Chemical and Biological Aspects of the Natural 1,4-Benzoquinone Embelin and its (semi-)Synthetic Derivatives

Unlocking Potentially Therapeutic Phytochemicals in Capadulla (Doliocarpus dentatus) from Guyana Using Untargeted Mass Spectrometry-Based Metabolomics

Doliocarpus dentatus is thought to have a wide variety of therapeutic phytochemicals that allegedly improve libido and cure impotence. Although a few biomarkers have been identified with potential antinociceptive and cytotoxic properties, an untargeted mass spectrometry-based metabolomics approach has never been undertaken to identify therapeutic biofingerprints for conditions, such as erectile dysfunction, in men. This study executes a preliminary phytochemical screening of the woody vine of two ecotypes of D. dentatus with renowned differences in therapeutic potential for erectile dysfunction. Liquid chromatography-mass spectrometry-based metabolomics was used to screen for flavonoids, terpenoids, and other chemical classes found to contrast between red and white ecotypes. Among the metabolite chemodiversity found in the ecotype screens, using a combination of GNPS, MS-DIAL, and SIRIUS, approximately 847 compounds were annotated at levels 2 to 4, with the majority of compounds falling under lipid and lipid-like molecules, benzenoids and phenylpropanoids, and polyketides, indicative of the contributions of the flavonoid, shikimic acid, and terpenoid biosynthesis pathways. Despite the extensive annotation, we report on 138 tentative compound identifications of potentially therapeutic compounds, with 55 selected compounds at a level-2 annotation, and 22 statistically significant therapeutic biomarkers, the majority of which were polyphenols. Epicatechin methyl gallate, catechin gallate, and proanthocyanidin A2 had the greatest significant differences and were also relatively abundant among the red and white ecotypes. These putatively identified compounds reportedly act as antioxidants, neutralizing damaging free radicals, and lowering cell oxidative stress, thus aiding in potentially preventing cellular damage and promoting overall well-being, especially for treating erectile dysfunction (ED).

Embelin and Its Derivatives: Design, Synthesis, and Potential Delivery Systems for Cancer Therapy

Embelin is a naturally occurring benzoquinone that inhibits the growth of cancer cells, making it a potent anticancer drug. However, the low water solubility of embelin restricts its clinical applicability. This review provides a concise summary and in-depth analysis of the published literature on the design and synthesis of embelin derivatives possessing increased aqueous solubility and superior therapeutic efficacy. In addition, the potential of drug delivery systems to improve the anticancer capabilities of embelin and its derivatives is discussed.

A comprehensive insight on the biological potential of embelin and its derivatives

Naturally occurring bioactive molecules are known for their diverse biological applications such as antimicrobial, anticancer, anti-inflammatory, and analgesic activities. Also, some of the natural products act as medicinal drugs. Further, bioactive cell-permeable molecule embelin has been reported for its diverse biological activities such as antimalarial, anticancer, and anti-inflammatory in the literature. With the continuation of our research work on biologically active molecules, based on structural activity relationship and docking studies of embelin and its derivatives, we have reported target-specific anticancer and antimalarial activities of embelin and its analogs. Also, it has been reported in many recent research articles that embelin and its derivatives are known to possess medicinal properties. This review mainly highlights recent reports on broad-spectrum biological activities of the embelin and its analogs to date.

Embelin's Versatile Photochemistry Makes It a Potent Photosensitizer for Photodynamic Therapy

Embelin, a natural product isolated from Embelia ribes, is a promising small-molecular drug for photodynamic anticancer therapy. Using modern quantum chemical methodology, embelin is shown to possess a versatile photochemistry comprising the capability of singlet oxygen generation, excited-state proton transfer, and oxidation. In particular, the detailed molecular mechanisms of singlet oxygen generation and proton transfer upon excitation are studied in great detail. While excited-state proton transfer can damage the protein itself, it also mediates intersystem crossing along its reaction pathway, thus facilitating singlet oxygen generation. When embelin is bound to proteins, all these processes can lead to protein damage and the desired phototoxicity.

Current Updates on Naturally Occurring Compounds Recognizing SARS-CoV-2 Druggable Targets

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been identified in China as the etiologic agent of the recent COVID-19 pandemic outbreak. Due to its high transmissibility, this virus quickly spread throughout the world, causing considerable health issues. The scientific community exerted noteworthy efforts to obtain therapeutic solutions for COVID-19, and new scientific networks were constituted. No certified drugs to efficiently inhibit the virus were identified, and the development of de-novo medicines requires approximately ten years of research. Therefore, the repurposing of natural products could be an effective strategy to handle SARS-CoV-2 infection. This review aims to update on current status of the natural occurring compounds recognizing SARS-CoV-2 druggable targets. Among the clinical trials actually recruited, some natural compounds are ongoing to examine their potential role to prevent and to treat the COVID-19 infection. Many natural scaffolds, including alkaloids, terpenes, flavonoids, and benzoquinones, were investigated by in-silico, in-vitro, and in-vivo approaches. Despite the large data set obtained by a computational approach, experimental evidences in most cases are not available. To fill this gap, further efforts to validate these results are required. We believe that an accurate investigation of naturally occurring compounds may provide insights for the potential treatment of COVID-19 patients.

