7-Iodo-8-aza-7-deaza-2′-deoxy­adenosine and 7-bromo-8-aza-7-deaza-2′-deoxyadenosine

The isomorphous structures of the title molecules, 4-amino-1-(2-deoxy-β-D-erythro-pento­furan­osyl)-3-iodo-1H-pyrazolo-[3,4-d]pyrimidine, (I), C₁₀H₁₂IN₅O₃, and 4-amino-3-bromo-1-(2-deoxy-β-D-erythro-pento­furan­osyl)-1H-pyrazolo[3,4-d]­pyrimidine, (II), C₁₀H₁₂BrN₅O₃, have been determined. The sugar puckering of both compounds is C1′-endo (^1′E). The N-­glycosidic bond torsion angle χ¹ is in the high-anti range [−73.2 (4)° for (I) and −74.1 (4)° for (II)] and the crystal structure is stabilized by hydrogen bonds.

S1. Comment

Oligonucleotides containing 7-iodo-8-aza-7-deaza-2'-deoxyadenosine, (I), or 7-bromo-8-aza-7-deaza-2'-deoxyadenosine, (II) (Seela & Zulauf, 1998), show enhanced stability of duplexes with antiparallel (aps) chain orientation (Seela et al., 1997; Seela & Zulauf, 1999). Purine skeleton numbering is used throughout the following discussion. The X-ray structures of the related 7-bromo- and 7-iodo-8-aza-7-deazaguanine 2'-deoxynucleosides show that the steric and stereoelectronic effects of the nucleobase are responsible for the high-anti conformation of the base and also for the sugar-ring conformation (Seela, Becher et al., 1999). In the light of this, it was of interest to evaluate the crystal structures of the 7-halogeno-8-aza-7-deaza-2'-deoxyadenosines, (I) and (II), and compare them with that of the unsubstituted 8-aza-7-deaza-2'-deoxyadenosine (Seela, Zulauf et al., 1999). Both compounds can now be prepared in a one-pot reaction with increased yield compared with the two-step procedure (Seela & Zulauf, 1998). Compounds (I) and (II) crystallize isomorphously. \scheme

The ribonucleoside 8-aza-7-deazaadenosine (8-azatubercidin) exhibits a C1'-exo-C2'-endo conformation (Sprang et al., 1978), and for the unsubstituted 8-aza-7-deaza-2'-deoxyadenosine a ²'T₃' (S-type sugar) sugar-ring conformation was determined (Seela, Zulauf et al., 1999). In contrast to this, an unusual C1'-endo (¹'E) sugar-ring conformation is observed for (I) and (II). This can be seen from the torsion angle ν₃ (C2'-C3'-C4'-O4') of -2.8 (4) for (I) and -3.8 (4)° for (II), implying an almost planar arrangement of these four atoms, with a deviation of C1' from the least-squares planes of 0.488 (5) for (I) and 0.496 (5) Å for (II). The puckering amplitude τ_m and the pseudorotation phase angle P (Rao et al., 1981) for (I) are τ_m = 34.8 (3)° and P = 309.4 (4)°, while for (II) τ_m = 35.0 (3)° and P = 310.9 (4)°.

The orientation of the base relative to the sugar (syn/anti) is defined by the torsion angle χ¹ (O4'-C1'-N9—C4) (IUPAC-IUB Joint Commission on Biochemical Nomenclature, 1983); the preferred conformation around the N-glycosidic bond of a natural 2'-deoxynucleoside is usually in the anti range. It was shown that Coulomb repulsion between the non-bonding electron pairs of O4' and N8 of 8-azatubercidin (Sprang et al., 1978), formycin (Prusiner et al., 1973) and 7-halogeno-8-aza-7-deaza-2'-deoxypurines (Seela, Becher et al., 1999) forces the N-glycosidic conformation into the high-anti (-sc) range (Klyne & Prelog, 1960). Compounds (I) and (II) also adopt a high-anti conformation [χ¹ = -73.2 (4) for (I) and -74.1 (4)° for (II)].

The halogeno substituents possess a stereoelectronic effect (Seela, Becher et al., 1999; Rosemeyer et al., 1997); as a result, the torsion angle χ¹ is significantly lower compared with that for 8-aza-7-deaza-2'-deoxyadenosine [χ¹ = -106.3 (2)°; Seela, Zulauf et al., 1999] and the high-anti conformation is strengthened. Compared with (I) and (II), the 7-iodo-7-deaza-2'-deoxyadenosine adopts a C3'-exo (₃'E) sugar-conformation with an almost perfect anti orientation of the base [χ¹ = -147.1 (8)°; Seela et al., 1996]. The high-anti conformation of (I) and (II) may be stabilized through van der Waals interactions resulting from the contact between N8 and C2' or one of its H atoms [N—C = 2.761 (5) and N—H = 2.45 Å for (I); N—C = 2.777 (5) and N—H = 2.47 Å for (II)]. Similar interactions were also observed for 8-azaadenosine (Singh & Hodgson, 1974) and 8-azatubercidin (Sprang et al., 1978).

