1,7-Dideaza-2′-deoxy-6-nitro­nebularine: a pyrrolo­[2,3-b]pyridine nucleoside with an intra­molecular hydrogen bond stabilizing the syn conformation

The title compound [systematic name: 1-(2-de­oxy-β-D-erythro-pento­furanos­yl)-4-nitro-1H-pyrrolo­[2,3-b]pyridine], C₁₂H₁₃N₃O₅, forms an intra­molecular hydrogen bond between the pyridine N atom as acceptor and the 5′-hy­droxy group of the sugar residue as donor. Consequently, the N-glycosylic bond exhibits a syn conformation, with a χ torsion angle of 61.6 (2)°, and the pento­furanosyl residue adopts a C2′-endo envelope conformation (²E, S-type), with P = 162.1 (1)° and τ_m = 36.2 (1)°. The orientation of the exocyclic C4′—C5′ bond is +sc (gauche, gauche), with a torsion angle γ = 49.1 (2)°. The title nucleoside forms an ordered and stacked three-dimensional network. The pyrrole ring of one layer faces the pyridine ring of an adjacent layer. Additionally, inter­molecular O—H...O and C—H...O hydrogen bonds stabilize the crystal structure.

S1. Experimental

Crystal data, data collection and structure refinement details are summarized in Table 1.

S1.1. Synthesis and crystallization

Compound (I) was synthesized according to the method of Seela & Gumbiowski (1989). Slow crystallization from propan-2-ol afforded (I) as yellow needles (m.p. 428 K). For the diffraction experiment, a single crystal was mounted on a MiTeGen Micro-Mounts fibre in a thin smear of oil.

S1.2. Refinement

The known configuration of the parent molecule was used to define the enanti­omer employed in the refined model. 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 [0.0 (6)]. Further confirmation of the configuration was sought by the Hooft analysis. The absolute structure parameter y (Hooft et al., 2008) was calculated using PLATON (Spek, 2009). The resulting Hooft anaysis parameters were P2(true) = P3(true) = 1.000, P3(false) = 0.3 × 10^-16, P3(rac-twin) = 0.3 × 10^-4 and y = -0.05 (12), calculated for 1470 Bijvoet pairs (100% coverage), indicating that the known absolute configuration used for analysis is correct. All H atoms were found in a difference Fourier synthesis. In order to maximize the data/parameter ratio, the H atoms were placed in geometrically idealized positions, with C—H = 0.95–1.00 Å, and constrained to ride on their parent atoms, with U_iso(H) = 1.2U_eq(C) = U_eq(N) [No N-bound H atoms present?]. The hy­droxy groups were refined as groups allowed to rotate but not tip, with O—H = 0.84 Å and U_iso(H) = 1.5U_eq(O).

S2. Comment

A broad variety of base-modified nucleoside shape mimics show anti­biotic, anti­viral or cytostatic activity (Suhadolnik, 1970, 1979; Simons, 2001). As components of DNA and RNA, these nucleosides are useful tools for studying base-pair recognition or protein binding, and they find application as oligonucleotide therapeutics (Agrawal, 1996; Broderick & Zamore, 2011; Herdewijn, 2008). Nucleosides carrying nitro groups, such as 5-nitro­indole, 3-iodo-5-nitro­indole or 3-nitro­pyrrole 2'-de­oxy­ribonucleosides, can act as universal nucleosides, which base-pair equally well with all four canonical DNA constituents (Loakes & Brown, 1994; Loakes, 2001; Harki et al., 2007; Leonard et al., 2005).

1,7-Dide­aza­purine (pyrrolo­[2,3-b]pyridine) nucleosides represent a rather unexplored class of purine nucleosides that display a reduced number of hydrogen-bond acceptor sites (N1 and N7 are replaced by CH) (purine numbering is used throughout this article) (Revankar & Robins, 1991). Thus, base-pair recognition is altered, and inter­actions between the sugar residue and the nucleobase are affected.

Early attempts at furnishing 1,7-dide­aza­purine nucleosides by conventional glycosyl­ation protocols encountered difficulties due to insufficient regio- and stereoselectivity (Antonini et al., 1982; Cristalli et al., 1993). Therefore, nucleobase anion glycosyl­ation was applied to circumvent these problems (Seela et al., 1988). The title compound, (I), was synthesized from a protected halogenose and 6-nitro-1,7-dide­aza­purine, followed by sugar deprotection (Seela & Gumbiowski, 1989). Crystallization from propan-2-ol afforded (I) as yellow needles.

