organic compounds
tert-Butyl 6-bromo-1,4-dimethyl-9H-carbazole-9-carboxylate
aLaboratoire de Chimie Moléculaire et Thio-organique, UMR CNRS 6507, FR CNRS 3038 INC3M, ENSICAEN – Université de Caen, 14050 Caen, France, and bCentre d'Études et de Recherche sur le Médicament de Normandie (CERMN), EA 3915, FR CNRS 3038 INC3M, Université de Caen, boulevard Becquerel, 14032 Caen, France
*Correspondence e-mail: jean-francois.lohier@ensicaen.fr
The title compound, C19H20BrNO2, consists of a carbazole skeleton with methyl groups at positions 1 and 4, a protecting group located at the N atom and a Br atom at position 6. The pyrrole ring is oriented at dihedral angles of 1.27 (7) and 4.86 (7)° with respect to the adjacent benzene rings. The dihedral angle between the benzene rings is 5.11 (7). The is determined mainly by intramolecular C—H⋯O and intermolecular π–π interactions. π-stacking between adjacent molecules forms columns with a parallel arrangement of the carbazole ring systems. The presence of the tert-butoxycarbonyl group on the carbazole N atom and the intramolecular hydrogen bond induce a particular conformation of the exocyclic N—C bond within the molecule.
Related literature
For the pharmaceutical properties of carbazole derivatives, see: Itoigawa et al. (2000); Laronze et al. (2005); Thevissen et al. (2009). For their electroactivity and luminescent properties, see: Grazulevicius et al. (2003) and for their their applications in the light-emitting field, see: Zhang et al. (2006). For the synthesis of carbazoles and ellipticine derivatives, see: Ergün et al. (1998); Knölker et al. (2002); Liu et al. (2007). For related structures, see: Caruso et al. (2007); Sopková-de Oliveira Santos et al. (2008). For bond-length data, see: Allen et al. (1987). The title compound constitutes a cheap and reactive intermediate for the preparation of new analogs of the anticancer agent 9-methoxyellipticine, see: Le Pecq et al. (1974). A lengthening of N—C bond lengths due to the presence of a protecting group has been observed in similar compounds, see: Back et al. (2001); Chakkaravarthi et al. (2009); Terpin et al. (1998) For N-sulfonyl carbazole derivatives with similar conformations, see: Chakkaravarthi et al. (2008). For non N-atom-substituted analogs, see: Viossat et al. (1988).
Experimental
Crystal data
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Refinement
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Data collection: APEX2 (Bruker, 2007); cell SAINT (Bruker, 2007); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: Mercury (Macrae et al., 2008); software used to prepare material for publication: SHELXL97.
Supporting information
https://doi.org/10.1107/S1600536810026528/om2338sup1.cif
contains datablocks I, global. DOI:Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S1600536810026528/om2338Isup2.hkl
6-Bromo-9-tert-butoxycarbonyl-1,4-dimethyl-9H-carbazole was prepared by reaction of 6-bromo-1,4-dimethyl-9H-carbazole (5.0 g, 18.2 mmol) with di-tert-butyl dicarbonate (8.0 g, 36.5 mmol) in the presence of DMAP (4.46 g, 36.5 mmol) and triethylamine (5.1 ml, 36.5 mmol) in acetonitrile (70 ml). The mixture was stirred for 1 h at 0°C, then left at room temperature for 3 h. The residue obtained after removal of the solvent was diluted with EtOAc (100 ml) and shaken with water (2 x 100 ml). The residue obtained after an usual work-up was purified by silica gel
using cyclohexane/ether (7:3) as to give the compound as a yellow solid (63% yield). Transparent crystals suitable for X-ray analysis were grown from an acetonitrile solution at room temperature.All non-hydrogen atoms were refined anisotropically. The H atoms were refined with fixed geometry, riding on their carrier atoms with Uiso(H) values set at 1.2 (1.5 for methyl H atoms) times Ueq of the parent atom (C—H = 0.93–0.96 Å) for (I).
Over the past few years, large interest has been observed in chemistry of carbazole derivatives since they can be widely used as organic materials due to their electroactivity and luminescent properties (Grazulevicius et al., 2003) or their applications in the light-emitting field (Zhang et al., 2006). This class of compounds also displays various pharmacological activities such as, among others, anticancer (Itoigawa et al., 2000; Laronze et al., 2005), antibacterial and antifungal activities (Thevissen et al., 2009).
