Mr = 268.25Dx = 1.490 Mg m3
Orthorhombic, P212121Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2ac 2abCell parameters from 50 reflections
a = 5.5515 (8) Åθ = 2.4–14.9°
b = 12.6547 (12) ŵ = 0.12 mm1
c = 17.0171 (19) ÅT = 293 K
V = 1195.5 (2) Å3Plate, colourless
Z = 40.5 × 0.3 × 0.3 mm
Data collection top
Bruker P4
diffractometer
Rint = 0.032
Radiation source: fine-focus sealed tubeθmax = 29.0°, θmin = 2.4°
Graphite monochromatorh = 17
2θ/ω scansk = 171
2481 measured reflectionsl = 231
1846 independent reflections3 standard reflections every 97 reflections
1586 reflections with I > 2σ(I) intensity decay: none
Refinement top
Refinement on F2Hydrogen site location: inferred from neighbouring sites
Least-squares matrix: fullH-atom parameters constrained
R[F2 > 2σ(F2)] = 0.042 w = 1/[σ2(Fo2) + (0.061P)2 + 0.1652P]
where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.115(Δ/σ)max < 0.001
S = 1.04Δρmax = 0.18 e Å3
1846 reflectionsΔρmin = 0.22 e Å3
175 parametersExtinction correction: SHELXL97, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
0 restraintsExtinction coefficient: 0.016 (3)
Primary atom site location: structure-invariant direct methodsAbsolute structure: established on the basis of the previously known absolute configuration of the molecule
Secondary atom site location: difference Fourier map
Crystal data top
C11H13FN4O3V = 1195.5 (2) Å3
Mr = 268.25Z = 4
Orthorhombic, P212121Mo Kα radiation
a = 5.5515 (8) ŵ = 0.12 mm1
b = 12.6547 (12) ÅT = 293 K
c = 17.0171 (19) Å0.5 × 0.3 × 0.3 mm
Data collection top
Bruker P4
diffractometer
Rint = 0.032
2481 measured reflections3 standard reflections every 97 reflections
1846 independent reflections intensity decay: none
1586 reflections with I > 2σ(I)
Refinement top
R[F2 > 2σ(F2)] = 0.0420 restraints
wR(F2) = 0.115H-atom parameters constrained
S = 1.04Δρmax = 0.18 e Å3
1846 reflectionsΔρmin = 0.22 e Å3
175 parametersAbsolute structure: established on the basis of the previously known absolute configuration of the molecule
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*/Ueq
N11.0271 (5)0.89211 (15)0.74187 (12)0.0476 (5)
C21.0734 (6)0.7907 (2)0.74930 (16)0.0492 (7)
F21.2514 (4)0.76934 (13)0.80207 (12)0.0803 (8)
N30.9844 (5)0.70558 (14)0.71709 (11)0.0443 (5)
C40.8137 (5)0.73341 (16)0.66410 (12)0.0366 (5)
