Quinoxaline Scaffold Research Articles

Design, Synthesis and Biological Evaluation of Novel Fluorinated Heterocyclic Hybrid Molecules Based on Triazole & Quinoxaline Scaffolds Lead to Highly Potent Antimalarials and Antibacterials

A series of novel fluorinated heterocyclic hybrid molecules based on triazole & quinoxaline scaffold were designed, synthesized and evaluated for inhibition of Plasmodium falciparum, a virulent human malaria parasite. Mono and bis triazole tagged quinoxaline analogs were synthesized by propargylation of 6-amino quinoxaline followed by click reaction with various substituted aromatic azides under uncertain reaction conditions. The newly synthesized molecules were assessed for antimalarial activity and three of the analogs were identified as promising leads which killed parasites with IC50 values <10 μM and showed 27-70 selective indices. Keywords: Antimalarials, click reaction, hybrid molecules, plasmodium, quinoxalines, triazoles.

1,2,4-Triazolo[1,5-a]quinoxaline derivatives and their simplified analogues as adenosine A3 receptor antagonists. Synthesis, structure–affinity relationships and molecular modeling studies

The 1,2,4-triazolo[1,5-a]quinoxaline (TQX) scaffold was extensively investigated in our previously reported studies and recently, our attention was focused at position 5 of the tricyclic nucleus where different acyl and carboxylate moieties were introduced (compounds 2–15). This study produced some interesting compounds endowed with good hA3 receptor affinity and selectivity. In addition, to find new insights about the structural requirements for hA3 receptor–ligand interaction, the tricyclic TQX ring was destroyed yielding some 1,2,4-triazole derivatives (compounds 16–23). These simplified compounds, though maintaining the crucial structural requirements for adenosine receptor–ligand interaction, have a very low hA3 adenosine receptor affinity, the only exception being compound 23 (1-[3-(4-methoxyphenyl)-1-phenyl-1H-1,2,4-triazol-5-yl]-3-phenylurea) endowed with a Ki value in the micro-molar range and high hA3 selectivity versus both hA1 and hA2A AR subtypes. Evaluation of the side products obtained in the herein reported synthetic pathways led to the identification of some new triazolo[1,5-a]quinoxalines as hA3AR antagonists (compounds 24–27). These derivatives, though lacking the classical structural requirements for the anchoring at the hA3 receptor site, show high hA3 affinity and in some case selectivity versus hA1 and hA2A subtypes. Molecular docking of the herein reported tricyclic and simplified derivatives was carried out to depict their hypothetical binding mode to our model of hA3 receptor.

Recent advances in design of potential quinoxaline anti-infectives.

Antimicrobial diazanaphthalenes are indispensable in the treatment of various infections. The quinoxaline scaffold possesses unique physicochemical properties and provides a possibility of a great number of targeted modifications. Quinoxaline-based compounds have a wide range of promising biological properties; therefore a special attention is paid to them for research and designing of new drugs. In fact, quinoxaline can be considered as a privileged structure. The scaffold can be easily and rapidly constructed, which emphasizes the significance of this favourable structure. The review is focused on recently reported potential antibacterial, antimycobacterial, antifungal and antiprotozoal agents derived from the quinoxaline scaffold, their mechanism of action and structure-activity relationships. A brief classification of synthetic pathways of quinoxaline derivatives is provided too.

Histamine H4 receptor ligands: future applications and state of art.

Histamine is a chemical transmitter found practically in whole organism and exerts its effects through the interaction with H1 to H4 histaminergic receptors. Specifically, H4 receptors are found mainly in immune cells and blood-forming tissues, thus are involved in inflammatory and immune processes, as well as some actions in central nervous system. Therefore, H4 receptor ligands can have applications in the treatment of chronic inflammatory and immune diseases and may be novel therapeutic option in these conditions. Several H4 receptor ligands have been described from early 2000's until nowadays, being imidazole, indolecarboxamide, 2-aminopyrimidine, quinazoline, and quinoxaline scaffolds the most explored and discussed in this review. Moreover, several studies of molecular modeling using homology models of H4 receptor and QSAR data of the ligands are summarized. The increasing and promising therapeutic applications are leading these compounds to clinical trials, which probably will be part of the next generation of blockbuster drugs.

