Proof of Concept of Natural and Synthetic Antifouling Agents in Coatings.

Marine biofouling, caused by the deposition and accumulation of marine organisms on submerged surfaces, represents a huge concern for the maritime industries and also contributes to environmental pollution and health concerns. The most effective way to prevent this phenomenon is the use of biocide-based coatings which have proven to cause serious damage to marine ecosystems. Several research groups have focused on the search for new environmentally friendly antifoulants, including marine and terrestrial natural products and synthetic analogues. Some of these compounds have been incorporated into marine coatings and display interesting antifouling activities caused by the interference with the biofilm-forming species as well as by the inhibition of the settlement of macroorganisms. This review highlights the proof-of-concept studies of emerging natural or synthetic antifouling compounds in coatings, from lab-made to commercial ones, performed between 2019 and 2023 and their results in the field or in in vivo laboratorial tests.

The Role of Natural and Synthetic Flavonoids in the Prevention of Marine Biofouling.

Marine biofouling is a major concern for the maritime industry, environment, and human health. Biocides which are currently used in marine coatings to prevent this phenomenon are toxic to the marine environment, and therefore a search for antifoulants with environmentally safe properties is needed. A large number of scientific papers have been published showing natural and synthetic compounds with potential to prevent the attachment of macro- and microfouling marine organisms on submerged surfaces. Flavonoids are a class of compounds which are highly present in nature, including in marine organisms, and have been found in a wide range of biological activities. Some natural and synthetic flavonoids have been evaluated over the last few years for their potential to prevent the settlement and/or the growth of marine organisms on submerged structures, thereby preventing marine biofouling. This review compiles, for the first-time, natural flavonoids as well as their synthetic analogues with attributed antifouling activity against macrofouling and microfouling marine organisms.

A Chemical Toolbox to Unveil Synthetic Nature-Inspired Antifouling (NIAF) Compounds.

The current scenario of antifouling (AF) strategies to prevent the natural process of marine biofouling is based in the use of antifouling paints containing different active ingredients, believed to be harmful to the marine environment. Compounds called booster biocides are being used with copper as an alternative to the traditionally used tributyltin (TBT); however, some of them were recently found to accumulate in coastal waters at levels that are deleterious for marine organisms. More ecological alternatives were pursued, some of them based on the marine organism mechanisms' production of specialized metabolites with AF activity. However, despite the investment in research on AF natural products and their synthetic analogues, many studies showed that natural AF alternatives do not perform as well as the traditional metal-based ones. In the search for AF agents with better performance and to understand which molecular motifs were responsible for the AF activity of natural compounds, synthetic analogues were produced and investigated for structure-AF activity relationship studies. This review is a comprehensive compilation of AF compounds synthesized in the last two decades with highlights on the data concerning their structure-activity relationship, providing a chemical toolbox for researchers to develop efficient nature-inspired AF agents.

Chalcone derivatives as promising antifoulants: Molecular optimization, bioactivity evaluation and performance in coatings.

Marine biofouling remains a huge concern for maritime industries and for environmental health. Although the current biocide-based antifouling coatings can prevent marine biofouling, their use has been associated with toxicity for the marine environment, being urgent to find sustainable alternatives. Previously, our research group has identified a prenylated chalcone (1) with promising antifouling activity against the settlement of larvae of the macrofouling species Mytilus galloprovincialis (EC50 = 16.48 µM and LC50 > 200 µM) and lower ecotoxicity when compared to Econea®, a commercial antifouling agent in use. Herein, a series of chalcone 1 analogues were designed and synthesized in order to obtain optimized antifouling compounds with improved potency while maintaining low ecotoxicity. Compounds 8, 15, 24, and 27 showed promising antifouling activity against the settlement of M. galloprovincialis larvae, being dihydrochalcone 27 the most potent. The effect of compound 24 was associated with the inhibition of acetylcholinesterase activity. Among the synthesized compounds, compound 24 also showed potent complementary activity against Navicula sp. (EC50 = 4.86 µM), similarly to the lead chalcone 1 (EC50 = 6.75 µM). Regarding the structure-activity relationship, the overall results demonstrate that the substitution of the chalcone of the lead compound 1 by a dihydrochalcone scaffold resulted in an optimized potency against the settlement of mussel larvae. Marine polyurethane (PU)-based coatings containing the best performed compound concerning anti-settlement activity (dihydrochalcone 27) were prepared, and mussel larvae adherence was reduced compared to control PU coatings.

