(+/−)-Lucidumone, a COX-2 Inhibitory Caged Fungal Meroterpenoid from Ganoderma lucidum

Biosynthesis of a bacterial meroterpenoid reveals a non-canonical class II meroterpenoid cyclase

Meroterpenoids are hybrid natural products that arise from the integration of terpenoid and non-terpenoid biosynthetic pathways. While the biosynthesis of fungal meroterpenoids typically follows a well-established sequence of prenylation, epoxidation, and cyclization, the pathways for bacterial perhydrophenanthrene meroterpenoids remain poorly understood. In this study, we report the construction of an engineered metabolic pathway in Streptomyces for the production of the bacterial meroterpenoid, atolypene A (1). Our research reveals a novel biosynthetic pathway wherein the structure of 1 is assembled through a distinct sequence of epoxidation, prenylation, and cyclization, divergent from its fungal counterparts. We demonstrate that the noncanonical class II meroterpenoid cyclase (MTC) AtoE initiates cyclization by protonating the epoxide via the E314 residue, which acts as a Brønsted acid within the characteristic xxxE314TAE motif. Additionally, bioinformatic analysis of biosynthetic gene clusters (BGCs) that contain AtoE-like MTCs supports that bacteria have the potential to produce a wide array of meroterpenoids.

Photoinduced formal [4 + 2] cycloaddition of two electron-deficient olefins and its application to the synthesis of lucidumone

Electronically mismatched Diels-Alder reaction between two electron-deficient components is synthetically useful and yet underdeveloped under thermal conditions. Herein, a photoinduced formal [4 + 2] cycloaddition of enone with a variety of electron-deficient dienes is described. Key to the success of this stepwise methodology relies on a C - C bond cleavage/rearrangement of the cyclobutane based overbred intermediate via diversified mechanistic pathways. Based on this annulation method, total synthesis of lucidumone is achieved in nine steps.

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.

Asymmetric Total Synthesis of (+)-Chuanxiongnolide L1 via a Stereoselective Oxidative Dearomatization/Diels-Alder Strategy

The first asymmetric total synthesis of chuanxiongnolide L1 was achieved in 16 steps and 1.9% overall yield by employing a bioinspired chiral auxiliary strategy. The key steps involving asymmetric oxidative dearomatization of chiral amino ether and subsequent asymmetric Diels-Alder reaction of the resulting masked chiral ortho-benzoquinone were adopted.

Enantioselective total synthesis of (‒)-lucidumone enabled by tandem prins cyclization/cycloetherification sequence

The Ganoderma meroterpenoids are a growing class of natural products with architectural complexity, and exhibit a wide range of biological activities. Here, we report an enantioselective total synthesis of the Ganoderma meroterpenoid (‒)-lucidumone. The synthetic route features several key transformations, including a) a Cu-catalyzed enantioselective silicon-tethered intramolecular Diels-Alder cycloaddition to construct the highly functionalized bicyclo[2.2.2]octane moiety; b) Brønsted acid promoted tandem O-deprotection/Prins cyclization/Cycloetherification sequence followed by oxidation to install concurrently the tetrahydrofuran and the fused indanone framework; c) Fleming-Tamao oxidation to generate the secondary hydroxyl; d) an iron-catalyzed Wacker-type oxidation of hindered vinyl group to methyl ketone.

A Comprehensive Review on the Chemical Composition, Pharmacology and Clinical Applications of Ganoderma

Ganoderma is the dried fruiting bodiy of Ganoderma lucidum (Leyss.ex Fr.) Karst. or Ganoderma sinense Zhao, Xu et Zhang, belonging to the family Polyporaceae, which grows mainly in tropical, subtropical, and temperate regions. As a traditional Chinese medicine, Ganoderma has been used in China for more than 2000 years because of its medicinal properties, such as relieving cough and asthma, providing nourishment, and strengthening. Currently, more than 470 natural compounds have been obtained from the fungus, mainly including terpenoids, steroids, alkaloids, phenols, and other types of compounds. Modern pharmacological studies have shown that Ganoderma has antitumor, anti-inflammatory, hypoglycemic, hypolipidemic, and immunomodulatory effects. It is mainly used in clinical practice for the treatment of Diabetic Nephropathy and malignant tumors, with few side effects and high safety. This paper reviews the progress of research on its chemical composition, pharmacological effects, and clinical applications, with the goal of providing a basis for the better development and utilization of Ganoderma.

