Development of Novel 1,2,3,4-Tetrahydroquinoline Scaffolds as Potent NF-κB Inhibitors and Cytotoxic Agents

Regioselective Partial Hydrogenation and Deuteration of Tetracyclic (Hetero)aromatic Systems Using a Simple Heterogeneous Catalyst

The introduction of added '3-dimensionality' through late-stage functionalisation of extended (hetero)aromatic systems is a powerful synthetic approach. The abundance of starting materials and cross-coupling methodologies to access the precursors allows for highly diverse products. Subsequent selective partial reduction can alter the core structure in a manner of interest to medicinal chemists. Herein, we describe the precise, partial reduction of multicyclic heteroaromatic systems using a simple heterogeneous catalyst. The approach can be extended to introduce deuterium (again at late-stage). Excellent yields can be obtained using simple reaction conditions.

Ground State Generation and Cyclization of Aminium Radicals in the Formation of Tetrahydroquinolines

This paper reports the first examples of ground state radical-mediated intramolecular C-H amination to afford 1-methyl-1,2,3,4-tetrahydroquinolines from N-2,4-dinitrophenoxy derivatives of arylpropylamines. Whereas the photoactivation of N-2,4-dinitrophenoxyamines for intermolecular reactions has been established, ground state chemistry provides the desired cyclization products in moderate to excellent yields using Ru(bpy)3Cl2 (42-95% yields) under acidic conditions under an air atmosphere.

Core-Shell Nano-Cobalt Catalyzed Chemoselective Reduction of N-Heteroarenes with Ammonia Borane

An easily prepared core-shell heterogeneous nanocobalt catalyst was reported, which could achieve selective reduction of N-heteroarenes with ammonia borane under mild conditions and ambient atmosphere. Various quinoline, quinoxaline, naphthyridine, isoquinoline, acridine, and phenanthroline derivatives were hydrogenated with high selectivity and efficiency. Notably, substrates bearing sensitive functional groups under molecular hydrogen reduction conditions, such as cyano, ester, and halogens were well tolerated by the catalytic system. Moreover, with our novel method several bioactive molecules were prepared. Also, this catalyst could be applied in the liquid organic hydrogen storage system by reversible hydrogenation and dehydrogenation of heteroarene in high efficiencies.

Tetrahydroquinoline: an efficient scaffold as mTOR inhibitor for the treatment of lung cancer

Efforts have been made to find an efficient scaffold (and its substitution) that can be used for the treatment of lung cancer via mTOR inhibition. A detailed literature search was carried out for previously reported mTOR inhibitors. The present review is focused on lung cancer; therefore, descriptions of some mTOR inhibitors that are currently in clinical trials for the treatment of lung cancer are provided. Based on previous research findings, tetrahydroquinoline was found to be the most efficient scaffold to be explored for the treatment of lung cancer. A possible efficient substitution of the tetrahydroquinoline scaffold could also be beneficial for the treatment of lung cancer.

[4-(3,4-Dimethoxyphenyl)-3,6-dimethyl-2-phenyl-3,4-dihydroquinolin-1(2H)-yl)](furan-2-yl)methanone

A N-(2,4-diaryltetrahydroquinolin-1-yl) furan-2-carboxamide derivative, [4-(3,4-dimethoxyphenyl)-3,6-dimethyl-2-phenyl-3,4-dihydroquinolin-1(2H)-yl)](furan-2-yl)methanone, was synthesized in a two-step procedure from p-toluidine, benzaldehyde, and trans-methyl-isoeugenol as commercial starting reagents through a sequence of Povarov cycloaddition reaction/N-furoylation processes. The structure of the compound was fully characterized by IR, 1H, 13C-NMR, and X-ray diffraction data. Such types of derivatives are known as relevant therapeutic agents exhibiting potent anticancer, antibacterial, antifungal, anti-inflammatory, and immunological modulator properties.

