The regioisomeric 1H(2H)-pyrazolo[3,4-d]pyrimidine N¹- and N²-(2′-deoxy-β-D-ribofuranosides)

In the title regioisomeric nucleosides, alternatively called 1-(2-deoxy-β-D-erythro-furan­osyl)-1H-pyrazolo­[3,4-d]­pyrimidine, C₁₀H₁₂N₄O₃, (II), and 2-(2-deoxy-β-D-erythro-furan­osyl)-2H-pyrazolo­[3,4-d]pyrimidine, C₁₀H₁₂N₄O₃, (III), the conformations of the gly­cosyl­ic bonds are anti [−100.4 (2)° for (II) and 15.0 (2)° for (III)]. Both nucleosides adopt an S-type sugar pucker, which is C2′-endo-C3′-exo (²T₃) for (II) and 3′-exo (between ₃E and ⁴T₃) for (III).

S1. Comment

During a search for more stable `dA-dT' base pairs, various 3-substituted pyrazolo[3,4-d]pyrimidine 2'-deoxyribonucleosides (7-substituted 8-aza-7-deazapurine 2'-deoxyribonucleosides) were studied as analogues of 2'-deoxyadenosine and were incorporated in oligonucleotides (systematic numbering is used throughout the paper). The interchange of the five-membered ring atoms and the presence of substituents (Br or I) on the 3-position in the modified purine bases exert an influence on the base-pair stability (Seela, Becher & Zulauf, 1999; He & Seela, 2002a). Common 2'-deoxyribonucleosides tend to adopt an anti conformation. The orientation of the base relative to the sugar (syn/anti) is defined by the torsion angle χ (O4'—C1'—N9—C4) (purine numbering; IUPAC-IUB Joint Commision on Biochemical Nomenclature, 1983). 2'-Deoxyadenosine shows an anti conformation, with a torsion angle χ (O4'—C1'—N1—C7a) of -165.1° (Sato, 1984), while that of pyrazolo[3,4-d]pyrimidin-4-amine 2'-deoxyribonucleoside (8-aza-7-deaza-2'-deoxyadenosine), (I), is between an anti and a high-anti conformation [χ = -106.3 (2)°; Seela, Zulauf et al., 1999]. Further substitution (Br or I) at the 3-position drives the conformation to high-anti [for the 3-bromo derivative, χ = -74.1 (4)°, while for the 3-iodo derivative, χ = -73.2 (4)°; Seela et al., 2000]. The steric and stereo-electronic effects of the nucleobases are supposed to be responsible for this change.

To the best of our knowledge, there is no reported crystal structure of a pyrazolo[3,4-d]pyrimidin-2-yl 2'-deoxyribonucleoside. Here, the X-ray crystallographic analyses of a pair of N¹– and N²-glycosylated pyrazolo[3,4-d]pyrimidines, viz. (II) and (III), respectively, are described. Both nucleosides have the same β-D configuration. According to the systematic numbering for compound (II), the torsion angle χ is defined by O4'—C1'—N1—C7a. The definition for the N²-nucleoside, (II), follows that of other N²-nucleosides (Seela & Debelak, 2000). Here, the base is anti relative to the sugar moiety when the distance between H—C1' and H—C3 is minimal and syn when this distance is maximal, which is different from that of common nucleosides. Thus, the torsion angle is defined, in this case, by O4'—C1'—N2—C3.

From the crystal structure of compound (II) (Fig. 1), the conformation of the glycosylic bond is between the anti and the high-anti range, χ = -100.4 (2)°, which is very close to that of compound (I) (Seela, Zulauf et al., 1999). Compound (III) adopts an anti conformation, with χ = 15.0 (2)°. The glycosylic bond between atoms N2 and C1' of compound (III) is 0.034 Å longer than that between atoms N1 and C1' of compound (II).