Structural diversity, hypothetical biosynthesis, chemical synthesis, and biological activity of Ganoderma meroterpenoids

Covering: 2018 to 2022Meroterpenoids found in fungal species of the genus Ganoderma and known as Ganoderma meroterpenoids (GMs) are substances composed of a 1,2,4-trisubstituted benzene and a polyunsaturated side chain. These substances have attracted the attention of chemists and pharmacologists due to their diverse structures and significant bioactivity. In this review, we present the structures and possible biosynthesis of representative GMs newly found from 2018 to 2022, as well as chemical synthesis and biological activity of some interesting GMs. We propose for the first time a plausible biosynthetic pathway for GMs, which will certainly motivate further research on the biosynthetic pathway in Ganoderma species, as well as on chemical synthesis of GMs as important bioactive compounds for the purpose of drug development.

Design, Synthesis, and Evaluation of the COX-2 Inhibitory Activities of New 1,3-Dihydro-2H-indolin-2-one Derivatives

Thirty-three 1,3-dihydro-2H-indolin-2-one derivatives bearing α, β-unsaturated ketones were designed and synthesized via the Knoevenagel condensation reaction. The cytotoxicity, in vitro anti-inflammatory ability, and in vitro COX-2 inhibitory activity of all the compounds were evaluated. Compounds 4a, 4e, 4i-4j, and 9d exhibited weak cytotoxicity and different degrees of inhibition against NO production in LPS-stimulated RAW 264.7 cells. The IC₅₀ values of compounds 4a, 4i, and 4j were 17.81 ± 1.86 μM, 20.41 ± 1.61 μM, and 16.31 ± 0.35 μM, respectively. Compounds 4e and 9d showed better anti-inflammatory activity with IC₅₀ values of 13.51 ± 0.48 μM and 10.03 ± 0.27 μM, respectively, which were lower than those of the positive control ammonium pyrrolidinedithiocarbamate (PDTC). Compounds 4e, 9h, and 9i showed good COX-2 inhibitory activities with IC₅₀ values of 2.35 ± 0.04 µM, 2.422 ± 0.10 µM and 3.34 ± 0.05 µM, respectively. Moreover, the possible mechanism by which COX-2 recognized 4e, 9h, and 9i was predicted by molecular docking. The results of this research suggested that compounds 4e, 9h, and 9i might be new anti-inflammatory lead compounds for further optimization and evaluation.

Retro-[4+2]/Intramolecular Diels–Alder Cascade Allows a Concise Total Synthesis of Lucidumone

Lucidumone is a recently isolated meroterpenoid displaying interesting biological activity. This natural product possesses a complex structure, including a bicyclo[2.2.2]octane possessing 6 contiguous stereogenic centers. Herein, we discuss strategies to solve this synthetic challenge. In particular, we developed a new method for the inverse electron-demand Diels–Alder cycloaddition between 2-pyrones and acyclic enol ethers, as a mean to obtain a ‘masked’ cyclohexadiene. This method allowed an expeditious enantioselective synthesis of (+)-lucidumone through a retro-[4+2]/intramolecular Diels–Alder reaction cascade.

1 Introduction

2 Retrosynthetic Considerations on the Bicyclo[2.2.2]octane

3 Development of a Methodology for Enantioselective IEDDA Cycloadditions

4 Enantioselective Total Synthesis of (+)-Lucidumone

5 Conclusion

COX-2 and iNOS inhibitory epimeric meroterpenoids from Ganoderma cochlear and structure revision of cochlearol Q

Four novel epimeric meroterpenoids, ganadone A (1), 3',10'-di-epi-ganadone A (2), 10'-epi-ganadone A (3), and 3'-epi-ganadone A (4) as well as another pairs of epimers, ganadone B (5) and 10'-epi-ganadone B (6), with a same basic skeleton compound ganadone C (7), together with two lactonized meroterpenoids, ganadones D and E (8 and 9) were isolated from the fruiting bodies of Ganoderma cochlear. Compounds 1-7 were constructed with fascinating adjacent 6',7'-bifuran ring system. Fortunately, we have revised our previously reported structure cochlearol Q, which was proposed pyrano[6',7'-b]pyran ring system into 6',7'-bifuran motif. All the isolates were characterized by analysis of HRESIMS, NMR spectroscopy and 1 was supported by X-ray crystallography analysis. The absolute stereochemistry of 1-9 were assigned by quantum chemical calculations. Biological evaluation of 1-9 showed that 5, 6, and 9 have significant anti-inflammatory potentials.