Many elegant methods for the synthesis of ellipticine and related carbazole
have been reported (Ergün et al., 1998; Knölker et al., 2002; Liu et al., 2007). In our laboratory, the quest to discover new potential bioactive compounds possessing a carbazole core has attracted all our attention and recently, we have synthesized and characterized a series of carbazole derivatives (Caruso et al., 2007; Sopková-de Oliveira Santos et al., 2008). In this paper, we present the results of structural investigation of a new intermediate (Scheme 1): 6-bromo-9-tert-butoxycarbonyl-1,4-dimethyl-9H- carbazole (Fig. 1) which constitutes a very interesting, cheap and reactive intermediate for the preparation of new analogs of the anticancer agent 9-methoxyellipticine (Le Pecq et al., 1974).The carbazole ring system (C1—C9A/N9) is nearly planar and the maximum deviation from the least-squares planes does not exceed 0.0662 (14) Å. The pyrrole ring is oriented with respect to the adjacent benzene rings at dihedral angles of 1.27 (7) and 4.86 (7)°.
The N—C bond lengths, namely N9—C8A and N9—C9A [1.408 (2)Å and 1.417 (2) Å] deviate slightly from the normal mean value reported in the literature (Allen et al., 1987). This indicates that the presence of protecting group at atom N9, probably through its electron-withdrawing character, causes the lengthening of N—C bond lengths which has been already observed with similar compounds (Back et al., 2001; Terpin et al., 1998; Chakkaravarthi et al., 2009). Methyl substituent C9 is coplanar with the aromatic rings, methyl substituent C10 closed to N-protecting group displays slight deviation from the carbazole plane with torsion angle values C4A—C9A—C1—C10 of -172.72 (15). This is probably due to minimize the steric hinderance induced by the carbamate group. No particular increase in the widening angle, namely C9A—C1—C10, has been observed compared to non substituted nitrogen atom analogs (Viossat et al., 1988). Weak intramolecular C—H···O interaction is present in the molecule. In fact, atom C8 acts, throught H8, as hydrogen-bond donor to O2, distance between H8 and O2 being 2.33 Å (Table 1). Thus, in order to optimize previous H-bond and minimize steric hinderance of N-protecting group, carbamate is forced to adopt a particular conformation, specially a very twisted torsion angle which have been also seen with N-sulfonyl carbazole derivatives displaying intramolecular H-bonds (Chakkaravarthi et al., 2008). Thus, the torsion angle C1—C9A—N9—C11 is as high as 30.8 (2)°.
In the crystal packing, π–π interactions may be effective in the stabilization of the structure. Stacking interactions occur between aromatic rings leading to columns along a axis. The arrangement of carbazole ring systems within column is parallel but non equally spaced and molecules rotate of 180° alternatively. More precisely, π–π contacts are present with Cg2···Cg3 distance = 3.755 (2)Å [symmetry code: 1 - x,-y, 1 - z] and 3.811 (2)Å [symmetry code:-x,-y, 1 - z]. Cg1···Cg1 distance is 3.927 (2)Å [symmetry code: 1 - x,-y, 1 - z] and 4.199 (2)Å [symmetry code:-x,-y, 1 - z] with a center-to-edge arrangement (Table 2). Cg1, Cg2 and Cg3 are the centroids of N9—C9A—C4A—C5A—C8A, C5A—C5—C6—C7—C8—C8A and C9A—C1—C2—C3—C4—C4A rings, respectively. The carbazole systems are inclined at an angle of about 13.4° to [100] plan.
