7-Amino-1-(2-de­oxy-β-erythro-pentofuranos­yl)-1H-1,2,3-triazolo[4,5-d]pyrimidine: an 8-aza­adenine nucleoside with the nucleobase in a syn conformation

The title compound, C₉H₁₂N₆O₃, shows a syn-glycosylic bond orientation [χ = 64.17 (16)°]. The 2′-de­oxy­furanosyl moiety exhibits an unusual C1′-exo–O4′-endo (₁T⁰; S-type) sugar pucker, with P = 111.5 (1)° and τ_m = 40.3 (1)°. The conformation at the exocyclic C4′—C5′ bond is +sc (gauche), with γ = 64.4 (1)°. The two-dimensional hydrogen-bonded network is built from inter­molecular N—H...O and O—H...N hydrogen bonds. An intra­molecular bifurcated hydrogen bond, with an amino N—H group as hydrogen-bond donor and the ring and hy­droxy­methyl O atoms of the sugar moiety as acceptors, constrains the overall conformation of the nucleoside.

S1. Comment

The formation of regioisomeric glycosylation products is a common problem in nucleoside synthesis and has been investigated in detail for purine nucleosides (Garner & Ramakanth, 1988; Robins et al., 1996; Golankiewicz et al., 2002). It was reported that the outcome of the glycosylation reaction depends on the catalyst, solvent, temperature and time, and is also influenced by the structure of the base and the activated sugar. Under kinetically controlled conditions, the formation of the N7-isomer is favoured, whereas the N9-isomers predominate under thermodynamic control (Garner & Ramakanth, 1988). The incorporation of unusual N7-glycosylated nucleosides into DNA can lead to new base-pairing modes and eventually to new DNA structures. N7-Glycosylated adenine and guanine form stable base pairs in double-stranded DNA (Seela & Winter, 1993, 1994; Seela & Leonard, 1996, 1997) and triplex DNA (Hunziker et al., 1995; Brunar & Dervan, 1996).

Glycosylation of 8-azapurines is further complicated, due to the additional N atom enlarging the number of regioisomers. The synthesis of 8-aza-2'-deoxyadenosine, (IIa), was first described by Tong et al. (1965), followed by other reports employing various protocols (Montgomery & Thomas, 1972; Kazimierczuk et al., 1989; Rose et al., 2002). Our laboratory used nucleobase-anion glycosylation conditions (NaH, MeCN) for the synthesis and isolated 8-aza-2'-deoxyadenosine, (IIa), and its N7-isomer, the title compound, (I) (Kazimierczuk et al., 1989).

We report here the conformation and hydrogen-bonding of (I) in the crystalline state and compare the structure with those of the related molecules of 8-azaadenosine, (IIb) (Singh & Hodgson, 1974, 1977), 8-aza-7-deaza-2'-deoxyadenosine, (III) (Seela et al., 1999), and the N-7 regioisomer of 2-chloro-2'-deoxyadenosine, (IV) (Worthington et al., 1995). The three-dimensional structure of (I) is shown in Fig. 1 and selected geometric parameters are listed in Table 1.

For the common N9-glycosylated purine nucleosides, the orientation of the nucleobase relative to the sugar moiety (syn/anti) is defined by the torsion angle χ(O4'—C1'—N9—C4) (IUPAC–IUB Joint Commission on Biochemical Nomenclature, 1983). The corresponding torsion angle in (I), namely χ(O4'—C1'—N7—C5) is 64.2 (2)°, reflects a syn conformation. This is contrary to the usually preferred anti conformation at the N-glycosylic bond of the common purine nucleosides (Saenger, 1984). However, inspection of the hydrogen-bonding pattern of (I) reveals a bifurcated intramolecular hydrogen bond between the amino group of the nucleobase and atoms O5' and O4' of the sugar moiety, imposing the syn conformation of nucleoside (I). A very similar situation was observed for the closely related N-7 regioisomer of 2-chloro-2'-deoxyadenosine, (IV). In this case, the syn conformation (χ = 67.0°) is also stabilized by a bifurcated intramolecular hydrogen bond, with atom H6 of the amino group as donor and atoms O5' and O4' of the glycon as acceptors (Worthington et al., 1995).

