Discovery of N-Phenylphthalimides Containing Ether Moiety as Potential Protoporphyrinogen IX Oxidase Inhibitors

The discovery of novel protoporphyrinogen IX oxidase (PPO) inhibitors has become a key focus in herbicide development. To explore new PPO inhibitors, a series of N-phenylphthalimide derivatives with ether moieties were designed and successfully synthesized. Among these, compound B18 (Ki = 10.3 nM) exhibited a strong inhibitory effect on NtPPO, outperforming flumiclorac-pentyl (Ki = 46.3 nM) and flumioxazin (Ki = 52.0 nM). It is noted that compounds A3, B18, B19, and B20 showed broad-spectrum herbicidal activity against the tested weeds at 75 g a.i./ha. In addition, results of molecular simulation and density functional theory (DFT) calculations indicated that compound B18 possessed not only a robust hydrogen bond with Arg98 of NtPPO but also superior chemical reactivity, electrostatic field, and strong polarity. Therefore, compound B18 may be regarded as a promising lead compound for the development of high-efficiency PPO inhibitors.

Transformative reactions in nitroarene chemistry: C-N bond cleavage, skeletal editing, and N-O bond utilization

Nitroarenes are highly versatile building blocks in organic synthesis, playing a pivotal role in various reactions. Common transformations involving nitroarenes include nucleophilic aromatic substitution (SNAr) reactions, where the nitro group functions both as a potent electron-withdrawing group that activates the aromatic ring and as a leaving group facilitating the substitution. Additionally, the direct transformation of nitro groups, such as reduction-driven syntheses of amines and carboxylic acids, as well as ipso-substitution SNAr reactions, have been extensively explored. Interactions between ortho-nitro groups and neighboring substituents also provide unique opportunities for selective transformations. However, beyond these well-established processes, direct transformations of nitro groups have been relatively limited. In recent years, significant advancements have been made in alternative methodologies for nitro group transformations. This review focuses on the latest progress in novel transformations of nitroarenes, with emphasis on three major categories: (i) functional group transformations involving C-N bond cleavage in nitroarenes, (ii) skeletal editing via nitrene intermediates generated by N-O bond cleavage, and (iii) the utilization of nitroarenes as an oxygen source through N-O bond cleavage. These developments under-score the expanding utility of nitroarenes in modern organic synthesis.

Three-component synthesis of β-sulfonyl enamines and dienamines enabled by silver(i) acetate

We have developed a novel three-component synthesis of sulfonyl enamines by reacting secondary and tertiary amines with sodium sulfinic acid salt, a reaction that is mediated by silver acetate. The choice of solvent determines whether sulfonyl enamines or dienamines are obtained. The overall atom economy of this multicomponent reaction was further improved by isolating the resulting elemental silver and reconverting it into silver acetate.

Cross-Coupling Reactions with Nickel, Visible Light, and tert-Butylamine as a Bifunctional Additive

Transition metal catalysis is crucial for the synthesis of complex molecules, with ligands and bases playing a pivotal role in optimizing cross-coupling reactions. Despite advancements in ligand design and base selection, achieving effective synergy between these components remains challenging. We present here a general approach to nickel-catalyzed photoredox reactions employing tert-butylamine as a cost-effective bifunctional additive, acting as the base and ligand. This method proves effective for C-O and C-N bond-forming reactions with a diverse array of nucleophiles, including phenols, aliphatic alcohols, anilines, sulfonamides, sulfoximines, and imines. Notably, the protocol demonstrates significant applicability in biomolecule derivatization and facilitates sequential one-pot functionalizations. Spectroscopic investigations revealed the robustness of the dynamic catalytic system, while elucidation of structure-reactivity relationships demonstrated how computed molecular properties of both the nucleophile and electrophile correlated to reaction performance, providing a foundation for effective reaction outcome prediction.

Scale-Up of Continuous Metallaphotoredox Catalyzed C-O Coupling to a 10 kg-Scale Using Small Footprint Photochemical Taylor Vortex Flow Reactors

