A Catalyst-Free Benzylic C–H Bond Olefination of Azaarenes for Direct Mannich-like Reactions

Cu-Catalyzed Direct Asymmetric Mannich Reaction of 2-Alkylazaarenes and Isatin-Derived Ketimines

The first direct catalytic asymmetric Mannich reaction of 2-alkylazaarenes and ketimines was realized with a chiral Cu-bis(oxazoline) complex as the catalyst. The asymmetric addition of 2-alkylpyridines to isatin-derived ketimines proceeded smoothly to afford α,β-functionalized 2-substituted pyridines bearing 3-amino-3,3-disubstituted oxindole motifs with excellent results (≤99% yield, 99:1 dr, and 98% ee). The catalytic system was also extended to 2-alkylbenzothiazoles as nucleophiles for the asymmetric Mannich reaction of ketimines.

Catalyst-free C(sp3)-H functionalization of methyl azaarenes with heteroaromatic trifluoromethyl ketone hydrates: "all-water" synthesis of α-trifluoromethyl tertiary alcohols

An efficient catalyst-free C(sp³)-H bond functionalization of methyl azaarenes with heteroaromatic trifluoromethyl ketone hydrates in neat water has been developed for the synthesis of α-trifluoromethyl tertiary alcohols bearing N-heteroaromatics. This method not only features excellent efficiency, broad substrate scope, catalyst-free conditions, and easy gram-scale preparation but also represents a new and rare example of "all-water" synthesis of trifluoromethylated molecules.

Design, synthesis, and biological evaluation of 1-styrenyl isoquinoline derivatives for anti-hepatocellular carcinoma activity and effect on mitochondria

In this study, 18 derivatives of 1-styrene-isoquinoline were designed and synthesized from resveratrol and isoquinoline. The IC₅₀ of compound 1c against Huh7 and SK-Hep-1 cells were 2.52 μM and 4.20 μM, respectively. Mice were treated with 650 mg/kg compound 1c, and the survival status of mice was good. Further studies showed that compound 1c could inhibit cell proliferation by arresting the cell cycle in the G2/M phase, induce cell apoptosis, and inhibit cell migration and invasion by regulating epithelial-mesenchymal transition (EMT). It is worth noting that numbers of studies have pointed that resveratrol can trigger mitochondrial apoptosis to induce apoptosis of cancer cells. Therefore, we investigated the mechanism of compound 1c induced apoptosis of Huh7 and SK-Hep-1 cells. The results indicated that compound 1c could regulate the expression of proteins which are related to mitochondrial apoptosis pathway and inhibit the phosphorylation of PI3K/Akt/mTOR signaling pathway. In addition, compound 1c could inhibit the growth of Huh7-xenografts, and perform a tumor inhibitory rate of 41.44% when administered 30 mg/kg once a day. This work provides a potential anti-hepatocellular carcinoma compound that warrants further investigation.

Highly Chemoselective Synthesis of Azaarene-Equipped CF3-Tertiary Alcohols under Metal-Free Conditions and Their Fungicidal Activities

A highly chemoselective reaction between α,β-unsaturated trifluoromethyl ketones with azaarenes under metal-free conditions was carried out, affording a range of valuable azaarene-equipped CF₃-tertiary alcohols in moderate to excellent yields (up to 95% yield) with good tolerance of functional groups, and their structures were confirmed by NMR, HRMS, and X-ray diffraction for validation. This method features simple reaction conditions (only solvent), high atom- and step-economy, and broad substrate scope. Moreover, most of the target products exhibited promising fungicidal activities, and compound 3al exhibited 91.65% fungicidal activity against R. solani, with an EC₅₀ value of 0.18 mg/mL.

Palladium-Catalyzed Selective [2 + 2 + 2] Annulation of 2-(2-Enynyl)pyridines with Arynes

The palladium-catalyzed chemo- and stereoselective [2 + 2 + 2] annulation reaction of 2-(2-enynyl)pyridines with arynes has been developed. A wide range of (E)- or (E/Z)-isomers of 2-(2-enynyl)pyridines and arynes was tolerated, providing a spectrum of (E)-phenanthrenylated 2-alkenylpyridines in good yield, together with the generation of a chiral axis between an alkene and a phenanthrene ring.