The regular 8-azaadenine ribonucleoside, (IIb), with atom N9 as the glycosylation site, shows a conformation within the high-anti range, with χ = -78.0° (Singh & Hodgson, 1974, 1977). The corresponding 8-aza-7-deaza-2'-deoxyadenosine, (III), however, adopts an anti conformation of the glycosyl bond [χ = -106.3 (2)°; Seela et al., 1999]. The length of the N7—C1' glycosylic bond is 1.459 (1) Å for (I), which is longer than the N9—C1' glycosylic bonds of 8-azaadenosine, (IIb) [1.447 (3) Å; Singh & Hodgson, 1974, 1977], and 8-aza-7-deaza-2'-deoxyadenosine, (III) [1.442 (2) Å; Seela et al., 1999].

C2'-endo (south, S) and C3'-endo (north, N) are the most frequently observed sugar-ring conformations of nucleosides (Saenger, 1984). In the crystalline state of (I), the sugar moiety shows a less common conformation with a major C1'-exo sugar pucker (C1'-exo-O4'-endo, ₁T⁰), corresponding to an S-type. The pseudorotation phase angle P is 111.5 (1)° and the maximum amplitude τ_m is 40.3 (1)°. Again, the situation is very close to that of the N-7 regioisomer of 2-chloro-2'-deoxyadenosine, (IV) (S-type, C1'-exo-O4'-endo, ₁T⁰, P = 110° and τ_m = 38.6°; Worthington et al., 1995). The N9 nucleosides (IIb) and (III) also adopt an S sugar-ring conformation, but with the common C2'-endo sugar pucker [in (IIb), C2'-endo-C1'-exo, ²T₁; Singh & Hodgson, 1974, 1977; in (III), C2'-endo-C3'-exo, ²T₃ with P = 182.2 (2)° and τ_m = 41.2 (1)°; Seela et al., 1999].

The conformation about the exocyclic C4'—C5' bond is defined by the torsion angle γ(O5'—C5'—C4'—C3'), which is 64.4 (1)° for (I), corresponding to a +sc (gauche) conformation. This conformation was also observed for the hydroxyl group of (IV) (γ = 57.8°; Worthington et al., 1995). By contrast, for 8-azaadenosine, (IIb) (γ = 179.1; Singh & Hodgson, 1974, 1977), and 8-aza-7-deaza-2'-deoxyadenosine, (III) [γ = -178.7 (2)°; Seela et al., 1999], conformations about the C4'—C5' bond were reported which are situated in the ap (gauche,trans) range. The 8-azapurine ring system of (I) is nearly planar. The deviations of the ring atoms from the least-squares plane of atoms N1/C2/N3/C4–C6/N7–N9 range from -0.054 (1) (atom C6) to 0.046 (1) Å (atom C2), with an r.m.s. deviation of 0.0337 Å. The C1' substituent lies 0.261 (2) Å above this plane and atom N6 0.161 (2) Å below.

An unsymmetric bifurcated intramolecular hydrogen bond is formed between N6—H6B of the amino group as donor and atoms O5' and O4' of the sugar residue as acceptors. According to Steiner (2002), for bifurcated hydrogen bonds with distinctly different hydrogen-acceptor separations, the shorter interaction is defined as the major component and the longer one as the minor. In the case of nucleoside (I), the major component of the bifurcated hydrogen bond is N6—H6B···O5', with N6···O5' = 2.819 (2) Å and N6—H6B···O5' = 137.7°. The minor component utilizes atom O4' as acceptor, with N6···O4' = 3.168 (2) Å and N6—H6B···O4' = 143.0°. A similar intramolecular bifurcated hydrogen-bonding pattern was also observed in the crystal structures of 2-chloro-2'-deoxyadenosine, (IV) (Worthington et al., 1995), and 2'-deoxy-5-methylisocytidine, (V) (Seela et al., 2000).

