Quinoxalinylethylpyridylthioureas (QXPTs) as potent non-nucleoside HIV-1 reverse transcriptase (RT) inhibitors. Further SAR studies and identification of a novel orally bioavailable hydrazine-based antiviral agent

Copper-catalyzed oxidative cyclization of 2-(1H-pyrrol-1-yl)aniline and alkylsilyl peroxides: a route to pyrrolo[1,2-a]quinoxalines

An efficient method was developed for the one-pot construction of pyrrolo[1,2-a]quinoxalines via a Cu(II)-catalyzed domino reaction between 2-(1H-pyrrol-1-yl)anilines and alkylsilyl peroxides. This reaction proceeds through C-C bond cleavage and new C-C and C-N bond formation. A mechanistic study suggests that alkyl radical species participate in the cascade reaction.

Synthesis of Functionalized 3H-pyrrolo-[1,2,3-de] Quinoxalines via Gold-Catalyzed Intramolecular Hydroamination of Alkynes

A gold-catalyzed protocol to obtain functionalized 3H-pyrrolo [1,2,3-de] quinoxalines from suitable substituted N-alkynyl indoles has been proposed. The mild reaction conditions were revealed to be compatible with different functional groups, including halogen, alkoxyl, cyano, ketone, and ester, allowing the isolation of title compounds with yields from good to high. A reaction mechanism has been proposed, and theoretical calculations have been provided to rationalize the final step of the hypothesized reaction mechanism. As quinoxaline-containing polycyclic compounds, this class of molecules may represent a valuable template in medicinal chemistry and material science.

Synthesis of Hydroxylated Polycyclic Pyrrolo/Indolo[1,2-a]quinoxaline-Fused Lactam Derivatives via PhI(OAc)2-Promoted 1,2-Bond Migration and Solvent Insertion

PhI(OAc)₂-mediated ring expansion via 1,2-bond migration and concurrent solvent insertion generate hydroxylated polycyclic pyrrolo/indolo[1,2-a]quinoxaline-fused lactam derivatives in a highly diastereoselective fashion from spiro-fused quinoxalines in good-to-excellent yield. X-ray crystal structure analysis reveals that the polycyclic lactams are nonplanar molecules devoid of any symmetry as they possess one or two axially chiral biaryl or N-arylindolyl bridges along with one chiral center at the bridgehead carbon.

Synthesis, Crystal Structure and Anti-Leukemic Activity of 1,3-Dihydro-1-{1-[4-(4-phenylpyrrolo[1,2-a]quinoxalin-3-yl)benzyl]piperidin-4-yl}-2H-benzimidazol-2-one

1,3-Dihydro-1-{1-[4-(4-phenylpyrrolo[1,2-a]quinoxalin-3-yl)benzyl]piperidin-4-yl}-2H-benzimidazol-2-one has been synthesized through a multi-step pathway starting from commercially available 2-nitroaniline. A structure characterization of this new substituted pyrrolo[1,2-a]quinoxaline compound was achieved by using FT-IR, 1H-NMR, 13C-NMR, X-Ray and HRMS spectral analysis. This new pyrroloquinoxaline derivative shows an interesting cytotoxic potential against several human leukemia cell lines (HL60, K562 and U937 cells).

Pd-Catalyzed direct C-H arylation of pyrrolo[1,2-a]quinoxalines

An efficient Pd-catalyzed direct C-H arylation of pyrrolo[1,2-a]quinoxalines with aryl iodides is described, providing a selective route toward a series of 1-arylated and 1,3-diarylated pyrrolo[1,2-a]quinoxalines in good yields. This method features a broad substrate scope, good functional group tolerance and gram-scale synthesis. Furthermore, the C3-thiocyanation of the arylated product is also achieved. We believe that these novel aryl-substituted pyrrolo [1,2-a]quinoxalines will have a variety of applications in organic synthesis and medicinal chemistry.