Another intramolecular attraction was determined between the 7-halogeno substituent and one of the amino H atoms of (I) and (II). This hydrogen bond leads to a hindered rotation of the amino group. Therefore, two signals for the amino protons can be observed in the ¹H-NMR spectra at ambient temperature. The proton signals become indistinguishable at a coalescence temperature of 340 K.

The exocyclic angle N8—N9—C1' is smaller than C4—N9—C1', by 6.3 (4)° for (I) and by 5.6 (4)° for (II), as observed for other nucleosides adopting the high-anti conformation (Sprang et al., 1978; Prusiner et al., 1973). The conformation about the C4'-C5' bond of (I) and (II) is in the trans (+ap) range [γ = 175.4 (3) for (I), 175.2 (3)° for (II)]. The halogeno substituents of (I) and (II) lead to a lengthening of the glycosidic bond, while the other bond lengths and torsion angles of (I) and (II) are similar to those of 8-aza-7-deaza-2'-deoxyadenosine (Seela, Zulauf et al., 1999).

Intermolecular hydrogen bonds formed by (I) and (II) generate a three-dimensional network and provide additional crystal stabilization (Tables 2 and 4).

The 8-aza-7-deazaadenine base of (I) and (II) is planar. The deviations of the ring C and N atoms from the least-squares plane are in the range of -0.031 (5)–0.043 (3) for (I) and -0.037 (5)–0.045 (3) Å for (II). The bulky iodo substituent of (I) lies -0.091 (6) Å and the bromo substituent of (II) -0.084 (6) Å out of the heterocyclic plane. For comparison, the iodo atom of 7-iodo-7-deaza-2'-deoxyadenosine is located -0.135 (14) Å out of the plane (Seela et al., 1996).

S2. Experimental

Compound (I) was prepared from 1-[2-deoxy-3,5-di-O-(p-toluoyl)-β-D-erythro-pentofuranosyl]- 3-iodo-4-methoxy-1H-pyrazolo[3,4-d]pyrimidine (Seela & Zulauf, 1998; 500 mg, 0.8 mmol) by treatment with saturated NH₃/MeOH (150 ml, 3:1 v/v) for 5 h at 363 K in an autoclave. The solvent was evaporated and the residue purified by flash chromatography on silica gel (column 10 × 3 cm, methanol-dichloromethane 1:9). Crystallization from ⁱPrOH yielded colourless needles (yield 138 mg, 46%) which showed identical ¹H– and ¹³C-NMR data to those of a verified sample (Seela & Zulauf, 1998). Compound (II) was prepared from 3-bromo-1-[2-deoxy-3,5-di-O-(p-toluoyl)-β-D-erythro- pentofuranosyl]-4-methoxy-1H-pyrazolo[3,4-d]pyrimidine (Seela & Zulauf, 1998; 500 mg, 0.86 mmol) by treatment with saturated NH₃/MeOH (150 ml, 3:1 v/v) for 5 h at 363 K in an autoclave. The solvent was evaporated and the residue purified by flash chromatography on silica gel (column 10 × 3 cm, methanol-dichloromethane 1:9). Crystallization from ⁱPrOH yielded colourless needles (yield 148 mg, 52%) which showed identical ¹H– and ¹³C-NMR data to those of a verified sample (Seela & Zulauf, 1998).

S3. Refinement

All H atoms were found in difference Fourier syntheses but were constructed in geometrically reasonable positions, with the exception of the amino H atoms. These were first refined with a common N—H distance and then fixed on the amino N atoms with a riding model. For all H atoms a common isotropic displacement parameter was refined. The absolute configurations were confidently proven by the diffraction experiment.

Computing details

For both compounds, data collection: XSCANS (Siemens, 1996); cell refinement: XSCANS; data reduction: SHELXTL (Sheldrick, 1997a); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997c); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997b); molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.

Figures

	Fig. 1. A perspective view of (I) showing the atomic numbering scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as spheres of small arbitrary size.
	Fig. 2. A perspective view of (II) showing the atomic numbering scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as spheres of small arbitrary size.