Design, synthesis, and biological evaluation of potent 1,2,3,4-tetrahydroisoquinoline derivatives as anticancer agents targeting NF-κB signaling pathway

The multifunctional transcription factor, nuclear factor-κB (NF-κB), is broadly involved in multiple human diseases, such as cancer and chronic inflammation, through abnormal modulations of the NF-κB signaling cascades. In patients with several types of cancer diseases, NF-κB is excessively activated, which could result in the stimulation of proliferation and/or suppression of apoptosis. Herein, we present a new series of 1,2,3,4-tetrahydroisoquinoline derivatives with good anticancer activities against various human cancer cell lines, which are rationally designed based on our novel NF-κB inhibitors. The SAR studies demonstrated that compound 5d with a methoxy group at the R₃ position exhibits the most anti-proliferative activity with GI₅₀ values, ranging 1.591 to 2.281 μM. Similar to KL-1156, the compound 5d (HSR1304) blocked NF-κB nuclear translocation step in LPS-stimulated MDA-MB-231 cells, probably leading to cytotoxic potency against tumor cells. Together with known potent NF-κB inhibitors containing diverse core heterocyclic moieties, the 1,2,3,4-tetrahydroisoquinoline derivatives can provide structural diversity, enhancing a potential for the development of a novel class of anticancer drugs.

Metal-free regioselective C5-cyanoalkylation of the 8-aminoquinolineamides/sulfonamides via oxidative cross-dehydrogenative coupling with alkylnitriles

A practical, versatile and Metal-free regioselective C5-cyanoalkylation of the 8-aminoquinolineamides/sulfonamides with acetonitrile has been described.

Suppression of Pax3-MITF-M Axis Protects from UVB-Induced Skin Pigmentation by Tetrahydroquinoline Carboxamide

Paired box gene 3 (Pax3) and cAMP responsive element-binding protein (CREB) directly interact with the cis-acting elements on the promoter of microphthalmia-associated transcription factor isoform M (MITF-M) for transcriptional activation in the melanogenic process. Tyrosinase (Tyro) is a target gene of MITF-M, and functions as a key enzyme in melanin biosynthesis. Tetrahydroquinoline carboxamide (THQC) was previously screened as an antimelanogenic candidate. In the current study, we evaluated the antimelanogenic activity of THQC in vivo and elucidated a possible mechanism. Topical treatment with THQC mitigated ultraviolet B (UVB)-induced skin pigmentation in guinea pig with decreased messenger RNA (mRNA) and protein levels of melanogenic genes such as MITF-M and Tyro. Moreover, THQC inhibited cAMP-induced melanin production in α-melanocyte-stimulating hormone (α-MSH)- or histamine-activated B16-F0 cells, in which it suppressed the expression of the MITF-M gene at the promoter level. As a mechanism, THQC normalized the protein levels of Pax3, a transcriptional activator of the MITF-M gene, in UVB-exposed and pigmented skin, as well as in α-MSH-activated B16-F0 culture. However, THQC did not affect UVB- or α-MSH-induced phosphorylation (activation) of CREB. The results suggest that suppression of the Pax3–MITF-M axis might be a potential strategy in the treatment of skin pigmentary disorders that are at high risk under UVB radiation.

Helquats as Promoters of the Povarov Reaction: Synthesis of 1,2,3,4-Tetrahydroquinoline Scaffolds Catalyzed by Helicene-Viologen Hybrids

Helquats (HQs) are structurally linked to helicenes and viologens, and they represent an attractive field of research in chemistry and medicinal chemistry. In the present work they were used as catalysts for the synthesis of 1,2,3,4-tetrahydroquinolines in good yields by the Povarov reaction. The substrate scope and the capability of different helquats to promote Povarov reactions are demonstrated. Studies to elucidate mechanistic details revealed that helquats act as single-electron transfer oxidants through a cation-radical mechanism. The screening of the catalytic activity of HQs confirmed that an active HQ must have a LUMO energy below -8.67 eV and the standard redox potential higher (less negative) than -1.2 V vs. the ferrocene/ferrocenium redox couple.

