Novel bioactive breviane spiroditerpenoids from Penicillium brevicompactum Dierckx

Three-membered ring formation catalyzed by α-ketoglutarate-dependent nonheme iron enzymes

Epoxides, aziridines, and cyclopropanes are found in various medicinal natural products, including polyketides, terpenes, peptides, and alkaloids. Many classes of biosynthetic enzymes are involved in constructing these ring structures during their biosynthesis. This review summarizes our current knowledge regarding how α-ketoglutarate-dependent nonheme iron enzymes catalyze the formation of epoxides, aziridines, and cyclopropanes in nature, with a focus on enzyme mechanisms.

Synthesis of arene-functionalized fused heterocyclic scaffolds via a regioselective cascade 1,4-conjugate addition/5-exo-dig annulation strategy

Facile access to furan fused heterocyclic scaffolds through a regioselective cascade reaction of propargylamines with 4-hydroxy-2H-pyran-2-ones and 4-hydroxy-6-methylpyridin-2(1H)-one has been achieved. This cascade reaction presumably involves the formation of ortho-alkynyl quinone methide (o-AQM), 1,4-conjugate addition, followed by regioselective 5-exo-dig annulation, and a 1,3-H shift process. Moreover, the reaction provides a new and efficient method for the synthesis of highly sterically congested 3-phenolic furo[3,2-c]pyran-4-ones and furo[3,2-c]pyridin-4(5H)-ones by the formation of a furan ring from readily available starting materials in good to high yields (50-82%) with broad functional group compatibility in a single step. Significantly, the strategy described here is easily scalable and several useful synthetic transformations of the prepared arene-functionalized 4H-furo[3,2-c]pyran-4-ones were also performed.

S-Adenosylmethionine: more than just a methyl donor

Covering: from 2000 up to the very early part of 2023S-Adenosyl-L-methionine (SAM) is a naturally occurring trialkyl sulfonium molecule that is typically associated with biological methyltransfer reactions. However, SAM is also known to donate methylene, aminocarboxypropyl, adenosyl and amino moieties during natural product biosynthetic reactions. The reaction scope is further expanded as SAM itself can be modified prior to the group transfer such that a SAM-derived carboxymethyl or aminopropyl moiety can also be transferred. Moreover, the sulfonium cation in SAM has itself been found to be critical for several other enzymatic transformations. Thus, while many SAM-dependent enzymes are characterized by a methyltransferase fold, not all of them are necessarily methyltransferases. Furthermore, other SAM-dependent enzymes do not possess such a structural feature suggesting diversification along different evolutionary lineages. Despite the biological versatility of SAM, it nevertheless parallels the chemistry of sulfonium compounds used in organic synthesis. The question thus becomes how enzymes catalyze distinct transformations via subtle differences in their active sites. This review summarizes recent advances in the discovery of novel SAM utilizing enzymes that rely on Lewis acid/base chemistry as opposed to radical mechanisms of catalysis. The examples are categorized based on the presence of a methyltransferase fold and the role played by SAM within the context of known sulfonium chemistry.

ent-Herqueidiketal and epi-Peniciherqueinone Isolated from a Mushroom Derived Fungus Penicillium herquei YNJ-35

A new polyaromatic metabolite, ent-herqueidiketal (1), and a new phenalenone derivative, epi-peniciherqueinone (2), along with twelve known compounds 3-14, were isolated from the fungus Penicillium herquei YNJ-35, a symbiotic fungus of Pulveroboletus brunneopunctatus collected from Nangunhe Nature Reserve, Yunnan Province, China. The structures of 1-14 and the absolute configurations of 1 and 2 were determined by their spectroscopic data or by their single-crystal X-ray diffraction analysis or optical rotation values. Compound 1 showed strong antibacterial activity against Staphylococcus aureus (ATCC 29213) with minimum inhibitory concentration (MIC) of 8 μg/mL. In the cytotoxicity assays, compound 1 showed weak inhibitory activity against breast cancer MCF-7 and mice microglial BV2 cells with half maximal inhibitory concentration (IC50 ) of 17.58 and 29.56 μM; compound 14 showed stronger cytotoxicity against BV2 and MCF-7 cells with IC50 values of 6.57 and 10.26 μM.

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 euphylonoid A from Euphorbia hylonoma.

Euphylonoids A and B, Two Highly Modified Jatrophane Diterpenoids with Potent Lipid-Lowering Activity from Euphorbia hylonoma

Euphylonoids A (1) and B (2), two highly modified jatrophane diterpenoids, were isolated from Euphorbia hylonoma. 1 represents a new 9(10→18)-abeo-8,12-cyclojatrophane skeleton containing a cage-like 3,8-dioxatricyclo[5.1.2.0^4,9]decane core, while 2 is a 14(13→20)-abeo-8,12-cyclojatrophane featuring an unusual 17-oxatetracyclo[12.2.1.0^1,5.0^9,13]heptadecane framework. Their structural elucidation was completed by spectroscopic, chemical, computational, and single-crystal X-ray diffraction means. 2 significantly inhibited early adipogenesis in 3T3-L1 adipocytes via activating AMP-activated protein kinase signaling.