(I) 4-amino-1-(2-deoxy-β-D-erythro-pentofuranosyl)- 3-iodo-1H-pyrazolo[3,4-d]pyrimidine

Crystal data

C10H12IN5O3	F(000) = 368
Mr = 377.15	Dx = 2.029 Mg m^−3
Monoclinic, P21	Mo Kα radiation, λ = 0.71073 Å
a = 9.259 (3) Å	Cell parameters from 40 reflections
b = 7.2787 (10) Å	θ = 5.1–17.8°
c = 9.767 (3) Å	µ = 2.61 mm^−1
β = 110.29 (2)°	T = 293 K
V = 617.4 (3) Å^3	Needle, colourless
Z = 2	0.55 × 0.15 × 0.15 mm

Data collection

Siemens P4 diffractometer	2668 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.020
Graphite monochromator	θmax = 27.0°, θmin = 2.2°
2θ/ω scans	h = −11→11
Absorption correction: ψ-scan SHELXTL (Sheldrick, 1997a)	k = −9→9
Tmin = 0.445, Tmax = 0.704	l = −12→12
3057 measured reflections	3 standard reflections every 97 reflections
2694 independent reflections	intensity decay: none

Refinement

Refinement on F^2	Hydrogen site location: inferred from neighbouring sites
Least-squares matrix: full	Only H-atom displacement parameters refined
R[F^2 > 2σ(F^2)] = 0.026	w = 1/[σ^2(Fo^2) + (0.0411P)^2 + 0.436P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.069	(Δ/σ)max = 0.001
S = 1.04	Δρmax = 0.63 e Å^−3
2694 reflections	Δρmin = −0.65 e Å^−3
174 parameters	Extinction correction: SHELXL97 (Sheldrick, 1997b), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
1 restraint	Extinction coefficient: 0.0102 (11)
Primary atom site location: structure-invariant direct methods	Absolute structure: Flack (1983)
Secondary atom site location: difference Fourier map	Absolute structure parameter: −0.01 (2)

Special details

Experimental. For the diffraction experiments single crystals were fixed at the top of Lindemann capillaries with epoxy resin.