Silver-catalyzed direct C-H oxidative carbamoylation of quinolines with oxamic acids

A silver-catalyzed efficient and direct C-H carbamoylation of quinolines with oxamic acids to access carbamoylated quinolines has been developed through oxidative decarboxylation reaction. The reaction proceeds smoothly over a broad range of substrates with excellent functional group tolerance and excellent yields under mild conditions.

Inhibition of inflammatory mediators and cell migration by 1,2,3,4-tetrahydroquinoline derivatives in LPS-stimulated BV2 microglial cells via suppression of NF-κB and JNK pathway

Novel 1,2,3,4-tetrahydroquinoline derivatives with N-alkanoyl, N-benzoyl, or chlorobenzoyl substituents were designed and synthesized to inhibit nuclear factor-kappa B (NF-κB) known to be involved in the regulation of many immune and inflammatory responses. These compounds have been previously reported to inhibit NF-κB transcriptional activity in Raw 267.4 macrophage cells and exhibit cytotoxicities to several human cancer cell lines (Jo et al., ACS Med. Chem. Lett. 7 (2016) 385-390). Accumulating evidence indicated that NF-κB is also involved in neuroinflammation implicated in many neurodegenerative diseases. Thus, the present study investigated effects of 1,2,3,4-tetrahydroquinoline derivatives on LPS-stimulated inflammatory mediators and cell migration using BV2 microglial cells as a model. We found that seven compounds tested in this study inhibited LPS-induced pro-inflammatory mediators including interleukin-6, tumor necrosis factor-α, and nitric oxide in concentration-dependent manners. Among these compounds, ELC-D-2 exhibited the most potent inhibition without showing significant cytotoxicity. We also found that ELC-D-2 attenuated levels of LPS-induced inducible nitric oxide synthase and cyclooxygenase-2. Moreover, ELC-D-2 inhibited nuclear translocation of NF-κB by suppressing inhibitor of kappa Bα phosphorylation. Furthermore, ELC-D-2 inhibited LPS-induced activation of c-Jun N-terminal kinase (JNK), which was associated with suppression of inflammatory mediators and migration of LPS-treated BV2 cells. Collectively, our findings demonstrate that ELC-D-2 inhibits LPS-induced pro-inflammatory mediators and cell migration by suppressing NF-κB translocation and JNK phosphorylation in BV2 microglial cells. These results suggest that ELC-D-2 might have a beneficial impact on various brain disorders in which neuroinflammation involving microglial activation plays a crucial role in the pathogenesis of these diseases.

Boric acid catalyzed chemoselective reduction of quinolines

Boric acid promoted transfer hydrogenation of substituted quinolines to synthetically versatile 1,2,3,4-tetrahydroquinolines (1,2,3,4-THQs) was described under mild reaction conditions using a Hantzsch ester as a mild organic hydrogen source. This methodology is practical and efficient, where isolated yields are excellent and reducible functional groups are well tolerated in the N-heteroarene moiety. The reaction parameters and tentative mechanistic pathways are demonstrated by various control experiments and NMR studies. The present work can also be scaled up to obtain gram quantities and the utility of the developed process is illustrated by the transformation of 1,2,3,4-THQs into a series of biologically important molecules including the antiarrhythmic drug nicainoprol.