In conclusion, the π stacking. Thus, flat similar compounds could be used as anticancer agents through their intercalation effect like ellipticine.
of an interesting carbazole intermediate has been elucidated. A strong displacement of the N-protecting group out of the plane has been observed. Nevertheless, presence of the tert-Butyloxycarbonyl group does not prevent parallel arrangement of carbazole systems byFor the pharmaceutical properties of carbazole derivatives, see: Itoigawa et al. (2000); Laronze et al. (2005); Thevissen et al. (2009). For their electroactivity and luminescent properties, see: Grazulevicius et al. (2003) and for their their applications in the light-emitting field, see: Zhang et al. (2006). For the synthesis of carbazoles and ellipticine derivatives, see: Ergün et al. (1998); Knölker et al. (2002); Liu et al. (2007). For related structures, see: Caruso et al. (2007); Sopková-de Oliveira Santos et al. (2008). For bond-length data, see: Allen et al. (1987). The title compound constitutes a very interesting, cheap and reactive intermediate for the preparation of new analogs of the anticancer agent 9-methoxyellipticine, see: Le Pecq et al. (1974). A lengthening of N—C bond lengths due to the presence of a protecting group has been observed in similar compounds, see: Back et al. (2001); Chakkaravarthi et al. (2009); Terpin et al. (1998) For N-sulfonyl carbazole derivatives with similar conformations, see: Chakkaravarthi et al. (2008). For non N-atom-substituted analogs, see: Viossat et al. (1988).
Data collection: APEX2 (Bruker, 2007); cell
SAINT (Bruker, 2007); data reduction: SAINT (Bruker, 2007); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: Mercury (Macrae et al., 2008); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).Fig. 1. the title compound showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability levels; For the sake of clarity H atoms have been omitted. | |
Fig. 2. Part of the crystal packing showing the way in which a column along a axis is formed through π–π interactions. For the sake of clarity H atoms have been omitted. [Symmetry codes: (*)-x,-y, 1 - z; (#) 1 - x,-y, 1 - z.] |
C19H20BrNO2 | Z = 2 |
Mr = 374.27 | F(000) = 384 |
Triclinic, P1 | Dx = 1.435 Mg m−3 |
Hall symbol: -P 1 | Mo Kα radiation, λ = 0.71073 Å |
a = 7.521 (4) Å | Cell parameters from 9940 reflections |
b = 9.715 (5) Å | θ = 5.4–57.6° |
c = 11.930 (6) Å | µ = 2.38 mm−1 |
α = 91.10 (4)° | T = 291 K |
β = 96.40 (4)° | Block, colorless |
γ = 90.96 (4)° | 0.46 × 0.37 × 0.34 mm |
V = 865.9 (8) Å3 |
Bruker–Nonius APEXII Kappa CCD diffractometer | 5718 independent reflections |
Radiation source: fine-focus sealed tube | 4268 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.025 |
