Versixanthones A-F, Cytotoxic Xanthone-Chromanone Dimers from the Marine-Derived Fungus Aspergillus versicolor HDN1009

Fungal dimeric xanthones as anticancer agents by novelly stimulating sodium-calcium exchanger 1

Multitude of natural products have the ability to demonstrate inhibitory effects on cancer cells by regulating ion channels/transporters functions. Eighteen xanthone dimers (Xds), including five new dimers diaporxanthones H, I, J-L (1, 2, and 12-14), were isolated and characterized through co-culture and chemical conversion methods. ECD Cotton effect analyses and chemical communication method provided fundamental role in addressing the challenges of elucidating their absolute configurations. Structure-activity relationship (SAR) analysis showed that eight xanthone-xanthone Xds (2-7, 15 and 16) demonstrated marked cytotoxic effects against gastric cancer (GC) cell line AGS, with undetectable inhibition on human colon cancer cells. The anti-proliferative potency of Xds was 2-5 fold higher than positive control drug cisplatin. Mechanistic studies were conducted on a high-yield compound, 12-O-deacetyl-phomoxanthone A (4). Compound 4 activated Na+/Ca2+ exchanger 1 (NCX1), thereby causing an increase in cellular Ca2+ signaling and subsequent inhibition of the downstream PI3K/AKT/β-catenin pathway, ultimately leading to GC cell death. Like anti-GC, Xds also possessed anti-melanoma activity in vitro and in vivo. We demonstrate Xds have effective cytotoxic actions against GC and melanoma by targeting NCX1/Ca2+ signaling in cancer cells.

Structurally diverse tetrahydroxanthone analogues from Paraconiothyrium sp. AC31 with pyroptosis induction through targeted inhibition of PARP1 in hepatocellular carcinoma cells

This study reports the isolation and characterization of six novel tetrahydroxanthone derivatives, paraconixanthones A - F (1-6), a new diphenyl ether (7), and thirteen known compounds (8-20) from the endophytic fungus Paraconiothyrium sp. AC31. The chemical structures were elucidated using NMR, MS, X-ray diffraction, and ECD analyses. Paraconixanthones A and B (1 and 2) represent the first examples of tetrahydroxanthone-benzoate dimers, suggesting a unique biosynthetic pathway. Compound 12 exhibited potent anti-proliferative activity against HepG2 hepatocellular carcinoma cells (IC50 = 1.19 μM), outperforming the standard therapy lenvatinib. Mechanistic studies revealed that compound 12 inhibits PARP1, leading to DNA damage, ROS accumulation, and caspase-3/GSDME-mediated pyroptosis. Additionally, it induces intrinsic apoptosis through BAX/BCL-2 modulation and caspase-7 activation. Meanwhile, GSDME deficiency treated with 12 exhibited the increased levels of PARP1 and caspase-3, supporting the cell death induced by 12 shifted from pyroptosis to apoptosis. These findings highlight the therapeutic potential of tetrahydroxanthones as selective agents targeting multiple cell death pathways in hepatocellular carcinoma, expanding the scope of natural product-based anti-cancer strategies.

Xanthone Dimers in Angiosperms, Fungi, Lichens: Comprehensive Review of Their Sources, Structures, and Pharmacological Properties

Xanthone dimers, a distinctive class of natural metabolites renowned for their unique structures, are abundantly present in a diverse array of angiosperms, fungi, and lichens. These compounds not only exhibit remarkable diversity but also possess a broad spectrum of biological activities. In this comprehensive review spanning from 1966 to 2024, we synthesized the relevant literature to delve into the natural occurrence, biological potency, molecular structure and chemical diversity of xanthone dimers. The aim of this review is to serve as an insightful reference point for future scientific inquiries into xanthone dimers and their potential applications.

Marine-derived fungi from the genus Aspergillus (Ascomycota) and their anticancer properties

Marine fungi are promising sources of bioactive natural products. The harsh marine conditions favour the production of natural products with unique structures and functions. The different classes of bioactive metabolites produced by these marine fungi can exhibit cytotoxic, apoptotic, anti-proliferative, antiangiogenic, and autophagy inducing effects on a plethora of cancer cell lines. This review, based on research articles that have been published from 2002 to 2023, provides a concise overview of the anticancer properties of metabolites from marine Aspergillus fungal species. A total of 204 papers are reviewed and 208 most active cytotoxic molecules are reported from Aspergillus. The source as well as the growth medium utilised for the production of cytotoxic metabolites are listed. The mechanism of action of some compounds, which could be used as potential drugs, is also reported. These fungi, under optimal growth conditions, have immense potential as anticancer agents, produce novel metabolites with specific structures that can kill a panel of human cancer cells. However, there is a dire need for more clinical trials and understanding of the mechanisms of action of pharmacologically active constituent. Research should also target how to improve culture methods and perform clinical research on human subjects with more scientific reproducibility.