Synthesis of N-arylindazole-3-carboxamide and N-benzoylindazole derivatives and their evaluation against α-MSH-stimulated melanogenesis

We have designed and synthesized twenty-six N-arylindazole-3-carboxamide (3a-p) and N-benzoylindazole (6a-j) derivatives to discover with excellent inhibition activities of α-MSH-stimulated melanogenesis. In the bio evaluation studies of these compounds, we discovered eighteen compounds, out of twenty-six exhibited more potent inhibition than the positive control arbutin. From the SAR studies, we identified 3k and 6g as lead compounds which displayed almost 5 and 9 times more potent inhibition of α-MSH-stimulated melanogenesis respectively than the reference arbutin. It is also evident the presence of electron withdrawing group at para position (R³) for the compounds (3a-p) and presence of +M group at ortho position (R⁵) for the compounds (6a-j) were crucial for their excellent inhibition activities of α-MSH-stimulated melanogenesis.

Palladium-Catalyzed Regioselective Syn-Chloropalladation-Olefin Insertion-Oxidative Chlorination Cascade: Synthesis of Dichlorinated Tetrahydroquinolines

A palladium catalyzed cascade process involving syn-chloropalladation, intramolecular olefin insertion, and oxidative C-Cl bond formation reactions was demonstrated for the synthesis of dichlorinated tetrahydroquinolines in high yields (up to 93%). The N-propargyl arylamines having a tethered α,β-unsaturated carbonyl moiety underwent a regioselective syn-chloropalladation followed by a Heck-type reaction to deliver the tetrahydroquinoline scaffold. The rare insertion of the second chlorine atom was rationalized comprising a Pd^II/IV catalytic cycle and oxidative cleavage of the C-Pd^II bond.

Progress in the Chemistry of Tetrahydroquinolines

Tetrahydroquinoline is one of the most important simple nitrogen heterocycles, being widespread in nature and present in a broad variety of pharmacologically active compounds. This Review summarizes the progress achieved in the chemistry of tetrahydroquinolines, with emphasis on their synthesis, during the period from mid-2010 to early 2018.

Theoretical investigation on the mechanism of Cu(ii)-catalyzed synthesis of 4-quinolones: effects of additives HOTf vs. HOTs

Hydrogen-bond donor/proton-donor ability is revealed to be the primary factor that controls the catalytic capability of additives (HOTf vs. HOTs).

Development of 13H-benzo[f]chromeno[4,3-b][1,7]naphthyridines and their salts as potent cytotoxic agents and topoisomerase I/IIα inhibitors

A novel series of 35 angularly fused pentacyclic 13H-benzo[f]chromeno[4,3-b][1,7]naphthyridines and 13H-benzo[f]chromeno[4,3-b][1,7]naphthyridin-5-ium chlorides were designed and synthesized. Their cytotoxic activities were investigated against six human cancer cell lines (NCIH23, HCT15, NUGC-3, ACHN, PC-3, and MDA-MB-231). Among all screened compounds; 28, 30, 34, 35, 46, 48, 52, and 53 compounds exhibited potent cytotoxic activities against all tested human cancer cell lines. Further, these potent lead cytotoxic agents were evaluated against human Topoisomerase I and IIα inhibition. Among them, the compound 48 exhibited dual Topoisomerase I and IIα inhibition especially at 20 μM concentrations the compound 48 exhibited 1.25 times more potent Topoisomerase IIα inhibitory activity (38.3%) than the reference drug etoposide (30.6%). The compound 52 also exhibited excellent (88.4%) topoisomerase I inhibition than the reference drug camptothecin (66.7%) at 100 μM concentrations. Molecular docking studies of the compounds 48 and 52 with topo I discovered that they both intercalated into the DNA single-strand cleavage site where the compound 48 have van der Waals interactions with residues Arg364, Pro431, and Asn722 whilst the compound 52 have with Arg364, Thr718, and Asn722 residues. Both the compounds 48 and 52 have π-π stacking interactions with the stacked DNA bases. The docking studies of the compound 48 with topo IIα explored that it was bound to the topo IIα DNA cleavage site where etoposide was situated. The benzo[f]chromeno[4,3-b][1,7]naphthyridine ring of the compound 48 was stacked between the DNA bases of the cleavage site with π-π stacking interactions and there were no hydrogen bond interactions with topo IIα.