Coumarin-Chalcone Hybrids as Peroxyl Radical Scavengers: Kinetics and Mechanisms

Synthesis of Benzopyran-Phenylpropanoid Hybrids via Matsuda-Heck-Arylation and Allylic Oxidation

The synthesis of coumarin- and flavonoid-chalcone hybrids via Pd-catalyzed Heck-type coupling of arene diazonium salts and 8-allylcoumarins and -flavonoids is reported. The β-hydride elimination step proceeds with high regioselectivity if an OMOM-substituent is present at the position C7, adjacent to the allyl group. A selective allylic oxidation of the coupling products was accomplished using DDQ in the presence of silica to furnish the chalcones.

Synthesis of liposomal nanoparticles to load 4-farnesyloxycoumarin and investigating its anti-cancer and anti-metastatic effects

The aim of this study was to load 4-farnesyloxycoumarin (4-FLC) in nanoliposomes (4-FLC-LNPs) and evaluate its anti-cancer and anti-metastatic effects. 4-FLC-LNPs were synthesized using a combination of lecithin-cholesterol-polyethylene glycol. The physicochemical properties were evaluated using DLS, FTIR, and microscopy methods. The toxicity against breast cancer (MCF-7), prostate cancer (PS3), pancreatic cancer (PANC), gastric cancer (AGS), and normal cell lines (HUVEC) was evaluated using the MTT assay. Fluorescent staining and flow cytometry were used to assess the occurrence of apoptosis. Molecular analysis methods were used to study the apoptosis and metastasis effects of these nanoliposomes. The antioxidant power of 4-FLC-LNPs was measured using the ABTS and DPPH free radicals methods. 4-FLC-LNPs exhibit a spherical morphology, with an average size of 57.43 nm, a polydispersity index of 0.29, and a zeta potential of -31.4 mV. They demonstrate an encapsulation efficiency of 82.4% for 4-FLC. The IC50 value of 4-FLC-LNPs against the breast cancer cell line was reported as the most sensitive, at approximately 60 μg/mL. ABTS and DPPH results were reported at approximately 30 µg/mL. The inductive effects of nanoliposomes on the apoptosis process were confirmed by an increase in the number of apoptotic cells, as well as the arrest of cells in various phases of cell growth. The increased expression of BAX and decreased expression of Bcl-2, MMP-2, and MMP-9 confirmed the pro-apoptotic and anti-metastatic effects of 4-FLC-LNPs. These finding validate the therapeutic potential of 4-FLC-LNPs, which may be utilized in preclinical studies.

Synthesis and Biological Applications of Coumarinyl-Chalcones

Abstract:

This survey provides information on the synthesis and biological applications of coumarinyl-chalcones. Chalcones are unsaturated ketones involving the reactive ketoethylenic group (CO-CH=CH). Chalcones are naturally abundant in many medical plants, including vegetables, fruits, and foods. Natural and synthetic chalcone compounds exhibit a broad spectrum of biological properties like anticancer, anti-inflammatory, anti-HIV, antioxidant, antimalarial, and antimicrobial. Some conventional, microwave, and grinding techniques have been utilized for the synthesis of chalcones. Noteworthy, the Claisen- Schmidt condensation reaction remains the most popular and effective method for synthesis. It summarizes information about its synthetic methods as building blocks in some reactions like cyclization reactions and medical applications. This review article presents an overview of approaches and biological data for chalcones bearing a coumarin scaffold.

Investigation of the radical scavenging potential of vanillin-based pyrido-dipyrimidines: experimental and in silico approach

