In vitro antitubercular and antimicrobial activities of 1-substituted quinoxaline-2,3(1H,4H)-diones

Synthesis and Antiviral Properties against SARS-CoV-2 of Epoxybenzooxocino[4,3-b]Pyridine Derivatives

The COVID-19 pandemic is ongoing as of mid-2022 and requires the development of new therapeutic drugs, because the existing clinically approved drugs are limited. In this work, seven derivatives of epoxybenzooxocinopyridine were synthesized and tested for the ability to inhibit the replication of the SARS-CoV-2 virus in cell cultures. Among the described compounds, six were not able to suppress the SARS-CoV-2 virus’ replication. One compound, which is a derivative of epoxybenzooxocinopyridine with an attached side group of 3,4-dihydroquinoxalin-2-one, demonstrated antiviral activity comparable to that of one pharmaceutical drug. The described compound is a prospective lead substance, because the half-maximal effective concentration is 2.23 μg/μL, which is within a pharmacologically achievable range.

Discovery of potent antitubercular agents: Design, synthesis and biological evaluation of 4-(3-(4-substitutedpiperazin-1-yl)-quinoxalin-2-yl)-naphthalen-1-ol analogues

A series of twenty-five novel 4-(3-(4-substituted piperazin-1-yl)-quinoxalin-2-yl)-naphthalen-1-ol analogues were synthesized, characterized and screened for in vitro antitubercular activity against Mycobacterium tuberculosis H37Rv strain. These compounds exhibited minimum inhibitory concentration in the range of 1.56-50 μg/mL. Among these derivatives, compounds 5a, 5b, 5f, 5m, 5p, and 5r displayed moderate activity (MIC 6.25 μg/mL). Compounds 5c, 5d, 5g, 5l, and 5o showed significant antitubercular activity (MIC 3.125 μg/mL), while compounds 5h, 5n, and 5q exhibited potent antitubercular activity (MIC 1.56 μg/mL). In addition, MTT assay was performed on the active analogues of the series against mouse macrophage cells to assess the cytotoxic effect of the newly synthesized compounds, and a selectivity index of the compounds was established. Selectivity index values of the most active compounds (5h, 5n, and 5q) are >47, indicating the compounds' suitability for further potential drug development. A molecular docking study was performed to understand the putative binding mode and binding strength of the selected significantly active and weakly active compounds with the target enzyme mycobacterial topoisomerase II using moxifloxacin as standard. In-silico ADME prediction and bioavailability studies of the titled compounds obey Lipinski's rule of five and Jorgensen's rule of three. To further ascertain the structure of the compounds, a suitable single crystal for the compounds 5a, 6, and 7d was developed and studied.

Controlled microwave-assisted reactions: A facile synthesis of polyfunctionally substituted phthalazines as dual EGFR and PI3K inhibitors in CNS SNB-75 cell line

Brain tumors are stubborn cancers with poor prognosis and disappointing survival rates. Targeted cancer therapeutics with higher efficacy and lower resistance are highly demanded. An efficient one-pot synthesis of polyfunctionalized phthalazines derivatives was developed by reacting ethyl 1-aryl-5-cyano-1,6-dihydro-4-methyl-6-oxo-3-pyridazine-carboxylates with cinnamonitrile derivatives and the cycloaddition reaction of thieno[3,4-d]pyridazines with activated double or triple bond systems under controlled microwave heating with high yields. The resultant synthesized phthalazines (5a-e, 9 and 13) were tested for their in vitro anti-cancer activities by using in vitro one dose assay at National Cancer institute, USA. Only phthalazine (5b) showed broad spectrum anti-tumor activity against most tested cancer cell lines from all subpanels with mean % GI = 22.61. Interestingly, all tested compounds showed varying growth inhibitory activity against a particular cell line, CNS SNB-75 cell line, but (5b) exhibited the highest growth inhibitory activity against CNS-SNB-75 cell line with (GI% = 108.81) and (IC₅₀ = 3.703 ± 0.2) compared to erlotinib; (IC₅₀ = 12.5 ± 0.68). It caused Pre-G1 apoptosis and growth arrest at S phase. It also increased percentage of the total apoptotic cells in CNS-SNB-75 cell line (39.26%) compared to control cells (2.17%) in the annexin V-FITC experiment. It revealed pronounced EGFR inhibitory activity (IC₅₀ = 47.27 ± 2.41 ng/mL) compared to erlotinib (IC₅₀ = 30.7 ± 1.56 ng/mL). It also inhibited the different PI3K isoforms α, β, γ and δ (with IC₅₀ of 4.39, 13.6, 12.5 and 3.11 μg/mL, respectively compared to LY294002 (with IC₅₀ of 12.7, 8.57, 6.89 and 5.7 μg/mL, respectively). It also caused significant lower protein expression levels of pPI3K, AKT, pAKT and Bcl2 and higher protein expression levels of BAX, Casp3 and Casp9 when compared to untreated cells. Conclusion: Phthalazine (5b) may be an effective, convenient and safe anti-cancer agent acting via proapoptotic and dual EGFR and PI3K kinase inhibitory actions in CNS SNB-75 cell line.