We report the development and optimization of a scalable flow process for metallaphotoredox (Ir/Ni) C-O coupling, a mild and efficient approach for forming alkyl-aryl ethers, a common motif in medicinal and process chemistry settings. Time-resolved infrared spectroscopy (TRIR) highlighted the amine as the major quencher of the photocatalyst triplet excited state, along with the formation of an Ir(II) species that, in the presence of the Ni cocatalyst, has its lifetime shortened, suggesting reductive quenching of Ir(III)*, followed by reoxidation facilitated by the Ni cocatalyst. TRIR and batch reaction screening was used to develop conditions transferrable to flow, and many processing benefits of performing the reaction in flow were then demonstrated using a simple to construct/operate, small-footprint FEP coil flow reactor, including short (<10 min) space times and reduced catalyst loadings (down to 0.1 mol % Ir, 1 mol % Ni) while retaining good yield/conversion. Scalability was demonstrated by increasing the length or diameter of the FEP coil flow reactor tubing, however, due to suspected mass transfer/mixing limitations, the yield decreased upon scale-up in some cases. Therefore, we applied a modified version of our previously reported photochemical Taylor Vortex Flow Reactor (PhotoVortex), where Taylor vortices and a short-irradiated path length allow photochemical reactions to be performed efficiently via excellent mixing. In a small PhotoVortex (8 mL irradiated volume), we have demonstrated projected productivities around 1 kg day-1 and >10 kg day-1 in a large PhotoVortex (185 mL irradiated volume) with good product yields (>90%) and low catalyst loadings (0.1 to 0.5 mol % of [Ir{dF(CF3)ppy}2dtbbpy]PF6), enabled by excellent mixing ensuring sufficient mass transfer between short-lived photoexcited and other transient species.

Adaptive alcohols-alcohols cross-coupling via TFA catalysis: access of unsymmetrical ethers

Ethers are high value organic compounds widely applied in chemical industry, natural products, material, pharmaceuticals, argochemicals, as well as modern organic synthesis. Herein, we report an adaptive TFA-catalyzed cross-coupling of alcohols with various oxygen nucleophiles (nitro-, halogen-, sulfur-, nitrogen-, aryl-, and alkynyl-substituted aliphatic alcohols), delivering diverse unsymmetrical ethers under mild conditions and simple operation. This protocol features a broad range of substrate scope and high catalytic efficiency (54 examples, up to 99% yield). The decagram scale performance and one-step synthesis of drug molecules evidenced the potential industrial production and practicability of this protocol.

3D-QSAR model-oriented optimization of Pyrazole β-Ketonitrile derivatives with diphenyl ether moiety as novel potent succinate dehydrogenase inhibitors

BACKGROUND

Succinate dehydrogenase inhibitor (SDHI) fungicides play important roles in the control of plant fungal diseases. However, they are facing serious challenges from issues with resistance and cross-resistance, primarily attributed to their frequent application and structural similarities. There is an urgent need to design and develop SDHI fungicides with novel structures.

RESULTS

Aiming to discover novel potent SDHI fungicides, 31 innovative pyrazole β-ketonitrile derivatives with diphenyl ether moiety were rationally designed and synthesized, which were guided by a 3D-QSAR model from our previous study. The optimal target compound A23 exhibited not only outstanding in vitro inhibitory activities against Rhizoctonia solani with a half-maximal effective concentration (EC50) value of 0.0398 μg mL-1 comparable to that for fluxapyroxad (EC50 = 0.0375 μg mL-1), but also a moderate protective efficacy in vivo against rice sheath blight. Porcine succinate dehydrogenase (SDH) enzymatic inhibitory assay revealed that A23 is a potent inhibitor of SDH, with a half-maximal inhibitory concentration of 0.0425 μm. Docking study within R. solani SDH indicated that A23 effectively binds into the ubiquinone site mainly through hydrogen-bonds, and cation-π and π-π interactions.

CONCLUSION

The identified β-ketonitrile compound A23 containing diphenyl ether moiety is a potent SDH inhibitor, which might be a good lead for novel fungicide research and optimization. © 2024 Society of Chemical Industry.

Oxalamide ligands with additional coordinating groups for Cu-catalyzed arylation of alcohols and phenols

A novel class of chain-like multidentate oxalamide ligands with additional coordinating groups was developed for the coupling of (hetero)aryl bromides with both alcohols and phenols under mild conditions. Introduction of oxygen atoms in N-alkyl chains is pivotal for the high catalytic efficiency and broad substrate versatility.

A Novel AHAS-Inhibiting Herbicide Candidate for Controlling Leptochloa chinensis: A Devastating Weedy Grass in Rice Fields

Given the prevalence of the malignant weed Chinese Sprangletop (Leptochloa chinensis (L.) Nees) in rice fields, the development of novel herbicides against this weed has aroused wide interest. Here, we report a novel diphenyl ether-pyrimidine hybrid, DEP-5, serving as a systematic pre/postemergence herbicide candidate for broad-spectrum weed control in rice fields, specifically for L. chinensis. Notably, DEP-5 exhibits over 80% herbicidal activity against the resistant biotypes even at 37.5 g a.i./ha under greenhouse conditions and has complete control of L. chinensis at 150 g a.i./ha in the rice fields. We uncover that DEP-5 acts as a noncompetitive inhibitor of acetohydroxyacid synthase (AHAS) with an inhibition constant (Ki) of 39.4 μM. We propose that DEP-5 binds to AHAS in two hydrophobic-driven binding modes that differ from commercial AHAS inhibitors. Overall, these findings demonstrate that DEP-5 has great potential to be developed into a herbicide for L. chinensis control and inspire fresh concepts for novel AHAS-inhibiting herbicide design.

