Tautomeric 6-oxoisocytidine (methanol solvate)

Ambiguity concerning the base structure of 6-oxoisocytidine methanol solvate {systematic name: 4-(R)-[4-amino-2,6-dioxo­pyrimidine-1-yl]-3(S)-hydroxy-2(R)-furanmethanol methanol solvate}, C₁₈H₁₈N₁₈O₁₈·CH₃OH, is resolved by the crystal structure reported here. The 3-imine N site is protonated and forms a hydrogen bond with the 6-oxo carbonyl group of an adjacent mol­ecule. The solid-state packing leads to the formation of sheets of mol­ecules with the intervening space occupied by disordered methanol solvent mol­ecules.

Key indicators

• Single-crystal X-ray study
• T = 180 K
• Mean [sigma](C-C) = 0.006 Å
• Disorder in solvent or counterion
• R factor = 0.052
• wR factor = 0.128
• Data-to-parameter ratio = 6.0

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry


 Alert Level B:



PLAT_420  Alert B D-H Without Acceptor       O3'    -   H3'               ?

Author response: The O3'-H3' hydroxyl group does in fact hydrogen bond to the disordered methanol solvent molecule. Please see the _geom_hbond_ table in the cif for details

 Alert Level C:



PLAT_302  Alert C Anion/Solvent Disorder .......................      25.00 Perc.

General Notes



REFLT_03
         From the CIF: _diffrn_reflns_theta_max           25.00
         From the CIF: _reflns_number_total               1237
         Count of symmetry unique reflns         1240
         Completeness (_total/calc)             99.76%
         TEST3: Check Friedels for noncentro structure
         Estimate of Friedel pairs measured         0
         Fraction of Friedel pairs measured     0.000
         Are heavy atom types Z>Si present           no
          Please check that the estimate of the number of Friedel pairs is
          correct. If it is not, please give the correct count in the
          _publ_section_exptl_refinement section of the submitted CIF.


 0 Alert Level A = Potentially serious problem

 1 Alert Level B = Potential problem

 1 Alert Level C = Please check

---

S1. Comment

Isomeric nucleosides (or isonucleosides), a novel class of nucleosides, have attracted much interest recently because of their significant anti-HIV and anti-HSV activity, as well as their stability towards acidic and enzymatic deamination (Nair & Jahnke, 1995). For example, 4(S)-(6-amino-9H-purin-9-yl)-tetrahydro-1(S)-furanmethanol (IsoddA), an isomeric dideoxynucleoside synthesized in our laboratory, has antiviral activity against HIV-1 and HIV-2 (Nair et al., 1995; Nair & Nuesca, 1992). In addition, it has been reported that the isodeoxynucleoside, IsodG, with guanine as the nucleobase, has activity against HSV-1 and HSV-2 (Kakefuda et al., 1994). Our interest in isomeric nucleosides with new nucleobases led us to the synthesis 6-oxoisocytidine (I). However, in the literature, there is some ambiguity about the structure of the base moiety of 6-oxocytidine. Two different structures have been suggested for this base moiety in compounds (II) (Falco et al., 1970) and (III) (Lipkin et al., 1968). Thus, it was important, not only to synthesize compound (I) for antiviral studies, but, prior to those biological studies, it was important to establish unequivocally the structure of the target molecule by physicochemical techniques including single-crystal X-ray data. The target nucleoside (I) was synthesized from 5-iodoisocytidine via anhydronucleoside intermediate.

The furanose ring adopts a C2'-envelope conformation. The envelope (O1'/C3'/C4'/C5') is nearly perpendicular [dihedral angle = 89.5 (2)°] to the planar cytidine ring (N1/C2/N3/C4/C5/C6; r.m.s. deviation = 0.003 Å). The CH₂OH equitorial substituent at C2' exhibits threefold disorder, with each of the C2'–C6' anti conformers equally represented. [The C6'—O6' orientation is anti to C2'—C3' (site 1), C6'B—O6'B is anti to C2'—O1' (site 2), and C6'C—O6'C is anti to C2'—H2'1 (site 3).]