Recent advances in the transition-metal-free synthesis of quinoxalines

Quinoxalines, also known as benzo[a]pyrazines, constitute an important class of nitrogen-containing heterocyclic compounds as a result of their widespread prevalence in natural products, biologically active synthetic drug candidates, and optoelectronic materials. Owing to their importance and chemists' ever-increasing imagination of new transformations of these products, tremendous efforts have been dedicated to finding more efficient approaches toward the synthesis of quinoxaline rings. The last decades have witnessed a marvellous outburst in modifying organic synthetic methods to create them sustainable for the betterment of our environment. The exploitation of transition-metal-free catalysis in organic synthesis leads to a new frontier to access biologically active heterocycles and provides an alternative method from the perspective of green and sustainable chemistry. Despite notable developments achieved in transition-metal catalyzed synthesis, the high cost involved in the preparation of the catalyst, toxicity, and difficulty in removing it from the final products constitute disadvantageous effects on the atom economy and eco-friendly nature of the transformation. In this review article, we have summarized the recent progress achieved in the synthesis of quinoxalines under transition-metal-free conditions and cover the reports from 2015 to date. This aspect is presented alongside the mechanistic rationalization and limitations of the reaction methodologies. The scopes of future developments are also highlighted.

Tandem 6π-Azatriene Electrocyclization of Fused Amino-cyclopentenones: Synthesis of Functionalized Pyrrolo- and Indolo-quinoxalines

A tandem 6π-azacyclization approach for the synthesis of diversified pyrrolo/indolo[1,2-a]quinoxalines from amino-cyclopentenones has been developed. The reaction proceeds through a trifluoroacetic-acid-mediated 6π-electrocyclization and concomitant opening of the cyclopentenone ring. The advantageous features of the developed chemistry include transition-metal-free conditions, operational simplicity, and a broad substrate scope. Further X-ray crystallographic studies confirm the assigned structures of the fused heterocycles.

Relative assessment of different statistical instruments and measures for the prediction of promising outcomes using docking, virtual screening and ADMET analysis against HIV-RT

Reverse transcriptase is the most therapeutic target for the discovery of novel, potent, and non-toxic new anti-retroviral drugs. In the present work, various docking software such as Sybyl Surflex-Dock, OpenEye FRED, and Hermes GOLD were evaluated for their efficiency to reproduce known cognate inhibitors' conformations. Three metrics were used and compared to assess the performance of the applied scoring functions, i.e. enrichment factor, receiver operating characteristic (ROC) curves, and Bedroc analysis. Twelve different scoring functions of three softwares were used to assess their ability to rank the cognate ligand within the active site of its proteins. The extensive virtual screening task was performed on eight crystal structures, and the performance of docking and scoring was assessed by their ability to efficiently detect known active compounds enriched in the top-ranked of the list among a randomly selected dataset of the ten thousand compounds of the NCI database. The effectiveness of post-docking relaxation in Surflex was also evaluated. The top 20, 50, and 100 compounds were selected based on consensus scoring functions from all 48 proteins with different ligand complexes. Further, the shortlisted leads were subjected to ADMET via using Discovery Studio. The results further implicate the importance of various statistical tools that should be followed before large-scale virtual screening for the drug discovery process. In silico results demonstrating the experiment was successful. The study of the research covers the combinatorial in silico techniques such as benchmarking of the softwares and scoring functions, statistical tools applied for screening and different conformations of HIV-RT crystal structures for virtual screening with rigid and flexible molecular docking and molecular dynamics simulation approach. This study reveals a clear roadmap to identify novel scaffolds against HIV-RT for antiretroviral therapy, thus providing the remedial solutions of HIV related infections and other diseases caused by malfunctioning of the target protein.Communicated by Ramaswamy H. Sarma.

