1-Acetyl-6-bromo-1H-imidazo[4,5-b]pyridin-2(3H)-one

The two fused five- and six-membered rings in the mol­ecule of the title compound, C₈H₆BrN₃O₂, are approximately coplanar, the largest deviation from the mean plane being 0.011 (3) Å at the NH atom. The acetyl group is slightly twisted with respect to the imidazo[4,5-b]pyridine system, making a dihedral angle of 2.7 (2)°. In the crystal, adjacent mol­ecules are linked by inter­molecular N—H...N and C—H...O hydrogen bonds, forming infinite chains.

Key indicators

• Single-crystal X-ray study
• T = 298 K
• Mean [sigma](C-C) = 0.004 Å
• R factor = 0.028
• wR factor = 0.074
• Data-to-parameter ratio = 13.2

checkCIF/PLATON results

No syntax errors found



Alert level B
PLAT029_ALERT_3_B _diffrn_measured_fraction_theta_full Low .......       0.95
PLAT430_ALERT_2_B Short Inter D...A Contact  O2     ..  O2      ..       2.81 Ang.

Alert level C
PLAT250_ALERT_2_C Large U3/U1 Ratio for Average U(i,j) Tensor ....       2.37
PLAT431_ALERT_2_C Short Inter HL..A Contact  Br1    ..  O1      ..       3.13 Ang.
PLAT911_ALERT_3_C Missing # FCF Refl Between THmin & STh/L=  0.600         72
PLAT912_ALERT_4_C Missing # of FCF Reflections Above STh/L=  0.600          9

   0 ALERT level A = Most likely a serious problem - resolve or explain
   2 ALERT level B = A potentially serious problem, consider carefully
   4 ALERT level C = Check. Ensure it is not caused by an omission or oversight
   0 ALERT level G = General information/check it is not something unexpected

   0 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   3 ALERT type 2 Indicator that the structure model may be wrong or deficient
   2 ALERT type 3 Indicator that the structure quality may be low
   1 ALERT type 4 Improvement, methodology, query or suggestion
   0 ALERT type 5 Informative message, check

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S1. Comment

Imidazo[4,5-b]pyridines represent the major backbone of numerous medical and biochemical agents possessing different chemical and pharmacological features (Kale et al., 2009; Silverman, 2004), which impart them diverse biological properties like antiviral (Cristalli et al.,1995; Cundy et al., 1997; Banie et al., 2007), and anti-inflammatory (Mader, 2008) activity. Substituted imidazo[4,5-b]pyridines have also been tested for their potential selective antihistamine (H1) agents (Janssens et al.,1985). Imidazo[4,5-b]pyridine derivatives were also reported as Aurora kinases (Bavetsias et al., 2007) and cyclic PDE inhibitors (Coates et al.,1993). Importantly,imidazo[4,5-b]pyridine is a structural analogue of purine whose derivatives easily interact with large biomolecules such as DNA, RNA or diverse proteins in vivo.

The molecular plot of the crystal structure of 3-Acetyl-6-bromo-1,3-dihydro- imidazo[4,5-b]pyridin-2-one is shown in Fig.1. The two fused five and six-membered rings building the molecule are nearly planar with the maximum deviation from the mean plane being -0.011 (3) A ° at N2. They form a dihedral angle of 2.7 (2)° with the acetyl group. In the crystal, adjacent molecules are linked by intermolecular N—H···N and C—H···O hydrogen bonding in the way to form infinite chains as shown in Fig. 2 and Table 1.

Related literature

For background information on the pharmacological activities of imidazo[4,5-b]pyridines, see: Kale et al. (2009); Silverman (2004); Cristalli et al. (1995); Cundy et al. (1997); Banie et al. (2007); Mader (2008); Janssens et al. (1985); Bavetsias et al. (2007); Coates et al. (1993).

S2. Experimental

To a stirred solution of 6-bromo-1,3-dihydro-imidazo[4,5 - b-]pyridin-2-one (0.2 g; 93.4 mmol), K₂CO₃ (0.38 g; 2.8 mmol), and tetra n-butyl ammonium bromide (0.03 g; 9.34 10–5 mol) in DMF, acetyl chloride (0.08 ml; 1.12 mmol) was added dropwise. The mixture was heated under reflux for 24 h. After completion of reaction (monitored by TLC), the salt was filtered and the solvent was removed under reduced pressure. The resulting residue was purified by column chromatography on silica gel using (ethylacetate/hexane) (1/1) as eluent. Crystals were isolated after the solvent was allowed to evaporate.

S3. Refinement

H atoms were located in a difference map and treated as riding with C—H = 0.93 Å for all aromatic H atoms and 0.96 Å for the methyl with U_iso(H) = 1.2 U_eq and U_iso(H) = 1.5 U_eq for the aromatic and methyl respectively.