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	−0.0462 (3)	0.5011 (9)	0.3298 (3)	0.0339 (6)
C2	0.0909 (4)	0.5121 (14)	0.3087 (3)	0.0364 (7)
H2	0.0858	0.5021	0.2122	0.039 (3)*
N3	0.2312 (3)	0.5350 (5)	0.4059 (3)	0.0292 (8)
C4	0.2281 (4)	0.5398 (4)	0.5436 (3)	0.0231 (8)
C5	0.0976 (3)	0.5182 (7)	0.5831 (3)	0.0233 (6)
C6	−0.0465 (3)	0.5014 (10)	0.4673 (3)	0.0265 (6)
N6	−0.1806 (3)	0.4918 (9)	0.4888 (3)	0.0349 (7)
H61	−0.2631	0.4627	0.4176	0.039 (3)*
H62	−0.1799	0.5151	0.5755	0.039 (3)*
C7	0.1545 (4)	0.5305 (7)	0.7374 (3)	0.0254 (9)
I7	0.030846 (19)	0.50678 (5)	0.876307 (18)	0.03127 (10)
N8	0.3052 (3)	0.5582 (4)	0.7894 (3)	0.0273 (7)
N9	0.3498 (3)	0.5667 (4)	0.6687 (3)	0.0251 (6)
C1'	0.5137 (4)	0.5883 (5)	0.6842 (4)	0.0227 (6)
H1'	0.5235	0.6787	0.6136	0.039 (3)*
C2'	0.6087 (4)	0.6487 (5)	0.8387 (4)	0.0260 (8)
H2'1	0.5486	0.7263	0.8796	0.039 (3)*
H2'2	0.7001	0.7150	0.8402	0.039 (3)*
C3'	0.6511 (3)	0.4680 (4)	0.9225 (3)	0.0233 (8)
H3'	0.5794	0.4420	0.9740	0.039 (3)*
O3'	0.8063 (3)	0.4698 (4)	1.0232 (3)	0.0340 (8)
H3'1	0.8086	0.5177	1.0999	0.039 (3)*
C4'	0.6339 (4)	0.3240 (5)	0.8035 (4)	0.0221 (7)
H4'	0.7360	0.2736	0.8167	0.039 (3)*
O4'	0.5780 (3)	0.4185 (4)	0.6637 (3)	0.0249 (5)
C5'	0.5286 (4)	0.1664 (5)	0.8086 (4)	0.0280 (7)
H5'1	0.5736	0.1015	0.9003	0.039 (3)*
H5'2	0.4305	0.2162	0.8061	0.039 (3)*
O5'	0.5021 (3)	0.0393 (4)	0.6918 (3)	0.0335 (7)
H5'	0.5845	0.0109	0.6837	0.039 (3)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
N1	0.0255 (12)	0.0541 (16)	0.0184 (11)	−0.004 (2)	0.0029 (9)	0.003 (2)
C2	0.0323 (16)	0.059 (2)	0.0175 (13)	−0.006 (3)	0.0082 (12)	0.000 (3)
N3	0.0238 (12)	0.045 (2)	0.0200 (12)	−0.0032 (13)	0.0088 (10)	−0.0004 (12)
C4	0.0188 (13)	0.032 (2)	0.0169 (13)	0.0019 (11)	0.0041 (11)	0.0013 (11)
C5	0.0172 (12)	0.0337 (15)	0.0179 (11)	−0.0001 (16)	0.0047 (10)	0.0035 (18)
C6	0.0207 (13)	0.0333 (14)	0.0223 (13)	−0.007 (2)	0.0035 (11)	−0.002 (3)
N6	0.0168 (11)	0.061 (2)	0.0252 (12)	−0.006 (2)	0.0053 (9)	−0.002 (2)
C7	0.0171 (12)	0.040 (3)	0.0199 (13)	0.0007 (14)	0.0071 (10)	−0.0021 (15)
I7	0.02131 (12)	0.05438 (15)	0.02086 (12)	−0.00449 (13)	0.01080 (8)	−0.00330 (14)
N8	0.0165 (13)	0.0488 (19)	0.0173 (12)	0.0009 (11)	0.0068 (10)	−0.0014 (10)
N9	0.0137 (12)	0.0456 (15)	0.0170 (12)	−0.0018 (10)	0.0065 (10)	−0.0003 (10)
C1'	0.0157 (15)	0.0322 (15)	0.0197 (16)	−0.0003 (13)	0.0055 (14)	0.0013 (12)
C2'	0.0183 (17)	0.0337 (18)	0.0242 (18)	−0.0015 (13)	0.0050 (14)	−0.0048 (14)
C3'	0.0159 (13)	0.036 (2)	0.0180 (13)	0.0003 (11)	0.0060 (11)	−0.0006 (12)
O3'	0.0194 (10)	0.063 (2)	0.0163 (10)	0.0003 (12)	0.0021 (8)	−0.0037 (11)
C4'	0.0168 (15)	0.0320 (16)	0.0174 (15)	−0.0006 (13)	0.0060 (12)	−0.0004 (13)
O4'	0.0241 (13)	0.0360 (11)	0.0180 (11)	0.0059 (10)	0.0115 (10)	0.0008 (9)
C5'	0.0235 (16)	0.0342 (17)	0.0278 (17)	−0.0038 (14)	0.0109 (14)	−0.0030 (13)
O5'	0.0262 (11)	0.040 (2)	0.0340 (13)	−0.0067 (10)	0.0096 (10)	−0.0095 (11)

Geometric parameters (Å, º)