C50.7403 (5)0.83631 (16)0.64632 (12)0.0370 (5)
C60.8525 (5)0.91714 (16)0.69033 (13)0.0367 (5)
N60.7931 (5)1.01961 (14)0.68420 (12)0.0439 (5)
H6A0.86581.06600.71260.053*
H6B0.68241.03890.65190.053*
C70.5593 (5)0.82845 (19)0.58714 (14)0.0446 (6)
H70.47860.88420.56320.054*
C80.5273 (6)0.72416 (19)0.57248 (15)0.0482 (6)
H80.41830.69640.53650.058*
N90.6824 (4)0.66466 (14)0.61944 (11)0.0411 (5)
C1'0.6930 (5)0.55026 (16)0.62439 (13)0.0383 (5)
H1'0.79020.53000.67000.046*
C2'0.4482 (5)0.49669 (18)0.62964 (15)0.0455 (6)
H2'10.32160.54830.63820.055*
H2'20.44520.44560.67210.055*
C3'0.4173 (4)0.44234 (16)0.55042 (14)0.0375 (5)
H3'10.34360.49060.51230.045*
O3'0.2834 (3)0.34664 (13)0.55535 (13)0.0523 (5)
H3'0.17550.34720.52240.078*
C4'0.6772 (4)0.41982 (15)0.52841 (13)0.0327 (4)
H4'0.73390.35800.55780.039*
C5'0.7188 (5)0.40208 (18)0.44208 (13)0.0412 (5)
H5'10.59890.35310.42230.049*
H5'20.69890.46850.41430.049*
O5'0.9538 (4)0.36091 (14)0.42630 (11)0.0505 (5)
H5'0.94330.29830.41450.076*
O4'0.8063 (3)0.51118 (12)0.55392 (9)0.0413 (4)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
N10.0639 (14)0.0319 (9)0.0471 (10)0.0044 (10)0.0149 (11)0.0046 (8)
C20.0607 (17)0.0374 (11)0.0494 (12)0.0018 (13)0.0207 (13)0.0009 (10)
F20.1040 (19)0.0452 (8)0.0916 (13)0.0015 (10)0.0657 (13)0.0053 (9)
N30.0566 (13)0.0302 (8)0.0461 (10)0.0021 (9)0.0173 (10)0.0021 (8)
C40.0443 (12)0.0295 (9)0.0361 (9)0.0013 (10)0.0053 (10)0.0036 (8)
C50.0473 (13)0.0302 (9)0.0334 (9)0.0031 (10)0.0021 (9)0.0011 (8)
C60.0459 (12)0.0294 (9)0.0348 (9)0.0009 (10)0.0044 (10)0.0005 (8)
N60.0608 (13)0.0270 (8)0.0439 (9)0.0016 (10)0.0026 (11)0.0015 (8)
C70.0517 (14)0.0362 (10)0.0459 (11)0.0076 (11)0.0104 (12)0.0001 (10)
C80.0555 (15)0.0407 (11)0.0482 (12)0.0060 (12)0.0192 (12)0.0034 (10)
N90.0511 (11)0.0298 (8)0.0424 (9)0.0033 (9)0.0135 (10)0.0056 (7)
C1'0.0466 (12)0.0290 (9)0.0392 (10)0.0002 (10)0.0046 (11)0.0042 (9)
C2'0.0472 (13)0.0379 (11)0.0515 (12)0.0012 (11)0.0085 (12)0.0060 (10)
C3'0.0320 (10)0.0273 (9)0.0531 (12)0.0001 (9)0.0013 (10)0.0030 (9)
O3'0.0376 (8)0.0371 (8)0.0822 (13)0.0086 (8)0.0049 (10)0.0034 (9)
C4'0.0329 (10)0.0249 (8)0.0402 (10)0.0017 (9)0.0028 (9)0.0023 (8)
C5'0.0466 (12)0.0360 (10)0.0409 (10)0.0035 (10)0.0045 (11)0.0046 (9)
O5'0.0496 (10)0.0466 (9)0.0554 (10)0.0006 (9)0.0122 (9)0.0146 (8)
