2,3-Dichloroquinoxaline as a versatile building block for heteroaromatic nucleophilic substitution: A review of the last decade

Synthesis of 2-benzyl N-substituted anilines via imine condensation-isoaromatization of (E)-2-arylidene-3-cyclohexenones and primary amines

A catalyst- and additive-free synthesis of 2-benzyl N-substituted anilines from (E)-2-arylidene-3-cyclohexenones and primary amines has been reported. The reaction proceeds smoothly through a sequential imine condensation-isoaromatization pathway, affording a series of synthetically useful aniline derivatives in acceptable to high yields. Mild reaction conditions, no requirement of metal catalysts, operational simplicity and the potential for scale-up production are some of the highlighted advantages of this transformation.

A new class of anti-proliferative activity and apoptotic inducer with molecular docking studies for a novel of 1,3-dithiolo[4,5-b]quinoxaline derivatives hybrid with a sulfonamide moiety

A new series of 6-(pyrrolidin-1-ylsulfonyl)-[1,3]dithiolo[4,5-b]quinoxaline-2-ylidines 10a-f, 12, 14, 16, and 18 were designed, synthesized, and evaluated for their in vitro anticancer activity. The structures of the novel compounds were systematically characterized by ¹H NMR, ¹³C NMR, and elemental analysis. The synthesized derivatives were evaluated for their in vitro antiproliferative activity against three human cancer cell lines (HepG-2, HCT-116, and MCF-7) with more sensitivity to MCF-7. Moreover, three derivatives 10c, 10f, and 12 were the most promising candidates with sub-micromole values. These derivatives were further evaluated against MDA-MB-231, and the results displayed significant IC₅₀ values ranging from 2.26 ± 0.1 to 10.46 ± 0.8 μM and showed low cellular cytotoxicity against WI-38. Surprisingly, the most active derivative 12 revealed sensitivity towards the breast cell lines MCF-7 (IC₅₀ = 3.82 ± 0.2 μM) and MDA-MB-231 (IC₅₀ = 2.26 ± 0.1 μM) compared with doxorubicin (IC₅₀ = 4.17 ± 0.2 and 3.18 ± 0.1 M). Cell cycle analysis showed that compound 12 arrests and inhibits the growth of MCF-7 cells in the S phase with values of 48.16% compared with the untreated control 29.79% and exhibited a significantly higher apoptotic effect in MCF-7 with a value of 42.08% compared to control cell at 1.84%. Furthermore, compound 12 decreased Bcl-2 protein 0.368-fold and activation on pro-apoptotic genes Bax and P53 by 3.97 and 4.97 folds, respectively, in MCF-7 cells. Compound 12 exhibited higher inhibitory activity to EGFR^Wt, EGFR^L858R, and VEGFR-2 with IC₅₀ values (0.19 ± 0.009, 0.026 ± 0.001, and 0.42 ± 0.021 μM) compared with erlotinib (IC₅₀ = 0.037 ± 0.002 and 0.026 ± 0.001 μM) and sorafenib (IC₅₀ = 0.035 ± 0.002 μM). Finally, in silico ADMET prediction presented that 1,3-dithiolo[4,5-b]quinoxaline derivative 12 obeys the Lipinski rule of five and the Veber rule with no PAINs alarms and moderately soluble properties. Additionally, toxicity prediction revealed that compound 12 demonstrated inactivity to hepatotoxic carcinogenicity, immunotoxicity, mutagenicity, and cytotoxicity. Moreover, molecular docking studies showed good binding affinity with lower binding energy inside the active site of Bcl-2 (PDB: 4AQ3), EGFR (PDB: 1M17), and VEGFR (PDB: 4ASD).

Synthesis of quinoxaline derivatives via aromatic nucleophilic substitution of hydrogen

The electrophilic nature of quinoxaline has been explored in the vicarious nucleophilic substitution (VNS) of hydrogen with various carbanions as nucleophiles in an attempt to develop a general method for functionalizing the heterocyclic ring. Only poorly stabilized nitrile carbanions were found to give the VNS products. 2-Chloroquinoxaline gave products of S_NAr of chlorine preferentially. A variety of quinoxaline derivatives containing cyanoalkyl, sulfonylalkyl, benzyl or ester substituents, including fluorinated ones, have been prepared in the VNS reactions with quinoxaline N-oxide.