As the conformational parameters of (I) are unknown, a single-crystal X-ray analysis was performed and the results are reported herein. The three-dimensional structure of (I) is shown in Fig. 1 and selected geometric parameters are summarized in Table 1. The conformational and molecular dimensions of (I) are compared with those of the closely related structures of the two crystal forms of 1-de­aza-2'-de­oxy­adenosine, (II) [plates, denoted (IIa), and needles, denoted (IIb); Seela et al., 1999], 1-de­aza­adenosine, (III), and 4-nitro­indazole 2'-de­oxy­ribonucleoside, (IV) (Seela et al., 2004).

All four nucleosides, (I), (IIa), (IIb), (III) and (IV), crystallize in the same space group (orthorhombic, P2₁2₁2₁) (Seela et al., 1999, 2004).

The orientation of the nucleobase relative to the sugar residue (syn–anti) is defined by the torsion angle χ (O4'—C1'—N9—C4) (IUPAC–IUB Joint Commission on Biochemical Nomenclature, 1983). For natural purine 2'-de­oxy­ribonucleosides, the preferred conformation around the N-glycosidic bond is anti. However, (I), with the non-natural 1,7-dide­aza­purine fragment as a nucleobase mimic, adopts a syn conformation with a torsion angle χ = 61.6 (2)°. This conformation is stabilized by an intra­molecular hydrogen bond between the O5'—H5O group of the sugar residue as donor and atom N3 of the heterocyclic ring as acceptor [O5'(—H5O)···N3 = 2.787 (2) Å and O5'—H5O···N3) = 170°; Table 2]. Most inter­estingly, similar findings were made for the related ribonucleoside, (III), employing a 1-de­aza­purine fragment as nucleobase (Seela et al., 1999). This compound also shows a syn conformation around the glycosylic bond [χ = 56.1 (3)°], which is constrained by an intra­molecular hydrogen bond with the O5'—H5O group as donor and atom N3 as acceptor. In contrast, the related crystal structures of (IIa), (IIb) and (IV) lack intra­molecular hydrogen bonds and show anti conformations around the glycosylic bond. For the crystals structures of (IIb) and (IV), torsion angles χ = -116.5 (3)° and χ = -105.3 (2)°, respectively, were observed (Seela et al., 1999, 2004), while the torsion angle for (IIa) is shifted towards the high-anti range [χ = -90.7 (4)°; Seela et al., 1999].

The length of the glycosylic N9—C1' bond is within the same range for all four crystal structures, viz. 1.453 (2) Å for (I), 1.441 (4) Å for (IIa), 1.465 (4) Å for (IIb), 1.453 (3) Å for (III) (Seela et al., 1999) and 1.449 (2) Å for (IV) (Seela et al., 2004).

The 2'-de­oxy­ribose ring of (I) shows an S-type conformation, with a pseudorotation phase angle P = 162.1 (1)° and a maximum puckering amplitude τ_m = 36.2 (1)° (Cremer & Pople, 1975), referring to a major C2'-endo envelope conformation (²E). A very similar ²E conformation was also observed for 1-de­aza­adenosine (III), with P = 167.5° and τ_m = 37.6° (Seela et al., 1999). Moreover, the crystal structures of (IIa) and (IV) exhibit S conformations, with P = 179.8° and τ_m = 36.4° (C2'-endo-C3'-exo, ²T₃; Seela et al., 1999) for (IIa), and P = 192.6° and τ_m = 37.5° (C3'-exo-C2'-endo, ₃T²; Seela et al., 2004) for (IV), while in (IIb) an N-type sugar pucker was found, with P = 21.2° and τ_m = 33.6° (C3'-endo-C4'-exo, ³T₄; Seela et al., 1999).

The γ torsion angle (O5'—C5'—C4'—C3') characterizes the orientation of the exocyclic 5'-hy­droxy group relative to the sugar ring. The C4'—C5' bond conformation of (I) is synclinal (+sc; gauche, gauche), with a torsion angle γ = 49.1 (2)°. Again, ribonucleoside (III) displays a similar +sc conformation around the C5'—C4' bond [γ = 46.6 (4)°], as does (IIb), with γ = 46.8 (4)° (Seela et al., 1999). In contrast, nucleoside (IIa) adopts an anti­periplanar (ap; gauche, trans) conformation, with a torsion angle γ = 177.9 (3)°, while it is -sc (trans, gauche) in the case of (IV) (Seela et al., 2004).