Antioxidants have a significant contribution in the cell protection against free radicals which may induce oxidative stress, and permanently damage the cells causing different disorders such as tumors, degenerative diseases, and accelerated aging. Nowadays, a multi-functionalized heterocyclic framework plays an important role in drug development, and it is of great importance in organic synthesis and medicinal chemistry. Encouraged by the bioactivity of the pyrido-dipyrimidine scaffold and vanillin core, herein, we made an effort to thoroughly investigate the antioxidant potential of the vanillin-based pyrido-dipyrimidines A-E to reveal novel promising free radical inhibitors. The structural analysis and the antioxidant action of the investigated molecules were performed in silico by DFT calculations. Studied compounds were screened for their antioxidant capacity using in vitro ABTS and DPPH assays. All the investigated compounds showed remarkable antioxidant activity, especially derivative A exhibiting inhibition of free radicals at the IC50 value (ABTS and DPPH assay 0.1 mg ml-1 and 0.081 mg ml-1, respectively). Compound A has higher TEAC values implying its stronger antioxidant activity compared to a trolox standard. The applied calculation method and in vitro tests confirmed that compound A has a strong potential against free radicals and may be a novel candidate for application in antioxidant therapy.

Theoretical study on the free radical scavenging potency and mechanism of natural coumestans: Roles of substituent, noncovalent interaction and solvent

The free radical scavenging potency and mechanisms of seven representative natural coumestans were systematically evaluated using density functional theory (DFT) approach. Thermodynamic feasibility of different mechanisms was assessed by various physio-chemical descriptors involved in the double (2H⁺/2e^‒) radical-trapping processes. Energy diagram and related transition state structures of the reaction between wedelolactone (WEL) and hydroperoxyl radical were constructed to further uncover the radical-trapping details. Results showed that the studied coumestans prefer to scavenge radicals via formal hydrogen atom transfer (fHAT) mechanism in the gas phase and non-polar environment, whereas sequential proton loss electron transfer (SPLET) is favored in polar media. Moreover, the feasibility of second fHAT and SPLET processes was also revealed. Sequential double proton loss double electron transfer (SdPLdET) mechanism represents the preferred pathway in aqueous solution at physiological pH. Our findings highlight the essential role of ortho-dihydroxyl group, noncovalent interaction and solvents on radical-trapping potency. 4'-OH in D-ring was found to be the most favorable site to trap radical for most of the studied coumestans, whereas 3-OH in A-ring for lucernol (LUN).

Influence of the pKa value on the antioxidant activity of licorice flavonoids under solvent-mediated effects

Licorice flavonoids (LCFs) have been widely used in food care and medical treatment due to their significant antioxidant activities. However, the molecular mechanism of their antioxidant activity remains unclear. Therefore, network pharmacology, ADMET, density functional theory (DFT), molecular docking, and molecular dynamics (MD) simulation were employed to explore the molecular mechanism of the antioxidant effects of LCF. The network pharmacology and ADMET studies showed that the active molecules of kumatakenin (pK_a  = 6.18), licoflavonol (pK_a  = 6.86), and topazolin (pK_a  = 6.21) in LCF are key antioxidant components and have good biosafety. Molecular docking and MD simulation studies demonstrated that active molecules interacted with amino acid residues in target proteins to form stable protein-ligand complexes and exert their antioxidant effects. DFT studies showed that the antioxidant activity of LCF could be significantly modulated under the solvent-mediated effect. In addition, based on the derivation of the Henderson-Hasselbalch and van't Hoff formulas, the functional relationships between the reaction-free energy (ΔG) of LCF and the pH and pK_a values were established. The results showed that active molecules with larger pK_a values will be more conducive to the improvement of their antioxidant activity under solvent-mediated effects. In conclusion, this study found that increasing the pK_a value of LCF would be an effective strategy to improve their antioxidant activity under the effect of solvent mediation. The pK_a value of an LCF will be a direct standard to evaluate its solvent-mediated antioxidant activity. This study will provide theoretical guidance for the development of natural antioxidants.