Cobalt-Catalyzed Direct C-H Carbonylative Synthesis of Free (NH)-Indolo[1,2-a]quinoxalin-6(5H)-ones

A cobalt-catalyzed direct C-H carbonylative reaction of N-(2-(1H-indol-1-yl)phenyl)picolinamides for the synthesis of (NH)-indolo[1,2-a]quinoxalin-6(5H)-one skeletons has been developed. Using benzene-1,3,5-triyl triformate (TFBen) as the CO source and picolinamide as the traceless directing group, various free (NH)-indolo[1,2-a]quinoxalin-6(5H)-ones were obtained in good yields (up to 88%). Additionally, a series of product derivatizations were demonstrated, and the core fragment of PARP-1 inhibitor C can be readily constructed by this protocol.

Synthesis of novel 4,5-dihydropyrrolo[1,2-a]quinoxalines, pyrrolo[1,2-a]quinoxalin]-2-ones and their antituberculosis and anticancer activity

A facile strategy was developed for the synthesis of biologically important 4,5-dihydropyrrolo[1,2-a]quinoxalines and pyrrolo[1,2-a]quinoxalin]-2-ones by treating 2-(1H-pyrrol-1-yl)anilines with imidazo[1,2-a]pyridine-3-carbaldehyde or isatin, using amidosulfonic acid (NH₃ SO₃ ) as a solid catalyst in water at room temperature. The protocol has been extended to electrophile ninhydrin. The catalyst could be recycled for six times without the loss of activity. The compounds were evaluated for their antituberculosis, antibacterial, and anticancer activities. It is worth noting that compounds 3d and 3e demonstrated a minimum inhibitory concentration value of 6.25 µM against Mycobacterium tuberculosis H37Rv, whereas compounds 3d, 3g, 5d, 5e, and 5i showed a remarkable inhibition of A549, DU145, HeLa, HepG2, MCF-7, and B16-F10 cell lines, respectively. Staphylococcus aureus was inhibited by compounds 5b, 5e, 5d, 5g, and 5l at 32 µg/ml.

Regioselective Ring Expansion of 3-Ylideneoxindoles with Tosyldiazomethane (TsDAM): A Metal-Free and Greener Approach for the Synthesis of Pyrazolo-[1,5-c]quinazolines

An efficient, metal-free approach to access pyrazolo-[1,5-c]quinazolines with 3-ylideneoxindoles and tosyldiazomethane (TsDAM) under mild aqueous reaction conditions has been developed and the solvent involvement in the present reaction has also been explored for the first time. This greener approach involves 1,3-dipolar cycloaddition, regioselective ring expansion, followed by the elimination of tosyl group with aqueous base in a single operation, and the product can be isolated in high purity without column chromatographic separation. The method is also compatible with a large variety of functional groups, providing good to excellent yields in water, thus resulting in a decrease of environmental impact in the pharmaceutical industry.

1-Phenyl-8-[[4-(pyrrolo[1,2-a]quinoxalin-4-yl)phenyl]methyl]-1,3,8-triazaspiro[4.5]decan-4-one: Synthesis, Crystal Structure and Anti-Leukemic Activity

1-Phenyl-8-[[4-(pyrrolo[1,2-a]quinoxalin-4-yl)phenyl]methyl]-1,3,8-triazaspiro[4.5]decan-4-one has been successfully synthesized via a multi-step pathway starting from 2-nitroaniline. Structure characterization of this original pyrrolo[1,2-a]quinoxaline derivative was achieved by FT-IR, 1H-NMR, 13C-NMR, X-Ray and HRMS spectral analysis. This title compound shows interesting cytotoxic potential against several human leukemia cell lines (K562, HL60, and U937 cells).