Both nucleosides show an S-type sugar conformation, but with different ring puckering. The sugar conformation of nucleoisde (II) is C2'-endo-C3'-exo (²T₃), with pseudo-rotation parameters (Rao et al., 1981) P = 185.6 (2)° and τ_m = 40.3 (1)°, while the sugar part of nucleoside (III) is 3'-exo (between ₃E and ⁴T₃), with P = 203.3 (1)° and τ_m = 37.0 (1)°. These two nucleosides have the same ap (g-) conformation about the C4'—C5' bond; the values of γ (C3'—C4'—C5'—O5') are 177.97 (18) and 175.73 (13)° for (II) and (III), respectively. This means that the base and the hydroxymethyl group undergo the same disrotatory motion so that the Coulomb repulsion between atoms N2 and O5' or between atoms N1 and O4' is minimized (Seela, Becher et al., 1999). Similarly, nucleoside (I) adopts the C2'-endo-C3'-exo-type (S-type) sugar puckering, but with an -ap conformation around the C4'—C5' bond [γ = -178.73 (16)°; Seela, Zulauf et al., 1999], while 2'-deoxyadenosine has a C3'-endo conformation (Sato, 1984). These results have an influence on the stability of oligonucleotide duplexes (He & Seela, 2002a).

The base moieties of (II) and (III) are nearly planar. The r.m.s. deviations of the ring atoms (N1/N2/C3/C3a/C4/N5/C6/N7/C7A) from their calculated least-squares planes are 0.018 and 0.013 Å, respectively, with the maximum deviations being 0.028 (2) (N1) and 0.019 (1) Å (C3A), respectively. Atom C1' is displaced from this plane by 0.033 (2) and 0.139 (1) Å in (II) and (III), respectively. The bases are strongly stacked in both crystal structures.

Structures (II) and (III), which differ only in the glycosylation positions (N1 versus N2), each form two different types of hydrogen bonds. Structure (II) is stabilized by intermolecular hydrogen bonds between O3'—H and O4'(2 - x, y - 1/2, 3/2 - z) of two sugar moieties and between O5'—OH of the sugar moiety and N7(1 + x, y, z) of an adjacent nucleobase unit. These interactions link the molecules into an infinite two-dimensional network in which the bases are stacked and tilted against each other. In contrast, structure (III) is stabilized by hydrogen bonds between the bases and the sugar units exclusively [O3'—H with N7(1 - x, 1/2 + y, 2 - z) and O5'—H with N5(2 - x, 1/2 + y, 1 - z)]. These interactions link the molecules into an infinite two-dimensional network, with piles of stacked bases tilted only slightly against each other.

S2. Experimental

Nucleoside (II) (Seela & Steker, 1984) was prepared by the glycosylation reaction of pyrazolo[3,4-d]pyrimidine with 2-deoxy-3,5-di-O-(p-toluoyl)-α-D-erythro-furanosyl chloride (Hoffer, 1960), followed by deprotection of the sugar moiety (He & Seela, 2002b); m.p.: 421 K, R_F (silica gel thin-layer chromatography): 0.22 (CH₂Cl₂/CH₃OH, 9:1). Suitable crystals were grown from a solution in methanol. Nucleoside (III) was obtained as the minor product from the above glycosylation reaction followed by the deprotection of the sugar moiety; m.p.: 427 K, R_F (silica gel thin-layer chromatography): 0.13 (CH₂Cl₂/CH₃OH, 9:1). Suitable crystals were grown from a solution in acetone.

S3. Refinement

In the absence of suitable anomalous scattering, Friedel equivalents could not be use to determine the absotute structure. Refinement of the Flack (1983) parameter led to inconclusive values (Flack & Bernardinelli, 2000) for this parameter [-0.2 (16) for (II) and 0.4 (10) for (III)]. Therefore, the Friedel equivalents [416 for (II) and 119 for (III)] were merged before the final refinements. The known configuration of the parent molecule was used to define the enantiomer employed in the refined model. All H atoms were initially found in a difference Fourier synthesis. In order to maximize the data-to-parameter ratio, the H atoms bonded to C atoms were placed in geometrically idealized positions (C—H = 0.93–0.98 Å) and constrained to ride on their parent atoms. The hydroxy H atoms were initially placed in the difference map positions, then geometrically idealized and constrained to ride on their parent O atoms, although the chemically equivalent O—H bond lengths were allowed to refine while being constrained to be equal. An overall isotropic displacement parameter was refined for all H atoms.

Computing details

For both compounds, 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.

Figures

Fig. 1. Perspective views of nucleosides (II) (top) and (III) (bottom). Displacement ellipsoids for non-H atoms are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary size.

