Bipolarolides A–G: Ophiobolin‐Derived Sesterterpenes with Three New Carbon Skeletons from Bipolaris sp. TJ403‐B1

Undobolins A-L, Ophiobolin-Type Sesterterpenoids from Aspergillus undulatus

Twelve previously undescribed ophiobolin-type sesterterpenoids, undobolins A-L (1-12), were isolated from Aspergillus undulatus, and their structures were elucidated by spectroscopic analysis, ECD calculations, and single-crystal X-ray diffraction experiments. Compound 1 was the second example of 20-nor-ophiobolin reported, while compounds 2-6 were notable for oxygenation of C-2, and compound 6 showed significant inhibitory activity against ConA-induced T lymphocyte proliferation with an IC50 value of 2.3 μM, which suggests a promising new direction in the quest for immunosuppressive agents.

Concise Total Synthesis of (-)-Bipolarolide D

Here we report the first and concise total synthesis of a complex ophiobolin-derived sesterterpene, bipolarolide D, which hinges on two strategic applications of pentafulvene: (1) enantioselective pentafulvene-involved [6+2] cycloaddition; (2) regioselective and diastereoselective pentafulvene-involved Heck cyclization. Late-stage selective allylic addition to the ketone moiety facilitates the successful installation of the side chain. This strategy enabled the accomplishment of its first enantioselective total synthesis through a modular approach. This synthesis will facilitate the investigation of relevant biological activities and provide a synthetic blueprint for utilizing fulvenes as versatile synthons in other complex natural product synthesis.

Armochaetoglasins L and M, new cytochalasans from an arthropod-derived fungus Chaetomium globosum

Armochaetoglasins L (1) and M (2), two new cytochalasans, were isolated from the EtOAc extract of an arthropod-derived fungus Chaetomium globosum. Armochaetoglasin L (1) is a rare 19,20-seco-chaetoglobosin. Their structures were elucidated by NMR spectroscopy and comparison of their electronic circular dichroism (ECD) data. Compounds 1 and 2 were evaluated for anti-inflammatory activity against the NO production by using LPS-stimulated murine macrophage RAW264.7 cells and antibacterial activity against three drug-resistant microbial pathogens.

Alkaloid constituents from Anacyclus pyrethrum

Twelve undescribed alkaloids, including eight pyrrolo[3,2-g]isoquinoline alkaloids (+)/(-)-anacyquinoline A (1a/1b), (±)-anacyquinoline B (2), (+)/(-)-anacyquinoline C (3a/3b), (±)-anacyquinoline D (4), (±)-anacyquinoline E (5), and (±)-anacyquinoline F (6), together with four pyrrolo[2,3-g]quinoline alkaloids (+)/(-)-anacyquinoline G (7a/7b), (±)-anacyquinoline H (8), and (±)-anacyquinoline I (9), were isolated from the root of Anacyclus pyrethrum (L.) DC. Their structures were determined via spectroscopic analyses (UV, IR, NMR), HRESIMS, quantum chemical calculations of ECD and NMR data, and single-crystal X-ray diffraction analysis (Cu Kα). In bioassay, (+)/(-)-anacyquinoline G (7a/7b), and (±)-anacyquinoline H (8) showed inhibition on NO production with IC50 values of 41.4, 44.1, and 31.4 μM, respectively.

New pimarane diterpenoids with antibacterial activity from fungus Arthrinium sp. ZS03

A comprehensive chemical study of the endophytic fungus Arthrinium sp. ZS03, associated with Acorus tatarinowii Schott, yielded eleven pimarane diterpenoids (compounds 1-11), including seven novel compounds designated arthrinoids A-G (1-7). The determination of their structures and absolute configurations was achieved through extensive spectroscopic techniques, quantum chemical calculations of electronic circular dichroism (ECD), and single-crystal X-ray diffraction analysis. Furthermore, 7 demonstrated inhibitory activity against Klebsiella pneumoniae, comparable to the reference antibiotic amikacin, with a minimum inhibitory concentration (MIC) of 8 μg·mL-1.

