Caged Garcinia Xanthones, a Novel Chemical Scaffold with Potent Antimalarial Activity

Caged xanthone derivatives to promote mitochondria-mediated apoptosis in breast cancer cells

Caged xanthones represent a class of natural secondary metabolites exhibiting significant potential as antitumor agents. These compounds are characterized by their distinct cage-like structures, which offer novel and compelling frameworks for drug design. Nonetheless, there exists a dearth of research focused on the structural modification of these compounds, particularly in relation to their cage-like architectures. This study aims to address this gap by introducing an innovative synthetic method for constructing a novel caged structure that incorporates a widely employed maleimide group. Drawing upon the well-established synthetic approach for dihydroxanthones previously developed within our research group, we successfully synthesized 13 new caged xanthones using the Diels-Alder reaction. Subsequently, we evaluated their anti-proliferative activity against HepG2, A549, and MDA-MB-231 cell lines. The results revealed that compound 10i exhibited IC50 values of 15.86 µM ± 1.29, 19.27 µM ± 1.58, and 12.96 µM ± 0.09 against these cell lines, respectively. Further investigations into the mechanism of action of 10i demonstrated its ability to induce G2/M cell cycle arrest and initiate mitochondria-mediated apoptosis in breast cancer cells.

Antimicrobial potential of quaternary phosphonium salt compounds: a review

Given that mitochondrial dysregulation is a biomarker of many cancers, cationic quaternary phosphonium salt (QPS) conjugation is a widely utilized strategy for anticancer drug design. QPS-conjugated compounds exhibit greater cell permeation and accumulation in negatively charged mitochondria, and thus, show enhanced activity. Phylogenetic similarities between mitochondria and bacteria have provided a rationale for exploring the antibacterial properties of mitochondria-targeted compounds. Additionally, due to the importance of mitochondria in the survival of pathogenic microbes, including fungi and parasites, this strategy can be extended to these organisms as well. This review examines recent literature on the antimicrobial activities of various QPS-conjugated compounds and provides future directions for exploring the medicinal chemistry of these compounds.

Title: A Comprehensive Review on Classifying Fast-acting and Slow-acting Antimalarial Agents Based on Time of Action and Target Organelle of Plasmodium sp

The clinical resistance towards malarial parasites has rendered many antimalarials ineffective, likely due to a lack of understanding of time of action and stage specificity of all life stages. Therefore, to tackle this problem a more incisive comprehensive analysis of the fast and slow-acting profile of antimalarial agents relating to parasite time-kill kinetics and the target organelle on the progression of blood-stage parasites was carried out. It is evident from numerous findings that drugs targeting food vacuole, nuclear components, and endoplasmic reticulum mainly exhibit a fast-killing phenotype within 24h affecting first-cycle activity. Whereas drugs targeting mitochondria, apicoplast, microtubules, parasite invasion and egress exhibit a largely slow-killing phenotype within 96-120h, affecting second-cycle activity with few exemptions as moderately fast-killing. It is essential to understand the susceptibility of drugs on rings, trophozoites, schizonts, merozoites, and the appearance of organelle at each stage of 48h intraerythrocytic parasite cycle. Therefore, these parameters may facilitate the paradigm for understanding the timing of antimalarials action in deciphering its precise mechanism linked with time. Thus, classifying drugs based on the time of killing may promote designing new combination regimens against varied strains of P. falciparum and evaluating potential clinical resistance.

Antibacterial activities of plant-derived xanthones

The increasing threat to global health posed by antibiotic resistance remains a serious concern. This troublesome scenario has steered a need for the discovery and evaluation of novel antibacterial agents. Natural products are the main sources of antimicrobials used in clinical practice, serving as a rich reservoir for the discovery of new antibiotics. Pharmaceutical phenolics especially xanthones widely exist in the plant kingdom, and are important plant metabolites. They possess versatile biological activities, including antiviral, antibacterial, neurotrophic, and anticancer. In the present study, we focus on the antibacterial activities of phytoxanthones and summarize their structures and sources, categories and drug-likeness evaluations, and antibacterial activities. A total of 226 different plant xanthones are identified through the NETs screening, and most of them are distributed in Clusiaceae family. These phytoxanthones are divided into four groups according to the intrinsic structural properties, including the most common simple xanthones and the majority of biprenylated ones. Moreover, their physicochemical parameters are calculated and the structure-activity relationships are discussed as well. These results indicate that the biprenylated xanthone derivatives may be promising antibacterial candidates and that the natural products of plants may be a poorly understood repository for the discovery of novel antibacterial agents.

Antimalarial Natural Products

Natural products have made a crucial and unique contribution to human health, and this is especially true in the case of malaria, where the natural products quinine and artemisinin and their derivatives and analogues, have saved millions of lives. The need for new drugs to treat malaria is still urgent, since the most dangerous malaria parasite, Plasmodium falciparum, has become resistant to quinine and most of its derivatives and is becoming resistant to artemisinin and its derivatives. This volume begins with a short history of malaria and follows this with a summary of its biology. It then traces the fascinating history of the discovery of quinine for malaria treatment and then describes quinine's biosynthesis, its mechanism of action, and its clinical use, concluding with a discussion of synthetic antimalarial agents based on quinine's structure. The volume then covers the discovery of artemisinin and its development as the source of the most effective current antimalarial drug, including summaries of its synthesis and biosynthesis, its mechanism of action, and its clinical use and resistance. A short discussion of other clinically used antimalarial natural products leads to a detailed treatment of other natural products with significant antiplasmodial activity, classified by compound type. Although the search for new antimalarial natural products from Nature's combinatorial library is challenging, it is very likely to yield new antimalarial drugs. The chapter thus ends by identifying over ten natural products with development potential as clinical antimalarial agents.

