Novel, potent, and selective quinoxaline-based 5-HT(3) receptor ligands. 1. Further structure-activity relationships and pharmacological characterization

Electrochemical oxidative dehydrogenative annulation of 1-(2-aminophenyl)pyrroles with cleavage of ethers to synthesize pyrrolo[1,2-a]quinoxaline derivatives

An array of pyrrolo[1,2-a]quinoxaline derivatives were achieved with moderate to good yields via the electrochemical redox reaction, which includes the functionalization of C(sp3)-H bonds and the construction of C-C and C-N bonds. In this atom economic reaction, THF was used as both a reactant and a solvent, and H2 was the sole by-product.

Development of 1-(2-aminophenyl)pyrrole-based amides acting as human topoisomerase I inhibitors

Topoisomerases are ubiquitous enzymes in the human body, particularly involved in cancer development and progression. Topoisomerase I (topoI) performs DNA relaxation reactions by "controlled rotation" rather than by "strand passage." The inhibition of topoI has become a useful strategy to control cancer cell proliferation. Nowadays, different compounds have undergone clinical trials, but the search for new molecular entities is necessary and benefits from medicinal chemistry efforts. Pyrrole-based compounds emerged as promising antiproliferative agents, with particular interest in breast cancer therapy and topoI inhibition. Starting from these observations and based on the scaffold-hopping approach, we developed a small library of 1-(2-aminophenyl)pyrrole-based amides (7a-f) as new anticancer agents. Tested on a panel of cancer cell lines, 7a-f displayed the most interesting profile in MDA-MB-231 cells, where the most active compounds, 7d-f, were able to induce death by apoptosis. Direct enzymatic assays and docking simulations on the topoI active site (PDB: 1A35) revealed the inhibitory activity and potential binding site for the newly developed 1-(2-aminophenyl)pyrrole-based amides.

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.

RhIII-Catalyzed formal [5 + 1] cyclization of 2-pyrrolyl/indolylanilines using vinylene carbonate as a C1 synthon

A rhodium(iii)-catalyzed formal C–H [5 + 1] cyclization of 2-pyrrolyl/indolylanilines with vinylene carbonate has been explored towards the potent assembly of diverse 4-methylpyrrolo[1,2-a]quinoxalines.

Recent advances with 5-HT3 modulators for neuropsychiatric and gastrointestinal disorders

Serotonin (5-hydroxytryptophan [5-HT]) is a biologically active amine expressed in platelets, in gastrointestinal (GI) cells and, to a lesser extent, in the central nervous system (CNS). This biogenic compound acts through the activation of seven 5-HT receptors (5-HT_1-7 Rs). The 5-HT₃ R is a ligand-gated ion channel belonging to the Cys-loop receptor family. There is a wide variety of 5-HT₃ R modulators, but only receptor antagonists (known as setrons) have been used clinically for chemotherapy-induced nausea and vomiting and irritable bowel syndrome treatment. However, since the discovery of the setrons in the mid-1980s, a large number of studies have been published exploring new potential applications due their potency in the CNS and mild side effects. The results of these studies have revealed new potential applications, including the treatment of neuropsychiatric disorders such as schizophrenia, depression, anxiety, and drug abuse. In this review, we provide information related to therapeutic potential of 5-HT₃ R antagonists on GI and neuropsychiatric disorders. The major attention is paid to the structure, function, and pharmacology of novel 5-HT₃ R modulators developed over the past 10 years.

