A novel route to synthesis of flavones from salicylaldehyde and acetophenone derivatives

Iodine-PEG as a unique combination for the metal-free synthesis of flavonoids through iodonium-triiodide ion-pair complexation

An efficient metal-free single-step protocol has been developed for the direct synthesis of flavones from 2-hydroxyacetophenone and substituted benzaldehydes. This chemical transformation is exclusively promoted by the iodonium-triiodide ion couple formed through iodine and PEG-400 complexation. The triiodide anion not only helps in the abstraction of a proton from the acetophenone but also promotes the cyclization of intermediate chalcone to the corresponding flavones. The flavones were obtained in very high yields without using any toxic metal catalysts or harsh reaction conditions. The reaction mechanism was established through a series of test reactions and entrapping of reaction intermediates. The developed protocol provides direct access to flavones in high yields under milder reaction conditions with great substrate compatibility, including hydroxylated derivatives.

Investigating the Antioxidant Capacity of Newly Synthesized Flavonoids via DPPH Assay

BACKGROUND

Numerous naturally occurring and artificially synthesized flavonoids have garnered attention for their impressive ability to combat oxidative stress and scavenge free radicals when evaluated in laboratory settings. The core aim of our investigation revolved around assessing the antioxidant potential of a diverse range of synthesized flavonoids through in vitro experiments.

METHOD

We crafted 29 distinct flavonoids using the aldol condensation mechanism via a chalcone intermediate to accomplish this. We meticulously characterized these newly formed compounds using a variety of spectroscopic techniques. We employed the widely recognized DPPH free radical method for the crucial antioxidant evaluation, a benchmark in such studies.

RESULT

The radical scavenging efficacy of our synthesized flavonoids was then meticulously compared to that of the positive control, ascorbic acid, renowned for its antioxidant prowess, and the IC50 values for each compound were calculated and examined. Surprisingly, our results showed that the flavonoids we tested had a wide range of antioxidant activity, with IC50 values that ranged from 75.8 ± 8.30 to 397 ± 25.10 μg/mL.

CONCLUSION

Intriguingly, compounds US5, US13, US16, US17, US18, and US21 outshone even ascorbic acid in their antioxidant potential, displaying remarkable scavenging abilities against free radicals. This discovery holds promise for further exploration of these compounds as potential antioxidants with potential applications in health and wellness.

Efficient access to domain-integrated estradiol-flavone hybrids via the corresponding chalcones and their in vitro anticancer potential

Structural modification of the phenolic A-ring of estrogens at C-2 and/or C-3 significantly reduces or eliminates the hormonal effects of the compounds, thus the incorporation of other pharmacophores into these positions can provide biologically active derivatives suitable for new indications, without possessing unwanted side effects. As part of this work, A-ring integration of estradiol with chalcones and flavones was carried out in the hope of obtaining novel molecular hybrids with anticancer action. The syntheses were performed from 2-acetylestradiol-17β-acetate which was first reacted with various (hetero)aromatic aldehydes in a pyrrolidine-catalyzed reaction in DMSO. The chalcones thus obtained were then subjected to oxidative cyclization with I₂ in DMSO to afford estradiol-flavone hybrids in good yields. All newly synthesized derivatives were tested in vitro for cytotoxicity on human malignant cell lines of diverse origins as well as on a non-cancerous cell line, and the results demonstrated that estradiol-flavone hybrids containing a structure-integrated flavone moiety were the most active and cancer cell-selective agents. The minimal inhibitory concentration values (IC₅₀) were calculated for selected compounds (3c, 3d and 3e) and their apoptosis inducing capacity was verified by RT-qPCR (real-time quantitative polymerase chain reaction). The results suggest an important structure-activity relationship regarding estradiol-flavone hybrids that could form a promising synthetic platform and rationale for future drug developments.

