6-Aza-2′-deoxy­uridine and N³-anisoyl-6-aza-2′-deoxy­uridine

In 2-(2-deoxy-β-D-erythro-pentofuranosyl)-1,2,4-triazine-3,5(2H,4H)-dione (6-aza-2′-deoxy­uridine), C₈H₁₁N₃O₅, (I), the conformation of the glycosylic bond is between anti and high-anti [χ = −94.0 (3)°], whereas the derivative 2-(2-deoxy-β-D-erythro-pentofuranosyl)-N⁴-(2-methoxy­benzoyl)-1,2,4-triazine-3,5(2H,4H)-dione (N³-anisoyl-6-aza-2′-deoxy­uridine), C₁₆H₁₇N₃O₇, (II), displays a high-anti conformation [χ = −86.4 (3)°]. The furanosyl moiety in (I) adopts the S-type sugar pucker (²T₃), with P = 188.1 (2)° and τ_m = 40.3 (2)°, while the sugar pucker in (II) is N (³T₄), with P = 36.1 (3)° and τ_m = 33.5 (2)°. The crystal structures of (I) and (II) are stabilized by inter­molecular N—H...O and O—H...O inter­actions.

S1. Comment

6-Azapyrimidine nucleosides show significant antiviral activity (Mitchell et al., 1986), while the N³-substituted derivatives possess hypnotic and sedative properties to exhibit central depressant effects in mice (Koshigami et al., 1991). 6-Azauridine 5'-monophosphate is a strong inhibitor of the enzyme orotidine 5'-monophosphate decarboxylase (Miller et al., 2000) which, when linked to agarose, leads to an affinity resin used for the purification of this enzyme (Rosemeyer & Seela, 1979). The first synthesis of an anomeric mixture of 6-aza-2'-deoxyuridine was reported in 1963 (Pliml et al., 1963), employing Hg derivatives of 6-azauracil and 2-deoxy-3,5-di-O-(4-methylbenzoyl)-α-D-erythro-pentofuranosyl chloride. Introducing an N atom at the 6-position of the pyrimidine moiety has a profound effect on the physical and biological properties of the nucleobase, which plays a significant role in the catalytic activity of ribozymes (Oyelere & Strobel, 2001) and promotes M-DNA formation under neutral conditions (Seela, Peng et al., 2005). The pK_a value of (I) is 6.8 and that of 2'-deoxyuridine is 9.5. Compared with these pK_a values, the 6-azapyrimidine nucleoside is acidic and therefore it is already deprotonated under neutral conditions. We have shown that this influences the duplex stability when (I) is a constituent of a nucleic acid. Oligonucleotides containing 6-aza-2'-deoxyuridine show a pH dependence on base-pair formation. The lower pK_a value of (I) causes problems during phosphoramidite synthesis. To circumvent this problem, various protecting groups were introduced at the N³-position. The o-anisoyl residue was found to be efficient at allowing multiple incorporations into the oligonucleotide chain using phosphoramidite chemistry, with coupling yields identical to those of standard phosphoramidites. These properties prompted single-crystal analyses of (I) and its N³-protected derivative, (II).

6-Aza-2'-deoxyuridine, (I), has an O4'—C1'—N1—C2 torsion angle χ = -94.0 (3)° (IUPAC–IUB Joint Commission on Biochemical Nomenclature, 1983) (Fig. 1, Table 1), which falls into the range of anti/high-anti conformations and which is almost identical to that of the corresponding ribonucleoside, (III), with χ = -93.3° (Schwalbe et al., 1971; Schwalbe & Saenger, 1973). The protected nucleoside, (II), exhibits a high-anti conformation, with a torsion angle χ = -86.4 (3)° (Fig. 2 and Table 3), and these values are similar to those of other ortho-azanucleosides with an N atom next to the glycosylation position, with χ values close to -90°. This results from the coulombic repulsion between the non-bonding electron pairs of atom O4' and atom at position N-6 in pyrimidine nucleosides or N-8 in 8-azapurine nucleosides (8-aza-7-deaza-7-iodo-2'-deoxyadenosine with χ = -106.3°; Seela et al., 1999). The glycosylic torsion angles of related nucleosides, such as 6-aza-2'-deoxythymidine (χ = -86.6°; Banerjee & Saenger, 1978) and 6-aza-2'-deoxy-5-methyl-isocytidine (χ = -103.4°; Seela et al., 2003), also lie in the anti/high-anti range.