(II) 1-(2-deoxy-β-D-erythro-furanosyl)-1H-pyrazolo[3,4-d]pyrimidine

Crystal data

C10H12N4O3	Dx = 1.481 Mg m^−3
Mr = 236.24	Melting point: 421.15 K
Orthorhombic, P212121	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2ac 2ab	Cell parameters from 40 reflections
a = 6.9306 (8) Å	θ = 6.9–12.5°
b = 11.1084 (15) Å	µ = 0.11 mm^−1
c = 13.7591 (11) Å	T = 293 K
V = 1059.3 (2) Å^3	Transparent needle, colourless
Z = 4	0.58 × 0.28 × 0.28 mm
F(000) = 496

Data collection

Bruker P4 diffractometer	Rint = 0.021
Radiation source: fine-focus sealed tube	θmax = 30.0°, θmin = 2.4°
Graphite monochromator	h = −1→9
2θ/ω scans	k = −15→1
2375 measured reflections	l = −19→1
1784 independent reflections	3 standard reflections every 97 reflections
1474 reflections with I > 2σ(I)	intensity decay: none

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)] = 0.042	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.105	w = 1/[σ^2(Fo^2) + (0.0518P)^2 + 0.1719P] where P = (Fo^2 + 2Fc^2)/3
S = 1.03	(Δ/σ)max < 0.001
1784 reflections	Δρmax = 0.21 e Å^−3
164 parameters	Δρmin = −0.18 e Å^−3
4 restraints	Extinction correction: SHELXTL, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.023 (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	0.8924 (3)	0.39168 (15)	0.57596 (12)	0.0360 (4)
N2	1.0487 (3)	0.40571 (19)	0.51553 (14)	0.0477 (5)
C3	1.0090 (4)	0.4989 (2)	0.45950 (16)	0.0479 (6)
H3A	1.0911	0.5288	0.4118	0.051 (2)*
C3A	0.8249 (3)	0.54761 (19)	0.48135 (15)	0.0379 (5)
C4	0.7003 (4)	0.6378 (2)	0.44932 (17)	0.0463 (6)
H4A	0.7374	0.6872	0.3981	0.051 (2)*
N5	0.5300 (3)	0.65408 (18)	0.49068 (15)	0.0520 (5)
C6	0.4842 (4)	0.5813 (2)	0.56550 (18)	0.0489 (6)
H6A	0.3653	0.5956	0.5947	0.051 (2)*
N7	0.5877 (3)	0.49145 (16)	0.60313 (12)	0.0379 (4)
C7A	0.7571 (3)	0.47689 (16)	0.55842 (13)	0.0310 (4)
C1'	0.8940 (3)	0.30189 (17)	0.65227 (14)	0.0342 (4)
H1'A	0.7628	0.2935	0.6779	0.051 (2)*
C2'	0.9654 (4)	0.17831 (17)	0.62058 (15)	0.0412 (5)
