Synthesis of 5-subsituted flavonols via the Algar-Flynn-Oyamada (AFO) reaction: The mechanistic implication

Synthesis of selenophene-containing flavonols and 2-styrylchromones: Evaluation of their activities compared with selenophene-containing chalcones as potential anticancer agents

Previously, we documented the synthesis and assessed the biological effects of chalcones containing selenium against HT-29 human colorectal adenocarcinoma cells, demonstrating their significant potential. As research on selenium-containing flavonoids remains limited, this article outlines our design and synthesis of three selenium-based flavonols and three 2-styrylchromones. We conducted evaluations of these compounds to determine their impact on human lung cancer cells (A549, H1975, CL1-0, and CL1-5) and their influence on normal lung fibroblast MRC5 cells. Additionally, we included selenium-based chalcones in our testing for comparative purposes. Our findings highlight that the simplest compound, designated as compound 1, exhibited the most promising performance among the tested molecules.

Synthesis of Flavonols and Assessment of Their Biological Activity as Anticancer Agents

A series of flavanols were synthesized to assess their biological activity against human non-small cell lung cancer cells (A549). Among the sixteen synthesized compounds, it was observed that compounds 6k (3.14 ± 0.29 µM) and 6l (0.46 ± 0.02 µM) exhibited higher potency compared to 5-fluorouracil (5-Fu, 4.98 ± 0.41 µM), a clinical anticancer drug which was used as a positive control. Moreover, compound 6l (4'-bromoflavonol) markedly induced apoptosis of A549 cells through the mitochondrial- and caspase-3-dependent pathways. Consequently, compound 6l might be developed as a candidate for treating or preventing lung cancer.

Structure-Photoreactivity Relationship Study of Substituted 3-Hydroxyflavones and 3-Hydroxyflavothiones for Improving Carbon Monoxide Photorelease

Carbon monoxide (CO) is notorious for its toxic effects but is also recognized as a gasotransmitter with considerable therapeutic potential. Due to the inherent challenges in its delivery, the utilization of organic CO photoreleasing molecules (photoCORMs) represents an interesting alternative to CO administration characterized by high spatial and temporal precision of release. This paper focused on the design, synthesis, and photophysical and photochemical studies of 20 3-hydroxyflavone (flavonol) and 3-hydroxyflavothione derivatives as photoCORMs. Newly synthesized compounds bearing various electron-donating and electron-withdrawing groups show bathochromically shifted absorption maxima and considerably enhanced CO release yields compared to the parent unsubstituted flavonol, exceeding 0.8 equiv of released CO in derivatives exhibiting excited states with a charge-transfer character. Until now, such outcomes have been limited to flavonol derivatives possessing a π-extended aromatic system. In addition, thione analogs of flavonols, 3-hydroxyflavothiones, show substantial bathochromic shifts of their absorption maxima and enhanced photosensitivity but provide lower yields of CO formation. Our study elucidates in detail the mechanism of CO photorelease from flavonols and flavothiones, utilizing steady-state and time-resolved spectroscopies and photoproduct analyses, with a particular emphasis on unraveling the structure-photoreactivity relationship and understanding competing side processes.

Halogenated Rocaglate Derivatives: Pan-antiviral Agents against Hepatitis E Virus and Emerging Viruses

The synthesis of a library of halogenated rocaglate derivatives belonging to the flavagline class of natural products, of which silvestrol is the most prominent example, is reported. Their antiviral activity and cytotoxicity profile against a wide range of pathogenic viruses, including hepatitis E, Chikungunya, Rift Valley Fever virus and SARS-CoV-2, were determined. The incorporation of halogen substituents at positions 4', 6 and 8 was shown to have a significant effect on the antiviral activity of rocaglates, some of which even showed enhanced activity compared to CR-31-B and silvestrol.

