Synthesis, Anticancer Activity, and Docking Studies of Novel Hydroquinone-Chalcone-Pyrazoline Hybrid Derivatives

A novel series of antitumor hybrids was synthesized using 1,4-benzohydroquinone and chalcone, furane, or pyrazoline scaffolds. This were achieved through isosteric substitution of the aryl group of the chalcone β-carbon with the furanyl moiety and structural modification of the α,β-unsaturated carbonyl system. The potential antitumor activity of these hybrids was evaluated in vivo on MCF-7 breast adenocarcinoma and HT-29 colorectal carcinoma cells, demonstrating cytotoxic activity with IC50 values ranging from 28.8 to 124.6 µM. The incorporation of furan and pyrazoline groups significantly enhanced antiproliferative properties compared to their analogues and precursors (VII-X), which were inactive against both neoplastic cell lines. Compounds 4, 5, and 6 exhibited enhanced cytotoxicity against both cell lines, whereas compound 8 showed higher cytotoxic activity against HT-29 cells. Molecular docking studies revealed superior free-energy values (ΔGbin) for carcinogenic pathway-involved kinase proteins, with our in silico data suggesting that these derivatives could be promising chemotherapeutic agents targeting kinase pathways. Among all the synthesized PIBHQ compounds, derivatives 7 and 8 exhibited the best drug-likeness properties, with values of 0.53 and 0.83, respectively. ADME results collectively suggest that most of these compounds hold promise as potential candidates for preclinical assays.

Genome Mining of a Deep-Sea-Derived Penicillium allii-sativi Revealed Polyketide-Terpenoid Hybrids with Antiosteoporosis Activity

Two novel meroterpenoids, alliisativins A and B (1, 2) were discovered through a genome-based exploration of the biosynthetic gene clusters of the deep-sea-derived fungus Penicillium allii-sativi MCCC entry 3A00580. Extensive spectroscopic analysis, quantum calculations, chemical derivatization, and biogenetic considerations were utilized to establish their structures. Alliisativins A and B (1, 2) possess a unique carbon skeleton featuring a drimane sesquiterpene with a highly oxidized polyketide. Noteworthily, alliisativin A (1) showed dual activity in promoting osteogenesis and inhibiting osteoclast, indicating an antiosteoporosis potential.

Quinones from Cordia species from 1972 to 2023: isolation, structural diversity and pharmacological activities

Plants of the genus Cordia (Boraginaceae family) are widely distributed in the tropical regions of America, Africa, and Asia. They are extensively used in folk medicine due to their rich medicinal properties. This review presents a comprehensive analysis of the isolation, structure, biogenesis, and biological properties of quinones from Cordia species reported from 1972 to 2023. Meroterpenoids were identified as the major quinones in most Cordia species and are reported as a chemotaxonomic markers of the Cordia. In addition to this property, quinones are reported to display a wider and broader spectrum of activities, are efficient scaffold in biological activity, compared to other classes of compounds reported in Cordia, hence our focus on the study of quinones reported from Cordia species. About 70 types of quinones have been isolated, while others have been identified by phytochemical screening or gas chromatography. Although the biosynthesis of quinones from Cordia species is not yet fully understood, previous reports suggest that they may be derived from geranyl pyrophosphate and an aromatic precursor unit, followed by oxidative cyclization of the allylic methyl group. Studies have demonstrated that quinones from this genus exhibit antifungal, larvicidal, antileishmanial, anti-inflammatory, antibiofilm, antimycobacterial, antioxidant, antimalarial, neuroinhibitory, and hemolytic activities. In addition, they have been shown to exhibit remarkable cytotoxic effects against several cancer cell lines which is likely related to their ability to inhibit electron transport as well as oxidative phosphorylation, and generate reactive oxygen species (ROS). Their biological activities indicate potential utility in the development of new drugs, especially as active components in drug-carrier systems, against a broad spectrum of pathogens and ailments.

A Review of Phytochemicals and Bioactive Properties in the Proteaceae Family: A Promising Source of Functional Food

In recent decades, natural plant-based foods have been increasingly used to improve human health due to unhealthy modern dietary patterns, such as the consumption of foods high in sugar and fat. Many indigenous species have been used by Aboriginal peoples for their food and therapeutic properties. Thus, it is important to understand the health-enhancing bioactive profile of Australian indigenous species. The Proteaceae family, such as the genera of Protea, Macadamia, and Grevillea, have been commercially used in the horticulture and food industries. Researchers have reported some findings about Persoonia species, one of the genera in the Proteaceae family. The aim of this review was to provide an overview of the family Proteaceae and the genus Persoonia, including distribution, traditional and commercial uses, phytochemicals, bioactive properties, potential opportunities, and challenges. In this review, bioactive compounds and their properties related to the health benefits of the Proteaceae family, particularly the Persoonia genus, were reviewed for potential applications in the food industry.

Metal-Free C-H Sulfamidation of 1,4-Naphthoquinone in Water

Direct sulfamidation of 1,4-naphthoquinones using N-methoxy sulfonamides under metal-free conditions in water was developed. Base-mediated nucleophilic addition of N-methoxy sulfonamides, followed by N-O bond cleavage allowed the formation of enesulfonamides. Further, the synthesis of pyrrolonaphthoquinones proved the practicability of the current approach.

