A novel anti-HBeAg homolignan, taiwanschirin D from Kadsura matsudai

Plant-derived lignans as potential antiviral agents: a systematic review

Medicinal plants are one of the most important sources of antiviral agents and lead compounds. Lignans are a large class of natural compounds comprising two phenyl propane units. Many of them have demonstrated biological activities, and some of them have even been developed as therapeutic drugs. In this review, 630 lignans, including those obtained from medicinal plants and their chemical derivatives, were systematically reviewed for their antiviral activity and mechanism of action. The compounds discussed herein were published in articles between 1998 and 2020. The articles were identified using both database searches (e.g., Web of Science, Pub Med and Scifinder) using key words such as: antiviral activity, antiviral effects, lignans, HBV, HCV, HIV, HPV, HSV, JEV, SARS-CoV, RSV and influenza A virus, and directed searches of scholarly publisher's websites including ACS, Elsevier, Springer, Thieme, and Wiley. The compounds were classified on their structural characteristics as 1) arylnaphthalene lignans, 2) aryltetralin lignans, 3) dibenzylbutyrolactone lignans, 4) dibenzylbutane lignans, 5) tetrahydrofuranoid and tetrahydrofurofuranoid lignans, 6) benzofuran lignans, 7) neolignans, 8) dibenzocyclooctadiene lignans and homolignans, and 9) norlignans and other lignoids. Details on isolation and antiviral activities of the most active compounds within each class of lignan are discussed in detail, as are studies of synthetic lignans that provide structure-activity relationship information.

Development of an enolate alkynylation approach towards the synthesis of the taiwanschirin natural products

Through the use of model studies, an approach was conceived towards the synthesis of the taiwanschirin family of natural products. These are structurally complex compounds which represent highly challenging and biologically active targets for total synthesis. This work describes a successful synthesis of the complex taiwanschirin fused [8,6,5] core through a novel alkynylation reaction coupled with an intramolecular Heck reaction used to construct the 8-membered ring.

Hepatoprotective Dibenzocyclooctadiene and Tetrahydrobenzocyclooctabenzofuranone Lignans from Kadsura longipedunculata

Five new dibenzocyclooctadiene lignans, longipedlignans A-E (1-5), five new tetrahydrobenzocyclooctabenzofuranones (6-10), and 18 known analogues (11-28) were isolated from the roots of Kadsura longipedunculata. Compounds 6-10 are new spirobenzofuranoid-dibenzocyclooctadiene-type lignans. Their structures and absolute configurations were established using a combination of MS, NMR, and electronic circular dichroism data. Spirobenzofuranoids 6 and 15 showed moderate hepatoprotective activity against N-acetyl- p-aminophenol-induced toxicity in HepG2 cells with cell survival rates at 10 μM of 52.2% and 50.2%, respectively.

Total Synthesis of Ovafolinins A and B: Unique Polycyclic Benzoxepin Lignans through a Cascade Cyclization

Ovafolinins A and B, isolated from Lyonia ovalifolia var. elliptica, are lignans that contain a unique bridged structure containing a penta- and tetracyclic benzoxepin and an aryl tetralin. We report the first total synthesis of these natural products in which an acyl-Claisen rearrangement was initially utilized to construct the lignan backbone with correct relative stereochemistry. Judicious use of a bulky protecting group placed reactive moieties in the correct orientation, thereby resulting in a cascade reaction to form the bridged benzoxepin/aryl tetralin from a linear precursor in a single step. Modification of this route allowed the enantioselective synthesis of (+)-ovafolinins A and B, which confirmed the absolute stereochemistry, and comparison of optical rotation suggests that these compounds are found as scalemic mixtures in nature.

Nickel-Catalyzed Chemo-, Regio- and Diastereoselective Bond Formation through Proximal C-C Cleavage of Benzocyclobutenones

The first catalytic intermolecular proximal C1-C2 cleavage of benzocyclobutenones (BCB) without prior carbonyl activation or employing noble metals has been developed. This protocol operates at room temperature and is characterized by an exquisite chemo-, regio- and diastereoselectivity profile, constituting a unique platform for preparing an array of elusive carbocyclic skeletons.

Antiviral Properties of Phytochemicals

In recent years, significant progress has been achieved for the development of novel anti-viral drugs. These newly developed drugs belong to three groups of compounds, nucleoside analogues, thymidine kinase-dependent nucleotide analogues and specific viral enzyme inhibitors. It has been found that the natural products, like plant-derived compounds (phytochemicals) as well as traditional medicines, like traditional Chinese medicines (TCM), Ayurvedic medicines and so on, are the important sources for potential and novel anti-viral drugs. In this chapter, the history of natural products as antiviral drugs, the approaches to discover potential lead compounds, and the anti-viral properties of phytochemicals with different action mechanisms are discussed. The key conclusion is that natural products are most important sources for novel anti-viral drugs.

Novel antiviral agents: a medicinal plant perspective

Several hundred plant and herb species that have potential as novel antiviral agents have been studied, with surprisingly little overlap. A wide variety of active phytochemicals, including the flavonoids, terpenoids, lignans, sulphides, polyphenolics, coumarins, saponins, furyl compounds, alkaloids, polyines, thiophenes, proteins and peptides have been identified. Some volatile essential oils of commonly used culinary herbs, spices and herbal teas have also exhibited a high level of antiviral activity. However, given the few classes of compounds investigated, most of the pharmacopoeia of compounds in medicinal plants with antiviral activity is still not known. Several of these phytochemicals have complementary and overlapping mechanisms of action, including antiviral effects by either inhibiting the formation of viral DNA or RNA or inhibiting the activity of viral reproduction. Assay methods to determine antiviral activity include multiple-arm trials, randomized crossover studies, and more compromised designs such as nonrandomized crossovers and pre- and post-treatment analyses. Methods are needed to link antiviral efficacy/potency- and laboratory-based research. Nevertheless, the relative success achieved recently using medicinal plant/herb extracts of various species that are capable of acting therapeutically in various viral infections has raised optimism about the future of phyto-antiviral agents. As this review illustrates, there are innumerable potentially useful medicinal plants and herbs waiting to be evaluated and exploited for therapeutic applications against genetically and functionally diverse viruses families such as Retroviridae, Hepadnaviridae and Herpesviridae