The incredible story of ophiobolin A and sphaeropsidin A: two fungal terpenes from wilt-inducing phytotoxins to promising anticancer compounds

Covering: 2000 to 2023This review presents the exceptional story of ophiobolin A (OphA) and sphaeropsidin A (SphA), a sesterterpene and a diterpene, respectively, which were initially isolated as fungal phytotoxins and subsequently shown to possess other interesting biological activities, including promising anticancer activities. Ophiobolin A is a phytotoxin produced by different fungal pathogens, all belonging to the Bipolaris genus. Initially, it was only known as a very dangerous phytotoxin produced by fungi attacking essential cereals, such as rice and barley. However, extensive and interesting studies were carried out to define its original carbon skeleton, which is characterized by a typical 5 : 8 : 5 ring system and shared with fusicoccins and cotylenins, and its phytotoxic activity on host and non-host plants. The biosynthesis of OphA was also defined by describing the different steps starting from mevalonate and through the rearrangement of the acyclic C-25 precursor lead the toxin is obtained. OphA was also produced as a bioherbicide from Drechslera gigantea and proposed for the biocontrol of the widespread and dangerous weed Digitaria sanguinaria. To date, more than sixty ophiobolins have been isolated from different fungi and their biological activities and structure-activity relationship investigated, which were also described using their hemisynthetic derivatives. In the last two decades, thorough studies have been performed on the potential anticancer activity of OphA and its original mode of action, attracting great interest from scientists. Sphaeropsidin A has a similar story. It was isolated as the main phytotoxin from Diplodia cupressi, the causal agent of Italian cypress canker disease, resulting in the loss of millions of plants in a few years in the Mediterranean basin. The damage to the forest, environment and ornamental heritage are noteworthy and economic losses are also suffered by tree nurseries and the wood industry. Six natural analogues of SphA were isolated and several interesting hemisynthetic derivatives were prepared to study its structure-activity relationship. Surprisingly, sphaeropsidin A showed other interesting biological activities, including antibiotic, antifungal, and antiviral. In the last decade, extensive studies have focused on the anticancer activity and original mode of action of SphA. Furthermore, specific hemisynthetic studies enable the preparation of derivatives of SphA, preserving its chromophore, which showed a noteworthy increase in anticancer activity. It has been demonstrated that ophiobolin A and sphaeropsidin A are promising natural products showing potent activity against some malignant cancers, such as brain glioblastoma and different melanomas.

Bioinspired Total Synthesis of Bipolarolides A and B

We have achieved the first total synthesis of bipolarolides A and B, which possess an intriguing and complex 5/6/6/6/5 caged pentacyclic skeleton with seven contiguous stereocenters. The synthesis features a lithium-halogen exchange/intermolecular nucleophilic addition to link two enantioenriched fragments, two ring-closing metathesis reactions to assemble the five- and eight-membered rings, and a bioinspired Prins reaction/ether formation cascade cyclization to construct the 5/6/6/6/5 caged skeleton.

Bipoladien A, a Sesterterpenoid Containing an Undescribed 5/8/5/7 Carbon Skeleton from Bipolaris maydis

Bipoladiens A-E (1-5), five new ophiobolin-derived sesterterpenoids, and a known compound 6 (bipolaricin R) were isolated from the cultures of the phytopathogenic fungus Bipolaris maydis. Their structures and absolute configurations were elucidated based on comprehensive spectroscopic analyses, HRESIMS, electronic circular dichroism (ECD) calculations, and single-crystal X-ray diffraction analyses. Notably, compound 1 has an undescribed tetracyclic 5/8/5/7 fused carbon skeleton, and compound 2 possesses a rare multicyclic caged ring system. The biosynthetic pathway of 1 was proposed starting from 6 via a series of oxidation and cyclization reactions. Compound 6 showed excellent antiproliferation and apoptosis induction effects against A549 cell line. Additionally, compounds 5 and 6 exhibited noticeable antimicrobial ability against Bacillus cereus, Staphylococcus aureus, and Staphylococcus epidermidis. These findings not only developed the chemical and bioactivities diversities of ophiobolin-sesterterpenoid but also provided an idea to boost the application of natural products in the control of food pathogens.