Asymmetric Formal Coupling of β-Ketoesters with Quinones Promoted by a Chiral Bifunctional N-Heterocyclic Olefin

A highly enantioselective formal coupling of β-ketoesters with quinones was accomplished by a chiral bifunctional N-heterocyclic olefin organocatalyst. With as low as 1 mol % catalyst loading, a number of enantioenriched quinone derivatives were afforded in good yields with high enantioselectivities and regioselectivities (up to 96% yield, 98% ee, and 19:1 rr). Gram-scale synthesis and the high inhibitory effect of several products on the viability of cancer cells demonstrate the potential utility of the current method.

Discovery of Novel Naphthoquinone-Chalcone Hybrids as Potent FGFR1 Tyrosine Kinase Inhibitors: Synthesis, Biological Evaluation, and Molecular Modeling

This work presents a flexible synthesis of 10 novel naphthoquinone-chalcone derivatives (1-10) by nucleophilic substitution of readily accessible aminochalcones and 2,3-dichloro-1,4-naphthoquinone. All compounds displayed broad-spectrum cytotoxic activities against all the tested cancer cell lines (i.e., HuCCA-1, HepG2, A549, MOLT-3, T47D, and MDA-MB-231) with IC50 values in the range of 0.81-62.06 μM, especially the four most potent compounds 1, 3, 8, and 9. The in vitro investigation on the fibroblast growth factor receptor 1 (FGFR1) inhibitory effect indicated that eight derivatives (1-2, 4-5, and 7-10) were active FGFR1 inhibitors (IC50 = 0.33-3.13 nM) with more potency than that of the known FGFR1 inhibitor, AZD4547 (IC50 = 12.17 nM). Promisingly, compounds 5 (IC50 = 0.33 ± 0.01 nM), 9 (IC50 = 0.50 ± 0.04 nM), and 7 (IC50 = 0.85 ± 0.08 nM) were the three most potent FGFR1 inhibitors. Molecular docking, molecular dynamics simulations, and MM/GBSA-based free energy calculation revealed that the key amino acid residues involved in the binding of the compounds 5, 7, and 9 and the target FGFR1 protein were similar with those of the AZD4547 (i.e., Val492, Lys514, Ile545, Val561, Ala640, and Asp641). These findings revealed that the newly synthesized naphthoquinone-chalcone scaffold is a promising structural feature for an efficient inhibition of FGFR1.

Divergent Synthesis of Tetrasubstituted Phenols via [3 + 3] Cycloaddition Reaction of Vinyl Sulfoxonnium Ylides with Cyclopropenones

Two categories of tetrasubstituted phenols were prepared via the cycloaddition reaction of vinyl sulfoxonnium ylides with cyclopropenones in a switchable manner. Copper carbenoid was proposed as the active intermediate in the process of 2,3,4,5-tetrasubstituted phenols formation, while 2,3,5,6-tetrasubstituted phenols were generated via the direct [3 + 3] annulation of vinyl sulfoxonnium ylides with cyclopropenones under metal-free conditions. Further synthetic applications were also demonstrated.

Late-Stage Formal Double C-H Oxidation of Prenylated Molecules to Alkylidene Oxetanes and Azetidines by Strain-Enabled Cross-Metathesis

Prenylation is a ubiquitous late-stage modification in nature that often confers significantly improved bioactivity for secondary metabolites. While this lipophilic modification renders enhanced potency, the lipophilic tag(s) can diminish bioavailability and adversely alter drug transportation and metabolism. Thus, a functional-group-tolerant, mild, and selective late-stage C-H functionalization of prenyl tags would present a great potential in drug discovery programs but could also impact other fields, such as agrochemistry and chemical biology. Herein we report an exocyclic-strain-driven cross-metathesis reaction of prenyl tags, a formal double C-H oxidation protocol, that can be used for the selective late-stage derivatization of prenylated compounds and natural products. This methodology avoids the need for prefunctionalization of target molecules and affords ready access to an unprecedented library of oxo- and aza-prenylated complex molecules. Thus, in a broader context, this methodology extends late-stage functionalization beyond that available to nature.

In Silico Methodologies to Improve Antioxidants' Characterization from Marine Organisms

Marine organisms have been reported to be valuable sources of bioactive molecules that have found applications in different industrial fields. From organism sampling to the identification and bioactivity characterization of a specific compound, different steps are necessary, which are time- and cost-consuming. Thanks to the advent of the -omic era, numerous genome, metagenome, transcriptome, metatranscriptome, proteome and microbiome data have been reported and deposited in public databases. These advancements have been fundamental for the development of in silico strategies for basic and applied research. In silico studies represent a convenient and efficient approach to the bioactivity prediction of known and newly identified marine molecules, reducing the time and costs of "wet-lab" experiments. This review focuses on in silico approaches applied to bioactive molecule discoveries from marine organisms. When available, validation studies reporting a bioactivity assay to confirm the presence of an antioxidant molecule or enzyme are reported, as well. Overall, this review suggests that in silico approaches can offer a valuable alternative to most expensive approaches and proposes them as a little explored field in which to invest.