The H3···O6 and H4B···O6 hydrogen bonds form ribbons of molecules parallel to the b axis. These ribbons stack parallel to the a axis to form sheets. The stacks are held together via π-stacking interactions [cytidine–cytidineⁱ = 3.419 Å and cytidine–cytidineⁱⁱ = 3.333 Å; symmetry codes: (i) 1 − x, −y, 0.5 + z; (ii) 2 − x, −y, 0.5 + z] and the H4A···O3' hydrogen bond. The inter-sheet space [centered on the (x, y, 0) and (x, y, 1/2) planes] is occupied by disordered methanol of solvation. Four partially occupied [occ(C21—O21) = 1/3, occ(C21'-O21') = 1/3, occ(C31—O31) = 0.166 and occ(C31'-O31') = 0.166] sites are included in the structure. The O3'—H3' hydroxyl group hydrogen bonds to the methanol O atom (for each of the disorder sites). There is a correlation between the location of the >C2'—CH₂OH substituent and the methanol disorder sites. For site 1, the methanol molecule is located at the C31—O31 and C31'—O31 sites, for site 2 at the C21'—O21' site, and for site 3 at the C21—O21 site. See Table 3 for the hydrogen-bonding geometries (including the disordered structure).

The conclusion from the X-ray data is supported by the high-field ¹³C NMR spectrum.

S2. Experimental

Compound A: to a solution of 5-iodoisocytidine (0.36 g, 1 mmol) in DMSO/t-BuOH (1:1, 40 ml) was added t-BuOK (0.45 g, 4 mmol). The reaction mixture was heated at 333 K for 24 h. The solution was neutralized with 0.5 M aqueous HCl, evaporated to dryness and purified over silica gel to give the anhydro derivative. The anhydro derivative was dissolved in 0.2 M Ba(OH)₂ (10 ml) and heated at 373 K for 1 h. The solution was neutralized with 0.5 M HCl and evaporated to dryness. The residue was purified over HPLC on C-18 reverse-phase column (H₂O/MeOH) to give A (0.04 g, 16%) as a white powder. Compound A was crystallized from MeOH (m.p. 454 K). ¹H NMR (DMSO-d₆, p.p.m.): 10.40 (bs, 1H); ¹³C NMR (DMSO-d₆, p.p.m.): 163.3, 153.8, 151.1, 85.0, 74.2, 71.2, 65.3, 61.9, 57.7; UV (MeOH): λ_max 266; HRMS (FAB): (M + H)⁺ calculated for C₉H₁₄N₃O₅ 244.0933, found 244.0923.

S3. Refinement

The CH₂OH substituent at C2' is disordered by rotation about the C2'—C6' bond to three orientations of equal occupancy (1/3). In one orientation (C6'/H6'1/H6'2/O6'/H6'), the C—O bond is anti to the C2'—C3' bond, another (C6'B/H6'3/H6'4/O6'B/H6'B) has the C—O bond anti to the C2'—O1' bond, and the third (C6'C/H6'5/H6'6/O6'C/H6'C) has the C—O bond anti to the C2'—H2'1 bond. The occupancies of each refined to approximately 1/3 so each was fixed to 0.3333 for the final refinement cycles. The coordinates of H2'1 were allowed to refine with a U_iso vale of 1.1U_iso(C2'). The methanol molecule of solvation is also disordered and each orientation was refined as a rigid group (C—H = 0.99 Å, C—O = 1.45 Å and O—H = 0.84 Å, tetrahedral angles). One orientation (C21/H21A—C/O21/H21) was refined with occupancy 0.3333 as was the second (C21'/H21D—F/O21'/H21'). For these two orientations, the C and O atoms were refined with individual isotropic displacement parameters. The third orientation exhibited high thermal motion and was split into two groups (C31/H31A—C/O31/H31 and C31'/H31D—F/O31'/H31') with occupancy 0.1666 and one isotropic displacement parameter for both C and both O atoms. All H atoms (except H2'1) were included with the riding model (or were part of a rigid group) with program defaults. The largest shift (0.034) occurred for the rotz parameter of the O31 rigid group. The average shift was 0.003. 433 Friedel pairs were merged for the final cycles of refinement.

