2,2′-Anhydro-1-(3′,5′-di-O-acetyl-β-D-arabinofuranosyl)uracil, a cyclo­uridine nucleoside with a C4′-endo furanosyl conformation

2,2′-Anhydro-1-(3′,5′-di-O-acetyl-β-D-arabinofuranosyl)uracil, C₁₃H₁₄N₂O₇, was obtained by refluxing 2′,3′-O-(meth­oxy­methyl­ene)uridine in acetic anhydride. The structure exhibits a nearly perfect C4′-endo (⁴E) conformation. The best four-atom plane of the five-membered furan­ose ring is O—C—C—C, involving the C atoms of the fused five-membered oxazolidine ring, and the torsion angle is only −0.4 (2)°. The oxazolidine ring is essentially coplanar with the six-membered uracil ring [r.m.s. deviation = 0.012 (5) Å and dihedral angle = −3.2 (3)°]. The conformation at the exocyclic C—C bond is gauche–trans which is stabilized by various C—H...π and C—O...π inter­actions.

S1. Comment

Conformationally restricted cyclonucleoside analogues are of considerable importance in biochemistry, medicinal chemistry and nucleoside-based drug discovery (Wnuk et al., 2002; Bennett & Swayze, 2010). These compounds are key intermediates for the synthesis of a considerable number of nucleoside analogues (Dai et al., 2008; Belostotskii et al., 2012). Besides their utility in synthetic chemistry, cyclonucleosides, with a rigid fused polyring system, are good reference compounds to correlate X-ray data with dihedral angles obtained from proton–proton coupling constants (Jardetzky, 1960; Cross & Schleich, 1973) and circular dichroism (Miles et al. 1979).

In our attempt to synthesize deoxyuridine derivatives, we attempted to make use of a pivotal intermediate, 1-(5-O-acetyl-2,3-dideoxy-β-D-glycero-pent-2-enofuranosy1)uracil, (II), which was reported to be readily obtained from 2',3'-O-(methoxymethylene)uridine, (III) (Shiragami et al. 1988). However, when repeating this procedure in our laboratory, we found that 2,2'-anhydro-1-(3',5'-di-O-acetyl-β-D-arabinofuranosyl)uracil, (I), was the main product instead of (II). The expected product (II) formed but in low yield (23%) and was found to be unstable in boiling acetic anhydride. 3',5'-Diacetylated cyclouridine, (I), was obtained in 65% yield after boiling for 5 h. To confirm its molecular structure, as well as to provide the solid-state conformation of this fused polyring system, we report here the crystal structure of (I) (Fig. 1) and compare the structure with those of related cyclouridine molecules.

The preferred sugar puckering modes in nucleosides are C2'-endo and C3'-endo (Saenger, 1984), whereas the C4'-endo (⁴E) conformation was considered to be unlikely considering the short O2'—O3' distance and the fact that some adjacent bonds would be in an eclipsed conformation (Jardetzky, 1960). However, with the cyclization of O2' and C2', the ribosyl furanose ring changes to the arabinosyl configuration, thus eliminating the steric congestion at O3'. The fused oxazolidine ring demands C1'—N1 and C2'—O2' to be eclipsed in order to conform to the sp² character of atoms N1 and C2 in the pyrimidine ring. The X-ray study of (I) shows that the five-membered furanosyl ring adopts a perfect C4'-endo puckered conformation. The best four-atom plane, comprised of atoms O4', C1', C2' and C3', is planar, as the O4'—C1'—C2'—C3' torsion angle is only 0.2 (3)°. Atom C4' is displaced by 0.48 (6) Å to the same side of this plane as C5'. A quantitative analysis of the ring conformations was performed using the method of Cremer & Pople (1975) for the calculation of puckering parameters. The polar parameters for the furanose ring are Q = 0.313 (2) Å and ϕ = 142.0 (8)°, comparable with an ideal envelope C4'-endo conformation (ideal ϕ = 144°). This conformation is also found in cyclonucleosides such as 2,2'-anhydro-1-(β-D-arabinofuranosyl)uracil (Suck & Saenger, 1973) and 1,2-di-O-isopropylidenepentofuranose (Doboszewski et al. 2012).

