Continuous-flow hydration-condensation reaction: Synthesis of α,β-unsaturated ketones from alkynes and aldehydes by using a heterogeneous solid acid catalyst

Significance of Chalcone Scaffolds in Medicinal Chemistry

Chalcone is a simple naturally occurring α,β-unsaturated ketone with biological importance, which can also be easily synthesized in laboratories by reaction between two aromatic scaffolds. In plants, chalcones occur as polyphenolic compounds of different frameworks which are bioactive molecules that have been in traditional medicinal practice for many years. Chalcone-based lead molecules have been developed, possessing varied potentials such as antimicrobial, antiviral, anti-inflammatory, anticancer, anti-oxidant, antidiabetic, antihyperurecemic, and anti-ulcer effects. Chalcones contribute considerable fragments to give important heterocyclic molecules with therapeutic utilities targeting various diseases. These characteristic features have made chalcone a topic of interest among researchers and have attracted investigations into this widely applicable structure. This review highlights the extensive exploration carried out on the synthesis, biotransformations, chemical reactions, hybridization, and pharmacological potentials of chalcones, and aims to provide an extensive, thorough, and critical review of their importance, with emphasis on their properties, chemistry, and biomedical applications to boost future investigations into this potential scaffold in medicinal chemistry.

Catalytic Ketonization over Oxide Catalysts (Part XIV): The Ketonization and Cross-Ketonization of Anhydrides, Substituted Acids and Esters

A series of 20 wt.% MO2/S catalysts (where M = Ce, Mn or Zr and S = SiO2 or Al2O3) were prepared using various precursors of the active phases. The resulting catalysts were characterized using different methods (XRD, TPR and SBET). For the first time, anhydrides were used as potential starting materials for ketone synthesis. This novel reaction was performed on various aliphatic anhydrides in the presence of catalysts within a temperature range of 523-723 K. For all anhydrides, except for pivalic anhydride, the appropriate ketones were obtained with good or very good yields. The vapor-phase catalytic ketonization of esters of benzene-1,x-dicarboxylic acids (x = 2, 3 or 4) with acetic acid were studied in the range of 673-723 K in order to obtain 1,x-diacetylbenzenes. Their yields strongly increased with an increase in the x value (0, 8 and 43% for x = 2, 3 and 4, respectively). The presence of acetophenone as a side product was always noted. In the case of ω-phenylalkanoic acids, their vapor-phase ketonization with acetic acid led to the formation of appropriate ketones with 47-49% yields. Much lower yields of ketones (3-19%) were obtained for acids and ethyl esters containing heterocycle substituents (with O or S atoms) and/or vinyl groups. In the reaction between ethyl 4-nitrophenylacetate and acetic acid, only the products of ester decomposition (p-toluidine and p-nitrotoluene) were determined.

Transition-Metal-Free Dehydrogenation of Benzyl Alcohol for C-C and C-N Bond Formation for the Synthesis of Pyrazolo[3,4-b]pyridine and Pyrazoline Derivatives

A series of cascade reactions that produce a range of functionalized aromatic heterocyclic compounds with pyrazole/pyrazoline cores have been developed. The method relies on a metal-free dehydrogenative process to produce in-situ benzaldehydes. The produced benzaldehyde was then allowed to react with some other substances, including acetophenone, pyrazole amine, and phenylhydrazine. The intermediate produced from these substrates underwent several chemical processes, including electrocyclization, the aza-Diels-Alder reaction, and the formation of intramolecular C-N bonds. These positive outcomes would open up the possibility of producing biologically active pyrazolo[3,4-b]pyridine and pyrazoline derivatives through a variety of possible reactions.

Chalcones: Promising therapeutic agents targeting key players and signaling pathways regulating the hallmarks of cancer

The need for innovative anticancer treatments with high effectiveness and low toxicity is urgent due to the development of malignancies that are resistant to chemotherapeutic agents and the poor specificity of existing anticancer treatments. Chalcones are 1,3-diaryl-2-propen-1-ones, which are the precursors for flavonoids and isoflavonoids. Chalcones are readily available from a wide range of natural resources and consist of very basic chemical scaffolds. Because the ease with which the synthesis it allows for the production of several chalcone derivatives. Various in-vitro and in-vivo studies indicate that naturally occurring and synthetic chalcone derivatives exhibit promising biological activities against cancer hallmarks such as proliferation, angiogenesis, invasion, metastasis, inflammation, stemness, and regulation of cancer epigenetics. According to their structure and functional groups, chalcones derivatives and their hybrid compounds exert a broad range of biological activities through targeting key elements and signaling molecules relevant to cancer progression. This review will provide valuable insights into the latest updates of chalcone groups as anticancer agents and extensively discuss their underlying molecular mechanisms of action.