Synthesis and Characterization of New Pyrano[2,3-c]pyrazole Derivatives as 3-Hydroxyflavone Analogues

In this paper, an efficient synthetic route from pyrazole-chalcones to novel 6-aryl-5-hydroxy-2-phenylpyrano[2,3-c]pyrazol-4(2H)-ones as 3-hydroxyflavone analogues is described. The methylation of 5-hydroxy-2,6-phenylpyrano[2,3-c]pyrazol-4(2H)-one with methyl iodide in the presence of a base yielded a compound containing a 5-methoxy group, while the analogous reaction of 5-hydroxy-2-phenyl-6-(pyridin-4-yl)pyrano[2,3-c]pyrazol-4(2H)-one led to the zwitterionic 6-(N-methylpyridinium)pyrano[2,3-c]pyrazol derivative. The treatment of 5-hydroxy-2,6-phenylpyrano[2,3-c]pyrazol-4(2H)-one with triflic anhydride afforded a 5-trifloylsubstituted compound, which was further used in carbon-carbon bond forming Pd-catalyzed coupling reactions to yield 5-(hetero)aryl- and 5-carbo-functionalized pyrano[2,3-c]pyrazoles. The excited-state intramolecular proton transfer (ESIPT) reaction of 5-hydroxypyrano[2,3-c]pyrazoles from the 5-hydroxy moiety to the carbonyl group in polar protic, polar aprotic, and nonpolar solvents was observed, resulting in well-resolved two-band fluorescence. The structures of the novel heterocyclic compounds were confirmed by 1H-, 13C-, 15N-, and 19F-NMR spectroscopy, HRMS, and single-crystal X-ray diffraction data.

Flavones and Related Compounds: Synthesis and Biological Activity

This review focuses on the synthesis and biological activity of flavones and their related flavonoidic compounds, namely flavonols and aurones. Among the biological activities of natural and synthetic flavones and aurones, their anticancer, antioxidant, and antimicrobial properties are highlighted and detailed in this review. Starting from the structures of natural flavones acting on multiple anticancer targets (myricetin, genkwanin, and other structurally related compounds), new flavone analogs were recently designed and evaluated for their anticancer activity. The most representative compounds and their anticancer activity are summarized in this review. Natural flavones recognized for their antimicrobial properties (baicalein, luteolin, quercetol, apigenin, kaempferol, tricin) have been recently derivatized or structurally modulated by chemical synthetic methods in order to obtain new effective antimicrobial flavonoidic derivatives with improved biological properties. The most promising antimicrobial agents are systematically highlighted in this review. The most applied method for the synthesis of flavones and aurones is based on the oxidative cyclization of o-hydroxychalcones. Depending on the reaction conditions and the structure of the precursor, in some cases, several cyclization products result simultaneously: flavones, flavanones, flavonols, and aurones. Based on the literature data and the results obtained by our research group, our aim is to highlight the most promising methods for the synthesis of flavones, as well as the synthetic routes for the other structurally related cyclization products, such as hydroxyflavones and aurones, while considering that, in practice, it is difficult to predict which is the main or exclusive cyclization product of o-hydroxychalcones under certain reaction conditions.

Structural derivatization strategies of natural phenols by semi-synthesis and total-synthesis

Structural derivatization of natural products has been a continuing and irreplaceable source of novel drug leads. Natural phenols are a broad category of natural products with wide pharmacological activity and have offered plenty of clinical drugs. However, the structural complexity and wide variety of natural phenols leads to the difficulty of structural derivatization. Skeleton analysis indicated most types of natural phenols can be structured by the combination and extension of three common fragments containing phenol, phenylpropanoid and benzoyl. Based on these fragments, the derivatization strategies of natural phenols were unified and comprehensively analyzed in this review. In addition to classical methods, advanced strategies with high selectivity, efficiency and practicality were emphasized. Total synthesis strategies of typical fragments such as stilbenes, chalcones and flavonoids were also covered and analyzed as the supplementary for supporting the diversity-oriented derivatization of natural phenols.

Chromone a Privileged Scaffold in Drug Discovery: Developments on the Synthesis and Bioactivity

Chromones are the class of secondary metabolites broadly occurred in the plant kingdom in a noticeable quantity. This rigid bicyclic system has been categorized "as privileged scaffolds in compounds" in medicinal chemistry. The wide biological responses made them an important moiety in a drug discovery program. This review provides updates on the various methods of synthesis of chromones and biological applications in medicinal chemistry. Various synthetic strategies for the construction of chromones include readily available phenols, salicylic acid and its derivatives, ynones, chalcones, enaminones, chalcones and 2-hydroxyarylalkylketones as starting materials. Synthesis of chromones by using metal, metal free, nanomaterials and different catalysts are included. Details of diverse biological activities such as anti-cancer agents, antimicrobial agents, anti-viral property, anti-inflammatory agents, antioxidants, Monoamine Oxidase-B (MAO-B) Inhibitors, anti-Alzheimer's agents, anti-diabetic agent, antihistaminic potential, antiplatelet agents of chromone derivatives are diecussed.

