Diarylcyclopentendione metabolite obtained from a Preussia typharum isolate procured using an unconventional cultivation approach

Rationally Minimizing Natural Product Libraries Using Mass Spectrometry

Natural product libraries are crucial to drug development, but large libraries drastically increase the time and cost during initial high throughput screens. Here, we developed a method that leverages liquid chromatography-tandem mass spectrometry spectral similarity to dramatically reduce library size, with minimal bioactive loss. This method offers a broadly applicable strategy for accelerated drug discovery with cost reductions, which enable implementation in resource-limited settings.

Verbalide A~F: new phthalide derivatives from the endophytic fungus Preussia sp. CPCC 400972

There are six new phthalide derivatives Verbalide A ~ F (1-6) together with another known derivative (7) isolated from the endophytic fungus Preussia sp. CPCC 400972. Their structures were established by comprehensive spectroscopic analyses, including NMR and HRESIMS. In addition, compounds 1-7 exhibited excellent inhibitory effect against influenza A virus.

Antibiofilm and Antivirulence Activities of Gold and Zinc Oxide Nanoparticles Synthesized from Kimchi-Isolated Leuconostoc sp. Strain C2

The rapid emergence of antimicrobial resistance (AMR) among bacterial pathogens results in antimicrobial treatment failure and the high mortality rate associated with AMR. The application of nanoparticles synthesized from probiotics will be widely accepted due to their efficacy and biocompatibility in treating microbial infections in humans. The current work sought to isolate and identify lactic acid bacteria (LAB) from Kimchi. Based on 16S rRNA gene sequencing, the LAB isolate C2 was identified as a member of the genus Leuconostoc. The obtained supernatant from Leuconostoc sp. strain C2 was employed for the green synthesis of metal (AuNPs) and metal oxide (ZnONPs) nanoparticles. UV–vis absorption spectra, FTIR analysis, XRD, DLS, FE-TEM, and EDS mapping were used to fully characterize these C2-AuNPs and C2-ZnONPs. The C2-AuNPs were found to be spherical in shape, with a size of 47.77 ± 5.7 nm and zeta potential of −19.35 ± 0.67 mV. The C2-ZnONPs were observed to be rod-shaped and 173.77 ± 14.53 nm in size. The C2-ZnONPs zeta potential was determined to be 26.62 ± 0.35 mV. The C2-AuNPs and C2-ZnONPs were shown to have antimicrobial activity against different pathogens. Furthermore, these nanoparticles inhibited the growth of Candida albicans. The antibiofilm and antivirulence properties of these NPs against Pseudomonas aeruginosa and Staphylococcus aureus were thoroughly investigated. C2-AuNPs were reported to be antibiofilm and antivirulence against P. aeruginosa, whereas C2-ZnONPs were antibiofilm and antivirulence against both P. aeruginosa and S. aureus. Furthermore, these nanoparticles disrupted the preformed mature biofilm of P. aeruginosa and S. aureus. The inhibitory impact was discovered to be concentration-dependent. The current research demonstrated that C2-AuNPs and C2-ZnONPs exhibited potential inhibitory effects on the biofilm and virulence features of bacterial pathogens. Further studies are needed to unravel the molecular mechanism behind biofilm inhibition and virulence attenuation.

Bioactive specialised metabolites from the endophytic fungus Xylaria sp. of Cudrania tricuspidata

Fourteen undescribed compounds, including five 2,5-diarylcyclopentenones xylariaones A1-B2, seven α-pyrone derivatives xylaripyones A-G, one γ-pyrone derivative xylaripyone H, one diketopiperazine cyclo-(L-Leu-N-ethyl-L-Glu), and two known diketopiperazines, were isolated from cultures of the endophytic fungus Xylaria sp., which was separated from Cudrania tricuspidata Bureau ex Lavallée. Their structures were determined by analysing extensive spectroscopic data (HRESIMS and NMR) and electronic circular dichroism (ECD) calculations. Furthermore, these compounds were evaluated for potential antiproliferative activity against the human tumour cell lines PC3 and A549, and the results showed that xylaripyone D exhibited moderate inhibitory activity against the proliferation of PC3 cell lines with an IC₅₀ value of 14.75 μM. Meanwhile, xylariaone A3 and xylaripyone F displayed weak inhibitory effects on NO production in RAW 264.7 murine macrophages with IC₅₀ values of 49.76 and 69.68 μM, respectively.