H2'A	1.0645	0.1845	0.5710	0.051 (2)*
H2'B	0.8606	0.1286	0.5966	0.051 (2)*
O3'	0.8964 (3)	0.09209 (14)	0.77947 (14)	0.0558 (5)
H3'O	0.877 (4)	0.0222 (19)	0.7689 (17)	0.051 (2)*
C3'	1.0469 (3)	0.12955 (16)	0.71604 (15)	0.0366 (5)
H3'C	1.1407	0.0651	0.7048	0.051 (2)*
C4'	1.1416 (3)	0.24088 (16)	0.75843 (13)	0.0323 (4)
H4'	1.1428	0.2349	0.8295	0.051 (2)*
O4'	1.0180 (3)	0.33941 (11)	0.72936 (10)	0.0393 (4)
C5'	1.3446 (4)	0.2612 (2)	0.72202 (16)	0.0451 (5)
H5'A	1.4254	0.1936	0.7404	0.051 (2)*
H5'B	1.3440	0.2668	0.6517	0.051 (2)*
O5'	1.4201 (3)	0.3684 (2)	0.76204 (12)	0.0683 (6)
H5'O	1.483 (4)	0.401 (2)	0.7210 (16)	0.051 (2)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
N1	0.0363 (9)	0.0364 (8)	0.0354 (8)	0.0026 (8)	0.0028 (8)	0.0077 (7)
N2	0.0410 (10)	0.0561 (11)	0.0461 (9)	0.0032 (10)	0.0103 (9)	0.0122 (9)
C3	0.0466 (13)	0.0568 (13)	0.0402 (10)	−0.0023 (12)	0.0071 (11)	0.0144 (10)
C3A	0.0445 (12)	0.0370 (10)	0.0323 (9)	−0.0062 (9)	−0.0047 (10)	0.0029 (8)
C4	0.0593 (15)	0.0379 (10)	0.0417 (11)	−0.0043 (11)	−0.0107 (11)	0.0090 (10)
N5	0.0586 (13)	0.0423 (10)	0.0551 (11)	0.0082 (10)	−0.0069 (11)	0.0093 (9)
C6	0.0463 (13)	0.0447 (11)	0.0556 (13)	0.0100 (11)	0.0005 (13)	0.0018 (11)
N7	0.0386 (9)	0.0349 (8)	0.0402 (8)	0.0008 (8)	0.0014 (8)	0.0011 (7)
C7A	0.0357 (10)	0.0277 (8)	0.0296 (8)	−0.0028 (8)	−0.0068 (8)	−0.0011 (8)
C1'	0.0375 (10)	0.0291 (8)	0.0361 (9)	0.0008 (8)	−0.0006 (9)	0.0046 (8)
C2'	0.0519 (13)	0.0279 (9)	0.0437 (10)	−0.0034 (10)	−0.0042 (10)	−0.0079 (8)
O3'	0.0634 (12)	0.0287 (7)	0.0754 (11)	−0.0061 (8)	0.0228 (11)	0.0080 (8)
C3'	0.0439 (11)	0.0216 (7)	0.0444 (10)	0.0019 (8)	0.0067 (10)	0.0007 (8)
C4'	0.0419 (11)	0.0253 (8)	0.0297 (8)	0.0037 (8)	0.0016 (9)	0.0029 (7)
O4'	0.0573 (10)	0.0230 (6)	0.0378 (7)	0.0074 (7)	−0.0082 (8)	−0.0025 (5)
C5'	0.0461 (12)	0.0483 (12)	0.0408 (10)	−0.0065 (11)	0.0039 (11)	−0.0028 (10)
O5'	0.0808 (14)	0.0824 (13)	0.0418 (8)	−0.0455 (12)	0.0150 (10)	−0.0154 (9)

