Solvent-free synthesis of heteroannulated carbazoles: a novel class of anti-tumor agents.

A series of novel carbazole analogues that hold pyrido, isoxazolo, pyrimido and pyrazolo templates were designed and synthesised in good yield by grinding conditions. All the synthesised compounds were screened for their anti-tumor activity and displayed enviable selective growth inhibition on HeLa cell line compared to AGS cell line. Among these compounds, compound 2-(3',4'-diethoxy-benzylidene)-6-methyl-2,3,4,9-tetrahydro-carbazol-1-one,6-chloro-2-(3',4'-diethoxy-benzylidene)-2,3,4,9-tetrahydro-carbazol-1one, 2-(3',4'-diethoxy-benzylidene)-8-methyl-2,3,4,9-tetrahydro-carbazol-1-one, 3-(3',4'-diethoxyphenyl)-7-methyl-4,5-dihydro-10H-isoxazolo[3,4-a]carbazole, 7-chloro-3-(3',4'-diethoxyphenyl)-4,5-dihydro-10H-isoxazolo[3,4-a]carbazole, 4-(3',4'-diethoxyphenyl)-2-ethoxy-8-methyl-6,11-dihydro-5H-pyrido[2,3-a]carbazole-3-nitrile, 8-chloro-4-(3',4'-diethoxyphenyl)-2-ethoxy-6,11-dihydro-5H-pyrido[2,3-a]carbazole-3-nitrile, 4-(3',4'-diethoxyphenyl)-2-ethoxy-10-methyl-6,11-dihydro-5H-pyrido[2,3-a]carbazole-3-nitrile were found to have promising anti-tumor properities with reference to the standard ellipticine against the HeLa cancer cell line. All these intermediates showed IC50 outranged the standard ellipticine. The same compounds showed moderate activity against AGS cancer cell lines. The efforts were undertaken to optimize potency and selectivity of this class of compounds.

10-Methyl-2-oxo-4-phenyl-2,11-di-hydro-pyrano[2,3-a]carbazole-3-carbo-nitrile.

In the title mol-ecule, C23H14N2O2, the atoms in the carbazole unit deviate from planarity [maximum deviation from mean plane = 0.1018 (8) Å]. The pyrrole ring makes dihedral angles of 4.44 (5), 3.84 (5), 2.18 (5) and 56.44 (5)° with the pyran, fused benzene rings and phenyl ring, respectively. In the crystal, pairs of N-H⋯O hydrogen bonds generate R 2 (2)(14) loops and a C-H⋯N inter-action is also found. Mol-ecules are further linked by a number of π-π interactions [centroid-centroid distances vary from 3.5702 (5) to 3.7068 (6) Å], forming a three-dimensional network.

(E)-2-[(Furan-2-yl)methyl-idene]-7-methyl-2,3,4,9-tetra-hydro-1H-carbazol-1-one.

In the title mol-ecule, C(18)H(15)NO(2), the atoms in the carbazole unit deviate from planarity [maximum deviation from mean plane = 0.1317 (12) Å]. The pyrrole ring makes dihedral angles of 1.01 (8) and 18.56 (10)° with the benzene and furan rings, respectively. The cyclo-hexene ring adopts a half-chair conformation. In the crystal, pairs of N-H⋯O hydrogen bonds form an R(2) (2)(10) ring. Mol-ecules are further linked by C-H⋯O and C-H⋯π inter-actions, forming a three-dimensional network.

7-Methyl-1-phenyl-1,10-di-hydro-pyrazolo-[3,4-a]carbazole.

In the title mol-ecule, C20H15N3, the atoms in the carbazole unit deviate from planarity [maximum deviation from mean plane = 0.1082 (15) Å]. The pyrrole ring makes dihedral angles of 3.17 (8)/4.10 (9), 7.20 (9) and 44.62 (9)° with the fused benzene, pyrazole and phenyl rings, respectively. In the crystal, mol-ecules are linked via N-H⋯N hydrogen bonds, forming an infinite chain along [010]. Mol-ecules are further linked by nine π-π [centroid-centroid distances vary from 3.6864 (11) to 3.9802 (11) Å] and one C-H⋯π inter-action, forming a three-dimensional network.

2-Chloro-7,8,9,10-tetra-hydro-cyclo-hepta-[b]indol-6(5H)-one.

In the title mol-ecule, C(13)H(12)ClNO, the dihedral angle between the benzene and pyrrole rings is 1.38 (9)°. The cyclo-heptene ring adopts a distorted twist chair and sofa conformation. Inter-molecular N-H⋯O hydrogen bonds form an R(2) (2)(10) loop in the crystal packing. Further, weak C-H⋯O and C-H⋯π (involving the benzene ring) inter-actions are found in the crystal structure.