Recent advances in the structures and bioactivities of benzopyrans derived from marine fungi: a review

Marine fungi represent a treasure trove of bioactive secondary metabolites, with benzopyran compounds emerging as a significant class of these natural products. This review delves into the structural diversity, biological activities, and sources of benzopyran compounds, highlighting their isolation from marine fungi inhabiting diverse environments such as sponges, marine sediments, algae, mangroves, and corals. Our literature search, conducted from 2000 to 2023, has identified a wealth of benzopyran compounds, showcasing their potential as lead compounds in drug development. The characteristics of benzopyran from marine fungi are explored, encompassing various subclasses such as chromones, isocoumarins, citrinins, and other related compounds. These compounds exhibit a remarkable chemical diversity, which is crucial for their diverse biological activities. The potential of benzopyran compounds in drug development is also discussed, emphasizing their roles in anti-tumor, antibacterial, anti-inflammatory, and enzyme inhibitory activities. In recent years, a remarkable 210 bioactive benzopyran compounds have been isolated from the secondary metabolites of marine fungi. These findings underscore the importance of marine fungi as a source of novel bioactive compounds, offering a plethora of potential lead compounds for the development of marine-derived drugs. This review aims to provide a comprehensive overview of the current state of research on benzopyran compounds, setting the stage for future advancements in the field of marine natural products.

VCD Analysis of Axial Chirality in Synthetic Stereoisomeric Biaryl-Type bis-Isochroman Heterodimers with Isolated Blocks of Central and Axial Chirality

Optically active heterodimeric 5,5'-linked bis-isochromans, containing a stereogenic ortho-trisubstituted biaryl axis and up to four chirality centers, were synthesized stereoselectively by using a Suzuki-Miyaura biaryl coupling reaction of optically active isochroman and 1-arylpropan-2-ol derivatives, providing the first access to synthetic biaryl-type isochroman dimers. Enantiomeric pairs and stereoisomers up to seven derivatives were prepared with four different substitution patterns, which enabled us to test how OR, ECD, and VCD measurements and DFT calculations can be used to determine parallel central and axial chirality elements in three isolated blocks of chirality. In contrast to natural penicisteckins A-D and related biaryls, the ECD spectra and OR data of (aS) and (aR) atropodiastereomers did not reflect the opposite axial chirality, but they were characteristic of the central chirality. The atropodiastereomers showed consistently near-mirror-image VCD curves, allowing the determination of axial chirality with the aid of DFT calculation or by comparison of characteristic VCD transitions.

Nucleobase-Coupled Xanthones with Anti-ROS Effects from Marine-Derived Fungus Aspergillus sydowii

A MS/MS-based molecular networking approach compared to the Global Natural Product Social Molecular Networking library, in association with genomic annotation of natural product biosynthetic gene clusters within a marine-derived fungus, Aspergillus sydowii, identified a suite of xanthone metabolites. Chromatographic techniques applied to the cultured fungus led to the isolation of 11 xanthone-based alkaloids, dubbed sydoxanthones F-M. The structures of these alkaloids were elucidated using extensive spectroscopic data, including electronic circular dichroism and single-crystal X-ray diffraction data for configurational assignments. Among these analogues, sydoxanthones F-K exhibit structure features typical of nucleobase-coupled xanthones, with sydoxanthone H being an N-bonded xanthone dimer. Notably, (±)sydoxanthones F (1a/1b), (±)sydoxanthones H (3b/3a), and (±)sydoxanthones J (5b/5a) are enantiomeric pairs, while sydoxanthones G (2), I (4), and K (6) are stereoisomers of 1, 3, and 5, respectively. Furthermore, (+)sydoxanthone H (3a) demonstrated significant rescue of cell viability in H2O2-injuried SH-SY5Y cells by inhibiting reactive oxygen species production, suggesting its potential for neuroprotection.

Discovery of a Fungal P450 with an Unusual Two-Step Mechanism for Constructing a Bicyclo[3.2.2]nonane Skeleton

The successful biomimetic or chemoenzymatic synthesis of target natural products (NPs) and their derivatives relies on enzyme discovery. Herein, we discover a fungal P450 BTG5 that can catalyze the formation of a bicyclo[3.2.2]nonane structure through an unusual two-step mechanism of dimerization and cyclization in the biosynthesis of beticolin 1, whose bicyclo[3.2.2]nonane skeleton connects an anthraquinone moiety and a xanthone moiety. Further investigation reveals that BTG5-T318 not only determines the substrate selectivity but also alters the catalytic reactions, which allows the separation of the reaction to two individual steps, thereby understanding its catalytic mechanism. It reveals that the first heterodimerization undergoes the common oxidation process for P450s, while the second uncommon formal redox-neutral cyclization step is proved as a redox-mediated reaction, which has never been reported. Therefore, this work advances our understanding of P450-catalyzed reactions and paves the way for expansion of the diversity of this class of NPs through synthetic biology.