N1—C6	1.344 (4)	C1'—C2'	1.524 (5)
N1—C2	1.357 (4)	C1'—H1'	0.9800
C2—N3	1.327 (4)	C2'—C3'	1.527 (5)
C2—H2	0.9300	C2'—H2'1	0.9700
N3—C4	1.356 (4)	C2'—H2'2	0.9700
C4—N9	1.359 (4)	C3'—O3'	1.432 (4)
C4—C5	1.399 (4)	C3'—C4'	1.532 (5)
C5—C7	1.416 (4)	C3'—H3'	0.9800
C5—C6	1.424 (4)	O3'—H3'1	0.8200
C6—N6	1.331 (4)	C4'—O4'	1.454 (4)
N6—H61	0.8620	C4'—C5'	1.518 (5)
N6—H62	0.8615	C4'—H4'	0.9800
C7—N8	1.325 (4)	C5'—O5'	1.423 (4)
C7—I7	2.064 (3)	C5'—H5'1	0.9700
N8—N9	1.378 (4)	C5'—H5'2	0.9700
N9—C1'	1.480 (4)	O5'—H5'	0.8200
C1'—O4'	1.416 (4)
C6—N1—C2	118.5 (2)	C2'—C1'—H1'	109.9
N3—C2—N1	129.3 (3)	C1'—C2'—C3'	103.6 (3)
N3—C2—H2	115.3	C1'—C2'—H2'1	111.0
N1—C2—H2	115.3	C3'—C2'—H2'1	111.0
C2—N3—C4	111.2 (3)	C1'—C2'—H2'2	111.0
N3—C4—N9	126.9 (3)	C3'—C2'—H2'2	111.0
N3—C4—C5	126.0 (3)	H2'1—C2'—H2'2	109.0
N9—C4—C5	107.1 (3)	O3'—C3'—C2'	111.8 (3)
C4—C5—C7	104.4 (3)	O3'—C3'—C4'	110.0 (3)
C4—C5—C6	116.9 (3)	C2'—C3'—C4'	104.1 (3)
C7—C5—C6	138.6 (3)	O3'—C3'—H3'	110.3
N6—C6—N1	118.9 (3)	C2'—C3'—H3'	110.3
N6—C6—C5	123.2 (3)	C4'—C3'—H3'	110.3
N1—C6—C5	117.9 (3)	C3'—O3'—H3'1	109.5
C6—N6—H61	119.9	O4'—C4'—C5'	111.4 (3)
C6—N6—H62	117.1	O4'—C4'—C3'	107.3 (3)
H61—N6—H62	123.0	C5'—C4'—C3'	113.0 (3)
N8—C7—C5	111.8 (3)	O4'—C4'—H4'	108.3
N8—C7—I7	120.8 (2)	C5'—C4'—H4'	108.3
C5—C7—I7	127.5 (2)	C3'—C4'—H4'	108.3
C7—N8—N9	105.5 (3)	C1'—O4'—C4'	108.1 (3)
C4—N9—N8	111.2 (3)	O5'—C5'—C4'	113.5 (3)
C4—N9—C1'	127.5 (3)	O5'—C5'—H5'1	108.9
N8—N9—C1'	121.2 (3)	C4'—C5'—H5'1	108.9
O4'—C1'—N9	111.1 (3)	O5'—C5'—H5'2	108.9
O4'—C1'—C2'	105.4 (3)	C4'—C5'—H5'2	108.9
N9—C1'—C2'	110.5 (3)	H5'1—C5'—H5'2	107.7
O4'—C1'—H1'	109.9	C5'—O5'—H5'	109.5
N9—C1'—H1'	109.9
C4—N9—C1'—O4'	−73.2 (4)	C7—C5—C6—N1	177.6 (7)
C2'—C3'—C4'—O4'	−2.8 (4)	C4—C5—C7—N8	0.3 (6)
C3'—C4'—C5'—O5'	175.4 (3)	C6—C5—C7—N8	−175.4 (7)
N8—N9—C1'—O4'	101.6 (4)	C4—C5—C7—I7	−178.8 (3)
C1'—C2'—C3'—C4'	21.3 (4)	C6—C5—C7—I7	5.6 (11)
C2'—C1'—O4'—C4'	32.8 (3)	C5—C7—N8—N9	0.7 (5)
C3'—C4'—O4'—C1'	−18.8 (3)	I7—C7—N8—N9	179.9 (3)
O3'—C3'—C4'—C5'	114.1 (3)	N3—C4—N9—N8	−178.3 (3)
O4'—C4'—C5'—O5'	54.4 (4)	C5—C4—N9—N8	1.8 (4)
C6—N1—C2—N3	−4.6 (16)	N3—C4—N9—C1'	−3.0 (6)
N1—C2—N3—C4	2.7 (13)	C5—C4—N9—C1'	177.1 (4)
C2—N3—C4—N9	−177.9 (6)	C7—N8—N9—C4	−1.6 (4)
C2—N3—C4—C5	1.9 (7)	C7—N8—N9—C1'	−177.2 (3)
N3—C4—C5—C7	178.9 (4)	C4—N9—C1'—C2'	170.1 (3)
N9—C4—C5—C7	−1.3 (5)	N8—N9—C1'—C2'	−15.0 (4)
N3—C4—C5—C6	−4.3 (7)	O4'—C1'—C2'—C3'	−33.5 (4)
N9—C4—C5—C6	175.5 (5)	N9—C1'—C2'—C3'	86.6 (3)
C2—N1—C6—N6	179.6 (6)	C1'—C2'—C3'—O3'	140.0 (3)
C2—N1—C6—C5	1.6 (13)	O3'—C3'—C4'—O4'	−122.7 (3)
C4—C5—C6—N6	−175.6 (6)	C2'—C3'—C4'—C5'	−126.0 (3)
C7—C5—C6—N6	−0.3 (13)	N9—C1'—O4'—C4'	−87.0 (3)
C4—C5—C6—N1	2.3 (9)	C5'—C4'—O4'—C1'	105.4 (3)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N6—H61···O5′^i	0.86	2.17	2.907 (4)	143
N6—H62···I7	0.86	2.91	3.610 (3)	140
O3′—H3′1···N1^ii	0.82	2.18	2.837 (4)	137
O5′—H5′···N3^iii	0.82	2.18	2.940 (4)	155