Protective effects and DNA repair induction of a coumarin-chalcone hybrid against genotoxicity induced by mutagens

Coumarins and chalcones are compounds widely found in plants or obtained by synthetic methods which possess several biological properties including antioxidant, anti-inflammatory, and antitumor effects. A series of coumarin-chalcone hybrids were synthesized to improve their biological actions and reduce potential adverse effects. Considering the applications of these molecules, a coumarin-chalcone hybrid [7-methoxy-3-(E)-3-(3,4,5-trimethoxyphenyl) acryloyl-2 H-chromen-2-one] (4-MET) was synthesized and the genotoxic, cytotoxic, and protective effects assessed against damage induced by different mutagens. First, in silico tools were used to predict biological activity of 4-MET which indicated a chemopreventive potential. Subsequently, the genotoxic/antigenotoxic activities of 4-MET were determined both in vitro (Ames test) and in vivo (micronucleus (MN) test and comet assay). In addition, molecular docking simulations were performed between 4-MET and glutathione reductase, an important cellular detoxifying enzyme. Our results indicated that 4-MET was not mutagenic in the Ames test; however, when co-treated with sodium azide or 4-nitroquinoline 1-oxide (4-NQO), 4-MET significantly reduced the harmful actions of these mutagens. Except for a cytotoxic effect after 120 hr treatment, 4-MET alone did not produce cytotoxicity or genotoxicity in the MN test and comet assay. Nonetheless, all treatments of 4-MET with cyclophosphamide (CPA) showed a chemoprotective effect against DNA damage induced by CPA. Further, molecular docking analysis indicated a strong interaction between 4-MET and the catalytic site of glutathione reductase. These effects may be related to (1) damage prevention, (2) interaction with detoxifying enzymes, and (3) DNA-repair induction. Therefore, data demonstrated that 4-MET presents a favorable profile to be used in chemopreventive therapies.

Two Important Anticancer Mechanisms of Natural and Synthetic Chalcones

ATP-binding cassette subfamily G and tubulin pharmacological mechanisms decrease the effectiveness of anticancer drugs by modulating drug absorption and by creating tubulin assembly through polymerization. A series of natural and synthetic chalcones have been reported to have very good anticancer activity, with a half-maximal inhibitory concentration lower than 1 µM. By modulation, it is observed in case of the first mechanism that methoxy substituents on the aromatic cycle of acetophenone residue and substitution of phenyl nucleus by a heterocycle and by methoxy or hydroxyl groups have a positive impact. To inhibit tubulin, compounds bind to colchicine binding site. Presence of methoxy groups, amino groups or heterocyclic substituents increase activity.

Identification of new biologically active synthetic molecules: comparative experimental and theoretical studies on the structure-antioxidant activity relationship of cyclic 1,3-ketoamides

Antioxidant agent is a chemical that prevents the oxidation of other chemical substances. Its use is the most effective means of protecting the organism by neutralizing the harmful effects of free radicals caused by oxidative stress. In the present work, a series of β-ketoamides containing a variety of monosubstituted amide groups were synthesized and tested as antioxidant agents. In order to establish a possible structure-antioxidant activity relationship, we are presenting a systematic theoretical study of these molecules with the aim of clarifying the active sites. In particular, we discuss the selectivity resulting from the choice of a free radical/antioxidant system. The theoretical study of these molecules was carried out using density functional theory (DFT) calculations at the B3LYP/6-311G (d,p) level of theory. In order to shed light on the antioxidant properties of β-ketoamides, O-H bond dissociation enthalpies (BDEs), ionization potentials (IPs), electron affinities (EAs), proton affinities (PAs), and electron transfer enthalpies (ETEs) are performed in the gas phase and in ethanol. The results obtained show that the HAT mechanism is thermodynamically more favored in the gas phase, while the SPLET is preferred in the polar solvent.

Oxidative Stress, Antioxidant Capabilities, and Bioavailability: Ellagic Acid or Urolithins?

Oxidative stress (OS), triggered by overproduction of reactive oxygen and nitrogen species, is the main mechanism responsible for several human diseases. The available one-target drugs often face such illnesses, by softening symptoms without eradicating the cause. Differently, natural polyphenols from fruits and vegetables possess multi-target abilities for counteracting OS, thus representing promising therapeutic alternatives and adjuvants. Although in several in vitro experiments, ellagitannins (ETs), ellagic acid (EA), and its metabolites urolithins (UROs) have shown similar great potential for the treatment of OS-mediated human diseases, only UROs have demonstrated in vivo the ability to reach tissues to a greater extent, thus appearing as the main molecules responsible for beneficial activities. Unfortunately, UROs production depends on individual metabotypes, and the consequent extreme variability limits their potentiality as novel therapeutics, as well as dietary assumption of EA, EA-enriched functional foods, and food supplements. This review focuses on the pathophysiology of OS; on EA and UROs chemical features and on the mechanisms of their antioxidant activity. A discussion on the clinical applicability of the debated UROs in place of EA and on the effectiveness of EA-enriched products is also included.

