Quinoxalinone (Part II). Discovery of (Z)-3-(2-(pyridin-4-yl)vinyl)quinoxalinone derivates as potent VEGFR-2 kinase inhibitors

Substrate-Controlled Product Divergence in Iron(III)-Catalyzed Reactions of Propargylic Alcohols: Easy Access to Spiro-indenyl 1,4-Benzoxazines and 2-(2,2-Diarylvinyl)quinoxalines

We report herein unprecedented cascade reactions of O-propargyl-N-tosyl-amino phenols with 10 mol% FeCl₃ in DCE at room temperature for 0.67-3 h to form spiro-indenyl 1,4-benzoxazines with 38-89 % yield. Replacing the substrates' oxygen atom by a N-tosylimine group followed by treatment with the same catalyst and solvent at 80 °C produced 2-(2,2-diarylvinyl)quinoxalines in 12-20 h with up to 62 % yield. Mechanistic understanding provided an insight into the transformations. The use of simple substrates and an environmentally benign low-cost catalyst, broad substrate scope and tolerance of diverse functional groups makes the methodology inherently attractive.

An Activity-Based Photosensitizer to Reverse Hypoxia and Oxidative Resistance for Tumor Photodynamic Eradication

Photodynamic therapy (PDT) has been a well-accepted clinical treatment for malignant tumors owing to its noninvasiveness and high spatiotemporal selectivity. However, the treatment outcome of current PDT applications is hindered by hypoxia and intracellular oxidative resistance of solid tumors. Recent studies have shown that inhibiting histone deacetylases (HDACs) can induce cell ferroptosis, reverse hypoxia, and elevate oxidative status. Theoretically, the design and synthesis of activity-based photosensitizers that target HDACs can address the bottlenecks of PDT. Herein, the concept of an activity-based photosensitizer is presented for targeting HDACs, which is designed based on a quinoxalinone scaffold through a pharmacophore migration strategy. The developed activity-based photosensitizer can inhibit HDACs, and overcome hypoxia and intracellular oxidative resistance, realizing the full potential of photosensitizers for malignant tumor treatment. The molecular design strategy proposed in this project should provide theoretical guidance for the development of ideal photosensitizers for practical applications.

Functionalized quinoxalinones as privileged structures with broad-ranging pharmacological activities

Quinoxalinones are a class of heterocyclic compounds which attract extensive attention owing to their potential in the field of organic synthesis and medicinal chemistry. During the past few decades, many new synthetic strategies toward the functionalization of quinoxalinone based scaffolds have been witnessed. Regrettably, there are only a few reports on the pharmacological activities of quinoxalinone scaffolds from a medicinal chemistry perspective. Therefore, herein we intend to outline the applications of multifunctional quinoxalinones as privileged structures possessing various biological activities, including anticancer, neuroprotective, antibacterial, antiviral, antiparasitic, anti-inflammatory, antiallergic, anti-cardiovascular, anti-diabetes, antioxidation, etc. We hope that this review will facilitate the development of quinoxalinone derivatives in medicinal chemistry.

Synthesis and vasorelaxant evaluation of novel 7-methoxyl-2,3-disubstituted-quinoxaline derivatives

An array of novel 7-methoxyl-2,3-disubstituted quinoxaline derivatives was designed, synthesized and their potential antihypertensive activities were examined, in an attempt to discover potent small molecules with vasorelaxant effects. The vasoactivities of these compounds on vascular tone, as well as underlying mechanisms were hereby explored. Results showed that five compounds (7s, 7t, 7v, 7w, 7γ) could induce endothelium-independent relaxation in high extracellular K⁺- and phenylephrine-precontracted C57 mice aortic rings. These five compounds, unlike other commonly used vasodilators, could slowly but effectively inhibit vasoconstriction.