6-Methyl-2,3,4,9-tetra-hydro-1H-carbazole-1-thione.

In the title mol-ecule, C(13)H(13)NS, the dihedral angle between the benzene ring and the fused pyrrole ring is 0.71 (8)° and the cyclo-hexene ring is in an envelope form. The (CH(2))(3) atoms of the cyclo-hexene ring are disordered over two positions; the site-occupancy factor for the major component refined to 0.862 (4). In the crystal, inter-molecular N-H⋯S hydrogen bonds lead to the formation of centrosymmetric aggregates via an R(2) (2)(10) ring.

9-Ethyl-N-(3-nitro-benzyl-idene)-9H-carbazol-3-amine.

The title compound, C(21)H(17)N(3)O(2), crystallizes with two mol-ecules in the asymmetric unit. The carbazole groups show relatively small deviations from planarity [maximum displacements from the mean carbazole plane are 0.077 (7) and 0.101 (7) Å]. The dihedral angles between the 3-nitro-benzyl-idene-amine and carbazole groups are 37.9 (1) and 37.0 (1)° in the two mol-ecules.

5-Methyl-7,8,9,10-tetra-hydro-cyclo-hepta-[b]indol-6(5H)-one.

In the title mol-ecule, C(14)H(15)NO, the dihedral angle between the benzene and pyrrole rings is 1.99 (12)°. The cyclo-heptene ring adopts a slightly distorted boat conformation.

Synthesis and crystal structure of 1-hy-droxy-8-methyl-9H-carbazole-2-carbaldehyde.

Two crystallographically independent mol-ecules are present in the asymmetric unit of the title compound, C14H11NO2, with virtually identical geometries. The carbazole units are planar. The hy-droxy group at position 1, carbaldehyde group at position 2, and methyl group at position 8 (with the exception of two H atoms) are coplanar with the attached benzene rings. The dihedral angle between the two benzene rings is 2.20 (9)° in mol-ecule A and 2.01 (9)° in mol-ecule B. The pyrrole ring makes dihedral angles of 0.82 (10) and 1.40 (10)° [0.84 (10) and 1.18 (10)° in mol-ecule B] with the (-CH3)-substituted and (-OH and -CHO) substituted benzene rings, respectively. The mol-ecular structure is stabilized by the intra-molecular O-H⋯O hydrogen bonds, while the crystal structure features N-H⋯O and C-H⋯O hydrogen bonds. A range of π-π contacts further stabilizes the crystal structure.

8-Methyl-2,3,4,9-tetra-hydro-1H-carbazol-1-one.

In the title compound, C(13)H(13)NO, the dihedral angle between the benzene ring and the fused pyrrole ring is 0.96 (7)°. The cyclohexenone ring adopts an envelope conformation. Inter-molecular N-H⋯O hydrogen bonds form R(2) (2)(10) ring motifs in the crystal structure. Weak C-H⋯π inter-actions involving the benzene ring also occur.

2,5-Dimethyl-7,8,9,10-tetra-hydro-cyclo-hepta-[b]indol-6(5H)-one.

In the title mol-ecule, C(15)H(17)NO, the dihedral angle between the benzene and pyrrole rings is 1.45 (13)°. The cyclo-heptene ring adopts a slightly distorted boat conformation. In the crystal structure, inter-molecular C-H⋯O hydrogen bonds are found.

(E)-2-(Furan-2-yl-methyl-idene)-8-methyl-2,3,4,9-tetra-hydro-1H-carbazol-1-one.

In the title mol-ecule, C(18)H(15)NO(2), the carbazole unit is not planar [maximum deviation from mean plane = 0.236 (2) Å]. The pyrrole ring makes dihedral angles of 1.21 (10) and 16.74 (12)° with the benzene and the furan rings, respectively. The cyclo-hexene ring adopts a half-chair conformation. In the crystal, inversion dimers linked by pairs of N-H⋯O hydrogen bonds generate R(2) (2)(10) loops.

1-(1-Hy-droxy-8-methyl-9H-carbazol-2-yl)ethanone.

The title compound, C(15)H(13)NO(2), crystallizes with four independent mol-ecules (A, B, C and D) in the asymmetric unit. The carbazole units are almost planar [maximum deviations = 0.015 (3) for A, 0.024 (3) for B, 0.026 (3) for C and 0.046 (3) Šfor D]. In all four mol-ecules, there is an O-H⋯O hydrogen bond involving the hy-droxy substituent and the carbonyl O atom of the adjacent acetyl group, which forms a six-membered ring. In the crystal, the four independent mol-ecules are linked via N-H⋯O and C-H⋯O inter-actions.