Sustainable synthesis of biomass-derived carbon quantum dots and their catalytic application for the assessment of α,β-unsaturated compounds

Herein, we demonstrate a simple, reproducible, and environment-friendly strategy for the synthesis of carbon quantum dots (CQDs) utilizing the mango (Mangifera indica) kernel as a renewable green carbon source. Various analytical tools characterized the as-prepared CQDs. These fluorescent CQDs showed significant water solubility with a uniform size of about 6 nm. The as-synthesized CQDs show significantly enhanced catalytic activity for the production of α,β-unsaturated compounds from the derivatives of aromatic alkynes and aldehydes under microwave irradiation in aqueous media. A potential mechanistic pathway and role of carboxylic functionalities were also revealed via various control experiments. The protocol shows outstanding selectivity towards the assessment of α,β-unsaturated compounds over other possible products. A comparative evaluation suggested the as-synthesized CQDs show higher catalytic activity under microwave radiation as compared to the conventional ways. These recyclable CQDs represent a sustainable alternative to metals in synthetic organic chemistry. A cleaner reaction profile, low catalyst loading, economic viability and recyclability of the catalyst, atom economy, and comprehensive substrate applicability are additional benefits of the current protocol according to green chemistry.

Synthesis of Chalcones Derivatives and Their Biological Activities: A Review

Chalcone derivatives are considered valuable species because they possess a ketoethylenic moiety, CO-CH=CH-. Due to the presence of a reactive α,β-unsaturated carbonyl group, chalcones and their derivatives possess a wide spectrum of antiproliferative, antifungal, antibacterial, antiviral, antileishmanial, and antimalarial pharmacological properties. Recent developments in heterocyclic chemistry have led to the synthesis of chalcone derivatives, which had been biologically investigated toward certain disease targets. The major aspect of this review is to present the most recent synthesis of chalcones bearing N, O, and/or S heterocycles, revealing their biological potential during the past decade (2010-2021). Based on a review of the literature, many chalcone-heterocycle hybrids appear to exhibit promise as future drug candidates owing to their similar or superior activities compared to those of the standards. Thus, this review may prove to be beneficial for the development and design of new potent therapeutic drugs based on previously developed strategies.

Aggregation induced emission of chalcones

There is always a need for efficient luminescent materials with simple synthesis and possible ease of hydrogen atom or functional group manipulation for use in different optoelectronic and biological applications. However, for certain real-world uses aggregation caused quenching effect of luminophores in their solid/aggregate state is undesirable, and is a cause of concern in areas, wherein the solid-state optical performance is more crucial. In this regard, chalcones have been explored for their ability to display aggregation-induced emission (AIE) or aggregation-induced enhanced emission (AIEE), which can be of practical use. This article is thus focused on an integrated evidence-based report on the AIE/AIEE-active chalcone systems for potential technological and biological applications.

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Computer-Aided Drug Design Applied to Secondary Metabolites as Anticancer Agents

Computer-Aided Drug Design (CADD) techniques have garnered a great deal of attention in academia and industry because of their great versatility, low costs, possibilities of cost reduction in in vitro screening and in the development of synthetic steps; these techniques are compared with highthroughput screening, in particular for candidate drugs. The secondary metabolism of plants and other organisms provide substantial amounts of new chemical structures, many of which have numerous biological and pharmacological properties for virtually every existing disease, including cancer. In oncology, compounds such as vimblastine, vincristine, taxol, podophyllotoxin, captothecin and cytarabine are examples of how important natural products enhance the cancer-fighting therapeutic arsenal. In this context, this review presents an update of Ligand-Based Drug Design and Structure-Based Drug Design techniques applied to flavonoids, alkaloids and coumarins in the search of new compounds or fragments that can be used in oncology. A systematical search using various databases was performed. The search was limited to articles published in the last 10 years. The great diversity of chemical structures (coumarin, flavonoids and alkaloids) with cancer properties, associated with infinite synthetic possibilities for obtaining analogous compounds, creates a huge chemical environment with potential to be explored, and creates a major difficulty, for screening studies to select compounds with more promising activity for a selected target. CADD techniques appear to be the least expensive and most efficient alternatives to perform virtual screening studies, aiming to selected compounds with better activity profiles and better "drugability".