Persulfated Ascorbic Acid Glycoside as a Safe and Stable Derivative of Ascorbic Acid for Skin Care Application.

The pursuit of cosmetic ingredients with proven efficacy and safety that meet consumer needs drives the advancement of new products. Ascorbic acid (AA) is utilized in cosmetic products, predominantly for its potent antioxidant properties. Nonetheless, its instability compromises its efficacy. In this work, ascorbyl 2-O-glucoside persulfate (AAGS) was synthesized, characterized, and evaluated regarding its safety profile and potential bioactivities and the results were compared to AA and its glycoside AAG. Pre-formulation studies were performed to assess the stability of the compounds and their compatibility with typical excipients commonly used in topical formulations. AAGS did not affect the metabolic activity of keratinocyte, macrophage, and monocyte cell lines, up to 500 µM. AAGS also exhibited a non-prooxidant and non-sensitizing profile and anti-allergic activity by impeding the allergen-induced maturation of THP-1 cells. When compared to AA and AAG, AAGS was shown to be more stable at pH values between 5 and 7, as well as superior thermostability and photostability. AAGS demonstrated higher stability in metal solutions of Fe(II) and Mg(II) than AA. AAGS demonstrated similar DPPH radical scavenging activity compared to AA. These results provide useful information for the development of new AA derivatives, highlighting AAGS as a novel cosmetic ingredient.

A Hydrophilic Sulfated Resveratrol Derivative for Topical Application: Sensitization and Anti-Allergic Potential.

Resveratrol (RSV), a naturally occurring metabolite, is widely used in skincare products, but its hydrophobicity impairs its own incorporation into cosmetic formulations. RSV-GS is a synthetic hydrophilic sulfated glycosylated derivative inspired by marine natural products that present a lower cytotoxicity than RSV while exhibiting similar levels of bioactivity. Herein, we predict the skin sensitization potential of this new compound using an in vitro approach based on the OECD 442E guideline. Furthermore, the anti-allergic potential of RSV-GS was also disclosed. The monocyte THP-1 cell line was stimulated with RSV and RSV-GS in the presence or absence of the extreme skin allergen 1-fluoro-2,4-dinitrobenzene (DNFB). The results demonstrated that RSV-GS alone (500 µM) evoked a relative fluorescence index (RFI) lower than the thresholds established by the OECD guideline for CD54 (200%) and CD86 (150%), indicating the absence of a skin sensitization potential. Interestingly, in the presence of the skin allergen DNFB, RSV-GS exhibited the ability to rescue the DNFB-induced maturation of THP-1 cells, with RFI values lower than those for RSV, suggesting the potential of RSV-GS to mitigate skin sensitization evoked by allergens and, consequently, allergic contact dermatitis. These results open new avenues for the use of RSV-GS as a safe and anti-allergic active cosmetic ingredient.

Evaluation of the Cytotoxic and Antiviral Effects of Small Molecules Selected by In Silico Studies as Inhibitors of SARS-CoV-2 Cell Entry.