The sugar moiety of (I) shows a pseudorotational phase angle P = 188.1 (2)° with an amplitude τ_m = 40.3 (2)°, indicating an S-type sugar pucker (C2'-endo–C3'-exo, ²T₃; Rao et al., 1981), whereas its anisoyl-protected derivative, (II), adopts an N sugar conformation (C4'-exo, ³T₄), with P = 36.1 (3)° and τ_m = 33.5 (2)°. This is similar to that of ribonucleoside (III) (C3'-endo, ³E; Schwalbe & Saenger, 1973), which has P = 27.6° and τ_m = 37.6°. The N conformation is uncommon for 2'-deoxyribonucleosides. The conformation around the C4'—C5' bond defined by the torsion angle χ (O5'—C5'—C4'—C3') is similar for these two nucleosides [-175.3 (2)° for (I) and -176.2 (2)° for (II)], representing an ap (trans) orientation.

The base moiety of (I) is nearly planar, with an r.m.s deviation of the ring atoms (N1/C2/N3/C4/C5/N6) from the least-squares plane of 0.0173 (2) Å and a maximum deviation of 0.025 (7) Å for atom C2. The maximum deviation of the pyrimidine ring (N1/N2/C3/C4/N5/C6) of (II) is 0.023 (2) Å [0.034 (5) Å for atom N5 and 0.020 (3) Å for atom N1]. The presence of the N³-anisoyl protecting group does not show much influence on the bond lengths of the nucleobase.

Compound (I) is stabilized by three intermolecular hydrogen bonds (N3—H3···O5', O3'—H3'···O2 and O5'—H5'···O4) and two intramolecular hydrogen bonds (C1'—H1'···O2 and C2'—H2'···N6), leading to the formation of layered sheets (Fig. 3 and Table 2) where the nucleobases stack. Compound (II) forms a three-dimensional network which is stabilized by both intermolecular hydrogen bonds (O3'—H3'···O5' and O5'—H5'···O2) and intramolecular hydrogen bonds formed between the sugar and the nucleobase (C1'—H1'···O2 and C2'—H2'···N6). In the close-packed network of (II), the protecting group shows a perpendicular orientation with respect to the nucleobase in the ac plane. The aromatic H atoms (on atoms C15 and C17) form weak intermolecular hydrogen bonds with atoms O2 (3.310 Å) and O4 (3.211 Å) of the adjacent nucleobase, and there is also an intramolecular C12—H12···O1 hydrogen bond (Fig. 4 and Table 4).

Related literature

For related literature, see: Banerjee & Saenger (1978); Flack (1983); IUPAC–IUB (1983); Koshigami et al. (1991); Miller et al. (2000); Mitchell et al. (1986); Oyelere & Strobel (2001); Pliml et al. (1963); Rao et al. (1981); Rosemeyer & Seela (1979); Schwalbe & Saenger (1973); Schwalbe et al. (1971); Seela et al. (1999); Seela, Chittepu, He, He & Xu (2005); Seela, He & Eickmeier (2003); Seela, Peng, Li, Chittepu, Shaikh, He, He & Mikhailopulo (2005).

S2. Experimental

Compound (I) was prepared according to the method described by Freskos (l989). The anomeric configuration assignment has been reported previously (Seela et al., 2003). Suitable crystals were grown from CH₂Cl₂–CH₃OH (9:1 v/v). Compound (II) was prepared from (I) by protection of the lactam group with o-anisoyl chloride using transient protection (Seela, Chittepu et al., 2005). Crystallization from methanol furnished colourless crystals (m.p. 414 K).

S3. Refinement

In the absence of suitable anomalous scattering, refinement of the Flack parameter (Flack, 1983) led to inconclusive values. Therefore, Friedel equivalents 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 found in a difference Fourier synthesis. In order to maximize the data:parameter ratio, 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

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 and PLATON (Spek, 2003).

Figures

	Fig. 1. A perspective view of (I), with the atomic numbering scheme. Displacement ellipsoids are drawn at the 30% probability level and H atoms are shown as small spheres of arbitrary radii.
	Fig. 2. A perspective view of (II), with the atomic numbering scheme. Displacement ellipsoids are drawn at the 30% probability level and H atoms are shown as small spheres of arbitrary radii.
	Fig. 3. A stereoview of the packing in (I), viewed in the bc plane, with hydrogen bonds shown as dashed lines. H atoms not involved in hydrogen bonding have been omitted for clarity. [The diagram submitted is not a stereoview. Please correct either the plot or the caption]
	Fig. 4. The principal interactions in (II), shown as dashed lines. H atoms not involved in hydrogen bonding have been omitted for clarity. [Symmetry codes: (i) -x, y - 1/2, 3/2 - z; (#) x, 1 + y, z; ($) -x, y + 1/2, 3/2 - z.] [No symmetry codes are shown. Please correct either the plot or the caption]