Computing details

Data collection: COLLECT (Nonius, 1997-2000); cell refinement: HKL SCALEPACK (Otwinowski & Minor, 1997); data reduction: HKL DENZO (Otwinowski & Minor, 1997) and SCALEPACK; program(s) used to solve structure: SHELXTL (Sheldrick, 1997); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.

Figures

Fig. 1. View of the title compound. Displacement ellipsoids are shown at the 35% probability level. Only one orientation of the disorder CH2OH group is shown.

4-(R)-[4-amino-2,6-dioxopyrimidine-1-yl]-3(S)-hydroxy-2(R)-furan methanol solvate

Crystal data

C9H13N3O5·CH4O	Dx = 1.507 Mg m^−3
Mr = 275.27	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, C2221	Cell parameters from 4008 reflections
a = 6.7571 (14) Å	θ = 3.3–25.0°
b = 12.430 (3) Å	µ = 0.13 mm^−1
c = 28.880 (6) Å	T = 180 K
V = 2425.7 (9) Å^3	Plate, colorless
Z = 8	0.13 × 0.11 × 0.03 mm
F(000) = 1168

Data collection

Nonius KappaCCD diffractometer	1078 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.058
Graphite monochromator	θmax = 25.0°, θmin = 3.3°
Detector resolution: 9 pixels mm^-1	h = −8→8
CCD scans	k = −14→14
13640 measured reflections	l = −34→34
1237 independent reflections

Refinement

Refinement on F^2	Hydrogen site location: inferred from neighbouring sites
Least-squares matrix: full	H atoms treated by a mixture of independent and constrained refinement
R[F^2 > 2σ(F^2)] = 0.052	w = 1/[σ^2(Fo^2) + (0.0581P)^2 + 4.8516P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.128	(Δ/σ)max = 0.034
S = 1.06	Δρmax = 0.20 e Å^−3
1231 reflections	Δρmin = −0.26 e Å^−3
206 parameters	Extinction correction: SHELXTL, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
14 restraints	Extinction coefficient: 0.0091 (16)
Primary atom site location: structure-invariant direct methods	Absolute structure: syn
Secondary atom site location: difference Fourier map

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. 433 Friedel pairs were averaged during the final cycles of refinement. Disordered methanol solvent molecules refined as rigid groups. H atoms included with the riding model using program defaults.

11 reflections were removed as outliers.