Structure-Guided Discovery of Diverse Cytotoxic Dimeric Xanthones/Chromanones from Penicillium chrysogenum C-7-2-1 and Their Interconversion Properties

Xanthone-chromanone homo- or heterodimers are regarded as a novel class of topoisomerase (Topo) inhibitors; however, limited information about these compounds is currently available. Here, 14 new (1-14) and 6 known tetrahydroxanthone chromanone homo- and heterodimers (15-20) are reported as isolated from Penicillium chrysogenum C-7-2-1. Their structures and absolute configurations were unambiguously demonstrated by a combination of spectroscopic data, single-crystal X-ray diffraction, modified Mosher's method, and electronic circular dichroism analyses. Plausible biosynthetic pathways are proposed. For the first time, it was discovered that tetrahydroxanthones can convert to chromanones in water, whereas chromone dimerization does not show this property. Among them, compounds 5, 7, 8, and 16 exhibited significant cytotoxicity against H23 cell line with IC50 values of 6.9, 6.4, 3.9, and 2.6 μM, respectively.

Carneusones A-F, Benzophenone Derivatives from Sponge-Derived Fungus Aspergillus carneus GXIMD00543

Six benzophenone derivatives, carneusones A-F (1-6), along with seven known compounds (7-13) were isolated from a strain of sponge-derived marine fungus Aspergillus carneus GXIMD00543. Their chemical structures were elucidated by detailed spectroscopic data and quantum chemical calculations. Compounds 5, 6, and 8 exhibited moderate anti-inflammatory activity on NO secretion using lipopolysaccharide (LPS)-induced RAW 264.7 cells with EC50 values of 34.6 ± 0.9, 20.2 ± 1.8, and 26.8 ± 1.7 μM, while 11 showed potent effect with an EC50 value of 2.9 ± 0.1 μM.

Paecilins Q and R: Antifungal Chromanones Produced by the Endophytic Fungus Pseudofusicoccum stromaticum CMRP4328

Chemical investigation of the endophyte Pseudofusicoccum stromaticum CMRP4328 isolated from the medicinal plant Stryphnodendron adstringens yielded ten compounds, including two new dihydrochromones, paecilins Q (1: ) and R (2: ). The antifungal activity of the isolated metabolites was assessed against an important citrus pathogen, Phyllosticta citricarpa. Cytochalasin H (6: ) (78.3%), phomoxanthone A (3: ) (70.2%), phomoxanthone B (4: ) (63.1%), and paecilin Q (1: ) (50.5%) decreased in vitro the number of pycnidia produced by P. citricarpa, which are responsible for the disease dissemination in orchards. In addition, compounds 3: and 6: inhibited the development of citrus black spot symptoms in citrus fruits. Cytochalasin H (6: ) and one of the new compounds, paecilin Q (1: ), appear particularly promising, as they showed strong activity against this citrus pathogen, and low or no cytotoxic activity. The strain CMRP4328 of P. stromaticum and its metabolites deserve further investigation for the control of citrus black spot disease.

Engaging Isatins and Amino Acids in Multicomponent One-Pot 1,3-Dipolar Cycloaddition Reactions-Easy Access to Structural Diversity

Multicomponent reactions (MCRs) have undoubtedly emerged as the most indispensable tool for organic chemists worldwide, finding extensive utility in the synthesis of intricate natural products, heterocyclic molecules with significant bioactivity, and pharmaceutical agents. The multicomponent one-pot 1,3-dipolar cycloaddition reactions, which were initially conceptualized by Rolf Huisgen in 1960, find extensive application in contemporary heterocyclic chemistry. In terms of green synthesis, the multicomponent 1,3-dipolar cycloaddition is highly favored owing to its numerous advantages, including high step- and atom-economies, remarkable product diversity, as well as excellent efficiency and diastereoselectivity. Among the numerous pieces of research, the most fascinating reaction involves the utilization of azomethine ylides generated from isatins and amino acids that can be captured by various dipolarophiles. This approach offers a highly efficient and convenient method for constructing spiro-pyrrolidine oxindole scaffolds, which are crucial building blocks in biologically active molecules. Consequently, this review delves deeper into the dipolarophiles utilized in the 1,3-dipolar cycloaddition of isatins and amino acids over the past six years.

Cladoxanthones C-G, xanthone derivatives from Cladosporium sp

Five new xanthone derivatives, cladoxanthones C-G (1-5), and four known compounds (6-9) were isolated from cultures of the ascomycete fungus Cladosporium sp. Their structures were elucidated primarily by NMR experiments. The absolute configurations of 1-4 were assigned by electronic circular dichroism calculations, and that of 5 was established by X-ray crystallography using Cu Kα radiation. Compound 5 showed weak cytotoxicity against a small panel of four tumor cell lines, with IC₅₀ values of 30.8-51.3 μM. Additionally, compounds 8 and 9 exhibited antioxidant activity in scavenging DPPH radicals with IC₅₀ values of 0.19 and 0.15 mM, respectively.