A comprehensive review in improving delivery of small-molecule chemotherapeutic agents overcoming the blood-brain/brain tumor barriers for glioblastoma treatment

Glioblastoma (GBM) is the most common and lethal primary brain tumor which is highly resistant to conventional radiotherapy and chemotherapy, and cannot be effectively controlled by surgical resection. Due to inevitable recurrence of GBM, it remains essentially incurable with a median overall survival of less than 18 months after diagnosis. A great challenge in current therapies lies in the abrogated delivery of most of the chemotherapeutic agents to the tumor location in the presence of blood-brain barrier (BBB) and blood-brain tumor barrier (BBTB). These protective barriers serve as a selectively permeable hurdle reducing the efficacy of anti-tumor drugs in GBM therapy. This work systematically gives a comprehensive review on: (i) the characteristics of the BBB and the BBTB, (ii) the influence of BBB/BBTB on drug delivery and the screening strategy of small-molecule chemotherapeutic agents with promising BBB/BBTB-permeable potential, (iii) the strategies to overcome the BBB/BBTB as well as the techniques which can lead to transient BBB/BBTB opening or disruption allowing for improving BBB/BBTB-penetration of drugs. It is hoped that this review provide practical guidance for the future development of small BBB/BBTB-permeable agents against GBM as well as approaches enhancing drug delivery across the BBB/BBTB to GBM.

A perspective review on fatty acid amide hydrolase (FAAH) inhibitors as potential therapeutic agents

Fatty acid amide hydrolase (FAAH) is an important enzyme creditworthy of hydrolyzing endocannabinoids and related-amidated signalling lipids, discovery of which has pioneered novel arena of pharmacological canvasses to unwrap its curative potency in various diseased circumstances. It presents contemporary basis for understanding molecules regulating and mediating inflammatory reactions, pain, anxiety, depression, and neurodegeneration. FAAH inhibitors form vital approach for discovery of therapeutic agents that are concerned with local elevation of endocannabinoids under certain stimuli, debarring adverse/unwanted secondary effects from global activation of cannabinoid receptors by exogenous cannabimimetics. During past decades, several molecules with excellent potency developed through tailor-made approaches entered into clinical trials, but none could reach market. Hence, hunt for novel, non-toxic and selective FAAH inhibitors are on horizon. This review summarizes present perception on FAAH in conjunction with its structure, mechanism of catalysis and biological functions. It also foregrounds recent development of molecules belonging to diverse chemical classes as potential FAAH inhibitors bobbing up from in-depth chemical, mechanistic and computational studies published since 2015-November 2019, focusing on their potency. This review will assist readers to obtain rationale on FAAH as potential target for addressing various disease conditions, acquiring significant knowledge on recently established inhibitor scaffolds and their development potentials. New technologies including MD-MM simulations and 3D-QSAR studies allow mechanistic characterization of enzyme. Assessment of in-vitro and in-vivo efficacy of existing FAAH inhibitors will facilitate researchers to design novel ligands utilizing modern drug design methods. The discussions will also impose precaution in decision making process, quashing possibility of late stage failure.

TFAA-Catalyzed Annulation Synthesis of Spiro Pyrrolo[1,2-a]quinoxaline Derivatives from 1-(2-Aminophenyl)pyrroles and Benzoquinones/Ketones

A metal-free trifluorosulfonate anhydride (TFAA)-catalyzed strategy for the synthesis of spiro pyrrolo[1,2-a]quinoxalines from 1-(2-aminophenyl)pyrroles and benzoquinones/ketones has been developed. With this general method, spiro pyrrolo[1,2-a]quinoxalines have been accessed via nucleophilic addition and cyclization. This reaction exhibits good functional group tolerance, and a wide range of products are obtained in moderate to good yields.

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.

Design, synthesis, and cytotoxic activity of novel 7-substituted camptothecin derivatives incorporating piperazinyl-sulfonylamidine moieties

In our continuing search for camptothecin (CPT)-derived antitumor drugs, novel 7-substituted CPT derivatives incorporating piperazinyl-sulfonylamidine moieties were designed, synthesized and evaluated for cytotoxicity against five tumor cell lines (A-549, MDA-MB-231, MCF-7, KB, and KB-VIN). All of the derivatives showed promising in vitro cytotoxic activity against the tested tumor cell lines, and were more potent than irinotecan. Remarkably, most of the compounds exhibited comparable cytotoxicity against the multidrug-resistant (MDR) KB-VIN and parental KB tumor cell lines, while irinotecan lost activity completely against KB-VIN. Especially, compounds 13r and 13p (IC₅₀ 0.38 and 0.85μM, respectively) displayed the greatest cytotoxicity against the MDR KB-VIN cell line and merit further development into preclinical and clinical drug candidates for treating cancer, including MDR phenotype.