Unprecedented sesterterpenoids, orientanoids A-C: discovery, bioinspired total synthesis and antitumor immunity

Sesterterpenoids are a very rare class of important natural products. Three new skeletal spiro sesterterpenoids, named orientanoids A-C (1-3), were isolated from Hedyosmum orientale. Their structures were determined by a combination of spectroscopic data, X-ray crystallography, and total synthesis. To obtain adequate materials for biological research, the bioinspired total syntheses of 1-3 were effectively achieved in 7-8 steps in overall yields of 2.3-6.4% from the commercially available santonin without using any protecting groups. In addition, this work also revised the stereochemistry of hedyosumins B (6) and C (10) as 11R-configuration. Tumor-associated macrophages (TAMs) have emerged as important therapeutic targets in cancer therapy. The in-depth biological evaluation revealed that these sesterterpenoids antagonized the protumoral and immunosuppressive functional phenotype of macrophages in vitro. Among them, the most potent and major compound 1 inhibited protumoral M2-like macrophages and activated cytotoxic CD8+ T cells, and consequently inhibited tumor growth in vivo.

Research Progress on Fungal Sesterterpenoids Biosynthesis

Sesterterpenes are 25-carbon terpenoids formed by the cyclization of dimethyl allyl diphosphate (DMAPP) and isopentenyl diphosphate (IPP) as structural units by sesterterpenes synthases. Some (not all) sesterterpenoids are modified by cytochrome P450s (CYP450s), resulting in more intricate structures. These compounds have significant physiological activities and pharmacological effects in anti-inflammatory, antibacterial, antitumour, and hypolipidemic communities. Despite being a rare class of terpenoids, sesterterpenoids derived from fungi show a wide range of structural variations. The discovered fungal sesterterpenoid synthases are composed of C-terminal prenyltransferase (PT) and N-terminal terpene synthase (TS) domains, which were given the name PTTSs. PTTSs have the capacities to catalyze chain lengthening and cyclization concurrently. This review summarizes all 52 fungal PTTSs synthases and their biosynthetic pathways involving 100 sesterterpenoids since the discovery of the first PTTSs synthase from fungi in 2013.

A review on natural products with cage-like structure

Natural products with diverse structures and significant biological activities are essential sources of drug lead compounds, and play an important role in the research and development of innovative drugs. Cage-like compounds have various structures and are widely distributed in nature, especially caged xanthones isolated from Garcinia genus, paeoniflorin and its derivatives isolated from Paeonia lactiflora Pall, tetrodotoxin (TTX) and its derivatives, and so on. In recent years, the development and utilization of cage-like compounds have been a research hotspot in chemistry, biology and other fields due to their special structures and remarkable biological activities. In this review, we mainly summarized the cage-like compounds with various structures found and isolated from natural drugs since 1956, summarized its broad biological activities, and introduced the progress in the biosynthesis of some compounds, so as to provide a reference for the discovery of more novel compounds, and the development and application of innovative drugs.

Soil Microbial Communities Affect the Growth and Secondary Metabolite Accumulation in Bletilla striata (Thunb.) Rchb. f

Bletilla striata (Thunb.) Rchb.f. is a perennial herb belonging to the Orchidaceae family. Its tubers are used in traditional Chinese medicine to treat gastric ulcers, inflammation, silicosis tuberculosis, and pneumogastric hemorrhage. It has been reported that different soil types can affect the growth of B. striata and the accumulation of secondary metabolites in its tubers, but the biological mechanisms underlying these effects remain unclear. In this study, we compared agronomic traits and the accumulation of secondary metabolites (extractum, polysaccharide, total phenol, militarine) in B. striata grown in sandy loam or sandy clay soil. In addition, we compared physicochemical properties and microbial communities between the two soil types. In pot experiments, we tested how irradiating soil or transplanting microbiota from clay or loam into soil affected B. striata growth and accumulation of secondary metabolites. The results showed that sandy loam and sandy clay soils differed significantly in their physicochemical properties as well as in the structure and composition of their microbial communities. Sandy loam soil had higher pH, SOM, SOC, T-Ca, T-N, T-Mg, T-Mn, T-Zn, A-Ca, A-Mn, and A-Cu than sandy clay soil, but significantly lower T-P, T-K, T-Fe, and A-P content. Sandy loam soil showed 7.32% less bacterial diversity based on the Shannon index, 19.59% less based on the Ace index, and 24.55% less based on the Chao index. The first two components of the PCoA explained 74.43% of the variation in the bacterial community (PC1 = 64.92%, PC2 = 9.51%). Similarly, the first two components of the PCoA explained 58.48% of the variation in the fungal community (PC1 = 43.67%, PC2 = 14.81%). The microbiome associated with sandy clay soil can promote the accumulation of militarine in B. striata tubers, but it inhibits the growth of B. striata. The accumulation of secondary metabolites such as militarine in B. striata was significantly higher in sandy clay than in sandy loam soil. Conversely, B. striata grew better in sandy loam soil. The microbiome associated with sandy loam soil can promote the growth of B. striata, but it reduces the accumulation of militarine in B. striata tubers. Pot experiment results further confirmed that the accumulation of secondary metabolites such as militarine was higher in soil transplanted with loam microbiota than in soil transplanted with clay microbiota. These results may help guide efforts to improve B. striata yield and its accumulation of specific secondary metabolites.