(I) 2-(2-deoxy-β-D-erythro-pentofuranosyl)-1,2,4-triazin-3,5(2H,4H)-dione

Crystal data

C8H11N3O5	Dx = 1.527 Mg m^−3
Mr = 229.20	Melting point: 414 K
Orthorhombic, P212121	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2ac 2ab	Cell parameters from 40 reflections
a = 7.8817 (17) Å	θ = 4.9–12.5°
b = 8.6832 (11) Å	µ = 0.13 mm^−1
c = 14.5715 (15) Å	T = 293 K
V = 997.2 (3) Å^3	Block, colourless
Z = 4	0.4 × 0.3 × 0.2 mm
F(000) = 480

Data collection

Bruker P4 diffractometer	Rint = 0.020
Radiation source: fine-focus sealed tube	θmax = 30.0°, θmin = 2.7°
Graphite monochromator	h = −1→10
ω/2θ scans	k = −1→12
2127 measured reflections	l = −1→20
1580 independent reflections	3 standard reflections every 97 reflections
1313 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)] = 0.045	H-atom parameters constrained
wR(F^2) = 0.121	w = 1/[σ^2(Fo^2) + (0.055P)^2 + 0.2159P] where P = (Fo^2 + 2Fc^2)/3
S = 1.07	(Δ/σ)max = 0.001
1580 reflections	Δρmax = 0.37 e Å^−3
148 parameters	Δρmin = −0.23 e Å^−3
0 restraints	Extinction correction: SHELXTL (Sheldrick, 1997), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.026 (4)

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	0.9203 (3)	0.3721 (2)	0.97874 (13)	0.0382 (5)
C2	0.9105 (4)	0.2146 (3)	0.98997 (16)	0.0394 (6)
O2	0.8824 (4)	0.1266 (2)	0.92734 (13)	0.0626 (7)
N3	0.9340 (3)	0.1642 (2)	1.07827 (13)	0.0388 (5)
H3	0.9223	0.0672	1.0885	0.047*
C4	0.9744 (4)	0.2558 (3)	1.15120 (17)	0.0394 (6)
O4	0.9992 (3)	0.2042 (3)	1.22786 (12)	0.0582 (6)
C5	0.9896 (4)	0.4186 (3)	1.12720 (17)	0.0443 (6)
H5	1.0187	0.4876	1.1734	0.053*
N6	0.9652 (3)	0.4720 (3)	1.04659 (15)	0.0432 (5)
C1'	0.9134 (4)	0.4360 (3)	0.88600 (16)	0.0405 (6)
H1'	0.8538	0.3636	0.8457	0.049*
C2'	0.8285 (4)	0.5929 (4)	0.8795 (2)	0.0530 (8)
H2'1	0.8442	0.6523	0.9353	0.064*
H2'2	0.7082	0.5836	0.8667	0.064*
C3'	0.9239 (4)	0.6641 (4)	0.7989 (2)	0.0506 (7)
H3'1	0.9159	0.7767	0.7983	0.061*
O3'	0.8573 (3)	0.5964 (4)	0.71685 (16)	0.0712 (8)
H3'	0.9181	0.6191	0.6733	0.107*
C4'	1.1034 (4)	0.6083 (3)	0.81644 (16)	0.0385 (6)
H4'	1.1634	0.6010	0.7577	0.046*
O4'	1.0825 (3)	0.4558 (2)	0.85361 (12)	0.0410 (4)
C5'	1.2065 (4)	0.7061 (3)	0.88127 (19)	0.0442 (6)
H5'1	1.2067	0.8119	0.8598	0.053*
H5'2	1.1547	0.7042	0.9417	0.053*
O5'	1.3768 (3)	0.6518 (2)	0.88754 (14)	0.0458 (5)
H5'	1.4320	0.6853	0.8442	0.069*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
N1	0.0489 (13)	0.0361 (10)	0.0297 (9)	−0.0050 (10)	−0.0015 (9)	0.0029 (8)
C2	0.0457 (14)	0.0377 (12)	0.0347 (11)	−0.0096 (12)	0.0015 (11)	0.0029 (10)
O2	0.103 (2)	0.0462 (11)	0.0388 (9)	−0.0221 (13)	−0.0059 (12)	−0.0028 (9)
N3	0.0501 (13)	0.0328 (9)	0.0334 (9)	−0.0050 (10)	−0.0005 (10)	0.0034 (8)
C4	0.0444 (14)	0.0399 (12)	0.0339 (10)	−0.0004 (11)	−0.0011 (11)	0.0015 (10)
O4	0.0857 (16)	0.0513 (11)	0.0377 (10)	0.0010 (12)	−0.0159 (11)	0.0068 (9)
C5	0.0578 (16)	0.0376 (12)	0.0375 (12)	−0.0004 (13)	−0.0012 (12)	−0.0060 (11)
N6	0.0568 (14)	0.0333 (10)	0.0393 (10)	−0.0012 (10)	0.0015 (10)	−0.0014 (9)
C1'	0.0428 (13)	0.0438 (13)	0.0349 (11)	−0.0063 (12)	−0.0015 (11)	0.0086 (11)
C2'	0.0398 (14)	0.0614 (19)	0.0578 (16)	0.0084 (14)	0.0005 (14)	0.0199 (16)
C3'	0.0475 (15)	0.0523 (15)	0.0520 (14)	−0.0057 (14)	−0.0086 (13)	0.0186 (13)
O3'	0.0641 (15)	0.0954 (19)	0.0541 (11)	−0.0226 (15)	−0.0222 (11)	0.0224 (13)
C4'	0.0440 (14)	0.0385 (12)	0.0330 (10)	−0.0050 (12)	−0.0018 (11)	0.0062 (9)
O4'	0.0451 (10)	0.0369 (9)	0.0409 (8)	−0.0010 (9)	0.0075 (8)	0.0035 (8)
C5'	0.0466 (14)	0.0364 (12)	0.0496 (13)	−0.0007 (12)	−0.0048 (13)	−0.0035 (12)
O5'	0.0443 (11)	0.0400 (10)	0.0531 (11)	−0.0014 (9)	−0.0058 (9)	0.0061 (9)

