Indole Ring System Research Articles

N′-[(E)-3-Indol-3-ylmethylene]isonicotinohydrazide monohydrate

Crystals of the title compound, C15H12N4O·H2O, were obtained from a condensation reaction of isonicotinylhydrazine and 3-indolylformaldehyde. The mol­ecule assumes an E configuration, with the isonicotinoylhydrazine and indole units located on the opposite sites of the C=N double bond. In the mol­ecular structure the pyridine ring is twisted with respect to the indole ring system, forming a dihedral angle of 44.72 (7)°. Extensive classical N—H⋯N, N—H⋯O, O—H⋯O and O—H⋯N hydrogen bonding and weak C—H⋯O inter­actions are present in the crystal structure.

Ethyl 2-(3,4-dimethoxybenzyl)-1-phenylsulfonyl-1H-indole-3-carboxylate

In the title compound, C26H25NO6S, the phenyl ring forms a dihedral angle of 82.5 (1)° with the indole ring system. The mol­ecular structure is stabilized by weak intra­molecular C—H⋯O inter­actions and the crystal structure is stabilized by weak inter­molecular C—H⋯O inter­actions.

Ethyl 1-oxo-1,2,3,4-tetrahydro-9H-carbazole-3-carboxylate

The title compound, C15H15NO3, contains a carbazole skeleton with an ethoxy­carbonyl group at the 3 position. In the indole ring system, the benzene and pyrrole rings are nearly coplanar, forming a dihedral angle of 1.95 (8)°. The cyclo­hexenone ring has an envelope conformation. In the crystal structure, pairs of strong N—H⋯O hydrogen bonds link the mol­ecules into centrosymmetric dimers with R 2 2(10) ring motifs. π–π contacts between parallel pyrrole rings [centroid–centroid distance = 3.776 (2) Å] may further stabilize the structure. A weak C—H⋯π inter­action is also observed.

5-Hydroxy-1,7-bis(1H-indol-3-yl)hepta-1,4,6-trien-3-one hemihydrate

The title compound, C23H18N2O2·0.5H2O, a derivative of the biologically active compound curcumin, crystallizes with two organic mol­ecules and a solvent water mol­ecule in the asymmetric unit. Each of the two independent mol­ecules is close to being planar (the dihedral angles between the indole ring systems are approximately 9 and 12°) and each exists in the keto–enol form. There is an intra­molecular O—H⋯O hydrogen bond between the keto and enol groups. In the crystal, the components interact by way of N—H⋯N, N—H⋯O and O—H⋯O hydrogen bonds.

Diethyl 2-[(5-methoxy-2-methyl-1-phenylsulfonyl-1H-indol-3-yl)methylene]malonate

In the title compound, C24H25NO7S, the sulfonyl-bound phenyl ring is approximately perpendicular to the indole ring system [dihedral angle = 87.72 (5)°]. The methyl group of one of the ester units is disordered over two positions with occupancies of 0.527 (13) and 0.473 (13). An intra­molecular C—H⋯O hydrogen bond is observed. In the crystal structure, mol­ecules are linked into a ribbon structure running along the c axis by inter­molecular C—H⋯O hydrogen bonds and C—H⋯π inter­actions involving the pyrrole ring.

1,1′,2,2′-Tetramethyl-3,3′-(4-methoxybenzylidene)di-1H-indole

The title compound, C28H28N2O, was prepared by condensation of 1,2-bimethyl­indole and 4-methoxy­benzaldehyde. In the mol­ecular structure, the plane of the non-fused benzene ring is twisted with respect to the planes of the two indole ring systems, exhibiting dihedral angles of 72.04 (7) and 72.24 (7)°, while the planes of the two indole ring systems are oriented at a dihedral angle of 87.05 (5)°. Neither hydrogen bonding nor π–π stacking is observed in the crystal structure.

Ethyl 2-benzyl-1-propyl-1H-indole-3-carboxylate

In the title compound, C21H23NO2, the dihedral angle between the indole ring system and the benzyl ring is 75.92 (9)°. The crystal packing is controlled by C—H⋯O and C—H⋯π inter­actions.