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	Occ. (<1)
N1	0.7557 (7)	0.7210 (2)	0.31294 (11)	0.0254 (8)
C2	0.7575 (8)	0.8315 (3)	0.30362 (13)	0.0257 (9)
O2	0.7638 (6)	0.8993 (2)	0.33402 (9)	0.0337 (8)
N3	0.7515 (7)	0.8574 (3)	0.25810 (10)	0.0270 (8)
H3	0.7534	0.9262	0.2509	0.032*
C4	0.7425 (8)	0.7857 (3)	0.22244 (13)	0.0254 (9)
N4	0.7335 (7)	0.8274 (3)	0.17932 (11)	0.0322 (9)
H4B	0.7336	0.8976	0.1754	0.039*
H4A	0.7276	0.7844	0.1552	0.039*
C5	0.7424 (8)	0.6766 (3)	0.23169 (13)	0.0275 (10)
H5	0.7386	0.6259	0.2071	0.033*
C6	0.7481 (8)	0.6420 (3)	0.27765 (13)	0.0265 (9)
O6	0.7482 (6)	0.5458 (2)	0.29005 (9)	0.0340 (8)
O1'	0.8542 (5)	0.5247 (3)	0.40043 (13)	0.0429 (10)
C3'	0.5742 (7)	0.6229 (4)	0.37870 (16)	0.0270 (11)
H3'1	0.5290	0.5742	0.3533	0.032*
O3'	0.4135 (5)	0.6871 (2)	0.39306 (11)	0.0325 (8)
H3'	0.4549	0.7366	0.4103	0.049*
C4'	0.7601 (8)	0.6860 (3)	0.36203 (13)	0.0285 (10)
H4'1	0.7688	0.7526	0.3814	0.034*
C5'	0.9328 (8)	0.6156 (4)	0.37540 (18)	0.0357 (13)
H5'2	1.0040	0.5909	0.3474	0.043*
H5'1	1.0265	0.6562	0.3951	0.043*
C2'	0.6636 (7)	0.5566 (4)	0.41629 (17)	0.0336 (12)
H2'1	0.689 (7)	0.578 (4)	0.4466 (7)	0.040*
C6'	0.557 (4)	0.4481 (14)	0.4244 (8)	0.029 (2)	0.3333
H6'1	0.4127	0.4608	0.4277	0.035*	0.3333
H6'2	0.5774	0.4006	0.3973	0.035*	0.3333
O6'	0.6292 (15)	0.3976 (7)	0.4644 (3)	0.035 (2)	0.3333
H6'	0.6675	0.3352	0.4578	0.052*	0.3333
C6'B	0.537 (2)	0.4537 (11)	0.4210 (9)	0.029 (2)	0.3333
H6'3	0.5633	0.4082	0.3936	0.035*	0.3333
H6'4	0.5856	0.4137	0.4484	0.035*	0.3333
O6'B	0.3311 (15)	0.4630 (9)	0.4254 (4)	0.047 (3)	0.3333
H6'B	0.2794	0.4654	0.3990	0.070*	0.3333
C6'C	0.551 (3)	0.4647 (11)	0.4410 (5)	0.029 (2)	0.3333
H6'5	0.6251	0.4403	0.4687	0.035*	0.3333
H6'6	0.4181	0.4888	0.4507	0.035*	0.3333
O6'C	0.5379 (16)	0.3821 (10)	0.4083 (3)	0.039 (3)	0.3333
H6'C	0.6452	0.3773	0.3938	0.059*	0.3333
O21	0.0591 (18)	0.3522 (10)	0.4448 (4)	0.034 (3)*	0.3333
H21	−0.0104	0.3999	0.4321	0.051*	0.3333
C21	0.066 (2)	0.3710 (12)	0.4943 (4)	0.036 (4)*	0.3333
H21A	−0.0674	0.3602	0.5077	0.054*	0.3333
H21B	0.1601	0.3201	0.5088	0.054*	0.3333
H21C	0.1100	0.4457	0.5003	0.054*	0.3333
O21'	0.044 (2)	0.3421 (9)	0.4633 (5)	0.047 (3)*	0.3333
H21'	0.1510	0.3547	0.4494	0.070*	0.3333
C21'	0.087 (4)	0.3125 (17)	0.5109 (5)	0.070 (6)*	0.3333
H21D	−0.0285	0.2741	0.5242	0.105*	0.3333
H21E	0.2041	0.2648	0.5118	0.105*	0.3333
H21F	0.1135	0.3781	0.5293	0.105*	0.3333
O31	0.488 (3)	0.1606 (14)	0.5506 (7)	0.052 (4)*	0.1666
H31	0.4070	0.1233	0.5658	0.077*	0.1666
C31	0.677 (4)	0.107 (2)	0.5564 (10)	0.052 (4)*	0.1666
H31A	0.7805	0.1475	0.5392	0.077*	0.1666
H31B	0.7121	0.1054	0.5897	0.077*	0.1666
H31C	0.6690	0.0331	0.5443	0.077*	0.1666
O31'	0.470 (3)	0.2318 (15)	0.5193 (6)	0.052 (4)*	0.1666
H31'	0.5308	0.2905	0.5213	0.077*	0.1666
C31'	0.620 (4)	0.153 (3)	0.5076 (7)	0.052 (4)*	0.1666
H31D	0.5575	0.0810	0.5047	0.077*	0.1666
H31E	0.6826	0.1726	0.4778	0.077*	0.1666
H31F	0.7213	0.1507	0.5323	0.077*	0.1666