Advances on nanoformulation approaches for delivering plant-derived antioxidants: A case of quercetin

Oxidative stress has been implicated in tumorigenic, cardiovascular, neuro-, and age-related degenerative changes. Antioxidants minimize the oxidative damage through neutralization of reactive oxygen species (ROS) and other causative agents. Ever since the emergence of COVID-19, plant-derived antioxidants have received enormous attention, particularly in the Indian subcontinent. Quercetin (QCT), a bio-flavonoid, exists in the glycosylated form in fruits, berries and vegetables. The antioxidant potential of QCT analogs relates to the number of free hydroxyl groups in their structure. Despite presence of these groups, QCT exhibits substantial hydrophobicity. Formulation scientists have tested nanotechnology-based approaches for its improved solubilization and delivery to the intended site of action. By the virtue of its hydrophobicity, QCT gets encapsulated in nanocarriers carrying hydrophobic domains. Apart from passive accumulation, active uptake of such formulations into the target cells can be facilitated through well-studied functionalization strategies. In this review, we have discussed the approaches of improving solubilization and bioavailability of QCT with the use of nanoformulations.

Cp*Ir(III) and Cp*Rh(III)-catalyzed annulation of salicylaldehydes with fluorinated vinyl tosylates

A mild, selective and redox-neutral Cp*Ir(III)- and Cp*Rh(III)-catalyzed C-H activation/annulation of salicylaldehydes with fluorovinyl tosylates is reported. The use of monofluorovinyl tosylate favors the synthesis of C2- and C3-substitution-free chromones via C-H activation/β-F elimination/annulation, whereas difluorovinyl tosylate leads to the construction of C2-fluoroalkoxy chromones. Mild reaction conditions and good functional-group tolerance were observed. Further functionalization of the resulting chromones via halogenation, alkynylation, alkylation and hydrocyanation was successfully realized.

In-vitro Cytotoxicity and Aromatase Inhibitory Activity of Flavonoids: Synthesis, Molecular Docking and In-silico ADME Prediction

BACKGROUND

Many natural and synthetic flavonoids have been studied and documented by inhibiting aromatase enzymes for their anti-cancer activity against breast carcinoma. The aromatase enzyme is a possible target for the estrogen's positive breast cancer receptor.

OBJECTIVE

Hence, a series of flavonoids have been synthesized and assessed for their in vitro cytotoxicity and aromatase inhibitory activity.

METHODS

39 flavonoids were synthesized and characterized by spectroscopic techniques, and their computational study was performed using the maestro version of the Schrodinger. In-silico ADME properties were checked by QikPro software. A total of 18 compounds were evaluated based on the docking score using cytotoxicity assay in human breast cancer cell line MCF-7.

RESULTS

Of the 18 compounds tested, 07 compounds, namely 2b, 8b, 14b, 15b, 19b, 24b, and 30b flavonoids were found to be more active with their IC₅₀ values of 20.73 μM, 1.636 μM, 16.08 μM, 22.02 μM, 15.75 μM, 0.345 μM and 16.08 μM, respectively, compared with the reference drug letrozole. The in-vitro aromatase inhibitory activity of six compounds 2b, 8b, 14b, 19b, 24b, and 30b was conducted using a fluorogenic assay kit. The values of IC₅₀ for compounds 2b and 24b were found to be 0.31 μM and 0.36 μM, respectively.

CONCLUSION

Therefore, it was concluded that compounds 2b and 24b had a potent inhibitory effect of aromatase compared with letrozole with an IC₅₀ value of 0.86 μM. At the same time, the other compounds 8b, 14b, 30b, and 19b were considered to have similar aromatase inhibitory activity. Hence, their essential aromatase inhibitory activities make them good lead candidates for developing potent inhibitors of aromatase.

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.

Fluorine-Containing Chrysin Derivatives

Chrysin, a flavonoid, has played a great role in the fields of anticancer, antibacterial, and antiviral drug discovery. A large number of chrysin derivatives have been synthesized recently. The fluorine atom represents an important substituent group for a great number of natural products and pharmaceuticals. Taking into account the importance of both chrysin and the fluorine atom in medicinal chemistry, the synthesis of fluorine-containing chrysin derivatives has gained great interest. Chemically, the synthetic methods for these new chrysin derivatives have also been developed rapidly. In recent years, research on their synthesis has been focused on speeding up the reaction process by changing the catalyst. Biologically, the purpose of introducing fluorine into chrysin was to improve its lipophilicity, but today it is mainly focused on the enhancement and improvement of either its anticancer or antimicrobial activities by incorporating the special properties of fluorine atoms. In this review, synthetic methods for the introduction of fluorine atoms into chrysin are summarized, and their anticancer, antibacterial, antiviral, and hypoglycemic effects are discussed.