Redetermination ofL-tryptophan hydrobromide

The redetermined crystal structure of the title compound, C11H13N2O2 +·Br−, is reported. Data collection at 100 K about three crystallographic axes resulted in a crystal structure with significantly higher precision in comparison to the two-dimensional data collected at 176 K [Takigawa et al. [(1966) Bull. Chem. Soc. Jpn, 39, 2369–2378]. The carboxyl group and indole ring system are planar, with maximum deviations of 0.002 (2) and 0.007 (2) Å, respectively, and make an angle of 70.17 (1)° with each other. The mol­ecules are arranged in double layers of carboxyl and amino groups parallel to the ab plane, stabilized by an extensive network of N—H⋯Br and O—H⋯Br hydrogen bonds. The polar layer is held together by a network of three N—H⋯Br hydrogen bonds and one O—H⋯Br hydrogen bond. In the non-polar layer, the indole rings are linked mainly by electrostatic N—H⋯C inter­actions between the polarized bond N—H (H is δ+) of the pyrrole unit and two of the ring C atoms (δ−) of the benzene rings of adjacent mol­ecules. The distances of these electrostatic inter­actions are 2.57 and 2.68 Å, respectively. C—H⋯O and C—H⋯π inter­actions are also present.

Synthesis of the new ring system 2-oxo-[1,4]oxazino[3,2- e]indole, heteroanalogue of Angelicin

A convenient synthesis of the 2-oxo-[1,4]oxazino[3,2- e]indole ring system, an heteroanalogue of Angelicin, is reported. Our synthetic approach consisted of the annelation of the oxazine ring on the indole moiety using 4-amino-5-hydroxy indoles as building blocks. The antiproliferative activity of the new compounds either in the dark or under UVA irradiation was investigated.

6-(1H-Indol-3-yl)-4-phenyl-2,2′-bipyridine-5-carbonitrile

In the mol­ecule of the title compound, C25H16N4, the pyridine rings are oriented at a dihedral angle of 0.92 (3)°, while the dihedral angle between the benzene ring and the adjacent pyridine ring is 56.51 (3)°. In the crystal structure, inter­molecular N—H⋯N hydrogen bonds link the mol­ecules into centrosymmetric dimers, forming R 2 2(16) ring motifs. π–π contacts between the pyridine ring and the indole ring system and between the pyridine rings [centroid–centroid distances = 3.923 (2) and 3.724 (2) Å] may further stabilize the structure. Two weak C—H⋯π inter­actions are also present.

2-[(E)-2-(1H-Indol-3-yl)ethenyl]-1-methylpyridinium 4-bromobenzenesulfonate

In the title compound, C16H15N2 +·C6H4BrO3S−, the cation exists in the E configuration and is essentially planar with a dihedral angle of 3.10 (5)° between the pyridinium ring and the indole ring system. The π-conjugated planes of the cation and the anion are inclined to each other at a dihedral angle of 64.32 (4)°. In the crystal structure, the cations are stacked in an anti­parallel manner along the a axis. The anions are linked into a chain along the a axis. The cations and the anions are linked into a three-dimensional network by N—H⋯O and weak C—H⋯O hydrogen bonds. The crystal structure is further stabilized by C—H⋯π inter­actions. A π–π inter­action between the five-membered heterocyclic ring of the indole system and the pyridinium ring is also observed with a centroid–centroid distance of 3.5855 (7) Å.

Domino or Single‐Step Tsuji–Trost/Heck Reactions and Their Application in the Synthesis of 3‐Benzazepines and Azepino[4,5‐b]indole Ring Systems

AbstractA series of methods for palladium‐mediated single‐step and domino Tsuji–Trost/Heck reactions are described. These methods are applied to the synthesis of both 3‐benzazepines and azepino[4,5‐b]indoles in the category of complex 6‐7‐6 and 6‐5‐7 ring heterocycles. In addition, a domino Heck/Heck sequence of reactions that produces the azepinobenzindolizine tetracyclic ring system from N‐diallylated precursors is described. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

A New and Facile Synthesis of Thieno[2,3-b]indole Derivatives via Condensation of Isocyanide and Indolin-2-thiones

A new one-pot synthesis ofthieno[2,3-6]indole ring systems is described. Condensation of cyclohexyl isocyanide with indolin-2-thiones yielded 3-cyclohexyaminomethylene-indolin-2-thiones, which upon reaction with α-halocarbonyl compounds produced the title compounds.