A new pair of cytotoxic enantiomeric isoprenylated chromone derivatives from Pestalotiopsis sp

A new pair of enantiomeric isoprenylated chromone derivatives, (±)-pestaloficiol X [(±)-1], along with a known compound pestaloficiol J (2), were isolated from the plant endophytic fungus Pestalotiopsis sp. The racemic mixture 1 was separated through chiral HPLC. The structures of new compounds (±)-1 were elucidated on the basis of extensive spectroscopic data and their absolute configurations were further configured through computational analysis of their electronic circular dichroism (ECD) spectra. Compound (+)-1 showed significant inhibitory potency against HL-60 and HEP-3B cell lines, with IC₅₀ values of 1.35 ± 0.15 and 3.70 ± 0.33 μM, respectively, while compound (-)-1 showed significant inhibitory potency against HL-60 and HEP-3B cell lines, with IC₅₀ values of 2.39 ± 0.26 and 2.99 ± 0.35 μM, respectively.

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.

The Biosynthesis and Transport of Ophiobolins in Aspergillus ustus 094102

Ophiobolins are a group of sesterterpenoids with a 5-8-5 tricyclic skeleton. They exhibit a significant cytotoxicity and present potential medicinal prospects. However, the biosynthesis and transport mechanisms of these valuable compounds have not been fully resolved. Herein, based on a transcriptome analysis, gene inactivation, heterologous expression and feeding experiments, we fully explain the biosynthesis pathway of ophiobolin K in Aspergillus ustus 094102, especially proved to be an unclustered oxidase OblC_Au that catalyzes dehydrogenation at the site of C16 and C17 of both ophiobolin F and ophiobolin C. We also find that the intermediate ophiobolin C and final product ophiobolin K could be transported into a space between the cell wall and membrane by OblD_Au to avoid the inhibiting of cell growth, which is proved by a fluorescence observation of the subcellular localization and cytotoxicity tests. This study completely resolves the biosynthesis mechanism of ophiobolins in strain A. ustus 094102. At the same time, it is revealed that the burden of strain growth caused by the excessive accumulation and toxicity of secondary metabolites is closely related to compartmentalized biosynthesis.

Genome Mining Reveals a New Cyclopentane-forming Sesterterpene Synthase with Unprecedented Stereo-control

Fungal bifunctional terpene synthases (BFTSs) catalyze formation of diverse ring systems in diterpene/sesterterpene structures. Through genome mining of fungal BFTSs, we discovered a novel sesterterpenoids gene cluster pst, consisting of...

Spectanoids A-H: Eight undescribed sesterterpenoids from Aspergillus spectabilis

Ten sesterterpenoids, including eight undescribed ones named spectanoids A-H and two known analogs, were obtained from Aspergillus spectabilis. Their structures, including absolute configurations, were determined based on HRESIMS, NMR, ECD calculations and single-crystal X-ray diffraction analyses. Spectanoids A-G are tricyclic sesterterpenoids with an unusual 5/12/5 ring system, while spectanoid H possesses a 5/8/6/5 ring system. All of these compounds were evaluated for their cytotoxic activities against three human cancer cells, and spectanoid A, spectanoid C and spectanoid F exhibited moderate cytotoxic activities with IC₅₀ values ranging from 12.1 to 26.1 μM.