The 1,7-dide­aza­purine ring of (I) is almost planar. The deviations of the ring atoms (N1/C2–C6/N7/C8/C9) from the least-squares plane range from -0.028 (1) Å for atom C1 to 0.028 (1) Å for atom N3, with an r.m.s. deviation of 0.0173 Å. The C1' substituent and atom N6 of the nitro group lie on the same side of the plane of the heterocycle [at 0.011 (2) and 0.038 (2) Å, respectively].

Nucleoside (I) forms a highly ordered three-dimensional network. The nucleobases and sugar residues are both stacked (the nucleobases parallel to the bc plane and the sugar residues parallel to the ac plane), forming alternating nucleobase and sugar columns (Fig. 2). The nucleobases are ordered in a reverse head-to-tail orientation. Consequently, the electron-deficient 6-nitro­pyridine ring of the heterocyclic ring of one layer faces the electron-rich pyrrole ring of another nucleobase of an adjacent layer.

The extended crystal structure of (I) is further stabilized by inter­molecular hydrogen bonds between the sugar residues and the heterocyclic ring (Table 2). A strong hydrogen bond is formed between the 3'-hy­droxy group as donor and atom O5' of a neighbouring molecule as acceptor (O3'—H3O···O5'ⁱ; see Table 2 for symmetry codes and geometry). An additional weak hydrogen bond (Steiner, 2002) is formed between the C2—H2 group of the nucleobase as donor and atom O3' of the sugar residue as acceptor (C2—H2···O3'ⁱⁱ; Table 2).

Both (I) and ribonucleoside (III) belong to the class of nucleoside crystal structures which show a constrained syn orientation of the nucleobase about the glycosylic bond due to the formation of an intra­molecular O5'—H5O···N3 hydrogen bond. The majority of nucleosides belonging to this class adopt close conformational similarities, including an S conformation of the sugar residue, a +sc conformation of the C4'—C5' bond and a syn conformation around the N-glycosylic bond in the range χ = 50–90° (Seela et al., 1998).

Related literature

For related literature, see: Agrawal (1996); Antonini et al. (1982); Broderick & Zamore (2011); Cremer & Pople (1975); Cristalli et al. (1993); Flack (1983); Harki et al. (2007); Herdewijn (2008); Hooft et al. (2008); IUPAC–IUB (1983); Leonard et al. (2005); Loakes (2001); Loakes & Brown (1994); Revankar & Robins (1991); Seela & Gumbiowski (1989); Seela et al. (1988, 1998, 1999, 2004); Simons (2001); Spek (2009); Steiner (2002); Suhadolnik (1970, 1979).

Computing details

Data collection: APEX2 (Bruker, 2008); cell refinement: SAINT (Bruker, 2008); data reduction: SAINT (Bruker, 2008); program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008) and DIAMOND (Brandenburg, 2004); software used to prepare material for publication: SHELXTL (Sheldrick, 2008) and PLATON (Spek, 2009).

Figures

	Fig. 1. A perspective view of (I), showing the intramolecular hydrogen bond (dashed line) and the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level.
	Fig. 2. The crystal packing of (I), showing the highly ordered arrangement of nucleosides (parallel to the ac plane). Hydrogen bonds are shown as dashed lines. For the sake of clarity, H atoms not involved in the intermolecular hydrogen-bonding motifs have been omitted.

1-(2-Deoxy-β-D-erythro-pentofuranosyl)-4-nitro-1H-pyrrolo[2,3-b]pyridine

Crystal data

C12H13N3O5	F(000) = 584
Mr = 279.25	Dx = 1.546 Mg m^−3
Orthorhombic, P212121	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2ac 2ab	Cell parameters from 9767 reflections
a = 6.4621 (4) Å	θ = 2.4–30.6°
b = 9.1450 (5) Å	µ = 0.12 mm^−1
c = 20.2969 (12) Å	T = 130 K
V = 1199.46 (12) Å^3	Needle, yellow
Z = 4	0.33 × 0.22 × 0.08 mm

Data collection

Bruker APEXII CCD area-detector diffractometer	2024 independent reflections
Radiation source: fine-focus sealed tube	1957 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.027
ϕ and ω scans	θmax = 30.0°, θmin = 3.3°
Absorption correction: multi-scan (SADABS; Bruker, 2008)	h = −9→9
Tmin = 0.961, Tmax = 0.990	k = −12→12
56551 measured reflections	l = −28→28