URJC-1: Stable and Efficient Catalyst for O-Arylation Cross-Coupling

The design of metal-organic frameworks (MOFs) allows the definition of properties for their final application in small-scale heterogeneous catalysis. Incorporating various catalytic centers within a single structure can produce a synergistic effect, which is particularly intriguing for cross-coupling reactions. The URJC-1 material exhibits catalytic duality: the metal centers act as Lewis acid centers, while the nitrogen atoms of the organic ligand must behave as basic centers. The impact of reaction temperature, catalyst concentration, and basic agent concentration was evaluated. Several copper-based catalysts, including homogeneous and heterogeneous MOF catalysts with and without the presence of nitrogen atoms in the organic ligand, were assessed for their catalytic effect under optimal conditions. Among the catalysts tested, URJC-1 exhibited the highest catalytic activity, achieving complete conversion of 4-nitrobenzaldehyde with only 3% mol copper concentration in one hour. Furthermore, URJC-1 maintained its crystalline structure even after five reaction cycles, demonstrating remarkable stability in the reaction medium. The study also examined the impact of various substituents of the substrate alcohol on the reaction using URJC-1. The results showed that the reaction had high activity when activating substituents were present and for most cyclic alcohols rather than linear ones.

Atroposelective Synthesis of Axially Chiral Diaryl Ethers by N-Heterocyclic-Carbene-Catalyzed Sequentially Desymmetric/Kinetic Resolution Process

We describe herein an N-heterocyclic-carbene-catalyzed atroposelective synthesis of axially chiral diaryl ethers. Through a sequentially enantioselective desymmetric process and a kinetic resolution process, the products could be constructed in good yields with excellent enantiopurities. Both alcohols and phenols were compatible with this catalytic system. The axially chiral carboxylic acids derived from the esters were proven to be potential chiral ligands for asymmetric synthesis, for example, Rh(III)-catalyzed enantioselective C-H functionalization.

Recent advances in oxidative phenol coupling for the total synthesis of natural products

Covering: 2008 to 2023This review will describe oxidative phenol coupling as applied in the total synthesis of natural products. This review covers catalytic and electrochemical methods with a brief comparison to stoichiometric and enzymatic systems assessing their practicality, atom economy, and other measures. Natural products forged by C-C and C-O oxidative phenol couplings as well as from alkenyl phenol couplings will be addressed. Additionally, exploration into catalytic oxidative coupling of phenols and other related species (carbazoles, indoles, aryl ethers, etc.) will be surveyed. Future directions of this particular area of research will also be assessed.

The Bis(indolylmethyl) ethers: Design, Prototypical Synthesis, and Scope Studies

The design, prototypical synthesis, isolation, and characterization of bis(indolylmethyl) ethers from corresponding indolylcarbinols is described. This approach involves very mild conditions and exhibits good scope for indolylcarbinols (both N-electron withdrawing group and N-electron donating group). Cross etherification between two electronically different indolylcarbinols is also demonstrated for the generation of unsymmetrical ethers. For the first time, the intermediacy of the bis(indolylmethyl) ethers for the formation of bis(indolyl)methanes from indolylcarbinols is proved experimentally and by 1H NMR analysis.

Diaryl ether derivative inhibits GPX4 expression levels to induce ferroptosis in thyroid cancer cells

Papillary thyroid carcinoma contributes to about 80% of the total thyroid cancer cases. BRAFV600E is a frequently occurring mutation in PTCs. Although several BRAF inhibitors are available, many thyroid cancer patients acquire resistance to BRAF inhibitors. Therefore, new targets and drugs need to be identified as therapies. Ferroptosis is a recently discovered type of cell death, and inhibiting glutathione peroxidase 4 (GPX4) using small molecules was found to trigger ferroptosis. But it is unknown whether inhibiting GPX4 renders thyroid cancer cells susceptible to ferroptosis. To identify novel GPX4 inhibitors, we focused on our previously reported cohort of diaryl ether and dibenzoxepine molecules. In this study, we asked whether diaryl ether and dibenzoxepine derivatives trigger ferroptosis in thyroid cancer cells. To answer this question, we screened diaryl ether and dibenzoxepine derivatives in cell-based assays and performed mechanism of action studies. We found that a diaryl ether derivative, 16 decreased thyroid cell proliferation and triggered ferroptosis by inhibiting GPX4 expression levels. Molecular modeling and dynamics simulations showed that 16 binds to the active site of GPX4. Upon deciphering the mode of 16-induced ferroptosis, we found that 16 treatments decrease mitochondrial polarization and reduce mitochondrial respiration similar to a ferroptosis inducer, RSL3. We conclude that the diaryl ether derivative, 16 inhibits GPX4 expression levels to induce ferroptosis in thyroid cancer cells. Based on our observations, we suggest that 16 can be lead-optimized and developed as a ferroptosis-inducing agent to treat thyroid cancers.