The Medicinal Chemistry of Chalcones as Anti-Mycobacterium tuberculosis Agents

Abstract:

Tuberculosis (TB), a highly fatal infectious disease, is caused by Mycobacterium tuberculosis (Mtb) that has inflicted mankind for several centuries. In 2019, the staggering number of new cases reached 10 million resulting in 1.2 million deaths. The emergence of multidrug-resistance-Mycobacterium tuberculosis (MDR-TB) and extensively drug-resistant-Mycobacterium tuberculosis (XDR-TB) is a global concern that requires the search for novel, effective, and safer short-term therapies. Nowadays, among the few alternatives available to treat resistant-Mtb strains, the majority have limitations, which include drug-drug interactions, long-term treatment, and chronic induced toxicities. Therefore, it is mandatory to develop new anti-Mtb agents to achieve health policy goals to mitigate the disease by 2035. Among the several bioactive anti-Mtb compounds, chalcones have been described as the privileged scaffold useful for drug design. Overall, this review explores and analyzes 37 chalcones that exhibited anti-Mtb activity described in the literature up to April 2021 with minimum inhibitory concentration (MIC90) values inferior to 20 µM and selective index superior to 10. In addition, the correlation of some properties for most active compounds was evaluated, and the main targets for these compounds were discussed.

Unravelling the Selectivity of 6,7-Dimethyl Quinoxaline Analogs for Kinase Inhibition: An Insight towards the Development of Alzheimer's Therapeutics

Untangling the most selective kinase inhibitors via pharmacological intervention remains one of the challenging affairs to date. In accordance to this drift, herein we describe the design and synthesis of a set of new heterocyclic analogs consisting of 6,7-dimethyl Quinoxaline, appended to a connector, employing Schiff base strategy (Compounds I-IX). The compounds were characterized by various spectroscopic techniques and the kinase inhibition assay were performed on few prime members of the CMGC family namely the GSK3β, DYRK1A and CLK1 receptors, respectively, that have been known to be directly involved in hyperphosphorylation of Tau. Interestingly the biological evaluation results revealed that Compounds IV and V, with bromo/chloro functionalities in the aromatic core were advantaged of being highly selective towards the target GSK3β over others. To strengthen our analysis, we adopted molecular modelling studies, where compounds IV/V were redocked in the same grid 4AFJ, as that of the reference ligand, 5-aryl-4-carboxamide-1,3-oxazole. Surprisingly, our investigation underpinned that for both the compounds IV/V, a primary H-bonding existed between the designed molecules (IV/V) and Val 135 residue in the receptor GSK3β, in line with the reference ligand. We attribute this interaction to instigate potency in the compounds. Indeed the other non-covalent interaction, between the derivative's aromatic nucleus and Arg 141/Thr 138 in the receptor GSK3β, might have been responsible for enhancing the selectivity in the targets. Overall, we feel that the present work depicts a logical demonstration towards fine tuning the efficacy of the inhibitors through systematic adjustment of electron density at appropriate positions in the aromatic ring be it the main quinoxaline or the other aromatic nucleus. Thus this pathway offers a convenient strategy for the development of efficient therapeutics for diversified neurodegenerative diseases like that of Alzheimer's.