What is responsible for antioxidant properties of polyphenolic compounds from plants?

Due to the negative impact of reactive species (including free radicals) on humans and animals, the investigations to find effective substances (antioxidants), which protect living organisms against their damaging influence are carried out throughout the world. As most widespread synthetic antioxidants are suspected of having a noxious effect on the human body, more and more attention is paid to natural antioxidant compounds found in plants (especially phenolic compounds). The aim of this paper is to present the data about antioxidant activity of polyphenolic compounds with the emphasis on the main factors having influence on their antioxidant activity: chemical structure, ability to form hydrogen bonds, capability of metal ions chelation and reduction, adduct formation, kinetic solvents effect, mechanism of antioxidant reaction, capability of antioxidant enzyme activation and reduction potential.

Rational approaches, design strategies, structure activity relationship and mechanistic insights for therapeutic coumarin hybrids

Hybrid molecules, furnished by combining two or more pharmacophores is an emerging concept in the field of medicinal chemistry and drug discovery that has attracted substantial traction in the past few years. Naturally occurring scaffolds such as coumarins display a wide spectrum of pharmacological activities including anticancer, antibiotic, antidiabetic and others, by acting on multiple targets. In this view, various coumarin-based hybrids possessing diverse medicinal attributes were synthesized in the last five years by conjugating coumarin moiety with other therapeutic pharmacophores. The current review summarizes the recent development (2014 and onwards) of these pharmacologically active coumarin hybrids and demonstrates rationale behind their design, structure-activity relationships (SAR) and mechanistic studies performed on these hybrid molecules. This review will be beneficial for medicinal chemist and chemical biologist, and in general to the drug discovery community and will facilitate the synthesis and development of novel, potent coumarin hybrid molecules serving as lead molecules for the treatment of complex disorders.

Thiophenols, Promising Scavengers of Peroxyl Radicals: Mechanisms and kinetics

The activity of 12 thiophenols as primary antioxidants in aqueous solution has been studied using density functional theory. Twelve different substituted thiophenols were tested as peroxyl radicals scavengers. Single electron transfer (SET) and formal hydrogen transfer (FHT) were investigated. The SET mechanism was found to be the main mechanism, with rate constants that are close to the diffusion limit, which means that these thiophenolic compounds have the capacity to scavenge peroxyl radicals before they can damage biomolecules. All 12 thiophenolic compounds react faster with methylperoxyl than with hydroperoxyl radicals. In addition, it was found that pH plays an important role in the reactivity of these compounds. © 2019 Wiley Periodicals, Inc.

Radical Scavenging Activity of Natural-Based Cassaine Diterpenoid Amides and Amines

The radical scavenging capacities of four new cassaine diterpenoid amides including 3β-hydroxydinorerythrosuamide (1), 3β-acetoxydinorerythrosuamide (2), 3β-tigloyloxydinorerythrosuamide (3), and 6α-hydroxydinorcassamide (4) present in leaf extract and four new cassaine diterpenoid amines namely erythroformine A (5), erythroformine B (6), 6α-hydroxy-nor-cassamine (7), and nor-erythrosuamine (8) recently identified in the extract of the bark of Erythrophleum fordii were elucidated using density functional theory (DFT) method. Different thermochemical properties characterizing antioxidant potential including bond dissociation enthalpy (BDE), proton affinity (PA), and adiabatic ionization potential (IP) were calculated at the B3LYP/6-311G(d,p) level of theory. Scavenging reaction mechanisms of cassaine diterpenes toward HOO^• radical including formal hydrogen transfer (FHT; either hydrogen atom transfer (HAT) or proton coupled electron transfer (PCET)), radical adduct formation (RAF), single electron transfer (SET), and proton transfer (PT) were studied in the gas phase, water, and benzene. The potential energy profiles and kinetic calculations for the FHT and RAF reactions were calculated at 298.15 K. The results showed that all the studied compounds present strong antioxidant activity via HAT mechanism with BDEs varying from 69.4 to 77.9 kcal/mol. While solvents have only a slight effect on HAT and RAF mechanisms, SET and PT reactions are likely to occur in polar media. Among the studied compounds, 3 is the most reactive one both for HAT (H-abstraction at C7, Δ H -11.3 kcal/mol) and for RAF (radical addition at C13 = C15 bond, Δ H -5.2 kcal/mol) reactions. The rate constants of these reactions are also comparable with several referenced antioxidants such as Trolox and ascorbic acid.