The spike protein of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) relies on host cell surface glycans to facilitate interaction with the angiotensin-converting enzyme 2 (ACE-2) receptor. This interaction between ACE2 and the spike protein is a gateway for the virus to enter host cells and may be targeted by antiviral drugs to inhibit viral infection. Therefore, targeting the interaction between these two proteins is an interesting strategy to prevent SARS-CoV-2 infection. A library of glycan mimetics and derivatives was selected for a virtual screening performed against both ACE2 and spike proteins. Subsequently, in vitro assays were performed on eleven of the most promising in silico compounds to evaluate: (i) their efficacy in inhibiting cell infection by SARS-CoV-2 (using the Vero CCL-81 cell line as a model), (ii) their impact on ACE2 expression (in the Vero CCL-81 and MDA-MB-231 cell lines), and (iii) their cytotoxicity in a human lung cell line (A549). We identified five synthetic compounds with the potential to block SARS-CoV-2 infection, three of them without relevant toxicity in human lung cells. Xanthene 1 stood out as the most promising anti-SARS-CoV-2 agent, inhibiting viral infection and viral replication in Vero CCL-81 cells, without causing cytotoxicity to human lung cells.

Gallic acid derivatives as inhibitors of mussel (Mytilus galloprovincialis) larval settlement: Lead optimization, biological evaluation and use in antifouling coatings.

The addition of biocides to marine coatings has been the most used solution to avoid marine biofouling, however they are persistent, bioaccumulative, and toxic (PBT) to marine ecosystems. The development of natural products or Nature-inspired synthetic compounds to replace these harmfull biocides has been pursued as one of the most promising antifouling (AF) alternatives. Following a bioprospection strategy, we have previously reported the AF activity of gallic acid persulfate (1) against the settlement of Mytilus galloprovincialis larvae (EC50 = 18 µM and LC50/EC50 = 27) without exhibiting ecotoxicity to Artemia salina. In this work, a lead optimization strategy was applied to compound 1 in order to improve potency while maintaining a low ecotoxicity profile. In this direction, twenty-seven compounds were synthesized, from which eighteen were obtained for the first time. An AF screening was performed against the settlement of mussel M. galloprovincialis larvae and derivative 26, 2-(3,4,5-trihydroxybenzamido)ethan-1-aminium bromide, was found to be more potent (EC50 = 3 µM and LC50/EC50 = 73) than compound 1 and the biocide Econea® (EC50 = 4 µM). The potential impact on neurotransmission, and ecotoxicity against two non-target marine organisms was also evaluated. Marine polyurethane (PU)-based coatings containing compound 26 were prepared and lower adherence of mussel larvae was observed compared to compound 26 free PU-coatings. Studies concerning the leaching of compound 26 from the prepared coating were also conducted, and < 10% of this compound was detected after 45 days of submersion in water. Overall, we have optimized the potency against the settlement of mussels of our initial lead compound, not compromising the toxicity and compatibility with PU-based coatings.

Quantification of a Sulfated Marine-Inspired Antifouling Compound in Several Aqueous Matrices: Biodegradation Studies and Leaching Assays from Polydimethylsiloxane Coatings.

The development of marine-inspired compounds as non-toxic antifouling (AF) agents has been pursued in the last years. Sulfur is the third most common element in seawater. Sulfur is present in oxygenated seawater as sulfate anion (SO42-), which is the most stable combination of sulfur in seawater, and several promising AF secondary metabolites with sulfate groups have been described. However, sulfated compounds proved to be an analytical challenge to quantify by HPLC. Taking these facts into consideration, this work presents the development and validation of a method for the quantification of gallic acid persulfate (GAP) in seawater and ultrapure water matrix, based on hydrophilic interaction liquid chromatography (HILIC). This method was used to evaluate GAP stability following several abiotic and biotic degradation assays, and to quantify its release in seawater from room-temperature-vulcanizing polydimethylsiloxane commercial coating. GAP was very stable in several water matrices, even at different pH values and in the presence/absence of marine microorganisms and presented a leaching value lower than 0.5%. This work discloses HILIC as an analytical method to overcome the difficulties in quantifying sulfated compounds in water matrices and highlights the potential of GAP as a promising long-lasting coating.

Antifouling Marine Coatings with a Potentially Safer and Sustainable Synthetic Polyphenolic Derivative.