Geometric parameters (Å, º)

N1—C7A	1.354 (3)	C1'—H1'A	0.9800
N1—N2	1.374 (2)	C2'—C3'	1.529 (3)
N1—C1'	1.448 (2)	C2'—H2'A	0.9700
N2—C3	1.320 (3)	C2'—H2'B	0.9700
C3—C3A	1.418 (3)	O3'—C3'	1.422 (3)
C3—H3A	0.9300	O3'—H3'O	0.80 (2)
C3A—C4	1.394 (3)	C3'—C4'	1.517 (3)
C3A—C7A	1.401 (3)	C3'—H3'C	0.9800
C4—N5	1.323 (3)	C4'—O4'	1.446 (2)
C4—H4A	0.9300	C4'—C5'	1.510 (3)
N5—C6	1.347 (3)	C4'—H4'	0.9800
C6—N7	1.334 (3)	C5'—O5'	1.412 (3)
C6—H6A	0.9300	C5'—H5'A	0.9700
N7—C7A	1.335 (3)	C5'—H5'B	0.9700
C1'—O4'	1.427 (2)	O5'—H5'O	0.80 (2)
C1'—C2'	1.523 (3)
C7A—N1—N2	111.02 (16)	C1'—C2'—C3'	101.15 (15)
C7A—N1—C1'	128.04 (18)	C1'—C2'—H2'A	111.5
N2—N1—C1'	120.69 (17)	C3'—C2'—H2'A	111.5
C3—N2—N1	106.14 (19)	C1'—C2'—H2'B	111.5
N2—C3—C3A	111.3 (2)	C3'—C2'—H2'B	111.5
N2—C3—H3A	124.4	H2'A—C2'—H2'B	109.4
C3A—C3—H3A	124.4	C3'—O3'—H3'O	107.1 (16)
C4—C3A—C7A	115.8 (2)	O3'—C3'—C4'	108.66 (17)
C4—C3A—C3	139.9 (2)	O3'—C3'—C2'	111.1 (2)
C7A—C3A—C3	104.37 (19)	C4'—C3'—C2'	101.62 (15)
N5—C4—C3A	121.0 (2)	O3'—C3'—H3'C	111.7
N5—C4—H4A	119.5	C4'—C3'—H3'C	111.7
C3A—C4—H4A	119.5	C2'—C3'—H3'C	111.7
C4—N5—C6	117.2 (2)	O4'—C4'—C5'	110.30 (16)
N7—C6—N5	128.3 (2)	O4'—C4'—C3'	104.74 (16)
N7—C6—H6A	115.9	C5'—C4'—C3'	113.41 (17)
N5—C6—H6A	115.9	O4'—C4'—H4'	109.4
C6—N7—C7A	112.62 (19)	C5'—C4'—H4'	109.4
N7—C7A—N1	127.69 (18)	C3'—C4'—H4'	109.4
N7—C7A—C3A	125.15 (19)	C1'—O4'—C4'	109.93 (14)
N1—C7A—C3A	107.15 (19)	O5'—C5'—C4'	110.00 (19)
O4'—C1'—N1	110.02 (16)	O5'—C5'—H5'A	109.7
O4'—C1'—C2'	106.30 (16)	C4'—C5'—H5'A	109.7
N1—C1'—C2'	114.57 (16)	O5'—C5'—H5'B	109.7
O4'—C1'—H1'A	108.6	C4'—C5'—H5'B	109.7
N1—C1'—H1'A	108.6	H5'A—C5'—H5'B	108.2
C2'—C1'—H1'A	108.6	C5'—O5'—H5'O	107.9 (16)
C7A—N1—N2—C3	−0.8 (3)	C3—C3A—C7A—N1	−1.9 (2)
C1'—N1—N2—C3	−175.5 (2)	C7A—N1—C1'—O4'	−100.4 (2)
N1—N2—C3—C3A	−0.5 (3)	N2—N1—C1'—O4'	73.3 (2)
N2—C3—C3A—C4	−177.2 (3)	C7A—N1—C1'—C2'	139.9 (2)
N2—C3—C3A—C7A	1.5 (3)	N2—N1—C1'—C2'	−46.4 (3)
C7A—C3A—C4—N5	0.4 (3)	O4'—C1'—C2'—C3'	30.5 (2)
C3—C3A—C4—N5	178.9 (3)	N1—C1'—C2'—C3'	152.21 (19)
C3A—C4—N5—C6	1.0 (3)	C1'—C2'—C3'—O3'	76.1 (2)
C4—N5—C6—N7	−1.6 (4)	C1'—C2'—C3'—C4'	−39.3 (2)
N5—C6—N7—C7A	0.6 (3)	O3'—C3'—C4'—O4'	−82.19 (18)
C6—N7—C7A—N1	−177.3 (2)	C2'—C3'—C4'—O4'	35.0 (2)
C6—N7—C7A—C3A	1.0 (3)	O3'—C3'—C4'—C5'	157.48 (17)
N2—N1—C7A—N7	−179.71 (19)	C2'—C3'—C4'—C5'	−85.3 (2)
C1'—N1—C7A—N7	−5.5 (3)	N1—C1'—O4'—C4'	−133.65 (17)
N2—N1—C7A—C3A	1.8 (2)	C2'—C1'—O4'—C4'	−9.1 (2)
C1'—N1—C7A—C3A	176.0 (2)	C5'—C4'—O4'—C1'	105.76 (19)
C4—C3A—C7A—N7	−1.4 (3)	C3'—C4'—O4'—C1'	−16.6 (2)
C3—C3A—C7A—N7	179.51 (19)	O4'—C4'—C5'—O5'	60.9 (2)
C4—C3A—C7A—N1	177.12 (18)	C3'—C4'—C5'—O5'	177.97 (18)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O3′—H3′O···O4′^i	0.80 (2)	2.16 (2)	2.871 (2)	149 (3)
O5′—H5′O···N7^ii	0.80 (2)	2.04 (2)	2.828 (3)	168 (3)