Discovery of Novel Isoxazoline Derivatives Containing Diaryl Ether against Fall Armyworms

With the continuous evolution of insect resistance, it is a tremendous challenge to control the fall armyworm (Spodoptera frugiperda) with traditional insecticides. To solve this pending issue, a series of novel isoxazoline derivatives containing diaryl ether structures were designed and synthesized, and most of the target compounds exhibited excellent insecticidal activity. Based on the three-dimensional quantitative structure-activity relationship (3D-QSAR) model analysis, we further optimized the molecular structure with compound L35 obtained and tested for its activity. Compound L35 (LC₅₀ = 1.69 mg/L) exhibited excellent insecticidal activity against S. frugiperda, which was better than those of commercial fipronil (LC₅₀ = 70.78 mg/L) and indoxacarb (LC₅₀ = 5.37 mg/L). The enzyme-linked immunosorbent assay showed that L35 could upregulate the levels of GABA in insects. In addition, molecular docking and transcriptomic results also indicated that compound L35 may affect the nervous system of S. frugiperda by acting on GABA receptors. Notably, through high-performance liquid chromatography (HPLC), we were able to obtain the two enantiomers of compound L35, and the insecticidal activity test revealed that S-(+)-L35 was 44 times more active than R-(-)-L35 against S. frugiperda. This study established the chemistry basis and mechanistic foundations for the future development of pesticide candidates against fall armyworms.

C-O Coupling/[4+2] Cycloaddition Tandem Reactions via Oxidative Dearomatization of BINOLs: Access to Bridged Polycyclic Compounds

Intramolecular C-H activation/C-O coupling, dearomatization, and [4+2] cycloaddition of BINOL units have been well developed in a one-pot approach with maleimide derivatives as the dienophiles. This tandem catalytic system generates a variety of functionalized bridged polycyclic products in a step-economical manner, which greatly enriches the modification methods and strategies for the BINOL skeletons.

Photocatalytic dehydrative etherification of alcohols with a nanoporous gold catalyst

A simple and efficient photocatalytic approach for dehydrative etherification of alcohols has been developed by a nanoporous gold catalyst. This protocol features no requirement of addition of acids or bases, broad substrate generality, and excellent acid-sensitive functional group tolerance. The mechanistic studies demonstrate the heterogeneous nature of the catalytic system and the recyclability of the catalyst was demonstrated repeatedly.

Synthesis and Antiproliferative Activity of Steroidal Diaryl Ethers

Novel 13α-estrone derivatives have been synthesized via direct arylation of the phenolic hydroxy function. Chan-Lam couplings of arylboronic acids with 13α-estrone as a nucleophilic partner were carried out under copper catalysis. The antiproliferative activities of the newly synthesized diaryl ethers against a panel of human cancer cell lines (A2780, MCF-7, MDA-MB 231, HeLa, SiHa) were investigated by means of MTT assays. The quinoline derivative displayed substantial antiproliferative activity against MCF-7 and HeLa cell lines with low micromolar IC₅₀ values. Disturbance of tubulin polymerization has been confirmed by microplate-based photometric assay. Computational calculations reveal significant interactions of the quinoline derivative with the taxoid binding site of tubulin.

Synthesis of Cyclic and Acyclic ortho-Aryloxy Diaryliodonium Salts for Chemoselective Functionalizations

Two regioselective, high-yielding one-pot routes to oxygen-bridged cyclic diaryliodonium salts and ortho-aryloxy-substituted acyclic diaryliodonium salts are presented. Starting from easily available ortho-iodo diaryl ethers, complete selectivity in formation of either the cyclic or acyclic product could be achieved by varying the reaction conditions. The complimentary reactivities of these novel ortho-oxygenated iodonium salts were demonstrated through a series of chemoselective arylations under metal-catalyzed and metal-free conditions, to deliver a range of novel, ortho-functionalized diaryl ether derivatives.

Visible Light-Induced Deoxygenation and Allylation/Vinylation of Pyridyl Ethers

The generation of alkyl radicals by deoxygenation of unactivated ethers under visible light catalysis is a hitherto unmet challenge. Herein, we report a visible light-induced deoxygenation of pyridyl ethers via formation of their pyridinium salts. The generated benzylic radicals further react with allyl/alkenyl sulfones to provide a series of coupling products in good to moderate yields. This process is proposed to undergo a reductive quenching cycle, which was elucidated by chemical, optical, and electrical experiments.

Copper-Catalyzed 6-endo-dig Cyclization-Coupling of 2-Bromoaryl Ketones and Terminal Alkynes toward Naphthyl Aryl Ethers in Water

The cyclization-coupling reaction of 2-bromoaryl ketones and terminal alkynes is first realized by copper catalysis, which produces polyfunctional naphthyl aryl ethers in moderate to excellent yields with broad substrate scope and good functional group tolerance. This reaction proceeds via 6-endo-dig cyclization and C(sp²)-O coupling using green H₂O as the unique solvent and 5-bromopyrimidin-2-amine as the critical additive. Mechanistically, a unique Cu(III)-acetylide probably is the key intermediate, which allows exclusive 6-endo-dig selectivity.