The exocyclic C4'—C5' bond adopts a gauche–trans conformation instead of the gauche–gauche conformation commonly observed in nucleosides (Shefter & Trueblood, 1965). The corresponding dihedral angles, as defined by Shefter & Trueblood (1965), are ϕ_OO = 55.7 (4)° and ϕ_OC = 173.2 (3)°. This geometric arrangement may lessen the short contacts that would occur if the conformation were gauche–gauche and syn (Seshadri et al., 1983). In addition, a significant intramolecular C5'—H5'2···π(pyrimidine) hydrogen bond and a C7—O7···π(pyrimidine) interaction were observed in this molecule, which we believe are the other main force stabilizing the C4'—C5' gauche–trans configuration. The present geometry is very similar to that of the 5'-O-tosyl and 5'-O-acetylated analogues (Gautham et al., 1983; Seshadri et al., 1983).

The uracil ring and the five-membered oxazolidine ring fused at atoms N1 and C2 are both essentially planar. The interplanar angle between the six- and five-membered rings is about 2°. The glycosidic torsion angle χ [O4'—C1'—N1—C6] is 296.8 (5)°, reflecting a syn conformation. The value agrees well with that for the similar fused-ring systems, 2,2'-anhydro-l-β-D-arabino-furanosyl cytosine hydrochloride (χ_CN = 299°; Sundaralingam, 1973) and 2,2'-anhydro-l-β-D-arabino-furanosyl uracil (χ_CN = 294.5°; Delbaere & James, 1973).

For the 5'-O-acetyl group, the C8—C7—O5'—C5' and O7—C7—O5'—C5' torsion angles are 176.4 (4) and -4.9 (6)°, respectively, and thus the C8—C7 bond is trans and the C7—O7 bond cis to the arabinose C5'—O5' bond. This is the same for the 3'-O-acetyl group, as the C10—C9—O3'—C3' and O9—C9—O3'—C3' torsion angles are 178.3 (3) and -2.8 (5)°, respectively, indicating that the C10—C9 bond is trans and the C9—O9 bond cis to the C3'—O3' bond.

Various C—O···π, C—H···π, C—H···O and C—H···N hydrogen bonds are present in the structure of (I). The C—O···π interactions can be observed with an intramolecular C7—O7···Cg interaction [O7···Cg = 3.509 (4) Å] and an intermolecular C9—O9···Cgⁱ interaction [Cg is the centroid of the N1/C2/N3/C4–C6 ring [Added text OK?]; symmetry code: (i) x - 1, y, z]. Molecules are arranged in chains in a head-to-tail fashion via C6—H6···N3ⁱⁱ hydrogen bonds and C1'—H1'···O4ⁱⁱⁱ short contacts [symmetry codes: (ii) x + 2, y - 1/2, -z; (iii) -x + 2, y + 1/2, -z] along the [010] direction (Table 1 and Fig. 2). These chains are further connected via weak C8—H8B···O7^iv hydrogen bonds [symmetry code: (iv) x + 1, y + 1/2, -z + 1] into a sheet and these sheets are in turn further connected via various weak C—H···O short contacts into a three-dimensional network.

Related literature

For related literature, see: Belostotskii et al. (2012); Bennett & Swayze (2010); Cremer & Pople (1975); Cross & Schleich (1973); Dai et al. (2008); Delbaere & James (1973); Doboszewski et al. (2012); Gautham et al. (1983); Jardetzky (1960); Miles et al. (1979); Saenger (1984); Seshadri et al. (1983); Shefter & Trueblood (1965); Shiragami et al. (1988); Suck & Saenger (1973); Sundaralingam (1973); Wnuk et al. (2002).

S2. Experimental

2',3'-O-(Methoxymethylene)uridine, (III), was prepared according to a previously reported method (Shiragami et al., 1988). All other chemicals were obtained commercially and were used without further purification. The title compound, (I), was prepared according to a similar procedure used for the synthesis of 1-(5-O-acetyl-2,3-dideoxy-β-D-glycero-pent-2-enofuranosy1)uracil, (II). A solution of (III) (7.0 g, 21.3 mmol) in acetic anhydride (50 ml) was bolied gently and the acetic acid which formed was boiled off. After the disappearance of the starting material (about 5 h), the remaining acetic anhydride was evaporated under reduced pressure, and the residue was dissolved in chloroform (100 ml) and washed with aqueous NaHCO₃ (50 ml). The aqueous layer was extracted with CHCl₃ (50 ml). The combined organic layers were dried over Na₂SO₄, concentrated and purified by silica-gel column chromatography (CHCl₃–MeOH 10:1 v/v) to give (I) (yield 4.3 g, 65%; m.p. 461–463 K). Crystals suitable for X-ray diffraction analysis were crystallized from a methanol–ethyl acetate mixture [Solvent ratio?].