Branching and converging pathways in fungal natural product biosynthesis

In nature, organic molecules with great structural diversity and complexity are synthesized by utilizing a relatively small number of starting materials. A synthetic strategy adopted by nature is pathway branching, in which a common biosynthetic intermediate is transformed into different end products. A natural product can also be synthesized by the fusion of two or more precursors generated from separate metabolic pathways. This review article summarizes several representative branching and converging pathways in fungal natural product biosynthesis to illuminate how fungi are capable of synthesizing a diverse array of natural products.

Biocatalytic and chemical derivatization of fungal meroditerpenoid chevalone E

Fungal meroditerpenoids include diverse molecules with structural complexity and a broad range of biological activities. We have previously obtained meroditerpenoid chevalone E (1) and its oxidized analogues by heterologously expressing...

Molecular and Computational Bases for Spirofuranone Formation in Setosusin Biosynthesis

The 3(2H)-furanone unit is observed in many biologically active natural products, as represented by the antifungal medication griseofulvin. Setosusin (1) is a fungal meroditerpenoid featuring a unique spiro-fused 3(2H)-furanone moiety; however, the biosynthetic basis for spirofuranone formation has not been investigated since its isolation. Therefore, in this study we identified the biosynthetic gene cluster of 1 in the fungus Aspergillus duricaulis CBS 481.65 and elucidated its biosynthetic pathway by heterologous reconstitution of related enzyme activities in Aspergillus oryzae. To understand the reaction mechanism to afford spirofuranone, we subsequently performed a series of in vivo and in vitro isotope-incorporation experiments and theoretical calculations. The results indicated that SetF, the cytochrome P450 enzyme that is critical for spirofuranone synthesis, not only performs the epoxidation of the polyketide portion of the substrate but also facilitates the protonation-initiated structural rearrangement to yield 1. Finally, a mutagenesis experiment using SetF identified Lys303 as one of the potential catalytic residues that are important for spirofuranone synthesis.

An Updated Review of Secondary Metabolites from Marine Fungi

Marine fungi are valuable and richest sources of novel natural products for medicinal and pharmaceutical industries. Nutrient depletion, competition or any other type of metabolic stress which limits marine fungal growth promotes the formation and secretion of secondary metabolites. Generally secondary metabolites can be produced by many different metabolic pathways and include antibiotics, cytotoxic and cyto-stimulatory compounds. Marine fungi produce many different types of secondary metabolites that are of commercial importance. This review paper deals with around 187 novel compounds and 212 other known compounds with anticancer and antibacterial activities with a special focus on the period from 2011-2019. Furthermore, this review highlights the sources of organisms, chemical classes and biological activities (anticancer and antibacterial) of metabolites, that were isolated and structurally elucidated from marine fungi to throw a helping hand for novel drug development.

Anti-inflammatory spiroditerpenoids from Penicillium bialowiezense

Inflammation is a vital process that maintains tissue homeostasis. However, it is widely known that uncontrolled inflammation can contribute to the development of various diseases. This study aimed to discover anti-inflammatory metabolites from Penicillium bialowiezense. Seven spiroditerpenoids, including two new compounds, breviones P and Q (1 and 2), were isolated and characterized by various spectroscopic and spectrometric methods. All isolated compounds were initially tested for their inhibitory effects against lipopolysaccharide-induced nitric oxide (NO) production in RAW 264.7 macrophages. Of these, brevione A (3) exhibited this activity with a half-maximal inhibitory concentration value of 9.5 μM. Further mechanistic studies demonstrated that 3 could suppress the expression of pro-inflammatory cytokines and mediators, such as NO, prostaglandin E₂, interleukin (IL)-1β, tumor necrosis factor-α, IL-6, and IL-12 by inhibiting the activation of nuclear factor-kappa B and c-Jun N-terminal kinase.

Natural diterpene pyrones: chemistry and biology

Diterpene pyrones (DTPs) are a group of well-known, mainly fungal, natural products, first isolated in 1966. As the name indicates, they are composed of two main structural features: a diterpenyl moiety and a pyrone ring. Various names have been given to this class of metabolites; however, biogenetic evidence indicates that they originate through the same metabolic pathway. Based on their biosynthesis, which leads to differences in their structural architecture, the DTPs can be classified into three main types. In addition to their intriguing chemistry, these compounds demonstrate a wide range of biological activities rendering them a desirable target for total synthesis. To date, sixty-seven DTPs have been isolated from various fungal species, with one example originating from the plant kingdom. This review aims at unifying the classification of these compounds, in addition to presenting a detailed description of their isolation, bioactivities, biosynthesis, and total synthesis.