Rapid Access to Benzimidazo[1,2-a]quinoline-Fused Isoxazoles via Pd(II)-Catalyzed Intramolecular Cross Dehydrogenative Coupling: Synthetic Versatility and Photophysical Studies

An efficient and atom-economical palladium-catalyzed intramolecular cross dehydrogenative coupling (CDC) reaction has been developed for the construction of highly π-conjugated benzimidazo[1,2-a]quinoline-fused isoxazole scaffolds using molecular oxygen as sole oxidant. The approach portrayed wide substrate scope with good functional group tolerance and depicted a useful tool for the generation of fluorescence active compounds with high quantum yield. Synthetic versatility of the method via Fe-catalyzed reductive isoxazole ring cleavage toward pyridine, pyrimidine, pyrazole fused heteropolycyclic compounds has been showcase.

Design, synthesis, and biological evaluation of novel 5,6,7-trimethoxy quinolines as potential anticancer agents and tubulin polymerization inhibitors

Objective(s):

Microtubules have key roles in essential cellular processes such as mitosis, cell motion, and intracellular organelle transport. Increasing interest has been given to tubulin binding compounds after the introduction of taxanes into clinical oncology. The object of this study was synthesis and biological evaluation of novel 5,6,7-trimethoxy quinolines as tubulin inhibitors.

Materials and Methods:

The cytotoxicity of the newly synthesized compounds was assessed against different human cancer cell lines including MCF-7, A2780, MCF-7/MX, A2780/RCIS, and normal cells. Compounds demonstrating the most antiproliferative activity, were chosen to examine their tubulin inhibition activity and their ability to arrest the cell cycle and induce apoptosis. Molecular docking studies and molecular dynamics simulation of compound 7e in the catalytic site of tubulin were performed.

Results:

Most of the synthesized quinolines showed moderate to significant cytotoxic activity against human cancer cells. Compounds 7e and 7f, possessing N-(4-benzoyl phenyl) and N-(4-phenoxy phenyl), respectively, exhibited the most antiproliferative activity more potent than the other compounds and exhibited similar antiproliferative activity on both resistant and parental cancer cells.

Conclusion:

Flow cytometry analysis of A2780, A2780/RCIS, MCF-7, and MCF-7/MX cancer cells treated with 7e and 7f exhibited that these compounds arrested the cell cycle (at the G2/M phase) and induced cellular apoptosis in A2780 cancer cells. These quinolines inhibited tubulin polymerization in a way resembling that of CA-4. Molecular dynamics simulation and molecular docking studies of compound 7e into the binding site of tubulin displayed the probable interactions of 7e with the binding site of tubulin.

Pyridylic anions are soft nucleophiles in the palladium-catalyzed C(sp3)-H allylation of 4-alkylpyridines

We report a mild palladium-catalyzed method for the selective allylation of 4-alkylpyridines in which highly basic pyridylic anions behave as soft nucleophiles. This method exploits alkylidene dihydropyridines, which are semi-stable intermediates readily formed using a ‘soft-enolization’ approach, in a new mechanistic manifold for decarboxylative allylation. Notably, the catalytic generation of pyridylic anions results in a substantially broader functional group tolerance compared to other pyridine allylation methods. Experimental and theoretical mechanistic studies strongly suggest that pyridylic anions are indeed the active nucleophiles in these reactions, and that they participate in an outer-sphere reductive elimination step. This finding establishes a new pK_a boundary of 35 for soft nucleophiles in transition metal-catalyzed allylations.

We report a mild palladium-catalyzed method for the selective allylation of 4-alkylpyridines in which highly basic pyridylic anions behave as soft nucleophiles.

Discovery of fast-acting dual-stage antimalarial agents by profiling pyridylvinylquinoline chemical space via copper catalyzed azide-alkyne cycloadditions

To identity fast-acting, multistage antimalarial agents, a series of pyridylvinylquinoline-triazole analogues have been synthesized via CuAAC. Most of the compounds display significant inhibitory effect on the drug-resistant malarial Dd2 strain at low submicromolar concentrations. Among the tested analogues, compound 60 is the most potent molecule with an EC₅₀ value of 0.04 ± 0.01 μM. Our current study indicates that compound 60 is a fast-acting antimalarial compound and it demonstrates stage specific action at the trophozoite phase in the P. falciparum asexual life cycle. In addition, compound 60 is active against both early and late stage P. falciparum gametocytes. From a mechanistic perspective, compound 60 shows good activity as an inhibitor of β-hematin formation. Collectively, our findings suggest that fast-acting agent 60 targets dual life stages of the malarial parasites and warrant further investigation of pyridylvinylquinoline hybrids as new antimalarials.