The development of harmless substances to replace biocide-based coatings used to prevent or manage marine biofouling and its unwanted consequences is urgent. The formation of biofilms on submerged marine surfaces is one of the first steps in the marine biofouling process, which facilitates the further settlement of macrofoulers. Anti-biofilm properties of a synthetic polyphenolic compound, with previously described anti-settlement activity against macrofoulers, were explored in this work. In solution this new compound was able to prevent biofilm formation and reduce a pre-formed biofilm produced by the marine bacterium, Pseudoalteromonas tunicata. Then, this compound was applied to a marine coating and the formation of P. tunicata biofilms was assessed under hydrodynamic conditions to mimic the marine environment. For this purpose, polyurethane (PU)-based coating formulations containing 1 and 2 wt.% of the compound were prepared based on a prior developed methodology. The most effective formulation in reducing the biofilm cell number, biovolume, and thickness was the PU-based coating containing an aziridine-based crosslinker and 2 wt.% of the compound. To assess the marine ecotoxicity impact of this compound, its potential to disrupt endocrine processes was evaluated through the modulation of two nuclear receptors (NRs), peroxisome proliferator-activated receptor γ (PPARγ), and pregnane X receptor (PXR). Transcriptional activation of the selected NRs upon exposure to the polyphenolic compound (10 µM) was not observed, thus highlighting the eco-friendliness towards the addressed NRs of this new dual-acting anti-macro- and anti-microfouling agent towards the addressed NRs.

New Chalcone-Triazole Hybrids with Promising Antimicrobial Activity in Multidrug Resistance Strains.

Resistance to antibiotics is an emerging problem worldwide, which leads to an increase in morbidity and mortality rates. Several mechanisms are attributed to bacterial resistance, overexpression of efflux pumps being one of the most prominent. As an attempt to develop new effective antimicrobial drugs, which could be able to act against resistant bacterial strains and considering the antimicrobial potential of flavonoids and triazolyl flavonoid derivatives, in particular chalcones, a small library of chalcone derivatives was synthesized and evaluated for its potential to act as antimicrobials and/or adjuvants in combination with antibiotics towards resistant bacteria. Although only compound 7 was able to act as antibacterial, compounds 1, 2, 4, 5, 7, and 9 revealed to be able to potentiate the activity of antibiotics in resistant bacteria. Moreover, five compounds (3, 5-8) demonstrated to be effective inhibitors of efflux pumps in Salmonella enterica serovar Typhimurium SL1344, and four compounds (1, 3, 7, and 10) showed higher ability than reserpine to inhibit biofilm formation of resistant Staphylococcus aureus 272123. Together, our results showed the potential of these compounds regarding reversion of bacterial resistance.

Derivatives of Trimethoxybenzoic Acid and Gallic Acid as Potential Efflux Pump Inhibitors: In Silico and In Vitro Studies.

The overexpression of efflux pumps is one of the strategies used by bacteria to resist antibiotics and could be targeted to circumvent the antibiotic crisis. In this work, a series of trimethoxybenzoic acid derivatives previously described as antifouling compounds was explored for potential antimicrobial activity and efflux pump (EP) inhibition. First, docking studies on the acridine resistance proteins A and B coupled to the outer membrane channel TolC (AcrAB-TolC) efflux system and a homology model of the quinolone resistance protein NorA EP were performed on 11 potential bioactive trimethoxybenzoic acid and gallic acid derivatives. The synthesis of one new trimethoxybenzoic acid derivative (derivative 13) was accomplished. To investigate the potential of this series of 11 derivatives as antimicrobial agents, and in reverting drug resistance, the minimum inhibitory concentration was determined on several strains (bacteria and fungi), and synergy with antibiotics and EP inhibition were investigated. Derivative 10 showed antibacterial activity against the studied strains, derivatives 5 and 6 showed the ability to inhibit EPs in the acrA gene inactivated mutant Salmonella enterica serovar Typhimurium SL1344, and 6 also inhibited EPs in Staphylococcus aureus 272123. Structure-activity relationships highlighted trimethoxybenzoic acid as important for EP inhibitory activity. Although further studies are necessary, these results show the potential of simple trimethoxybenzoic acid derivatives as a source of feasible EP inhibitors.