Highly oxygenated isoprenoid lipids derived from fungi and fungal endophytes: Origin and biological activities

This mini review is devoted to highly oxygenated isoprenoid lipids (HOIL) that are produced by fungi and fungal endophytes from various ecological niches, both terrestrial and aquatic. Steroids were distributed as from edible cultivated fungi, as well as fungi collected in forests. Fungal endophytes were generally isolated from plants and cultured to obtain sufficient biomass. Marine fungi were obtained from marine brown and red algae and marine invertebrates such as sponges, corals, worms, crustacea or from marine sediments. HOIL isolated from the terrestrial ecosystem have the pharmacological potential on anti-hypercholesterolemic, anti-neoplastic, anti-eczematic and anti-inflammatory activity estimated with a confidence of 84-90%. HOIL that produced by marine fungal species are predicted as having anti-inflammatory and anti-hypercholesterolemic activity with a confidence of 82-91%. In addition, they may have potential acetylcholinesterase and cell adhesion molecule inhibitors estimated with a confidence of 86-88%.

Asperversins A and B, Two Novel Meroterpenoids with an Unusual 5/6/6/6 Ring from the Marine-Derived Fungus Aspergillus versicolor

Asperversins A (1) and B (2), two novel meroterpenoids featuring an uncommon 5/6/6/6 ring system, along with five new analogues (3⁻7) and a known compound asperdemin (8), were obtained from the marine-derived fungus Aspergillus versicolor. Their structures and absolute configurations were confirmed by extensive spectroscopic analyses, single-crystal X-ray diffraction studies, and electronic circular dichroism (ECD) calculation. All new compounds were tested for their acetylcholinesterase enzyme (AChE) inhibitory activities and cytotoxic activities, of which compound 7 displayed moderate inhibitory activity against the AChE with an IC₅₀ value of 13.6 μM.

A New Breviane Spiroditerpenoid from the Marine-Derived Fungus Penicillium sp. TJ403-1

Marine-derived fungi are a promising and untapped reservoir for discovering structurally interesting and pharmacologically active natural products. In our efforts to identify novel bioactive compounds from marine-derived fungi, four breviane spiroditerpenoids, including a new compound, brevione O (1), and three known compounds breviones I (2), J (3), and H (4), together with a known diketopiperazine alkaloid brevicompanine G (5), were isolated and identified from an ethyl acetate extract of the fermented rice substrate of the coral-derived fungus Penicillium sp. TJ403-1. The absolute structure of 1 was elucidated by HRESIMS, one- and two-dimensional NMR spectroscopic data, and a comparison of its electronic circular dichroism (ECD) spectrum with the literature. Moreover, we confirmed the absolute configuration of 5 by single-crystal X-ray crystallography. All the isolated compounds were evaluated for isocitrate dehydrogenase 1 (IDH1) inhibitory activity and cytotoxicity, and compound 2 showed significant inhibitory activities against HL-60, A-549, and HEP3B tumor cell lines with IC₅₀ values of 4.92 ± 0.65, 8.60 ± 1.36, and 5.50 ± 0.67 µM, respectively.

Antiviral Merosesquiterpenoids Produced by the Antarctic Fungus Aspergillus ochraceopetaliformis SCSIO 05702

Five new highly oxygenated α-pyrone merosesquiterpenoids, ochraceopones A-E (1-5), together with one new double bond isomer of asteltoxin, isoasteltoxin (6), and two known asteltoxin derivatives, asteltoxin (7) and asteltoxin B (8), were isolated from an Antarctic soil-derived fungus, Aspergillus ochraceopetaliformis SCSIO 05702. Their structures were determined through extensive spectroscopic analysis, CD spectra, quantum mechanical calculations, and X-ray single-crystal diffraction. Ochraceopones A-D (1-4) are the first examples of α-pyrone merosesquiterpenoids possessing a linear tetracyclic carbon skeleton, which has not been previously described. All the isolated compounds were tested for their antiviral, cytotoxic, antibacterial, and antitubercular activities. Among these compounds, ochraceopone A (1), isoasteltoxin (6), and asteltoxin (7) exhibited antiviral activities against the H1N1 and H3N2 influenza viruses with IC50 values of >20.0/12.2 ± 4.10, 0.23 ± 0.05/0.66 ± 0.09, and 0.54 ± 0.06/0.84 ± 0.02 μM, respectively. A possible biosynthetic pathway for ochraceopones A-E (1-5) was proposed.