These findings indicate that the additional N atom of the 8-azapurine nucleoside, (I), compared with the corresponding purine nucleoside (IV) – both having the same glycosylation sites – has a negligible effect, and the intramolecular hydrogen bonding is mainly controlled by the spatial arrangement of the amino group in both nucleosides.

The crystal structure of (I) contains a two-dimensional hydrogen-bond network generated by translation. Within the crystal structure, the nucleosides form reverse-ordered strands with respect to each other. The sugar moieties are perpendicular to the nucleobases, leading to a `staircase'-like arrangement of nucleosides within each strand (Fig. 2). Every second strand shows the same orientation, and the nucleobases are parallel to each other.

This highly ordered array is connected by several intermolecular hydrogen bonds (Fig. 3 and Table 2). The hydroxyl groups of the sugar residues function as H-atom donors and atoms N3 and N9 of the heterocycle as H-atom acceptors (O3'—H3'O···N3ⁱⁱ and O5'—H5'O···N9ⁱⁱⁱ; see Table 2 for symmetry codes and geometry), and another hydrogen-bond is found between N6—H6A of the amino group and atom O3' of the ribofuranosyl moiety (N6—H6A···O3'ⁱ), leading to the formation of a hydrogen-bonded sheet parallel to (010) (Fig. 3).

S2. Experimental

Compound (I) was synthesized as previously reported (Kazimierczuk et al., 1989). Slow crystallization from EtOH afforded (I) as colourless needles (decomposition >473 K). For the diffraction experiment, a single crystal was mounted on a MiTeGen MicroMesh fibre in a thin smear of oil.

S3. Refinement

In the absence of suitable anomalous scattering, Friedel equivalents could not be used to determine the absolute structure. Refinement of the Flack parameter (Flack, 1983) led to an inconclusive value [0.4 (6)]. Therefore, 1693 Friedel equivalents were merged before the final refinement and the known configuration of the parent molecule was used to define the enantiomer of the final model. All H atoms were found in a difference Fourier synthesis. The OH groups were refined as rigid groups allowed to rotate but not to tilt, with O—H = 0.82 Å and U_iso(H) = 1.5U_eq(O). The remaining H atoms were placed in geometrically idealized positions, with C—H = 0.93–0.98 Å and N—H = 0.86 Å, and constrained to ride on their parent atoms, with U_iso(H) = 1.2U_eq(C,N).

Computing details

Data collection: APEX2 (Bruker, 2008); cell refinement: SAINT (Bruker, 2008); data reduction: SAINT (Bruker, 2008); program(s) used to solve structure: SHELXTL (Release 5.1; Sheldrick, 2008); program(s) used to refine structure: SHELXTL (Release 5.1; Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 1999); software used to prepare material for publication: SHELXTL (Release 5.1; Sheldrick, 2008) and PLATON (Spek, 2009).

Figures

	Fig. 1. A perspective view of the molecule of (I), showing the intramolecular bifurcated hydrogen bond (dashed lines) and the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii.
	Fig. 2. The crystal packing of (I), showing the `staircase'-like arrangement of nucleosides. For the sake of clarity, H atoms have been omitted.
	Fig. 3. A detailed view of the two-dimensional hydrogen-bonded (dashed lines) network of (I). The projection is parallel to the ac plane. For the sake of clarity, H atoms not involved in the hydrogen-bonding motifs shown have been omitted.

7-Amino-1-(2-deoxy-β-erythro-pentofuranosyl)-1H-1,2,3- triazolo[4,5-d]pyrimidine

Crystal data

C9H12N6O3	F(000) = 264
Mr = 252.25	Dx = 1.524 Mg m^−3
Monoclinic, P21	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2yb	Cell parameters from 9866 reflections
a = 7.1469 (3) Å	θ = 2.9–31.1°
b = 8.7025 (4) Å	µ = 0.12 mm^−1
c = 9.1100 (4) Å	T = 130 K
β = 104.056 (2)°	Block, colourless
V = 549.64 (4) Å^3	0.25 × 0.25 × 0.20 mm
Z = 2