φ and ω scans | θmax = 31.5°, θmin = 2.1° |
Absorption correction: numerical (SAINT; Bruker, 2007) | h = −11→11 |
Tmin = 0.378, Tmax = 0.429 | k = −14→14 |
37091 measured reflections | l = −17→17 |
Refinement on F2 | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.034 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.092 | H-atom parameters constrained |
S = 1.02 | w = 1/[σ2(Fo2) + (0.0409P)2 + 0.2555P] where P = (Fo2 + 2Fc2)/3 |
5718 reflections | (Δ/σ)max = 0.001 |
213 parameters | Δρmax = 0.63 e Å−3 |
0 restraints | Δρmin = −0.52 e Å−3 |
C19H20BrNO2 | γ = 90.96 (4)° |
Mr = 374.27 | V = 865.9 (8) Å3 |
Triclinic, P1 | Z = 2 |
a = 7.521 (4) Å | Mo Kα radiation |
b = 9.715 (5) Å | µ = 2.38 mm−1 |
c = 11.930 (6) Å | T = 291 K |
α = 91.10 (4)° | 0.46 × 0.37 × 0.34 mm |
β = 96.40 (4)° |
Bruker–Nonius APEXII Kappa CCD diffractometer | 5718 independent reflections |
Absorption correction: numerical (SAINT; Bruker, 2007) | 4268 reflections with I > 2σ(I) |
Tmin = 0.378, Tmax = 0.429 | Rint = 0.025 |
37091 measured reflections |
R[F2 > 2σ(F2)] = 0.034 | 0 restraints |
wR(F2) = 0.092 | H-atom parameters constrained |
S = 1.02 | Δρmax = 0.63 e Å−3 |
5718 reflections | Δρmin = −0.52 e Å−3 |
213 parameters |
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 > 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. |
x | y | z | Uiso*/Ueq | ||
C1 | 0.3387 (2) | −0.20146 (16) | 0.34933 (15) | 0.0458 (3) | |
C2 | 0.3632 (2) | −0.30773 (17) | 0.42578 (17) | 0.0542 (4) | |
H2 | 0.3978 | −0.3929 | 0.3996 | 0.065* | |
C3 | 0.3389 (2) | −0.29340 (17) | 0.53845 (17) | 0.0543 (4) | |
H3 | 0.3563 | −0.3690 | 0.5847 | 0.065* | |
C4 | 0.2894 (2) | −0.16985 (16) | 0.58456 (14) | 0.0444 (3) | |
C4A | 0.26189 (18) | −0.06062 (15) | 0.51011 (13) | 0.0376 (3) | |
C5 | 0.1845 (2) | 0.15877 (16) | 0.62353 (12) | 0.0411 (3) | |
H5 | 0.1796 | 0.1170 | 0.6927 | 0.049* | |
C5A | 0.22209 (18) | 0.08324 (14) | 0.52870 (12) | 0.0360 (3) | |
C6 | 0.1549 (2) | 0.29736 (16) | 0.61113 (13) | 0.0437 (3) | |
C7 | 0.1590 (2) | 0.36264 (16) | 0.50904 (14) | 0.0466 (3) | |
H7 | 0.1388 | 0.4567 | 0.5046 | 0.056* | |
C8 | 0.1928 (2) | 0.28895 (16) | 0.41425 (14) | 0.0455 (3) | |
H8 | 0.1944 | 0.3315 | 0.3452 | 0.055* | |
C8A | 0.22440 (19) | 0.14932 (15) | 0.42488 (12) | 0.0377 (3) | |
C9 | 0.2702 (3) | −0.1553 (2) | 0.70822 (16) | 0.0585 (4) | |
H9A | 0.3533 | −0.0863 | 0.7419 | 0.088* | |
H9B | 0.2945 | −0.2417 | 0.7440 | 0.088* | |
H9C | 0.1504 | −0.1286 | 0.7178 | 0.088* | |
C9A | 0.28247 (18) | −0.07791 (15) | 0.39496 (13) | 0.0383 (3) | |
C10 | 0.3831 (3) | −0.2220 (2) | 0.23079 (17) | 0.0601 (4) | |
H10A | 0.4583 | −0.3004 | 0.2270 | 0.090* | |
H10B | 0.4447 | −0.1415 | 0.2083 | 0.090* | |