Neuroprotective Strategies for Stroke by Natural Products: Advances and Perspectives

Cerebral ischemic stroke is a disease with high prevalence and incidence. Its management focuses on rapid reperfusion with intravenous thrombolysis and endovascular thrombectomy. Both therapeutic strategies reduce disability, but the therapy time window is short, and the risk of bleeding is high. Natural products (NPs) have played a key role in drug discovery, especially for cancer and infectious diseases. However, they have made little progress in clinical translation and pose challenges to the treatment of stroke. Recently, with the investigation of precise mechanisms in cerebral ischemic stroke and the technological development of NP-based drug discovery, NPs are addressing these challenges and opening up new opportunities in cerebral stroke. Thus, in this review, we first summarize the structure and function of diverse NPs, including flavonoids, phenols, terpenes, lactones, quinones, alkaloids, and glycosides. Then we propose the comprehensive neuroprotective mechanism of NPs in cerebral ischemic stroke, which involves complex cascade processes of oxidative stress, mitochondrial damage, apoptosis or ferroptosis-related cell death, inflammatory response, and disruption of the blood-brain barrier (BBB). Overall, we stress the neuroprotective effect of NPs and their mechanism on cerebral ischemic stroke for a better understanding of the advances and perspective in NPs application that may provide a rationale for the development of innovative therapeutic regimens in ischemic stroke.

Comparative analysis of p-terphenylquinone and seriniquinone derivatives as reactive oxygen species-modulating agents

Quinones are widespread in plants, animals, insects, and microorganisms. Several anticancer agents contain quinone structures as critical parts to show remarkable potential and distinctive modes of actions. The purpose of this study was to investigate the structure-activity relationships of microbial quinones and their derivatives as anticancer agents. A series of p-terphenylquinone and seriniquinone derivatives were therefore prepared. Treatment of the synthesized quinones possessed antiproliferative activity on human leukemia HL-60 cells in a dose-dependent fashion. In addition, seriniquinone derivatives elevated cellular reactive oxygen species (ROS) levels, thereby triggering the ensuing apoptotic events. Our findings emphasize the excellent potential of seriniquinone derivatives as redox cycling-induced ROS-modulating anticancer agents.

Organophotoredox-catalyzed cyanoalkylation of 1,4-quinones

A visible-light-induced metal-free cyanoalkylation of 1,4-quinones under mild and redox-neutral conditions is described. This reaction proceeds at room temperature without the need of extra base or additive and is suitable for a variety of 1,4-quinones and differently substituted cyclobutanone oxime esters. Further transformation of cyano functionality to tetrazole and amine has also been demonstrated to showcase the advantage of this method to prepare drug-like molecules.

Discovery of Anilino-1,4-naphthoquinones as Potent EGFR Tyrosine Kinase Inhibitors: Synthesis, Biological Evaluation, and Comprehensive Molecular Modeling

Epidermal growth factor receptor (EGFR) has been recognized as one of the attractive targets for anticancer drug development. Herein, a set of anilino-1,4-naphthoquinone derivatives (3-18) was synthesized and investigated for their anticancer and EGFR inhibitory potentials. Among all tested compounds, three derivatives (3, 8, and 10) were selected for studying EGFR inhibitory activity (in vitro and in silico) due to their most potent cytotoxic activities against six tested cancer cell lines (i.e., HuCCA-1, HepG2, A549, MOLT-3, MDA-MB-231, and T47D; IC50 values = 1.75-27.91 μM), high selectivity index (>20), and good predicted drug-like properties. The experimental results showed that these three promising compounds are potent EGFR inhibitors with nanomolar IC50 values (3.96-18.64 nM). Interestingly, the most potent compound 3 bearing 4-methyl substituent on the phenyl ring displayed 4-fold higher potency than the known EGFR inhibitor, erlotinib. Molecular docking, molecular dynamics simulation, and MM/GBSA-based free energy calculation revealed that van der Waals force played a major role in the accommodations of compound 3 within the ATP-binding pocket of EGFR. Additionally, the 4-CH3 moiety of the compound was noted to be a key chemical feature contributing to the highly potent EGFR inhibitory activity via its formations of alkyl interactions with A743, K745, M766, and L788 residues as well as additional interactions with M766 and T790.

Fe-Catalyzed Radical Trifluoromethyl-Alkenylation of Alkenes or Alkynes with 2-Amino-1,4-naphthoquinones

The first Fe-catalyzed three-component radical trifluoromethyl-alkenylation of alkenes with 2-amino-1,4-naphthoquinones and CF₃SO₂Na is reported. The developed reaction enables the highly regioselective preparation of a variety of valuable CF₃-substituted 1,4-naphthoquinones in acceptable yields. In the light of the catalytic system, alkynes smoothly afford the corresponding three- or four-component trifluoromethyl-alkenylation products. This protocol features use of easily available and inexpensive reagents, broad substrate scope, and simple reaction conditions.

Antifungal Activity and In Silico Studies on 2-Acylated Benzo- and Naphthohydroquinones

The high rates of morbidity and mortality due to fungal infections are associated with a limited antifungal arsenal and the high toxicity of drugs. Therefore, the identification of novel drug targets is challenging due to the several resemblances between fungal and human cells. Here, we report the in vitro antifungal evaluation of two acylphenols series, namely 2-acyl-1,4-benzo- and 2-acyl-1,4-naphthohydroquinones. The antifungal properties were assessed on diverse Candida and filamentous fungi strains through the halo of inhibition (HOI) and minimal inhibitory concentration (MIC). The antifungal activities of 2-acyl-1,4-benzohydroquinone derivatives were higher than those of the 2-acyl-1,4-naphthohydroquinone analogues. The evaluation indicates that 2-octanoylbenzohydroquinone 4 is the most active member of the 2-acylbenzohydroquinone series, with MIC values ranging from 2 to 16 μg/mL. In some fungal strains (i.e., Candida krusei and Rhizopus oryzae), such MIC values of compound 4 (2 and 4 μg/mL) were comparable to that obtained by amphotericin B (1 μg/mL). The compound 4 was evaluated for its antioxidant activity by means of FRAP, ABTS and DPPH assays, showing moderate activity as compared to standard antioxidants. Molecular docking studies of compound 4 and ADMET predictions make this compound a potential candidate for topical pharmacological use. The results obtained using the most active acylbenzohydroquinones are promising because some evaluated Candida strains are known to have decreased sensitivity to standard antifungal treatments.