Design, synthesis, antifungal, and antioxidant activities of (E)-6-((2-phenylhydrazono)methyl)quinoxaline derivatives.

Different substituted phenylhydrazone groups were linked to the quinoxaline scaffold to provide 26 compounds (6a-6z). Their structures were confirmed by (1)H and (13)C NMR, MS, elemental analysis, and X-ray single-crystal diffraction. The antifungal activities of these compounds against Rhizoctonia solani were evaluated in vitro. Compound 6p is the most promising one among all the tested compounds with an EC50 of 0.16 μg·mL(-1), more potent than the coassayed positive control fungicide carbendazim (EC50: 1.42 μg·mL(-1)). In addition, these compounds were subjected to antioxidant assay by employing diphenylpicrylhydrazyl (DPPH) and mice microsome lipid peroxidation (LPO) methods. Most of these compounds are potent antioxidants. The strongest compounds are 6e (EC50: 7.60 μg·mL(-1), DPPH) and 6a (EC50: 0.96 μg·mL(-1), LPO), comparative to or more potent than the positive control Trolox [EC50: 5.90 μg·mL(-1) (DPPH) and 18.23 μg·mL(-1) (LPO)]. The structure and activity relationships were also discussed.

An efficient protocol for the synthesis of benzoheterocyclic compounds via solid-state melt reaction (SSMR)

An efficient protocol for the synthesis of biologically active benzoheterocyclic compounds such as benzothiazoles, benzimidazoles, benzospirothiazoles, and quinoxaline scaffolds have been accomplished via solid state melt reaction (SSMR) with excellent yields. The new protocol does not require any catalyst, solvent, and workup. Two anti-tumor agents have been prepared to demonstrate the application of this new method.

Synthesis and in vitro evaluation of 4-trichloromethylpyrrolo[1,2-a]quinoxalines as new antiplasmodial agents

Thanks to a preliminary in vitro screening of several CCl3-substituted-nitrogen containing heterocycles belonging to our chemical library, the 2-trichloromethylquinoxaline scaffold appeared to be of potential interest for developing new antiplasmodial agents. Then, combining these experimental results to the antimalarial properties reported for various pyrrolo[1,2-a]quinoxaline derivatives, an original series of fifteen 7-substituted-4-trichoromethylpyrrolo[1,2-a]quinoxalines was synthesized in a 4 to 5 reaction steps pathway. All molecules were evaluated in vitro toward both their antiplasmodial activity on the K1 multi-resistant Plasmodium falciparum strain and their cytotoxicity on the HepG2 human cell line. Thus, 3 hit molecules were identified, displaying IC50 values in the micromolar range and low cytotoxicity values, reaching good selectivity indexes, in comparison with the reference drugs chloroquine and doxycycline. Structure–activity relationship studies showed that the pyrrolo[1,2-a]quinoxaline scaffold can support selective antiplasmodial activity when substituted at position 4 by a CCl3 group. However, substitution at position 7 of the same scaffold is neither beneficial for cytotoxicity nor favourable for the solubility in the biological media.

Design, synthesis and biological evaluation of type-II VEGFR-2 inhibitors based on quinoxaline scaffold

In an effort to develop ATP-competitive VEGFR-2 selective inhibitors, a series of new quinoxaline-based derivatives was designed and synthesized. The target compounds were biologically evaluated for their inhibitory activity against VEGFR-2. The design of the target compounds was accomplished after a profound study of the structure activity relationship (SAR) of type-II VEGFR-2 inhibitors. Among the synthesized compounds, 1-(2-((4-methoxyphenyl)amino)-3-oxo-3,4 dihydroquinoxalin-6-yl)-3-phenylurea (VIIa) displayed the highest inhibitory activity against VEGFR-2. Molecular modeling study involving molecular docking and field alignment was implemented to interpret the variable inhibitory activity of the newly synthesized compounds.