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

(III) 2-(2-deoxy-β-D-erythro-furanosyl)-2H-pyrazolo[3,4-d]pyrimidine

Crystal data

C10H12N4O3	F(000) = 248
Mr = 236.24	Dx = 1.514 Mg m^−3
Monoclinic, P21	Melting point: 427.15 K
Hall symbol: P 2yb	Mo Kα radiation, λ = 0.71073 Å
a = 4.9396 (7) Å	Cell parameters from 47 reflections
b = 13.1528 (14) Å	θ = 4.5–16.1°
c = 8.1780 (12) Å	µ = 0.12 mm^−1
β = 102.772 (9)°	T = 293 K
V = 518.17 (12) Å^3	Transparent block, yellow
Z = 2	0.57 × 0.57 × 0.48 mm

Data collection

Bruker P4 diffractometer	Rint = 0.021
Radiation source: fine-focus sealed tube	θmax = 30.0°, θmin = 3.0°
Graphite monochromator	h = −6→1
2θ/ω scans	k = −1→18
2202 measured reflections	l = −11→11
1562 independent reflections	3 standard reflections every 97 reflections
1524 reflections with I > 2σ(I)	intensity decay: none

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)] = 0.033	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.092	w = 1/[σ^2(Fo^2) + (0.0637P)^2 + 0.0228P] where P = (Fo^2 + 2Fc^2)/3
S = 1.07	(Δ/σ)max < 0.001
1562 reflections	Δρmax = 0.28 e Å^−3
164 parameters	Δρmin = −0.20 e Å^−3
51 restraints	Extinction correction: SHELXTL, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.026 (9)

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	0.5700 (3)	0.34085 (10)	0.75921 (16)	0.0342 (3)
N2	0.5129 (3)	0.44193 (10)	0.74881 (15)	0.0298 (3)
C3	0.6151 (3)	0.49316 (12)	0.63402 (17)	0.0319 (3)
H3	0.5962	0.5621	0.6090	0.0445 (17)*
C3A	0.7568 (3)	0.42020 (12)	0.55988 (17)	0.0302 (3)
C4	0.9209 (3)	0.41530 (13)	0.43949 (18)	0.0344 (3)
H4	0.9559	0.4739	0.3840	0.0445 (17)*
N5	1.0250 (3)	0.32733 (12)	0.40560 (17)	0.0380 (3)
C6	0.9690 (4)	0.24315 (15)	0.4897 (2)	0.0413 (4)
H6	1.0398	0.1821	0.4599	0.0445 (17)*
N7	0.8271 (3)	0.23774 (12)	0.60788 (18)	0.0400 (3)
C7A	0.7196 (3)	0.32771 (11)	0.64265 (17)	0.0306 (3)
C1'	0.3648 (3)	0.48283 (11)	0.87360 (17)	0.0299 (3)
H1'C	0.2016	0.4407	0.8748	0.0445 (17)*