Synthesis and Cytotoxic Activity of Novel Metal Complexes Derived from Methyl-3-(4-chlorophenyl)-3-hydroxy-2,2-dimethylpropanoate as Potential CDK8 Kinase Inhibitors

Several metal complexes of methyl-3-(4-chlorophenyl)-3-hydroxy-2,2-dimethylpropanoate derivatives were synthesized and tested for their anti-tumor activities. The ligands include 3-(4-chlorophenyl)-3-hydroxy-2,2-dimethylpropanoic acid (1), 3-(4-chlorophenyl)-3-hydroxy-2,2-dimethylpropanehydrazide (2), and 3-(4-chlorophenyl)-N'-(4-(dimethylamino)benzylidene)-3-hydroxy-2,2-dimethylpropanehydrazide (3). The ligands were reacted with Cu (II), Ni (II), and La (III) ions. The formed complexes were characterized using elemental analysis (M%), molar conductivity in DMF (0.001 M), DTA, TG, FTIR, ICP-AES, and magnetic susceptibility. The chemical structures of the obtained complexes were interpreted, and their chemical formulas were postulated. The anti-cancer activities of these complexes were examined on human colorectal carcinoma cells (HCT-116) and also on normal cells (HEK-293). The 48 h post treatments showed that out of 12 compounds, 10 compounds showed inhibitory actions on HCT-116 cells, whereas two compounds did not show any inhibitory actions. Compounds 6c and 4a showed the highest inhibitory actions with IC50 = 0.154 and 0.18 mM and additionally compounds 3, 4b, and 6a with IC50 = 0.267, 0.205, and 0.284 mM, respectively. All tested compounds did not show any inhibitory action on normal HEK-293 cells. Molecular docking results provided a good evidence for activity of the lead compounds 3 and 4a as CDK8-CYCC kinase inhibitors, which may proposed the mechanism of action toward colon cancer therapy.

Synthesis of novel quinoxaline-alkynyl derivatives and their anti-Mycobacterium tuberculosis activity

The study report on the synthesis of a series of novel quinoxaline-alkynyl derivatives that were evaluated for their activity against Mycobacterium tuberculosis (Mtb) H₃₇R_V strain. A total of 19 compounds bearing an alcohol, aldehyde, mesylate and ester groups on the alkynly group, and also containing a chloro and nitro groups at the 6-position, were prepared. Seven compounds (3c, 4a-b, 5a, 5c, 6c and 6i), were found to have MIC₉₀ < 10 µM, while five compounds (3b, 6a, 6b, 6d and 6h) had MIC₉₀ in the range 10-20 µM. Compounds bearing a nitro substituent in the 6-position were generally more active and demonstrated a better safety profile, when compared to the unsubstituted and 6-chloro derivatives. Of the seven most active compounds, four contained nitro group at the 6-position.

9-Arylacenaphtho[1,2-b]quinoxalines via Suzuki coupling reaction as cancer therapeutic and cellular imaging agents

A series of 9-arylacenaphtho[1,2-b]quinoxaline analogues have been synthesized via a Suzuki coupling reaction in a one pot sequence. These are capable of imaging, as well as terminating, cancer cells in the human body.

The synthesis and antiproliferative activity of new N-allyl quinoxalinecarboxamides and their O-regioisomers

We have designed a series of quinoxalinepeptidomimetic derivatives based on our previously reported scaffold in an attempt to find a promising lead compound.

Synthesis, biological activity and POM/DFT/docking analyses of annulated pyrano[2,3-d]pyrimidine derivatives: Identification of antibacterial and antitumor pharmacophore sites