Computing details

Data collection: APEX2 (Bruker, 2009); cell refinement: SAINT (Bruker, 2009); data reduction: SAINT (Bruker, 2009); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEPIII (Burnett & Johnson, 1996) and ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).

Figures

	Fig. 1. : Molecular view of the title compound with the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level. H atoms are represented as small circles of arbitrary radii.
	Fig. 2. : Partial packing view showing the N-H···N and C-H···O hydrogen bonds as dashed lines. H atoms not involved in hydrogen bonding have been omitted for clarity. [Symmetry codes: (i) -x-1, -y+2, -z+2; (ii) -x+1, -y+1, -z+2].

1-Acetyl-6-bromo-1H-imidazo[4,5-b]pyridin-2(3H)-one

Crystal data

C8H6BrN3O2	Z = 2
Mr = 256.07	F(000) = 252
Triclinic, P1	Dx = 1.887 Mg m^−3
Hall symbol: -P 1	Melting point: 507 K
a = 4.8302 (15) Å	Mo Kα radiation, λ = 0.71073 Å
b = 9.645 (3) Å	Cell parameters from 1685 reflections
c = 9.809 (3) Å	θ = 2.1–26.0°
α = 81.542 (7)°	µ = 4.53 mm^−1
β = 85.735 (7)°	T = 298 K
γ = 89.676 (8)°	Fiber, colourless
V = 450.8 (2) Å^3	0.41 × 0.16 × 0.11 mm

Data collection

Bruker APEXII CCD diffractometer	1685 independent reflections
Radiation source: fine-focus sealed tube	1583 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.019
φ and ω scans	θmax = 26.0°, θmin = 2.1°
Absorption correction: multi-scan (SADABS; Bruker, 2009)	h = −5→5
Tmin = 0.423, Tmax = 0.607	k = −11→11
2559 measured reflections	l = 0→12

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.028	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.074	H-atom parameters constrained
S = 1.07	w = 1/[σ^2(Fo^2) + (0.0374P)^2 + 0.2048P] where P = (Fo^2 + 2Fc^2)/3
1685 reflections	(Δ/σ)max = 0.001
128 parameters	Δρmax = 0.43 e Å^−3
0 restraints	Δρmin = −0.48 e Å^−3

Special details

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > 2σ(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
C1	−0.0666 (6)	0.9228 (3)	0.7492 (3)	0.0412 (6)
H1	−0.0912	0.9789	0.6654	0.049*
C2	0.1373 (5)	0.8216 (3)	0.7536 (2)	0.0371 (5)
C3	0.1881 (5)	0.7340 (3)	0.8759 (2)	0.0377 (5)
H3	0.3253	0.6658	0.8796	0.045*
C4	0.0199 (5)	0.7562 (3)	0.9904 (2)	0.0355 (5)
C5	−0.1838 (5)	0.8602 (3)	0.9766 (3)	0.0372 (5)
C6	−0.2202 (6)	0.7636 (3)	1.2009 (3)	0.0435 (6)
C7	0.1715 (7)	0.5870 (3)	1.1871 (3)	0.0466 (6)
C8	0.1168 (8)	0.5301 (3)	1.3357 (3)	0.0588 (8)
H8A	0.2348	0.4510	1.3590	0.088*
H8B	−0.0740	0.5012	1.3534	0.088*
H8C	0.1541	0.6013	1.3909	0.088*
N1	−0.2322 (5)	0.9436 (2)	0.8618 (2)	0.0426 (5)
N2	−0.3244 (5)	0.8613 (3)	1.1034 (2)	0.0435 (5)
H2	−0.4601	0.9164	1.1191	0.052*
N3	−0.0003 (5)	0.6957 (2)	1.1302 (2)	0.0395 (5)
O1	−0.2966 (5)	0.7398 (2)	1.3223 (2)	0.0595 (6)
O2	0.3528 (6)	0.5462 (3)	1.1138 (2)	0.0757 (8)
Br1	0.35286 (6)	0.80290 (3)	0.58804 (2)	0.04632 (13)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0412 (14)	0.0477 (14)	0.0338 (13)	0.0047 (11)	−0.0012 (10)	−0.0033 (10)
C2	0.0392 (14)	0.0439 (13)	0.0276 (11)	−0.0007 (10)	0.0057 (10)	−0.0072 (9)
C3	0.0387 (14)	0.0428 (12)	0.0310 (12)	0.0059 (10)	0.0035 (10)	−0.0064 (10)
C4	0.0369 (13)	0.0405 (12)	0.0283 (11)	0.0025 (10)	0.0032 (9)	−0.0050 (9)
C5	0.0330 (13)	0.0449 (13)	0.0341 (12)	0.0037 (10)	0.0031 (10)	−0.0100 (10)
C6	0.0405 (15)	0.0523 (15)	0.0366 (14)	0.0057 (11)	0.0085 (11)	−0.0088 (11)
C7	0.0598 (18)	0.0451 (14)	0.0325 (13)	0.0098 (12)	0.0069 (12)	−0.0034 (10)
C8	0.078 (2)	0.0572 (17)	0.0349 (15)	0.0131 (15)	0.0123 (14)	0.0039 (12)
N1	0.0397 (13)	0.0504 (12)	0.0371 (12)	0.0090 (10)	−0.0002 (9)	−0.0059 (9)
N2	0.0382 (12)	0.0550 (13)	0.0359 (12)	0.0105 (10)	0.0076 (9)	−0.0074 (9)
N3	0.0417 (12)	0.0461 (11)	0.0287 (10)	0.0075 (9)	0.0083 (8)	−0.0045 (8)
O1	0.0640 (14)	0.0745 (14)	0.0354 (11)	0.0152 (11)	0.0188 (9)	−0.0049 (9)
O2	0.0976 (19)	0.0822 (16)	0.0386 (11)	0.0532 (15)	0.0185 (11)	0.0060 (10)
Br1	0.0522 (2)	0.0565 (2)	0.02805 (16)	0.00477 (12)	0.00836 (11)	−0.00472 (11)

