Cochinolide, a new gamma-alkylidene bicyclic butenolide with antiviral activity, and its beta-glucopyranoside from Homalium cochinchinensis

Synthetic studies towards naturally occurring γ-(Z)/(E)-alkylidenebutenolides through bimetallic cascade cyclization and an adventitious photoisomerization method

A general and flexible visible light-induced photoisomerization method of γ-(Z)-alkylidenebutenolides to their corresponding E-components was reported in this article. Initially, a series of naturally occurring enantiopure γ-(Z)-alkylidenebutenolides was synthesized by employing a "Pd-Cu" bimetallic cascade cyclization protocol. In the later part, the synthesized γ-(Z)-alkylidenebutenolides were photoisomerized in the presence of a triplet photosensitizer to γ-(E)-alkylidenebutenolides in reasonably acceptable yields. Total synthesis of goniobutenolides, hygrophorones, ramariolide D, melodorinols/acetyl-melodorinols, versicolactones, and phomopsolidones was achieved by employing the developed methods.

Recent reports on the synthesis of γ-butenolide, γ-alkylidenebutenolide frameworks, and related natural products

γ-Butenolides are fundamental frameworks found in many naturally occurring compounds, and they exhibit tremendous biological activities. γ-Butenolides also have proven their potential as useful synthetic intermediates in the total synthesis of natural compounds. Over the years, many γ-butenolide natural products have been isolated, having exocyclic γ-δ unsaturation in their structure. These natural products are collectively referred to as γ-alkylidenebutenolides. Considering the different biological profiles and wide-ranging structural diversity of the optically active γ-butenolide, the development of synthetic strategies for assembling such challenging scaffolds has attracted significant attention from synthetic chemists in recent times. In this report, a brief discussion will be provided to address isolation, biogenesis, and current state-of-the-art synthetic protocols for such molecules. This report aims to focus on synthetic strategies for γ-butenolides from 2010-2020 with a particular emphasis on γ-alkylidenebutenolides and related molecules. Metal-mediated catalytic transformation and organocatalysis are the two main reaction types that have been widely used to access such molecules. Mechanistic considerations, enantioselective synthesis, and practical applications of the reported procedures are also taken into consideration.

Spermidine alkaloid and glycosidic constituents of Vietnamese Homalium cochinchinensis

Phytochemical investigation of the aerial parts of Homalium cochinchinensis led to the isolation of secondary metabolites belonging to the spermidine alkaloid, glycoside, depsidone and phenol classes. Of the eleven secondary metabolites isolated in this study, two spermidine alkaloids, dovyalicins H (1) and I (2), which belong to a rare group among this class, and six glycosides (3-8) are previously undescribed. The structures of all new isolates were determined by interpretation of spectroscopic and spectrometric data. In this report, the structural elucidation of these unprecedented secondary metabolites (1-8) is described.

Emerging paradigms of viral diseases and paramount role of natural resources as antiviral agents

In the current scenario, the increasing prevalence of diverse microbial infections as well as emergence and re-emergence of viral epidemics with high morbidity and mortality rates are major public health threat. Despite the persistent production of antiviral drugs and vaccines in the global market, viruses still remain as one of the leading causes of deadly human diseases. Effective control of viral diseases, particularly Zika virus disease, Nipah virus disease, Severe acute respiratory syndrome, Coronavirus disease, Herpes simplex virus infection, Acquired immunodeficiency syndrome, and Ebola virus disease remain promising goal amidst the mutating viral strains. Current trends in the development of antiviral drugs focus solely on testing novel drugs or repurposing drugs against potential targets of the viruses. Compared to synthetic drugs, medicines from natural resources offer less side-effect to humans and are often cost-effective in the productivity approaches. This review intends not only to emphasize on the major viral disease outbreaks in the past few decades and but also explores the potentialities of natural substances as antiviral traits to combat viral pathogens. Here, we spotlighted a comprehensive overview of antiviral components present in varied natural sources, including plants, fungi, and microorganisms in order to identify potent antiviral agents for developing alternative therapy in future.

Recent advances in sulfonylation reactions using potassium/sodium metabisulfite

Recently, sulfonylation reactions using potassium/sodium metabisulfite as the sulfur dioxide surrogate have been developed rapidly. In most cases, the transformations go through radical processes with the insertion of sulfur dioxide under mild conditions. Additionally, transition metal catalysis is applied in the reactions for the synthesis of sulfonyl-containing compounds. Among the approaches, photoinduced conversions under visible light or ultraviolet irradiation are also involved. In this updated report, the insertion of sulfur dioxide from potassium metabisulfite or sodium metabisulfite is summarized.

A new dihydrochalcone glycoside from the stems of Homalium stenophyllum

A new dihydrochalcone glycoside, phloretin-4-O-β-D-glucopyranoside (1), together with seven known flavonoids (2-8), were isolated from the stems of Homalium stenophyllum. The structure of 1 was elucidated by extensive spectroscopic methods and the known compounds were identified by comparisons with data reported in the literature. The known compounds (2-8) were isolated from the genus Homalium for the first time. All compounds were evaluated for their antibacterial activities against six pathogenic bacteria in vitro.

Cytoproliferative and Cytoprotective Effects of Striatisporolide A Isolated from Rhizomes of Athyrium multidentatum (Doell.) Ching on Human Umbilical Vein Endothelial Cells

OBJECTIVES

The aim of this study was to investigate the proliferative and protective effects of striatisporolide A (SA) obtained from the rhizomes of Athyrium multidentatum (Doell.) Ching on human umbilical vein endothelial cells (HUVECs).