Data collection

Bruker APEXII CCD area-detector diffractometer	1693 independent reflections
Radiation source: fine-focus sealed tube	1673 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.025
ϕ and ω scans	θmax = 30.0°, θmin = 3.3°
Absorption correction: multi-scan (SADABS; Bruker, 2008)	h = −9→10
Tmin = 0.971, Tmax = 0.977	k = −12→12
21532 measured reflections	l = −12→12

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.028	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.076	H-atom parameters constrained
S = 1.07	w = 1/[σ^2(Fo^2) + (0.0562P)^2 + 0.0539P] where P = (Fo^2 + 2Fc^2)/3
1693 reflections	(Δ/σ)max < 0.001
165 parameters	Δρmax = 0.36 e Å^−3
1 restraint	Δρmin = −0.22 e Å^−3

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
N1	1.01418 (16)	0.91374 (17)	1.02591 (12)	0.0238 (2)
C2	1.05938 (18)	0.91975 (19)	1.17820 (15)	0.0235 (3)
H2	1.1804	0.9597	1.2232	0.028*
N3	0.95410 (15)	0.87626 (15)	1.27269 (12)	0.0202 (2)
C4	0.77645 (17)	0.82784 (14)	1.19787 (12)	0.0166 (2)
C5	0.71038 (16)	0.82005 (14)	1.04174 (12)	0.0155 (2)
N6	0.80284 (15)	0.84202 (17)	0.80165 (12)	0.0226 (2)
H6A	0.8877	0.8675	0.7534	0.027*
H6B	0.6930	0.8064	0.7532	0.027*
C6	0.84157 (16)	0.85780 (16)	0.95148 (13)	0.0180 (2)
N7	0.52270 (14)	0.77255 (13)	1.01908 (11)	0.0152 (2)
N8	0.47826 (15)	0.75329 (13)	1.15331 (11)	0.0171 (2)
N9	0.63065 (16)	0.78445 (13)	1.26225 (12)	0.0180 (2)
C1'	0.36609 (16)	0.76372 (14)	0.88266 (12)	0.0145 (2)
H1'	0.2469	0.7314	0.9089	0.017*
C2'	0.33254 (17)	0.91406 (14)	0.79493 (13)	0.0156 (2)
H2A	0.4525	0.9695	0.8039	0.019*
H2B	0.2424	0.9792	0.8303	0.019*
C3'	0.24848 (16)	0.86185 (15)	0.63203 (13)	0.0151 (2)
H3'	0.3131	0.9141	0.5627	0.018*
O3'	0.04695 (12)	0.89200 (14)	0.59120 (10)	0.0220 (2)
H3O	0.0068	0.8844	0.4992	0.033*
O4'	0.41713 (13)	0.65566 (11)	0.78330 (10)	0.01679 (18)
C4'	0.29055 (17)	0.68698 (14)	0.63602 (13)	0.0164 (2)
H4'	0.1694	0.6308	0.6268	0.020*
C5'	0.38899 (19)	0.62807 (16)	0.51813 (14)	0.0207 (2)
H5A	0.3992	0.5170	0.5241	0.025*
H5B	0.3139	0.6554	0.4178	0.025*
O5'	0.57552 (14)	0.69419 (14)	0.54408 (10)	0.0233 (2)
H5O	0.5973	0.7191	0.4630	0.035*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
N1	0.0163 (4)	0.0401 (7)	0.0150 (5)	−0.0003 (5)	0.0038 (4)	−0.0023 (5)
C2	0.0167 (5)	0.0363 (7)	0.0160 (5)	0.0025 (5)	0.0013 (4)	−0.0039 (5)
N3	0.0192 (4)	0.0283 (5)	0.0118 (4)	0.0042 (4)	0.0010 (3)	−0.0022 (4)
C4	0.0203 (5)	0.0195 (5)	0.0102 (5)	0.0050 (4)	0.0037 (4)	0.0000 (4)
C5	0.0150 (4)	0.0203 (5)	0.0108 (4)	0.0023 (4)	0.0027 (3)	−0.0005 (4)
N6	0.0168 (4)	0.0400 (7)	0.0115 (4)	−0.0026 (4)	0.0047 (3)	−0.0014 (4)
C6	0.0150 (4)	0.0264 (6)	0.0129 (5)	0.0025 (4)	0.0038 (4)	−0.0005 (4)
N7	0.0168 (4)	0.0196 (5)	0.0099 (4)	0.0013 (4)	0.0047 (3)	0.0013 (4)
N8	0.0234 (5)	0.0183 (5)	0.0113 (4)	0.0025 (4)	0.0072 (3)	0.0013 (4)
N9	0.0233 (5)	0.0197 (5)	0.0118 (4)	0.0029 (4)	0.0056 (4)	0.0007 (4)
C1'	0.0159 (4)	0.0173 (5)	0.0105 (4)	−0.0005 (4)	0.0034 (4)	0.0000 (4)
C2'	0.0157 (4)	0.0154 (5)	0.0148 (5)	0.0001 (4)	0.0019 (4)	0.0006 (4)
C3'	0.0142 (4)	0.0200 (5)	0.0115 (4)	0.0004 (4)	0.0040 (3)	0.0019 (4)
O3'	0.0143 (4)	0.0386 (6)	0.0123 (4)	0.0034 (4)	0.0016 (3)	0.0004 (4)
O4'	0.0238 (4)	0.0161 (4)	0.0105 (4)	0.0015 (3)	0.0042 (3)	0.0002 (3)
C4'	0.0197 (5)	0.0181 (5)	0.0112 (5)	−0.0039 (4)	0.0037 (4)	−0.0006 (4)
C5'	0.0289 (6)	0.0205 (6)	0.0131 (5)	−0.0031 (5)	0.0060 (4)	−0.0037 (4)
O5'	0.0251 (4)	0.0339 (5)	0.0122 (4)	−0.0022 (4)	0.0074 (3)	−0.0011 (4)