Bipolaquinones A-J, Immunosuppressive Meroterpenoids from a Soil-Derived Bipolaris zeicola

Ten new meroterpenoids, bipolaquinones A-J (1-10), and one known congener, isocochlioquinone F (11), were isolated and identified from the fermented rice cultures of a soil-derived fungus, Bipolaris zeicola. The planar structures of 1-10 were elucidated based on extensive spectroscopic analyses (including HRESIMS and 1D and 2D NMR data), and their absolute configurations were determined by single-crystal X-ray diffraction analyses, comparison of experimental electronic circular dichroism (ECD) data, ECD calculations, and hydrolysis reaction. The immunosuppressive activity assay revealed that compounds 2, 3, and 7-10 showed significant inhibitory activity against concanavalin A (ConA)-induced T lymphocyte proliferation with IC₅₀ values ranging from 4.1 to 9.4 μM, which furnished potential lead molecules for the design and development of new immunosuppressants for treating autoimmune-associated diseases.

Bioactive sesterterpenoids from the fungus Penicillium roqueforti YJ-14

Seven previously undescribed sesterterpenes were characterized from Penicillium roqueforti YJ-14 by solid fermentation. Their structures were initially investigated in detail by spectroscopic analyses and HR-ESI-MS and were further confirmed by X-crystallography. In in vitro bioassays, compounds 1, 5 and 7 showed cytotoxic activity against the MCF-7 breast cancer cell line with IC₅₀ values of 7.98 ± 0.93, 6.42 ± 0.41 and 7.32 ± 0.18 μM, respectively. Compounds 5 and 7 displayed significant cytotoxicity against the A549 lung cancer cell line (IC₅₀ values of 4.83 ± 0.22 μM and 4.58 ± 0.85 μM, respectively). In addition, compound 5 showed an obvious inhibitory effect on nitric oxide production in LPS-activated RAW264.7 macrophages with an IC₅₀ value of 9.53 ± 0.16 μM.

Large-scale culture as a complementary and practical method for discovering natural products with novel skeletons

Covering: up to July 2020Fungal metabolites with diverse and novel scaffolds can be assembled from well-known biosynthetic precursors through various mechanisms. Recent examples of novel alkaloids (e.g., cytochalasans and diketopiperazine derivatives), terpenes (e.g., sesterterpenes and diterpenes) and polyketides produced by fungi are presented through case studies. We show that large-scale culture is a complementary and practical method for genome mining and OSMAC approaches to discover natural products of unprecedented skeletal classes from fungi. We also summarize the discovery strategies and challenges for characterizing these compounds.

Hyperbeanone A, a 5,6-seco-spirocyclic polycyclic polyprenylated acylphloroglucinol derivative with an unprecedented skeleton from Hypericum beanii

Hyperbeanone A (1), a novel 5,6-seco-polycyclic PPAP derivative characterized by an undescribed benz[f]indene-1,9(4H)-dione ring system fused to a tricyclic γ-lactone unit via a ketone carbonyl, was isolated from the aerial parts of Hypericum beanii.

Sesterterpenoids: chemistry, biology, and biosynthesis

Covering: July 2012 to December 2019Over the last seven years, expanding research efforts focused on sesterterpenoids has led to the isolation, identification, and characterization of numerous structurally novel and biologically active sesterterpenoids. These newly reported sesterterpenoids provide diverse structures that often incorporate unprecedented ring systems and new carbon skeletons, as well as unusual functional group arrays. Biological activities of potential biomedical importance including suppression of cancer cell growth, inhibition of enzymatic activity, and modulation of receptor signaling, as well as ecologically important functions such as antimicrobial effects and deterrence of herbivorous insects have been associated with a variety of sesterterpenoids. There has also been a rapid growth in our knowledge of the genomics, enzymology, and specific pathways associated with sesterterpene biosynthesis. This has opened up new opportunities for future sesterterpene discovery and diversification through the expression of new cryptic metabolites and the engineered manipulation of associated biosynthetic machinery and processes. In this paper we reviewed 498 new sesterterpenoids, including their structures, source organisms, country of origin, relevant bioactivities, and biosynthesis.