Metal-Free Oxidative Formal C(sp2)-H Arylation of Cyclopentene-1,3-diones with β-Naphthols

An efficient, mild, and transition-metal free formal C(sp2)−H arylation of prochiral 2,2-disubstituted cyclopentene-1,3-diones is reported. This oxidative arylation with β-naphthols proceeds via base-mediated C-Michael addition followed by aerial oxygen insertion...

Anti-cryptococcal activity of preussolides A and B, phosphoethanolamine-substituted 24-membered macrolides, and leptosin C from coprophilous isolates of Preussia typharum

Cryptococcus neoformans is a serious human pathogen with limited options for treatment. We have interrogated extracts from fungal fermentations to find Cryptococcus-inhibiting natural products using assays for growth inhibition and differential thermosensitivity. Extracts from fermentations of four fungal strains from wild and domestic animal dung from Arkansas and West Virginia, USA were identified as Preussia typharum. The extracts exhibited two antifungal regions. Purification of one region yielded new 24-carbon macrolides incorporating both a phosphoethanolamine unit and a bridging tetrahydrofuran ring. The structures of these metabolites were established mainly by analysis of high-resolution mass spectrometry and 2D NMR data. Relative configurations were assigned using NOESY data, and the structure assignments were supported by NMR comparison with similar compounds. These new metabolites are designated preussolides A and B. The second active region was caused by the cytotoxin, leptosin C. Genome sequencing of the four strains revealed biosynthetic gene clusters consistent with those known to encode phosphoethanolamine-bearing polyketide macrolides and the biosynthesis of dimeric epipolythiodioxopiperazines. All three compounds showed moderate to potent and selective antifungal activity toward the pathogenic yeast C. neoformans.

Challenges in the configuration assignment of natural products. A case-selective perspective

An overview by a case study approach on the currently available methods for the configurational analysis of natural products.

Auto-Tandem Catalysis: PdII -Catalysed Dehydrogenation/Oxidative Heck Reaction of Cyclopentane-1,3-diones

A Pd^II catalyst system has been used to successfully catalyse two mechanistically distinct reactions in a one-pot procedure: dehydrogenation of 2,2-disubstituted cyclopentane-1,3-diones and the subsequent oxidative Heck coupling. This auto-tandem catalytic reaction is applicable to both batch and continuous flow processes, with the latter being the first example of a tandem aerobic dehydrogenation/oxidative Heck in flow. In addition, a telescoped reaction involving enantioselective desymmetrisation of the all-C quaternary centre was successfully achieved.

Preussilides A-F, Bicyclic Polyketides from the Endophytic Fungus Preussia similis with Antiproliferative Activity

Six novel bioactive bicyclic polyketides (1-6) were isolated from cultures of an endophytic fungus of the medicinal plant Globularia alypum collected in Batna, Algeria. The producer organism was identified as Preussia similis using morphological and molecular phylogenetic methods. The structures of metabolites 1-6, for which the trivial names preussilides A-F are proposed, were elucidated using a combination of spectral methods, including extensive 2D NMR spectroscopy, high-resolution mass spectrometry, and CD spectroscopy. Preussilides were tested for antimicrobial and antiproliferative effects, and, in particular, compounds 1 and 3 showed selective activities against eukaryotes. Subsequent studies on the influence of 1 and 3 on the morphology of human osteosarcoma cells (U2OS) suggest that these two polyketides might target an enzyme involved in coordination of the cell division cycle. Hence, they might, for instance, affect timing or spindle assembly mechanisms, leading to defects in chromosome segregation and/or spindle geometry.

Acetophenone derivatives from a freshwater fungal isolate of recently described Lindgomyces madisonensis (G416)

The exploration of freshwater ascomycetes, which have undergone only limited investigation, may provide opportunities both to characterize new genera/species of fungi and to uncover new chemical diversity. In this study, seven acetophenone derivatives, madisone, 4'-methoxymadisone, dehydromadisone, 2″-methoxymadisone, dihydroallovisnaginone, dimadisone, and 4'-methoxydimadisone were characterized from an organic extract of a recently described Lindgomyces madisonensis (G416) culture, which was isolated from submerged wood collected in a stream in North Carolina. Madisone, dehydromadisone, 2″-methoxymadisone, dimadisone and 4'-demethoxydimadisone have not been reported previously, while 4'-methoxymadisone and dihydroallovisnaginone were previously unknown as natural products. Their structures were assigned on the basis of NMR and HRESIMS data, with the structure of madisone supported by X-ray crystallography. The antimicrobial activities of madisone, 4'-methoxymadisone and dihydroallovisnaginone were evaluated against a panel of bacteria and fungi. A heat map analysis of the surface of a G416 culture showed that most of the isolated compounds concentrated in the guttate compared with the vegetative mycelium of the fungus.