Ganoaustralins A and B, Unusual Aromatic Triterpenes from the Mushroom Ganoderma australe

Two triterpenes, ganoaustralins A (1) and B (2), featuring unprecedented 6/6/6/5/6 scaffolds were isolated from the fruiting bodies of the mushroom Ganoderma australe. The structures were determined by extensive NMR and HRESIMS spectroscopic analysis. The absolute configuration of the C-25 in ganoaustralin A was assigned by the phenylglycine methyl ester (PGME) method. The relative and absolute configurations of the polycyclic backbones were determined by NMR and ECD calculations, respectively. The plausible biosynthetic pathways of ganoaustralins A and B were proposed. Ganoaustralin B showed weak inhibition against β-secretase 1.

Gram-Scale Enantioselective Synthesis of (+)-Lucidumone

The first enantioselective total synthesis of (+)-lucidumone is described through a 13-step synthetic pathway (longest linear sequence). The key steps involve the formation of a bridged bicyclic lactone by an enantioselective inverse-electron-demand Diels-Alder cycloaddition, C-O bond formation to assemble two fragments, and a one-pot retro-[4 + 2]/[4 + 2] cycloaddition cascade. The synthesis is scalable, and more than one gram of natural product was synthesized in one batch.

Construction of the Skeleton of Lucidumone

The skeleton of lucidumone was constructed through oxidative dearomatization/intramolecular Diels-Alder reaction, Cu-mediated remote C-H hydroxylation, allyl oxidation, acid-promoted dynamic kinetic resolution cyclization, and benzylic oxidation.

Computational Analysis and Biological Activities of Oxyresveratrol Analogues, the Putative Cyclooxygenase-2 Inhibitors

Polyphenols are a large family of naturally occurring phytochemicals. Herein, oxyresveratrol was isolated from ethanolic crude extracts of Artocarpus lacucha Buch.-Ham., and chemically modified to derive its lipophilic analogues. Biological screening assays showed their inhibitory potency against cyclooxygenase-2 (COX-2) with very low cytotoxicity to the MRC-5 normal cell lines. At the catalytic site of COX-2, docking protocols with ChemPLP, GoldScore and AutoDock scoring functions were carried out to reveal hydrogen bonding interactions with key polar contacts and hydrophobic pi-interactions. For more accurate binding energetics, COX-2/ligand complexes at the binding region were computed in vacuo and implicit aqueous solvation using M06-2X density functional with 6-31G+(d,p) basis set. Our computational results confirmed that dihydrooxyresveratrol (4) is the putative inhibitor of human COX-2 with the highest inhibitory activity (IC₅₀ of 11.50 ± 1.54 µM) among studied non-fluorinated analogues for further lead optimization. Selective substitution of fluorine provides a stronger binding affinity; however, lowering the cytotoxicity of a fluorinated analogue to a normal cell is challenging. The consensus among biological activities, ChemPLP docking score and the binding energies computed at the quantum mechanical level is obviously helpful for identification of oxyresveratrol analogues as a putative anti-inflammatory agent.

Natural Enantiomers: Occurrence, Biogenesis and Biological Properties

The knowledge that natural products (NPs) are potent and selective modulators of important biomacromolecules (e.g., DNA and proteins) has inspired some of the world's most successful pharmaceuticals and agrochemicals. Notwithstanding these successes and despite a growing number of reports on naturally occurring pairs of enantiomers, this area of NP science still remains largely unexplored, consistent with the adage "If you don't seek, you don't find". Statistically, a rapidly growing number of enantiomeric NPs have been reported in the last several years. The current review provides a comprehensive overview of recent records on natural enantiomers, with the aim of advancing awareness and providing a better understanding of the chemical diversity and biogenetic context, as well as the biological properties and therapeutic (drug discovery) potential, of enantiomeric NPs.