Geometric parameters (Å, º)

N1—C6	1.3462 (15)	C1'—C2'	1.5215 (17)
N1—C2	1.3469 (16)	C1'—H1'	0.9800
C2—N3	1.3285 (17)	C2'—C3'	1.5286 (16)
C2—H2	0.9300	C2'—H2A	0.9700
N3—C4	1.3542 (16)	C2'—H2B	0.9700
C4—N9	1.3672 (16)	C3'—O3'	1.4218 (14)
C4—C5	1.3872 (15)	C3'—C4'	1.5499 (17)
C5—N7	1.3705 (14)	C3'—H3'	0.9800
C5—C6	1.4275 (16)	O3'—H3O	0.8200
N6—C6	1.3323 (14)	O4'—C4'	1.4503 (15)
N6—H6A	0.8600	C4'—C5'	1.5093 (17)
N6—H6B	0.8600	C4'—H4'	0.9800
N7—N8	1.3464 (13)	C5'—O5'	1.4181 (16)
N7—C1'	1.4586 (14)	C5'—H5A	0.9700
N8—N9	1.3113 (15)	C5'—H5B	0.9700
C1'—O4'	1.4132 (14)	O5'—H5O	0.8200
C6—N1—C2	119.61 (12)	C1'—C2'—C3'	103.24 (10)
N3—C2—N1	128.64 (12)	C1'—C2'—H2A	111.1
N3—C2—H2	115.7	C3'—C2'—H2A	111.1
N1—C2—H2	115.7	C1'—C2'—H2B	111.1
C2—N3—C4	111.83 (10)	C3'—C2'—H2B	111.1
N3—C4—N9	126.09 (10)	H2A—C2'—H2B	109.1
N3—C4—C5	125.13 (11)	O3'—C3'—C2'	109.48 (9)
N9—C4—C5	108.74 (10)	O3'—C3'—C4'	111.46 (10)
N7—C5—C4	104.25 (10)	C2'—C3'—C4'	103.94 (9)
N7—C5—C6	137.60 (11)	O3'—C3'—H3'	110.6
C4—C5—C6	118.15 (11)	C2'—C3'—H3'	110.6
C6—N6—H6A	120.0	C4'—C3'—H3'	110.6
C6—N6—H6B	120.0	C3'—O3'—H3O	109.5
H6A—N6—H6B	120.0	C1'—O4'—C4'	105.52 (9)
N6—C6—N1	119.36 (11)	O4'—C4'—C5'	107.50 (10)
N6—C6—C5	124.36 (11)	O4'—C4'—C3'	106.26 (9)
N1—C6—C5	116.28 (10)	C5'—C4'—C3'	115.98 (10)
N8—N7—C5	109.81 (10)	O4'—C4'—H4'	109.0
N8—N7—C1'	117.76 (10)	C5'—C4'—H4'	109.0
C5—N7—C1'	131.66 (10)	C3'—C4'—H4'	109.0
N9—N8—N7	109.02 (10)	O5'—C5'—C4'	108.99 (10)
N8—N9—C4	108.17 (10)	O5'—C5'—H5A	109.9
O4'—C1'—N7	108.47 (9)	C4'—C5'—H5A	109.9