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.

Efficient synthesis of pyrrolo[1,2-a]quinoxalines catalyzed by a Brønsted acid through cleavage of C-C bonds

An efficient and convenient one-pot domino reaction for the direct synthesis of pyrrolo[1,2-a]quinoxalines has been developed. This approach utilizes an imine formation reaction, SEAr reaction and cleavage of C-C bonds catalyzed by a Brønsted acid. β-Diketones and β-keto esters are both well tolerated to give the corresponding products in moderate to excellent yields.

Design and synthesis of extended quinoxaline derivatives and their charge transport properties

A scalable and convenient strategy is described to synthesize extended conjugation quinoxaline derivatives from phenylene-ethynylene arrays. The fabricated FET devices possess good performance, with mobilities of 0.47 cm² V⁻¹ s⁻¹ and 0.99 cm² V⁻¹ s⁻¹.

Harnessing the pyrroloquinoxaline scaffold for FAAH and MAGL interaction: definition of the structural determinants for enzyme inhibition

The pharmacogenic pyrroloquinoxaline scaffold has been exploited for developing piperazine and 4-aminopiperidine carboxamides/carbamates as inhibitors of the endocannabinoids’ catabolic enzymes fatty acid amide hydrolase and monoacylglycerol lipase.

I2-catalyzed one-pot synthesis of pyrrolo[1,2-a]quinoxaline and imidazo[1,5-a]quinoxaline derivatives via sp3and sp2C–H cross-dehydrogenative coupling

An efficient I₂-catalyzed cascade coupling protocol was developed for the synthesis of pyrrolo[1,2-a]quinoxaline and imidazo[1,5-a]quinoxaline derivativesviasp³and sp²C–H cross-dehydrogenative coupling.

Discriminating between 5-HT₃A and 5-HT₃AB receptors

The 5-HT3B subunit was first cloned in 1999, and co-expression with the 5-HT3A subunit results in heteromeric 5-HT₃AB receptors that are functionally distinct from homomeric 5-HT₃A receptors. The affinities of competitive ligands at the two receptor subtypes are usually similar, but those of non-competitive antagonists that bind in the pore often differ. A competitive ligand and allosteric modulator that distinguishes 5-HT₃A from 5-HT₃AB receptors has recently been described, and the number of non-competitive antagonists identified with this ability has increased in recent years. In this review, we discuss the differences between 5-HT₃A and 5-HT₃AB receptors and describe the possible sites of action of compounds that can distinguish between them.

Copper(II) catalyzed expeditious synthesis of furoquinoxalines through a one-pot three-component coupling strategy

Microwave assisted one-pot transformation has been developed for the synthesis of biologically significant polysubstituted furoquinoxalines in good to excellent yields through a copper(II) catalyzed three-component coupling of o-phenylenediamine, ethylglyoxalate, and terminal alkyne, known as A(3)-coupling, followed by 5-endo-dig cyclization.