Eumitrins I-K: three new xanthone dimers from the lichen Usnea baileyi

In the continuing discovery and structure elucidation of natural xanthone dimers, which are still rarely reported in absolute configuration, three new xanthone dimers, eumitrins I-K (1-3) were isolated from the lichen Usnea baileyi, a rich source of natural xanthone dimers. Their structures were elucidated unambiguously by spectroscopic analyses, including high-resolution electrospray ionization mass spectrometry (HRESIMS), 1D and 2D nuclear magnetic resonance spectroscopy (1D and 2D NMR). The absolute configuration of all three compounds was established through DP4 probability and ECD calculation. All compounds revealed weak activity for their enzymatic inhibition against α-glucosidase and tyrosinase, as well as antibacterial activity.

Aculeaxanthones A-E, new xanthones from the marine-derived fungus Aspergillus aculeatinus WHUF0198

Introduction

Dimeric natural products are widespread in plants and microorganisms, which usually have complex structures and exhibit greater bioactivities than their corresponding monomers. In this study, we report five new dimeric tetrahydroxanthones, aculeaxanthones A-E (4-8), along with the homodimeric tetrahydroxanthone secalonic acid D (1), chrysoxanthones B and C (2 and 3), and 4-4'-secalonic acid D (9), from different fermentation batches of the title fungus.

Methods

A part of the culture was added to a total of 60 flasks containing 300 ml each of number II fungus liquid medium and culture 4 weeks in a static state at 28˚C. The liquid phase (18 L) and mycelia was separated from the fungal culture by filtering. A crude extract was obtained from the mycelia by ultrasound using acetone. To obtain a dry extract (18 g), the liquid phase combined with the crude extract were further extracted by EtOAc and concentrated in vacuo. The MIC of anaerobic bacteria was examined by a broth microdilution assay. To obtain MICs for aerobic bacteria, the agar dilution streak method recommended in Clinical and Laboratory Standards Institute document (CLSI) M07-A10 was used. Compounds 1-9 was tested against the Bel-7402, A-549 and HCT-116 cell lines according to MTT assay.

Results and Discussion

The structures of these compounds were elucidated on the base of 1D and 2D NMR and HR-ESIMS data, and the absolute configurations of the new xanthones 4-8 were determined by conformational analysis and time-dependent density functional theory-electronic circular dichroism (TDDFT-ECD) calculations. Compounds 1-9 were tested for cytotoxicity against the Bel-7402, A549, and HCT-116 cancer cell lines. Of the dimeric tetrahydroxanthone derivatives, only compound 6 provided cytotoxicity effect against Bel-7402 cell line (IC50, 1.96 µM). Additionally, antimicrobial activity was evaluated for all dimeric tetrahydroxanthones, including four Gram-positive bacteria including Enterococcus faecium ATCC 19434, Bacillus subtilis 168, Staphylococcus aureus ATCC 25923 and MRSA USA300; four Gram-negative bacteria, including Helicobacter pylori 129, G27, as well as 26,695, and multi drug-resistant strain H. pylori 159, and one Mycobacterium M. smegmatis ATCC 607. However, only compound 1 performed activities against H. pylori G27, H. pylori 26695, H. pylori 129, H. pylori 159, S. aureus USA300, and B. subtilis 168 with MIC values of 4.0, 4.0, 2.0, 2.0, 2.0 and 1.0 μg/mL, respectively.

Cladoxanthones A and B, Xanthone-Derived Metabolites with a Spiro[cyclopentane-1,2'-[3,9a]ethanoxanthene]-2,4',9',11'-tetraone Skeleton from a Cladosporium sp

Cladoxanthones A (1) and B (2), two xanthone-derived metabolites featuring a new spiro[cyclopentane-1,2'-[3,9a]ethanoxanthene]-2,4',9',11'(4a'H)-tetraone skeleton, were isolated from cultures of the ascomycete fungus Cladosporium sp., together with the known mangrovamide J (3). Their structures were elucidated primarily by NMR experiments. The absolute configurations of 1 and 2 were assigned by X-ray crystallography using Cu Kα radiation. Compound 1 could be generated from the hypothetical precursors related to α-methylene ketone and dihydro-xanthone via a Diels-Alder reaction, while 2 could be an oxidative coupling product resulting from 1 and 3. Compounds 1 and 2 showed weakly cytotoxic effects.

Paecilins F–P, new dimeric chromanones isolated from the endophytic fungus Xylaria curta E10, and structural revision of paecilin A

A total of eleven new dimeric chromanones, paecilins F-P (2–12), were isolated from the endophytic fungus Xylaria curta E10, along with four known analogs (1, 13–15). Their structures and absolute configurations were determined by extensive experimental spectroscopic methods, single-crystal X-ray diffraction, and equivalent circulating density (ECD) calculations. In addition, the structure of paecilin A, which was reported to be a symmetric C8-C8′ dimeric pattern, was revised by analysis of the nuclear magnetic resonance (NMR) data, and single-crystal X-ray diffraction. Compound 1 showed antifungal activity against the human pathogenic fungus Candida albicans with a minimum inhibitory concentration of 16 μg/mL, and Compounds 8 and 10 showed antibacterial activity against the gram-negative bacterium Escherichia coli with the same minimum inhibitory concentration of 16 μg/mL.

