Unified Total Synthesis of Diverse Meroterpenoids from Ganoderma Applanatum

Concise total synthesis of (±)-applanatumol Y

Total synthesis of (±)-applanatumol Y was achieved in 5 steps, featuring a cascade annulation including Michael addition, aldol condensation, and oxy-Michael addition reactions, all promoted by DBU. This approach offers a streamlined and cost-effective route for constructing complex tricyclic frameworks under mild and metal-free conditions.

Enzymatic Ring Contraction for the Biosynthesis of Sulfur-Containing Cyclopentachromone

Cyclopentachromone, distinguished by its 6/6/5 heterotricyclic ring structure, is a key building block in many bioactive natural products, yet its enzymatic origin remains unclear. We identified a new class of cyclopentachromone-containing compounds, termed isochromosulfines, characterized by unique C-S bonds. A distinct FAD-dependent monooxygenase, IscL, was identified to catalyze the formation of the 6/6/5 cyclopentadiene intermediate, 2S-remisporine A, from a 6/6/6 xanthone precursor via benzene ring contraction. The high reactivity of 2S-remisporine A further promotes a spontaneous thiol-Michael addition reaction with thiol-containing compounds, forming the C-S bond in isochromosulfines. Additionally, we demonstrate that IscL homologues mediate a bifurcated pathway of benzene ring modification in the xanthone intermediate, leading to either ring contraction or cleavage, which is determined by a critical residue at position 230 to be phenylalanine or tyrosine. Our findings highlight the pivotal role of IscL in forming the 6/6/5 cyclopentachromone scaffold and offer deep insights into its catalytic mechanism. Our work lays the foundation for genome mining of cyclopentachromone-containing compounds and shows the potential application of IscL in biocatalysis.

Total Synthesis of Ganoapplanin Enabled by a Radical Addition/Aldol Reaction Cascade

The total synthesis of the Ganoderma meroterpenoid ganoapplanin, an inhibitor of T-type voltage-gated calcium channels, is reported. Our synthetic approach is based on the convergent coupling of a readily available aromatic polyketide scaffold with a bicyclic terpenoid fragment. The three contiguous stereocenters of the terpenoid fragment, two of which are quaternary, were constructed by a diastereoselective, titanium-mediated iodolactonization. For the fusion of the two fragments and to simultaneously install the crucial biaryl bond, we devised a highly effective two-component coupling strategy. This event involves an intramolecular 6-exo-trig radical addition of a quinone monoacetal followed by an intermolecular aldol reaction. A strategic late-stage oxidation sequence allowed the selective installation of the remaining oxygen functionalities and the introduction of the characteristic spiro bisacetal structure of ganoapplanin.

Insights into Ganoderma fungi meroterpenoids opening a new era of racemic natural products in mushrooms

Ganoderma meroterpenoids (GMs) containing 688 structures to date were discovered to have multiple remarkable biological activities. 65.6% of meroterpenoids featuring stereogenic centers from Ganoderma species are racemates. Further, GMs from different Ganoderma species seem to have their own characteristics. In this review, a comprehensive summarization of GMs since 2000 is presented, including GM structures, structure corrections, biological activities, physicochemical properties, total synthesis, and proposed biosynthetic pathways. Additionally, we especially discuss the racemic nature, species-related structural distribution, and structure-activity relationship of GMs, which will provide a likely in-house database and shed light on future studies on GMs.

Ganoderma lucidum-Derived Meroterpenoids Show Anti-Inflammatory Activity In Vitro

Ganoderma lucidum, known as the "herb of spiritual potency", is used for the treatment and prevention of various diseases, but the responsible constituents for its therapeutic effects are largely unknown. For the purpose of obtaining insight into the chemical and biological profiling of meroterpenoids in G. lucidum, various chromatographic approaches were utilized for the title fungus. As a result, six undescribed meroterpenoids, chizhienes A-F (1-6), containing two pairs of enantiomers (4 and 5), were isolated. Their structures were identified using spectroscopic and computational methods. In addition, the anti-inflammatory activities of all the isolates were evaluated by Western blot analysis in LPS-induced macrophage cells (RAW264.7), showing that 1 and 3 could dose dependently inhibit iNOS but not COX-2 expression. Further, 1 and 3 were found to inhibit nitric oxide (NO) production using the Greiss reagent test. The current study will aid in enriching the structural and biological diversity of Ganoderma-derived meroterpenoids.