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

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

Crystal data

C10H12BrN5O3	F(000) = 332
Mr = 330.16	Dx = 1.827 Mg m^−3
Monoclinic, P21	Mo Kα radiation, λ = 0.71073 Å
a = 9.0930 (9) Å	Cell parameters from 35 reflections
b = 7.2595 (10) Å	θ = 4.7–16.3°
c = 9.6369 (19) Å	µ = 3.44 mm^−1
β = 109.362 (11)°	T = 293 K
V = 600.16 (16) Å^3	Needle, colourless
Z = 2	0.50 × 0.12 × 0.12 mm

Data collection

Siemens P4 diffractometer	2381 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.035
Graphite monochromator	θmax = 27.0°, θmin = 2.2°
2θ/ω scans	h = −11→11
Absorption correction: ψ-scan SHELXTL (Sheldrick, 1997a)	k = −9→9
Tmin = 0.497, Tmax = 0.662	l = −12→12
2959 measured reflections	3 standard reflections every 97 reflections
2604 independent reflections	intensity decay: none

Refinement

Refinement on F^2	Hydrogen site location: inferred from neighbouring sites
Least-squares matrix: full	Only H-atom displacement parameters refined
R[F^2 > 2σ(F^2)] = 0.035	w = 1/[σ^2(Fo^2) + (0.0529P)^2 + 0.2516P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.093	(Δ/σ)max = 0.001
S = 1.05	Δρmax = 0.51 e Å^−3
2604 reflections	Δρmin = −0.54 e Å^−3
174 parameters	Extinction correction: SHELXL97 (Sheldrick, 1997b), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
1 restraint	Extinction coefficient: 0.0071 (17)
Primary atom site location: structure-invariant direct methods	Absolute structure: Flack (1983)
Secondary atom site location: difference Fourier map	Absolute structure parameter: −0.014 (11)

Special details

Experimental. For the diffraction experiments single crystals were fixed at the top of Lindemann capillaries with epoxy resin.