NaCl as Catalyst and Water as Solvent: Highly E-Selective Olefination of Methyl Substituted N-Heteroarenes with Benzyl Amines and Alcohols

Oxidative coupling of benzylamines and alcohols with methyl substituted N-heteroarenes such as quinolines and quinoxalines has been achieved using chloride, a sea abundant anion as the catalyst for practical synthesis of a wide range of E-disubstituted olefins in aqueous medium. Detailed mechanistic studies and control experiments were carried out to deduce the reaction mechanism which indicated that in situ formed ClO₂^- is the active form of the catalyst. We have successfully carried out a 1 g scale reaction using this methodology, and five pharmaceutically relevant conjugated olefins were also synthesized by this method in moderate to good yields.

Design, synthesis and biological evaluation of novel 5,6,7-trimethoxy-N-aryl-2-styrylquinolin-4-amines as potential anticancer agents and tubulin polymerization inhibitors

A new series of styrylquinolines was designed and synthesized as anticancer agents and tubulin polymerization inhibitors. The in vitro anticancer activity of the synthesized quinolines was evaluated against four human cancer cell lines including A-2780 (human ovarian carcinoma), A-2780/RCIS (cisplatin resistant human ovarian carcinoma), MCF-7 (human breast cancer cells), MCF-7/MX (mitoxantrone resistant human breast cancer cells) and normal Huvec cells. Generally, among the forty-eight newly synthesized quinolines, compounds possessing N-trimethoxy phenyl showed stronger cytotoxic activity with IC₅₀ values ranging from 0.38 to 5.01 μM against all four cancer cell lines. Compounds 9VII-c and 9IV-c showed significant cytotoxic activity on A-2780 cancer cells, stronger than the other compounds and comparable to reference drug CA-4. Compound 9IV-c possessing 3,4-dimethoxystyryl and N-trimethoxy phenyl groups demonstrated potent cytotoxic effects with IC₅₀ values ranging from 0.5 to 1.66 µM on resistant cancer cells as well as their parental cells. Annexin V binding staining assay in A-2780 and MCF-7/MX cancer cells, revealed that compound 9IV-c induced early and late apoptosis. Compounds 9IV-c and 9VII-b, inhibited tubulin polymerization similar to CA4. Finally, molecular docking studies of 9IV-c and 9VII-b into the colchicine-binding site of tubulin displayed the possible interactions of these compounds with tubulin.

Styrylquinoline – A Versatile Scaffold in Medicinal Chemistry

Background: :

Styrylquinolines are characteristic fully aromatic compounds with flat, rather lipophilic structures. The first reports on their synthesis and biological activity were published roughly a century ago. However, their low selectivity, unfavorable toxicity and problems with their mechanism of action significantly hampered their development. As a result, they have been abandoned for most of the time since they were discovered.

Objective: :

Their renaissance was observed by the antiretroviral activity of several styrylquinoline derivatives that have been reported to be HIV integrase inhibitors. Subsequently, other activities such as their antifungal and anticancer abilities have also been revisited.

Methods:

In the present review, the spectrum of the activity of styrylquinolines and their use in drug design is presented and analyzed.

Results:

New properties and applications that were reported recently have re-established styrylquinolines within medicinal and material chemistry. The considerable increase in the number of published papers regarding their activity spectrum will ensure further discoveries in the field.

Conclusions:

Styrylquinolines have earned a much stronger position in medicinal chemistry due to the discovery of their new activities, profound mechanisms of action and as drug candidates in clinical trials.

V. K, Hari K, Kaliyamoorthy A. Base-promoted 1,6-conjugate addition of alkylazaarenes to para-quinone methides

1,1,2-Triarylethanes embedded with an azaarene unit were prepared in a single step at ambient temperature via the sodium hexamethyldisilazide mediated 1,6-conjugate addition of unactivated alkylazaarenes on para-quinone methides (p-QMs).