Impact of Tralopyril and Triazolyl Glycosylated Chalcone in Human Retinal Cells' Lipidome.

Antifouling (AF) coatings containing booster biocides are used worldwide as one of the most cost-effective ways to prevent the attachment of marine organisms to submerged structures. Nevertheless, many of the commercial biocides, such as Econea® (tralopyril), are toxic in marine environments. For that reason, it is of extreme importance that new efficient AF compounds that do not cause any harm to non-target organisms and humans are designed. In this study, we measured the half-maximal inhibitory concentration (IC50) of a promising nature-inspired AF compound, a triazolyl glycosylated chalcone (compound 1), in an immortalized human retinal pigment epithelial cell line (hTERT-RPE-1) and compared the results with the commercial biocide Econea®. We also investigated the effects of these biocides on the cellular lipidome following an acute (24 h) exposure using liquid chromatography quadrupole time-of-flight mass spectrometry (LC-Q-TOF/MS). Our results showed that compound 1 did not affect viability in hTERT-RPE-1 cells at low concentrations (1 µM), in contrast to Econea®, which caused a 40% reduction in cell viability. In total, 71 lipids were found to be regulated upon exposure to 10 µM of both compounds. Interestingly, both compounds induced changes in lipids involved in cell death, membrane modeling, lipid storage, and oxidative stress, but often in opposing directions. In general, Econea® exposure was associated with an increase in lipid concentrations, while compound 1 exposure resulted in lipid depletion. Our study showed that exposure to human cells at sublethal Econea® concentrations results in the modulation of several lipids that are linked to cell death and survival.

Sulfated Oligomers of Tyrosol: Toward a New Class of Bioinspired Nonsaccharidic Anticoagulants.

Sulfated phenolic polymers have extensively been investigated as anticoagulant agents in view of their higher bioavailability and resistance to degradation compared to heparins, allowing for increased half-lives. In this frame, we report herein the preparation of sulfated derivatives of tyrosol, one of the most representative phenolic constituents of extra virgin olive oil, by different approaches. Mild sulfation of OligoTyr, a mixture of tyrosol oligomers, that has been reported to possess antioxidant properties and osteogenic activity, afforded OligoTyrS I in good yields. Elemental analysis, NMR, and MALDI-MS investigation provided evidence for an almost complete sulfation at the OH on the phenylethyl chain, leaving the phenolic OH free. Peroxidase/H2O2 oxidation of tyrosol sulfated at the alcoholic group (TyrS) also provided sulfated tyrosol oligomers (OligoTyrS II) that showed on structural analysis highly varied structural features arising likely from the addition of oxygen, derived from water or hydrogen peroxide, to the intermediate quinone methides and substantial involvement of the phenolic OH group in the oligomerization. In line with these characteristics, OligoTyrS I proved to be more active than OligoTyrS II as antioxidant in the 2,2-diphenyl-1-picrylhydrazyl (DPPH) and ferric reducing/antioxidant power (FRAP) assays and as anticoagulant in the classical clotting times, mainly in prolonging the activated partial thromboplastin time (APTT). After intraperitoneal administration in mice, OligoTyrS I was also able to significantly decrease the weight of an induced thrombus. Data from chromogenic coagulation assays showed that the anticoagulant effect of OligoTyrS I was not dependent on antithrombin or factor Xa and thrombin direct inhibition. These results clearly highlight how some structural facets of even closely related phenol polymers may be critical in dictating the anticoagulant activity, providing the key for the rationale design of active synthetic nonsaccharidic anticoagulant agents alternative to heparin.