Geometric parameters (Å, º)

N1—N6	1.362 (3)	C2'—C3'	1.526 (4)
N1—C2	1.380 (3)	C2'—H2'1	0.9700
N1—C1'	1.462 (3)	C2'—H2'2	0.9700
C2—O2	1.210 (3)	C3'—O3'	1.431 (4)
C2—N3	1.372 (3)	C3'—C4'	1.517 (4)
N3—C4	1.365 (3)	C3'—H3'1	0.9800
N3—H3	0.8600	O3'—H3'	0.8200
C4—O4	1.219 (3)	C4'—O4'	1.440 (3)
C4—C5	1.462 (4)	C4'—C5'	1.508 (4)
C5—N6	1.277 (3)	C4'—H4'	0.9800
C5—H5	0.9300	C5'—O5'	1.426 (3)
C1'—O4'	1.425 (4)	C5'—H5'1	0.9700
C1'—C2'	1.521 (4)	C5'—H5'2	0.9700
C1'—H1'	0.9800	O5'—H5'	0.8200
N6—N1—C2	124.0 (2)	C1'—C2'—H2'2	111.5
N6—N1—C1'	116.0 (2)	C3'—C2'—H2'2	111.5
C2—N1—C1'	118.9 (2)	H2'1—C2'—H2'2	109.4
O2—C2—N3	122.0 (2)	O3'—C3'—C4'	110.6 (3)
O2—C2—N1	123.1 (2)	O3'—C3'—C2'	107.2 (2)
N3—C2—N1	114.8 (2)	C4'—C3'—C2'	101.6 (2)
C4—N3—C2	125.1 (2)	O3'—C3'—H3'1	112.3
C4—N3—H3	117.4	C4'—C3'—H3'1	112.3
C2—N3—H3	117.4	C2'—C3'—H3'1	112.3
O4—C4—N3	122.5 (2)	C3'—O3'—H3'	109.5
O4—C4—C5	124.2 (2)	O4'—C4'—C5'	110.1 (2)
N3—C4—C5	113.4 (2)	O4'—C4'—C3'	104.5 (2)
N6—C5—C4	124.0 (2)	C5'—C4'—C3'	115.4 (2)
N6—C5—H5	118.0	O4'—C4'—H4'	108.9
C4—C5—H5	118.0	C5'—C4'—H4'	108.9
C5—N6—N1	118.4 (2)	C3'—C4'—H4'	108.9
O4'—C1'—N1	108.5 (2)	C1'—O4'—C4'	110.0 (2)
O4'—C1'—C2'	106.4 (2)	O5'—C5'—C4'	111.2 (2)
N1—C1'—C2'	114.5 (2)	O5'—C5'—H5'1	109.4
O4'—C1'—H1'	109.1	C4'—C5'—H5'1	109.4
N1—C1'—H1'	109.1	O5'—C5'—H5'2	109.4
C2'—C1'—H1'	109.1	C4'—C5'—H5'2	109.4
C1'—C2'—C3'	101.2 (2)	H5'1—C5'—H5'2	108.0
C1'—C2'—H2'1	111.5	C5'—O5'—H5'	109.5
C3'—C2'—H2'1	111.5
N6—N1—C2—O2	−174.4 (3)	C2—N1—C1'—C2'	147.3 (3)
C1'—N1—C2—O2	−6.2 (5)	O4'—C1'—C2'—C3'	29.4 (3)
N6—N1—C2—N3	6.0 (4)	N1—C1'—C2'—C3'	149.2 (2)
C1'—N1—C2—N3	174.2 (2)	C1'—C2'—C3'—O3'	76.9 (3)
O2—C2—N3—C4	176.5 (3)	C1'—C2'—C3'—C4'	−39.1 (3)
N1—C2—N3—C4	−3.9 (4)	O3'—C3'—C4'—O4'	−77.7 (2)
C2—N3—C4—O4	−177.6 (3)	C2'—C3'—C4'—O4'	35.9 (3)
C2—N3—C4—C5	0.7 (4)	O3'—C3'—C4'—C5'	161.3 (2)
O4—C4—C5—N6	179.2 (3)	C2'—C3'—C4'—C5'	−85.1 (3)
N3—C4—C5—N6	1.0 (5)	N1—C1'—O4'—C4'	−130.9 (2)
C4—C5—N6—N1	0.9 (5)	C2'—C1'—O4'—C4'	−7.3 (3)
C2—N1—N6—C5	−4.6 (4)	C5'—C4'—O4'—C1'	106.3 (3)
C1'—N1—N6—C5	−173.1 (3)	C3'—C4'—O4'—C1'	−18.2 (3)
N6—N1—C1'—O4'	75.1 (3)	O4'—C4'—C5'—O5'	66.8 (3)
C2—N1—C1'—O4'	−94.0 (3)	C3'—C4'—C5'—O5'	−175.2 (2)
N6—N1—C1'—C2'	−43.6 (4)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O5′—H5′···O4^i	0.82	2.02	2.816 (3)	163
O3′—H3′···O2^ii	0.82	2.15	2.948 (4)	164
N3—H3···O5′^iii	0.86	1.97	2.825 (3)	176
C1′—H1′···O2	0.98	2.39	2.764 (3)	102
C2′—H2′1···N6	0.97	2.45	2.862 (4)	105