C2'	0.5555 (3)	0.48418 (13)	1.04885 (18)	0.0344 (3)
H2'A	0.5155	0.4278	1.1163	0.0445 (17)*
H2'B	0.7494	0.4816	1.0430	0.0445 (17)*
C3'	0.4834 (3)	0.58572 (12)	1.11851 (17)	0.0315 (3)
H3'C	0.6403	0.6130	1.2019	0.0445 (17)*
O3'	0.2466 (3)	0.57069 (10)	1.18791 (17)	0.0433 (3)
H3'O	0.218 (4)	0.6217 (14)	1.244 (3)	0.0445 (17)*
C4'	0.4171 (3)	0.65211 (11)	0.96105 (17)	0.0287 (3)
H4O'	0.2865	0.7056	0.9758	0.0445 (17)*
O4'	0.2806 (2)	0.58275 (9)	0.82936 (13)	0.0330 (2)
C5'	0.6703 (3)	0.70013 (13)	0.91727 (19)	0.0337 (3)
H5'B	0.7573	0.7469	1.0049	0.0445 (17)*
H5'C	0.8043	0.6481	0.9062	0.0445 (17)*
O5'	0.5824 (3)	0.75256 (14)	0.76418 (19)	0.0530 (4)
H5'O	0.717 (4)	0.774 (2)	0.727 (2)	0.0445 (17)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
N1	0.0468 (7)	0.0271 (6)	0.0327 (6)	0.0008 (5)	0.0172 (5)	0.0007 (4)
N2	0.0364 (6)	0.0274 (6)	0.0274 (5)	−0.0008 (4)	0.0106 (4)	−0.0012 (4)
C3	0.0377 (6)	0.0297 (6)	0.0296 (6)	−0.0015 (5)	0.0106 (5)	0.0015 (5)
C3A	0.0346 (6)	0.0302 (6)	0.0264 (5)	−0.0025 (5)	0.0079 (5)	0.0012 (5)
C4	0.0373 (7)	0.0392 (8)	0.0283 (6)	−0.0038 (6)	0.0103 (5)	0.0031 (5)
N5	0.0401 (6)	0.0449 (7)	0.0322 (6)	0.0011 (6)	0.0150 (5)	−0.0008 (6)
C6	0.0513 (9)	0.0377 (8)	0.0393 (7)	0.0059 (7)	0.0198 (7)	−0.0017 (6)
N7	0.0561 (8)	0.0321 (6)	0.0364 (6)	0.0043 (6)	0.0201 (6)	0.0009 (5)
C7A	0.0382 (6)	0.0285 (6)	0.0265 (6)	−0.0014 (5)	0.0101 (5)	0.0008 (5)
C1'	0.0324 (6)	0.0294 (6)	0.0295 (6)	−0.0010 (5)	0.0102 (5)	−0.0028 (5)
C2'	0.0422 (7)	0.0329 (6)	0.0280 (6)	0.0052 (6)	0.0077 (5)	−0.0007 (5)
C3'	0.0359 (6)	0.0317 (6)	0.0287 (5)	−0.0036 (5)	0.0108 (5)	−0.0041 (5)
O3'	0.0552 (7)	0.0374 (6)	0.0468 (6)	−0.0086 (5)	0.0314 (5)	−0.0067 (5)
C4'	0.0272 (5)	0.0291 (6)	0.0316 (6)	0.0000 (4)	0.0107 (5)	−0.0028 (5)
O4'	0.0326 (5)	0.0316 (5)	0.0329 (4)	0.0041 (4)	0.0028 (4)	−0.0028 (4)
C5'	0.0288 (6)	0.0370 (7)	0.0378 (7)	−0.0023 (5)	0.0127 (5)	0.0017 (6)
O5'	0.0399 (6)	0.0720 (11)	0.0503 (8)	−0.0007 (7)	0.0169 (5)	0.0235 (7)