O4'0.0384 (8)0.0374 (8)0.0481 (8)0.0083 (7)0.0033 (8)0.0127 (7)
Geometric parameters (Å, º) top
N1—C21.315 (3)C1'—O4'1.442 (3)
N1—C61.345 (3)C1'—C2'1.521 (4)
C2—N31.305 (3)C1'—H1'0.9800
C2—F21.362 (3)C2'—C3'1.523 (3)
N3—C41.355 (3)C2'—H2'10.9700
C4—N91.366 (3)C2'—H2'20.9700
C4—C51.398 (3)C3'—O3'1.424 (3)
C5—C61.413 (3)C3'—C4'1.517 (3)
C5—C71.426 (3)C3'—H3'10.9800
C6—N61.342 (3)O3'—H3'0.8200
N6—H6A0.8600C4'—O4'1.428 (2)
N6—H6B0.8600C4'—C5'1.504 (3)
C7—C81.355 (3)C4'—H4'0.9800
C7—H70.9300C5'—O5'1.430 (3)
C8—N91.395 (3)C5'—H5'10.9700
C8—H80.9300C5'—H5'20.9700
N9—C1'1.451 (3)O5'—H5'0.8200
C2—N1—C6115.7 (2)N9—C1'—H1'109.2
N3—C2—N1133.7 (3)C2'—C1'—H1'109.2
N3—C2—F2112.8 (2)C1'—C2'—C3'104.5 (2)
N1—C2—F2113.5 (2)C1'—C2'—H2'1110.9
C2—N3—C4109.25 (19)C3'—C2'—H2'1110.9
N3—C4—N9125.3 (2)C1'—C2'—H2'2110.9
N3—C4—C5126.2 (2)C3'—C2'—H2'2110.9
N9—C4—C5108.5 (2)H2'1—C2'—H2'2108.9
C4—C5—C6115.5 (2)O3'—C3'—C4'110.56 (17)
C4—C5—C7107.06 (19)O3'—C3'—C2'113.0 (2)
C6—C5—C7137.4 (2)C4'—C3'—C2'101.32 (18)
N6—C6—N1117.1 (2)O3'—C3'—H3'1110.5
N6—C6—C5123.4 (2)C4'—C3'—H3'1110.5
N1—C6—C5119.5 (2)C2'—C3'—H3'1110.5
C6—N6—H6A120.0C3'—O3'—H3'109.5
C6—N6—H6B120.0O4'—C4'—C5'109.93 (18)
H6A—N6—H6B120.0O4'—C4'—C3'104.48 (16)
C8—C7—C5106.9 (2)C5'—C4'—C3'114.5 (2)
C8—C7—H7126.6O4'—C4'—H4'109.2
C5—C7—H7126.6C5'—C4'—H4'109.2
C7—C8—N9109.8 (2)C3'—C4'—H4'109.2
C7—C8—H8125.1O5'—C5'—C4'112.21 (19)
N9—C8—H8125.1O5'—C5'—H5'1109.2
C4—N9—C8107.72 (18)C4'—C5'—H5'1109.2
C4—N9—C1'125.5 (2)O5'—C5'—H5'2109.2
C8—N9—C1'126.6 (2)C4'—C5'—H5'2109.2
O4'—C1'—N9108.15 (19)H5'1—C5'—H5'2107.9
O4'—C1'—C2'106.60 (18)C5'—O5'—H5'109.5
N9—C1'—C2'114.3 (2)C4'—O4'—C1'108.16 (17)
O4'—C1'—H1'109.2
C6—N1—C2—N30.4 (5)C5—C4—N9—C1'175.6 (2)
C6—N1—C2—F2180.0 (2)C7—C8—N9—C40.1 (3)
N1—C2—N3—C41.9 (5)C7—C8—N9—C1'176.1 (3)
F2—C2—N3—C4178.4 (2)C4—N9—C1'—O4'110.2 (3)
C2—N3—C4—N9179.8 (3)C8—N9—C1'—O4'74.2 (3)
C2—N3—C4—C50.5 (4)C4—N9—C1'—C2'131.2 (3)
N3—C4—C5—C62.0 (4)C8—N9—C1'—C2'44.4 (4)
N9—C4—C5—C6177.4 (2)O4'—C1'—C2'—C3'10.1 (2)
N3—C4—C5—C7179.5 (3)N9—C1'—C2'—C3'109.3 (2)
N9—C4—C5—C71.1 (3)C1'—C2'—C3'—O3'147.47 (19)
C2—N1—C6—N6176.9 (3)C1'—C2'—C3'—C4'29.2 (2)
C2—N1—C6—C52.6 (4)O3'—C3'—C4'—O4'158.81 (18)
C4—C5—C6—N6175.9 (2)C2'—C3'—C4'—O4'38.8 (2)
C7—C5—C6—N62.0 (5)O3'—C3'—C4'—C5'80.9 (2)
C4—C5—C6—N13.6 (3)C2'—C3'—C4'—C5'159.07 (18)