Two new nucleoside derivatives isolated from the marine-derived Aspergillus versicolor and their intramolecular transesterification

Two new nucleoside derivatives, kipukasins M (1a) and N (1b), along with one known analogue, kipukasin J (2), were obtained from the marine-derived fungus Aspergillus versicolor, which was isolated from the mud collected in the South China Sea. The structures of compounds 1a and 1b were elucidated by extensive spectroscopic analysis, mainly including 1D & 2D NMR and HRESIMS data, and the absolute configuration of 1a was further confirmed by single-crystal X-ray diffraction analysis. Interestingly, intramolecular transesterification occurs in compounds 1a and 1b, which exist as a pair of inseparable regioisomers. All isolated compounds were tested for the cytotoxic and antimicrobial activities.

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.

Synthesis of Cyclohexane-Angularly-Fused Triquinanes

Cyclohexane-angularly-fused triquinanes, 6-5-5-5 tetracycles, have attracted the attention of synthetic chemists due to their highly congested core structures and multiple quaternary carbon centers. This review focuses on the six completed total synthesis of naturally occurring cyclohexane-angularly-fused triquinanes in addition to seven notable methodologies that have been developed for the synthesis of these structures.

A Concise Total Synthesis of (+)-Waihoensene Guided by Quaternary Center Analysis

The four contiguous all-carbon quaternary centers of waihoensene, coupled with the absence of any traditional reactive functional groups other than a single alkene, render it a particularly challenging synthetic target among angular triquinane natural products. Here, we show that its polycyclic frame can be assembled concisely by using a strategically chosen quaternary center to guide the formation of the other three through judiciously selected C-C bond formation reactions. Those events, which included a unique Conia-ene cyclization and a challenging Pauson-Khand reaction, afforded a 17-step synthesis of the molecule in enantioenriched form.

Proversilins A-E, Drimane-Type Sesquiterpenoids from the Endophytic Aspergillus versicolor

Five new drimane-type sesquiterpenoids, named proversilins A-E (1-5), were isolated from the endophytic fungus Aspergillus versicolor F210 isolated from the bulbs of Lycoris radiata. Their structures and absolute configurations were characterized by extensive spectroscopic analysis, including 1D and 2D NMR and HRESIMS data, comparison of experimental and calculated electronic circular dichroism data, and X-ray crystallography. Proversilins B-E (2-5) represent the first examples of natural products featuring an N-acetyl-β-phenylalanine moiety. Compounds 3 and 5 inhibited the growth of HL-60 cells with IC₅₀ values of 7.3 and 9.9 μM, respectively.

A new abietane-type diterpenoid and a new long-chain alkenone from fungus Daldinia sp. TJ403-LS1

A new abietane-type diterpenoid, dalterpenoid A (1), a new long-chain alkenone derivative, (3E,5E,10E)-8-hydroxytrideca-3,5,10,12-tetraen-2-one (2), together with six known compounds (3-8), namely epi-guaidiol A (3), xylaranol A (4), daldinone C (5), trans-3,4-dihydroxy-3,4-dihydro-anofinic acid (6), (R)-6-hydroxymellein (7), helicascolide A (8), were obtained from fungus Daldinia sp. TJ403-LS1, which was originally isolated from roots of the medicinally valuable plant Anoectochilus roxburghii. The structures of compounds 1 and 2 were established based on widespread spectroscopic methods, mainly including 1D & 2D NMR and HRESIMS analyses, and the absolute configuration of 1 was further confirmed by electronic circular dichroism (ECD) calculation. All new compounds were tested for the in vitro cytotoxicity against five human cancer cell lines.

Catalyst-free Tandem 1,3-Dipolar Cycloaddition/Aldol Condensation: Diastereoselective Construction of the Azatetraquinane Skeleton

The one-pot regioselective and diastereoselective method for the synthesis of 5-(het)aroyl-7-(het)arylhexahydrobenzo[4,5]pentaleno[1,6a-b](thia)pyrrolizine-6,12-diones from accessible 1,5-di(het)arylpent-4-ene-1,3-diones or curcuminoids in 38-98% yield was developed. This reaction proceeds as a sequence of 1,3-dipolar cycloaddition of azomethine ylide generated in situ from ninhydrin and (thia)proline at the C═C bond of corresponding enedione, followed by spontaneous intramolecular aldol condensation and leads to the formation of an azatetraquinane scaffold.