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
N1	0.0346 (19)	0.0194 (16)	0.0222 (17)	−0.003 (2)	0.000 (2)	−0.0008 (13)
C2	0.025 (2)	0.024 (2)	0.029 (2)	−0.003 (3)	−0.004 (2)	0.0034 (18)
O2	0.0476 (19)	0.0268 (15)	0.0267 (15)	−0.0099 (19)	−0.0022 (18)	−0.0095 (13)
N3	0.0358 (19)	0.0252 (16)	0.0201 (17)	0.000 (2)	0.001 (2)	0.0018 (13)
C4	0.023 (2)	0.029 (2)	0.024 (2)	0.000 (3)	0.005 (2)	−0.0015 (17)
N4	0.053 (2)	0.0216 (17)	0.0215 (18)	−0.004 (2)	0.003 (2)	0.0056 (14)
C5	0.027 (2)	0.030 (2)	0.025 (2)	0.000 (3)	−0.003 (3)	−0.0027 (17)
C6	0.027 (2)	0.028 (2)	0.025 (2)	0.002 (3)	0.002 (3)	−0.0008 (17)
O6	0.050 (2)	0.0250 (16)	0.0267 (15)	0.000 (2)	0.003 (2)	−0.0023 (12)
O1'	0.035 (2)	0.041 (2)	0.052 (2)	0.0084 (18)	0.0071 (18)	0.0136 (18)
C3'	0.033 (3)	0.021 (2)	0.027 (2)	−0.003 (2)	0.000 (2)	−0.006 (2)
O3'	0.0353 (18)	0.0309 (17)	0.0314 (18)	0.0062 (15)	−0.0002 (16)	0.0031 (14)
C4'	0.035 (2)	0.032 (2)	0.0185 (19)	0.000 (3)	0.003 (2)	0.0044 (17)
C5'	0.029 (3)	0.046 (3)	0.032 (3)	−0.008 (3)	0.000 (2)	0.008 (3)
C2'	0.038 (3)	0.035 (3)	0.028 (2)	−0.002 (2)	−0.004 (2)	0.017 (2)
C6'	0.036 (4)	0.031 (3)	0.019 (6)	0.004 (3)	0.008 (5)	0.013 (4)
O6'	0.055 (7)	0.023 (4)	0.025 (5)	0.013 (5)	0.006 (5)	0.014 (3)
C6'B	0.036 (4)	0.031 (3)	0.019 (6)	0.004 (3)	0.008 (5)	0.013 (4)
O6'B	0.045 (6)	0.052 (7)	0.043 (6)	−0.004 (5)	0.004 (5)	0.015 (5)
C6'C	0.036 (4)	0.031 (3)	0.019 (6)	0.004 (3)	0.008 (5)	0.013 (4)
O6'C	0.033 (6)	0.054 (7)	0.031 (6)	0.008 (5)	0.008 (5)	−0.011 (5)

Geometric parameters (Å, º)