Bioprospecting endophytic fungi for bioactive metabolites and use of irradiation to improve their bioactivities

The search for new bioactive compounds with innovative modes of action and chemistry are desperately needed to tackle the increased emergence of drug-resistant microbes. With this view, this paper was conducted for the isolation, identification, and biological evaluation of fungal endophytes of eleven different plant species. A total of 69 endophytic strains were isolated and tested for the presence of bioactive metabolites with antifungal, antibacterial, anticancer, and antioxidant properties in their extracts. Upon screening, two promising strains were found to have all the before-mentioned activities. These strains were Aspergillus sydowii isolated from the bark of Ricinus communis and Aspergillus flavus isolated from the twigs of Psidium guajava. Major compounds present in extracts of the two strains were identified by GC-Mass analyses. Several well-known bioactive compounds as well as unreported ones were identified in the fungal extracts of the two strains. Furthermore, gamma irradiation (at 1000 Gy) of the fungal cultures resulted in improved bioactivities of extracts from the two strains. These findings recommend the two fungal strains as sources of antimicrobial, anticancer, and antioxidant compounds which may aid in the development of novel drugs. The presented research also explains the high-value of fungal endophytes as untapped sources of bioactive metabolites.

Bioprospecting endophytic fungi for bioactive metabolites and use of irradiation to improve their bioactivities

The search for new bioactive compounds with innovative modes of action and chemistry are desperately needed to tackle the increased emergence of drug-resistant microbes. With this view, this paper was conducted for the isolation, identification, and biological evaluation of fungal endophytes of eleven different plant species. A total of 69 endophytic strains were isolated and tested for the presence of bioactive metabolites with antifungal, antibacterial, anticancer, and antioxidant properties in their extracts. Upon screening, two promising strains were found to have all the before-mentioned activities. These strains were Aspergillus sydowii isolated from the bark of Ricinus communis and Aspergillus flavus isolated from the twigs of Psidium guajava. Major compounds present in extracts of the two strains were identified by GC-Mass analyses. Several well-known bioactive compounds as well as unreported ones were identified in the fungal extracts of the two strains. Furthermore, gamma irradiation (at 1000 Gy) of the fungal cultures resulted in improved bioactivities of extracts from the two strains. These findings recommend the two fungal strains as sources of antimicrobial, anticancer, and antioxidant compounds which may aid in the development of novel drugs. The presented research also explains the high-value of fungal endophytes as untapped sources of bioactive metabolites.

Discovery of two promising fungal endophytes with divers’ range of bioactivities

Extracts of the two strains showed antimicrobial, anticancer, and antioxidant activities

Exposure to gamma rays at 1000 Gy significantly enhanced all the bioactivities.

In Vitro Antioxidant and Anticancer Properties of Various E. senegalensis Extracts

Although Erythrina senegalensis is a plant widely used in traditional medicine in sub-Saharan Africa, its biological properties have been poorly investigated to date. We first characterized by conventional reactions the composition of several stem bark extracts and evaluated in acellular and cellular assays their pro- or antioxidant properties supported by their high phenolic and flavonoid content, particularly with the methanolic extract. The pro- or antioxidant effects observed did not correlate with their IC₅₀ concentrations against five cancer cell lines determined by MTT assay. Indeed, the CH₂Cl₂ extract and its ethyl acetate (EtOAc) subfraction appeared more potent although they harbored lower pro- or antioxidant effects. Nevertheless, at equipotent concentration, both extracts induced ER- and mitochondria-derived vacuoles observed by fluorescent microscopy that further led to non-apoptotic cell death. LC coupled to high resolution MS investigations have been performed to identify chemical compounds of the extracts. These investigations highlighted the presence of compounds formerly isolated from E. senegalensis including senegalensein that could be retrieved only in the EtOAc subfraction but also thirteen other compounds, such as 16:3-Glc-stigmasterol and hexadecanoic acid, whose anticancer properties have been previously reported. Nineteen other compounds remain to be identified. In conclusion, E. senegalensis appeared rich in compounds with antioxidant and anticancer properties, supporting its use in traditional practice and its status as a species of interest for further investigations in anticancer drug research.

Fungal quinones: diversity, producers, and applications of quinones from Aspergillus, Penicillium, Talaromyces, Fusarium, and Arthrinium

Quinones represent an important group of highly structurally diverse, mainly polyketide-derived secondary metabolites widely distributed among filamentous fungi. Many quinones have been reported to have important biological functions such as inhibition of bacteria or repression of the immune response in insects. Other quinones, such as ubiquinones are known to be essential molecules in cellular respiration, and many quinones are known to protect their producing organisms from exposure to sunlight. Most recently, quinones have also attracted a lot of industrial interest since their electron-donating and -accepting properties make them good candidates as electrolytes in redox flow batteries, like their often highly conjugated double bond systems make them attractive as pigments. On an industrial level, quinones are mainly synthesized from raw components in coal tar. However, the possibility of producing quinones by fungal cultivation has great prospects since fungi can often be grown in industrially scaled bioreactors, producing valuable metabolites on cheap substrates. In order to give a better overview of the secondary metabolite quinones produced by and shared between various fungi, mainly belonging to the genera Aspergillus, Penicillium, Talaromyces, Fusarium, and Arthrinium, this review categorizes quinones into families such as emodins, fumigatins, sorbicillinoids, yanuthones, and xanthomegnins, depending on structural similarities and information about the biosynthetic pathway from which they are derived, whenever applicable. The production of these quinone families is compared between the different genera, based on recently revised taxonomy. KEY POINTS: • Quinones represent an important group of secondary metabolites widely distributed in important fungal genera such as Aspergillus, Penicillium, Talaromyces, Fusarium, and Arthrinium. • Quinones are of industrial interest and can be used in pharmacology, as colorants and pigments, and as electrolytes in redox flow batteries. • Quinones are grouped into families and compared between genera according to the revised taxonomy.