Symmetry codes: (i) −x+5/2, −y+1, z−1/2; (ii) −x+2, y+1/2, −z+3/2; (iii) x−1/2, −y+1/2, −z+2.

(II) 2-(2-deoxy-β-D-erythro-pentofuranosyl)-N⁴-(2-methoxybenzoyl)-1,2,4- triazin-3,5(2H,4H)-dione

Crystal data

C16H17N3O7	Dx = 1.433 Mg m^−3
Mr = 363.33	Melting point: 414 K
Orthorhombic, P212121	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2ac 2ab	Cell parameters from 52 reflections
a = 7.452 (3) Å	θ = 3.3–12.5°
b = 9.117 (1) Å	µ = 0.11 mm^−1
c = 24.780 (3) Å	T = 293 K
V = 1683.6 (7) Å^3	Block, colourless
Z = 4	0.4 × 0.2 × 0.1 mm
F(000) = 760

Data collection

Bruker P4 diffractometer	Rint = 0.036
Radiation source: fine-focus sealed tube	θmax = 25.0°, θmin = 2.4°
Graphite monochromator	h = −8→1
ω/2θ scans	k = −10→10
7561 measured reflections	l = −29→29
1732 independent reflections	3 standard reflections every 97 reflections
1367 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)] = 0.035	H-atom parameters constrained
wR(F^2) = 0.094	w = 1/[σ^2(Fo^2) + (0.0574P)^2 + 0.0428P] where P = (Fo^2 + 2Fc^2)/3
S = 1.02	(Δ/σ)max < 0.001
1732 reflections	Δρmax = 0.11 e Å^−3
239 parameters	Δρmin = −0.14 e Å^−3
0 restraints	Extinction correction: SHELXTL (Sheldrick, 1997), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0083 (16)