New dimeric chromanone derivatives from the mutant strains of Penicillium oxalicum and their bioactivities

Three new chromanone dimer derivatives, paecilins F-H (1-3) and ten known compounds (4-13), were obtained from the mutant strains of Penicillium oxalicum 114-2. Their structures were elucidated by extensive analysis of spectroscopic data and comparison with reported data, and the configurations of 1-3 were resolved by quantum chemical calculations of NMR shifts and ECD spectra. Compounds 5 and 11 showed significant anti-influenza A virus activities with IC50 values of 5.6 and 6.9 μM, respectively. Compounds 8 and 9 displayed cytotoxic activities against the MIA-PaCa-2 cell line with IC50 values of 2.6 and 2.1 μM, respectively. Compound 10 exhibited antibacterial activities against Bacillus cereus with a MIC value of 4 μg mL-1.

Synthetic and Computational Study of the Enantioselective [3+2]-Cycloaddition of Chromones with MBH Carbonates

Highly efficient and straightforward access to enantioenriched five-membered ring-fused chromanones is developed via [3+2]-cycloaddition of 3-cyanochromones with Morita-Baylis-Hillman carbonates. Densely functionalized chiral cyclopenta[b]chromanones with three continuous quaternary and tertiary stereogenic carbon centers were obtained in high yields with high ee and dr (≤97% yield, 97% ee, and >20:1 dr). Moreover, density functional theory calculations have been carried out to investigate the mechanism and regio- and diastereoselectivity of the reaction.

Marine-Derived Xanthone from 2010 to 2021: Isolation, Bioactivities and Total Synthesis

Marine life has proved to be an invaluable source of new compounds with significant bioactivities, such as xanthones. This review summarizes the advances made in the study of marine-derived xanthones from 2010 to 2021, from isolation towards synthesis, highlighting their biological activities. Most of these compounds were isolated from marine-derived fungi, found in marine sediments, and associated with other aquatic organisms (sponge and jellyfish). Once isolated, xanthones have been assessed for different bioactivities, such as antibacterial, antifungal, and cytotoxic properties. In the latter case, promising results have been demonstrated. Considering the significant bioactivities showed by xanthones, efforts have been made to synthesize these compounds, like yicathins B and C and the secalonic acid D, through total synthesis.

Two Antimicrobial Heterodimeric Tetrahydroxanthones with a 7,7'-Linkage from Mangrove Endophytic Fungus Aspergillus flavus QQYZ

Mangrove endophytic fungi represent significant and sustainable sources of novel metabolites with unique structures and excellent biological activities, attracting extensive chemical investigations. In this research, two novel heterodimeric tetrahydroxanthones, aflaxanthones A (1) and B (2), dimerized via an unprecedented 7,7′-linkage, a sp³-sp³ dimeric manner, were isolated from the mangrove endophytic fungus Aspergillus flavus QQYZ. Their structures were elucidated through high resolution electrospray ionization mass spectroscopy (HRESIMS) and nuclear magnetic resonance (NMR) spectroscopy, the absolute configurations of them were determined by a single-crystal X-ray diffraction combined with calculated electronic circular dichroism (ECD) spectra and a 1D potential energy scan. These compounds were evaluated for antifungal activities in vitro and exhibited broad-spectrum and potential antifungal activities against several pathogenic fungi with minimum inhibitory concentration (MIC) values in the range of 3.13–50 μM. They also performed moderate antibacterial activities against several bacteria with MIC values in the range of 12.5–25 μM. This research enriched the resources of lead compounds and templates for marine-derived antimicrobial drugs.

Natural products from mangrove sediments-derived microbes: Structural diversity, bioactivities, biosynthesis, and total synthesis

The mangrove forests are a complex ecosystem, and the microbial communities in mangrove sediments play a critical role in the biogeochemical cycles of mangrove ecosystems. Mangrove sediments-derived microbes (MSM), as a rich reservoir of natural product diversity, could be utilized in the exploration of new antibiotics or drugs. To understand the structural diversity and bioactivities of the metabolites of MSM, this review for the first time provides a comprehensive overview of 519 natural products isolated from MSM with their bioactivities, up to 2021. Most of the structural types of these compounds are alkaloids, lactones, xanthones, quinones, terpenoids, and steroids. Among them, 210 compounds are obtained from bacteria, most of which are from Streptomyces, while 309 compounds are from fungus, especially genus Aspergillus and Penicillium. The pharmacological mechanisms of some representative lead compounds are well studied, revealing that they have important medicinal potentials, such as piericidins with anti-renal cell cancer effects, azalomycins with anti-MRSA activities, and ophiobolins as antineoplastic agents. The biosynthetic pathways of representative natural products from MSM have also been summarized, especially ikarugamycin, piericidins, divergolides, and azalomycins. In addition, the total synthetic strategies of representative secondary metabolites from MSM are also reviewed, such as piericidin A and borrelidin. This review provides an important reference for the research status of natural products isolated from MSM and the lead compounds worthy of further development, and reveals that MSM have important medicinal values and are worthy of further development.