Geometric parameters (Å, º)

N1—C7A	1.3402 (18)	C1'—H1'C	0.9800
N1—N2	1.3579 (18)	C2'—C3'	1.525 (2)
N2—C3	1.3417 (18)	C2'—H2'A	0.9700
N2—C1'	1.4817 (18)	C2'—H2'B	0.9700
C3—C3A	1.402 (2)	C3'—O3'	1.4227 (18)
C3—H3	0.9300	C3'—C4'	1.530 (2)
C3A—C4	1.4083 (19)	C3'—H3'C	0.9800
C3A—C7A	1.424 (2)	O3'—H3'O	0.842 (15)
C4—N5	1.320 (2)	C4'—O4'	1.4579 (17)
C4—H4	0.9300	C4'—C5'	1.513 (2)
N5—C6	1.364 (2)	C4'—H4O'	0.9800
C6—N7	1.315 (2)	C5'—O5'	1.411 (2)
C6—H6	0.9300	C5'—H5'B	0.9700
N7—C7A	1.353 (2)	C5'—H5'C	0.9700
C1'—O4'	1.4017 (19)	O5'—H5'O	0.842 (15)
C1'—C2'	1.531 (2)
C7A—N1—N2	102.79 (12)	C3'—C2'—C1'	102.35 (12)
C3—N2—N1	115.49 (12)	C3'—C2'—H2'A	111.3
C3—N2—C1'	128.25 (13)	C1'—C2'—H2'A	111.3
N1—N2—C1'	116.08 (12)	C3'—C2'—H2'B	111.3
N2—C3—C3A	105.07 (13)	C1'—C2'—H2'B	111.3
N2—C3—H3	127.5	H2'A—C2'—H2'B	109.2
C3A—C3—H3	127.5	O3'—C3'—C2'	107.92 (13)
C3—C3A—C4	138.86 (15)	O3'—C3'—C4'	111.90 (13)
C3—C3A—C7A	104.48 (12)	C2'—C3'—C4'	102.11 (11)
C4—C3A—C7A	116.62 (14)	O3'—C3'—H3'C	111.5
N5—C4—C3A	119.86 (15)	C2'—C3'—H3'C	111.5
N5—C4—H4	120.1	C4'—C3'—H3'C	111.5
C3A—C4—H4	120.1	C3'—O3'—H3'O	110.9 (12)
C4—N5—C6	118.28 (13)	O4'—C4'—C5'	110.97 (11)
N7—C6—N5	127.96 (16)	O4'—C4'—C3'	104.04 (12)
N7—C6—H6	116.0	C5'—C4'—C3'	113.76 (12)
N5—C6—H6	116.0	O4'—C4'—H4O'	109.3
C6—N7—C7A	113.88 (15)	C5'—C4'—H4O'	109.3
N1—C7A—N7	124.48 (13)	C3'—C4'—H4O'	109.3
N1—C7A—C3A	112.17 (13)	C1'—O4'—C4'	109.49 (10)
N7—C7A—C3A	123.34 (13)	O5'—C5'—C4'	107.80 (12)
O4'—C1'—N2	109.03 (11)	O5'—C5'—H5'B	110.1
O4'—C1'—C2'	108.47 (11)	C4'—C5'—H5'B	110.1
N2—C1'—C2'	110.72 (12)	O5'—C5'—H5'C	110.1
O4'—C1'—H1'C	109.5	C4'—C5'—H5'C	110.1
N2—C1'—H1'C	109.5	H5'B—C5'—H5'C	108.5
C2'—C1'—H1'C	109.5	C5'—O5'—H5'O	112.0 (12)
C7A—N1—N2—C3	0.14 (17)	C3—N2—C1'—O4'	15.0 (2)
C7A—N1—N2—C1'	−175.41 (12)	N1—N2—C1'—O4'	−170.15 (12)
N1—N2—C3—C3A	−0.39 (17)	C3—N2—C1'—C2'	−104.29 (17)
C1'—N2—C3—C3A	174.52 (13)	N1—N2—C1'—C2'	70.59 (16)
N2—C3—C3A—C4	−176.77 (17)	O4'—C1'—C2'—C3'	19.55 (15)
N2—C3—C3A—C7A	0.44 (16)	N2—C1'—C2'—C3'	139.15 (12)
C3—C3A—C4—N5	178.72 (17)	C1'—C2'—C3'—O3'	84.82 (15)
C7A—C3A—C4—N5	1.7 (2)	C1'—C2'—C3'—C4'	−33.24 (15)
C3A—C4—N5—C6	0.0 (2)	O3'—C3'—C4'—O4'	−79.14 (13)
C4—N5—C6—N7	−2.3 (3)	C2'—C3'—C4'—O4'	36.04 (14)
N5—C6—N7—C7A	2.3 (3)	O3'—C3'—C4'—C5'	159.99 (12)
N2—N1—C7A—N7	179.37 (15)	C2'—C3'—C4'—C5'	−84.83 (15)
N2—N1—C7A—C3A	0.17 (17)	N2—C1'—O4'—C4'	−117.32 (12)
C6—N7—C7A—N1	−179.35 (16)	C2'—C1'—O4'—C4'	3.33 (14)
C6—N7—C7A—C3A	−0.2 (2)	C5'—C4'—O4'—C1'	97.79 (14)
C3—C3A—C7A—N1	−0.40 (18)	C3'—C4'—O4'—C1'	−24.93 (14)
C4—C3A—C7A—N1	177.55 (13)	O4'—C4'—C5'—O5'	58.82 (17)
C3—C3A—C7A—N7	−179.60 (14)	C3'—C4'—C5'—O5'	175.73 (13)
C4—C3A—C7A—N7	−1.7 (2)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O3′—H3′O···N7^i	0.84 (2)	1.99 (2)	2.832 (2)	175 (2)
O5′—H5′O···N5^ii	0.84 (2)	1.97 (2)	2.8011 (19)	168 (2)

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