H10C | 0.2747 | −0.2370 | 0.1812 | 0.090* | |
C11 | 0.2066 (2) | 0.06842 (17) | 0.22633 (13) | 0.0455 (3) | |
C12 | 0.2220 (3) | 0.2419 (2) | 0.08037 (15) | 0.0595 (4) | |
C13 | 0.3005 (4) | 0.1472 (3) | −0.00242 (19) | 0.0880 (8) | |
H13A | 0.2410 | 0.0588 | −0.0042 | 0.132* | |
H13B | 0.4259 | 0.1367 | 0.0206 | 0.132* | |
H13C | 0.2845 | 0.1858 | −0.0762 | 0.132* | |
C14 | 0.0229 (3) | 0.2543 (3) | 0.05422 (19) | 0.0749 (6) | |
H14A | −0.0326 | 0.1646 | 0.0537 | 0.112* | |
H14B | −0.0037 | 0.2946 | −0.0184 | 0.112* | |
H14C | −0.0221 | 0.3116 | 0.1107 | 0.112* | |
C15 | 0.3132 (5) | 0.3824 (3) | 0.0885 (2) | 0.0956 (9) | |
H15A | 0.2879 | 0.4284 | 0.0181 | 0.143* | |
H15B | 0.4401 | 0.3719 | 0.1047 | 0.143* | |
H15C | 0.2695 | 0.4360 | 0.1477 | 0.143* | |
Br1 | 0.10889 (3) | 0.40593 (2) | 0.738576 (16) | 0.06549 (9) | |
O1 | 0.12304 (19) | −0.01560 (14) | 0.16710 (11) | 0.0611 (3) | |
O2 | 0.26615 (18) | 0.19081 (13) | 0.19661 (10) | 0.0537 (3) | |
N9 | 0.25825 (17) | 0.05083 (13) | 0.34212 (10) | 0.0408 (3) |
U11 | U22 | U33 | U12 | U13 | U23 | |
C1 | 0.0374 (7) | 0.0426 (7) | 0.0575 (9) | 0.0008 (6) | 0.0074 (6) | −0.0080 (7) |
C2 | 0.0496 (9) | 0.0381 (8) | 0.0750 (12) | 0.0043 (7) | 0.0072 (8) | −0.0050 (7) |
C3 | 0.0532 (9) | 0.0395 (8) | 0.0700 (11) | 0.0029 (7) | 0.0048 (8) | 0.0088 (7) |
C4 | 0.0380 (7) | 0.0428 (7) | 0.0521 (8) | −0.0002 (6) | 0.0034 (6) | 0.0072 (6) |
C4A | 0.0305 (6) | 0.0376 (7) | 0.0448 (7) | 0.0003 (5) | 0.0040 (5) | 0.0011 (5) |
C5 | 0.0416 (7) | 0.0454 (8) | 0.0365 (7) | 0.0035 (6) | 0.0048 (6) | 0.0014 (6) |
C5A | 0.0312 (6) | 0.0383 (7) | 0.0386 (7) | 0.0023 (5) | 0.0030 (5) | 0.0015 (5) |
C6 | 0.0435 (8) | 0.0458 (8) | 0.0418 (7) | 0.0071 (6) | 0.0044 (6) | −0.0055 (6) |
C7 | 0.0504 (9) | 0.0386 (7) | 0.0507 (8) | 0.0091 (6) | 0.0041 (7) | −0.0004 (6) |
C8 | 0.0534 (9) | 0.0422 (7) | 0.0410 (7) | 0.0075 (6) | 0.0042 (6) | 0.0049 (6) |
C8A | 0.0359 (7) | 0.0395 (7) | 0.0376 (6) | 0.0027 (5) | 0.0032 (5) | −0.0010 (5) |
C9 | 0.0647 (11) | 0.0576 (10) | 0.0540 (10) | 0.0060 (8) | 0.0070 (8) | 0.0172 (8) |
C9A | 0.0324 (6) | 0.0377 (7) | 0.0446 (7) | −0.0002 (5) | 0.0044 (5) | −0.0006 (5) |
C10 | 0.0612 (11) | 0.0584 (10) | 0.0620 (11) | 0.0077 (8) | 0.0145 (8) | −0.0156 (8) |
C11 | 0.0471 (8) | 0.0499 (8) | 0.0400 (7) | 0.0040 (7) | 0.0068 (6) | −0.0013 (6) |
C12 | 0.0760 (12) | 0.0653 (11) | 0.0388 (8) | 0.0052 (9) | 0.0114 (8) | 0.0088 (7) |
C13 | 0.110 (2) | 0.109 (2) | 0.0513 (11) | 0.0309 (16) | 0.0346 (12) | 0.0106 (12) |
C14 | 0.0836 (15) | 0.0850 (15) | 0.0567 (11) | 0.0204 (12) | 0.0062 (10) | 0.0129 (11) |
C15 | 0.129 (2) | 0.0829 (17) | 0.0745 (16) | −0.0223 (16) | 0.0062 (15) | 0.0314 (13) |