Computational studies reveal mechanism by which quinone derivatives can inhibit SARS-CoV-2. Study of embelin and two therapeutic compounds of interest, methyl prednisolone and dexamethasone

BACKGROUND

Quinones are reactive to proteins containing cysteine residues and the main protease in Covid-19 contains an active site that includes Cys145. Embelin, a quinone natural product, is known to have antiviral activity against influenza and hepatitis B. Preliminary studies by our group also indicate its ability to inhibit HSV-1 in cultured cells.

METHODS

Docking and DFT methods applied to the protease target.

RESULTS

a mechanism for this inhibition of the SARS-CoV-2 Mpro protease is described, specifically due to formation of a covalent bond between S(Cys145) and an embelin C(carbonyl). This is assisted by two protein amino acids (1) N(imidazole-His41) which is able to capture H[S(Cys145)] and (2) HN(His163), which donates a proton to embelin O(carbonyl) forming an OH moiety that results in inhibition of the viral protease. A similar process is also seen with the anti-inflammatory drugs methyl prednisolone and dexamethasone, used for Covid-19 patients. Methyl prednisolone and dexamethasone are methide quinones, and possess only one carbonyl moiety, instead of two for embelin. Additional consideration was given to another natural product, emodin, recently patented against Covid-19, as well as some therapeutic quinones, vitamin K, suspected to be involved in Covid-19 action, and coenzyme Q10. All show structural similarities with embelin, dexamethasone and methyl prednisolone results.

CONCLUSIONS

Our data on embelin and related quinones indicate that these natural compounds may represent a feasible, strategic tool against Covid-19.

Embelin impact on paraquat-induced lung injury through suppressing oxidative stress, inflammatory cascade, and MAPK/NF-κB signaling pathway

The current examination was intended to observe the defensive impacts of embelin against paraquat-incited lung damage in relationship with its antioxidant and anti-inflammatory action. Oxidative stress marker, like malondialdehyde (MDA), antioxidative enzymes, for example, superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH Px), inflammatory cytokines, such as interleukin-1β (IL-1β), tumor necrosis factor-α, and IL-6, histological examination, and nuclear factor kappa B/mitogen-activated protein kinase (NF-κB/MAPK) gene expression were evaluated in lung tissue. Embelin treatment significantly decreased MDA and increased SOD, CAT, and GSH Px. Embelin significantly reduced levels of inflammatory cytokines in paraquat-administered and paraquat-intoxicated rats. In addition, embelin suggestively decreased relative protein expression of nuclear NF-κB p65, p-NF-κBp65, p38 MAPK, and p-p38 MAPKs in paraquat-intoxicated rats. The outcomes show the impact of embelin inhibitory action on NF-κB and MAPK and inflammatory cytokines release, and the decrease of lung tissue damage caused by paraquat.

An efficient synthesis of 2,3,5-trimethylbenzoquinone by metal-free oxidation of 1,2,4-trimethylbenzene

The oxidation of 1,2,4-trimethylbenzene with phthaloyl peroxide has been investigated under solvent-free and optimized conditions. 2,3,5-Trimethylbenzoquinone was obtained with great purity in 92% yield at 95% conversion of 1,2,4-trimethylbenzene at 120°C for 2.5 h under solvent-free conditions. The important factors such as the efficiency of the different cyclic acid anhydrides or carboxylic acid peroxides, the concentration of phthalic anhydride and 30% H2O2, the reaction time, the effect of solvent system, and the reaction temperature have been studied. An important advantage of this oxidizing system, aside from the organic solvent-free conditions, is that it is non-toxic, eco-friendly, and inexpensive. In addition, this methodology will be of great use in the preparation of commercially valuable benzoquinones from the corresponding aromatic compounds.

Discovery of natural products with metal-binding properties as promising antibacterial agents

INTRODUCTION

More than 50% of the clinically established antibiotics are either genuine natural products or derivatives thereof, featuring a mode of action decisively depending on their metal affinity and suitability as metal complex ligands. As their structural diversity and harvest from renewable sources is well-nigh inexhaustible, any future quest for affordable new antibiotics will have to concentrate on natural drugs with obvious metal ligating properties. Areas covered: The authors provide an overview of the promising developments in the field of antibiotic natural products with metal-binding properties with a specific focus on metal binders such as polyphenols, quinones, 3-acyltetramic and -tetronic acids. Works published by the authors are discussed in this manuscript as well as articles derived from PubMed and Scifinder. Expert opinion: Natural products with metal-binding properties possess a great potential for the development of drugs against various bacteria. There are many derivatives with great potential against multidrug-resistant bacteria as well. Synthetic approaches to structurally complex and/or rare natural products have added significantly to the cracking of synthetic problems. Thus, this field of scientific research appears attractive both to chemists and to clinicians.