New annulated pyrano[2,3-d]pyrimidine derivatives were synthesized with hydroxyl, methoxy, bromine, nitrile and nitro substituents on its skeleton. The correlated electronic effect of substituents on the magnitude of antibacterial activity was noted. The electron donating substituents (namely; 4-OH, 4-OCH₃, 4-Br) and electron withdrawing substituents (4-NO₂) on phenyl ring in the pyrano[2,3-d]pyrimidine skeleton exerted different influence on its antimicrobial activity against some Gram-positive and Gram-negative bacteria such as Pseudomonas aureus, E. coli, Staphylococcus aureus, Klebsiella pneumonia and Bacillus cereus. All the pyrano[2,3-d]pyrimidines were characterized by spectroscopic analyses. Antibacterial screening revealed that the presence of heteroaryl, cyano and amino groups on pyrano[2,3-d]pyrimidine skeleton increases its penetrating power on the bacterial cell wall so that the product becomes more biologically active. So the the nature of electron withdrawing or electro-donnor Impact of substituents should be taken in consideration in drug design. Hydrolysis of -CRN to amide restored vital Intramolecular interaction like ortho-nitrophenyl and ONO^δ-…NH^δ+/amide link, offering a crucial template for antibacterial NH, HO-pharmacophore sites, which ultimately elevated innate antimicrobial profiles. POM combinatorial analysis of tangible electronic contributions due to armed annulated pyrano[2,3-d]pyrimidines concluded their broad antimicrobial activity and viable/prominent drug score index through perspective parameters particularly: inter atomic distance/linkers, steric, electronic, polar parameters, and with a different polarising effect of electron donating/withdrawing environments of substituents. Furthermore, an anti-Kinase pharmacophore site (OCNHCO) was evaluated in continuation of the POM investigations. All synthesized products verified fewer side effects than standard streptomycin, but facile implication in selective cancer media (viz. breast or leucemia still needs to be screened).

Insights into the crystal structure of two newly synthesized quinoxalines derivatives as potent inhibitor for c-Jun N-terminal kinases

Two new compounds namely, ethyl (2E)-3-(dimethylamino)-2-(3-methoxyquinoxalin-2-yl)propen-2-enoate (II) and ethyl 2-(3-oxo-4-(prop-2-yn-1-yl)-3,4-dihydroquinoxalin-2-yl)-3-phenylpropanoate (III) have been synthesized from ethyl 2-(oxo-3,4-dihydroquinoxalin-2-yl) acetate (I). The compounds were characterized using NMR (¹H and ¹³C), Fourier transform infrared and confirmed by single crystal X-ray diffraction studies. The quinoxaline portion of II is almost planar with the substituent containing the dimethylamino and carboxyethyl groups rotated well out of its mean plane. In the crystal, C-H···O and C-H···N hydrogen bonds as well as C-H···π(ring) interactions form chains having a U-shaped cross-section and running along the c-axis direction. Two sets of pair-wise C-H···O hydrogen bonds connect the chains into corrugated sheets. In III, the three substituents on the dihydroquinoxaline moiety are rotated well out of its mean plane. Three sets of C-H···O hydrogen bonds as well as C-H···π(ring) and π-π-stacking interactions form layers approximately parallel to [001]. These are associated along the c-axis direction by additional C-H···π(ring) interactions. Additionally, the Hirshfeld surface analyses showed that the H···H contact is the most important interaction for both II and III. In addition to this, molecular docking and dynamics studies were carried for these two compounds with the c-Jun N-terminal kinases (JNK1) molecule.Communicated by Ramaswamy H. Sarma.

Synthetic and medicinal chemistry of phthalazines: Recent developments, opportunities and challenges

Fused diaza-heterocycles constitute the core structure of numerous bioactive natural products and effective therapeutic drugs. Among them, phthalazines have been recognized as remarkable structural leads in medicinal chemistry due to their wide application in pharmaceutical and agrochemical industries. Accessing such challenging pharmaceutical agents/drug candidates with high chemical complexity through synthetically efficient approaches remains an attractive goal in the contemporary medicinal chemistry and drug discovery arena. In this review, we focus on the recent developments in the synthetic routes towards the generation of phthalazine-based active pharmaceutical ingredients and their biological potential against various targets. The general reaction scope of these innovative and easily accessible strategies was emphasized focusing on the functional group tolerance, substrate and coupling partner compatibility/limitation, the choice of catalyst, and product diversification. These processes were also accompanied by the mechanistic insights where deemed appropriate to demonstrate meaningful information. Moreover, the rapid examination of the structure-activity relationship analyses around the phthalazine core enabled by the pharmacophore replacement/integration revealed the generation of robust, efficient, and more selective compounds with pronounced biological effects. A large variety of in silico methods and ADME profiling tools were also employed to provide a global appraisal of the pharmacokinetics profile of diaza-heterocycles. Thus, the discovery of new structural leads offers the promise of improving treatments for various tropical diseases such as tuberculosis, leishmaniasis, malaria, Chagas disease, among many others including various cancers, atherosclerosis, HIV, inflammatory, and cardiovascular diseases. We hope this review would serve as an informative collection of structurally diverse molecules enabling the generation of mature, high-quality, and innovative routes to support the drug discovery endeavors.