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
C11	0.0039 (5)	0.5317 (3)	0.92659 (11)	0.0734 (9)
C12	−0.0421 (7)	0.6787 (4)	0.93813 (13)	0.0946 (11)
H12	0.0409	0.7380	0.9557	0.113*
C13	−0.2012 (8)	0.7351 (5)	0.92455 (15)	0.1151 (14)
H13	−0.2285	0.8320	0.9329	0.138*
C14	−0.3248 (7)	0.6483 (4)	0.89809 (16)	0.1081 (13)
H14	−0.4359	0.6869	0.8886	0.130*
C15	−0.2845 (5)	0.5045 (4)	0.88569 (12)	0.0813 (9)
H15	−0.3686	0.4473	0.8676	0.098*
C16	−0.1235 (4)	0.4451 (4)	0.89952 (10)	0.0679 (8)
O17	−0.0785 (3)	0.3040 (2)	0.88841 (9)	0.0851 (7)
C17	−0.2083 (4)	0.2079 (4)	0.86577 (11)	0.0785 (9)
H17A	−0.2440	0.2437	0.8310	0.118*
H17B	−0.3111	0.2033	0.8890	0.118*
H17C	−0.1574	0.1117	0.8620	0.118*
C1	0.1808 (5)	0.4849 (4)	0.94492 (12)	0.0847 (10)
O1	0.2925 (4)	0.5603 (3)	0.96575 (13)	0.1370 (12)
N1	0.3002 (3)	0.1396 (2)	0.87928 (8)	0.0611 (6)
C2	0.2813 (4)	0.2866 (3)	0.88746 (10)	0.0583 (7)
O2	0.3132 (3)	0.37828 (18)	0.85317 (7)	0.0664 (5)
N3	0.2251 (3)	0.3277 (3)	0.93813 (8)	0.0683 (6)
C4	0.1672 (5)	0.2311 (5)	0.97691 (12)	0.0869 (10)
O4	0.0985 (4)	0.2730 (4)	1.01860 (8)	0.1170 (10)
C5	0.1913 (6)	0.0789 (4)	0.96162 (12)	0.0914 (11)
H5	0.1625	0.0077	0.9871	0.110*
N6	0.2494 (4)	0.0348 (3)	0.91567 (9)	0.0833 (8)
C1'	0.3325 (4)	0.0879 (3)	0.82376 (11)	0.0615 (7)
H1'	0.4012	0.1620	0.8039	0.074*
C2'	0.4282 (5)	−0.0580 (3)	0.82047 (13)	0.0773 (8)
H2'1	0.4768	−0.0855	0.8554	0.093*
H2'2	0.5253	−0.0541	0.7944	0.093*
C3'	0.2843 (4)	−0.1661 (3)	0.80256 (10)	0.0636 (7)
H3'1	0.2250	−0.2092	0.8341	0.076*
O3'	0.3602 (3)	−0.2777 (2)	0.77021 (9)	0.0825 (6)
H3'	0.2878	−0.3447	0.7666	0.124*
C4'	0.1546 (4)	−0.0682 (3)	0.77219 (10)	0.0599 (7)
H4'	0.1977	−0.0557	0.7351	0.072*
C5'	−0.0356 (5)	−0.1193 (3)	0.77074 (13)	0.0789 (9)
H5'1	−0.0399	−0.2181	0.7563	0.095*
H5'2	−0.0828	−0.1220	0.8072	0.095*
O5'	−0.1443 (4)	−0.0264 (3)	0.73873 (11)	0.1120 (9)
H5'	−0.1889	−0.0740	0.7141	0.168*
O4'	0.1620 (3)	0.07015 (19)	0.79935 (7)	0.0663 (5)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C11	0.077 (2)	0.085 (2)	0.0581 (15)	−0.0076 (18)	−0.0038 (15)	−0.0131 (15)
C12	0.127 (3)	0.072 (2)	0.085 (2)	−0.005 (2)	−0.009 (2)	−0.0090 (18)
C13	0.152 (4)	0.084 (2)	0.109 (3)	0.022 (3)	−0.014 (3)	0.014 (2)
C14	0.105 (3)	0.108 (3)	0.111 (3)	0.017 (3)	−0.009 (3)	0.035 (2)
C15	0.074 (2)	0.096 (2)	0.0739 (18)	−0.004 (2)	−0.0064 (17)	0.0161 (17)
C16	0.0627 (18)	0.086 (2)	0.0551 (13)	−0.0055 (17)	0.0016 (14)	−0.0028 (14)
O17	0.0565 (12)	0.0937 (16)	0.1050 (15)	−0.0065 (12)	−0.0114 (11)	−0.0389 (13)
C17	0.0633 (18)	0.100 (2)	0.0724 (16)	−0.0202 (18)	−0.0066 (15)	−0.0250 (16)
C1	0.079 (2)	0.097 (2)	0.0783 (19)	−0.010 (2)	−0.0106 (18)	−0.0355 (18)
O1	0.101 (2)	0.135 (2)	0.175 (3)	−0.0096 (19)	−0.042 (2)	−0.089 (2)
N1	0.0650 (14)	0.0607 (12)	0.0575 (11)	−0.0097 (12)	−0.0090 (12)	0.0053 (10)
C2	0.0507 (15)	0.0673 (16)	0.0570 (14)	−0.0090 (14)	−0.0154 (13)	−0.0008 (13)
O2	0.0724 (13)	0.0615 (10)	0.0652 (10)	−0.0085 (10)	−0.0097 (10)	−0.0003 (9)
N3	0.0655 (15)	0.0836 (15)	0.0558 (12)	−0.0092 (14)	−0.0114 (12)	−0.0118 (11)
C4	0.080 (2)	0.127 (3)	0.0532 (16)	−0.023 (2)	−0.0106 (16)	−0.0052 (18)
O4	0.121 (2)	0.176 (3)	0.0541 (11)	−0.020 (2)	0.0023 (13)	−0.0137 (15)
C5	0.113 (3)	0.105 (2)	0.0557 (16)	−0.038 (2)	−0.0133 (19)	0.0148 (16)
N6	0.103 (2)	0.0788 (16)	0.0678 (14)	−0.0242 (17)	−0.0182 (15)	0.0168 (12)
C1'	0.0551 (16)	0.0640 (15)	0.0653 (14)	−0.0019 (14)	−0.0095 (13)	−0.0006 (12)
C2'	0.0646 (18)	0.0685 (17)	0.0989 (19)	0.0087 (16)	−0.0138 (17)	−0.0065 (16)
C3'	0.0716 (18)	0.0576 (14)	0.0617 (13)	0.0059 (15)	0.0064 (14)	−0.0002 (12)
O3'	0.0869 (15)	0.0629 (11)	0.0978 (13)	0.0111 (11)	0.0139 (13)	−0.0090 (11)
C4'	0.0711 (19)	0.0585 (15)	0.0502 (12)	0.0016 (15)	0.0022 (13)	−0.0092 (12)
C5'	0.076 (2)	0.0707 (18)	0.091 (2)	0.0000 (18)	−0.0107 (18)	−0.0268 (16)
O5'	0.105 (2)	0.0998 (16)	0.132 (2)	0.0273 (16)	−0.0571 (17)	−0.0463 (15)
O4'	0.0671 (12)	0.0569 (10)	0.0749 (11)	0.0061 (10)	−0.0185 (10)	−0.0096 (9)