Synthetic approaches to potent heterocyclic inhibitors of tuberculosis: A decade review

Tuberculosis (TB) continues to be a significant global health concern with about 1.5 million deaths annually. Despite efforts to develop more efficient vaccines, reliable diagnostics, and chemotherapeutics, tuberculosis has become a concern to world health due to HIV, the rapid growth of bacteria that are resistant to treatment, and the recently introduced COVID-19 pandemic. As is well known, advances in synthetic organic chemistry have historically enabled the production of important life-saving medications that have had a tremendous impact on patients’ lives and health all over the world. Small-molecule research as a novel chemical entity for a specific disease target offers in-depth knowledge and potential therapeutic targets. In this viewpoint, we concentrated on the synthesis of a number of heterocycles reported in the previous decade and the screening of their inhibitory action against diverse strains of Mycobacterium tuberculosis. These findings offer specific details on the structure-based activity of several heterocyclic scaffolds backed by their in vitro tests as a promising class of antitubercular medicines, which will be further useful to build effective treatments to prevent this terrible illness.

Structure guided generation of thieno[3,2-d]pyrimidin-4-amine Mycobacterium tuberculosis bd oxidase inhibitors

Cytochrome bd oxidase (Cyt-bd) is an attractive drug target in Mycobacterium tuberculosis, especially in the context of developing a drug combination targeting energy metabolism. However, currently few synthetically assessable scaffolds target Cyt-bd. Herein, we report that thieno[3,2-d]pyrimidin-4-amines inhibit Cyt-bd, and report an initial structure-activity-relationship (SAR) of 13 compounds in three mycobacterial strains: Mycobacterium bovis BCG, Mycobacterium tuberculosis H37Rv and Mycobacterium tuberculosis clinical isolate N0145 in an established ATP depletion assay with or without the cytochrome bcc : aa 3 (QcrB) inhibitor Q203. All compounds displayed activity against M. bovis BCG and the M. tuberculosis clinical isolate strain N0145 with ATP IC50 values from 6 to 54 μM in the presence of Q203 only, as expected from a Cyt-bd inhibitor. All derivatives were much less potent against M. tuberculosis H37Rv compared to N0145 (IC50's from 24 to >100 μM and 9-52 μM, respectively), an observation that may be attributed to the higher expression of the Cyt-bd-encoding genes in the laboratory-adapted M. tuberculosis H37Rv strain. N-(4-(tert-butyl)phenethyl)thieno[3,2-d]pyrimidin-4-amine (19) was the most active compound with ATP IC50 values from 6 to 18 μM against all strains in the presence of Q203, making it a good chemical probe for interrogation the function of the mycobacterial Cyt-bd under various physiological conditions.

Recent advances in the synthesis and reactivity of quinoxaline

Quinoxalines are observed in several bioactive molecules and have been widely employed in designing molecules for DSSC's, optoelectronics, and sensing applications. Therefore, developing newer synthetic routes as well as novel ways for their functionalization is apparent.

Nucleophilicity of cysteine and related biothiols and the development of fluorogenic probes and other applications

Biothiols such as l-cysteine, l-homocysteine, and glutathione play essential roles in many biological processes, and are directly associated with several health conditions. Therefore, the development of fast, selective, sensitive, and inexpensive methods for quantitatively analyzing biothiols in aqueous solution, but especially in biological samples, is a very attractive research field. In this feature review, we have approached the relevance of biothiols' nucleophilicity to develop selective fluorogenic probes. Since biothiols have considerable structural similarity, relevant strategies are in full development, including several fluorescent molecular platforms, specific receptor sites, reaction conditions, and optical responses. All of these features are properly presented and discussed. Biothiol sensing protocols are based on traditional organic chemistry reactions such as (hetero)aromatic nucleophilic substitution, addition, and substitution at carbonyl carbon, conjugate addition, and nucleophilic substitution at saturated carbon, amongst others including combined processes; furthermore, mechanistic aspects are detailed herein, including some interesting historical contexts. The feasibility of related fluorogenic probes is illustrated by analysis in complex matrices such as serum, cells, tissues, and animal models. Applications of these reactions in more complex systems such as sulfhydryl-based peptides and proteins are also presented, aiming at functionalizing and detecting these nucleophiles. Most literature cited in this review is recent; however, some other prominent works are also detailed. It is believed that this review may be accessible for many academic levels and may efficiently contribute not only to popularizing science but also to the rational development of fluorogenic probes for biothiol sensing.

Convenient Synthesis of New Heterocycles Containing the Quinoxaline Ring System

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The aim of the current article was to describe simple procedures for the synthesis of new heterocycles incorporating the quinoxaline moiety using benzene-1,2-diamine and quinoxaline-2,3- dithiol as precursors. Simple synthetic methods are described for the synthesis of new heterocycles using commercially available chemicals. Also, the new compounds were determined using analytical and spectroscopic methods including single X-ray crystal structures. A series of new heterocycles containing the quinoxaline nucleus have been synthesized in good yields using simple and convenient procedures. A process has been described for the synthesis of new heterocycles containing the quinoxaline moiety that might be difficult to synthesize by other routes.