Comparison of the reactivity of 2-amino-3-chloro- and 2,3-dichloroquinoxalines towards Ph2PH and Ph2PLi and of the properties of diphenylphosphanyl-quinoxaline P,N and P,P ligands

The synthesis of quinoxaline P,N ligands by monoamination of 2,3-dichloroquinoxaline (1) to 2-amino-3-chloroquinoxalines 2a,b and the subsequent substitution of chlorine by a diphenylphosphanyl group was studied. Whereas the reaction of 2a,b with Ph2PH in the presence (or absence) of catalytic amounts of palladium acetate furnished only minor amounts of the expected ligands in favor of tetraphenyldiphosphane and dechlorinated quinoxalines, the coupling with Ph2PLi in ether provided the novel NH-functional P,N hybrid ligands 3a,b with a quinoxaline scaffold in moderate to good yields. 3a is slightly and 3b somewhat more sensitive to air oxidation, leading to the P-oxides 4a,b. The more reactive 1 forms with Ph2PH only a small amount of 2-chloro-3-diphenylphosphanylquinoxaline 5 and traces of the quinoxaline-bis(phosphane) 6. The main products are 2,2′-bis(quinoxaline) and Ph2PCl, which converts residual Ph2PH into tetraphenyldiphosphane. The coupling with Ph2PLi in diethyl ether, however, gave in a fast reaction high yields of 6, exceeding those of 3a,b, with interfering NH functions. Semi-empirical quantum chemical calculations (PM6) illuminate the background of the air sensitivity of 3a,b, whereas the recently reported 6 is air stable. Preliminary studies for use of the ligands in catalysis with the air-stable 6, showed moderate to good yields in the Pd-catalyzed C–N cross coupling of 2-bromopyridine with mesityl amine. Complex formation was confirmed by isolation of the Pd complex 7. The structure elucidation of the new compounds is based on conclusive NMR data and crystal structure analyses for 2b, 3a, 4a and 4b.

Novel quinoxaline derivatives for in vivo imaging of β-amyloid plaques in the brain

In a search for new probes to detect β-amyloid plaques in the brain of patients with Alzheimer's disease (AD), we have synthesized and evaluated a series of quinoxaline derivatives containing a '6+6-6' ring system. These quinoxaline derivatives showed excellent affinity for Aβ(1-42) aggregates with K(i) values ranging from 2.6 to 10.7nM. Autoradiography with sections of brain tissue from an animal model of AD mice (APP/PS1) and AD patients revealed that [(125)I]5 labeled β-amyloid plaques specifically. In biodistribution experiments using normal mice, [(125)I]5 displayed high uptake (6.03% ID/g at 2min) into and a moderately fast washout from the brain. Although additional refinements are needed to decrease the lipophilicity and improve the washout rate, the quinoxaline scaffold may be useful as a backbone structure to develop novel β-amyloid imaging agents.

Spectroscopy, structure, and electrochemistry of transition metal complexes having [M2N2OS2] coordination sphere

Binuclear transition metal complexes of bicompartmental SNONS donors were synthesized and characterized by various physico-chemical techniques. Two different precursors with chloromethyl/formyl functionality at the 2 and 6 positions of phenolate ring are used to construct the ligands. The quinoxaline scaffolds provide SN donors incorporated at the 2 and 6 positions. Copper and zinc complexes are square pyramidal, whereas nickel and cobalt complexes are octahedral. The influence of two metal centers in terms of cooperative effect on the electronic, magnetic, electrochemical, and structural properties was investigated.

Ugi/Smiles access to pyrazine scaffolds

New pyrazine and quinoxaline scaffolds were obtained via an Ugi/Smiles four-component coupling of pyrazinone or quinoxalinone derivatives with isocyanides, aldehydes, and primary amines.

Ugi-Smiles Access to Quinoxaline Derivatives

Two different Ugi-Smiles post-condensations strategies have been used for new three and four-component formation of quinoxaline scaffolds. In the first approach, a one-pot hydrogenation-cyclization affords the heterocycle with loss of the initial isocyanide moiety. In the second one, the use of o-iodonitrophenol as starting phenol, coupled with copper catalyzed cyclization gave us similar quinoxaline derivatives resulting from a four coupling.