The Artist's Conk Medicinal Mushroom Ganoderma applanatum (Agaricomycetes): Mycological, Mycochemical, and Pharmacological Properties: A Review

As a commonly used Chinese herbal medicine, Ganoderma applanatum (Pers.) Pat., also known as flat-ling Ganoderma (Chinese name bianlingzhi), old mother fungus (laomujun), and old ox liver (laoniugan), has high medicinal value. It is used as an anti-cancer drug in China and Japan. Besides, it can treat rheumatic tuberculosis and has the effect of relieving pain, clearing away heat, eliminating accumulation, stopping bleeding and eliminating phlegm. The purpose of this review is to analyze the research progress systematically and comprehensively in mycology, mycochemistry and pharmacological activities of G. applanatum, and discuss the prospect of prospective research and implementation of this medicinal material. A comprehensive literature search was performed on G. applanatum using scientific databases including Web of Science, PubMed, Google Scholar, CNKI, Elsevier. Collected data from different sources was comprehensively summarized for mycology, mycochemistry and pharmacology of G. applanatum. A total of 324 compounds were recorded, the main components of which were triterpenoids, meroterpenoids, steroids, and polysaccharides. G. applanatum and its active ingredients have a variety of pharmacological effects, including anti-tumor, liver protection, hypoglycemic, anti-fat, anti-oxidation, antibacterial and other activities. Although G. applanatum is widely used in traditional medicine and has diverse chemical constituents, more studies should be carried out in animals and humans to evaluate the cellular and molecular mechanisms involved in its biological activity.

Visible Light Promoted [3+2]-Cycloaddition for the Synthesis of Cyclopenta[b]chromenocarbonitrile Derivatives

In the manuscript, a novel method for the preparation of cyclopenta[b]chromenocarbonitrile derivatives via [3+2] cycloaddition reaction of substituted 3-cyanochromones and N-cyclopropyloamines initiated by visible light catalysis has been described. The reaction was performed in the presence of Eosin Y as a photocatalyst. The key parameters responsible for the success of the described strategy are visible light, a small amount of photoredox catalyst, an anhydrous solvent, and an inert atmosphere.

Organic Synthesis Using Nitroxides

Nitroxides, also known as nitroxyl radicals, are long-lived or stable radicals with the general structure R1R2N-O•. The spin distribution over the nitroxide N and O atoms contributes to the thermodynamic stability of these radicals. The presence of bulky N-substituents R1 and R2 prevents nitroxide radical dimerization, ensuring their kinetic stability. Despite their reactivity toward various transient C radicals, some nitroxides can be easily stored under air at room temperature. Furthermore, nitroxides can be oxidized to oxoammonium salts (R1R2N═O+) or reduced to anions (R1R2N-O-), enabling them to act as valuable oxidants or reductants depending on their oxidation state. Therefore, they exhibit interesting reactivity across all three oxidation states. Due to these fascinating properties, nitroxides find extensive applications in diverse fields such as biochemistry, medicinal chemistry, materials science, and organic synthesis. This review focuses on the versatile applications of nitroxides in organic synthesis. For their use in other important fields, we will refer to several review articles. The introductory part provides a brief overview of the history of nitroxide chemistry. Subsequently, the key methods for preparing nitroxides are discussed, followed by an examination of their structural diversity and physical properties. The main portion of this review is dedicated to oxidation reactions, wherein parent nitroxides or their corresponding oxoammonium salts serve as active species. It will be demonstrated that various functional groups (such as alcohols, amines, enolates, and alkanes among others) can be efficiently oxidized. These oxidations can be carried out using nitroxides as catalysts in combination with various stoichiometric terminal oxidants. By reducing nitroxides to their corresponding anions, they become effective reducing reagents with intriguing applications in organic synthesis. Nitroxides possess the ability to selectively react with transient radicals, making them useful for terminating radical cascade reactions by forming alkoxyamines. Depending on their structure, alkoxyamines exhibit weak C-O bonds, allowing for the thermal generation of C radicals through reversible C-O bond cleavage. Such thermally generated C radicals can participate in various radical transformations, as discussed toward the end of this review. Furthermore, the application of this strategy in natural product synthesis will be presented.