Chalcones: Retrospective Synthetic Approaches and Mechanistic Aspects of a Privileged Scaffold

This review summarizes the synthetic methodologies used in the last 25 years for the synthesis of chalcones, which are a class of flavonoids having a 1,3-diphenyl-2-propene-1-one backbone. These compounds are considered a hot topic in the field of medicinal chemistry, due to their pharmacological activity and because they are important precursors for the synthesis of heterocyclic compounds with therapeutic applications such as: flavones, flavanones, isoxazolines, benzothiazepines, pyrimidines and pyrazolines derivatives.

Promising anti-inflammatory effects of chalcones via inhibition of cyclooxygenase, prostaglandin E2, inducible NO synthase and nuclear factor κb activities

Chalcones (1, 3-Diphenyl-2-propen-1-one) consist of a three carbon α, β-unsaturated carbonyl system and act as precursors for the biosynthesis of flavonoids in plants. However, laboratory synthesis of various chalcones has also been reported. Both natural and synthetic chalcones are known to exhibit a variety of pharmacological activities such as anti-inflammatory, antitumor, antibacterial, antifungal, antimalarial and antituberculosis. These promising activities, ease of synthesis and simple chemical structure have awarded chalcones considerable attraction. This review focuses on the anti-inflammatory effects of chalcones, caused by their inhibitory action primarily against the activities and expressions of four key inflammatory mediators viz., cyclooxygenase, prostaglandin E₂, inducible NO synthase, and nuclear factor κB. Various methodologies for the synthesis of chalcones have been discussed. The potency of recently synthesized chalcones is given in terms of their IC₅₀ values. Structure-Activity Relationships (SARs) of a variety of chalcone derivatives have been discussed. Computational methods were applied to calculate the ideal orientation of a typical chalcone scaffold against three enzymes, namely, cyclooxygenase-1, cyclooxygenase-2 and inducible NO synthase for the formation of stable complexes. The global market of anti-inflammatory drugs and its expected growth (from 2018 to 2026) have been discussed. SAR analysis, docking studies, and future prospects all together provide useful clues for the synthesis of novel chalcones of improved anti-inflammatory activities.

Chalcone Derivatives: Promising Starting Points for Drug Design

Medicinal chemists continue to be fascinated by chalcone derivatives because of their simple chemistry, ease of hydrogen atom manipulation, straightforward synthesis, and a variety of promising biological activities. However, chalcones have still not garnered deserved attention, especially considering their high potential as chemical sources for designing and developing new effective drugs. In this review, we summarize current methodological developments towards the design and synthesis of new chalcone derivatives and state-of-the-art medicinal chemistry strategies (bioisosterism, molecular hybridization, and pro-drug design). We also highlight the applicability of computer-assisted drug design approaches to chalcones and address how this may contribute to optimizing research outputs and lead to more successful and cost-effective drug discovery endeavors. Lastly, we present successful examples of the use of chalcones and suggest possible solutions to existing limitations.

Synthesis of α,β-unsaturated ketones from alkynes and aldehydes over Hβ zeolite under solvent-free conditions

A facile Hβ zeolite-catalyzed approach has been developed for the synthesis of α,β-unsaturated ketones from alkynes and aldehydes under solvent-free conditions.

Chalcones, semicarbazones and pyrazolines as inhibitors of cathepsins B, H and L

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Three bio macromolecules cathepsins B, H and L of physiological and pathological significance have been selected for the study.

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The molecules have been designed by combining two important pharmacophores their cyclized analogues and were studied for their inhibitory effects on selected enzymes.

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Two isomeric forms of chalconesemicarbazones are reported for the first time.

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The synthesized compounds showed a competitive inhibition towards cathepsins B, H and L.

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Docking experiments were run along with to relate with in vitro studies.

Cathepsin B [EC 3.4.22.1], cathepsin H [EC 3.4.22.16] and cathepsin L [EC 3.4.22.15] are the most versatile lysosomal cysteine proteases and are responsible for intracellular protein degradation. These are involved in a number of pathological conditions including tissue degenerative processes. In the present work, we report the synthesis and systematic evaluation of differently substituted chalcones, chalconesemicarbazones, and diarylpyrazolines on cathepsins B, H and L activity. It was found that after a preliminary screening as cysteine protease inhibitors, chalconesemicarbazones were better inhibitors to these cysteine proteases than diarylpyrazolines followed by chalcones. All the synthesized compounds were identified as the best inhibitors to cathepsin L followed by cathepsin B and then cathepsin H. The results are compared with docking studies and it was found that all the compounds resulted in decrease in energy while interacting with the active site of the enzyme.