Comprehensive review in current developments of imidazole-based medicinal chemistry

Imidazole ring is an important five-membered aromatic heterocycle widely present in natural products and synthetic molecules. The unique structural feature of imidazole ring with desirable electron-rich characteristic is beneficial for imidazole derivatives to readily bind with a variety of enzymes and receptors in biological systems through diverse weak interactions, thereby exhibiting broad bioactivities. The related research and developments of imidazole-based medicinal chemistry have become a rapidly developing and increasingly active topic. Particularly, numerous imidazole-based compounds as clinical drugs have been extensively used in the clinic to treat various types of diseases with high therapeutic potency, which have shown the enormous development value. This work systematically gives a comprehensive review in current developments of imidazole-based compounds in the whole range of medicinal chemistry as anticancer, antifungal, antibacterial, antitubercular, anti-inflammatory, antineuropathic, antihypertensive, antihistaminic, antiparasitic, antiobesity, antiviral, and other medicinal agents, together with their potential applications in diagnostics and pathology. It is hoped that this review will be helpful for new thoughts in the quest for rational designs of more active and less toxic imidazole-based medicinal drugs, as well as more effective diagnostic agents and pathologic probes.

Structure-activity relationships of quinoxaline-based 5-HT3A and 5-HT3AB receptor-selective ligands

Until recently, discriminating between homomeric 5-HT3A and heteromeric 5-HT3AB receptors was only possible with ligands that bind in the receptor pore. This study describes the first series of ligands that can discriminate between these receptor types at the level of the orthosteric binding site. During a recent fragment screen, 2-chloro-3-(4-methylpiperazin-1-yl)quinoxaline (VUF10166) was identified as a ligand that displays an 83-fold difference in [(3)H]granisetron binding affinity between 5-HT3A and 5-HT3AB receptors. Fragment hit exploration, initiated from VUF10166 and 3-(4-methylpiperazin-1-yl)quinoxalin-2-ol, resulted in a series of compounds with higher affinity at either 5-HT3A or 5-HT3AB receptors. These ligands reveal that a single atom is sufficient to change the selectivity profile of a compound. At the extremes of the new compounds were 2-amino-3-(4-methylpiperazin-1-yl)quinoxaline, which showed 11-fold selectivity for the 5-HT3A receptor, and 2-(4-methylpiperazin-1-yl)quinoxaline, which showed an 8.3-fold selectivity for the 5-HT3AB receptor. These compounds represent novel molecular tools for studying 5-HT3 receptor subtypes and could help elucidate their physiological roles.

One-pot synthesis of pyrrolo[1,2-a]quinoxaline derivatives via iron-promoted aryl nitro reduction and aerobic oxidation of alcohols

Here, we describe a new one-pot method to synthesize 4,7-substituted pyrrolo[1,2-a]quinoxalines and related heterocyles through a cascade of redox reactions/imine formation/intramolecular cyclization. This procedure tolerates readily available substituted 1-(2-nitrophenyl)pyrrole derivatives and aliphatic or benzylic alcohols as starting materials using iron powder and acidic conditions. This is the first example of constructing N-heterocycles via iron-mediated aryl nitro reduction and aerobic oxidation of alcohols in one pot.

5-HT receptors and reward-related behaviour: a review

The brain's serotonin (5-HT) system is key in the regulation of reward-related behaviours, from eating and drinking to sexual activity. The complexity of studying this system is due, in part, to the fact that 5-HT acts at many receptor subtypes throughout the brain. The recent development of drugs with greater selectivity for individual receptor subtypes has allowed for rapid advancements in our understanding of this system. Use of these drugs in combination with animal models entailing selective reward measures (i.e. intracranial self-stimulation, drug self-administration, conditioned place preference) have resulted in a greater understanding of the pharmacology of reward-related processing and behaviour (particularly regarding drugs of abuse). The putative roles of each 5-HT receptor subtype in the pharmacology of reward are outlined and discussed here. It is concluded that the actions of 5-HT in reward are receptor subtype-dependent (and thus should not be generalized) and that all studied subtypes appear to have a unique profile which is determined by content (e.g. receptor function, localization - both throughout the brain and within the synapse) and context (e.g. type of behavioural paradigm, type of drug). Given evidence of altered reward-related processing and serotonergic function in numerous neuropsychiatric disorders, such as depression, schizophrenia, and addiction, a clearer understanding of the role of 5-HT receptor subtypes in this context may lead to improved drug development and therapeutic approaches.