Natural Benzo/Acetophenones as Leads for New Synthetic Acetophenone Hybrids Containing a 1,2,3-Triazole Ring as Potential Antifouling Agents.

Marine biofouling is a natural process that represents major economic, environmental, and health concerns. Some booster biocides have been used in biofouling control, however, they were found to accumulate in environmental compartments, showing negative effects on marine organisms. Therefore, it is urgent to develop new eco-friendly alternatives. Phenyl ketones, such as benzophenones and acetophenones, have been described as modulators of several biological activities, including antifouling activity (AF). In this work, acetophenones were combined with other chemical substrates through a 1,2,3-triazole ring, a strategy commonly used in Medicinal Chemistry. In our approach, a library of 14 new acetophenone-triazole hybrids was obtained through the copper(I)-catalyzed alkyne-azide cycloaddition "click" reaction. All of the synthesized compounds were evaluated against the settlement of a representative macrofouling species, Mytilus galloprovincialis, as well as on biofilm-forming marine microorganisms, including bacteria and fungi. The growth of the microalgae Navicula sp. was also evaluated after exposure to the most promising compounds. While compounds 6a, 7a, and 9a caused significant inhibition of the settlement of mussel larvae, compounds 3b, 4b, and 7b were able to inhibit Roseobacter litoralis bacterial biofilm growth. Interestingly, acetophenone 7a displayed activity against both mussel larvae and the microalgae Navicula sp., suggesting a complementary action of this compound against macro- and microfouling species. The most potent compounds (6a, 7a, and 9a) also showed to be less toxic to the non-target species Artemia salina than the biocide Econea®. Regarding both AF potency and ecotoxicity activity evaluation, acetophenones 7a and 9a were put forward in this work as promising eco-friendly AF agents.

From Natural Xanthones to Synthetic C-1 Aminated 3,4-Dioxygenated Xanthones as Optimized Antifouling Agents.

Biofouling, which occurs when certain marine species attach and accumulate in artificial submerged structures, represents a serious economic and environmental issue worldwide. The discovery of new non-toxic and eco-friendly antifouling systems to control or prevent biofouling is, therefore, a practical and urgent need. In this work, the antifouling activity of a series of 24 xanthones, with chemical similarities to natural products, was exploited. Nine (1, 2, 4, 6, 8, 16, 19, 21, and 23) of the tested xanthones presented highly significant anti-settlement responses at 50 µM against the settlement of mussel Mytilus galloprovincialis larvae and low toxicity to this macrofouling species. Xanthones 21 and 23 emerged as the most effective larval settlement inhibitors (EC50 = 7.28 and 3.57 µM, respectively). Additionally, xanthone 23 exhibited a therapeutic ratio (LC50/EC50) > 15, as required by the US Navy program attesting its suitability as natural antifouling agents. From the nine tested xanthones, none of the compounds were found to significantly inhibit the growth of the marine biofilm-forming bacterial strains tested. Xanthones 4, 6, 8, 16, 19, 21, and 23 were found to be non-toxic to the marine non-target species Artemia salina (<10% mortality at 50 µM). Insights on the antifouling mode of action of the hit xanthones 21 and 23 suggest that these two compounds affected similar molecular targets and cellular processes in mussel larvae, including that related to mussel adhesion capacity. This work exposes for the first time the relevance of C-1 aminated xanthones with a 3,4-dioxygenated pattern of substitution as new non-toxic products to prevent marine biofouling.

Multidimensional characterization of a new antifouling xanthone: Structure-activity relationship, environmental compatibility, and immobilization in marine coatings.