Spiroindole Alkaloids and Spiroditerpenoids from Aspergillus duricaulis and Their Potential Neuroprotective Effects

Six new spiroindole alkaloids (1-6) and two new spiroditerpenoids (7 and 8) were isolated from an EtOAc extract of Aspergillus duricaulis culture media together with five known compounds. The structures of the isolated compounds were elucidated by analysis of NMR and MS data, and the absolute configurations of compounds 1-8 were confirmed by CD spectroscopic methods. All isolated compounds were evaluated for their inhibition of beta-amyloid (Aβ) aggregate-induced toxicity in PC12 cells and Aβ aggregation. Compounds 8-11 efficiently protected PC12 cells against Aβ aggregate-induced toxicity, but only compound 9 inhibited Aβ aggregation. On the other hand, compounds 4 and 5 exhibited moderate inhibitory effects on Aβ aggregation, but did not protect the cells from Aβ aggregate-induced toxicity. Preincubating Aβ monomers with compounds 4 and 5 rescued PC12 cells against Aβ aggregate-induced toxicity by reducing neurotoxic Aβ aggregates. Compound 9 inhibited both Aβ aggregate-induced toxicity and Aβ aggregation.

Structure-activity relationship studies of the phytotoxic properties of the diterpenic moiety of breviones

BACKGROUND

Brevianes are a family of bioactive meroterpenoids originally described in fungi of the family Penicillium. These compounds have attracted a great deal of interest not only because of their unusual skeleton, suggesting a mixed mevalonate and polyketide biogenetic pathway, and their unusual oxa-spiro ring fused to an α-pyrone, but also because of the bioactivities shown by many members of this family.

RESULTS

During the course of a project aimed at the total synthesis of natural breviones A to E, the authors were able to synthesise the diterpenic moiety of brevianes and abeo-brevianes. As a result, a collection of 25 compounds were synthesised and tested for bioactivity by two different bioassays. The bioassays used were etiolated wheat coleoptiles (Triticum aestivum) and seedlings in petri dishes. The plant species tested in the seedling bioassay were the commercial dicots lettuce and cress and the monocot weeds Echinochloa crus-galli and Lolium rigidum.

CONCLUSIONS

The results clearly show that expanded phenanthrene-like compounds corresponding to the diterpenic moiety of abeo-brevianes are more selective towards E. crus-galli in comparison with L. rigidum. Such selectivity can reach up to one order of magnitude (200-fold) and makes some of the compounds good candidates as leads for the development of more specific herbicides.

A sterol and spiroditerpenoids from a Penicillium sp. isolated from a deep sea sediment sample

A new polyoxygenated sterol, sterolic acid (1), three new breviane spiroditerpenoids, breviones I–K (2–4), and the known breviones (5–8), were isolated from the crude extract of a Penicillium sp. obtained from a deep sea sediment sample that was collected at a depth of 5115 m. The structures of 1–4 were elucidated primarily by NMR experiments, and 1 was further confirmed by X-ray crystallography. The absolute configurations of 2 and 3 were deduced by comparison of their CD spectra with those of the model compounds. Compounds 2 and 5 showed significant cytotoxicity against MCF-7 cells, which is comparable to the positive control cisplatin.

Breviane spiroditerpenoids from an extreme-tolerant Penicillium sp. isolated from a deep sea sediment sample

Breviones F-H (1-3), three new bioactive breviane spiroditerpenoids, have been isolated from the crude extract of an extreme-tolerant Penicillium sp. obtained from a deep sea sediment sample that was collected at a depth of 5115 m. The structures of these compounds were elucidated primarily by NMR spectroscopy. The absolute configurations of 1 and 3 were assigned by application of the modified Mosher method, and 3 is further confirmed by X-ray crystallographic analysis of its S-MTPA ester. Compound 2 could be the precursor for 3, which features a previously undescribed skeleton of mixed biogenesis.

Preparation and phytotoxicity of novel kaurane diterpene amides with potential use as herbicides

Novel kaurane ditepene monoamides were synthesized in good yields directly from kaurenoic ( 1) and grandiflorenic ( 2) acids and unprotected symmetrical diamines, using a modified protocol for monoacylation. Amides from 1 and 2 and monoamines were also obtained and tested against seed germination and growth of radicle and shoot of Lactuca sativa (lettuce), at 10 (-3), 10 (-5), and 10 (-7) M. Amides from symmetrical diamines showed significant inhibitory activity at higher concentrations.

A new meroditerpenoid from Mayodendron igeum

A new meroditerpenoid, igeumone (1), together with 18 known compounds (2-19), were isolated from ethanolic extract of the bark of Mayodendron igeum. Their structures were determined by analysis of spectral data or comparison with authentic samples. X-ray crystallographic analysis was employed to unambiguously determine the structure of 1.