Organosulphur and organoselenium compounds as emerging building blocks for catalytic systems for O-arylation of phenols, a C-O coupling reaction

Diaryl ethers form an important class of organic compounds. The classic copper-mediated Ullmann diaryl ether synthesis has been known for many years and involves the coupling of phenols with aryl halides. However, the use of high reaction temperature, high catalyst loading and expensive ligands has created a need for the development of alternative catalytic systems. In the recent past, organosulphur and organoselenium compounds have been used as building blocks for developing homogeneous, heterogeneous and nanocatalysts for this C-O coupling reaction. Homogeneous catalytic systems include preformed complexes of metals with organosulphur and organoselenium ligands. The performance of such complexes is influenced dramatically by the nature of the chalcogen (S or Se) donor site of the ligand. Nanocatalytic systems (including Pd₁₇Se₁₅, Pd₁₆S₇ and Cu_1.8S) have been designed using a single-source precursor route. Heterogeneous catalytic systems contain either metal (Cu or Pd) or metal chalcogenides (Pd₁₇Se₁₅ or Cu_1.8S) as catalytically active species. This article aims to cover the simple and straightforward methodologies and approaches that are adopted for developing catalytically relevant organosulfur and organoselenium ligands, their homogeneous metal complexes, heterogeneous and nanocatalysts. The effects of chalcogen (S or Se) donor, halogen (Cl/Br/I) of aryl halide, nature (electron withdrawing or electron donating) of substituents present on the aromatic ring of aryl halides or substituted phenols and position (ortho or para) of substitution on the results of catalytic reactions have been critically analyzed and summarized. The effect of composition (Pd₁₇Se₁₅ or Pd₁₆S₇) on the performance of nanocatalytic systems is also highlighted. Substrate scope has also been discussed in all three types of catalysis. The superiority of heterogeneous catalytic systems (e.g., Pd₁₇Se₁₅ immobilised on graphene oxide) indicates the bright future possibilities for the development of efficient catalytic systems using similar or tailored ligands for this reaction.

Transition-Metal-Free O-Arylation of Alcohols and Phenols with S-Arylphenothiaziniums

Herein, we report the transition-metal-free O-arylation of alcohols and phenols with S-arylphenothiaziniums, which can be easily synthesized from boronic acids. Aryl substituents derived from arylboronic acids were selectively introduced into the hydroxy groups in alcohols and phenols, and a variety of aryl ethers were synthesized. This selectivity is supported by theoretical calculations.

[Synthetic Studies on Small Molecule Natural Products with Neurotrophic Activity]

Neurotrophic factors have been shown to potentially be beneficial for the treatment of neurodegenerative diseases such as Alzheimer's disease, because endogenous neurotrophic factors (NGF, BDNF) have been recognized to play critical roles in the promotion of neurogenesis, differentiation, and neuroprotection throughout the development of the central nervous system. However, high-molecular-weight proteins are unable to cross the blood-brain barrier and are easily decomposed under physiological conditions. Thus, small molecules that can mimic the functions of neurotrophic factors are promising alternatives for the treatment of neurodegenerative disease. Since 1990, the author has been involved in searching for natural products with typical neurotrophic properties that can cause neurogenesis, enhance neurite outgrowth, and protect against neuronal death by using three cellular systems (PC12, rat cortical neurons, and MEB5 cells). Through these research activities on neurotrophic natural products, the author has tried to induce a paradigm shift from the discipline of natural products chemistry to science disciplines. This review focuses on our independent synthetic studies of the neurotrophic natural products discovered in the plants. The following synthetic elaborations are described: syntheses of dimeric isocuparane-type sesquiterpenes mastigophorenes A and B, macrocyclic bis-bibenzyls plagiochins A-D and cavicularin through a Pd-catalyzed Stille-Kelly reaction; the formal synthesis of merrilactone A and jiadifenin, which are seco-prezizaane-type sesquiterpenes, through intramolecular Pd-catalyzed Mizoroki-Heck and Tsuji-Trost reactions; and finally the first enantioselective synthesis of neovibsanin B, a vibsane-type diterpene, through a Pd-catalyzed cyclic carbopalladation-carbonyl tandem reaction.