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.029	H-atom parameters constrained
wR(F^2) = 0.084	w = 1/[σ^2(Fo^2) + (0.0528P)^2 + 0.2211P] where P = (Fo^2 + 2Fc^2)/3
S = 1.09	(Δ/σ)max = 0.001
2024 reflections	Δρmax = 0.38 e Å^−3
183 parameters	Δρmin = −0.20 e Å^−3
0 restraints	Absolute structure: established by known chemical absolute configuration
Primary atom site location: structure-invariant direct methods

Special details

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 (Ų)

	x	y	z	Uiso*/Ueq
C1	0.1898 (2)	0.82918 (14)	0.92896 (6)	0.0182 (2)
H1	0.1909	0.9327	0.9248	0.022*
C2	0.1967 (2)	0.74012 (14)	0.87329 (6)	0.0179 (2)
H2	0.2057	0.7860	0.8314	0.021*
N3	0.19142 (19)	0.59404 (12)	0.87528 (5)	0.0167 (2)
C4	0.1749 (2)	0.53544 (13)	0.93510 (6)	0.0148 (2)
C5	0.1725 (2)	0.61178 (14)	0.99647 (6)	0.0157 (2)
C6	0.1813 (2)	0.76390 (14)	0.99025 (6)	0.0165 (2)
N6	0.1839 (2)	0.85863 (13)	1.04865 (6)	0.0201 (2)
O61	0.1756 (2)	0.99127 (12)	1.04056 (6)	0.0292 (3)
O62	0.1965 (2)	0.79876 (13)	1.10279 (5)	0.0300 (3)
C7	0.1577 (2)	0.50434 (14)	1.04702 (6)	0.0195 (3)
H7	0.1541	0.5214	1.0932	0.023*
C8	0.1497 (2)	0.37154 (15)	1.01597 (6)	0.0198 (3)
H8	0.1390	0.2801	1.0379	0.024*
N9	0.15943 (19)	0.38846 (11)	0.94840 (5)	0.0169 (2)
C1'	0.1640 (2)	0.26882 (13)	0.90133 (6)	0.0174 (2)
H1'	0.1507	0.1743	0.9257	0.021*
C2'	0.0016 (2)	0.27333 (15)	0.84673 (7)	0.0185 (2)
H2A	−0.0272	0.3749	0.8325	0.022*
H2B	−0.1292	0.2263	0.8608	0.022*
C3'	0.1084 (2)	0.18579 (14)	0.79239 (6)	0.0187 (2)
H3'	0.0582	0.2153	0.7477	0.022*
O3'	0.0868 (2)	0.03239 (11)	0.80260 (5)	0.0265 (2)
H3O	−0.0314	0.0056	0.7902	0.040*
C4'	0.3379 (2)	0.22328 (14)	0.80175 (6)	0.0187 (2)
H4'	0.4221	0.1326	0.7955	0.022*
O4'	0.35938 (16)	0.27241 (11)	0.86920 (4)	0.0192 (2)
C5'	0.4192 (2)	0.34119 (16)	0.75620 (6)	0.0222 (3)
H5A	0.5598	0.3696	0.7707	0.027*
H5B	0.4307	0.3006	0.7111	0.027*
O5'	0.29165 (18)	0.46863 (11)	0.75426 (5)	0.0226 (2)
H5O	0.2734	0.4999	0.7927	0.034*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0181 (6)	0.0133 (5)	0.0233 (6)	−0.0001 (5)	−0.0002 (5)	0.0005 (4)
C2	0.0202 (6)	0.0148 (5)	0.0187 (5)	−0.0001 (5)	−0.0001 (5)	0.0026 (4)
N3	0.0190 (5)	0.0140 (4)	0.0170 (4)	0.0001 (4)	0.0011 (4)	0.0013 (4)
C4	0.0155 (5)	0.0130 (5)	0.0161 (5)	0.0006 (4)	0.0007 (5)	0.0001 (4)
C5	0.0155 (5)	0.0162 (5)	0.0152 (5)	0.0007 (5)	0.0007 (5)	−0.0008 (4)
C6	0.0141 (5)	0.0159 (5)	0.0196 (6)	0.0007 (5)	0.0001 (5)	−0.0043 (4)
N6	0.0172 (5)	0.0197 (5)	0.0233 (5)	−0.0005 (4)	0.0016 (5)	−0.0066 (4)
O61	0.0330 (6)	0.0184 (5)	0.0361 (6)	0.0015 (5)	0.0011 (5)	−0.0083 (4)
O62	0.0402 (7)	0.0297 (6)	0.0200 (4)	−0.0024 (5)	0.0018 (5)	−0.0043 (4)
C7	0.0242 (6)	0.0193 (6)	0.0150 (5)	0.0011 (5)	0.0011 (5)	0.0015 (4)
C8	0.0255 (6)	0.0175 (5)	0.0163 (5)	0.0017 (5)	0.0009 (5)	0.0041 (4)
N9	0.0233 (5)	0.0120 (4)	0.0153 (4)	0.0009 (4)	0.0014 (4)	0.0010 (3)
C1'	0.0229 (6)	0.0126 (5)	0.0169 (5)	0.0005 (5)	0.0000 (5)	−0.0003 (4)
C2'	0.0182 (5)	0.0165 (5)	0.0208 (5)	−0.0015 (5)	−0.0010 (5)	0.0001 (5)
C3'	0.0246 (6)	0.0135 (5)	0.0180 (5)	0.0007 (5)	−0.0045 (5)	−0.0002 (4)
O3'	0.0375 (6)	0.0126 (4)	0.0292 (5)	−0.0020 (4)	−0.0096 (5)	−0.0001 (4)
C4'	0.0222 (6)	0.0171 (5)	0.0168 (5)	0.0039 (5)	−0.0014 (5)	−0.0028 (4)
O4'	0.0192 (4)	0.0220 (4)	0.0165 (4)	0.0037 (4)	−0.0022 (3)	−0.0026 (3)
C5'	0.0223 (6)	0.0245 (6)	0.0198 (5)	0.0020 (5)	0.0038 (5)	−0.0009 (5)
O5'	0.0295 (5)	0.0199 (4)	0.0185 (4)	0.0007 (4)	0.0030 (4)	0.0012 (3)