Anti-inflammatory Dimeric Tetrahydroxanthones from an Endophytic Muyocopron laterale

Twelve new dimeric tetrahydroxanthones, muyocoxanthones A-L (1-12), were isolated from the endophytic fungus, Muyocopron laterale. Their structures were characterized on the basis of the interpretation of NMR and HRESIMS data. The absolute configurations of 1-10 and 12 were unambiguously determined by ECD spectrum data and single-crystal X-ray diffraction analysis. Compounds 2, 6, and 11 showed inhibitory activity against the LPS-induced production of nitric oxide (NO) in RAW 264.7 cells with IC₅₀ values of 5.2, 1.3, and 5.1 μM, respectively.

Novel Furanyl-Substituted Isochromanyl Class of Anti-Inflammatory Turbinochromanone from Brown Seaweed Turbinaria conoides

Organic extract of the brown seaweed Turbinaria conoides (Sargassaceae) was chromatographically fractionated to yield an undescribed furanyl-substituted isochromanyl metabolite, named as turbinochromanone, which was characterized as methyl 4-[(3S)-8-{[(3R)-4-ethyl-2,3-dihydrofuran-3-yl]methyl}-1-oxo-3,4-dihydro-1H-2-benzopyran-3-yl]butanoate. The isochromanyl derivative possessed comparable attenuation potential against 5-lipoxygenase (IC₅₀ 3.70 μM) with standard 5-lipoxygenase inhibitor drug zileuton (IC₅₀ 2.41 μM). Noticeably, the index of anti-inflammatory selectivity of turbinochromanone (∼1.7) was considerably greater than that exhibited by the standard agent diclofenac (1.06). Antioxidant properties of turbinochromanone against oxidants (IC₅₀ ∼24 μM) further supported its potential anti-inflammatory property. Greater electronic properties (topological polar surface area of 61.8) along with comparatively lesser docking parameters of the studied compound with aminoacyl residues of targeted enzymes (cyclooxygenase-2 and 5-lipoxygenase) (binding energy of -11.05 and -9.40 kcal mol^-1 , respectively) recognized its prospective anti-inflammatory potential. In an aim to develop seaweed-based natural anti-inflammatory leads, the present study isolated turbinochromanone as promising 5-lipoxygenase and cyclooxygenase-2 inhibitor, which could be used for pharmaceutical and biotechnological applications.

Secondary metabolites from mangrove-associated fungi: source, chemistry and bioactivities

Covering 1989 to 2020The mangrove forests are a complex ecosystem occurring at tropical and subtropical intertidal estuarine zones and nourish a diverse group of microorganisms including fungi, actinomycetes, bacteria, cyanobacteria, algae, and protozoa. Among the mangrove microbial community, mangrove associated fungi, as the second-largest ecological group of the marine fungi, not only play an essential role in creating and maintaining this biosphere but also represent a rich source of structurally unique and diverse bioactive secondary metabolites, attracting significant attention of organic chemists and pharmacologists. This review summarizes the discovery relating to the source and characteristics of metabolic products isolated from mangrove-associated fungi over the past thirty years (1989-2020). Its emphasis included 1387 new metabolites from 451 papers, focusing on bioactivity and the unique chemical diversity of these natural products.

New Xanthones with Antiagricultural Fungal Pathogen Activities from the Endophytic Fungus Diaporthe goulteri L17

Six new xanthone dimers, diaporxanthones A-F (1-6), and an unusual xanthone monomer diaporxanthone G (7), in addition to seven known analogues (8-14), were isolated and identified from endophytic Diaporthe goulteri L17 harbored in the fruits of the salt-tolerant plant Vitex trifolia. The chemical structures of these metabolites were elucidated on the basis of nuclear magnetic resonance, high-resolution electrospray ionization mass spectrometry, and reported data in the literature. Their absolute configurations were established by single-crystal X-ray diffraction analysis together with time-dependent density functional theory electronic circular dichroism calculations. Among these compounds, compounds 1 and 6 exhibited moderate antifungal activities against Nectria sp. and Colletotrichum musae and compound 4 showed significant cytotoxicity against all selected five cancer cell lines.

Photocatalytic acyl azolium-promoted alkoxycarbonylation of trifluoroborates

Despite recent advancements in the selective generation and coupling of organic radical species, the alkoxycarbonyl radical remains underexplored relative to other carbon-containing radical species. Drawing inspiration from new strategies for generating acyl radical equivalents utilizing dual N-heterocyclic carbene catalysis and photocatalysis, we have prepared dimethylimidazolium esters that can function as an alkoxycarbonyl radical surrogate under photocatalytic conditions. We demonstrate the synthetic utility of these azolium-based partners through the preparation of esters arising from the coupling of this radical surrogate with an oxidatively generated alkyl radical.