C-F bond activation under transition-metal-free conditions

The unique properties of fluorine-containing organic compounds make fluorine substitution attractive for the development of pharmaceuticals and various specialty materials, which have inspired the evolution of diverse C-F bond activation techniques. Although many advances have been made in functionalizations of activated C-F bonds utilizing transition metal complexes, there are fewer approaches available for nonactivated C-F bonds due to the difficulty in oxidative addition of transition metals to the inert C-F bonds. In this regard, using Lewis acid to abstract the fluoride and light/radical initiator to generate the radical intermediate have emerged as powerful tools for activating those inert C-F bonds. Meanwhile, these transition-metal-free processes are greener, economical, and for the pharmaceutical industry, without heavy metal residues. This review provides an overview of recent C-F bond activations and functionalizations under transition-metal-free conditions. The key mechanisms involved are demonstrated and discussed in detail. Finally, a brief discussion on the existing limitations of this field and our perspective are presented.

Seasonal Variation in Antimicrobial Activity of Crude Extracts of Psammaplysilla sp. 1 from Phillips Reef, South Africa

Marine invertebrates constitute a diverse group of marine organisms beneficial to humanity due to their therapeutic significance. The marine sponge species Psammaplysilla sp. 1 was collected from Philips Reef, South Africa, over a four-season period and assayed for antimicrobial potential. The physicochemical parameters of the collection site were also recorded. The sponge crude extracts' antimicrobial activity was evaluated using an agar well diffusion assay against 5 pathogens. Phytochemical screening was conducted to identify the presence of 7 critical phytochemical groups. During the four seasons, the mean water temperature was 17.35°C ± 2.06, with autumn recording the highest (20°C) temperature. Antifungal activity was observed by Psammaplysilla sp. 1 (30 mm) against C. albicans, and this was higher than that showed by standard drugs ICZ-10 µg (15 ± 0.1 mm), FLU-15 µg (21 ± 0.2 mm), and VCZ-5 µg (17 ± 0.1 mm), respectively. Similar bioactivities were observed seasonally with Psammaplysilla sp. 1 (22 mm and 24 mm) during autumn and spring, respectively, against C. difficile while only crude extracts collected in spring showed bioactivity against C. albicans. Psammaplysilla sp. crude extracts showed broad-spectrum bioactivity against all test pathogens. DCM : ME crude extracts tested positive for the presence of 2/7 of the phytochemicals (terpenoids and flavonoids). GC-MS revealed several previously reported biologically active compounds such bicyclo[4.2.0]octa-1,3,5-trien-7-ol and phenol, 2,6-dibromo, some of which have been found in plants. This study revealed that sponge bioactivity is dependent on the season and further validated the antimicrobial potential of South African marine sponges.

Cytotoxic Compounds of Two Demosponges (Aplysina aerophoba and Spongia sp.) from the Aegean Sea

The class of demosponges is the biggest and most diverse of all described sponge species and it is reported to produce a plethora of chemically different metabolites with interesting biological activities. The focus of the present study was to investigate the chemical composition of two Mediterranean demosponges, targeting their brominated compounds and prenylated hydroquinones, compounds with interesting cytotoxic and anti-microbial properties. In order to gain a deeper insight into the chemical diversity of their metabolites and their activities, 20 pure secondary metabolites including new natural products were isolated from two different species (Aplysina aerophoba and Spongia sp.) using various chromatographic techniques. Their structures were confirmed by NMR and HRMS, revealing molecules with various chemical scaffolds, mainly prenylated hydroquinones from Spongia sp. and halogenated compounds from Aplysina aerophoba, including 5 novel natural products. The isolated compounds were investigated for their cytotoxic properties using 9 different cell lines, and especially one compound, 2,6-dibromo-4-hydroxy-4-methoxycarbonylmethylcyclohexa-2,5-dien-1-one showed good activities in all tested models.

A new prenylated benzoquinone from Cyathocalyx pruniferus abrogates LPS-induced inflammatory responses associated with PGE2, COX-2 and cytokines biosynthesis in human plasma