Chemical constituents from the flowers of Hypericum monogynum L. with COX-2 inhibitory activity

Hypericum monogynum L. (Hypericaceae) has been used as a folk Chinese medicine for the treatment of inflammatory related diseases. Cyclooxygenase-2 (COX-2) is a crucial target for the development of agents to treat inflammation. To search for anti-inflammatory compounds from traditional Chinese medicines, a chemical constituent study along with COX-2 inhibitory activity analysis was performed for this plant. In this study, sixteen chemical monomers, including three undescribed oxidative degradation polycyclic polyprenylated acylphloroglucinols (PPAPs, hypemoins C-E), two undescribed PPAPs (hypemoins A and B), and 11 known compounds, were identified from the flowers of H. monogynum. Their structures were characterized by HRESIMS, NMR techniques, ECD, and single crystal X-ray diffraction. Four flavonoid derivatives showed remarkable COX-2 inhibitory activities, with IC₅₀ values ranging from 0.220 ± 0.006 to 1.655 ± 0.098 μM. Among these compounds, the possible recognition mechanism between quercetin 3-(6″-O-caffeoyl)-β-3-D-galactoside and COX-2 was predicted by molecular docking analysis. Moreover, the multidrug resistance reversal activities for the selected compounds were evaluated.

Meroterpenoids From Ganoderma lucidum Mushrooms and Their Biological Roles in Insulin Resistance and Triple-Negative Breast Cancer

Ganoderma fungi as popular raw materials of numerous functional foods have been extensively investigated. In this study, five pairs of meroterpenoid enantiomers beyond well-known triterpenoids and polysaccharides, dayaolingzhiols I−M (1–5), were characterized from Ganoderma lucidum. Their structures were identified using spectroscopic and computational methods. Structurally, compound 1 features a novel dioxabicyclo[2.2.2]octan-3-one motif in the side chain. Ethnoknowledge-derived biological evaluation found that (+)-5 could activate Akt and AMPK phosphorylation in insulin-stimulated C2C12 cells, and (+)-5 could activate glucose uptake dose dependently in C2C12 cells. Furthermore, we found that (+)-1 (+)-4, and (–)-4 could significantly inhibit cell migration of the MDA-MB-231 cell line, of which (+)-4 showed significant inhibitory effects against cell migration of the MDA-MB-231 cell line in a dose-dependent manner. These findings revealed the meroterpenoidal composition of G. lucidum and its roles in the prevention of chronic diseases such as diabetes mellitus and triple-negative breast cancer.

The chemistry and biology of fungal meroterpenoids (2009-2019)

Fungal meroterpenoids are secondary metabolites from mixed terpene-biosynthetic origins. Their intriguing chemical structural diversification and complexity, potential bioactivities, and pharmacological significance make them attractive targets in natural product chemistry, organic synthesis, and biosynthesis. This review provides a systematic overview of the isolation, chemical structural features, biological activities, and fungal biodiversity of 1585 novel meroterpenoids from 79 genera terrestrial and marine-derived fungi including macrofungi, Basidiomycetes, in 441 research papers in 2009-2019. Based on the nonterpenoid starting moiety in their biosynthesis pathway, meroterpenoids were classified into four categories (polyketide-terpenoid, indole-, shikimate-, and miscellaneous-) with polyketide-terpenoids (mainly tetraketide-) and shikimate-terpenoids as the primary source. Basidiomycota produced 37.5% of meroterpenoids, mostly shikimate-terpenoids. The genera of Ganoderma, Penicillium, Aspergillus, and Stachybotrys are the four dominant producers. Moreover, about 56% of meroterpenoids display various pronounced bioactivities, including cytotoxicity, enzyme inhibition, antibacterial, anti-inflammatory, antiviral, antifungal activities. It's exciting that several meroterpenoids including antroquinonol and 4-acetyl antroquinonol B were developed into phase II clinically used drugs. We assume that the chemical diversity and therapeutic potential of these fungal meroterpenoids will provide biologists and medicinal chemists with a large promising sustainable treasure-trove for drug discovery.