Synthesis and photophysical properties of selenopheno[2,3-b]quinoxaline and selenopheno[2,3-b]pyrazine heteroacenes

In this paper, we report the novel synthesis of three different heterocycles, namely 2-arylselenopheno[2,3-b]quinoxaline, 3-(aryl/alkylselanyl)-2-arylselenopheno[2,3-b]quinoxaline and 6-phenyl-7-(arylselanyl)selenopheno[2,3-b]pyrazine derivatives, from the corresponding 2,3-dichloroquinoxaline and 2,3-dichloropyrazine derivatives. Furthermore, photophysical properties were investigated to study the effect of heteroatoms on UV-absorbance and fluorescence properties.

Antimicrobial evaluation of thiadiazino and thiazolo quinoxaline hybrids as potential DNA gyrase inhibitors; design, synthesis, characterization and morphological studies

A series of thiadiazino[5,6-b]quinoxaline and thiazolo[4,5-b]quinoxaline derivatives was designed and synthetized from the reaction of 2,3-dichloro-6-(morpholinosulfonyl)quinoxaline (2) with thiosemicarbazide or thiocarbohydrazide and thiourea derivatives to give nineteen quinoxaline derivatives 3-16. All the synthesized compounds were evaluated for in vitro antimicrobial potential against various bacteria and fungi strains that showed considerable antimicrobial activity against tested microorganisms. The most potent compounds 2, 7, 9, 10, 12 and 13c were exhibited bactericidal activity, in addition to fungistatic activity by dead live assay. Moreover, these compounds showed a significant result against all multi-drug resistance (MDRB) used especially compound 13c that displayed the best results with MICs of MDRB (1.95, 3.9, 2.6, 3.9 µg/mL) for stains used in this study, compared with Norfloxacin (1.25, 0.78, 1.57, 3.13 µg/mL). Also, cytotoxicity on normal cell (Vero cells ATCC CCL-81) by MTT assay was performed with lower toxicity results. Additionally, morphological studies, immunostimulatory potency and DNA gyrase inhibition assay of most active compounds was done. A molecular docking study has also been carried out to support the effective binding of the most promising compounds at the active site of the target enzyme S. aureus DNA gyrase (2XCT).

Green synthesis of enantiopure quinoxaline alcohols using Daucus carota

Green chemistry comprises a new approach in the synthesis of biologically active compounds using biocatalysts, thus diminishing the hazards for human health and environmental pollution. Asymmetric bioreduction is one of the most widely employed strategies in chemoenzymatic synthesis to produce enantiomerically pure chiral alcohols. The present study highlights the use biocatalyst Daucus carota for selective bioreduction of quinoxaline ketones 1a-6a to their corresponding optically pure alcohols 1b-6b in high yields (up to 84%) and good enantioselectivity (up to 98%). The absolute configuration of the chiral product (R)-1-(3-methyl 7-nitroquinoxalin-2-yl) ethan-1-ol 2b was confirmed by X-ray crystallography studies. The chiral R-configuration of the products obtained was confirmed by absolute configuration studies and was assigned following anti-Prelogs rule. Quinoxaline pharmacophores form a part of well-known potent drug molecules; hence, the chiral products were studied for determination of their molecular properties using SwissADME property analyser. All the chiral products show no Lipinski rule violations and are expected to have good oral bioavailability. As per the molecular properties prediction studies, the compound 6b (R)-1-(6,7-dichloro-3- methylquinoxalin-2-yl) ethanol is observed to show the best physicochemical properties to be a good lead molecule. Thus, the sustainable methodology was developed, and it confirms the synthesis of novel quinoxaline chiral alcohols in a simple, inexpensive, and eco-friendly condition using D carota.