In our previous laboratory findings, Cyathocalyx pruniferus extracts exhibited platelet-activating factor inhibition, suggesting their anti-inflammatory potential. Hence, this study was designed with the aim to isolate phyto-constituents from C. pruniferus with potent anti-inflammatory activities. Column and volume liquid chromatography were used for isolation of phyto-constituents. The structure elucidation was carried out using spectroscopic analysis (HRESI-MS, ¹H and ¹³C-NMR) and compared with published literature. For cytotoxicity analysis, 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium-bromide assay was performed on peripheral blood mononuclear cells. Anti-inflammatory activities were evaluated against the levels of inflammatory cytokines (IL-1β and IL-6), prostaglandin-E₂ (PGE₂) and cyclooxegenase-2 (COX-2), in lipopolysaccharide (LPS)-induced human plasma using ELISA and radioimmunoassay (RIA). The chromatographic purification of methanol leaves extract afforded 13 (1-13) secondary metabolites. Additionally, cytotoxicity analysis suggested that isolates were non-cytotoxic at 100 μM. In anti-inflammatory evaluation, 2-octaprenyl-1, 4-benzoquinone (5) produced strong (≥ 70%) inhibition of PGE₂, COX-2, IL-1β and IL-6 at 50 µM. Moreover, 2-octaprenyl-1,4-benzoquinone (5) exhibited concentration-dependent inhibition with IC₅₀ values (µM) of 11.21, 6.61, 2.20 and 3.56 as compared to controls; indomethacin for PGE₂ (11.84) and dexamethasone in COX-2 (5.19), IL-1β (1.83) and IL-6 (3.76) analysis, respectively. In conclusion, two new compounds including 2-octaprenyl-1, 4-benzoquinone (5) and 14-methyloctadec-1-ene (6) are reported for the first time from plant species. Additionally, 2-octaprenyl-1, 4-benzoquinone (5) dose-dependently suppressed the production of pro-inflammatory mediators involved in acute and chronic inflammation at non-cytotoxic concentrations.

Cytotoxic Naphthoquinone Analogues, Including Heterodimers, and Their Structure Elucidation Using LR-HSQMBC NMR Experiments

Approximately 1700 naphthoquinones have been reported from a range of natural product source materials, but only 283 have been isolated from fungi, fewer than 75 of those were dimers, and only 2 were heterodimers with a head-to-tail linkage. During a search for anticancer leads from fungi, a series of new naphthoquinones (1-4), including two heterodimers (3 and 4), were isolated from Pyrenochaetopsis sp. (strain MSX63693). In addition, the previously reported 5-hydroxy-6-(1-hydroxyethyl)-2,7-dimethoxy-1,4-naphthalenedione (5), misakimycin (6), 5-hydroxy-6-[1-(acetyloxy)ethyl]-2,7-dimethoxy-1,4-naphthalenedione (7), 6-ethyl-2,7-dimethoxyjuglone (8), and kirschsteinin (9) were isolated. While the structure elucidation of 1-9 was achieved using procedures common for natural products chemistry studies (high-resolution electrospray ionization mass spectrometry (HRESIMS), 1D and 2D NMR), the elucidation of the heterodimers was facilitated substantially by data from the long-range heteronuclear single quantum multiple bond correlation (LR-HSQMBC) experiment. The absolute configuration of 1 was established by analysis of the measured vs calculated ECD data. The racemic mixture of 4 was established via X-ray crystallography of an analogue that incorporated a heavy atom. All compounds were evaluated for cytotoxicity against the human cancer cells lines MDA-MB-435 (melanoma), MDA-MB-231 (breast), and OVCAR3 (ovarian), where the IC₅₀ values ranged between 1 and 20 μM.

Concise Syntheses of Violaceoids A and C

The concise syntheses of two alkylated hydroquinone natural products, violaceoids A and C, were accomplished by a protecting-group-free method employing the commercially available 2,5-dihydroxybenzaldehyde as the starting material. The key strategy of the syntheses is the utilization of alkenylboronic acid as both the coupling and temporary protective reagents to efficiently introduce the requisite alkenyl side chain of violaceoid A. Moreover, the synthesis of violaceoid C is reported here for the first time.

New Antineoplastic Naphthohydroquinones Attached to Labdane and Rearranged Diterpene Skeletons

Terpenylquinones are mixed biogenesis primary or secondary metabolites widespread in Nature with many biological activities, including the antineoplastic cytotoxicity, that have inspired this work. Here, we present a cytotoxic structure-activity relationship of several diterpenylhydroquinone (DTHQ) derivatives, obtained from the natural labdane diterpenoid myrceocommunic acid used as starting material. Different structural modifications, that changed the functionality and stereochemistry of the decalin, have been implemented on the bicyclic core through epoxidation, ozonolysis or decarboxylation, and through induction of biomimetic breaks and rearrangements of the diterpene skeleton. All the isomers generated were completely characterized by spectroscopic procedures. The resulting compounds have been tested in vitro on cultured cancer cells, showing their relevant antineoplastic cytotoxicity, with GI₅₀ values in the μM and sub-μM range. The rearranged compound 8 showed the best cytotoxic results, with GI₅₀ at the submicromolar range, retaining the cytotoxicity level of the parent compounds. In this report, the versatility of the labdane skeleton for chemical transformation and the interest to continue using structural modifications to obtain new bioactive compounds are demonstrated.

Chemical Diversity of Soft Coral Steroids and Their Pharmacological Activities

The review is devoted to the chemical diversity of steroids produced by soft corals and their determined and potential activities. There are about 200 steroids that belong to different types of steroids such as secosteroids, spirosteroids, epoxy- and peroxy-steroids, steroid glycosides, halogenated steroids, polyoxygenated steroids and steroids containing sulfur or nitrogen heteroatoms. Of greatest interest is the pharmacological activity of these steroids. More than 40 steroids exhibit antitumor and related activity with a confidence level of over 90 percent. A group of 32 steroids shows anti-hypercholesterolemic activity with over 90 percent confidence. Ten steroids exhibit anti-inflammatory activity and 20 steroids can be classified as respiratory analeptic drugs. Several steroids exhibit rather rare and very specific activities. Steroids exhibit anti-osteoporotic properties and can be used to treat osteoporosis, as well as have strong anti-eczemic and anti-psoriatic properties and antispasmodic properties. Thus, this review is probably the first and exclusive to present the known as well as the potential pharmacological activities of 200 marine steroids.