Lucidumones B-H, racemic meroterpenoids that inhibit tumor cell migration from Ganoderma lucidum

Seven new meroterpenoids, lucidumones B-H (1 and 3-8), along with one known meroterpenoid (2), were isolated from the fruiting bodies of Ganoderma lucidum. The structures of the new compounds were assigned by spectroscopic and computational methods. All the isolated compounds were tested for their inhibition on human cancer cell migration. It was found that compounds (-)-1, (+)-2, (-)-4, (+)-6, and (+)-8 could significantly inhibit cell migration in KYSE30 cell line. Further examination disclosed that cell migration inhibition of (+)-6 and (+)-8 might be related with downregulation of N-cadherin.

Applanmerotic acids A and B, two meroterpenoid dimers with an unprecedented polycyclic skeleton from Ganoderma applanatum that inhibit formyl peptide receptor 2

Applanmerotic acids A and B (1 and 2) with a polycyclic skeleton isolated from Ganoderma applantum showed anti-inflammatory activity via inhibiting the activation of FPR2.

Survey of natural products reported by Asian research groups in 2019

The new natural products reported in 2019 in peer-reviewed articles in journals with good reputations were reviewed and analyzed. The advances made by Asian research groups in the field of natural products chemistry in 2019 were summarized. Compounds with unique structural features and/or promising bioactivities originating from Asian natural sources were discussed based on their structural classification.

Meroterpenoids produced by fungi: Occurrence, structural diversity, biological activities, and their molecular targets

Meroterpenoids are partially derived from the terpenoids, distributing widely in the plants, animals and fungi. The complex structures and diverse bioactivities of meroterpenoids have attracted more attention for chemists and pharmacologists. Since the first review summarized by Geris in 2009, there are absent of systematic reviews reported about meroterpenoids from the higher and lower fungi up to now. In the past decades, myriads of meroterpenoids were discovered, and it is necessary to summarize these meroterpenoids about their unique structures and promising bioactivities. In this review, we use a new classification method based on the non-terpene precursors, and also highlight the structural features, bioactivity of natural meroterpenoids from the higher and lower fungi covering the period of September 2008 to February 2020. A total of 709 compounds were discussed and cited the 182 references. Meanwhile, we also primarily summarize their occurrence, structural diversity, biological activities, and molecular targets.

Catalytic Hydroxycyclopropanol Ring-Opening Carbonylative Lactonization to Fused Bicyclic Lactones

A novel palladium-catalyzed ring opening carbonylative lactonization of readily available hydroxycyclopropanols was developed to efficiently synthesize tetrahydrofuran (THF) or tetrahydropyran (THP)-fused bicyclic γ-lactones, two privileged scaffolds often found in natural products. The reaction features mild reaction conditions, good functional group tolerability, and scalability. Its application was demonstrated in a short total synthesis of (±)-paeonilide. The fused bicyclic γ-lactone products can be easily diversified to other medicinally important scaffolds, which further broadens the application of this new carbonylation method.

Ganoderma cochlear Metabolites as Probes to Identify a COX-2 Active Site and as in Vitro and in Vivo Anti-Inflammatory Agents

(±)-Dispirocochlearoids A-C (1-3), meroterpenoids with a 6/6/5/6/6/6 ring system, were isolated from Ganoderma cochlear. 1-3 are selective COX-2 inhibitors with an IC₅₀ value of (-)-2 at 386 nM. Site-directed mutagenesis identified His351 as a COX-2 active site. In vivo anti-inflammatory activities of (-)-2 were performed against acute lung injury in mice.

Fused multicyclic polyketides with a two-spiro-carbon skeleton from mangrove-derived endophytic fungus Epicoccum nigrum SCNU-F0002

A pair of uncommon fused multicyclic polyketides, (±)-isoepicolactone and one new isobenzofuranone monomer, together with four other known biosynthetically related compounds were isolated from the fermentation of fungus Epicoccum nigrum SCNU-F0002.

Hot off the Press

A personal selection of 32 recent papers is presented covering various aspects of current developments in bioorganic chemistry and novel natural products such as burlemarxione A from Clusia burle-marxii.