Synthesis and antiviral activity of a new coumarin derivative against spring viraemia of carp virus

Coumarin as a lead structure have received a considerable attention in the last three decades for the discovery of antiviral agents. Our previous study indicated that imidazole coumarins possessed antiviral activities against SVCV. Based on the structure-activity relationship in that study, a new imidazole coumarin derivative, 7-(4-benzimidazole-butoxy)-coumarin (BBC), was designed, synthesized and its anti-SVCV activity was evaluated. By comparing inhibitory concentration at half-maximal activity (IC₅₀), we found that BBC (IC₅₀ = 0.56 mg/L) possessed a higher antiviral activity than those imidazole coumarins in our previous study. Besides, BBC can significantly inhibit cell death and reduce cellular morphological damage induced by SVCV. Our further data indicated that intraperitoneal injection of BBC increased the survival rate of zebrafish by 17.5%, decreased viral titer in fish body and inhibited SVCV glycoprotein expression in kidney and spleen. In uninfected zebrafish, the expression levels of ifnγ, ifnφ1, ifnφ2 and rig1 genes were up-regulated after BBC treatment, which indicated that BBC could activate interferon response. In addition, data of the antioxidant enzymes activities and results of the antioxidant enzymes-related genes expressions suggested BBC could reduce SVCV-induced oxidative damage in infected zebrafish. Altogether, BBC is expected to be a therapeutic agent against SVCV infection in the field of aquaculture.

Structure-antioxidant capacity relationship of dihydrochalcone compounds in Malus

The antioxidant capacity (AC) of six dihydrochalcone compounds was evaluated using DPPH and ABTS assays. In water-based solution 3-hydroxyphlorizin exhibited the highest AC among all dihydrochalcones. In acetone and acidic solutions (pH = 2.5 or 2.0), presence of an o-dihydroxyl at the B-ring increased AC, whereas glycosylation at the A-ring decreased AC of dihydrochalcones. By comparing the AC of dihydrochalcones with similar structures, it was found that the o-dihydroxyl at the B-ring and 2'-hydroxyl group at the A-ring were critical for maintaining the AC of dihydrochalcones by promoting hydrogen atom transfer or single electron transfer mechanism. Sequential proton-loss electron transfer commonly occurred during free radical scavenging in water-based solution. Moreover, we report a unique phenomenon in which glycosylation at the 2'-position enhanced the dissociation ability of the 4'-hydroxyl group and increased the AC of dihydrochalcones containing o-dihydroxyl. We speculate that this increase in AC might occur through intramolecular electron transfer.

Theoretical insight into the substituent effects on the antioxidant properties of 8-hydroxyquinoline derivatives in gas phase and in polar solvents

The objective of this work is to perform a theoretical analysis of the antioxidant properties of a series of 8-hydroxyquinolines (8-HQs) to rationalize the available experimental results and to design new potent 8-HQ derivatives. The study was carried out in gas phase and in methanol at the DFT/B3LYP/ 6-311++G(d,p) computational level. The formation of stable ArO• radicals is discussed on the basis of different mechanisms, namely, hydrogen atom transfer (HAT), single electron transfer followed by proton transfer (SET-PT), and single proton loss electron transfer (SPLET). The obtained results show that the HAT mechanism is, thermodynamically, more favoured in gas phase, whereas the SPLET pathway is more favoured in polar solvents. The calculated thermochemical descriptors allow classification of the antioxidant power of the studied compounds.