Br1 | 0.08728 (16) | 0.05996 (12) | 0.05042 (11) | 0.01706 (10) | 0.01285 (9) | −0.01170 (8) |
O1 | 0.0717 (8) | 0.0602 (8) | 0.0484 (7) | −0.0039 (6) | −0.0046 (6) | −0.0062 (6) |
O2 | 0.0680 (8) | 0.0550 (7) | 0.0382 (5) | −0.0045 (6) | 0.0059 (5) | 0.0051 (5) |
N9 | 0.0451 (7) | 0.0402 (6) | 0.0374 (6) | 0.0032 (5) | 0.0056 (5) | −0.0012 (5) |
C1—C2 | 1.392 (3) | C9—H9C | 0.9600 |
C1—C9A | 1.399 (2) | C9A—N9 | 1.417 (2) |
C1—C10 | 1.499 (3) | C10—H10A | 0.9600 |
C2—C3 | 1.381 (3) | C10—H10B | 0.9600 |
C2—H2 | 0.9300 | C10—H10C | 0.9600 |
C3—H3 | 0.9300 | C11—O1 | 1.193 (2) |
C4—C3 | 1.384 (3) | C11—O2 | 1.332 (2) |
C4—C4A | 1.400 (2) | C11—N9 | 1.407 (2) |
C4—C9 | 1.502 (3) | C12—O2 | 1.486 (2) |
C4A—C9A | 1.407 (2) | C12—C13 | 1.511 (3) |
C5—C5A | 1.394 (2) | C12—C15 | 1.514 (3) |
C5—H5 | 0.9300 | C13—H13A | 0.9600 |
C5A—C8A | 1.408 (2) | C13—H13B | 0.9600 |
C5A—C4A | 1.452 (2) | C13—H13C | 0.9600 |
C6—C5 | 1.376 (2) | C14—C12 | 1.502 (3) |
C6—C7 | 1.387 (2) | C14—H14A | 0.9600 |
C7—C8 | 1.377 (2) | C14—H14B | 0.9600 |
C7—H7 | 0.9300 | C14—H14C | 0.9600 |
C8—C8A | 1.387 (2) | C15—H15A | 0.9600 |
C8—H8 | 0.9300 | C15—H15B | 0.9600 |
C8A—N9 | 1.408 (2) | C15—H15C | 0.9600 |
C9—H9A | 0.9600 | Br1—C6 | 1.9004 (18) |
C9—H9B | 0.9600 | ||
C1—C2—H2 | 118.3 | C8A—N9—C9A | 108.07 (12) |
C1—C9A—C4A | 122.57 (15) | C9A—C1—C10 | 125.22 (16) |
C1—C9A—N9 | 128.35 (14) | C9A—C4A—C5A | 107.15 (13) |
C1—C10—H10A | 109.5 | H9A—C9—H9B | 109.5 |
C1—C10—H10B | 109.5 | H9A—C9—H9C | 109.5 |
C1—C10—H10C | 109.5 | H9B—C9—H9C | 109.5 |
C2—C1—C9A | 114.58 (16) | H10A—C10—H10B | 109.5 |
C2—C1—C10 | 120.08 (16) | H10A—C10—H10C | 109.5 |
C2—C3—C4 | 122.00 (17) | H10B—C10—H10C | 109.5 |
C2—C3—H3 | 119.0 | C11—O2—C12 | 121.26 (14) |
C3—C2—C1 | 123.47 (16) | C11—N9—C8A | 122.65 (13) |
C3—C2—H2 | 118.3 | C11—N9—C9A | 125.02 (13) |
C3—C4—C4A | 116.27 (16) | C12—C13—H13A | 109.5 |
C3—C4—C9 | 121.07 (16) | C12—C13—H13B | 109.5 |
C4—C3—H3 | 119.0 | C12—C13—H13C | 109.5 |
C4—C4A—C9A | 121.03 (14) | C12—C14—H14A | 109.5 |
C4—C4A—C5A | 131.72 (15) | C12—C14—H14B | 109.5 |
C4—C9—H9A | 109.5 | C12—C14—H14C | 109.5 |
C4—C9—H9B | 109.5 | C12—C15—H15A | 109.5 |
C4—C9—H9C | 109.5 | C12—C15—H15B | 109.5 |
C4A—C4—C9 | 122.65 (16) | C12—C15—H15C | 109.5 |
C4A—C9A—N9 | 108.67 (13) | C13—C12—C15 | 111.9 (2) |
C5—C5A—C8A | 119.61 (14) | H13A—C13—H13C | 109.5 |
C5—C5A—C4A | 133.06 (14) | H13B—C13—H13C | 109.5 |
C5—C6—C7 | 122.74 (14) | H13A—C13—H13B | 109.5 |
C5—C6—Br1 | 119.29 (12) | C14—C12—C13 | 112.2 (2) |
C5A—C5—H5 | 121.2 | C14—C12—C15 | 110.9 (2) |
C5A—C8A—N9 | 108.75 (13) | H14A—C14—H14B | 109.5 |
C6—C5—C5A | 117.59 (14) | H14A—C14—H14C | 109.5 |
C6—C5—H5 | 121.2 | H14B—C14—H14C | 109.5 |
C6—C7—H7 | 119.8 | H15A—C15—H15C | 109.5 |