Ligand-Free Copper-Catalyzed Ullmann-Type C-O Bond Formation in Non-Innocent Deep Eutectic Solvents under Aerobic Conditions

An efficient and novel protocol was developed for a Cu-catalyzed Ullmann-type aryl alkyl ether synthesis by reacting various (hetero)aryl halides (Cl, Br, I) with alcohols as active components of environmentally benign choline chloride-based eutectic mixtures. Under optimized conditions, the reaction proceeded under mild conditions (80 °C) in air, in the absence of additional ligands, with a catalyst [CuI or CuII species] loading up to 5 mol% and K2 CO3 as the base, providing the desired aryloxy derivatives in up to 98 % yield. The potential application of the methodology was demonstrated in the valorization of cheap, easily available, and naturally occurring polyols (e. g., glycerol) for the synthesis of some pharmacologically active aryloxypropanediols (Guaiphenesin, Mephenesin, and Chlorphenesin) on a 2 g scale in 70-96 % yield. Catalyst, base, and deep eutectic solvent could easily and successfully be recycled up to seven times with an E-factor as low as 5.76.

Formal dual C(sp2)–H cross-dehydrogenative C–O bond formation to construct highly functionalized diaryl ethers with O2

A formal dual C(sp2)–H cross-dehydrogenative C–O bond formation reaction between phenols and naphthylamine derivatives to construct diaryl ethers has been developed under mild conditions.

A review on synthetic chalcone derivatives as tubulin polymerisation inhibitors

Microtubules play an important role in the process of cell mitosis and can form a spindle in the mitotic prophase of the cell, which can pull chromosomes to the ends of the cell and then divide into two daughter cells to complete the process of mitosis. Tubulin inhibitors suppress cell proliferation by inhibiting microtubule dynamics and disrupting microtubule homeostasis. Thereby inducing a cell cycle arrest at the G2/M phase and interfering with the mitotic process. It has been found that a variety of chalcone derivatives can bind to microtubule proteins and disrupt the dynamic balance of microtubules, inhibit the proliferation of tumour cells, and exert anti-tumour effects. Consequently, a great number of studies have been conducted on chalcone derivatives targeting microtubule proteins. In this review, synthetic or natural chalcone microtubule inhibitors in recent years are described, along with their structure-activity relationship (SAR) for anticancer activity.

Synthesis and biological evaluation of halogenated phenoxychalcones and their corresponding pyrazolines as cytotoxic agents in human breast cancer

Novel halogenated phenoxychalcones 2a–f and their corresponding N-acetylpyrazolines 3a–f were synthesised and evaluated for their anticancer activities against breast cancer cell line (MCF-7) and normal breast cell line (MCF-10a), compared with staurosporine. All compounds showed moderate to good cytotoxic activity when compared to control. Compound 2c was the most active, with IC₅₀ = 1.52 µM and selectivity index = 15.24. Also, chalcone 2f showed significant cytotoxic activity with IC₅₀ = 1.87 µM and selectivity index = 11.03. Compound 2c decreased both total mitogen activated protein kinase (p38α MAPK) and phosphorylated enzyme in MCF-7 cells, suggesting its ability to decrease cell proliferation and survival. It also showed the ability to induce ROS in MCF-7 treated cells. Compound 2c exhibited apoptotic behaviour in MCF-7 cells due to cell accumulation in G2/M phase and elevation in late apoptosis 57.78-fold more than control. Docking studies showed that compounds 2c and 2f interact with p38alpha MAPK active sites.

Nickel-Catalyzed Etherification of Phenols and Aryl Halides through Visible-Light-Induced Energy Transfer

Notwithstanding some progress in nickel-catalyzed etherification of alkanols and arylhalides, the ability of such a Ni-catalyzed transformation employing phenols to diaryl ethers is unsuccessful due to phenolates with much lower reduction potentials, which suppress the oxidation of nickel(II) intermediates into requisite Ni(III) species. We herein report visible-light-initiated, nickel-catalyzed O-arylation of phenols with arylhalides using t-BuNH(i-Pr) as the base and thioxanthen-9-one as the photosensitizer under visible light. This photocoupling exhibits a broad substrate scope.

Catalytic Reductive Alcohol Etherifications with Carbonyl-Based Compounds or CO2 and Related Transformations for the Synthesis of Ether Derivatives

Ether derivatives have myriad applications in several areas of chemical industry and academia. Hence, the development of more effective and sustainable protocols for their production is highly desired. Among the different methodologies reported for ether synthesis, catalytic reductive alcohol etherifications with carbonyl-based moieties (aldehydes/ketones and carboxylic acid derivatives) have emerged in the last years as a potential tool. These processes constitute appealing routes for the selective production of both symmetrical and asymmetrical ethers (including O-heterocycles) with an increased molecular complexity. Likewise, ester-to-ether catalytic reductions and hydrogenative alcohol etherifications with CO2 to dialkoxymethanes and other acetals, albeit in less extent, have undergone important advances, too. In this Review, an update of the recent progresses in the area of catalytic reductive alcohol etherifications using carbonyl-based compounds and CO2 have been described with a special focus on organic synthetic applications and catalyst design. Complementarily, recent progress made in catalytic acetal/ketal-to-ether or ester-to-ether reductions and other related transformations have been also summarized.