Geometric parameters (Å, º)

C1—C6	1.3810 (17)	C1'—O4'	1.4215 (17)
C1—C2	1.3935 (18)	C1'—C2'	1.5269 (18)
C1—H1	0.9500	C1'—H1'	1.0000
C2—N3	1.3370 (16)	C2'—C3'	1.5278 (19)
C2—H2	0.9500	C2'—H2A	0.9900
N3—C4	1.3316 (15)	C2'—H2B	0.9900
C4—N9	1.3746 (15)	C3'—O3'	1.4250 (16)
C4—C5	1.4279 (16)	C3'—C4'	1.534 (2)
C5—C6	1.3981 (17)	C3'—H3'	1.0000
C5—C7	1.4237 (17)	O3'—H3O	0.8400
C6—N6	1.4683 (16)	C4'—O4'	1.4477 (15)
N6—O61	1.2252 (16)	C4'—C5'	1.5143 (19)
N6—O62	1.2304 (16)	C4'—H4'	1.0000
C7—C8	1.3692 (18)	C5'—O5'	1.4278 (17)
C7—H7	0.9500	C5'—H5A	0.9900
C8—N9	1.3815 (15)	C5'—H5B	0.9900
C8—H8	0.9500	O5'—H5O	0.8400
N9—C1'	1.4528 (16)
C6—C1—C2	118.62 (11)	O4'—C1'—H1'	108.9
C6—C1—H1	120.7	N9—C1'—H1'	108.9
C2—C1—H1	120.7	C2'—C1'—H1'	108.9
N3—C2—C1	123.97 (12)	C1'—C2'—C3'	101.48 (11)
N3—C2—H2	118.0	C1'—C2'—H2A	111.5
C1—C2—H2	118.0	C3'—C2'—H2A	111.5
C4—N3—C2	115.58 (11)	C1'—C2'—H2B	111.5
N3—C4—N9	125.34 (11)	C3'—C2'—H2B	111.5
N3—C4—C5	126.84 (11)	H2A—C2'—H2B	109.3
N9—C4—C5	107.82 (10)	O3'—C3'—C2'	111.49 (11)
C6—C5—C7	138.98 (12)	O3'—C3'—C4'	107.28 (11)
C6—C5—C4	114.03 (11)	C2'—C3'—C4'	103.33 (10)
C7—C5—C4	106.97 (11)	O3'—C3'—H3'	111.5
C1—C6—C5	120.87 (12)	C2'—C3'—H3'	111.5
C1—C6—N6	118.15 (12)	C4'—C3'—H3'	111.5
C5—C6—N6	120.97 (11)	C3'—O3'—H3O	109.5
O61—N6—O62	124.27 (12)	O4'—C4'—C5'	108.86 (11)
O61—N6—C6	118.38 (12)	O4'—C4'—C3'	106.20 (11)
O62—N6—C6	117.34 (11)	C5'—C4'—C3'	114.75 (11)
C8—C7—C5	106.44 (11)	O4'—C4'—H4'	109.0
C8—C7—H7	126.8	C5'—C4'—H4'	109.0
C5—C7—H7	126.8	C3'—C4'—H4'	109.0
C7—C8—N9	110.85 (11)	C1'—O4'—C4'	109.98 (10)
C7—C8—H8	124.6	O5'—C5'—C4'	113.45 (11)