Synthesis, inverse docking-assisted identification and in vitro biological characterization of Flavonol-based analogs of fisetin as c-Kit, CDK2 and mTOR inhibitors against melanoma and non-melanoma skin cancers

Due to hurdles, including resistance, adverse effects, and poor bioavailability, among others linked with existing therapies, there is an urgent unmet need to devise new, safe, and more effective treatment modalities for skin cancers. Herein, a series of flavonol-based derivatives of fisetin, a plant-based flavonoid identified as an anti-tumorigenic agent targeting the mammalian targets of rapamycin (mTOR)-regulated pathways, were synthesized and fully characterized. New potential inhibitors of receptor tyrosine kinases (c-KITs), cyclin-dependent kinase-2 (CDK2), and mTOR, representing attractive therapeutic targets for melanoma and non-melanoma skin cancers (NMSCs) treatment, were identified using inverse-docking, in vitro kinase activity and various cell-based anticancer screening assays. Eleven compounds exhibited significant inhibitory activities greater than the parent molecule against four human skin cancer cell lines, including melanoma (A375 and SK-Mel-28) and NMSCs (A431 and UWBCC1), with IC50 values ranging from 0.12 to < 15 μM. Seven compounds were identified as potentially potent single, dual or multi-kinase c-KITs, CDK2, and mTOR kinase inhibitors after inverse-docking and screening against twelve known cancer targets, followed by kinase activity profiling. Moreover, the potent compound F20, and the multi-kinase F9 and F17 targeted compounds, markedly decreased scratch wound closure, colony formation, and heightened expression levels of key cancer-promoting pathway molecular targets c-Kit, CDK2, and mTOR. In addition, these compounds downregulated Bcl-2 levels and upregulated Bax and cleaved caspase-3/7/8 and PARP levels, thus inducing apoptosis of A375 and A431 cells in a dose-dependent manner. Overall, compounds F20, F9 and F17, were identified as promising c-Kit, CDK2 and mTOR inhibitors, worthy of further investigation as therapeutics, or as adjuvants to standard therapies for the control of melanoma and NMSCs.

Halogenated Flavones and Isoflavones: A State-of-Art on their Synthesis

BACKGROUND

Flavonoid is a family of compounds present in the everyday consumption plants and fruits, contributing to a balanced diet and beneficial health effects. Being a scaffold for new drugs and presenting a wide range of applicability in the treatment of illnesses give them also an impact in medicine. Among the several types of flavonoids, flavone and isoflavone derivatives can be highlighted due to their prevalence in nature and biological activities already established. The standard synthetic route to obtain both halogenated flavones and isoflavones is through the use of already halogenated starting materials. Halogenation of the flavone and isoflavone core is less common because it is more complicated and involves some selectivity issues.

OBJECTIVE

Considering the importance of these flavonoids, we aim to present the main and more recent synthetic approaches towards their halogenation.

METHODS

The most prominent methodologies for the synthesis of halogenated flavones and isoflavones were reviewed. A careful survey of the reported data, using mainly the Scopus database and halogenation, flavones and isoflavones as keywords, was conducted.

RESULTS

Herein, a review is provided on the latest and more efficient halogenation protocols of flavones and isoflavones. Selective halogenation and the greener methodologies, including enzymatic and microbial halogenations, were reported. Nevertheless, some interesting protocols that allowed the synthesis of halogenated flavone and isoflavone derivatives in specific positions using halogenated reagents are also summarized.

CONCLUSION

Halogenated flavones and isoflavones have risen as noticeable structures; however, most of the time, the synthetic procedures involve toxic reagents and harsh reaction conditions. Therefore, the development of new synthetic routes with low environmental impact is desirable.