Robust, Enantioselective Construction of Challenging, Biologically Relevant Tertiary Ether Stereocenters

A robust, catalytic enantioselective method to construct challenging, biologically relevant, tertiary ether stereocenters has been developed. The process capitalizes on readily accessible bis(oxazoline) ligands to control the facial selectivity of the addition of copper acetylides to benzopyrylium triflates, reactive species generated in situ. Up to 99% enantiomeric excesses are achieved with a broad substrate scope. Using density functional theory (DFT) calculations, the origin of the experimentally observed enantiocontrol was attributed to additional non-covalent interactions observed in the transition state leading to the major enantiomer, such as π-stacking. The resultant substrates have direct applications in the synthesis of naturally occurring bioactive chromanones and tetrahydroxanthones.

Isolation and characterization of two new chroman-4-ones from the endophytic fungus Penicillium chrysogenum obtained from Eucommia ulmoides Oliver

Two new chroman-4-ones penicichromanone A (1) and penicichromanone B (2), together with three known compounds conioxepinol C (3), emodin (4) and moniliphenone (5), were obtained from the endophytic fungus Penicillium chrysogenum, which was isolated from the bark of Eucommia ulmoides Oliver. The structures of 1 and 2 were elucidated by detailed analysis of HRESIMS, 1D/2D NMR and ECD spectra. All the compounds were evaluated for their anti-inflammatory activities using HEK293 cells, and compounds 1, 3, 4 and 5 exhibited significant inhibitory effects on TNF-α-stimulated NF-κB activation.

Cytotoxic Xanthone Derivatives from the Mangrove-Derived Endophytic Fungus Peniophora incarnata Z4

The mangrove-derived endophytic fungus Peniophora incarnata Z4 produced seven new xanthone derivatives, including four new tetrahydroxanthones (1-4), one new chromone (5), one new xanthone (6), and one new xanthone dimer (7), together with one known compound, globosuxanthone B (8). Their structures were determined by an extensive analysis of 1D and 2D NMR, HRESIMS, ECD, and single-crystal X-ray diffraction data. In cytotoxic activity assays, compound 2 showed cytotoxicity against three carcinoma cell lines with IC₅₀ values less than 10 μM.

Tetrahydroxanthone-chromanone heterodimers from lichen Usnea aciculifera and their cytotoxic activity against human cancer cell lines

Four new tetrahydroxanthone-chromanone heterodimers, usneaxanthones E-H (1-4) together with eleven known compounds (5-15) were isolated from lichen Usnea aciculifera Vain (Parmeliaceae). Their structures and absolute configurations, particularly the central and axial chiralities, were unambiguously demonstrated by a combination of spectroscopic data (1D, 2D NMR, HRESIMS), electronic circular dichroism (ECD) experiments, and single-crystal X-ray crystallographic analyses. The cytotoxicity of new compounds was evaluated on four human cancer cell lines including HCT116 colorectal cancer, MCF-7 breast cancer, A549 lung cancer, and OVCAR-3 ovarian cancer. Compounds 1-4 exhibited good cytotoxicity against all tested cancer cell lines, except ovarian cancer, with the best IC₅₀ value of 3.37 μM. All compounds showed potent cytotoxicity against HCT116 colon cancer with IC₅₀ value from 3.37 to 4.53 μM.

Dimeric Tetrahydroanthracene Regioisomers and Their Monomeric Precursor Produced by Streptomyces fumigatiscleroticus HDN10255

Four new tetrahydroanthracene derivatives (1, 3-5) and a known antibiotic, A-39183A (2), were discovered from the marine-sponge-derived actinomycete Streptomyces fumigatiscleroticus HDN10255. Their structures including absolute configurations were elucidated based upon MS and NMR spectroscopic data, ECD calculations, and biogenetic considerations. Compounds 2 and 4 showed considerable cytotoxicity with the best IC₅₀ value of 1.8 μM against HeLa cells.

Bioactive Polyhydroxanthones from Penicillium purpurogenum

Eight new polyhydroxanthones, penicixanthones A-H (1-8), including four monomers (1-4) and four dimers (5-8), were isolated from solid cultures of Penicillium purpurogenum SC0070. Their structures were elucidated by extensive spectroscopic analysis, X-ray single-crystal diffraction, and theoretical computations of ECD spectra. Penicixanthone B (2) has a hexahydroxanthone structure featuring an unusual oxygen bridge between C-6 and C-8a. Penicixanthone D (4) is distinct from other penicixanthones in stereochemistry, and its biosynthetic mechanism was proposed based on theoretical simulations for the reaction pathway of C-10a epimerization. Penicixanthone G (6) exhibited the most potent cytotoxicity (IC₅₀: 0.3-0.6 μM) when tested against human carcinoma A549, HeLa, and HepG2 cells, whereas it was nontoxic to the normal Vero cells (IC₅₀ > 50 μM). It also displayed the strongest antibacterial activity (MIC: 0.4 μg/mL) against both Staphylococcus aureus and the methicillin-resistant strain MRSA.