Reprogramming Substrate and Catalytic Promiscuity of Tryptophan Prenyltransferases

Prenylation is a process widely prevalent in primary and secondary metabolism, contributing to functionality and chemical diversity in natural systems. Due to their high regio- and chemoselectivities, prenyltransferases are also valuable tools for creation of new compounds by chemoenzymatic synthesis and synthetic biology. Over the last ten years, biochemical and structural investigations shed light on the mechanism and key residues that control the catalytic process, but to date crucial information on how certain prenyltransferases control regioselectivity and chemoselectivity is still lacking. Here, we advance a general understanding of the enzyme family by contributing the first structure of a tryptophan C5-prenyltransferase 5-DMATS. Additinally, the structure of a bacterial tryptophan C6-prenyltransferase 6-DMATS was solved. Analysis and comparison of both substrate-bound complexes led to the identification of key residues for catalysis. Next, site-directed mutagenesis was successfully implemented to not only modify the prenyl donor specificity but also to redirect the prenylation, thereby switching the regioselectivity of 6-DMATS to that of 5-DMATS. The general strategy of structure-guided protein engineering should be applicable to other related prenyltransferases, thus enabling the production of novel prenylated compounds.

Naphthoquinone-Based Meroterpenoids from Marine-Derived Streptomyces sp. B9173

Naphthoquinone-based meroterpenoids are hybrid polyketide-terpenoid natural products with chemical diversity and a broad range of biological activities. Here, we report the isolation of a group of naphthoquinone-containing compounds from Streptomyces sp. B9173, and their structures were elucidated by using a combination of spectroscopic techniques, including 1D, 2D NMR, and high-resolution mass (HRMS) analysis. Seven flaviogeranin congeners or intermediates, three of which were new, have been derived from common naphthoquinone backbone and subsequent oxidation, methylation, prenylation, and amino group incorporation. Both flaviogeranin B1 (1) and B (2) contain an amino group which was incorporated into the C8 of 1,3,6,8-terhydroxynaphthalene (THN). Flaviogeranin D (3) contains an intact C-geranylgeranyl residue attached to the C2 of THN, while the O-geranylgeranyl group of 2 links with the hydroxyl on the C2 site of THN. Four compounds were selected and tested for antibacterial activity and cytotoxicity, with 3 and flaviogeranin C2 (5) displaying potent activity against selected bacteria and cancer cell lines. In light of the structure features of isolated compounds and the biosynthetic genes, a biosynthetic pathway of naphthoquinone-based flaviogeranins has been proposed. These isolated compounds not only extend the structural diversity but also represent new insights into the biosynthesis of naphthoquinone-based meroterpenoids.

Fungal benzene carbaldehydes: occurrence, structural diversity, activities and biosynthesis

Covering: up to April 2020Fungal benzene carbaldehydes with salicylaldehydes as predominant representatives carry usually hydroxyl groups, prenyl moieties and alkyl side chains. They are found in both basidiomycetes and ascomycetes as key intermediates or end products of various biosynthetic pathways and exhibit diverse biological and pharmacological activities. The skeletons of the benzene carbaldehydes are usually derived from polyketide pathways catalysed by iterative fungal polyketide synthases. The aldehyde groups are formed by direct PKS releasing, reduction of benzoic acids or oxidation of benzyl alcohols.

Antitumoral compounds from vertebrate sister group: A review of Mediterranean ascidians

Among the diseases that afflict the human population, cancer is one for which many drug treatments are not yet known or effective. Moreover, the pharmacological treatments used often create serious side effects in sick patients and for this reason, it is essential to find effective and less harmful treatments. To date, marine biodiversity is a real source of metabolites with antitumoral activity and among invertebrates' ascidians have been the main source to obtain them. Mediterranean area is the richest in biodiversity and contains several ascidian species used in drugs development during the years. However, many more Mediterranean ascidian species have not been studied and could be a source of useful bioactive compounds. This review aims to summarize the scientific studies that analyzed the antitumor compounds obtained from different Mediterranean ascidians species, encouraging them to search further compounds in other new species to improve pharmacological treatments and human population life.

Norhierridin B, a New Hierridin B-Based Hydroquinone with Improved Antiproliferative Activity

Hierridin B (6), a methylated hydroquinone isolated from the marine picocyanobacterium Cyanobium sp. LEGE 06113, moderately inhibited the growth of colon adenocarcinoma HT-29 cells. Aiming to improve the potential antitumor activity of this natural product, the demethylated analogue, norhierridin B (10), as well as its structurally-related quinone (9), were synthesized and evaluated for their growth inhibitory effect on a panel of human tumor cell lines, including the triple-negative breast cancer (TNBC) cells MDA-MB-231, SKBR3, and MDA-MB-468. Norhierridin B (10) showed a potent growth inhibitory effect on all cancer cell lines. Moreover, the growth inhibitory effect of compound 10 on MDA-MB-231 cells was associated with cell cycle arrest and apoptosis. Norhierridin B (10) interfered with several p53 transcriptional targets, increasing p21, Bax, and MDM2, while decreasing Bcl-2 protein levels, which suggested the potential activation of a p53 pathway. Altogether, these results evidenced a great improvement of the antitumor activity of hydroquinone 10 when compared to 6 and its structurally-related quinone (9). Notably, hydroquinone 10 displayed a prominent growth inhibitory activity against TNBC cells, which are characterized by high therapeutic resistance.