Geometric parameters (Å, º)

C11—C16	1.405 (4)	N3—C4	1.373 (4)
C11—C12	1.412 (5)	C4—O4	1.215 (4)
C11—C1	1.459 (5)	C4—C5	1.450 (5)
C12—C13	1.335 (6)	C5—N6	1.282 (4)
C12—H12	0.9300	C5—H5	0.9300
C13—C14	1.380 (6)	C1'—O4'	1.416 (3)
C13—H13	0.9300	C1'—C2'	1.511 (4)
C14—C15	1.380 (5)	C1'—H1'	0.9800
C14—H14	0.9300	C2'—C3'	1.523 (4)
C15—C16	1.360 (5)	C2'—H2'1	0.9700
C15—H15	0.9300	C2'—H2'2	0.9700
C16—O17	1.357 (4)	C3'—O3'	1.414 (3)
O17—C17	1.421 (3)	C3'—C4'	1.516 (4)
C17—H17A	0.9600	C3'—H3'1	0.9800
C17—H17B	0.9600	O3'—H3'	0.8200
C17—H17C	0.9600	C4'—O4'	1.431 (3)
C1—O1	1.197 (4)	C4'—C5'	1.492 (5)
C1—N3	1.480 (4)	C4'—H4'	0.9800
N1—C2	1.363 (3)	C5'—O5'	1.415 (4)
N1—N6	1.367 (3)	C5'—H5'1	0.9700
N1—C1'	1.474 (3)	C5'—H5'2	0.9700
C2—O2	1.215 (3)	O5'—H5'	0.8200
C2—N3	1.376 (3)
C16—C11—C12	117.8 (3)	N3—C4—C5	113.1 (3)
C16—C11—C1	126.5 (3)	N6—C5—C4	125.0 (3)
C12—C11—C1	115.7 (3)	N6—C5—H5	117.5
C13—C12—C11	122.0 (4)	C4—C5—H5	117.5
C13—C12—H12	119.0	C5—N6—N1	117.4 (3)
C11—C12—H12	119.0	O4'—C1'—N1	106.8 (2)
C12—C13—C14	119.5 (4)	O4'—C1'—C2'	107.5 (2)
C12—C13—H13	120.3	N1—C1'—C2'	114.1 (2)
C14—C13—H13	120.3	O4'—C1'—H1'	109.5
C15—C14—C13	120.4 (4)	N1—C1'—H1'	109.5
C15—C14—H14	119.8	C2'—C1'—H1'	109.5
C13—C14—H14	119.8	C1'—C2'—C3'	104.7 (2)
C16—C15—C14	120.9 (4)	C1'—C2'—H2'1	110.8
C16—C15—H15	119.5	C3'—C2'—H2'1	110.8
C14—C15—H15	119.5	C1'—C2'—H2'2	110.8
O17—C16—C15	123.0 (3)	C3'—C2'—H2'2	110.8
O17—C16—C11	117.5 (3)	H2'1—C2'—H2'2	108.9
C15—C16—C11	119.5 (3)	O3'—C3'—C4'	113.4 (2)
C16—O17—C17	119.8 (2)	O3'—C3'—C2'	110.5 (2)
O17—C17—H17A	109.5	C4'—C3'—C2'	102.3 (2)
O17—C17—H17B	109.5	O3'—C3'—H3'1	110.1
H17A—C17—H17B	109.5	C4'—C3'—H3'1	110.1
O17—C17—H17C	109.5	C2'—C3'—H3'1	110.1
H17A—C17—H17C	109.5	C3'—O3'—H3'	109.5
H17B—C17—H17C	109.5	O4'—C4'—C5'	108.9 (2)
O1—C1—C11	126.5 (3)	O4'—C4'—C3'	105.1 (2)
O1—C1—N3	116.8 (3)	C5'—C4'—C3'	115.7 (2)
C11—C1—N3	116.7 (3)	O4'—C4'—H4'	109.0
C2—N1—N6	124.1 (2)	C5'—C4'—H4'	109.0
C2—N1—C1'	118.0 (2)	C3'—C4'—H4'	109.0