Chalcone scaffolds as anti-infective agents: structural and molecular target perspectives

In recent years, widespread outbreak of numerous infectious diseases across the globe has created havoc among the population. Particularly, the inhabitants of tropical and sub-tropical regions are mainly affected by these pathogens. Several natural and (semi) synthetic chalcones deserve the credit of being potential anti-infective candidates that inhibit various parasitic, malarial, bacterial, viral, and fungal targets like cruzain-1/2, trypanopain-Tb, trans-sialidase, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), fumarate reductase, falcipain-1/2, β-hematin, topoisomerase-II, plasmepsin-II, lactate dehydrogenase, protein kinases (Pfmrk and PfPK5), and sorbitol-induced hemolysis, DEN-1 NS3, H1N1, HIV (Integrase/Protease), protein tyrosine phosphatase A/B (Ptp-A/B), FtsZ, FAS-II, lactate/isocitrate dehydrogenase, NorA efflux pump, DNA gyrase, fatty acid synthase, chitin synthase, and β-(1,3)-glucan synthase. In this review, a comprehensive study (from Jan. 1982 to May 2015) of the structural features of anti-infective chalcones, their mechanism of actions (MOAs) and structure activity relationships (SARs) have been highlighted. With the knowledge of molecular targets, structural insights and SARs, this review may be helpful for (medicinal) chemists to design more potent, safe, selective and cost effective anti-infective agents.

Generation and Trapping of Ketenes in Flow

Ketenes were generated by the thermolysis of alkoxyalkynes under flow conditions, and then trapped with amines and alcohols to cleanly give amides and esters. For a 10 min reaction time, temperatures of 180, 160, and 140 °C were required for >95 % conversion of EtO, iPrO, and tBuO alkoxyalkynes, respectively. Variation of the temperature and flow rate with inline monitoring of the output by IR spectroscopy allowed the kinetic parameters for the conversion of 1-ethoxy-1-octyne to be easily estimated (Ea = 105.4 kJ/mol). Trapping of the in-situ-generated ketenes by alcohols to give esters required the addition of a tertiary amine catalyst to prevent competitive [2+2] addition of the ketene to the alkoxyalkyne precursor.

Design and synthesis of chalcone derivatives as inhibitors of the ferredoxin - ferredoxin-NADP+ reductase interaction of Plasmodium falciparum: pursuing new antimalarial agents

Some chalcones have been designed and synthesized using Claisen-Schmidt reactions as inhibitors of the ferredoxin and ferredoxin-NADP⁺ reductase interaction to pursue a new selective antimalaria agent. The synthesized compounds exhibited inhibition interactions between PfFd-PfFNR in the range of 10.94%–50%. The three strongest inhibition activities were shown by (E)-1-(4-aminophenyl)-3-(4-methoxyphenyl)prop-2-en-1-one (50%), (E)-1-(4-aminophenyl)-3-(2,4-dimethoxyphenyl)prop-2-en-1-one (38.16%), and (E)-1-(4-aminophenyl)-3-(2,3-dimethoxyphenyl)prop-2-en-1-one (31.58%). From the docking experiments we established that the amino group of the methoxyamino chlacone derivatives plays an important role in the inhibition activity by electrostatic interaction through salt bridges and that it forms more stable and better affinity complexes with FNR than with Fd.

Driving an equilibrium acetalization to completion in the presence of water

A polymeric acid membrane was generated at the laminar flow interface in a microflow reactor. The polymeric acid membrane-installed microflow devices achieved condensation of a variety of carbonyl substrates with diols to give the corresponding acetals in yields of up to 97% for residence times of 19 to 38 s.

A facile access to substituted benzo[a]fluorenes from o-alkynylbenzaldehydes via in situ formed acetals

Brønsted acid catalysed reaction of o-alkynylbenzaldehydes with arylalkynes in the presence of trimethyl orthoformate takes a different reaction pathway and results in benzo[a]fluorenes.

Continuous flow photocyclization of stilbenes - scalable synthesis of functionalized phenanthrenes and helicenes

A continuous flow oxidative photocyclization of stilbene derivatives has been developed which allows the scalable synthesis of backbone functionalized phenanthrenes and helicenes of various sizes in good yields.

On being green: can flow chemistry help?

The principles of Green Chemistry are important but challenging drivers for most modern synthesis programs. To meet these challenges new flow chemistry tools are proving to be very effective by providing improved heat/mass transfer opportunities, lower solvent usage, less waste generation, hazardous compound containment, and the possibility of a 24/7 working regime. This machine-assisted approach can be used to effect repetitive or routine scale-up steps or when combined with reagent and scavenger cartridges, to achieve multi-step synthesis of complex natural products and pharmaceutical agents.