C7—C6—Br1 | 117.97 (12) | H15A—C15—H15B | 109.5 |
C7—C8—C8A | 117.97 (15) | H15B—C15—H15C | 109.5 |
C7—C8—H8 | 121.0 | O1—C11—O2 | 127.27 (16) |
C8—C7—C6 | 120.33 (15) | O1—C11—N9 | 123.67 (16) |
C8—C7—H7 | 119.8 | O2—C11—N9 | 109.06 (14) |
C8—C8A—C5A | 121.75 (14) | O2—C12—C14 | 110.07 (16) |
C8—C8A—N9 | 129.48 (14) | O2—C12—C13 | 109.40 (17) |
C8A—C5A—C4A | 107.33 (13) | O2—C12—C15 | 101.86 (17) |
C8A—C8—H8 | 121.0 | ||
C1—C9A—N9—C11 | 30.8 (2) | C8A—N9—C11—O1 | −128.47 (18) |
C8—C8A—N9—C11 | −22.4 (2) | C9A—C4A—C4—C9 | 179.52 (15) |
C9A—N9—C11—O2 | −154.38 (14) | C2—C3—C4—C9 | −177.79 (17) |
C9A—N9—C11—O1 | 25.5 (3) | C3—C2—C1—C10 | 174.71 (17) |
C8A—N9—C11—O2 | 51.6 (2) | C4A—C9A—C1—C10 | −172.72 (15) |
Experimental details
Crystal data | |
Chemical formula | C19H20BrNO2 |
Mr | 374.27 |
Crystal system, space group | Triclinic, P1 |
Temperature (K) | 291 |
a, b, c (Å) | 7.521 (4), 9.715 (5), 11.930 (6) |
α, β, γ (°) | 91.10 (4), 96.40 (4), 90.96 (4) |
V (Å3) | 865.9 (8) |
Z | 2 |
Radiation type | Mo Kα |
µ (mm−1) | 2.38 |
Crystal size (mm) | 0.46 × 0.37 × 0.34 |
Data collection | |
Diffractometer | Bruker–Nonius APEXII Kappa CCD |
Absorption correction | Numerical (SAINT; Bruker, 2007) |
Tmin, Tmax | 0.378, 0.429 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 37091, 5718, 4268 |
Rint | 0.025 |
(sin θ/λ)max (Å−1) | 0.735 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.034, 0.092, 1.02 |
No. of reflections | 5718 |
No. of parameters | 213 |
H-atom treatment | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 0.63, −0.52 |
Computer programs: APEX2 (Bruker, 2007), SAINT (Bruker, 2007), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), Mercury (Macrae et al., 2008).
Cg1, Cg2 and Cg3 are the centroids of the N9–C9A–C4A–C5A–C8A, C9A–C1–C2–C3–C4–C4A and C5A–C5–C6–C7–C8–C8A rings, respectively, ccd is the distance between ring centroids, sa is the mean slippage angle (angle subtended by the intercentroid vector to the plane normal) and ipd is the mean interplanar distance (distance from one plane to the neighbouring centroid). For details, see Janiak (2000). |
Group 1/group 2 | ccd | sa | ipd |
Cg2/Cg3i | 3.755 (2) | 24 | 3.532 (1) |
Cg3/Cg2i | 3.755 (2) | 20 | 3.433 (1) |
Cg1/Cg1i | 3.927 (2) | 22 | 3.638 (1) |
Cg2/Cg3ii | 3.811 (2) | 18 | 3.654 (1) |
Cg3/Cg2ii | 3.811 (2) | 16 | 3.626 (1) |
Cg1/Cg1ii | 4.199 (2) | 32 | 3.578 (1) |
Symmetry codes: (i) -x+1, -y, -z+1; (ii) -x, -y, -z+1. |
References
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This is an open-access article distributed under the terms of the Creative Commons Attribution (CC-BY) Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original authors and source are cited.
