A New Selaginellin from Selaginella moellendorffii Inhibits Hepatitis B Virus Gene Expression and Replication

Two New C21 Steroidal Glycosides from Selaginella Braunii Baker

Two new C21 steroidal glycosides, brapreguanes A and B (1-2) were isolated from 75 % aqueous ethanol extract of Selaginella braunii Baker. Their structures were established by spectroscopic analyses (1D/2D NMR spectra and HR-ESI-MS). The absolute configurations of sugar were elucidated by enzymatic hydrolysis and GCMS analysis. In addition, all compounds were evaluated for the anti-proliferative activities against various human cancer cells in vitro. Compounds exhibited no inhibition to various human cancer cells.

Plant-Based Natural Products and Extracts: Potential Source to Develop New Antiviral Drug Candidates

Viral infections are among the most complex medical problems and have been a major threat to the economy and global health. Several epidemics and pandemics have occurred due to viruses, which has led to a significant increase in mortality and morbidity rates. Natural products have always been an inspiration and source for new drug development because of their various uses. Among all-natural sources, plant sources are the most dominant for the discovery of new therapeutic agents due to their chemical and structural diversity. Despite the traditional use and potential source for drug development, natural products have gained little attention from large pharmaceutical industries. Several plant extracts and isolated compounds have been extensively studied and explored for antiviral properties against different strains of viruses. In this review, we have compiled antiviral plant extracts and natural products isolated from plants reported since 2015.

Molecular Networking Discloses the Chemical Diversity of Flavonoids and Selaginellins in Selaginella convoluta

Selaginella convoluta is a desiccation tolerant plant native to the Brazilian semiarid region (Caatinga), endowed with an effective drought resistance mechanism. As part of our research efforts to understand the chemical diversity of S. convoluta, dehydrated (harvested in their natural habitat in the dry season) and hydrated (plant acclimated in a laboratory after rehydration) specimens were analyzed by HR-LC-ESI-MS/MS followed by a structural annotation on the Global Natural Products Social Molecular Networking Web platform. The molecular networking approach allowed for putative annotation of 39 metabolites, mainly selaginellins and flavonoids. Based on MS/MS data, three unprecedented selaginellins were annotated: 29-hydroxy selaginellin O, 29-hydroxy selaginellin A, and 4-{[2-(4-hydrophenyl)-6-[2-(4-hydroxyphenyl)ethynyl]phenyl](4-oxocyclohexa-2,5-dien-1-ylidene)methyl}benzaldehyde. Th results pointed out that valuable scientific knowledge can be obtained from studies conducted with plants in their natural habitat by allowing a more realistic profile of chemical diversity. The present study adds new information on specialized metabolites of S. convoluta, mainly flavonoids and selaginellins, and highlights the species as an untapped source of chemobiodiversity from Caatinga.

Selaginellins from the genus Selaginella: isolation, structure, biological activity, and synthesis

Covering: 2007 to 2020 Selaginellins are a small group of pigments exclusively found in the ancient genus Selaginella. Since the first report of selaginellin from S. sinensis in 2007, more than 110 selaginellins with diverse polyphenolic skeletons have been reported. This review provides extensive coverage of the selaginellins discovered from 2007 to 2020, including 61 natural ones and 52 synthetic analogues. The isolation, chemical structures, plausible biosynthetic pathways, bioactivity, and total synthesis of these selaginellins have been summarized for the first time, and this highlights the fact that the vast uninvestigated Selaginella species may serve as a potential treasure trove of chemically diverse selaginellins waiting to be discovered.

Comparison of Chemical Composition and Biological Activities of Eight Selaginella Species

Selaginella P. Beauv. is a group of vascular plants in the family Selaginellaceae Willk., found worldwide and numbering more than 700 species, with some used as foods and medicines. The aim of this paper was to compare methanolic (MeOH) and dichloromethane (DCM) extracts of eight Selaginella species on the basis of their composition and biological activities. Six of these Selaginella species are underinvestigated. Using ultra-high performance liquid chromatography-high-resolution mass spectrometry (UHPLC-HRMS) analysis, we identified a total of 193 compounds among the tested Selaginella species, with flavonoids predominating. MeOH extracts recovered more constituents that were detected, including selaginellins, the occurrence of which is only typical for this plant genus. Of all the tested species, Selaginella apoda contained the highest number of identified selaginellins. The majority of the compounds were identified in S. apoda, the fewest compounds in Selaginella cupressina. All the tested species demonstrated antioxidant activity using oxygen radical absorption capacity (ORAC) assay, which showed that MeOH extracts had higher antioxidant capacity, with the half maximal effective concentration (EC₅₀) ranging from 12 ± 1 (Selaginella myosuroides) to 124 ± 2 (Selaginella cupressina) mg/L. The antioxidant capacity was presumed to be correlated with the content of flavonoids, (neo)lignans, and selaginellins. Inhibition of acetylcholinesterase (AChE) was mostly discerned in DCM extracts and was only exhibited in S. myosuroides, S. cupressina, Selaginella biformis, and S. apoda extracts with the half maximal inhibitory concentration (IC₅₀) in the range of 19 ± 3 to 62 ± 1 mg/L. Substantial cytotoxicity against cancer cell lines was demonstrated by the MeOH extract of S. apoda, where the ratio of the IC₅₀ HEK (human embryonic kidney) to IC₅₀ HepG2 (hepatocellular carcinoma) was 7.9 ± 0.2. MeOH extracts inhibited the production of nitrate oxide and cytokines in a dose-dependent manner. Notably, S. biformis halved the production of NO, tumor necrosis factor (TNF)-α, and interleukin (IL)-6 at the following concentrations: 105 ± 9, 11 ± 1, and 10 ± 1 mg/L, respectively. Our data confirmed that extracts from Selaginella species exhibited cytotoxicity against cancer cell lines and AChE inhibition. The activity observed in S. apoda was the most promising and is worth further exploration.