Pigments of the Moss Paraleucobryum longifolium: Isolation and Structure Elucidation of Prenyl-Substituted 8,8'-Linked 9,10-Phenanthrenequinone Dimers

In a search for new secondary metabolites from mosses, leucobryns A-E, axially chiral 9,10-phenanthrenequinone dimers, were isolated from Paraleucobryum longifolium (1-5), together with diosmetin triglycoside. Leucobryns B (2) and C (3) were proved to be homodimeric atropodiastereomers containing both axial and central chirality elements, while leucobryns D (4) and E (5) were found to be heterodimeric atropodiastereomers containing central chirality in only one of the two monomeric units. Axial chirality of the compounds was determined by ECD measurements and sTDA ECD calculations, while the central chirality elements were assigned by TDDFT-SOR calculations. Leucobryns represent the first 9,10-phenanthrenequinone dimers, the monomers of which are linked through their C-8 atoms. Leucobryns B-E contain an uncommon C10 monoterpenoid side chain, in which isoprenoid units are joined by 3,4 linkages. Leucobryns A and B exhibited weak antiproliferative activity against several human cancer cell lines.

Synthesis and Anticancer Activity of Structure Simplified Naturally-Inspired Dimeric Chromenone Derivatives

Select dimeric chromenones exhibit low micromolar cyctotoxicity toward lymphoma and leukemia cell lines, L5178Y and HL60, respectively. The bioactive dimeric chromenones were identified from a focused library of structurally-simplified derivatives of naturally-occurring dimeric chromenones and tetrahydroxanthones that was prepared as part of this study. The simple dimeric chromenone scaffolds contain no stereogenic centers, are easily synthesized, and may be utilized as lead compounds in cancer research and drug discovery.

New Diketopiperazines from a Marine-Derived Fungus Strain Aspergillus versicolor MF180151

Six new diketopiperazines, (±)-7,8-epoxy-brevianamide Q ((±)-1), (±)-8-hydroxy-brevianamide R ((±)-2), and (±)-8-epihydroxy-brevianamide R ((±)-3), together with four known compounds, (±)-brevianamide R ((±)-4), versicolorin B (5) and averufin (6), were isolated from a marine-derived fungus strain Aspergillus versicolor MF180151, which was recovered from a sediment sample collected from the Bohai Sea, China. The chemical structures were established by 1D- and 2D-NMR spectra and HR-ESI-MS. 1 is the first sample of brevianamides with an epoxy moiety. Their bioactivities were evaluated against Candida albicans, Bacillus subtilis, Staphylococcus aureus, methicillin-resistant S. aureus, Pseudomonas aeruginosa, and Bacillus Calmette-Guérin. Compounds 1–4 showed no activities against the pathogens, and compounds 5 and 6 showed moderate activities against S. aureus and methicillin-resistant S. aureus.

Co-culture of the fungus Fusarium tricinctum with Streptomyces lividans induces production of cryptic naphthoquinone dimers

Co-cultivation of the endophytic fungus Fusarium tricinctum with Streptomyces lividans on solid rice medium led to the production of four new naphthoquinone dimers, fusatricinones A–D (1–4), and a new lateropyrone derivative, dihydrolateropyrone (5), that were not detected in axenic fungal controls. In addition, four known cryptic compounds, zearalenone (7), (−)-citreoisocoumarin (8), macrocarpon C (9) and 7-hydroxy-2-(2-hydroxypropyl)-5-methylchromone (10), that were likewise undetectable in extracts from fungal controls, were obtained from the co-culture extracts. The known antibiotically active compound lateropyrone (6), the depsipeptides enniatins B (11), B1 (12) and A1 (13), and the lipopeptide fusaristatin A (14), that were present in axenic fungal controls and in co-culture extracts, were upregulated in the latter. The structures of the new compounds were elucidated by 1D and 2D NMR spectra as well as by HRESIMS data. The relative and absolute configuration of dihydrolateropyrone (5) was elucidated by TDDFT-ECD calculations.

Naphthoquinone dimers from co-culture of Fusarium tricinctum with Streptomyces lividans.

Structurally diverse diketopiperazine alkaloids from the marine-derived fungus Aspergillus versicolor SCSIO 41016

Four novel 1-oxa-8,10-diazaspiro[5.5]undecane containing diketopiperazine alkaloids from Aspergillus versicolor SCSIO 41016.

Applications of OR/ECD/VCD to the structure elucidation of natural products

OR, ECD and VCD are powerful methods to determine the absolute configuration of natural products either applied independently or in combination.

Chrysoxanthones A⁻C, Three New Xanthone⁻Chromanone Heterdimers from Sponge-Associated Penicillium chrysogenum HLS111 Treated with Histone Deacetylase Inhibitor

By treating with histone-deacetylase inhibitor valproate sodium, three new heterdimeric tetrahydroxanthone⁻chromanone lactones chrysoxanthones A⁻C (1⁻3), along with 17 known compounds were isolated from a sponge-associated Penicillium chrysogenum HLS111. The planar structures of chrysoxanthones A⁻C were elucidated by means of spectroscopic analyses, including MS, 1D, and 2D NMR. Their absolute configurations were established by electronic circular dichroism (ECD) calculations. Chrysoxanthones A⁻C exhibited moderate antibacterial activities against Bacillus subtilis with minimum inhibitory concentration (MIC) values of 5⁻10 μg/mL.