Quinoxaline Ring System Research Articles

Identification and preliminary structure–activity relationship of brain‐penetrant quinoxaline‐based compounds with in vitro anti‐glioblastoma activity

AbstractA central nervous system (CNS)‐oriented compound collection was screened to find hit compounds for human glioblastoma T98G cell growth inhibition. A series of quinoxaline‐based derivatives were identified as hit compounds having one‐ to two‐digit micromolar GI50 values. Anti‐glioblastoma activity was improved in structure–activity relationship studies varying the substituents on the quinoxaline ring system, resulting in the discovery of four compounds exhibiting sub‐micromolar GI50 values. The potentials of the four compounds to induce apoptosis were confirmed by annexin V staining assay. The development potential of the four compounds as CNS drug leads was evaluated by in vitro MDR‐MDCK cell permeability and in vivo brain disposition in mice. The mouse pharmacokinetic and kinome profiling studies for compound 10g, which showed high brain‐penetrating ability, revealed that the compound is orally bioavailable and inhibits the kinase activities of anaplastic lymphoma kinase (ALK) and Erb‐B2 receptor tyrosine kinase (ERBB3).

Crystal structure, Hirshfeld surface analysis and density functional theory study of 1-nonyl-3-phenyl-quinoxalin-2-one.

In the title mol-ecule, C23H28N2O, the phenyl ring is inclined to the quinoxaline ring system at a dihedral angle of 20.40 (9)°. In the crystal, C-H⋯O inter-actions between neighbouring mol-ecules form chains along the a-axis direction. Hirshfeld surface analysis indicates that the most important contributions to the crystal packing are from H⋯H (70.6%), H⋯C/C⋯H (15.5%) and H⋯O/O⋯H (4.6%) inter-actions. The optimized structure calculated using density functional theory at the B3LYP/6-311 G(d,p) level is compared with the experimentally determined structure in the solid state. The calculated highest occupied mol-ecular orbital (HOMO) and lowest unoccupied mol-ecular orbital (LUMO) energy gap is 3.8904 eV. Part of the n-nonyl chain attached to one of the nitro-gen atoms of the quinoxaline ring system shows disorder and was refined with a double conformation with occupancies of 0.604 (11) and 0.396 (11).

11,11-Diphenyl-11H-indeno-[1,2-b]quinoxaline.

In the title compound, C27H18N2, the mean planes of the pendant benzene rings are approximately perpendicular to one another, making a dihedral angle of 79.3 (5)°; the indeno-[1,2-b]quinoxaline ring system (r.m.s. deviation = 0.1197 Å) is twisted with respect to the pendant benzene rings by 70.0 (4) and 67.6 (3)°. Weak aromatic π-π stacking [centroid-centroid separation = 3.628 (2) Å] and C-H⋯π inter-actions occur in the crystal.

Ethyl 6′-cyano-7′-phenyl-1′,6′,7′,7a'-tetrahydro-3′H-spiro[indeno[1,2-b]quinoxaline-11,5′-pyrrolo[1,2-c]thiazole-6′-carboxylate

In the title compound, C22H22ClN4O2S, the angle between the mean planes of the indene ring and the quinoxaline ring system is 3.93 (11)°. The five-membered indene and thiazole rings both adopt envelope conformations while the pyrrole ring adopts a twisted conformation. The two acceptor O atoms form a chelated three-centred hydrogen bond with a phenyl C atom.

Synthesis of New Pyrimido[5′,4′:5,6][1,4]thiazino[2,3‐b]quinoxaline Derivatives in One Step

As a continuation of our search for new heterocyclic compounds, the synthesis of pyrimido[5′,4′:5,6][1,4]thiazino[2,3‐b]quinoxaline ring system is described. A series of new derivatives of this heterocyclic system (3a–d) have been synthesized through the one‐pot heterocyclization of the appropriate 5‐amino6‐methylpyrimidine‐4‐thiols and 2,3‐dichloroquinoxaline in the presence of K2CO3 in dimethylformamide under reflux. N‐alkylation of the synthesized compounds with alkyl halides in KOH/dimethylformamide also gave the desired new derivatives of N‐alkylated pyrimido[5′,4′:5,6][1,4]thiazino[2,3‐b]quinoxalines (4a–h). All the synthesized products were characterized and confirmed by their spectroscopic and microanalytical data.