Synthesis of new piperazinyl-pyrrolo[1,2-a]quinoxaline derivatives as inhibitors of Candida albicans multidrug transporters by a Buchwald-Hartwig cross-coupling reaction

Two series of piperazinyl-pyrrolo[1,2-a]quinoxaline derivatives were prepared via a Buchwald–Hartwig cross-coupling reaction and then evaluated for their ability to inhibit the drug efflux activity of CaCdr1p and CaMdr1p transporters of Candida albicans overexpressed in a Saccharomyces cerevisiae strain. In the initial screening of twenty-nine piperazinyl-pyrrolo[1,2-a]quinoxaline derivatives, twenty-three compounds behaved as dual inhibitors of CaCdr1p and CaMdr1p. Only four compounds showed exclusive inhibition of CaCdr1p or CaMdr1p. Further biological investigations were developed and for example, their antifungal potential was evaluated by measuring the growth of control yeast cells (AD1-8u⁻) and efflux pump-overexpressing cells (AD-CDR1 and AD-MDR1) after exposition to variable concentrations of the tested compounds. The MIC₈₀ values of nineteen compounds ranging from 100 to 901 μM for AD-CDR1 demonstrated that relative resistance index (RI) values were between 8 and 274. In comparison, only seven compounds had RI values superior to 4 in cells overexpressing Mdr1p. These results indicated substrate behavior for nineteen compounds for CaCdr1p and seven compounds for CaMdr1p, as these compounds were transported via MDR transporter overexpressing cells and not by the AD1-8u⁻ cells. Finally, in a combination assay with fluconazole, two compounds (1d and 1f) have shown a synergistic effect (fractional inhibitory concentration index (FICI) values ≤ 0.5) at micromolar concentrations in the AD-MDR1 yeast strain overexpressing CaMdr1p-protein, indicating an excellent potency toward chemosensitization.

Two series of piperazinyl-pyrrolo[1,2-a]quinoxaline derivatives were prepared via a Buchwald–Hartwig cross-coupling reaction and then evaluated for their ability to inhibit the drug efflux activity of two Candida albicans transporters.

NCS-promoted thiocyanation and selenocyanation of pyrrolo[1,2-a]quinoxalines

An efficient NCS-promoted thiocyanation of pyrrolo[1,2-a]quinoxalines with NH₄SCN or KSCN was developed. Moreover, in the presence of KSeCN, the selenocyanation of pyrrolo[1,2-a]quinoxalines was also achieved.

KI/TBHP-promoted [3 + 2] cycloaddition of pyrrolo[1,2-a]quinoxalines and N-arylsulfonylhydrazones

A series of diverse fused [1,2,4]triazolo[3,4-c]quinoxalines was obtained by an efficient KI/TBHP-promoted [3 + 2] cycloaddition of pyrrolo[1,2-a]quinoxalines and N-arylsulfonylhydrazones.

Terminal methyl as a one-carbon synthon: synthesis of quinoxaline derivatives via radical-type transformation

An iron-promoted method for the construction of pyrrolo[1,2-a]quinoxaline derivatives has been developed. Various solvents with terminal methyl group, including ethers, amines and dimethyl sulfoxide, were utilized as carbon sources for the synthesis.

Copper-catalyzed tandem aerobic oxidative cyclization for the synthesis of 4-cyanoalkylpyrrolo[1,2-a]quinoxalines from 1-(2-aminophenyl)pyrroles and cyclobutanone oxime esters

A copper-catalyzed tandem ring-opening/cyclization reaction for the synthesis of 4-cyanoalkylpyrrolo[1,2-a]quinoxalines from 1-(2-aminophenyl)pyrroles and cyclobutanone oxime esters has been developed.

Molecular iodine-catalysed oxidative CO–C(alkyl) bond cleavage of aryl/heteroaryl alkyl ketones: an efficient strategy to access fused polyheterocycles

An efficient molecular iodine-catalysed one-pot strategy has been accomplished for the construction of various fused heterocycles under metal and oxidant free conditions.