S3. Refinement

C-bound H atoms were placed geometrically and refined using a riding model, with C—H = 0.93 Å and U_iso(H) = 1.2U_eq(C) for aromatic H atoms, C—H = 0.98 Å and U_iso(H) = 1.2U_eq(C) for methine H atoms, C—H = 0.97 Å and U_iso(H) = 1.2U_eq(C) for methylene H atoms, and C—H = 0.96 Å and U_iso(H) = 1.5U_eq(C) for methyl H atoms. The chirality of (I) was known from the synthetic route and the absolute structure was assigned on the basis of the known chirality of uridine used in the chemical synthesis.

Computing details

Data collection: CrysAlis PRO (Agilent, 2012); cell refinement: CrysAlis PRO (Agilent, 2012); data reduction: CrysAlis PRO (Agilent, 2012); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: OLEX2 (Dolomanov et al., 2009); software used to prepare material for publication: OLEX2 (Dolomanov et al., 2009).

Figures

	Fig. 1. The molecular structure of (I), showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level.
	Fig. 2. The C—H···π and C—O···π interactions of (I) (dotted lines). H atoms have been omitted for clarity. [Please provide a revision with no bond lengths shown and with any atom labels not touching atoms or bonds]

2,2'-Anhydro-1-(2'-deoxy-3',5'-di-O-acety-β-D- arabinofuranosyl)uracil

Crystal data

C13H14N2O7	Dx = 1.433 Mg m^−3
Mr = 310.26	Melting point = 461–463 K
Monoclinic, P21	Mo Kα radiation, λ = 0.7107 Å
a = 8.1032 (3) Å	Cell parameters from 1211 reflections
b = 10.0065 (3) Å	θ = 3.1–28.4°
c = 8.8704 (4) Å	µ = 0.12 mm^−1
β = 90.609 (4)°	T = 294 K
V = 719.21 (5) Å^3	Block, colourless
Z = 2	0.3 × 0.3 × 0.3 mm
F(000) = 324

Data collection

Agilent SuperNova (Dual, Cu at zero, Eos) diffractometer	2483 independent reflections
Radiation source: SuperNova (Mo) X-ray Source	2160 reflections with I > 2σ(I)
Mirror monochromator	Rint = 0.015
Detector resolution: 16.0733 pixels mm^-1	θmax = 26.4°, θmin = 3.1°
ω scans	h = −6→10
Absorption correction: multi-scan (CrysAlis PRO; Agilent, 2012)	k = −12→12
Tmin = 0.710, Tmax = 1.000	l = −11→8
2985 measured reflections

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)] = 0.039	H-atom parameters constrained
wR(F^2) = 0.091	w = 1/[σ^2(Fo^2) + (0.0345P)^2 + 0.0609P] where P = (Fo^2 + 2Fc^2)/3
S = 1.09	(Δ/σ)max < 0.001
2483 reflections	Δρmax = 0.14 e Å^−3
201 parameters	Δρmin = −0.17 e Å^−3
1 restraint	Absolute structure: Flack (1983), 933 Friedel pairs
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: −0.2 (12)

Special details

Experimental. Absorption correction: CrysAlisPro, Agilent Technologies, Version 1.171.36.20, Empirical absorption correction using spherical harmonics, implemented in SCALE3 ABSPACK scaling algorithm.