Structurally diverse and bioactive alkaloids from an insect-derived fungus Neosartorya fischeri

Seven undescribed alkaloids, namely fischeramides A and B, 5,6-dimethoxycircumdatin C, 6-hydroxyacetylaszonalenin, 3-methoxyglyantrypine, 9-methoxyfumitremorgin C, and spirotryprostatin M, one undescribed natural product, namely 11-deacetyl pyripyropene A, together with nine known congeners, were isolated from the solid cultures of fungus Neosartorya fischeri, which was separated from a medicinal insect Cryptotympana atrata. Their structures were elucidated by extensive spectroscopic data, electronic circular dichroism (ECD) calculations, and single-crystal X-ray diffraction analyses. Structurally, fischeramides A and B represented a pair of rare geometric isomers of the benzodiazepinedione derivatives with a highly conjugated feature. Fischeramide A showed potential immunosuppressive activity in LPS and anti-CD3/anti-CD28 mAbs activated murine splenocytes proliferation with IC₅₀ values of 7.08 and 6.31 μM, respectively, and also showed anti-inflammatory activity against the lipopolysaccharide-induced nitric oxide production with an IC₅₀ value of 25 ± 1 μM. In addition, 5,6-dimethoxycircumdatin C showed remarkable antibacterial activity against ESBL-producing E. coli with an MIC value of 2.0 μg/mL.

Modified Fusicoccane-Type Diterpenoids from Alternaria brassicicola

Seven new modified fusicoccane-type diterpenoids (1-7), together with two known congeners (8 and 9), were obtained from Alternaria brassicicola. Their structures were elucidated from a combination of NMR and HRESIMS data and ¹³C NMR calculation as well as DP4+ probability analyses, and the absolute configurations of 1-5 were determined by ECD calculation and single-crystal X-ray diffraction (Cu Kα). Compounds 1-3 belong to a rare class of 16-nor-dicyclopenta[a,d]cyclooctane diterpenoids, and compounds 2 and 4 represent the first examples of fusicoccane-type diterpenoids featuring two previously undescribed tetracyclic 5/6/6/5 ring systems, while compound 5 features a previously undescribed tetracyclic 5/8/5/3 ring system. Compound 7 was moderately anti-inflammatory, and compounds 2, 3, 5, and 7 were weakly cytotoxic.

Novel Antimicrobial Compounds as Ophiobolin-Type Sesterterpenes and Pimarane-Type Diterpene From Bipolaris Species TJ403-B1

Six previously undescribed ophiobolin-type sesterterpenes, namely, bipolatoxins A–F (1–6); and one previously undescribed pimarane-type diterpene, namely, 1β-hydroxy momilactone A (7); together with three known compounds, namely, 25-hydroxyophiobolin I (8), ophiobolin I (9), and ophiobolin A lactone (10); were isolated and identified from the endophytic fungus Bipolaris species TJ403-B1. Their structures with absolute configurations were elucidated on the basis of extensive spectroscopic analyses (including 1D and 2D nuclear magnetic resonance (NMR) and high-resolution electrospray ionization mass spectroscopy data), single-crystal X-ray diffraction analyses, and comparison of experimental circular dichroism data. All compounds (except for 5) were evaluated for antimicrobial potential, which indicated that bipolatoxin D (4) showed significant inhibitory activity against Enterococcus faecalis with a minimum inhibitory concentration (MIC) value of 8 μg/mL, and ophiobolin A lactone (10) showed significant inhibitory activity against Acinetobacter baumannii and E. faecalis with MIC values of 8 and 8 μg/mL, respectively.

