Quinoxaline N-oxide containing potent angiotensin II receptor antagonists: synthesis, biological properties, and structure-activity relationships

Radical Ions of 3-Styryl-quinoxalin-2-one Derivatives Studied by Pulse Radiolysis in Organic Solvents

The absorption-spectral and kinetic behaviors of radical ions and neutral hydrogenated radicals of seven 3-styryl-quinoxalin-2(1 H)-one (3-SQ) derivatives, one without substituents in the styryl moiety, four others with electron-donating (R = -CH₃, -OCH₃, and -N(CH₃)₂) or electron-withdrawing (R = -OCF₃) substituents in the para position in their benzene ring, and remaining two with double methoxy substituents (-OCH₃), however, at different positions (meta/para and ortho/meta) have been studied by UV-vis spectrophotometric pulse radiolysis in neat acetonitrile saturated with argon (Ar) and oxygen (O₂) and in 2-propanol saturated with Ar, at room temperature. In acetonitrile solutions, the radical anions (4R-SQ^•-) are characterized by two absorption maxima located at λ_max = 470-490 nm and λ_max = 510-540 nm, with the respective molar absorption coefficients ε_470-490 = 8500-13 100 M^-1 cm^-1 and ε_510-540 = 6100-10 300 M^-1 cm^-1, depending on the substituent (R). All 4R-SQ^•- decay in acetonitrile via first-order kinetics, with the rate constants in the range (1.2-1.5) × 10⁶ s^-1. In 2-propanol solutions, they decay predominantly through protonation by the solvent, forming neutral hydrogenated radicals (4R-SQH^•), which are characterized by weak absorption bands with λ_max = 480-490 nm. Being oxygen-insensitive, the radical cations (4R-SQ^•+) are characterized by a strong absorption with λ_max = 450-630 nm, depending on the substituent (R). They are formed in a charge-transfer reaction between a radical cation derived from acetonitrile (ACN^•+) and substituted 3-styryl-quinoxalin-2-one derivatives (4R-SQ) with a pseudo-first-order rate constant k = (2.7-4.7) × 10⁵ s^-1 measured in solutions containing 0.1 mM 4R-3-SQ. The Hammett equation plot gave a very small negative slope (ρ = -0.08), indicating a very weak influence of the substituents in the benzene ring on the rate of charge-transfer reaction. The decay of 4R-SQ^•+ in Ar-saturated acetonitrile solutions occurs with a pseudo-first-order rate constant k = (1.6-6.2) × 10⁴ s^-1 and, in principle, is not affected by the presence of O₂, suggesting charge-spin delocalization over the whole 3-SQ molecule. Most of the radiolytically generated transient spectra are reasonably well-reproduced by semiempirical PM3-ZINDO/S (for 4R-SQ^•-) and density functional theory quantum mechanics calculations employing M06-2x hybrid functional together with the def2-TZVP basis set (for 4R-SQ^•+).

An efficient lactamisation/N-acyliminium Pictet–Spengler domino strategy for the diasteroselective synthesis of polyhydroxylated quinoxalinone, β-carboline and quinazolinone derivatives

A novel Pictet–Spengler cascade sequence has been developed. It involves a lactamisation/N-acyliminium key step and gives a diverse set of sugar-derived fused polycyclic heterocycles diastereoselectively and efficiently.

Synthesis of quinoxaline azido and amino reverse ribofuranoside and their O-regioisomers

A series of quinoxaline azido reverse nucleosides 3a-c and their O-regioisomers 4a-c was prepared by reaction of quinoxaline 1a-c with 3-azido-3-deoxy-1,2-O-isopropylidene-5-p-toluenesulfonyl-D-ribofuranose (2) in the presence of sodium hydride. Structure modification of these interesting structures includes reduction and the subsequent acetylation reactions to give quinoxaline amino and acetyl amino reverse nucleosides and their O-regioisomers.

Ligand binding determinants for angiotensin II type 1 receptor from computer simulations

The ligand binding determinants for the angiotensin II type 1 receptor (AT1R), a G protein-coupled receptor (GPCR), have been characterized by means of computer simulations. As a first step, a pharmacophore model of various known AT1R ligands exhibiting a wide range of binding affinities was generated. Second, a structural model of AT1R was built making use of the growing set of crystal structures of GPCRs, which was further used for the docking of the AT1R ligands based on the devised pharmacophore model. Next, ligand-receptor-lipid bilayer systems were studied by means of molecular dynamics (MD) simulations. Overall, the present study has permitted, combining the pharmacophore model with binding free energy calculations obtained from the MD simulations, to propose the molecular mechanisms by which sartans interact with AT1R.

Concise route to a series of novel 3-(tetrazol-5-yl)quinoxalin-2(1H)-ones

This report presents a novel three step solution phase protocol to synthesize 3-(tetrazol-5-yl)quinoxalin-2(1H)-ones. The strategy utilizes ethyl glyoxalate and mono-N-Boc-protected-o-phenylenediamine derivatives in the Ugi-Azide multi-component reaction (MCR) to generate a unique 1,5-disubstituted tetrazole. Subsequent acid treatment stimulates a simultaneous Boc deprotection and intramolecular cyclization leading to bis-3,4-dihydroquinoxalinone tetrazoles. Direct oxidation using a stable solid-phase radical catalyst (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) with ceric ammonium nitrate (CAN) in catalytic fashion initiating aerobic oxidation, completes the entire procedure to generate a series of original unique bis-quinoxalinone tetrazoles. The method was also expanded to produce a bis-benzodiazepine tetrazole.