Alkyl lithium-catalyzed benzylic C–H bond addition of alkyl pyridines to α-alkenes

The alkyl lithium catalyst successfully achieved the benzylic C–H bond addition of alkyl pyridines to α-alkenes, and displayed distinct selectivity from those of transition metal catalysts.

Recent synthetic efforts in the preparation of 2-(3,4)-alkenyl (aryl) quinoline molecules towards anti-kinetoplastid agents

Leishmaniasis, Chagas disease and African sleeping sickness have been considered some of the most important tropical protozoan afflictions. As the number of drugs currently available to treat these human illnesses is severely limited and the majority has poor safety profiles and complicated administration schedules, actually there is an urgent need to develop new effective, safe and cost-effective drugs. Because quinoline alkaloids with antiprotozoal activity (quinine, chimanine, cryptolepine or huperzine groups) were historically and are still essential models for drug research to combat these parasitic infections, synthetic or semi-synthetic quinoline-based molecules are important for anti-kinetoplastid drug design approaches and synthetic methods of their preparation become a key task that is the central subject of this review. Its goal is to highlight the advances in the conventional and current syntheses of new 2-(3,4)-alkenyl (aryl) quinoline derivatives, which kill the most important kinetoplastid protozoa, – Leishmania and Trypanosoma and could be useful models for antileishmanial and antitrypanosomal research. An attempt has been made to present and discuss the more recent contributions in this field over the period 2015–2019, paying special attention to molecular design, synthetic efforts to new green reaction conditions for classical methods such as Skraup synthesis, Friedländer synthesis, Conrad–Limpach, Doebner–Miller, as well as contemporary methods like Gould–Jacobs, Meth–Cohn and Povarov reactions. This review includes brief general information on these neglected tropical diseases, their current chemotherapies, and primary natural models (quinoline alkaloids), suitable for development of anti-kinetoplastid quinoline-based agents. The main part of the review comprises critical discussion on the synthesis and chemistry of new quinolines diversely substituted by alkyl (alkenyl, aryl) fragments on the pyridine part of the quinoline skeleton, which could be considered interesting analogues of chimanine alkaloids. The methods described in this review were developed with the aim of overcoming the drawbacks of the traditional protocols using revolutionary precursors and strategies.

Leishmaniasis, Chagas disease and African sleeping sickness have been considered some of the most important tropical protozoan afflictions.

Transition metal-free α-methylation of 1,8-naphthyridine derivatives using DMSO as methylation reagent

A practical approach to the direct α-methylation of 1,8-naphthyridines under mild reaction conditions has been developed using simple and readily available DMSO as a convenient and environmentally friendly carbon source. This method is transition metal-free and highly chemoselective, shows good functional group tolerance, and uses DMSO as a methyl source, providing efficient and rapid access to an important compound class, 2-methyl-1,8-naphthyridines.

Microwave-assisted, rapid synthesis of 2-vinylquinolines and evaluation of their antimalarial activity

A rapid and efficient synthesis of 2-vinylquinolines via trifluoromethanesulfonamidemediated olefination of 2-methylquinoline and aldehyde under microwave irradiation is reported. Biological evaluation of these scaffolds demonstrates that 2-vinylquinolines 3x - 3z possess excellent antimalarial activities against chloroquine-resistant Dd2 strain of Plasmodium falciparum (IC50 < 100 nM).

Palladium-Catalyzed Decarboxylative ortho-Acylation of Anilines with Carbamate as a Removable Directing Group

An efficient palladium-catalyzed decarboxylative ortho-acylation of anilines with α-oxocarboxylic acids has been realized by using carbamate as a directing group (DG). The reaction proceeds smoothly with high regioselectivity to afford diverse acylation products of aniline derivatives in moderate to good yields under mild conditions. This transformation exhibits broad substrate scope and highly functional group tolerance. In addition, the employed DG can be easily removed to give the corresponding 2-amino aromatic ketones. Importantly, several transformations of the synthesized ortho-acylated anilines into several synthetically valuable products have been demonstrated for their utilities.