C7—C5—C6—N1178.6 (3)O4'—C4'—C5'—O5'74.4 (2)
C4—C5—C7—C81.0 (3)C3'—C4'—C5'—O5'168.39 (18)
C6—C5—C7—C8177.0 (3)C5'—C4'—O4'—C1'157.37 (18)
C5—C7—C8—N90.5 (3)C3'—C4'—O4'—C1'34.0 (2)
N3—C4—N9—C8179.9 (3)N9—C1'—O4'—C4'138.2 (2)
C5—C4—N9—C80.7 (3)C2'—C1'—O4'—C4'14.8 (2)
N3—C4—N9—C1'3.8 (5)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N6—H6A···N3i0.862.293.144 (3)172
N6—H6B···O5ii0.862.233.061 (3)162
O3—H3···O5iii0.822.052.864 (3)169
O5—H5···O3iv0.822.102.809 (3)145
Symmetry codes: (i) x+2, y+1/2, z+3/2; (ii) x1/2, y+3/2, z+1; (iii) x1, y, z; (iv) x+1/2, y+1/2, z+1.

Experimental details

Crystal data
Chemical formulaC11H13FN4O3
Mr268.25
Crystal system, space groupOrthorhombic, P212121
Temperature (K)293
a, b, c (Å)5.5515 (8), 12.6547 (12), 17.0171 (19)
V3)1195.5 (2)
Z4
Radiation typeMo Kα
µ (mm1)0.12
Crystal size (mm)0.5 × 0.3 × 0.3
Data collection
DiffractometerBruker P4
diffractometer
Absorption correction
No. of measured, independent and
observed [I > 2σ(I)] reflections
2481, 1846, 1586
Rint0.032
(sin θ/λ)max1)0.682
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.042, 0.115, 1.04
No. of reflections1846
No. of parameters175
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å3)0.18, 0.22
Absolute structureEstablished on the basis of the previously known absolute configuration of the molecule

Computer programs: XSCANS (Siemens, 1996), XSCANS, SHELXTL (Sheldrick, 1997), SHELXTL and PLATON (Spek, 1999).

Selected geometric parameters (Å, º) top
N1—C21.315 (3)C2—F21.362 (3)
N1—C61.345 (3)N3—C41.355 (3)
C2—N31.305 (3)N9—C1'1.451 (3)
N3—C2—F2112.8 (2)N6—C6—C5123.4 (2)
N1—C2—F2113.5 (2)C4—N9—C1'125.5 (2)
N6—C6—N1117.1 (2)C8—N9—C1'126.6 (2)
C6—N1—C2—F2180.0 (2)O3'—C3'—C4'—C5'80.9 (2)
F2—C2—N3—C4178.4 (2)O4'—C4'—C5'—O5'74.4 (2)
C4—N9—C1'—O4'110.2 (3)C3'—C4'—C5'—O5'168.39 (18)
C8—N9—C1'—O4'74.2 (3)C5'—C4'—O4'—C1'157.37 (18)
C1'—C2'—C3'—C4'29.2 (2)C3'—C4'—O4'—C1'34.0 (2)
C2'—C3'—C4'—O4'38.8 (2)C2'—C1'—O4'—C4'14.8 (2)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N6—H6A···N3i0.862.293.144 (3)171.7
N6—H6B···O5'ii0.862.233.061 (3)161.5
O3'—H3'···O5'iii0.822.052.864 (3)169.2
O5'—H5'···O3'iv0.822.102.809 (3)144.5
Symmetry codes: (i) x+2, y+1/2, z+3/2; (ii) x1/2, y+3/2, z+1; (iii) x1, y, z; (iv) x+1/2, y+1/2, z+1.
 

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