N1—C2	1.399 (5)	O6'—H6'	0.8400
N1—C6	1.417 (5)	C6'B—O6'B	1.399 (11)
N1—C4'	1.483 (5)	C6'B—H6'3	0.9900
C2—O2	1.218 (5)	C6'B—H6'4	0.9900
C2—N3	1.354 (5)	O6'B—H6'B	0.8400
N3—C4	1.364 (5)	C6'C—O6'C	1.397 (10)
N3—H3	0.8800	C6'C—H6'5	0.9900
C4—N4	1.350 (5)	C6'C—H6'6	0.9900
C4—C5	1.381 (6)	O6'C—H6'C	0.8400
N4—H4B	0.8800	O21—C21	1.45
N4—H4A	0.8800	O21—H21	0.84
C5—C6	1.396 (5)	C21—H21A	0.99
C5—H5	0.9500	C21—H21B	0.99
C6—O6	1.248 (5)	C21—H21C	0.99
O1'—C2'	1.423 (6)	O21'—C21'	1.45
O1'—C5'	1.442 (6)	O21'—H21'	0.84
C3'—O3'	1.410 (6)	C21'—H21D	0.99
C3'—C2'	1.491 (7)	C21'—H21E	0.99
C3'—C4'	1.557 (7)	C21'—H21F	0.99
C3'—H3'1	1.0000	O31—C31	1.45
O3'—H3'	0.8400	O31—H31	0.84
C4'—C5'	1.509 (7)	C31—H31A	0.99
C4'—H4'1	1.0000	C31—H31B	0.99
C5'—H5'2	0.9900	C31—H31C	0.99
C5'—H5'1	0.9900	O31'—C31'	1.45
C2'—C6'	1.547 (9)	O31'—H31'	0.84
C2'—H2'1	0.932 (11)	C31'—H31D	0.99
C6'—O6'	1.405 (10)	C31'—H31E	0.99
C6'—H6'1	0.9900	C31'—H31F	0.99
C6'—H6'2	0.9900
C2—N1—C6	122.8 (3)	C3'—C2'—H2'1	127 (3)
C2—N1—C4'	118.1 (3)	C6'—C2'—H2'1	101 (3)
C6—N1—C4'	119.0 (3)	O6'—C6'—C2'	110.5 (9)
O2—C2—N3	122.4 (4)	O6'—C6'—H6'1	109.5
O2—C2—N1	122.7 (3)	C2'—C6'—H6'1	109.5
N3—C2—N1	114.9 (3)	O6'—C6'—H6'2	109.5
C2—N3—C4	125.4 (3)	C2'—C6'—H6'2	109.5
C2—N3—H3	117.3	H6'1—C6'—H6'2	108.1
C4—N3—H3	117.3	C6'—O6'—H6'	109.5
N4—C4—N3	116.6 (3)	O6'B—C6'B—H6'3	107.5
N4—C4—C5	123.7 (4)	O6'B—C6'B—H6'4	107.5
N3—C4—C5	119.7 (4)	H6'3—C6'B—H6'4	107.0
C4—N4—H4B	120.0	C6'B—O6'B—H6'B	109.5
C4—N4—H4A	120.0	O6'C—C6'C—H6'5	110.7
H4B—N4—H4A	120.0	O6'C—C6'C—H6'6	110.7
C4—C5—C6	119.1 (4)	H6'5—C6'C—H6'6	108.8
C4—C5—H5	120.4	C6'C—O6'C—H6'C	109.5
C6—C5—H5	120.4	C21—O21—H21	109.5
O6—C6—C5	124.7 (4)	O21—C21—H21A	109.5
O6—C6—N1	117.2 (3)	O21—C21—H21B	109.5
C5—C6—N1	118.1 (3)	O21—C21—H21C	109.5
C2'—O1'—C5'	106.1 (4)	H21A—C21—H21B	109.4
O3'—C3'—C2'	114.3 (4)	H21A—C21—H21C	109.4
O3'—C3'—C4'	115.3 (4)	H21B—C21—H21C	109.4
C2'—C3'—C4'	100.2 (4)	C21'—O21'—H21'	109.5
O3'—C3'—H3'1	108.9	O21'—C21'—H21D	109.5
C2'—C3'—H3'1	108.9	O21'—C21'—H21E	109.5
C4'—C3'—H3'1	108.9	O21'—C21'—H21F	109.5
C3'—O3'—H3'	109.5	H21D—C21'—H21E	109.4
N1—C4'—C5'	115.5 (4)	H21D—C21'—H21F	109.4
N1—C4'—C3'	115.3 (4)	H21E—C21'—H21F	109.4
C5'—C4'—C3'	104.6 (3)	C31—O31—H31	105.2
N1—C4'—H4'1	107.0	O31—C31—H31A	109.5