Green chemistry meets medicinal chemistry: a perspective on modern metal-free late-stage functionalization reactions

The progress of drug discovery and development is paced by milestones reached in organic synthesis. In the last decade, the advent of late-stage functionalization (LSF) reactions has represented a valuable breakthrough. Recent literature has defined these reactions as the chemoselective modification of complex molecules by means of C-H functionalization or the manipulation of endogenous functional groups. Traditionally, these diversifications have been accomplished by organometallic means. However, the presence of metals carries disadvantages related to their cost, environmental hazard and health risks. Fundamentally, green chemistry directives can help minimize such hazards through the development of metal-free LSF methodologies. In this review, we expand the current discussion on metal-free LSF reactions by providing an overview of C(sp2)-H, and C(sp3)-H functionalizations, as well as the utilization of heteroatom-containing functional groups as chemical handles. Selected topics such as metal-free cross-dehydrogenative coupling (CDC) reactions, organocatalysis, electrochemistry and photochemistry are also discussed. By writing the first review on metal-free LSF methodologies, we aim to highlight current advances in the field with examples that reveal specific challenges and solutions, as well as future research opportunities.

Transition-Metal-Catalyzed Directing Group Assisted (Hetero)aryl C-H Functionalization: Construction of C-C/C-Heteroatom Bonds

Transition-metal-catalyzed C-H functionalization is one of the fascinating scientific fronts in organic synthesis for the formation of conjugated arenes and has emerged as a benchmark to revolutionize the synthetic enterprise since past decades. In this realm, chelation-guided functionalization of C-H bonds using an exogenous directing group has received considerable attention recently for the expedient regioselective construction of C-C and C-heteroatom bonds as an efficient and sustainable alternative. This article outlines our contribution towards a wide variety of transformations that have been achieved by the directed C-H functionalization through the fine tuning of catalytic systems.

Synthesis, Biological Evaluation and Molecular Docking Study of Cyclic Diarylheptanoids as Potential Anticancer Therapeutics

BACKGROUND

Cancer is one of the leading causes of mortality globally. To cope with cancer, it is necessary to develop anticancer drugs. Bioactive natural products, i.e. diarylheptanoids, have gained significant attention of researchers owing to their intriguing structures and potent biological activities. In this article, considering the development of anticancer drugs with enhanced selectivity towards cancerous cells, a series of Cyclic Diarylheptanoids (CDHs) are designed, synthesized and evaluated their biological activity.

OBJECTIVE

To establish an easy route for the synthesis of diarylheptanoids, and evaluate their antiproliferative, and topoisomerase-I & -IIα inhibitory activities, for developing potential anticancer drugs among CDHs.

METHODS

Diarylheptanoids were synthesized from reported linear diarylheptanoids using the classical Ullmann reaction. Antibacterial activity was evaluated by the filter paper disc diffusion method. Cell viability was assessed by measuring mitochondrial dehydrogenase activity with a Cell Counting Kit (CCK-8). Topoisomerases I and II (topo-I and -IIα) inhibitory activity was measured by the assessment of relaxation of supercoiled pBR322 plasmid DNA. IFD protocol of Schrodinger Maestro v11.1 was used to characterize the binding pattern of studied compounds with the ATPase domain of the human topo-IIα.

RESULTS

The synthesized CDHs were evaluated for their biological activities (antibacterial, antiproliferative, and topoisomerase-I & -IIα inhibitory activities, respectively). Leading to obtain a series of anticancer agents with the least inhibitory activities against different microbes, improving their selectivity for cancer cells. In brief, most of the synthesized CDHs had excellent antiproliferative activity against T47D (human breast cancer cell line). Pterocarine possessed the strongest activity (2i; IC50 = 0.63µM) against T47D. The cyclic diarylheptanoid 2b induced 30% inhibition of topoisomerase-IIα activity at 100μM compared with the reference of etoposide, which induced 72% inhibition. Among the tested compounds, galeon (2h) displayed very low activity against four bacterial strains. Compounds 2b, 2h, and 2i formed hydrogen bonds with Thr215, Asn91, Asn120, Ala167, Lys168 and Ile141 residues, which are important for binding of ligand compound to the ATPase binding site of topoisomerase IIα by acting as ATP competitive molecule validated by docking study. In silico Absorption, Distribution, Metabolism and Excretion (ADME) analysis revealed the predicted ADME parameters of the studied compounds which showed recommended values.

CONCLUSION

A series of CDHs were synthesized and evaluated for their antibacterial, antiproliferative, and topo-I & -IIα inhibitory activities. SARs study, molecular docking study and in silico ADME analysis were conducted. Five compounds exhibited excellent and selective antiproliferative activity against the human breast cancer cell line (T47D). Among them, a compound 2h showed topo-IIα activity by 30% at 100µM, which represented a moderate intensity of inhibition compared with etoposide. Three of them formed hydrogen bonds with Thr215, Asn91, Asn120, and Ala167 residues, which are considered as crucial residues for binding to the ATPase domain of topoisomerase IIα. According to in silico drug-likeness property analysis, three compounds are expected to show superiority over etoposide in case of absorption, distribution, metabolism and excretion.