New Perspectives for Fisetin

Fisetin is a flavonol that shares distinct antioxidant properties with a plethora of other plant polyphenols. Additionally, it exhibits a specific biological activity of considerable interest as regards the protection of functional macromolecules against stress which results in the sustenance of normal cells cytoprotection. Moreover, it shows potential as an anti-inflammatory, chemopreventive, chemotherapeutic and recently also senotherapeutic agent. In view of its prospective applications in healthcare and likely demand for fisetin, methods for its preparation and their suitability for pharmaceutical use are discussed herein.

Flavonols and 4-thioflavonols as potential acetylcholinesterase and butyrylcholinesterase inhibitors: Synthesis, structure-activity relationship and molecular docking studies

To explore new scaffolds for the treat of Alzheimer's disease appears to be an inspiring goal. In this context, a series of varyingly substituted flavonols and 4-thioflavonols have been designed and synthesized efficiently. All the newly synthesized compounds were characterized unambiguously by common spectroscopic techniques (IR, ¹H-, ¹³C NMR) and mass spectrometry (EI-MS). All the derivatives (1-24) were evaluated in vitro for their inhibitory potential against cholinesterase enzymes. The results exhibited that these derivatives were potent selective inhibitors of acetylcholinesterase (AChE), except the compound 11 which was selective inhibitor of butyrylcholinesterase (BChE), with varying degree of IC₅₀ values. Remarkably, the compounds 20 and 23 have been found the most potent almost dual inhibitors of AChE and BChE amongst the series with IC₅₀ values even less than the standard drug. The experimental results in silico were further validated by molecular docking studies in order to find their binding modes with the active pockets of AChE and BChE enzymes.

New Alkoxy Flavone Derivatives Targeting Caspases: Synthesis and Antitumor Activity Evaluation

The antitumor activity of natural flavonoids has been exhaustively reported. Previously it has been demonstrated that prenylation of flavonoids allows the discovery of new compounds with improved antitumor activity through the activation of caspase-7 activity. The synthesis of twenty-five flavonoids (4–28) with one or more alkyl side chains was carried out. The synthetic approach was based on the reaction with alkyl halide in alkaline medium by microwave (MW) irradiation. The in vitro cell growth inhibitory activity of synthesized compounds was investigated in three human tumor cell lines. Among the tested compounds, derivatives 6, 7, 9, 11, 13, 15, 17, and 18 revealed potent growth inhibitory activity (GI₅₀ < 10 μM), being the growth inhibitory effect of compound 13 related with a pronounced caspase-7 activation on MCF-7 breast cancer cells and yeasts expressing human caspase-7. A quantitative structure-activity relationship (QSAR) model predicted that hydrophilicity, pattern of ring substitution/shape, and presence of partial negative charged atoms were the descriptors implied in the growth inhibitory effect of synthesized compounds. Docking studies on procaspase-7 allowed predicting the binding of compound 13 to the allosteric site of procaspase-7.

Discovery of a Prenylated Flavonol Derivative as a Pin1 Inhibitor to Suppress Hepatocellular Carcinoma by Modulating MicroRNA Biogenesis

Peptidyl-prolyl cis-trans isomerase Pin1 plays a crucial role in the development of human cancers. Recently, we have disclosed that Pin1 regulates the biogenesis of miRNA, which is aberrantly expressed in HCC and promotes HCC progression, indicating the therapeutic role of Pin1 in HCC therapy. Here, 7-(benzyloxy)-3,5-dihydroxy-2-(4-methoxyphenyl)-8-(3-methylbut-2-en-1-yl)-4H-chromen-4-one (AF-39) was identified as a novel Pin1 inhibitor. Biochemical tests indicate that AF-39 potently inhibits Pin1 activity with an IC₅₀ values of 1.008 μm, and also displays high selectivity for Pin1 among peptidyl prolyl isomerases. Furthermore, AF-39 significantly suppresses cell proliferation of HCC cells in a dose- and time-dependent manner. Mechanistically, AF-39 regulates the subcellular distribution of XPO5 and increases miRNAs biogenesis in HCC cells. This work provides a promising lead compound for HCC treatment, highlighting the therapeutic potential of miRNA-based therapy against human cancer.

A novel 3-hydroxychromone fluorescent probe for hydrogen sulfide based on an excited-state intramolecular proton transfer mechanism

A novel fluorescent probe based on an excited-state intramolecular proton transfer mechanism can detect H₂S with high sensitivity and high selectivity.