The accumulation of marine biofouling on ship hulls causes material damage, the spread of invasive species, and, indirectly, an increase in full consumption and subsequent pollutant gas emissions. Most efficient antifouling (AF) strategies rely on the conventional release of persistent, bioaccumulative, and toxic biocides incorporated in marine coatings. A simple oxygenated xanthone, 3,4-dihydroxyxanthone (1), was previously reported as a promising AF agent toward the settlement of Mytilus galloprovincialis larvae, with a therapeutic ratio higher than the commercial biocide Econea®. In this work, a structure-AF activity relationship study, an evaluation of environmental fate, and an AF efficiency in marine coatings were performed with compound 1. Hydroxy or methoxy groups at 3 and 4 positions in compound 1 favored AF activity, and groups with higher steric hindrances were detrimental. Compound 1 demonstrated low water-solubility and a short half-life in natural seawater, contrary to Econea®. In silico environmental fate predictions showed that compound 1 does not bioaccumulate in organism tissues, in contrast to other current emerging biocides, has a moderate affinity for sediments and slow migrates to ground water. No toxicity was observed against Vibrio fischeri and Phaeodactylum tricornutum. Polyurethane-based marine coatings containing compound 1 prepared through an innovative non-release-strategy were as efficient as those containing Econea® with low releases to water after 45 days. This proof-of-concept helped to establish compound 1 as a promising eco-friendly AF agent.

Small Molecules of Marine Origin as Potential Anti-Glioma Agents.

Marine organisms are able to produce a plethora of small molecules with novel chemical structures and potent biological properties, being a fertile source for discovery of pharmacologically active compounds, already with several marine-derived agents approved as drugs. Glioma is classified by the WHO as the most common and aggressive form of tumor on CNS. Currently, Temozolomide is the only chemotherapeutic option approved by the FDA even though having some limitations. This review presents, for the first time, a comprehensive overview of marine compounds described as anti-glioma agents in the last decade. Nearly fifty compounds were compiled in this document and organized accordingly to their marine sources. Highlights on the mechanism of action and ADME properties were included. Some of these marine compounds could be promising leads for the discovery of new therapeutic alternatives for glioma treatment.

Recent Advances in Bioactive Flavonoid Hybrids Linked by 1,2,3-Triazole Ring Obtained by Click Chemistry.

As a result of the biological activities of natural flavonoids, several synthetic strategies aiming to obtain analogues with improved potency and/or pharmacokinetic profile have been developed. Since the triazole ring has been associated with several biological activities and metabolic stability, hybridization with a 1,2,3-triazole ring has been increasingly reported over the last years. The feasible synthesis through copper (I) catalyzed azide-alkyne cycloaddition (CuAAC) has allowed the accomplishment of several hybrids. Since 2017, almost 700 flavonoid hybrids conjugated with 1,2,3-triazole, including chalcones, flavones, flavanones and flavonols, among others, with antitumor, antimicrobial, antidiabetic, neuroprotective, anti-inflammatory, antioxidant, and antifouling activity have been reported. This review compiles the biological activities recently described for these hybrids, highlighting the mechanism of action and structure-activity relationship (SAR) studies.

From Natural Products to New Synthetic Small Molecules: A Journey through the World of Xanthones.

This work reviews the contributions of the corresponding author (M.M.M.P.) and her research group to Medicinal Chemistry concerning the isolation from plant and marine sources of xanthone derivatives as well as their synthesis, biological/pharmacological activities, formulation and analytical applications. Although her group activity has been spread over several chemical families with relevance in Medicinal Chemistry, the main focus of the investigation and research has been in the xanthone family. Xanthone derivatives have a variety of activities with great potential for therapeutic applications due to their versatile framework. The group has contributed with several libraries of xanthones derivatives, with a variety of activities such as antitumor, anticoagulant, antiplatelet, anti-inflammatory, antimalarial, antimicrobial, hepatoprotective, antioxidant, and multidrug resistance reversal effects. Besides therapeutic applications, our group has also developed xanthone derivatives with analytical applications as chiral selectors for liquid chromatography and for maritime application as antifouling agents for marine paints. Chemically, it has been challenging to afford green chemistry methods and achieve enantiomeric purity of chiral derivatives. In this review, the structures of the most significant compounds will be presented.