METHODS

Cell viability was measured by the MTT method. Cell apoptosis was determined by flow cytometry. Intracellular ROS was measured by the 2,7-dichlorodihydrofluorescein diacetate (DCFH-DA) fluorescent probe.

RESULTS

The viability rate in cells treated with 100 µM SA alone was increased to 128.72% ± 0.19% and showed a significant difference compared with the control group (p < 0.05). Meanwhile, SA augmented the cell viabilities in H₂O₂-treated HUVECs, and the cell viability was enhanced to 56.94% ± 0.13% (p < 0.01) when pre-incubated with 50 µM SA. The cell apoptosis rates were reduced to 2.17% ± 0.20% (p < 0.05) and 3.1% ± 0.34% (p < 0.01), respectively, after treatment with SA alone or SA/H₂O₂. SA inhibited the overproduction of reactive oxygen species (ROS) in HUVECs induced by H₂O₂ and the fluorescent intensity was abated to 9.47 ± 0.61 after pre-incubated with 100 μM SA.

CONCLUSIONS

The biological activities of SA were explored for the first time. Our results stated that SA exhibited significant cytoproliferative and minor cytoprotective effects on HUVECs. We presume that the mechanisms of the proliferation and protection actions of SA involve interference with the generation of ROS and the cell apoptosis. These findings provide a new perspective on the biological potential of butenolides.

(4R,6S)-2-Dihydromenisdaurilide is a Butenolide that Efficiently Inhibits Hepatitis C Virus Entry

Without a vaccine, hepatitis C virus (HCV) remains a significant threat, putting 170–300 million carriers worldwide at risk of cirrhosis and hepatocellular carcinoma. Although the direct-acting antivirals targeting HCV replication have revolutionized the treatment of hepatitis C, several obstacles persist, including resistance development, potential side-effects, and the prohibitive cost that limits their availability. Furthermore, treatment of HCV re-infection in liver transplantation remains a significant challenge. Developing novel antivirals that target viral entry could help expand the scope of HCV therapeutics and treatment strategies. Herein, we report (4R,6S)-2-dihydromenisdaurilide (DHMD), a natural butenolide, as an efficient inhibitor of HCV entry. Specifically, DHMD potently inhibited HCV infection at non-cytotoxic concentration. Examination on the viral life cycle demonstrated that DHMD selectively targeted the early steps of infection while leaving viral replication/translation and assembly/release unaffected. Furthermore, DHMD did not induce an antiviral interferon response. Mechanistic dissection of HCV entry revealed that DHMD could inactivate cell-free virus, abrogate viral attachment, and inhibit viral entry/fusion, with the most pronounced effect observed against the viral adsorption phase as validated using ELISA and confocal microscopy. Due to its potency, DHMD may be of value for further development as an entry inhibitor against HCV, particularly for application in transplant setting.

7,9-Diaryl-1,6,8-trioxaspiro[4.5]dec-3-en-2-ones: readily accessible and highly potent anticancer compounds

7,9-Diaryl-1,6,8-trioxaspiro[4.5]dec-3-en-2-ones are a recently described group of spirocyclic butenolides that can be generated rapidly and as a single diastereomer through a cascade process between γ-hydroxybutenolides and aromatic aldehydes. The following outlines our findings that these spirocycles are potently cytotoxic and have a dramatic structure-function profile that provides excellent insight into the structural features required for this potency.

Expedient synthesis of novel 1,4-benzoxazine and butenolide derivatives

A rapid and efficient protocol for the synthesis of 2-hydroxy-1,4-benzoxazine derivatives has been developed. These intermediates served as precursors for the synthesis of a series of novel butenolide derivatives and 2-amino-1,4-benzoxazine derivatives.

Synthesis and in vitro antitumor activity of new butenolide-containing dithiocarbamates

Three series of butenolide-containing dithiocarbamates were designed and synthesized. Their anti-tumor activity in vitro was evaluated. Among them compound I-14 exhibited broad spectrum anti-cancer activity against five human cancer cell lines with IC(50) <30 μM. Structure-activity relationship analysis showed that the introduction of dithiocarbamate side chains on the C-3 position of butenolide was crucial for anti-tumor activity.

Efficient desymmetrization of "pseudo"-C2-symmetric substrates: illustration in the synthesis of a disubstituted butenolide from arabitol

A short synthesis of the homochiral disubstituted butenolide 1 is described in four steps from arabitol. The key steps are the selective kinetic protection of arabitol and the cyclization of 11 to form the butenolide ring. This last transformation represents a rare example of a fully stereoselective cyclitive desymmetrization process of a "pseudo"-C2-symmetric substrate.

Natural Products as Antiviral Agents

Since the ancient times, natural products have served as a major source of drugs. About fifty percent of today's pharmaceutical drugs are derived from natural origin. Interest in natural products as a source of new drugs is growing due to many factors that will be discussed in this article. Viruses have been resistant to therapy or prophylaxis longer than any other form of life. Currently, there are only few drugs available for the cure of viral diseases including acyclovir which is modeled on a natural product parent. In order to combat viruses which have devastating effects on humans, animals, insects, crop plants, fungi and bacteria, many research efforts have been devoted for the discovery of new antiviral natural products. Recent analysis of the number and sources of antiviral agents reported mainly in the annual reports of medicinal chemistry from 1984 to 1995 indicated that seven out of ten synthetic agents approved by FDA between 1983-1994, are modeled on a natural product parent. It has been estimated that only 5-15% of the approximately 250,000 species of higher plants have been systematically investigated for the presence of bioactive compounds while the potential of the marine environment has barely been tapped. The aim of this review is to provide an overview on the central role of natural products in the discovery and development of new antiviral drugs by displaying 340 structures of plant, marine and microbial origin that show promising in vitro antiviral activity.