O4'—C1'—C2'	105.54 (9)	O5'—C5'—H5B	109.9
N7—C1'—C2'	113.12 (10)	C4'—C5'—H5B	109.9
O4'—C1'—H1'	109.9	H5A—C5'—H5B	108.3
N7—C1'—H1'	109.9	C5'—O5'—H5O	109.5
C2'—C1'—H1'	109.9
C6—N1—C2—N3	0.1 (3)	N3—C4—N9—N8	176.57 (12)
N1—C2—N3—C4	−3.5 (2)	C5—C4—N9—N8	−1.10 (14)
C2—N3—C4—N9	−175.89 (13)	N8—N7—C1'—O4'	−127.06 (11)
C2—N3—C4—C5	1.42 (19)	C5—N7—C1'—O4'	64.17 (16)
N3—C4—C5—N7	−177.14 (12)	N8—N7—C1'—C2'	116.20 (12)
N9—C4—C5—N7	0.57 (13)	C5—N7—C1'—C2'	−52.56 (17)
N3—C4—C5—C6	3.57 (19)	O4'—C1'—C2'—C3'	33.80 (11)
N9—C4—C5—C6	−178.73 (11)	N7—C1'—C2'—C3'	152.25 (9)
C2—N1—C6—N6	−175.31 (14)	C1'—C2'—C3'—O3'	105.17 (11)
C2—N1—C6—C5	5.1 (2)	C1'—C2'—C3'—C4'	−14.01 (11)
N7—C5—C6—N6	−5.3 (3)	N7—C1'—O4'—C4'	−162.33 (9)
C4—C5—C6—N6	173.72 (13)	C2'—C1'—O4'—C4'	−40.81 (11)
N7—C5—C6—N1	174.26 (15)	C1'—O4'—C4'—C5'	155.88 (10)
C4—C5—C6—N1	−6.75 (18)	C1'—O4'—C4'—C3'	31.10 (12)
C4—C5—N7—N8	0.15 (13)	O3'—C3'—C4'—O4'	−127.10 (10)
C6—C5—N7—N8	179.24 (15)	C2'—C3'—C4'—O4'	−9.28 (11)
C4—C5—N7—C1'	169.60 (12)	O3'—C3'—C4'—C5'	113.53 (11)
C6—C5—N7—C1'	−11.3 (2)	C2'—C3'—C4'—C5'	−128.66 (11)
C5—N7—N8—N9	−0.85 (14)	O4'—C4'—C5'—O5'	−54.35 (13)
C1'—N7—N8—N9	−171.95 (10)	C3'—C4'—C5'—O5'	64.36 (14)
N7—N8—N9—C4	1.19 (14)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N6—H6B···O5′	0.86	2.12	2.8194 (15)	138
N6—H6B···O4′	0.86	2.44	3.1676 (15)	143
N6—H6A···O3′^i	0.86	2.08	2.9211 (14)	164
O3′—H3O···N3^ii	0.82	2.01	2.8184 (14)	170
O5′—H5O···N9^iii	0.82	1.98	2.8027 (14)	176

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