Complex Polypropionates from a South China Sea Photosynthetic Mollusk: Isolation and Biomimetic Synthesis Highlighting Novel Rearrangements

Placobranchus ocellatus is well known to produce diverse and complex γ-pyrone polypropionates. In this study, the chemical investigation of P. ocellatus from the South China Sea led to the discovery and identification of ocellatusones A-D, a series of racemic non-γ-pyrone polyketides with novel skeletons, characterized by a bicyclo[3.2.1]octane (1, 2), a bicyclo[3.3.1]nonane (3) or a mesitylene-substituted dimethylfuran-3(2H)-one core (4). Extensive spectroscopic analysis, quantum chemical computation, chemical synthesis, and/or X-ray diffraction analysis were used to determine the structure and absolute configuration of the new compounds, including each enantiomer of racemic compounds 1-4 after chiral HPLC resolution. An array of new and diversity-generating rearrangements is proposed to explain the biosynthesis of these unusual compounds based on careful structural analysis and comparison with six known co-occurring γ-pyrones (5-10). Furthermore, the successful biomimetic semisynthesis of ocellatusone A (1) confirmed the proposed rearrangement through an unprecedented acid induced cascade reaction.

Bipolarins A-H, eight new ophiobolin-type sesterterpenes with antimicrobial activity from fungus Bipolaris sp. TJ403-B1

Bipolarins A-H (1-8), eight new tetracyclic ophiobolin-type sesterterpenes featuring a rare oxaspiro[4.4]nonane moiety, were isolated from cultures of fungus Bipolaris sp. TJ403-B1. Their structures and absolute configurations were elucidated by comprehensive spectroscopic analyses, single-crystal X-ray diffraction experiments, electronic circular dichroism and ¹³C NMR calculations. Additionally, compound 5 exhibited significant selective antimicrobial activity against Enterococcus faecalis with an MIC value 8 μg·mL^-1.

Reisolation and Configurational Reinvestigation of Cottoquinazolines E-G from an Arthropod-Derived Strain of the Fungus Neosartorya fischeri

The reported fumiquinazoline-related alkaloids cottoquinazolines E-G (1-3) were reisolated from solid cultures of the fungus Neosartorya fischeri, which was isolated from the medicinal arthropod Cryptotympana atrata. The unresolved issues regarding the absolute configurations (for cottoquinazolines E and F) prompted a reinvestigation of the configurations for all three compounds, as enabled by extensive spectroscopic methods, comparisons of experimental electronic circular dichroism data, and X-ray crystallography. In addition, cottoquinazoline F (2) showed significant antibacterial activity against ESBL-producing Escherichia coli, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterococcus faecalis with MIC values of 8, 32, 32, and 16 μg/mL, respectively.

Roquefornine A, a sesterterpenoid with a 5/6/5/5/6-fused ring system from the fungus Penicillium roqueforti YJ-14

Roquefornine A, a sesterterpenoid with an unprecedented 5/6/5/5/6-membered pentacyclic system, was characterized from Penicillium roqueforti YJ-14.

Bipolaricins A-I, Ophiobolin-Type Tetracyclic Sesterterpenes from a Phytopathogenic Bipolaris sp. Fungus

A preliminary phytochemical investigation on the EtOAc extracts of the fungus Bipolaris sp. TJ403-B1 resulted in the identification of 12 ophiobolin-type phytotoxins (1-12), including nine new ones, termed bipolaricins A-I (1-9). The structures of 1-9 were elucidated via spectroscopic data (including HRESIMS and 1D and 2D NMR) and single-crystal X-ray diffraction (Cu Kα) analyses. All of the isolated compounds were tested in terms of HMG-CoA reductase inhibitory, anti-inflammatory, and cytotoxic activities. Compound 10 showed HMG-CoA reductase inhibitory activity (IC₅₀ = 8.4 ± 0.4 μM), and 2, 3, and 10-12 showed significant inhibitory potency against lipopolysaccharide (LPS)-induced nitric oxide production, with IC₅₀ values in the range of 5.1 ± 0.3 to 20 ± 1 μM. Further experiments showed that 10 could significantly inhibit the production of IL-1β, RANTES, MIP-1β, and TNF-α as well as enhance the release of IL-13 in macrophages through the inhibition of HO-1 induction as well as the NF-κB pathway. These findings provide a scientific rationale for an anti-inflammatory therapeutic and a template for a new HMG-CoA reductase inhibitor to produce a potential anti-hyperlipidemia agent.

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A personal selection of 32 recent papers is presented covering various aspects of current developments in bioorganic chemistry and novel natural products such as phlegmadine A from Phlegmariurus phlegmaria.