Geometric parameters (Å, º)

C1—N1	1.354 (3)	C6—O1	1.209 (3)
C1—C2	1.381 (4)	C6—N2	1.363 (4)
C1—H1	0.9300	C6—N3	1.433 (3)
C2—C3	1.398 (4)	C7—O2	1.193 (4)
C2—Br1	1.894 (2)	C7—N3	1.409 (4)
C3—C4	1.379 (3)	C7—C8	1.486 (4)
C3—H3	0.9300	C8—H8A	0.9600
C4—C5	1.401 (4)	C8—H8B	0.9600
C4—N3	1.406 (3)	C8—H8C	0.9600
C5—N1	1.319 (3)	N2—H2	0.8600
C5—N2	1.374 (3)
N1—C1—C2	122.6 (2)	N2—C6—N3	105.9 (2)
N1—C1—H1	118.7	O2—C7—N3	118.5 (2)
C2—C1—H1	118.7	O2—C7—C8	123.7 (3)
C1—C2—C3	122.0 (2)	N3—C7—C8	117.8 (2)
C1—C2—Br1	118.30 (19)	C7—C8—H8A	109.5
C3—C2—Br1	119.66 (19)	C7—C8—H8B	109.5
C4—C3—C2	115.1 (2)	H8A—C8—H8B	109.5
C4—C3—H3	122.5	C7—C8—H8C	109.5
C2—C3—H3	122.5	H8A—C8—H8C	109.5
C3—C4—C5	119.2 (2)	H8B—C8—H8C	109.5
C3—C4—N3	134.3 (2)	C5—N1—C1	115.0 (2)
C5—C4—N3	106.5 (2)	C6—N2—C5	110.9 (2)
N1—C5—N2	125.6 (2)	C6—N2—H2	124.6
N1—C5—C4	126.0 (2)	C5—N2—H2	124.6
N2—C5—C4	108.4 (2)	C4—N3—C7	124.2 (2)
O1—C6—N2	127.0 (3)	C4—N3—C6	108.4 (2)
O1—C6—N3	127.1 (3)	C7—N3—C6	127.4 (2)
N1—C1—C2—C3	−0.5 (5)	N1—C5—N2—C6	−178.9 (3)
N1—C1—C2—Br1	179.6 (2)	C4—C5—N2—C6	0.7 (3)
C1—C2—C3—C4	0.1 (4)	C3—C4—N3—C7	0.3 (5)
Br1—C2—C3—C4	−179.98 (19)	C5—C4—N3—C7	−179.4 (3)
C2—C3—C4—C5	0.5 (4)	C3—C4—N3—C6	−179.8 (3)
C2—C3—C4—N3	−179.2 (3)	C5—C4—N3—C6	0.5 (3)
C3—C4—C5—N1	−0.8 (4)	O2—C7—N3—C4	2.8 (5)
N3—C4—C5—N1	178.9 (3)	C8—C7—N3—C4	−177.5 (3)
C3—C4—C5—N2	179.5 (2)	O2—C7—N3—C6	−177.1 (3)
N3—C4—C5—N2	−0.7 (3)	C8—C7—N3—C6	2.6 (5)
N2—C5—N1—C1	−179.9 (3)	O1—C6—N3—C4	−179.6 (3)
C4—C5—N1—C1	0.5 (4)	N2—C6—N3—C4	0.0 (3)
C2—C1—N1—C5	0.2 (4)	O1—C6—N3—C7	0.3 (5)
O1—C6—N2—C5	179.1 (3)	N2—C6—N3—C7	179.8 (3)
N3—C6—N2—C5	−0.4 (3)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N2—H2···N1^i	0.86	2.02	2.877 (3)	175
C3—H3···O2^ii	0.93	2.56	3.481 (3)	172

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