Total Synthesis of (S)-Cularine via Nucleophilic Substitution on a Catechol

Catechols are part of many essential chemicals and are valuable, typically nucleophilic intermediates used in synthesis. Here we describe an unexpected transformation in which they play the role of the electrophile in a formal nucleophilic aromatic substitution. We made this discovery while studying a seven-membered dioxepin ring formation during a synthesis of the benzyltetrahydroisoquinoline (S)-cularine. We suggest a chain mechanism for this new transformation that is triggered by molecular oxygen and that propagates an electrophilic ortho-quinone.

Controllable chemoselectivity in the reaction of 2H-indazoles with alcohols under visible-light irradiation: synthesis of C3-alkoxylated 2H-indazoles and ortho-alkoxycarbonylated azobenzenes

A high chemoselectivity in the visible-light-induced reaction of 2H-indazoles with alcohols controlled by the reaction atmosphere was achieved, providing C3-alkoxylated 2H-indazoles and ortho-alkoxycarbonylated azobenzenes.

Galeon: A Biologically Active Molecule with In Silico Metabolite Prediction, In Vitro Metabolic Profiling in Rat Liver Microsomes, and In Silico Binding Mechanisms with CYP450 Isoforms

Galeon, a natural cyclic-diarylheptanoid (CDH), which was first isolated from Myrica gale L., is known to have potent cytotoxicity against A549 cell lines, anti-tubercular activity against Mycobacterium tuberculosis H37Rv, chemo-preventive potential, and moderate topoisomerase inhibitory activity. Here, in silico metabolism and toxicity prediction of galeon by CYP450, in vitro metabolic profiling study in rat liver microsomes (RLMs), and molecular interactions of galeon-CYP450 isoforms were performed. An in silico metabolic prediction study showed demethyl and mono-hydroxy galeon were the metabolites with the highest predictability. Among the predicted metabolites, mono-hydroxy galeon was found to have plausible toxicities such as skin sensitization, thyroid toxicity, chromosome damage, and carcinogenicity. An in vitro metabolism study of galeon, incubated in RLMs, revealed eighteen Phase-I metabolites, nine methoxylamine, and three glutathione conjugates. Identification of possible metabolites and confirmation of their structures were carried out using ion-trap tandem mass spectrometry. In silico docking analysis of galeon demonstrated significant interactions with active site residues of almost all CYP450 isoforms.

Total Synthesis of the Ambigols: A Cyanobacterial Class of Polyhalogenated Natural Products

The first total synthesis of all members of the cyanobacterial natural product class of the ambigols is described. Key steps of the synthetic strategy are the formation of sterically demanding mono- and bis-iodonium salts to install the required biaryl ether structural elements and Suzuki cross-coupling giving straightforward access to the biaryl bonds. The synthetic methods are also utilized to construct unnatural or hypothetical ambigols that are still awaiting discovery from Nature.

Diaryl Ether: A Privileged Scaffold for Drug and Agrochemical Discovery

Diaryl ether (DE) is a functional scaffold existing widely both in natural products (NPs) and synthetic organic compounds. Statistically, DE is the second most popular and enduring scaffold within the numerous medicinal chemistry and agrochemical reports. Given its unique physicochemical properties and potential biological activities, DE nucleus is recognized as a fundamental element of medicinal and agrochemical agents aimed at different biological targets. Its drug-like derivatives have been extensively synthesized with interesting biological features including anticancer, anti-inflammatory, antiviral, antibacterial, antimalarial, herbicidal, fungicidal, insecticidal, and so on. In this review, we highlight the medicinal and agrochemical versatility of the DE motif according to the published information in the past decade and comprehensively give a summary of the target recognition, structure-activity relationship (SAR), and mechanism of action of its analogues. It is expected that this profile may provide valuable guidance for the discovery of new active ingredients both in drug and pesticide research.

Light-Promoted Nickel Catalysis: Etherification of Aryl Electrophiles with Alcohols Catalyzed by a NiII -Aryl Complex

A highly effective C-O coupling reaction of (hetero)aryl electrophiles with primary and secondary alcohols is reported. Catalyzed by a Ni^II -aryl complex under long-wave UV (390-395 nm) irradiation in the presence of a soluble amine base without any additional photosensitizer, the reaction enables the etherification of aryl bromides and aryl chlorides as well as sulfonates with a wide range of primary and secondary aliphatic alcohols, affording synthetically important ethers. Intramolecular C-O coupling is also possible. The reaction appears to proceed via a Ni^I -Ni^III catalytic cycle.