(E)-6-Chloro-2-(furan-2-yl-methyl-idene)-2,3,4,9-tetra-hydro-1H-carbazol-1-one.

In the title compound, C(17)H(12)ClNO(2), the carbazole unit is nearly planar [maximum deviation = 0.052 (1) Å]. The pyrrole ring makes dihedral angles of 1.92 (8) and 4.71 (11)° with the benzene and furan rings, respectively. Inter-molecular N-H⋯O hydrogen bonds form R(2) (2)(10) rings in the crystal structure.

2-(2,3,4,9-Tetra-hydro-1H-carbazol-1-ylidene)propane-dinitrile.

In the title mol-ecule, C(15)H(11)N(3), the dihedral angle between the benzene ring and the fused pyrrole ring is 1.07 (5)°. The cyclo-hexene ring adopts an envelope conformation: the dicyano-methyl-ene group at position 1 has a coplanar orientation. An intra-molecular N-H⋯N hydrogen bond generates an S(7) ring motif. Inter-molecular N-H⋯N hydrogen bonds form an R(2) (2)(14) ring in the crystal. A C-H⋯π inter-action involving the benzene ring is also found in the structure.

4-Methyl-7,8,9,10-tetra-hydro-cyclo-hepta-[b]indol-6(5H)-one.

In the title compound, C(14)H(15)NO, the seven-membered ring exhibits a slightly distorted twist-boat conformation. The pyrrole ring forms a dihedral angle of 1.44 (10)° with the fused benzene ring. N-H⋯O hydrogen bonds form a centrosymmetric dimer and weak C-H⋯π inter-actions are also found in the crystal structure.

4,8-Dimethyl-pyrano[2,3-a]carbazol-2(11H)-one.

The mol-ecule of the title compound, C(17)H(13)NO(2), is nearly planar, the r.m.s. deviation for all non-H atoms excluding the two methyl C atoms being 0.089 Å. Inter-molecular N-H⋯O and C-H⋯O hydrogen bonds are found in the crystal structure. C-H⋯π inter-actions are also found. The H atoms of the methyl group attached to the benzene ring are disordered equally over two positions.

3-Methyl-3,4-dihydro-9H-carbazol-1(2H)-one.

In the title mol-ecule, C(13)H(13)NO, the dihedral angle between the benzene ring and the fused pyrrole ring is 2.03 (5)°. The methyl group at the 3-position has an equatorial orientation. The cyclo-hexene ring adopts an envelope conformation. Three C atoms of the cyclo-hexene ring, with their attached H atoms, and all atoms of the methyl group are disordered over two positions, the site-occupancy factors being 0.883 (2) and 0.117 (2). In the crystal structure, mol-ecules are stabilized by inter-molecular N-H⋯O hydrogen bonds. A C-H⋯π inter-action, involving the benzene ring, is also found.

Antiacetylcholinesterase and antioxidant ent-Kaurene diterpenoid, melissoidesin from Isodon wightii (Bentham) H. Hara.

The ent kaurene diterpenoid, melissoidesin was isolated from the acetone extract of the leaves of Isodon wightii and the structure was designated as 3beta, 11beta, 15beta-trihydroxy-6alpha-acetoxy-ent-kaur-16-ene based on spectral data and previous reports. Melissoidesin isolated from the acetone extract of leaves showed potent antiacetylcholinesterase activity and the IC(50) value was observed as 215 microg mL(-1). DPPH (1, 1-diphenyl-2-picrylhydrazyl) free radical scavenging activity of melissoidesin was significant and the IC(50) value was 138 microg mL(-1). The significant reducing property of the melissoidesin was stronger in high concentration. IC(50) value of melissoidesin on hydroxyl radicals and metal chelation was observed as 99 and 143 microg mL(-1), respectively. The 50% inhibitory concentration of melissoidesin on lipid peroxidation was calculated as 133 microg mL(-1). These findings indicate that ent kaurene diterpenoid, melissoidesin was promising antiacetylcholinesterase and antioxidant which can be used as food and drug preparations.

Crystal structure of (E)-2-(furan-2-yl-methyl-idene)-2,3,4,9-tetra-hydro-1H-carbazol-1-one.

The title compound, C17H13NO2, crystallizes with two conformationally very similar independent mol-ecules (A and B) in the asymmetric unit. In the crystal, the individual mol-ecules are linked by pairs of N-H⋯O hydrogen bonds forming A-A and B-B inversion dimers, with R22(10) rings. They stack alternately up the a-axis direction and are linked by C-H⋯π inter-actions, forming sheets parallel to the ab plane.