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	−0.0508 (3)	0.5015 (8)	0.3335 (3)	0.0378 (7)
C2	0.0859 (4)	0.5149 (10)	0.3112 (4)	0.0387 (8)
H2	0.0810	0.5106	0.2133	0.044 (4)*
N3	0.2288 (3)	0.5335 (6)	0.4090 (3)	0.0316 (8)
C4	0.2254 (4)	0.5367 (5)	0.5473 (4)	0.0255 (8)
C5	0.0930 (3)	0.5166 (7)	0.5884 (3)	0.0258 (6)
C6	−0.0532 (3)	0.5034 (8)	0.4725 (3)	0.0290 (6)
N6	−0.1888 (3)	0.4958 (8)	0.4963 (3)	0.0388 (7)
H61	−0.2713	0.4667	0.4251	0.044 (4)*
H62	−0.1881	0.5190	0.5831	0.044 (4)*
C7	0.1509 (4)	0.5295 (7)	0.7437 (3)	0.0279 (8)
Br7	0.03469 (4)	0.50739 (6)	0.87120 (3)	0.04050 (14)
N8	0.3016 (3)	0.5546 (4)	0.7950 (3)	0.0304 (8)
N9	0.3477 (3)	0.5635 (4)	0.6726 (3)	0.0278 (7)
C1'	0.5126 (4)	0.5879 (5)	0.6857 (4)	0.0253 (7)
H1'	0.5220	0.6791	0.6141	0.044 (4)*
C2'	0.6108 (4)	0.6458 (5)	0.8412 (4)	0.0292 (8)
H2'1	0.7035	0.7117	0.8407	0.044 (4)*
H2'2	0.5513	0.7238	0.8848	0.044 (4)*
C3'	0.6538 (4)	0.4656 (5)	0.9246 (4)	0.0266 (8)
H3'	0.5802	0.4387	0.9767	0.044 (4)*
O3'	0.8091 (3)	0.4667 (5)	1.0253 (3)	0.0372 (8)
H3'1	0.8131	0.5300	1.0969	0.044 (4)*
C4'	0.6377 (4)	0.3218 (5)	0.8038 (4)	0.0256 (7)
H4'	0.7414	0.2728	0.8149	0.044 (4)*
O4'	0.5793 (3)	0.4169 (4)	0.6641 (3)	0.0283 (5)
C5'	0.5324 (4)	0.1629 (5)	0.8106 (4)	0.0294 (7)
H5'1	0.5786	0.0978	0.9027	0.044 (4)*
H5'2	0.4330	0.2118	0.8100	0.044 (4)*
O5'	0.5059 (3)	0.0359 (4)	0.6928 (3)	0.0345 (7)
H5'	0.5849	0.0269	0.6701	0.044 (4)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
N1	0.0247 (13)	0.0613 (19)	0.0223 (12)	−0.009 (2)	0.0010 (10)	−0.002 (2)
C2	0.0310 (16)	0.061 (2)	0.0241 (14)	−0.010 (3)	0.0093 (12)	−0.002 (3)
N3	0.0252 (13)	0.048 (2)	0.0226 (12)	−0.0060 (14)	0.0092 (10)	−0.0012 (14)
C4	0.0186 (13)	0.034 (2)	0.0215 (14)	0.0005 (14)	0.0033 (11)	0.0013 (14)
C5	0.0196 (13)	0.0364 (17)	0.0201 (13)	0.0024 (19)	0.0045 (10)	0.000 (2)
C6	0.0189 (12)	0.0385 (17)	0.0271 (14)	−0.002 (2)	0.0043 (11)	−0.001 (2)
N6	0.0198 (12)	0.069 (2)	0.0259 (12)	−0.004 (2)	0.0049 (10)	0.001 (2)
C7	0.0198 (13)	0.044 (2)	0.0213 (13)	0.0023 (18)	0.0092 (11)	0.0016 (18)
Br7	0.02521 (17)	0.0734 (3)	0.02591 (17)	−0.0061 (2)	0.01250 (12)	−0.0046 (3)
N8	0.0213 (13)	0.048 (2)	0.0218 (13)	0.0001 (12)	0.0074 (11)	−0.0026 (12)
N9	0.0163 (13)	0.046 (2)	0.0198 (13)	−0.0009 (11)	0.0046 (10)	−0.0015 (11)
C1'	0.0191 (16)	0.0322 (17)	0.0234 (16)	0.0005 (14)	0.0054 (14)	0.0003 (14)
C2'	0.0199 (17)	0.035 (2)	0.029 (2)	−0.0053 (14)	0.0033 (15)	−0.0067 (16)
C3'	0.0154 (13)	0.042 (2)	0.0223 (14)	−0.0016 (13)	0.0062 (11)	−0.0011 (14)
O3'	0.0201 (11)	0.067 (2)	0.0198 (10)	0.0010 (12)	0.0000 (8)	−0.0040 (12)
C4'	0.0187 (16)	0.0330 (18)	0.0238 (17)	0.0012 (15)	0.0053 (13)	0.0029 (14)
O4'	0.0268 (13)	0.0385 (13)	0.0215 (12)	0.0028 (11)	0.0107 (10)	0.0017 (10)
C5'	0.0252 (17)	0.034 (2)	0.0283 (17)	−0.0020 (14)	0.0083 (14)	0.0012 (14)
O5'	0.0242 (11)	0.0430 (19)	0.0369 (12)	−0.0061 (12)	0.0109 (9)	−0.0097 (13)

Geometric parameters (Å, º)