Anticancer Activities of Meroterpenoids Isolated from the Brown Alga Cystoseira usneoides against the Human Colon Cancer Cells HT-29

Colorectal cancer (CRC) is one of the most common types of cancers and a leading cause of cancer death worldwide. The current treatment for CRC mainly involves surgery, radiotherapy, and chemotherapy. However, due to the side effects and the emergence of drug resistance, the search for new anticancer agents, pharmacologically safe and effective, is needed. In the present study, we have investigated the anticancer effects of eight algal meroterpenoids (AMTs, 1-8) isolated from the brown seaweed Cystoseira usneoides and their underlying mechanisms of action using HT-29, a highly metastatic human colon cancer cell line. All the tested meroterpenoids inhibited the growth of HT-29 malignant cells and were less toxic towards non-cancer colon cells, with the AMTs 1 and 5 exhibiting selectivity indexes of 5.26 and 5.23, respectively. Treatment of HT-29 cells with the AMTs 1, 2, 3, 4, 5, and 7 induced cell cycle arrest in G2/M phase and, in some instances, apoptosis (compounds 2, 3, and 5). Compounds 1-8 also exhibited significant inhibitory effects on the migration and/or invasion of colon cancer cells. Mechanistic analysis demonstrated that the AMTs 1, 2, 5, 6, 7, and 8 reduced phosphorylation levels of extracellular signal-regulated kinase (ERK) and the AMTs 2, 3, 4, 5, 7, and 8 decreased phosphorylation of c-JUN N-terminal kinase (JNK). Moreover, the AMTs 1, 2, 3, 4, 7, and 8 inhibited phosphorylation levels of protein kinase B (AKT) in colon carcinoma cells. These results provide new insights into the mechanisms and functions of the meroterpenoids of C. usneoides, which exhibit an anticancer effect on HT-29 colon cancer cells by inducing cell cycle arrest and apoptosis via the downregulation of ERK/JNK/AKT signaling pathways.

Transition metal-free cyclobutene rearrangement in fused naphthalen-1-ones: controlled access to functionalized quinones

The divergent preparation of 1,4-naphthoquinones and tetraphene-7,12-diones, which bear the ABCD-ring of landomycins, has been accomplished directly through oxidative reorganization of previously non-isolable cyclobuta[a]naphthalen-4(2H)-ones.

Metachromins X and Y from a marine sponge Spongia sp. and their effects on cell cycle progression

New sesquiterpene quinones, metachromins X (1) and Y (2), together with the known metachromins C (3), J (4), and T (5), were isolated as inhibitors of cell cycle progression in the HeLa/Fucci2 cells. The structure of 1 was assigned by spectroscopic data and confirmed by a total synthesis. The planar structure of 2 was determined by interpretation of spectroscopic data, whereas its absolute configuration was analyzed by a combination of chiral HPLC and CD spectroscopy. Metachromins X (1) and C (3) arrested the cell cycle progression of HeLa/Fucci2 cells at S/G2/M phase.

Monocyclic Quinone Structure-Activity Patterns: Synthesis of Catalytic Inhibitors of Topoisomerase II with Potent Antiproliferative Activity

The monocyclic 1,4-benzoquinone, HU-331, the direct oxidation product of cannabidiol, inhibits the catalytic activity of topoisomerase II but without inducing DNA strand breaks or generating free radicals, and unlike many fused-ring quinones exhibits minimal cardiotoxicity. Thus, monocyclic quinones have potential as anticancer agents, and investigation of the structural origins of their biological activity is warranted. New syntheses of cannabidiol and (±)-HU-331 are here reported. Integrated synthetic protocols afforded a wide range of polysubstituted resorcinol derivatives; many of the corresponding novel 2-hydroxy-1,4-benzoquinone derivatives are potent inhibitors of the catalytic activity of topoisomerase II, some more so than HU-331, whose monoterpene unit replaced by a 3-cycloalkyl unit conferred increased antiproliferative properties in cell lines with IC₅₀ values extending below 1 mM, and greater stability in solution than HU-331. The principal pharmacophore of quinones related to HU-331 was identified. Selected monocyclic quinones show potential for the development of new anticancer agents.

Naphthoquinone Tryptophan Hybrids: A Promising Small Molecule Scaffold for Mitigating Aggregation of Amyloidogenic Proteins and Peptides

A current challenge faced by researchers is the lack of disease-modifying therapeutics for amyloid formation that is associated with several human diseases. Although the monomeric proteins or peptides involved in various amyloidogenic diseases do not have amino acid sequence homology, there appears to be a structural correlation among the amyloid assemblies, which are responsible for distinct pathological conditions. Here, we review our work on Naphthoquinone Tryptophan (NQTrp) hybrids, a small molecule scaffold that can generically modulate neuronal and non-neuronal amyloid aggregation both in vitro and in vivo. NQTrp reduces the net amyloid load by inhibiting the process of amyloid formation and disassembling the pre-formed fibrils, both in a dose-dependent manner. As a plausible mechanism of action, NQTrp effectively forms hydrogen bonding and hydrophobic interactions, such as π-π stacking, with the vital residues responsible for the initial nucleation of protein/peptide aggregation. This review highlights the effectiveness of the NQTrp hybrid scaffold for developing novel small molecule modulators of amyloid aggregation.