Design, synthesis and α-amylase inhibitory activity of novel chromone derivatives

Quercetin is one of the naturally occurring polyphenol flavonoid predominantly known for antidiabetic activity. In the present study, by considering the structural requirements, twenty two novel chromone derivatives (5-26) as α-amylase inhibitor were designed and subsequently in silico evaluated for drug likeness behavior. Designed compounds were synthesized, characterized by spectral analysis and finally evaluated for the inhibition of α-amylase activity by in vitro assay. Tested compounds exhibited significant to weak activity with IC₅₀ range of 12-125µM. Among the tested compounds, analogues 5, 8, 12, 13, 15, 17 and 22 exhibited significant human α-amylase inhibitory activity with IC₅₀ values <25µM, which can be further explored as anti-hyperglycemic agents. Putative binding mode of the significant and least active α-amylase inhibitors with the target enzyme was also explored by the docking studies.

A versatile approach to flavones via a one-pot Pd(ii)-catalyzed dehydrogenation/oxidative boron-Heck coupling sequence of chromanones

A variety of flavones were expediently synthesized from readily accessible chromanones via a one-pot sequence involving Pd(ii)-catalyzed dehydrogenation and oxidative boron-Heck coupling with arylboronic acid pinacol esters.

Functionalised Mn(VI)-nanoparticles: an advanced high-valent magnetic catalyst

We discover Mn(VI)-nanoparticles (NPs) bearing functional groups, high oxidation state, strong electron affinity, unique redox and paramagnetic nature, which opens up a new avenue to catalysis, magnetism and material application. However, its synthesis is challenging and remains unexplored because of associated serious difficulties. A simple benign synthetic strategy is devised to fabricate the high-valent NPs using mild reducing agent bromide, which transformed Mn(VII) to valuable Mn(VI)-species. The EELS-imaging of individual elements, ESI-MS, XPS and other techniques established its composition as Br(Me3SiO)Mn(VI)O2. It revealed significantly improved magnetic moment (SQUID) with isotropic hyperfine splitting of six line spectrum (EPR). The high-oxidation state and incorporated-ligands of the metals present on the active surface of the NPs led to development of a general catalytic process for oxidative heterodifunctionalisation to C-C triple bond towards formation of a new O-C/N-C/S-C and C-C coupling cum cyclisation to biologically important flavones and their aza- and marcapto-analogues, and valuable enaloxy synthons.

Flavones: an important scaffold for medicinal chemistry

Flavones have antioxidant, anti-proliferative, anti-tumor, anti-microbial, estrogenic, acetyl cholinesterase, anti-inflammatory activities and are also used in cancer, cardiovascular disease, neurodegenerative disorders, etc. Also, flavonoids are found to have an effect on several mammalian enzymes like protein kinases that regulate multiple cell signaling pathways and alterations in multiple cellular signaling pathways are frequently found in many diseases. Flavones have been an indispensable anchor for the development of new therapeutic agents. The majority of metabolic diseases are speculated to originate from oxidative stress, and it is therefore significant that recent studies have shown the positive effect of flavones on diseases related to oxidative stress. Due to the wide range of biological activities of flavones, their structure-activity relationships have generated interest among medicinal chemists. The outstanding development of flavones derivatives in diverse diseases in very short span of time proves its magnitude for medicinal chemistry research. The present review gives detail about the structural requirement of flavone derivatives for various pharmacological activities. This information may provide an opportunity to scientists of medicinal chemistry discipline to design selective, optimize as well as poly-functional flavone derivatives for the treatment of multi-factorial diseases.

Reactions of salicylaldehyde and enolates or their equivalents: versatile synthetic routes to chromane derivatives

The reported methodologies for the synthesis of chromane derivatives through the reaction of salicylaldehyde and enolates are discussed. The enolates and their equivalents involved in the reactions discussed in this article were derived from ketones, nitroalkanes, malononitrile and α,β-unsaturated compounds.