N9—C8—H8	124.6	O5'—C5'—H5A	108.9
C4—N9—C8	107.92 (10)	C4'—C5'—H5A	108.9
C4—N9—C1'	127.29 (10)	O5'—C5'—H5B	108.9
C8—N9—C1'	124.71 (11)	C4'—C5'—H5B	108.9
O4'—C1'—N9	107.59 (11)	H5A—C5'—H5B	107.7
O4'—C1'—C2'	106.08 (10)	C5'—O5'—H5O	109.5
N9—C1'—C2'	116.30 (11)
C6—C1—C2—N3	1.4 (2)	N3—C4—N9—C1'	1.9 (2)
C1—C2—N3—C4	1.2 (2)	C5—C4—N9—C1'	−177.36 (13)
C2—N3—C4—N9	177.57 (13)	C7—C8—N9—C4	0.23 (18)
C2—N3—C4—C5	−3.3 (2)	C7—C8—N9—C1'	177.08 (13)
N3—C4—C5—C6	2.4 (2)	C4—N9—C1'—O4'	61.64 (17)
N9—C4—C5—C6	−178.26 (12)	C8—N9—C1'—O4'	−114.60 (14)
N3—C4—C5—C7	−178.53 (14)	C4—N9—C1'—C2'	−57.10 (19)
N9—C4—C5—C7	0.76 (15)	C8—N9—C1'—C2'	126.66 (14)
C2—C1—C6—C5	−2.2 (2)	O4'—C1'—C2'—C3'	34.53 (12)
C2—C1—C6—N6	177.18 (12)	N9—C1'—C2'—C3'	154.09 (11)
C7—C5—C6—C1	−178.10 (16)	C1'—C2'—C3'—O3'	81.33 (13)
C4—C5—C6—C1	0.5 (2)	C1'—C2'—C3'—C4'	−33.60 (12)
C7—C5—C6—N6	2.5 (3)	O3'—C3'—C4'—O4'	−95.92 (11)
C4—C5—C6—N6	−178.91 (12)	C2'—C3'—C4'—O4'	21.99 (13)
C1—C6—N6—O61	6.12 (19)	O3'—C3'—C4'—C5'	143.78 (11)
C5—C6—N6—O61	−174.48 (14)	C2'—C3'—C4'—C5'	−98.31 (13)
C1—C6—N6—O62	−173.13 (13)	N9—C1'—O4'—C4'	−146.90 (10)
C5—C6—N6—O62	6.27 (19)	C2'—C1'—O4'—C4'	−21.79 (13)
C6—C5—C7—C8	178.03 (18)	C5'—C4'—O4'—C1'	123.74 (11)
C4—C5—C7—C8	−0.61 (15)	C3'—C4'—O4'—C1'	−0.31 (13)
C5—C7—C8—N9	0.25 (17)	O4'—C4'—C5'—O5'	−69.74 (14)
N3—C4—N9—C8	178.69 (13)	C3'—C4'—C5'—O5'	49.09 (15)
C5—C4—N9—C8	−0.61 (16)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O3′—H3O···O5′^i	0.84	1.94	2.7662 (17)	168
C2—H2···O3′^ii	0.95	2.45	3.1157 (17)	127
O5′—H5O···N3	0.84	1.96	2.7871 (15)	170

Symmetry codes: (i) −x, y−1/2, −z+3/2; (ii) x, y+1, z.