An insight into medicinal chemistry of anticancer quinoxalines

Quinoxalines are benzopyrazines containing benzene and pyrazine rings fused together. In the recent past, quinoxalines have attracted Medicinal Chemists considerably for their syntheses and chemistry due to their distinct pharmacological activities. Diverse synthetic protocols have been developed via multicomponent reactions, single pot synthesis and combinatorial approach using efficient catalysts, reagents, and nano-composites etc. Further, the versatility of the quinoxaline core and its reasonable chemical simplicity devise it extremely promising source of bioactive compounds. Therefore, a wide variety of bioactive quinoxalines has been realised as antitumour, antifungal, anti-inflammatory, antimicrobial, and antiviral agents. Already, a few of them are clinical drugs while many more are under various phases of clinical trials. Present review focuses on chemistry and pharmacology (both efficacy and safety) of quinoxalines and also provides some insight in to their structure-activity relationship.

Anti-Mycobacterium tuberculosis Activity of Esters of Quinoxaline 1,4-Di-N-Oxide

Tuberculosis continues to be a public health problem in the world, and drug resistance has been a major obstacle in its treatment. Quinoxaline 1,4-di-N-oxide has been proposed as a scaffold to design new drugs to combat this disease. To examine the efficacy of this compound, this study evaluates methyl, ethyl, isopropyl, and n-propyl esters of quinoxaline 1,4-di-N-oxide derivatives in vitro against Mycobacterium tuberculosis (pansusceptible and monoresistant strains). Additionally, the inhibitory effect of esters of quinoxaline 1,4-di-N-oxide on M. tuberculosis gyrase supercoiling was examined, and a stability analysis by ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS) was also carried out. Results showed that eight compounds (T-007, T-018, T-011, T-069, T-070, T-072, T-085 and T-088) had an activity similar to that of the reference drug isoniazid (minimum inhibitory concentration (MIC) = 0.12 µg/mL) with an effect on nonreplicative cells and drug monoresistant strains. Structural activity relationship analysis showed that the steric effect of an ester group at 7-position is key to enhancing its biological effects. Additionally, T-069 showed a high stability after 24 h in human plasma at 37 °C.

Synthesis and cytotoxic evaluation of some novel quinoxalinedione diarylamide sorafenib analogues

A series of novel sorafenib analogues containing a quinoxalinedione ring and amide linker were synthesized. A total of 9 novel compounds in 6 synthetic steps were synthesized. Briefly, the amino group of p-aminophenol was first protected which then followed by O-arylation with 5-chloro-2-nitroaniline to provide compound d. Reduction of the nitro group of compound d and cyclization of the diamine group of compound e with oxalic acid afforded compound f which on deacetylation yeilded compound g. Then compound g was reacted with different acyl halides to afford the target compounds 1h-1p. Chemical structures of synthesized compounds were confirmed by 1H NMR and FT-IR analysis. All compounds were evaluated at 1, 10, 50 and 100 μM concentrations for their cytotoxicity against HeLa and MCF-7 cancer cell lines. Some of the compounds showed good cytotoxic activity, especially compounds 1i and 1k-1n with the IC50 values of 19, 16, 22, 18, and 16 μM against MCF-7 cell line and 20, 18, 25, 20, and 18 μM against HeLa cell line, respectively.

Quinoxaline: An insight into the recent pharmacological advances

Quinoxaline, a fused heterocycle of benzene and pyrazine rings has gained considerable attention in the field of contemporary medicinal chemistry. The moiety is of substantial importance because of its wide array of pharmacological activities viz. anti-cancer, antimalarial, anti-inflammatory, antimicrobial, anti-HIV etc. Diversely substituted quinoxalines are important therapeutic agents in the pharmaceutical industry. This review focusses on the quinoxaline derivatives developed during the last decennial period and their biomedical applications. A compilation of patents on quinoxaline is also included herein.

In vitro and in vivo assessment of newer quinoxaline-oxadiazole hybrids as antimicrobial and antiprotozoal agents

A new series of N-(substituted-phenyl)-2-[5-(quinoxalin-2-yloxymethyl)-[1,3,4] oxadiazol-2-ylsulfanyl]-acetamides (5a-o) was designed and synthesised from the parent compound 2-hydroxy quinoxaline (1) through a multistep reaction sequence and was characterised by spectral and elemental analyses. All of the compounds synthesised were evaluated for their antimicrobial and antiprotozoal activities. The results revealed that quinoxaline-based 1,3,4-oxadiazoles displayed promising antibacterial, antifungal and anti-Trypanosoma cruzi activities compared with reference drugs, particularly the lead compound 5l in a short-term in vivo model in T. cruzi.