Synthesis of Spiro[indazole-3,3'-indolin]-2'-ones via [3 + 2] Dipolar Cycloaddition of Arynes with 3-Diazoindolin-2-ones and Indazolo[2,3-c]quinazolin-6(5H)-ones by Subsequent Thermal Isomerization

An efficient protocol for facile construction of spiro[indazole-3,3'-indolin]-2'-ones was developed via [3 + 2] dipolar cycloaddition of arynes with 3-diazoindolin-2-ones under mild conditions in excellent yields. Subsequent thermal isomerization of the spiro[indazole-3,3'-indolin]-2'-ones readily afforded indazolo[2,3-c]quinazolin-6(5H)-ones.

Chemical structure and correlation analysis of HIV-1 NNRT and NRT inhibitors and database-curated, published inhibition constants with chemical structure in diverse datasets

Human immunodeficiency virus (HIV-1) reverse transcriptase is a major target for designing anti-HIV drugs. Developed inhibitors are divided into non-nucleoside analog reverse-transcriptase inhibitors (NNRTIs) and nucleoside analog reverse-transcriptase inhibitors (NRTIs) depending on their mechanism. Given that many inhibitors have been studied and for many of them binding affinity constants have been calculated, it is beneficial to analyze the chemical landscape of these families of inhibitors and correlate these inhibition constants with molecular structure descriptors. For this, the HIV-1 RT data was retrieved from the ChEMBL database, carefully curated, and original literature verified, grouped into NRTIs and NNRTIs, analyzed using a hierarchical scaffold classification method and modelled with best multi-linear regression approach. Analysis of the HIV-1 NNRTIs subset results in ten different common structural parent types of oxazepanone, piperazinone, pyrazine, oxazinanone, diazinanone, pyridine, pyrrole, diazepanone, thiazole, and triazine. The same analysis for HIV-1 NRTIs groups structures into four different parent types of uracil, pyrimide, pyrimidione, and imidazole. Each scaffold tree corresponding to the parent types has been carefully analyzed and examined, and changes in chemical structure favorable to potency and stability are highlighted. For both subsets, descriptive and predictive QSAR models are derived, discussed and externally validated, revealing general trends in relationships between molecular structure and binding affinity constants in structurally diverse datasets. Data and QSAR models are available at the QsarDB repository (http://dx.doi.org/10.15152/QDB.202).

Application of α-amino acids for the transition-metal-free synthesis of pyrrolo[1,2-a]quinoxalines

A practical and concise protocol for the efficient synthesis of pyrrolo[1,2-a]quinoxalines from readily available α-amino acids and 2-(1H-pyrrol-1-yl)anilines under transition metal-free conditions has been established. This protocol, which includes the formation of new C–C and C–N bonds, features a wide substrate scope with a broad range of functional group tolerance.

Synthesis of pyrrolo[1,2-a]quinoxalines via copper or iron-catalyzed aerobic oxidative carboamination of sp3C–H bonds

We developed an aerobic oxidative carboamination of sp³C–H bonds with 2-(1H-pyrrol-1-yl)anilines for synthesis of pyrrolo[1,2-a]quinoxalines.

Synthesis of Kappa Opioid Antagonists Based On Pyrrolo[1,2-α]quinoxalinones Using an N-Arylation/Condensation/Oxidation Reaction Sequence

The quinoxaline and quinoxalinone family of nitrogen heterocycles is present in molecules of therapeutic relevance for diverse applications ranging from infectious diseases to neuroscience targets. Here, we describe a general synthetic sequence to afford pyrrolo[1,2-α]quinoxalinones from commercially available starting materials and their use in preparing potential kappa opioid receptor antagonists. The biological data obtained from the latter set of compounds is briefly presented and discussed.

The Cycloaddition of the Benzimidazolium Ylides with Alkynes: New Mechanistic Insights

New insights concerning the reaction mechanism in the cycloaddition reaction of benzimidazolium ylides to activated alkynes are presented. The proposed pathway leading both to 2-(1H-pyrrol-1-yl)anilines and to pyrrolo[1,2-a]quinoxalin-4(5H)-ones involves an opening of the imidazole ring from the cycloaddition product, followed by a nucleophilic attack of the aminic nitrogen to a proximal carbonyl group and the elimination of a leaving group. The mechanistic considerations are fully supported by experimental data, including the XRD resolved structure of the key reaction intermediate.