C5'—C4'—H4'1	107.0	O31—C31—H31B	109.5
C3'—C4'—H4'1	107.0	O31—C31—H31C	109.5
O1'—C5'—C4'	107.3 (4)	H31A—C31—H31B	109.4
O1'—C5'—H5'2	110.3	H31A—C31—H31C	109.4
C4'—C5'—H5'2	110.3	H31B—C31—H31C	109.4
O1'—C5'—H5'1	110.2	C31'—O31'—H31'	105.2
C4'—C5'—H5'1	110.3	O31'—C31'—H31D	109.5
H5'2—C5'—H5'1	108.5	O31'—C31'—H31E	109.5
O1'—C2'—C3'	106.6 (4)	O31'—C31'—H31F	109.5
O1'—C2'—C6'	103.2 (12)	H31D—C31'—H31E	109.4
C3'—C2'—C6'	113.7 (6)	H31D—C31'—H31F	109.4
O1'—C2'—H2'1	102 (3)	H31E—C31'—H31F	109.4
C6—N1—C2—O2	179.9 (5)	C2—N1—C4'—C3'	116.8 (5)
C4'—N1—C2—O2	0.4 (9)	C6—N1—C4'—C3'	−62.7 (6)
C6—N1—C2—N3	0.0 (8)	O3'—C3'—C4'—N1	−84.2 (5)
C4'—N1—C2—N3	−179.4 (4)	C2'—C3'—C4'—N1	152.7 (4)
O2—C2—N3—C4	−179.4 (5)	O3'—C3'—C4'—C5'	147.8 (4)
N1—C2—N3—C4	0.5 (8)	C2'—C3'—C4'—C5'	24.7 (4)
C2—N3—C4—N4	178.7 (5)	C2'—O1'—C5'—C4'	−20.1 (5)
C2—N3—C4—C5	−1.1 (8)	N1—C4'—C5'—O1'	−131.7 (4)
N4—C4—C5—C6	−178.7 (5)	C3'—C4'—C5'—O1'	−3.9 (4)
N3—C4—C5—C6	1.1 (8)	C5'—O1'—C2'—C3'	37.8 (5)
C4—C5—C6—O6	179.9 (5)	C5'—O1'—C2'—C6'	157.8 (7)
C4—C5—C6—N1	−0.6 (8)	O3'—C3'—C2'—O1'	−162.1 (4)
C2—N1—C6—O6	179.6 (5)	C4'—C3'—C2'—O1'	−38.3 (4)
C4'—N1—C6—O6	−1.0 (8)	O3'—C3'—C2'—C6'	84.8 (14)
C2—N1—C6—C5	0.1 (8)	C4'—C3'—C2'—C6'	−151.4 (14)
C4'—N1—C6—C5	179.5 (5)	O1'—C2'—C6'—O6'	74 (2)
C2—N1—C4'—C5'	−120.9 (5)	C3'—C2'—C6'—O6'	−171.2 (14)
C6—N1—C4'—C5'	59.7 (6)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N3—H3···O6^i	0.88	1.90	2.724 (4)	155
N4—H4A···O3′^ii	0.88	2.08	2.898 (5)	155
N4—H4B···O6^i	0.88	2.10	2.858 (5)	144
O6′—H6′···O31^iii	0.84	2.18	2.57 (3)	108
O6′—H6′···O31′^iii	0.84	2.30	2.85 (5)	123
O6′B—H6′B···O2^iv	0.84	2.05	2.793 (12)	147
O6′C—H6′C···N4^v	0.84	2.35	3.041 (10)	140
O6′C—H6′C···O1′	0.84	2.32	2.786 (12)	115
O3′—H3′···O21^vi	0.84	1.88	2.722 (12)	175
O3′—H3′···O21′^vi	0.84	2.11	2.936 (13)	170
O3′—H3′···O31^vii	0.84	1.72	2.55 (2)	168
O3′—H3′···O31′^vii	0.84	2.07	2.75 (15)	137
O21—H21···O1′^viii	0.84	2.02	2.856 (13)	173
O21′—H21′···O6′B	0.84	1.94	2.68 (2)	147
O31—H31···O1′^ix	0.84	2.11	2.851 (15)	146
O31′—H31′···O6′	0.84	2.22	2.81 (2)	128

Symmetry codes: (i) −x+3/2, y+1/2, −z+1/2; (ii) −x+1, y, −z+1/2; (iii) x+1/2, −y+1/2, −z+1; (iv) x−1/2, y−1/2, z; (v) −x+3/2, y−1/2, −z+1/2; (vi) x+1/2, y+1/2, z; (vii) x, −y+1, −z+1; (viii) x−1, y, z; (ix) x−1/2, −y+1/2, −z+1.