Ethyl 2-[(3-methylquinoxalin-2-yl)sulfanyl]acetate

In the title molecule, C13H14N2O2S, the dihedral angle between the pyrazine and benzene ring planes is 2.21 (5)°. The mean plane of the quinoxaline ring system is inclined to the sufanylacetate substituent by 81.74 (2)°. In the crystal, inversion-related C—H...N hydrogen bonds form dimers, which are linked into oblique stacks along thea-axis direction by C—H...O hydrogen bonds and π–π-stacking interactions.

2,3-Bis(benzylthio)-6-methylquinoxaline

In the title compound, C23H20N2S2, the mean planes of the phenyl rings are twisted with respect to the mean plane of the quinoxaline ring system by 73.8 (8) and 72.2 (8)°. A weak intramolecular C—H...N interactions is observed. The methyl group attached to the quinoxaline ring system is disordered over two sets of sites on the benzene ring having occupancies 0.531 (7) and 0.469 (7), respectively. One of the phenyl rings is disordered over two sets of sites having occupancies 0.649 (7) and 0.351 (10), respectively. In the crystal, π–π stacking interactions occur.

1,4-Dibenzyl-6-chloroquinoxaline-2,3(1H,4H)-dione

The title compound, C22H17ClN2O2, crystallizes with two independent molecules (AandB) in the asymmetric unit. The 6-chloroquinoxaline-2,3(1H,4H)-dione ring system is essentially planar. The dihedral angles between the mean planes of the 6-chloroquinoxaline-2,3(1H,4H)-dione ring and the phenyl rings of the benzyl substituents in the two molecules are 68.34 and 73.8 (7)° forA, and 73.8 (5) and 80.7 (1)° forB, so that these rings point away from the quinoxaline ring system. In the crystal, weak C—H...O hydrogen bonds and π–π stacking interactions link the molecules into a three-dimensional network.

Synthesis of some novel indeno[1,2-b]quinoxalin spiro-β-lactam conjugates

This article reports the synthesis of some new spiro-β-lactams bearing an indeno[1,2-b]quinoxaline ring system, prepared by a [2 + 2] cycloaddition of ketenes with imines derived from 11-H-indeno[1,2-b]quinoxalin-11-one. The structures of newly synthesized spiro-β-lactams 2a–i and 3a-i were characterized by FT-IR, 1H NMR, 13C NMR, mass spectrometry and elemental analyses. The relative stereochemistry of spiro-β-lactams 2a and 3a was determined unequivocally by X-ray crystallographic studies.

Dipolar Dyes with a Pyrrolo[2,3-b]quinoxaline Skeleton Containing a Cyano Group and a Bridged Tertiary Amino Group: Synthesis, Solvatofluorochromism, and Bioimaging.

Two strongly polarized dipolar chromophores possessing a cyclic tertiary amino group at one terminus of the molecule and a CN group at the opposite terminus were designed and synthesized. Their rigid skeleton contains the rarely studied pyrrolo[2,3-b]quinoxaline ring system. The photophysical properties of these regioisomeric dyes were different owing to differing π conjugation between the CN group and the electron-donor moiety. These dipolar molecules showed very intense emission, strong solvatofluorochromism, and sufficient two-photon brightness for bioimaging. One of these regioisomeric dyes, namely, 11-carbonitrile-2,3,4,5,6,7-hexahydro-1H-3a,8,13,13b-tetraazabenzo[b]cyclohepta[1,2,3-jk]fluorene, was successfully utilized in two-photon imaging of mouse organ tissues and showed distinct tissue morphology with high resolution.

Synthesis and in vivo diuretic activity of some new benzothiazole sulfonamides containing quinoxaline ring system

A series of new 6-substituted-N-[3-{2-(substituted phenyl)-ethenyl} quinoxaline-2(1H)-ylidene]-1,3-benzothiazole-2-amine (4a–f) were designed and synthesized by condensing 2-amino-benzothiazole-6-sulfonic acid amide (1) with chalcones of quinoxaline-2-one (3a–f) in a hope to obtain promising and a new class of diuretic agents. Structures of all the newly synthesized compounds were characterized by spectral data and elemental analysis. The pharmacological studies in experimental rats indicates that compound 4c possesses excellent in vivo diuretic activity of 1.13 and appears to be a better diuretic agent than the reference drugs, acetazolamide (1.0) and urea (0.88). Insight of the binding mode of the synthesized compounds (ligand) into the binding sites of carbonic anhydrase enzyme (PDF code: 4KUV) was provided by docking studies, performed with the help of Maestro 9.0 docking software. Further pharmacokinetic and toxicological studies are needed to confirm the safety of compound 4c which emerged as a lead diuretic compound.