Phosphine-catalyzed domino reactions of alkynyl ketones with sulfonylhydrazones: construction of diverse pyrazoloquinazoline derivatives

An efficient method for the synthesis of C-1 position acyl substituted pyrazoloquinazoline derivatives via a PBu₃-promoted domino process of sulfonylhydrazones and alkynyl ketones was developed.

Copper-catalysed oxidative amination of quinoxalin-2(1H)-ones with aliphatic amines

A novel, efficient and practical method for copper-catalysed oxidative C-3 amination of quinoxalin-2(1H)-ones with primary or secondary amines as the nitrogen sources has been developed.

Novel fluorine-containing DAPY derivatives as potent HIV-1 NNRTIs: a patent evaluation of WO2014072419

Diarylpyrimidine (DAPY) derivatives, one family of HIV non-nucleoside reverse transcriptase (RT) inhibitors (NNRTIs) with superior activities against wild-type (WT) HIV-1 and NNRTI-resistant strains, have attracted much attention in the past decade. A series of DAPY derivatives featuring a fluorine atom on the central ring were reported as novel NNRTIs in the patent WO2014072419. Some compounds exhibited robust potency against both WT and mutant strains, which were approximately equal to or higher than those of the reference drug TMC120. Moreover, it has become evident that fluorinated molecules have a remarkable record in many other potent NNRTIs. Thus, this survey provides a sampling of renowned fluorinated NNRTIs and their mode of action, with an analysis clarifying the functional roles and impact of fluorine substitution on antiviral potency. We envision that fluorinated NNRTIs will play a continuing role in affording anti-HIV drug candidates for therapeutic applications.

Microwave Controlled Reductive Cyclization: A Selective Synthesis of Novel Benzimidazole-alkyloxypyrrolo[1,2-a]quinoxalinones

An efficient cascade synthesis of novel benzimidazole linked alkyloxypyrrolo[1,2-a]quinoxalinones was explored on soluble polymer support under microwave irradiation. Two exclusive protocols have been developed for the partial and full reductive cyclization by controlling the microwave energy. Commencing from the same substrate, ortho nitro pyrrol carboxylates, N-hydroxy pyrroloquinoxalinones were obtained by partial reductive cyclization (60 °C, 7 min), and the synthesis of pyrroloquinoxalinones was accomplished by full reductive cyclization (85 °C, 12 min). This method represents the first synthesis of N-hydroxy pyrroloquinoxalinones using Pd/C and ammonium formate as reducing agents. Further employing a variety of alkyl bromides, the obtained pyrroloquinoxalinones were transformed to their corresponding O- and N-alkylated analogues to deliver the diversified, novel molecular entities.

Design, synthesis and biological evaluation of novel 4-alkapolyenylpyrrolo[1,2-a]quinoxalines as antileishmanial agents--part III

A series of new 4-alkapolyenylpyrrolo[1,2-a]quinoxaline derivatives, original and structural analogues of alkaloid chimanine B and of previously described 4-alkenylpyrrolo[1,2-a]quinoxalines, was synthesized in good yields using efficient palladium-catalyzed Suzuki-Miyaura cross-coupling reactions. These new compounds were tested for in vitro antiparasitic activity upon three Leishmania spp. strains. Biological results showed activity against the promastigote forms of L. major, L. mexicana and L. donovani with IC50 ranging from 1.2 to 14.7 μM. In attempting to investigate if our pyrrolo[1,2-a]quinoxaline derivatives are broad-spectrum antiprotozoal compounds activities toward one Trypanosoma brucei brucei strain and the W2 and 3D7 Plasmodium falciparum strains were also investigated. In parallel, the in vitro cytotoxicity of these molecules was assessed on the murine J774 and human HepG2 cell lines. Structure-activity relationships of these new synthetic compounds are here discussed.