Synthesis, characterization and antimicrobial activity of 3d transition metal complexes of a biambidentate ligand containing quinoxaline moiety

A new series of oxovanadium(IV), chromium(III), manganese(II), iron(III), cobalt(II), nickel(II), and copper(II) complexes of the 3-hydrazino quinoxaline-2-one (HQO) were prepared and characterized. The ligand exhibits biambidenticity. It behaves as a bidentate ON donor in oxovanadium(IV), iron(III) and copper(II) complexes and as a bis bidentate ONNN donor in chromium(III), manganese(II), cobalt(II) and nickel(II) complexes. The nature of bonding and the stereochemistry of the complexes have been deduced from elemental analyses, thermal, infrared, (1)H NMR, electronic spectra, magnetic susceptibility and conductivity measurements. An octahedral geometry was suggested for all the complexes. All the complexes show subnormal magnetic moments. The ligand, HQO, and its complexes were tested against one strain Gram +ve bacteria (Staphylococcus aureus), Gram -ve bacteria (Escherichia coli). The prepared metal complexes exhibited higher antimicrobial activities than the parent ligand.

New acyclic quinoxaline nucleosides. Synthesis and anti-hiv activity

A series of acyclonucleosides substituted 1-(4,5-dihydroxypentyl) (13-8) and 2-(4,5-dihydroxypentyloxy)quinoxalines (19-24) were synthesized by the sharpless asymmetric dihydroxylation of the derivatives 1-6 and 7-12, respectively. Treatment of the quinoxaline base 26 with (R)-2,2-dimethyl-1,3-dioxolan-4-ylmethyl-p-toluenesulfonate (27) in the presence of NaH/DMF furnished 28. Acid hydrolysis of 28 gave 1-(2,3-dihydroxypropyl)-6,7-dimethyl-quinoxaline-2-one (29). Alternatively, 29 was prepared by sharpless dihydroxylation of 30. All the compounds were evaluated for their in vitro anti-HIV-1 and HIV-2 in MT-4 cell and found inactive, except 29, which showed inhibition of HIV-1 with EC50 value of 0.15 +/- 0.1 microg/ml and a therapeutic index (SI) of 73.

2,3-Bis(4-bromophenyl)quinoxaline

The title compound, C₂₀H₁₂Br₂N₂, was prepared by the reaction of 1-(3-bromo­phen­yl)-2-(4-bromo­phen­yl)ethane-1,2-dione with o-phenyl­enediamine in refluxing ethanol. In the mol­ecule, all bond lengths and angles are within normal ranges. The dihedral angle between the two benzene rings is 34.89 (1)°. The dihedral angles between the benzene rings and the quinoxaline system are 57.23 (1) and 36.75 (1)°. The crystal packing is stabilized by van der Waals forces.

Quinoxalinylurea derivatives as a novel class of JSP-1 inhibitors

A series of quinoxalinylurea-based inhibitors are synthesized and shown to be the novel and potent inhibitors against Jnk Stimulatory Phosphatase-1 (JSP-1), which is a special member of dual-specificity protein phosphatase (DSP) family. Biological assay and computational modeling studies showed the compounds were reversible and noncompetitive inhibitors of JSP-1. JSP-1 inhibitors may be useful for the treatment of inflammatory, vascular, neurodegenerative, metabolic, and oncological diseases in humans associated with dysfunctional Jnk signaling.

Preparation of 6-substituted quinoxaline JSP-1 inhibitors by microwave accelerated nucleophilic substitution

A small library of 6-aminoquinoxalines has been prepared by nucleophilic substitution of 6-fluoroquinoxaline with amines and nitrogen-containing heterocycles under computer-controlled microwave irradiation. Some compounds were found to be potent inhibitors of JNK Stimulatory Phosphatase-1 (JSP-1) in an in vitro biological assay.

Lewis Acid-Promoted Annulation of o-Quinonediimines by Allylstannane: A Facile Synthesis of Quinoxaline Derivatives

[reaction: see text] Lewis acid-promoted addition of allyltri-n-butylstannane to o-quinonediimines afforded tetrahydroquinoxaline derivatives or allylated amides depending on the nature of the substituent on imine nitrogen.

The recent impact of solid-phase synthesis on medicinally relevant benzoannelated nitrogen heterocycles

Benzoannelated heterocycles such as benzodiazepines and indoles can be prepared efficiently through cyclization on solid supports, although no single approach is currently universal for the preparation of all benzoannelated N-heterocycle chemistries. In this review, a number of synthetic strategies for the generation of benzoannelated nitrogen heterocycles using resin-bound substrates have been described. Classical heterocycle forming reactions such as the Fischer indole, the Bischler-Napieralski tetrahydroisoquinoline, the Pictet-Spengler tetrahydro-beta-carboline, the Tsuge, the Nenitzescu and the Richter cinnoline reaction are presented. In addition, the Heck, Sonogashira, Wittig, Diels-Alder, and olefin metathesis reactions have been also used. Multicomponent reactions such as the Grieco three-component assembly have been exploited for the synthesis of heterocycles. Cyclative cleavage from the solid support is particularly suitable for the synthesis of heterocycles while particular emphasis has been focused on the synthesis of libraries and the use of combinatorial chemistry techniques. In addition, the most relevant pharmacological properties of benzoannelated nitrogen heterocycles are included.