Discovery of C-3 Tethered 2-oxo-benzo[1,4]oxazines as Potent Antioxidants: Bio-Inspired Based Design, Synthesis, Biological Evaluation, Cytotoxic, and in Silico Molecular Docking Studies

The discovery of C-3 tethered 2-oxo-benzo[1,4]oxazines as potent antioxidants is disclosed. All the analogs 20a-20ab have been synthesized via “on water” ultrasound-assisted irradiation conditions in excellent yields (upto 98%). All the compounds have been evaluated for their in vitro antioxidant activities using DPPH free radical scavenging assay as well as FRAP assay. The result showed promising antioxidant activities having IC₅₀ values in the range of 4.74 ± 0.08 to 92.20 ± 1.54 μg/mL taking ascorbic acid (IC₅₀ = 4.57 μg/mL) as standard reference. In this study, compounds 20b and 20t, the most active compound of the series, showed IC₅₀ values of 6.89 ± 0.07 μg/mL and 4.74 ± 0.08 μg/mL, respectively in comparison with ascorbic acid. In addition, the detailed SAR study shows that electron-withdrawing group increases antioxidant activity and vice versa. Furthermore, in the FRAP assay, eight compounds (20c, 20j, 20m, 20n, 20r, 20u, 20z, and 20aa) were found more potent than standard reference BHT (C_0.5FRAP = 546.0 ± 13.6 μM). The preliminary cytotoxic study reveals the non-toxic nature of active compounds 20b and 20t in non-cancerous 3T₃ fibroblast cell lines in MTT assay up to 250 μg/mL concentration. The results were validated via carrying out in silico molecular docking studies of promising compounds 20a, 20b, and 20t in comparison with standard reference. To the best of our knowledge, this is the first detailed study of C-3 tethered 2-oxo-benzo[1,4]oxazines as potential antioxidant agents.

Heterocyclic Schiff bases as non toxic antioxidants: Solvent effect, structure activity relationship and mechanism of action

Phenolic heterocyclic imine based Schiff bases from Thiophene-2-carboxaldehyde and Pyrrole-2-carboxaldehyde were synthesized and characterized as novel antioxidants. The solvent effects of these Schiff bases were determined and compared with standard antioxidants, BHA employing DPPH assay and ABTS assay. Fixed reaction time and Steady state measurement were used for study. IC₅₀ and EC₅₀ were calculated. Structure-activity relationship revealed that the electron donating group in the phenolic ring increases the activity where as the electron withdrawing moiety decreases the activity. The Schiff base derivatives showed antioxidant property by two different pathways namely SPLET and HAT mechanisms in DPPH assay. While in ABTS method, the reaction between ABTS radical and Schiff bases involves electron transfer followed by proton transfer (ET-PT) mechanism. The cytotoxicity of these compounds has been evaluated by MTT assay. The results showed that all these compounds are non toxic in nature.

Antioxidant properties and free radical scavenging mechanisms of cyclocurcumin

Cyclocurcumin has a strong ability to scavenge ˙OH by its 4′-OH phenolic hydroxyl via a hydrogen-atom transfer mechanism in a physiological environment.

Atypical antioxidant activity of non-phenolic amino-coumarins

Coumarin compounds have been described as anti-inflammatories, and chemotherapeutic agents as well as antioxidants. However, the origin of the antioxidant activity of non phenolic coumarins remains obscure. In the present report, we demonstrate that non-phenolic 7-dialkyl-aminocoumarins may also have significant antioxidant properties against free radicals derived from 2,2′-azobis(2-amidinopropane) dihydrochloride under aerobic conditions. This atypical behaviour is due to the presence of traces of very reactive hydroxycinnamic acid-type compounds. Changing functional groups at the C-3 and C-4 positions shifts the reactivity of the compounds from peroxyl to alkoxyl free radicals. Kinetic and theoretical studies based on Density Functional Theory support the formation of reactive hydroxycinnamic acid and directly link the antioxidant behaviour of the compounds to hydrogen atom transfer.