Design, synthesis, and in vitro evaluation of quinolinyl analogues for α-synuclein aggregation

Here we report the synthesis and in vitro evaluation of 25 new quinolinyl analogues for α-synuclein aggregates. Three lead compounds were subsequently labeled with carbon-11 or fluorine-18 to directly assess their potency in a direct radioactive competitive binding assay ng both α-synuclein fibrils and tissue homogenates from Alzheimer's disease (AD) cases. The modest binding affinities of these three radioligands toward α-synuclein were comparable with results from the Thioflavin T fluorescence assay. However, all three ligand also showed modest binding affinity to the AD homogenates and lack selectivity for α-synuclein. The structure-activity relationship data from these 25 analogues will provide useful information for design and synthesis of new compounds for imaging α-synuclein aggregation.

Strategy for Stereoselective Metal-free α-Functionalization of 2-Azaaryl Acetates with N-Boc Imines

We report the first diastereo- and enantioselective formal Mannich reaction of 2-pyridyl acetates which gives rise to α- and β-functionalized 2-substituted pyridines. Key for success is the previous azaarene N-oxide formation enabling α-carbon deprotonation by a mild bifunctional Brønsted base and subsequent reaction with N-Boc imines under almost perfect stereocontrol.

Oxidant-Controlled C-sp2/sp3-H Cross-Dehydrogenative Coupling of N-Heterocycles with Benzylamines

Oxidant controlled ionic liquid mediated cross-dehydrogenative coupling (CDC) of benzylamines with N-heterocycles having sp² or sp³ carbon resulted in the formation of C-benzoylated or alkenylated products. Benzoylation of N-heterocycles occurs via (NH₄)₂S₂O₈ catalyzed benzoyl radical formation. An oxidative alkenylation of N-heterocycles having C-sp³ carbon (2-methylaza-arenes) occurs via deamination of benzylamine followed by C-sp³-H bond activation in high stereoselectivity. Both benzoylation and alkenylation protocols are metal-free, green, simple, efficient, and tolerate a wide variety of functional groups.

Acetic Acid Promoted Redox Annulations with Dual C-H Functionalization

Amines such as 1,2,3,4-tetrahydroisoquinoline undergo redox-neutral annulations with 2-alkylquinoline-3-carbaldehydes as well as the corresponding 4-alkyl isomers and pyridine analogues. These processes involve dual C-H bond functionalization. Acetic acid is used as a cosolvent and acts as the sole promoter of these transformations.

4-Nitro styrylquinoline is an antimalarial inhibiting multiple stages of Plasmodium falciparum asexual life cycle

Drugs against malaria are losing their effectiveness because of emerging drug resistance. This underscores the need for novel therapeutic options for malaria with mechanism of actions distinct from current antimalarials. To identify novel pharmacophores against malaria we have screened compounds containing structural features of natural products that are pharmacologically relevant. This screening has identified a 4-nitro styrylquinoline (SQ) compound with submicromolar antiplasmodial activity and excellent selectivity. SQ exhibits a cellular action distinct from current antimalarials, acting early on malaria parasite's intraerythrocytic life cycle including merozoite invasion. The compound is a fast-acting parasitocidal agent and also exhibits curative property in the rodent malaria model when administered orally. In this report, we describe the synthesis, preliminary structure-function analysis, and the parasite developmental stage specific action of the SQ scaffold.

Highly efficient one-pot tandem Friedlander annulation and chemo-selective Csp3–H functionalization under calcium catalysis

Highly efficient and regioselective Friedlander synthesis of 2-methyl-3-acyl quinolines and their chemoselective C_sp3–H functionalization is described for the first time using Ca(OTf)₂ as the sustainable catalyst under solvent free conditions with atom and step economy.

Regioselective addition of C(sp3)–H bonds of alkyl pyridines to olefins catalysed by cationic zirconium complexes

The first group 4 metal catalysts are developed to catalyse C(sp³)–H addition of alkyl pyridines to olefins. Ligand-controlled regioselectivity was observed and verified.

Water-mediated and promoted eco-friendly one-pot synthesis of azaarene substituted isoxazoles

An efficient and green approach for the sp³ C–H bond functionalization of 2-methyl azaarenes to 3-methyl-4-nitro-5-styrylisoxazoles in water has been described.