Over the past few years, large interest has been observed in chemistry of carbazole derivatives since they can be widely used as organic materials due to their electroactivity and luminescent properties (Grazulevicius et al., 2003) or their applications in the light-emitting field (Zhang et al., 2006). This class of compounds also displays various pharmacological activities such as, among others, anticancer (Itoigawa et al., 2000; Laronze et al., 2005), antibacterial and antifungal activities (Thevissen et al., 2009).
Many elegant methods for the synthesis of ellipticine and related carbazole alkaloids have been reported (Ergün et al., 1998; Knölker et al., 2002; Liu et al., 2007). In our laboratory, the quest to discover new potential bioactive compounds possessing a carbazole core has attracted all our attention and recently, we have synthesized and characterized a series of carbazole derivatives (Caruso et al., 2007; Sopková-de Oliveira Santos et al., 2008). In this paper, we present the results of structural investigation of a new intermediate (Scheme 1): 6-bromo-9-tert-butoxycarbonyl-1,4-dimethyl-9H- carbazole (Fig. 1) which constitutes a very interesting, cheap and reactive intermediate for the preparation of new analogs of the anticancer agent 9-methoxyellipticine (Le Pecq et al., 1974).
The carbazole ring system (C1—C9A/N9) is nearly planar and the maximum deviation from the least-squares planes does not exceed 0.0662 (14) Å. The pyrrole ring is oriented with respect to the adjacent benzene rings at dihedral angles of 1.27 (7) and 4.86 (7)°.
The N—C bond lengths, namely N9—C8A and N9—C9A [1.408 (2)Å and 1.417 (2) Å] deviate slightly from the normal mean value reported in the literature (Allen et al., 1987). This indicates that the presence of protecting group at atom N9, probably through its electron-withdrawing character, causes the lengthening of N—C bond lengths which has been already observed with similar compounds (Back et al., 2001; Terpin et al., 1998; Chakkaravarthi et al., 2009). Methyl substituent C9 is coplanar with the aromatic rings, methyl substituent C10 closed to N-protecting group displays slight deviation from the carbazole plane with torsion angle values C4A—C9A—C1—C10 of -172.72 (15). This is probably due to minimize the steric hinderance induced by the carbamate group. No particular increase in the widening angle, namely C9A—C1—C10, has been observed compared to non substituted nitrogen atom analogs (Viossat et al., 1988). Weak intramolecular C—H···O interaction is present in the molecule. In fact, atom C8 acts, throught H8, as hydrogen-bond donor to O2, distance between H8 and O2 being 2.33 Å (Table 1). Thus, in order to optimize previous H-bond and minimize steric hinderance of N-protecting group, carbamate is forced to adopt a particular conformation, specially a very twisted torsion angle which have been also seen with N-sulfonyl carbazole derivatives displaying intramolecular H-bonds (Chakkaravarthi et al., 2008). Thus, the torsion angle C1—C9A—N9—C11 is as high as 30.8 (2)°.
In the crystal packing, π–π interactions may be effective in the stabilization of the structure. Stacking interactions occur between aromatic rings leading to columns along a axis. The arrangement of carbazole ring systems within column is parallel but non equally spaced and molecules rotate of 180° alternatively. More precisely, π–π contacts are present with Cg2···Cg3 distance = 3.755 (2)Å [symmetry code: 1 - x,-y, 1 - z] and 3.811 (2)Å [symmetry code:-x,-y, 1 - z]. Cg1···Cg1 distance is 3.927 (2)Å [symmetry code: 1 - x,-y, 1 - z] and 4.199 (2)Å [symmetry code:-x,-y, 1 - z] with a center-to-edge arrangement (Table 2). Cg1, Cg2 and Cg3 are the centroids of N9—C9A—C4A—C5A—C8A, C5A—C5—C6—C7—C8—C8A and C9A—C1—C2—C3—C4—C4A rings, respectively. The carbazole systems are inclined at an angle of about 13.4° to [100] plan.
In conclusion, the crystal structure of an interesting carbazole intermediate has been elucidated. A strong displacement of the N-protecting group out of the plane has been observed. Nevertheless, presence of the tert-Butyloxycarbonyl group does not prevent parallel arrangement of carbazole systems by π stacking. Thus, flat similar compounds could be used as anticancer agents through their intercalation effect like ellipticine.