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 > 2sigma(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
O2'	0.7319 (2)	0.39998 (15)	−0.0785 (2)	0.0440 (4)
O3'	0.3797 (2)	0.55971 (17)	−0.24786 (17)	0.0443 (4)
O4	1.1202 (3)	0.37929 (19)	0.2971 (2)	0.0594 (6)
O4'	0.5843 (2)	0.70443 (14)	−0.02277 (19)	0.0424 (4)
O5'	0.4859 (3)	0.6532 (2)	0.27176 (19)	0.0570 (6)
O7	0.6470 (3)	0.5328 (3)	0.4235 (2)	0.0886 (8)
O9	0.1443 (2)	0.48121 (19)	−0.1537 (2)	0.0605 (6)
N1	0.8368 (2)	0.58738 (17)	0.0164 (2)	0.0365 (5)
N3	0.9211 (3)	0.37845 (19)	0.1143 (2)	0.0416 (5)
C1'	0.7165 (3)	0.6383 (2)	−0.0916 (3)	0.0389 (6)
H1'	0.7682	0.6938	−0.1689	0.047*
C2	0.8376 (3)	0.4522 (2)	0.0244 (3)	0.0379 (6)
C2'	0.6476 (3)	0.5074 (2)	−0.1578 (3)	0.0396 (5)
H2'	0.6637	0.5021	−0.2670	0.048*
C3'	0.4659 (3)	0.5081 (2)	−0.1176 (2)	0.0353 (5)
H3'	0.4262	0.4195	−0.0882	0.042*
C4	1.0285 (3)	0.4446 (2)	0.2130 (3)	0.0430 (6)
C4'	0.4557 (3)	0.6092 (2)	0.0112 (3)	0.0382 (5)
H4'	0.3485	0.6544	0.0059	0.046*
C5	1.0296 (3)	0.5895 (3)	0.2110 (3)	0.0466 (6)
H5	1.0980	0.6354	0.2780	0.056*
C5'	0.4762 (3)	0.5453 (2)	0.1656 (2)	0.0433 (6)
H5'A	0.3828	0.4882	0.1874	0.052*
H5'B	0.5761	0.4919	0.1698	0.052*
C6	0.9345 (3)	0.6582 (2)	0.1148 (3)	0.0412 (6)
H6	0.9345	0.7511	0.1147	0.049*
C7	0.5792 (4)	0.6352 (3)	0.3962 (3)	0.0526 (7)
C8	0.5833 (5)	0.7582 (3)	0.4902 (4)	0.0828 (12)
H8A	0.5352	0.7397	0.5865	0.124*
H8B	0.5218	0.8276	0.4406	0.124*
H8C	0.6956	0.7865	0.5044	0.124*
C9	0.2144 (3)	0.5409 (3)	−0.2514 (3)	0.0469 (6)
C10	0.1376 (4)	0.6010 (4)	−0.3879 (3)	0.0728 (10)
H10A	0.1457	0.5396	−0.4707	0.109*
H10B	0.1940	0.6824	−0.4125	0.109*
H10C	0.0236	0.6199	−0.3690	0.109*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O2'	0.0470 (11)	0.0286 (8)	0.0562 (11)	0.0040 (8)	−0.0104 (9)	−0.0056 (8)
O3'	0.0443 (10)	0.0488 (10)	0.0395 (9)	−0.0025 (8)	−0.0049 (7)	0.0081 (8)
O4	0.0649 (14)	0.0506 (11)	0.0625 (12)	0.0135 (10)	−0.0152 (11)	0.0053 (10)
O4'	0.0427 (10)	0.0265 (7)	0.0581 (11)	0.0009 (7)	0.0009 (8)	−0.0029 (7)
O5'	0.0711 (14)	0.0549 (11)	0.0444 (11)	0.0133 (10)	−0.0170 (10)	−0.0116 (9)
O7	0.118 (2)	0.0762 (15)	0.0703 (14)	0.0182 (17)	−0.0367 (14)	0.0102 (14)
O9	0.0483 (12)	0.0631 (13)	0.0703 (13)	−0.0071 (10)	0.0032 (10)	0.0039 (11)
N1	0.0367 (12)	0.0264 (10)	0.0464 (12)	0.0004 (9)	−0.0038 (9)	0.0014 (9)
N3	0.0456 (13)	0.0306 (10)	0.0484 (13)	0.0065 (10)	−0.0023 (11)	0.0018 (9)
C1'	0.0415 (15)	0.0307 (11)	0.0444 (15)	−0.0004 (11)	0.0012 (11)	0.0035 (10)
C2	0.0381 (14)	0.0293 (12)	0.0463 (15)	0.0043 (10)	0.0067 (11)	−0.0015 (11)
C2'	0.0460 (13)	0.0336 (12)	0.0393 (12)	0.0037 (12)	−0.0028 (10)	0.0008 (11)
C3'	0.0424 (13)	0.0274 (11)	0.0360 (12)	−0.0002 (11)	−0.0057 (10)	0.0009 (10)
C4	0.0451 (16)	0.0408 (14)	0.0430 (15)	0.0067 (12)	0.0031 (12)	0.0016 (11)
C4'	0.0372 (14)	0.0342 (11)	0.0433 (13)	0.0004 (11)	−0.0029 (10)	−0.0031 (10)
C5	0.0483 (16)	0.0447 (14)	0.0468 (15)	0.0002 (13)	−0.0052 (12)	−0.0053 (12)
C5'	0.0465 (15)	0.0422 (14)	0.0410 (12)	0.0003 (12)	−0.0029 (11)	−0.0049 (11)
C6	0.0477 (16)	0.0317 (12)	0.0442 (15)	−0.0029 (11)	0.0038 (12)	−0.0007 (11)
C7	0.0574 (18)	0.0602 (18)	0.0401 (15)	−0.0141 (15)	−0.0092 (13)	0.0072 (13)
C8	0.134 (4)	0.066 (2)	0.0477 (18)	−0.039 (2)	−0.021 (2)	0.0018 (15)
C9	0.0467 (15)	0.0490 (15)	0.0450 (14)	0.0044 (13)	−0.0043 (12)	−0.0090 (13)
C10	0.062 (2)	0.101 (3)	0.0542 (17)	0.019 (2)	−0.0174 (15)	−0.0010 (17)