A Photoalkylative Fluorogenic Probe of Guttiferone A for Live Cell Imaging and Proteome Labeling in Plasmodium falciparum

Guttiferone A (GA) 1, a polycyclic polyprenylated acylphloroglucinol (PPAP) isolated from the plant Symphonia globulifera (Clusiaceae), constitutes a novel hit in antimalarial drug discovery. PPAPs do not possess identified biochemical targets in malarial parasites up to now. Towards this aim, we designed and evaluated a natural product-derived photoactivatable probe AZC-GA 5, embedding a photoalkylative fluorogenic motif of the 7-azidocoumarin (AZC) type, devoted to studying the affinity proteins interacting with GA in Plasmodium falciparum. Probe 5 manifested a number of positive functional and biological features, such as (i) inhibitory activity in vitro against P. falciparum blood-stages that was superimposable to that of GA 1, dose–response photoalkylative fluorogenic properties (ii) in model conditions using bovine serum albumin (BSA) as an affinity protein surrogate, (iii) in live P. falciparum-infected erythrocytes, and (iv) in fresh P. falciparum cell lysate. Fluorogenic signals by photoactivated AZC-GA 5 in biological settings were markedly abolished in the presence of excess GA 1 as a competitor, indicating significant pharmacological specificity of the designed molecular probe relative to the native PPAP. These results open the way to identify the detected plasmodial proteins as putative drug targets for the natural product 1 by means of proteomic analysis.

Antiplasmodial natural products: an update

Background

Malaria remains a significant public health challenge in regions of the world where it is endemic. An unprecedented decline in malaria incidences was recorded during the last decade due to the availability of effective control interventions, such as the deployment of artemisinin-based combination therapy and insecticide-treated nets. However, according to the World Health Organization, malaria is staging a comeback, in part due to the development of drug resistance. Therefore, there is an urgent need to discover new anti-malarial drugs. This article reviews the literature on natural products with antiplasmodial activity that was reported between 2010 and 2017.

Methods

Relevant literature was sourced by searching the major scientific databases, including Web of Science, ScienceDirect, Scopus, SciFinder, Pubmed, and Google Scholar, using appropriate keyword combinations.

Results and Discussion

A total of 1524 compounds from 397 relevant references, assayed against at least one strain of Plasmodium, were reported in the period under review. Out of these, 39% were described as new natural products, and 29% of the compounds had IC₅₀ ≤ 3.0 µM against at least one strain of Plasmodium. Several of these compounds have the potential to be developed into viable anti-malarial drugs. Also, some of these compounds could play a role in malaria eradication by targeting gametocytes. However, the research into natural products with potential for blocking the transmission of malaria is still in its infancy stage and needs to be vigorously pursued.

Synthetic Chiral Derivatives of Xanthones: Biological Activities and Enantioselectivity Studies

Many naturally occurring xanthones are chiral and present a wide range of biological and pharmacological activities. Some of them have been exhaustively studied and subsequently, obtained by synthesis. In order to obtain libraries of compounds for structure activity relationship (SAR) studies as well as to improve the biological activity, new bioactive analogues and derivatives inspired in natural prototypes were synthetized. Bioactive natural xanthones compromise a large structural multiplicity of compounds, including a diversity of chiral derivatives. Thus, recently an exponential interest in synthetic chiral derivatives of xanthones (CDXs) has been witnessed. The synthetic methodologies can afford structures that otherwise could not be reached within the natural products for biological activity and SAR studies. Another reason that justifies this trend is that both enantiomers can be obtained by using appropriate synthetic pathways, allowing the possibility to perform enantioselectivity studies. In this work, a literature review of synthetic CDXs is presented. The structures, the approaches used for their synthesis and the biological activities are described, emphasizing the enantioselectivity studies.

Ceric Ammonium Sulfate (CAS) Mediated Oxidations of Benzophenones Possessing a Phenolic Substituent for the Synthesis of Xanthones and Related Products

Work previously published by our group described novel methodology for the synthesis of xanthones and related products from phenolic benzophenones in a reaction mediated by ceric ammonium sulfate (CAS). In this paper we further explore this novel reaction by subjecting an additional set of phenolic benzophenones to CAS to afford a range of compounds, including xanthones, 9 H-xanthen-2,9(4a H)-diones, 3 H-spiro[benzofuran-2,1'-cyclohexa[2,5]diene]-3,4'-diones, and biaryl compounds. A comparison of these reactions with the more commonly used oxidant ceric ammonium nitrate (CAN) was also conducted. Based on these results, greater insight into the reaction mechanism has been gained. In addition, the conversion of the synthesized xanthen-2,9(4a H)-diones to xanthones by treatment with sodium dithionite is described.

Indolylalkyltriphenylphosphonium Analogues Are Membrane-Depolarizing Mycobactericidal Agents

Agents that selectively target the mycobacterial membrane could potentially shorten treatment time for tuberculosis, reduce relapse, and curtail emergence of resistant strains. The lipophilicity and extensive charge-delocalized state of the triphenylphosphonium cation strongly favor accumulation within bacterial membranes. Here, we explored the antimycobacterial activities and membrane-targeting properties of indolylalkyltriphenylphosphonium analogues. The most active analogues preferentially inhibited growth of Mycobacterium tuberculosis H37Rv (MIC₅₀ 2-4 μM) and were bactericidal against Mycobacterium bovis BCG (MBC₉₉ 3 μM). In spite of their propensity to accumulate within membranes, we found no evidence that these compounds permeabilized mycobacterial membranes or induced cell-envelope stress. Our investigations indicated that their bacterical effects stem from sustained depolarization of mycobacterial membranes and ensuing disruptive effects on electron transfer and cell division.