N1—C2	1.333 (4)	C1'—C2'	1.528 (5)
N1—C6	1.348 (4)	C1'—H1'	0.9800
C2—N3	1.335 (4)	C2'—C3'	1.517 (5)
C2—H2	0.9300	C2'—H2'1	0.9700
N3—C4	1.343 (4)	C2'—H2'2	0.9700
C4—N9	1.358 (4)	C3'—O3'	1.424 (4)
C4—C5	1.394 (4)	C3'—C4'	1.535 (5)
C5—C7	1.415 (4)	C3'—H3'	0.9800
C5—C6	1.428 (4)	O3'—H3'1	0.8200
C6—N6	1.328 (4)	C4'—O4'	1.448 (4)
N6—H61	0.8581	C4'—C5'	1.514 (5)
N6—H62	0.8504	C4'—H4'	0.9800
C7—N8	1.306 (4)	C5'—O5'	1.419 (5)
C7—Br7	1.874 (3)	C5'—H5'1	0.9700
N8—N9	1.378 (4)	C5'—H5'2	0.9700
N9—C1'	1.473 (4)	O5'—H5'	0.8200
C1'—O4'	1.426 (4)
C2—N1—C6	118.9 (3)	C2'—C1'—H1'	110.2
N1—C2—N3	129.4 (3)	C3'—C2'—C1'	104.3 (3)
N1—C2—H2	115.3	C3'—C2'—H2'1	110.9
N3—C2—H2	115.3	C1'—C2'—H2'1	110.9
C2—N3—C4	111.4 (3)	C3'—C2'—H2'2	110.9
N3—C4—N9	127.1 (3)	C1'—C2'—H2'2	110.9
N3—C4—C5	125.9 (3)	H2'1—C2'—H2'2	108.9
N9—C4—C5	107.0 (3)	O3'—C3'—C2'	112.3 (3)
C4—C5—C7	103.9 (3)	O3'—C3'—C4'	110.1 (3)
C4—C5—C6	116.9 (3)	C2'—C3'—C4'	104.0 (3)
C7—C5—C6	139.0 (3)	O3'—C3'—H3'	110.1
N6—C6—N1	119.6 (3)	C2'—C3'—H3'	110.1
N6—C6—C5	123.0 (3)	C4'—C3'—H3'	110.1
N1—C6—C5	117.4 (3)	C3'—O3'—H3'1	109.5
C6—N6—H61	119.1	O4'—C4'—C5'	111.2 (3)
C6—N6—H62	117.2	O4'—C4'—C3'	107.1 (3)
H61—N6—H62	123.7	C5'—C4'—C3'	112.8 (3)
N8—C7—C5	112.6 (3)	O4'—C4'—H4'	108.5
N8—C7—Br7	120.8 (2)	C5'—C4'—H4'	108.5
C5—C7—Br7	126.5 (2)	C3'—C4'—H4'	108.5
C7—N8—N9	105.2 (3)	C1'—O4'—C4'	108.8 (3)
C4—N9—N8	111.3 (3)	O5'—C5'—C4'	113.7 (3)
C4—N9—C1'	127.1 (3)	O5'—C5'—H5'1	108.8
N8—N9—C1'	121.5 (3)	C4'—C5'—H5'1	108.8
O4'—C1'—N9	110.7 (3)	O5'—C5'—H5'2	108.8
O4'—C1'—C2'	104.1 (3)	C4'—C5'—H5'2	108.8
N9—C1'—C2'	111.4 (3)	H5'1—C5'—H5'2	107.7
O4'—C1'—H1'	110.2	C5'—O5'—H5'	109.5
N9—C1'—H1'	110.2
C4—N9—C1'—O4'	−74.1 (4)	C7—C5—C6—N1	177.3 (6)
C2'—C3'—C4'—O4'	−3.8 (4)	C4—C5—C7—N8	0.0 (6)
C3'—C4'—C5'—O5'	175.2 (3)	C6—C5—C7—N8	−174.4 (7)
N8—N9—C1'—O4'	101.9 (4)	C4—C5—C7—Br7	−178.2 (4)
C1'—C2'—C3'—C4'	22.5 (4)	C6—C5—C7—Br7	7.4 (10)
C2'—C1'—O4'—C4'	32.5 (3)	C5—C7—N8—N9	1.4 (5)
C3'—C4'—O4'—C1'	−18.3 (3)	Br7—C7—N8—N9	179.7 (3)
O3'—C3'—C4'—C5'	113.1 (3)	N3—C4—N9—N8	−178.9 (4)
O4'—C4'—C5'—O5'	54.9 (4)	C5—C4—N9—N8	2.4 (5)
C6—N1—C2—N3	−1.1 (12)	N3—C4—N9—C1'	−2.6 (6)
N1—C2—N3—C4	0.6 (10)	C5—C4—N9—C1'	178.6 (4)
C2—N3—C4—N9	−176.3 (5)	C7—N8—N9—C4	−2.3 (5)
C2—N3—C4—C5	2.3 (7)	C7—N8—N9—C1'	−178.9 (3)
N3—C4—C5—C7	179.8 (5)	C4—N9—C1'—C2'	170.6 (4)
N9—C4—C5—C7	−1.4 (5)	N8—N9—C1'—C2'	−13.4 (5)
N3—C4—C5—C6	−4.3 (8)	O4'—C1'—C2'—C3'	−33.9 (3)
N9—C4—C5—C6	174.5 (5)	N9—C1'—C2'—C3'	85.4 (4)
C2—N1—C6—N6	178.0 (6)	C1'—C2'—C3'—O3'	141.5 (3)
C2—N1—C6—C5	−1.0 (9)	O3'—C3'—C4'—O4'	−124.3 (3)
C4—C5—C6—N6	−175.5 (5)	C2'—C3'—C4'—C5'	−126.4 (3)
C7—C5—C6—N6	−1.7 (12)	N9—C1'—O4'—C4'	−87.3 (3)
C4—C5—C6—N1	3.4 (8)	C5'—C4'—O4'—C1'	105.4 (3)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N6—H61···O5′^i	0.86	2.12	2.870 (4)	146
N6—H62···Br7	0.85	2.84	3.510 (3)	136
O3′—H3′1···N1^ii	0.82	2.21	2.828 (4)	132
O5′—H5′···N3^iii	0.82	2.08	2.890 (4)	172

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