1-(Prop-2-en-1-yl)-3-[(prop-2-en-1-yl)oxy]quinoxalin-2(1H)-one

In the title compound, C14H14N2O2, the dihydroquinoxaline moiety deviates slightly from planarity. In the crystal, zigzag chains are formed by inversion-related C—H...O hydrogen bonds. Adjacent chains are associated through pairwise C—H...π(ring) and π-stacking interactions.

Benzodiazines: recent synthetic advances

This review provides a comprehensive overview of the recent developments in synthetic strategies for benzodiazines, important scaffolds in medicinal chemistry.

Nucleophilic Substitution on 2-Monosubstituted Quinoxalines Giving 2,3-Disubstituted Quinoxalines: Investigating the Effect of the 2-Substituent

An investigation on the effect of substituent at the 2-position of mono-substituted quinoxalines in the synthesis of di-substituted quinoxaline derivatives via nucleophilic substitution reactions, is reported. Di-substituted quinoxalines bearing aryl-alky, aryl-aryl, aryl-heteroaryl, aryl-alkynyl, and amino-alkyl substituents were prepared in moderate to good yields. 2-Monosubstituted quinoxalines bearing a phenyl and butyl substituent reacted readily with alkyl-, aryl-, heteroaryl- and alkynyl- nucluephiles, giving di-substituted quinoxalines. 2-Monosubstituted quinoxalines bearing an amine and alkynyl substituent only reacted with alkyl nucleophiles. Oxidative rearomatization to give 2,3-disubstituted quinoxaline products occurred in atmospheric O₂.

New Conjugates of Quinoxaline as Potent Antitubercular and Antibacterial Agents

Considering quinoxaline as a privileged structure for the design of potent intercalating agents, some new sugar conjugates of quinoxaline were synthesized and characterized by IR, (1)HNMR, (13)C NMR, and mass spectral data. In vitro testing for antitubercular and antimicrobial activities was performed against Mycobacterium tuberculosis H 37 Rv and some pathogenic bacteria. Results revealed that conjugate containing ribose moiety demonstrated the most promising activity against Mycobacteria and bacteria with minimum inhibitory concentrations (MIC) of 0.65 and 2.07 μM, respectively. Other conjugates from xylose, glucose, and mannose were moderately active whilst disaccharides conjugates were found to be less active. In silico docking analysis of prototype compound revealed that ATP site of DNA gyrase B subunit could be a possible site for inhibitory action of these synthesized compounds.

Synthesis and Biological Evaluation of 2-Oxo/Thioxoquinoxaline and 2-Oxo/Thioxoquinoxaline-Based Nucleoside Analogues

Several O- and S-quinoxaline glycosides have been prepared by glycosidation of 3-methyl-2-oxo(thioxo)-1,2-dihydroquinoxalines 1a,b with α-D-glucopyranosyl, α-D-galactopyranosyl, and α-D-lactosyl bromide in the presence of K2CO3 followed by deacetylation with Et3N/H2O. Furthermore, alkylation of 1a,b with 4-bromobutyl acetate, 2-acetoxyethoxymethyl bromide, and 3-chloropropanol afforded the corresponding O- and S-acycloquinoxaline nucleosides. Reaction of 1b with chloroacetic acid followed by condensation with sulfacetamide and sulfadiazine in the presence of Et3N/THF and ethyl chloroformate gave the corresponding sulfonamide derivatives 14 and 15, respectively. The structures of new compounds were confirmed by using IR, (1)H, (13)C NMR spectra and microanalysis. Some of these compounds were screened in vitro for antitumor and antifungal activities.

Re-engineering nalidixic acid's chemical scaffold: A step towards the development of novel anti-tubercular and anti-bacterial leads for resistant pathogens

Occurrence of antibacterial and antimycobacterial resistance stimulated a thrust to discover new drugs for infectious diseases. Herein we report the work on re-engineering nalidixic acid's chemical scaffold for newer leads. Stepwise clubbing of quinoxaline, 1,2,4-triazole/1,3,4-oxadiazole with nalidixic acid yielded better compounds. Compounds were screened against ciprofloxacin resistant bacteria and Mycobacterium tuberculosis H37Rv species. Results were obtained as minimum inhibitory concentration, it was evident that molecule with quinoxaline linked azide as side chain served as antitubercular lead (<6.25 μg/ml) whilst molecule with oxadiazole or triazole linked quinoxaline side chain served as anti-bacterial lead. Few compounds were significantly active against Escherichia coli and Proteus vulgaris with MIC less than 0.06 μg/ml and relatively potent than ciprofloxacin. No true compound was potentially active against Salmonella species as compared to amoxicillin.