Geometric parameters (Å, º)

O2'—C2	1.350 (3)	C2'—C3'	1.518 (3)
O2'—C2'	1.451 (3)	C3'—H3'	0.9800
O3'—C3'	1.440 (3)	C3'—C4'	1.528 (3)
O3'—C9	1.353 (3)	C4—C5	1.450 (3)
O4—C4	1.234 (3)	C4'—H4'	0.9800
O4'—C1'	1.404 (3)	C4'—C5'	1.519 (3)
O4'—C4'	1.447 (3)	C5—H5	0.9300
O5'—C5'	1.434 (3)	C5—C6	1.335 (3)
O5'—C7	1.343 (3)	C5'—H5'A	0.9700
O7—C7	1.186 (4)	C5'—H5'B	0.9700
O9—C9	1.200 (3)	C6—H6	0.9300
N1—C1'	1.452 (3)	C7—C8	1.487 (4)
N1—C2	1.355 (3)	C8—H8A	0.9600
N1—C6	1.370 (3)	C8—H8B	0.9600
N3—C2	1.276 (3)	C8—H8C	0.9600
N3—C4	1.394 (3)	C9—C10	1.482 (4)
C1'—H1'	0.9800	C10—H10A	0.9600
C1'—C2'	1.539 (3)	C10—H10B	0.9600
C2'—H2'	0.9800	C10—H10C	0.9600
C2—O2'—C2'	109.45 (18)	O4'—C4'—C5'	113.11 (18)
C9—O3'—C3'	116.16 (19)	C3'—C4'—H4'	109.0
C1'—O4'—C4'	109.56 (16)	C5'—C4'—C3'	112.91 (19)
C7—O5'—C5'	117.7 (2)	C5'—C4'—H4'	109.0
C2—N1—C1'	112.8 (2)	C4—C5—H5	119.4
C2—N1—C6	118.7 (2)	C6—C5—C4	121.3 (3)
C6—N1—C1'	128.20 (19)	C6—C5—H5	119.4
C2—N3—C4	116.2 (2)	O5'—C5'—C4'	106.28 (19)
O4'—C1'—N1	112.9 (2)	O5'—C5'—H5'A	110.5
O4'—C1'—H1'	111.8	O5'—C5'—H5'B	110.5
O4'—C1'—C2'	107.0 (2)	C4'—C5'—H5'A	110.5
N1—C1'—H1'	111.8	C4'—C5'—H5'B	110.5
N1—C1'—C2'	101.02 (18)	H5'A—C5'—H5'B	108.7
C2'—C1'—H1'	111.8	N1—C6—H6	121.1
O2'—C2—N1	110.4 (2)	C5—C6—N1	117.9 (2)
N3—C2—O2'	121.8 (2)	C5—C6—H6	121.1
N3—C2—N1	127.8 (2)	O5'—C7—C8	111.0 (3)
O2'—C2'—C1'	106.17 (17)	O7—C7—O5'	122.6 (3)
O2'—C2'—H2'	111.8	O7—C7—C8	126.3 (3)
O2'—C2'—C3'	110.04 (18)	C7—C8—H8A	109.5
C1'—C2'—H2'	111.8	C7—C8—H8B	109.5
C3'—C2'—C1'	104.77 (19)	C7—C8—H8C	109.5
C3'—C2'—H2'	111.8	H8A—C8—H8B	109.5
O3'—C3'—C2'	106.06 (17)	H8A—C8—H8C	109.5
O3'—C3'—H3'	112.3	H8B—C8—H8C	109.5
O3'—C3'—C4'	109.44 (19)	O3'—C9—C10	111.7 (3)
C2'—C3'—H3'	112.3	O9—C9—O3'	121.9 (2)
C2'—C3'—C4'	103.84 (18)	O9—C9—C10	126.4 (3)
C4'—C3'—H3'	112.3	C9—C10—H10A	109.5