Crystal, Molecular Structure and DFT Study of 2,6,7-Trimethyl-3-p-tolylquinoxaline and 2-(4-Methoxyphenyl)-3,6,7-trimethylquinoxaline

The molecular structure of 2,6,7-trimethyl-3-p-tolylquinoxaline (hereafter denoted I) was confirmed by single crystal X-ray structure analysis. In the title compound, C18H18N2, I, the quinoxaline ring system is essentially planar. The phenyl ring at the 2-position makes a dihedral angle of 40.23° with the quinoxaline mean plane. In the crystal, molecules are linked into layers mainly by H2C–H···π and (π)C–H···π interactions. Stacking π···π interactions are absent in the structure. The experimental and theoretical structural aspects of I and the recently reported methoxy derivative, 2-(4-methoxyphenyl)-3,6,7-trimethylquinoxaline, II, have been investigated and compared. Experimental geometric parameters (bond lengths and bond angles and dihedral angles) were compared with computed values from density functional theory with B3LY6−31G(d,p) basis set. Results show that values are in good agreement. The highest occupied molecular orbitals (HOMO) and lowest unoccupied molecular orbitals (LUMO) energies have been also calculated and used to determine the charge transfer within the molecule. MEP surfaces analyses were performed by the DFT method. From the MEP map, negative region is mainly localized over the electronegative nitrogen atoms (in I), and the nitrogen and oxygen atoms (in II) and the maximum positive region is localized on the methyl groups. These surfaces seem to correlate well with the intermolecular interactions in the lattice. Time-dependent density functional theory has been carried out to study the UV spectra of both molecules in gas phase and in methanol using polarizable continuum model and the results are presented and discussed. Crystal, molecular structure, crystal supramolecularity and DFT calculations of 2,6,7-Trimethyl-3-p-tolylquinoxaline and 2-(4-Methoxyphenyl)-3,6,7-trimethylquinoxaline are reported.

Crystal structure of ethyl (2S,2'R)-1'-benzyl-3-oxo-3H-di-spiro-[1-benzo-thio-phene-2,3'-pyrrolidine-2',11''-indeno[1,2-b]quinoxaline]-4'-carboxyl-ate.

In the title compound, C35H27N3O3S, the spiro-linked five-membered rings both adopt twisted conformations. The pyrrolidine ring makes dihedral angles of 80.5 (1) and 77.4 (9)° with the benzo­thio­phene ring system and the quinoxaline ring system, respectively. The S atom and C=O unit of the benzo­thio­phene ring system are disordered over two opposite orientations in a 0.768 (4):0.232 (4) ratio. The atoms of the ethyl side chain are disordered over two sets of sites in a 0.680 (16):0.320 (16) ratio. In the crystal, mol­ecules are linked by C—H⋯O, C—H⋯N and π–π inter­actions [shortest centroid–centroid distance = 3.4145 (19) Å], resulting in a three-dimensional network.

Combination of cyclohexane and piperazine based κ-opioid receptor agonists: Synthesis and pharmacological evaluation of trans,trans-configured perhydroquinoxalines

Desymmetrization of the pseudochiral (2r)-configured cyclohexane-1,2,3-triamines 8 with dimethyl oxalate led to racemic aminoquinoxaline-2,3-diones 9. Selective introduction of the κ pharmacophoric structural elements pyrrolidine and 3,4-dichlorophenylacetamide with a two-carbon distance afforded conformationally restricted κ agonists 13–15 based on the quinoxaline ring system. In competitive radioligand receptor binding studies the benzylamine 13b, the secondary amine 14b, and the carbamate 15 displayed high κ receptor affinity. The Ki value of the lead compound derived methoxycarbonyl derivative 15 is 9.7nM. However, the κ affinity of 15 is exceeded by 13b and 14b with a basic functional group instead of the methoxycarbonyl group in 1-position of the quinoxaline system. The chlorine atoms of the dichlorophenylacetyl residue are essential, since the corresponding phenylacetyl analogs show considerably reduced κ affinity. The potent κ ligands 13b, 14b and 15 are selective over the related μ- and δ-opioid receptors, σ1, σ2 and NMDA receptors. In the [35S]GTPγS-binding assay 13b behaved as partial agonist with lower activity than U-69,593.