Design, synthesis and biological evaluation of novel 4-phenoxypyridine based 3-oxo-3,4-dihydroquinoxaline-2-carboxamide derivatives as potential c-Met kinase inhibitors

Blocking c-Met kinase activity by small-molecule inhibitors has been identified as a promising approach for the treatment of cancers. Herein, we described the design, synthesis, and biological evaluation of a series of 4-phenoxypyridine-based 3-oxo-3,4-dihydroquinoxaline derivatives as c-Met kinase inhibitors. Inhibitory activitives against c-Met kinase evaluation indicated that most of compounds showed excellent c-Met kinase activity in vitro, and IC₅₀ values of ten compounds (23a, 23e, 23f, 23l, 23r, 23s, 23v, 23w, 23x and 23y) were less than 10.00 nM. Notably, three of them (23v, 23w and 23y) showed remarkable potency with IC₅₀ values of 2.31 nM, 1.91 nM and 2.44 nM, respectively, and thus they were more potent than positive control drug foretinib (c-Met, IC₅₀ = 2.53 nM). Cytotoxic evaluation indicated the most promising compound 23w showed remarkable cytotoxicity against A549, H460 and HT-29 cell lines with IC₅₀ values of 1.57 μM, 0.94 μM and 0.65 μM, respectively. Furthermore, the acridine orange/ethidium bromide (AO/EB) staining, cell apoptosis assays by flow cytometry, wound-healing assays and transwell migration assays on HT-29 and/or A549 cells of 23w were performed. Especially compound 23w, which displayed potent antitumor, apoptosis induction and antimetastatic activity, could be used as a promising lead for further development. Meanwhile, their preliminary structure-activity relationships (SARs) were also discussed.

Malononitrile-activated synthesis and anti-cholinesterase activity of styrylquinoxalin-2(1H)-ones

Herein, we report a base-free malononitrile activated condensation of 3-methylquinoxaline-2(1H)-one (3MQ) 1 with aryl aldehydes 3a–3ad for synthesis of styrylquinoxalin-2(1H)-ones (SQs) 4a–4ad with excellent yields. In this reaction, malononitrile activates the aldehyde via Knoevenagel condensation towards reaction with 3MQ 1 and gets liberated during the course of reaction to yield the desired SQs 4a–4ad. The SQs were evaluated for in vitro cholinesterase inhibition and 4n was found to display a mixed type of inhibition of AChE, which was supported by molecular modelling studies. This study has led to the discovery of a new chemotype for cholinesterase inhibition which might be useful in finding a remedy for Alzheimer's disease.

SQs displaying anti-Alzheimer activity is serendipitous. Malononitrile as a handle to facilitate nucleophilic attack has been applied for the first time for the easy access of SQs.

K2S2O8 mediated C-3 arylation of quinoxalin-2(1H)-ones under metal-, photocatalyst- and light-free conditions

Two facile and effective C-3 arylation protocols of quinoxalin-2(1H)-ones with arylhydrazines and aryl boronic acids respectively via free radical cross-coupling reactions under metal-, photocatalyst- and light-free conditions have been unveiled. K2S2O8 has been used as an efficient oxidant to generate aryl radicals from arylhydrazines and aryl boronic acids under two different reaction conditions. The generated aryl radicals undergo a free radical coupling reaction at the C-3 position of quinoxalin-2(1H)-ones producing 3-arylquinoxalin-2(1H)-ones in good to excellent yields. The involvement of radicals in the course of the reaction has been demonstrated by radical trapping experiments with 2,2,6,6-tetramethylpiperidine-1-oxyl.

Pd(TFA)2-catalyzed direct arylation of quinoxalinones with arenes

Pd(TFA)₂-catalyzed cross-dehydrogenative coupling reaction for the direct C-3 arylation of quinoxalin-2-ones with arenes is described.

Reaction-Based Color-Convertible Fluorescent Probe for Ferroptosis Identification

Ferroptosis is an iron-mediated, caspase-independent pathway of cell death that is accompanied with the accumulations of reactive oxygen species (ROS) and oxygenases, as well as being involved in many other pathophysiological procedures. However, specific and rapid monitoring of ferroptosis in living cells or tissues has not been achieved so far. Herein, a quinoxalinone-based fluorescent probe (termed as Quinos-4, or QS-4) with a reactive aromatic thioether moiety was designed for ferroptosis identification. Upon exposing it to high levels of ROS and hemeoxygenase-1 (HO-1), which are considered as the biochemical characteristics of ferroptosis, QS-4 could be oxidized into a sulfoxide derivative (QSO-4) and its original aggregation-induced enhanced red fluorescence emission could be converted to green fluorescence emission sharply. On the basis of this unique reaction-induced color conversion, this molecular probe can be employed for identifying the occurrence of ferroptosis both in vitro and in vivo.

Dess–Martin periodinane oxidative rearrangement for preparation of α-keto thioesters

Facile preparation of α-keto thioesters via a new rearrangement reaction mediated by the Dess–Martin Periodinane reagent.