O4—C4—N3	119.7 (2)	C9—C10—H10B	109.5
O4—C4—C5	122.2 (3)	C9—C10—H10C	109.5
N3—C4—C5	118.1 (2)	H10A—C10—H10B	109.5
O4'—C4'—C3'	103.63 (18)	H10A—C10—H10C	109.5
O4'—C4'—H4'	109.0	H10B—C10—H10C	109.5
O2'—C2'—C3'—O3'	−149.97 (18)	C2—N3—C4—O4	−175.8 (2)
O2'—C2'—C3'—C4'	94.7 (2)	C2—N3—C4—C5	3.3 (4)
O3'—C3'—C4'—O4'	−81.4 (2)	C2'—O2'—C2—N1	−2.7 (3)
O3'—C3'—C4'—C5'	155.9 (2)	C2'—O2'—C2—N3	176.5 (2)
O4—C4—C5—C6	177.2 (2)	C2'—C3'—C4'—O4'	31.5 (2)
O4'—C1'—C2'—O2'	−116.8 (2)	C2'—C3'—C4'—C5'	−91.2 (2)
O4'—C1'—C2'—C3'	−0.4 (2)	C3'—O3'—C9—O9	−2.1 (4)
O4'—C4'—C5'—O5'	55.2 (3)	C3'—O3'—C9—C10	178.4 (2)
N1—C1'—C2'—O2'	1.4 (2)	C3'—C4'—C5'—O5'	172.5 (2)
N1—C1'—C2'—C3'	117.88 (19)	C4—N3—C2—O2'	178.7 (2)
N3—C4—C5—C6	−1.9 (5)	C4—N3—C2—N1	−2.3 (4)
C1'—O4'—C4'—C3'	−33.6 (2)	C4—C5—C6—N1	−0.8 (4)
C1'—O4'—C4'—C5'	89.1 (2)	C4'—O4'—C1'—N1	−88.8 (2)
C1'—N1—C2—O2'	3.9 (3)	C4'—O4'—C1'—C2'	21.4 (2)
C1'—N1—C2—N3	−175.3 (2)	C5'—O5'—C7—O7	−3.2 (4)
C1'—N1—C6—C5	175.9 (2)	C5'—O5'—C7—C8	177.0 (3)
C1'—C2'—C3'—O3'	96.3 (2)	C6—N1—C1'—O4'	−63.5 (3)
C1'—C2'—C3'—C4'	−19.0 (2)	C6—N1—C1'—C2'	−177.4 (2)
C2—O2'—C2'—C1'	0.7 (2)	C6—N1—C2—O2'	178.7 (2)
C2—O2'—C2'—C3'	−112.2 (2)	C6—N1—C2—N3	−0.5 (4)
C2—N1—C1'—O4'	110.7 (2)	C7—O5'—C5'—C4'	−148.2 (2)
C2—N1—C1'—C2'	−3.2 (3)	C9—O3'—C3'—C2'	165.25 (19)
C2—N1—C6—C5	2.0 (4)	C9—O3'—C3'—C4'	−83.3 (2)

Hydrogen-bond geometry (Å, º)

Cg is the centroid of the N1/C2/N3/C4–C6 ring [Added text OK?].

D—H···A	D—H	H···A	D···A	D—H···A
C1′—H1′···O4^i	0.98	2.36	3.308 (3)	162
C5′—H5′A···O4^ii	0.97	2.59	3.537 (3)	166
C5′—H5′B···Cg	0.97	2.50	3.026 (2)	114
C6—H6···O9^iii	0.93	2.42	3.313 (3)	162
C8—H8C···O4^iv	0.96	2.48	3.272 (4)	140
C6—H6···N3^i	0.93	2.68	3.226 (3)	118
C3′—H3′···O4′^v	0.98	2.37	3.311 (3)	161
C4′—H4′···O2′^iii	0.98	2.62	3.340 (3)	130

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