Synthesis and in vitro and in vivo biological evaluation of substituted nitroquinoxalin-2-ones and 2,3-diones as novel trichomonacidal agents

Two series of ten novel 7-nitroquinoxalin-2-ones and ten 6-nitroquinoxaline-2,3-diones with diverse substituents at positions 1 and 4 were synthesized and evaluated against the sexually transmitted parasite Trichomonas vaginalis. Furthermore, diverse molecular and drug-likeness properties were analyzed to predict the oral bioavailability following the Lipinski's "rule of five". 7-Nitroquinoxalin-2-one derivatives displayed moderate to high in vitro activity while the efficiency of most nitroquinoxaline-2,3-diones was rather low; both kinds of compounds did not show cytotoxic effects in mammalian cells. 7-Nitro-4-(3-piperidinopropyl)quinoxalin-2-one 9 achieved the highest trichomonacidal activity (IC50 = 18.26 μM) and was subsequently assayed in vivo in a murine model of trichomonosis. A 46.13% and a 50.70% reduction of pathogenic injuries were observed in the experimental groups treated orally during 7 days with 50 mg/kg and 100 mg/kg doses. The results obtained in the biological assays against T. vaginalis indicate that compounds with ω-(dialkylamino)alkyl substituents and a keto group at positions 4 and 2 of quinoxaline ring, respectively, provide interesting structural cores to develop novel prototypes to enhance the nitroquinoxalinones activity as trichomonacidal agents with interesting ADME properties according to virtual screening analysis.

Mannich bases in medicinal chemistry and drug design

The biological activity of Mannich bases, a structurally heterogeneous class of chemical compounds that are generated from various substrates through the introduction of an aminomethyl function by means of the Mannich reaction, is surveyed, with emphasis on the relationship between structure and biological activity. The review covers extensively the literature reports that have disclosed Mannich bases as anticancer and cytotoxic agents, or compounds with potential antibacterial and antifungal activity in the last decade. The most relevant studies on the activity of Mannich bases as antimycobacterial agents, antimalarials, or antiviral candidates have been included as well. The review contains also a thorough coverage of anticonvulsant, anti-inflammatory, analgesic and antioxidant activities of Mannich bases. In addition, several minor biological activities of Mannich bases, such as their ability to regulate blood pressure or inhibit platelet aggregation, their antiparasitic and anti-ulcer effects, as well as their use as agents for the treatment of mental disorders have been presented. The review gives in the end a brief overview of the potential of Mannich bases as inhibitors of various enzymes or ligands for several receptors.

A novel benzodioxole-containing inhibitor of Toxoplasma gondii growth alters the parasite cell cycle

Toxoplasma gondii is an obligate intracellular parasite that can cause disease in the developing fetus and in immunocompromised humans. Infections can last for the life of the individual, and to date there are no drugs that eliminate the chronic cyst stages that are characteristic of this parasite. In an effort to identify new chemical scaffolds that could form the basis for new therapeutics, we carried out a chemoinformatic screen for compounds that had the potential to interact with members of a superfamily of parasite-secreted kinases and assayed them for growth inhibition in vitro. Of 17 candidate compounds, we identified one with potent antiparasitic activity. The compound has a 50% inhibitory concentration (IC(50)) of ~2 nM, and structure-function analyses implicate the benzodioxole moiety in its action. The compound does not appear to be cytotoxic to host cells. Using microarray analyses of both parasites and host cells treated with the compound, we found that the levels of very few host cell transcripts are altered by the compound, while a large number of parasite transcripts have a different abundance after compound treatment. Gene ontology analyses of parasite transcripts with a different abundance revealed an enrichment of cell cycle-related genes, suggesting that the compound alters progression of the parasite through the cell cycle. Assaying the nuclear content of treated parasites demonstrated that compound treatment significantly increased the percentage of parasites in the S/M phase of the cell cycle compared to controls. This compound and its analogs represent a novel scaffold with antiparasitic activity.