N6—N1—C1'	115.9 (2)	O5'—C5'—C4'	111.7 (3)
O2—C2—N1	123.5 (2)	O5'—C5'—H5'1	109.3
O2—C2—N3	120.7 (3)	C4'—C5'—H5'1	109.3
N1—C2—N3	115.8 (2)	O5'—C5'—H5'2	109.3
C4—N3—C2	124.0 (3)	C4'—C5'—H5'2	109.3
C4—N3—C1	118.1 (3)	H5'1—C5'—H5'2	107.9
C2—N3—C1	115.8 (3)	C5'—O5'—H5'	109.5
O4—C4—N3	121.7 (3)	C1'—O4'—C4'	109.6 (2)
O4—C4—C5	125.2 (3)
C16—C11—C12—C13	0.6 (5)	C11—C1—N3—C2	81.0 (4)
C1—C11—C12—C13	−178.7 (3)	C2—N3—C4—O4	−170.9 (3)
C11—C12—C13—C14	−0.5 (6)	C1—N3—C4—O4	−7.8 (5)
C12—C13—C14—C15	0.0 (6)	C2—N3—C4—C5	7.1 (4)
C13—C14—C15—C16	0.5 (6)	C1—N3—C4—C5	170.1 (3)
C14—C15—C16—O17	179.6 (3)	O4—C4—C5—N6	173.6 (4)
C14—C15—C16—C11	−0.3 (5)	N3—C4—C5—N6	−4.3 (5)
C12—C11—C16—O17	179.8 (3)	C4—C5—N6—N1	3.2 (6)
C1—C11—C16—O17	−0.9 (5)	C2—N1—N6—C5	−4.8 (5)
C12—C11—C16—C15	−0.2 (4)	C1'—N1—N6—C5	−168.5 (3)
C1—C11—C16—C15	179.0 (3)	C2—N1—C1'—O4'	−86.4 (3)
C15—C16—O17—C17	−5.9 (4)	N6—N1—C1'—O4'	78.4 (3)
C11—C16—O17—C17	174.0 (2)	C2—N1—C1'—C2'	155.0 (3)
C16—C11—C1—O1	176.3 (3)	N6—N1—C1'—C2'	−40.2 (4)
C12—C11—C1—O1	−4.4 (5)	O4'—C1'—C2'—C3'	−11.0 (3)
C16—C11—C1—N3	−5.1 (5)	N1—C1'—C2'—C3'	107.2 (3)
C12—C11—C1—N3	174.2 (3)	C1'—C2'—C3'—O3'	147.5 (2)
N6—N1—C2—O2	−173.8 (3)	C1'—C2'—C3'—C4'	26.5 (3)
C1'—N1—C2—O2	−10.3 (4)	O3'—C3'—C4'—O4'	−152.0 (2)
N6—N1—C2—N3	7.2 (4)	C2'—C3'—C4'—O4'	−33.0 (3)
C1'—N1—C2—N3	170.7 (2)	O3'—C3'—C4'—C5'	87.9 (3)
O2—C2—N3—C4	172.3 (3)	C2'—C3'—C4'—C5'	−153.2 (2)
N1—C2—N3—C4	−8.6 (4)	O4'—C4'—C5'—O5'	65.7 (3)
O2—C2—N3—C1	8.9 (4)	C3'—C4'—C5'—O5'	−176.2 (2)
N1—C2—N3—C1	−172.0 (3)	N1—C1'—O4'—C4'	−133.2 (2)
O1—C1—N3—C4	95.3 (4)	C2'—C1'—O4'—C4'	−10.4 (3)
C11—C1—N3—C4	−83.4 (4)	C5'—C4'—O4'—C1'	152.3 (2)
O1—C1—N3—C2	−100.2 (4)	C3'—C4'—O4'—C1'	27.7 (3)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O3′—H3′···O5′^i	0.82	1.98	2.789 (3)	171
O5′—H5′···O2^i	0.82	1.96	2.743 (3)	161
C1′—H1′···O2	0.98	2.41	2.750 (3)	100
C2′—H2′1···N6	0.97	2.51	2.839 (5)	100
C12—H12···O1	0.93	2.49	2.802 (6)	100

Symmetry code: (i) −x, y−1/2, −z+3/2.