Two New Abietane Diterpenoids from Selaginella moellendorffii Hieron

Two new abietane diterpenoids, (3S,5R,10S)-3-hydroxy-12-O-demethyl-11-deoxy-19(4→3)-abeo-cryptojaponol, 12,19-dihydroxyabieta-8,11,13-trien-7-one, were isolated from Selaginella moellendorffii Hieron., together with one known abietane diterpenoid and four known tetracyclic triterpenoids. Their structures were characterized by their 1D- and 2D-NMR, ECD and mass spectral studies. All compounds were tested for their inhibitory effects on proliferation of three human cancer cells (human non-small-cell lung carcinoma cell lines A549 and human breast adenocarcinoma cell lines MDA-MB-231 and MCF-7) in vitro. Among them, three compounds displayed modest cytotoxic activities against the above three human cancer cell lines with IC₅₀ values ranging from 16.28 to 40.67 μM.

Synthesis of novel natural product-like diaryl acetylenes as hypoxia inducible factor-1 inhibitors and antiproliferative agents

The selaginellin derivatives are a type of novel natural pigments with an unusual alkynyl phenol skeleton from the genus Selaginella. Some of these natural compounds were previously reported to show important bioactivities, including anticancer activity, cardiovascular protection and phosphodiesterase-4 inhibition. We designed and synthesized fifteen biphenyl-containing diaryl acetylene derivatives mimicking the skeleton of natural alkynyl phenols. In MTT assay in cancer cells, compounds 1c, 2d, 2g, 2h, 2i and 2j exhibited potent antiproliferative activity. The evaluation of Hypoxia Inducible Factor-1 (HIF-1) pathway inhibitory activity in dual luciferase assay demonstrated that most tested compounds exhibited moderate to good activities. Compounds 1a, 2f and 2h displayed high HIF-1 inhibitory activities and relatively low cytotoxicity, demonstrating great potential as HIF-1 inhibitors. These results afford a new strategy for the discovery of new HIF-1 inhibitors and anti-proliferative agents from natural or synthetic diaryl acetylene derivatives.

A new selaginellin derivative and a new triarylbenzophenone analog from the whole plant of Selaginella pulvinata

Five selaginellin derivatives (1 and 3-6) including a new one, selaginellin T (1), and a new triarylbenzophenone analog, selagibenzophenone A (2), were isolated from the whole plants of Selaginella pulvinata. Their structures were determined by 1D- and 2D-NMR and HR-ESI-MS data. Selagibenzophenone A (2) is the first example of naturally occurring triarylbenzophenone. The results of the phosphodiesterase-4 (PDE4) inhibitory screening assays showed that compounds 1-6 exhibited potent activities with the IC₅₀ values in the range of 1.04-9.35 μM.

Modified Abietane Diterpenoids from Whole Plants of Selaginella moellendorffii

A new modified abietane diterpenoid, (3S,4S,5R,10S)-18(4→3)-abeo-3,4,12,18-tetrahydroxy-8,11,13-abietatrien-7-one (1), and two novel dimers, selaginedorffones A (2) and B (3), featuring a new cyclohexene moiety that was biogenetically constructed from two modified abietane diterpenoids through a Diels-Alder reaction were obtained from a methanolic extract of Selaginella moellendorffii, a traditional Chinese herb. The structures of 1-3 were identified by a combination of NMR spectroscopic analysis and ECD calculations. In the present study, diterpenoids were identified from S. moellendorffii for the first time, which supports the presence of diterpene synthases in this plant. These three diterpenoids (1-3) were evaluated for their growth-inhibitory activities against several human cancer cell lines. Of these substances, selaginedorffone B (3) showed cytotoxicity against the MCF-7 human-breast-cancer-cell line (IC₅₀ 9.0 μM).

Phytochemicals from fern species: potential for medicine applications

Ferns are an important phytogenetic bridge between lower and higher plants. Historically they have been used in many ways by humans, including as ornamental plants, domestic utensils, foods, and in handicrafts. In addition, they have found uses as medicinal herbs. Ferns produce a wide array of secondary metabolites endowed with different bioactivities that could potentially be useful in the treatment of many diseases. However, there is currently relatively little information in the literature on the phytochemicals present in ferns and their pharmacological applications, and the most recent review of the literature on the occurrence, chemotaxonomy and physiological activity of fern secondary metabolites was published over 20 years ago, by Soeder (Bot Rev 51:442-536, 1985). Here, we provide an updated review of this field, covering recent findings concerning the bioactive phytochemicals and pharmacology of fern species.