1′,1′′-Dimethyl-4′-phenyldispiro[11H-indeno[1,2-b]quinoxaline-11,2′-pyrrolidine-3′,3′′-piperidin]-4′′-one

In the title compound, C30H28N4O, the central pyrrolidine ring adopts an envelope conformation with the CH2 C atom as the flap. The quinoxaline and indene ring systems are planar, with r.m.s. deviations of 0.0165 and 0.0181 Å, respectively. The pyrrolidine ring mean plane forms dihedral angles of 88.84 (1) and 86.14 (1)° with the quinoxaline and indene ring systems, respectively. A weak intra­molecular C—H⋯N inter­action is observed. In the crystal, C—H⋯O inter­actions lead to helical supra­molecular chains along the b axis having a C(9) motif.

N′-Phenyl-N′-[3-(2,4,5-triphenyl-2,5-dihydro-1H-pyrazol-3-yl)quinoxalin-2-yl]benzohydrazide

The mol­ecule of the title compound, C42H32N6O, is built up from one pyrazole ring linked to three phenyl rings and to an approximately planar [maximum deviation = 0.0455 (15) Å] quinoxaline system connected to a phenyl­benzohydrazide group. The pyrazole ring assumes an envelope conformation, the C atom attached to the quinoxalin-3-yl ring system being the flap atom. The dihedral angle between the two phenyl rings of the phenyl­benzohydrazide group is of 58.27 (9)°. The mean plane through the pyrazole ring is nearly perpendicular to the quinoxaline ring system and to the phenyl ring attached to the opposite side, forming dihedral angles of 82.58 (7) and 87.29 (9)°, respectively. An intra­molecular C—H⋯O hydrogen bond is present. In the crystal, mol­ecules are linked by pairs of N—H⋯N hydrogen bonds, forming inversion dimers, which are further connected by C—H⋯N hydrogen bonds into chains parallel to the b axis.

Bis[2-(thiophen-2-yl)quinoxaline-κN4]silver(I) tetrafluoridoborate

In the title compound, [Ag(C12H8N2S)2]BF4, the two-coordinate AgI ion lies on a crystallographic inversion center and is linearly bonded to the N-donor atoms of two separate quinoxaline ligands. The thio­phenyl ring of the ligand is nearly coplanar with the quinoxaline ring system [dihedral angle = 9.15 (13)°]. In the crystal, the complex mol­ecules pack in layers parallel to (-102) and form weak π–π ring stacking inter­actions [minimum ring centroid separation = 3.7054 (17) Å]. The tetra­fluoridoroborate anion is equally disordered about an inversion center.

3-(Ferrocen-1-ylcarbonyl)-1-methyl-4-(4-methylphenyl)spiro[pyrrolidine-2,11′-indeno[1,2-b]quinoxaline

In the title compound, [Fe(C5H5)(C32H26N3O)], the pyrrolidine ring adopts a twist conformation. The indeno–quinoxaline ring system [86.44 (5)°], the methyl­phenyl ring [86.06 (7)°] and the ferrocene rings [82.00 (7) and 83.95 (9)°] are almost perpendicular to the pyrrolidine ring. The two cyclopentadienyl rings adopt an eclipsed conformation. The crystal structure features C—H⋯N inter­actions.

6,7-Dichloro-3-(2,4-dichlorobenzyl)quinoxalin-2(1H)-one

In the title compound, C15H8Cl4N2O, the quinoxaline ring system is almost planar, with a dihedral angle between the benzene and pyrazine rings of 3.1 (2)°. The 2,4-dichloro­phenyl ring is approximately perpendicular to the pyrazine ring, with a dihedral angle of 86.47 (13)° between them. The crystal packing features inter­molecular N—H⋯O hydrogen bonds and π–π stacking inter­actions, with centroid–centroid distances in the range 3.699 (3)–4.054 (3) Å.

2-(4-Fluorophenyl)quinoxaline

In the title compound, C14H9FN2, the dihedral angle between the benzene ring and the quinoxaline ring system is 22.2 (3)°. Any aromatic π–π stacking in the crystal must be very weak, with a minimum centroid–centroid separation of 3.995 (2) Å.