Tert-Butyl 3-[2,2-bis(ethoxycarbonyl)vinyl]-2-methyl-1H-indole-1-carboxylate

In the title compound, C22H27NO6, the indole ring system is planar and the ethoxy­carbonyl chains adopt extended conformations. In the crystal, inversion dimers linked by pairs of C—H⋯O hydrogen bonds occur, resulting in R 2 2(16) dimers, which are inter­linked into a chain propagating along the a axis by π–π stacking inter­actions [centroid–centroid distance 3.5916 (9) Å].

3-(4-Methoxybenzyl)-2-methyl-1-phenylsulfonyl-1H-indole

There are two crystallographically independent mol­ecules in the asymmetric unit of the title compound, C23H21NO3S. The indole ring system is approximately perpendicular to the sulfonyl phenyl ring in both mol­ecules [dihedral angles = 85.42 (8) and 88.30 (9)°]. C—H⋯O inter­actions between mol­ecules stabilize the crystal structure.

1-(5-Carboxyindol-1-yl)propan-2-ones as inhibitors of human cytosolic phospholipase A 2α: Synthesis and properties of bioisosteric benzimidazole, benzotriazole and indazole analogues

The indole ring systems of the cytosolic phospholipase A 2α (cPLA 2α) inhibitor 1-[3-(4-octylphenoxy)-2-oxopropyl]indole-5-carboxylic acid ( 2) and the isomeric 6-carboxylic acid ( 3) were replaced by benzimidazole, benzotriazole and indazole scaffolds, respectively. The effect of the structural variations on cPLA 2α inhibitory potency, metabolic stability and solubility was studied. The lead 2 and the indazole-5-carboxylic acid 28 were the metabolically most stable compounds in an assay with rat liver microsomes, while the benzimidazole-5-carboxylic acid derivative 13 possessed the best water solubility (22 μg/mL at pH 7.4). The indazole-5-carboxylic acid 28 revealed the highest cPLA 2α inhibitory potency of the compounds in this series. With an IC 50-value of 0.005 μM it was about sevenfold more active than the lead 2.

3,3-Ethylenedithio-3,3a,4,5,10,10b-hexahydro-2H-furo[2,3-a]carbazole

The title compound, C16H17NOS2, consists of a carbazole skeleton with tetra­hydro­furan and dithiol­ane rings. In the indole ring system, the benzene and pyrrole rings are nearly coplanar, forming a dihedral angle of 1.57 (15)°. The cyclo­hexenone and tetra­hydro­furan rings have envelope conformations, while the dithiol­ane ring adopts a twist conformation. In the crystal structure, pairs of weak inter­molecular N—H⋯S hydrogen bonds link the mol­ecules into centrosymmetric dimers with R 2 2(16) ring motifs. Weak C—H⋯π inter­actions may further stabilize the structure.

1-(2,6-Dichlorophenyl)indolin-2-one

In the mol­ecule of the title compound, C14H9Cl2NO, the planar indole ring system [with a maximum deviation of 0.020 (2) Å for the N atom] is oriented at a dihedral angle of 72.17 (3)° with respect to the phenyl ring. In the crystal structure, weak inter­molecular C—H⋯O hydrogen bonds link the mol­ecules. A weak C—H⋯π inter­action may further stabilize the structure.

2-(1H-indol-3-ylcarbon-yl)acetonitrile.

The title compound, C11H8N2O, crystallizes with two crystallographically independent mol­ecules in the asymmetric unit which are approximately perpendicular to each other [79.97 (6)°]. The indole ring system is planar [r.m.s. deviation = 0.010 (1) Å]. The crystal structure is stabilized by inter­molecular C—H⋯N and N—H⋯O inter­actions.

(E)-Methyl 3-(2-methyl-1-phenylsulfonyl-1H-indol-3-yl)but-2-enoate

In the title compound, C20H19NO4S, the indole ring system is planar [r.m.s. deviation = 0.023 (2) Å]. The sulfonyl-bound phenyl ring is almost perpendicular to the indole ring system [dihedral angle = 86.75 (7)°]. The ester group is almost planar (r.m.s. deviation = 0.030 Å) and is oriented at an angle of 62.53 (5)° with respect to the indole ring system. Mol­ecules are linked into a two-dimensional network parallel to the ab plane by inter­molecular C—H⋯O hydrogen bonds.