Relevant antioxidant properties of non-phenolic 7-dialkyl-aminocoumarins against free radicals derived from 2,2′-azobis(2-amidinopropane) dihydrochloride under aerobic conditions have been experimentally and theoretically demonstrated.

Synthesis and DFT Calculations of Novel Vanillin-Chalcones and Their 3-Aryl-5-(4-(2-(dimethylamino)-ethoxy)-3-methoxyphenyl)-4,5-dihydro-1H-pyrazole-1-carbaldehyde Derivatives as Antifungal Agents

Novel (E)-1-(aryl)-3-(4-(2-(dimethylamino)ethoxy)-3-methoxyphenyl) prop-2-en-1-ones 4 were synthesized by a Claisen-Schmidt reaction of 4-(2-(dimethylamino)ethoxy)-3-methoxy-benzaldehyde (2) with several acetophenone derivatives 3. Subsequently, cyclocondensation reactions of chalcones 4 with hydrazine hydrate afforded the new racemic 3-aryl-5-(4-(2-(dimethylamino)ethoxy)-3-methoxyphenyl)-4,5-dihydro-1H-pyrazole-1-carbaldehydes 5 when the reaction was carried out in formic acid. The antifungal activity of both series of compounds against eight fungal species was determined. In general, chalcone derivatives 4 showed better activities than pyrazolines 5 against all tested fungi. None of the compounds 4a–g and 5a–g showed activity against the three Aspergillus spp. In contrast, most of the compounds 4 showed moderate to high activities against three dermatophytes (MICs 31.25–62.5 µg/mL), being 4a followed by 4c the most active structures. Interestingly, 4a and 4c possess fungicidal rather than fungistatic activities, with MFC values between 31.25 and 62.5 μg/mL. The comparison of the percentages of inhibition of C. neoformans by the most active compounds 4, allowed us to know the role played by the different substituents of the chalcones’ A-ring. Also the most anti-cryptococcal compounds 4a–c and 4g, were tested in a second panel of five clinical C. neoformans strains in order to have an overview of their inhibition capacity not only of standardized but also of clinical C. neoformans strains. DFT calculations showed that the electrophilicity is the main electronic property to explain the differences in antifungal activities for the synthesized chalcones and pyrazolines compounds. Furthermore, a quantitative reactivity analysis showed that electron-withdrawing substituted chalcones presented the higher electrophilic character and hence, the greater antifungal activities among compounds of series 4.

Chalcone: A Privileged Structure in Medicinal Chemistry

Privileged structures have been widely used as an effective template in medicinal chemistry for drug discovery. Chalcone is a common simple scaffold found in many naturally occurring compounds. Many chalcone derivatives have also been prepared due to their convenient synthesis. These natural products and synthetic compounds have shown numerous interesting biological activities with clinical potentials against various diseases. This review aims to highlight the recent evidence of chalcone as a privileged scaffold in medicinal chemistry. Multiple aspects of chalcone will be summarized herein, including the isolation of novel chalcone derivatives, the development of new synthetic methodologies, the evaluation of their biological properties, and the exploration of the mechanisms of action as well as target identification. This review is expected to be a comprehensive, authoritative, and critical review of the chalcone template to the chemistry community.

Phenolic Melatonin-Related Compounds: Their Role as Chemical Protectors against Oxidative Stress

There is currently no doubt about the serious threat that oxidative stress (OS) poses to human health. Therefore, a crucial strategy to maintain a good health status is to identify molecules capable of offering protection against OS through chemical routes. Based on the known efficiency of the phenolic and melatonin (MLT) families of compounds as antioxidants, it is logical to assume that phenolic MLT-related compounds should be (at least) equally efficient. Unfortunately, they have been less investigated than phenols, MLT and its non-phenolic metabolites in this context. The evidence reviewed here strongly suggests that MLT phenolic derivatives can act as both primary and secondary antioxidants, exerting their protection through diverse chemical routes. They all seem to be better free radical scavengers than MLT and Trolox, while some of them also surpass ascorbic acid and resveratrol. However, there are still many aspects that deserve further investigations for this kind of compounds.