Generate a bioactive natural product library by mining bacterial cytochrome P450 patterns

The increased number of annotated bacterial genomes provides a vast resource for genome mining. Several bacterial natural products with epoxide groups have been identified as pre-mRNA spliceosome inhibitors and antitumor compounds through genome mining. These epoxide-containing natural products feature a common biosynthetic characteristic that cytochrome P450s (CYPs) and its patterns such as epoxidases are employed in the tailoring reactions. The tailoring enzyme patterns are essential to both biological activities and structural diversity of natural products, and can be used for enzyme pattern-based genome mining. Recent development of direct cloning, heterologous expression, manipulation of the biosynthetic pathways and the CRISPR-CAS9 system have provided molecular biology tools to turn on or pull out nascent biosynthetic gene clusters to generate a microbial natural product library. This review focuses on a library of epoxide-containing natural products and their associated CYPs, with the intention to provide strategies on diversifying the structures of CYP-catalyzed bioactive natural products. It is conceivable that a library of diversified bioactive natural products will be created by pattern-based genome mining, direct cloning and heterologous expression as well as the genomic manipulation.

Enantioselective oxidative boron Heck reactions

This review highlights the use of the oxidative boron Heck reaction in enantioselective Heck-type couplings.

The diversity and antimicrobial activity of endophytic fungi associated with medicinal plant Baccharis trimera (Asteraceae) from the Brazilian savannah

The fungal endophyte community associated with Baccharis trimera, a Brazilian medicinal plant, was characterized and screened for its ability to present antimicrobial activity. By using molecular methods, we identified and classified the endophytic fungi obtained into 25 different taxa from the phyla Ascomycota and Basidiomycota. The most abundant species were closely related to Diaporthe phaseolorum, Pestalotiopsis sp. 1, and Preussia pseudominima. The differences observed in endophytic assemblages from different B. trimera specimens might be associated with their crude extract activities. Plants that had higher α-biodiversity were also those that contributed more to the regional (γ) diversity. All fungal isolates were cultured and their crude extracts screened to examine the antimicrobial activities. Twenty-three extracts (12.8%) displayed antimicrobial activities against at least one target microorganism. Among these extracts, those obtained from Epicoccum sp., Pestalotiopsis sp. 1, Cochliobolus lunatus, and Nigrospora sp. presented the best minimum inhibitory concentration values. Our results show that the endophytic fungal community associated with the medicinal plant B. trimera included few dominant bioactive taxa, which may represent sources of compounds with antifungal activity. Additionally, the discovery of these bioactive fungi in association with B. trimera suggests that Brazilian plants used as folk medicine may shelter a rich fungal diversity as well as taxa able to produce bioactive metabolites with antimicrobial activities.

Recent advances in the use of vibrational chiroptical spectroscopic methods for stereochemical characterization of natural products

A comprehensive look into application of vibrational optical activity methods for conformational and configurational assignments in natural product molecules over the last 15 years is provided.

Oxidative Heck desymmetrisation of 2,2-disubstituted cyclopentene-1,3-diones

Oxidative Heck couplings have been successfully developed for 2,2-disubstituted cyclopentene-1,3-diones. The direct coupling onto the 2,2-disubstituted cyclopentene-1,3-dione core provides a novel, expedient and useful way of desymmetrising all-carbon quaternary centres.

Chlorinated polyketide obtained from a Daldinia sp. treated with the epigenetic modifier suberoylanilide hydroxamic acid

A new chlorinated pentacyclic polyketide, daldinone E (1), was purified from a Daldinia sp. fungal isolate treated with the epigenetic modifier suberoylanilide hydroxamic acid (SAHA). A biosynthetically related epoxide-containing daldinone analogue, 2, was also purified from the same fungus. The structures of both compounds were established by spectroscopic methods, and the absolute configurations were assigned by analysis of their NMR data (coupling constants and ROESY correlations) and DFT calculations of specific rotations and ECD spectra. During the course of these studies it was determined that metabolite 2 and the previously reported daldinone B shared the same spectroscopic data, leading to a revision of the reported structure. Both compounds 1 and 2 also exhibited DPPH radical scavenging activities with potency comparable to the positive control ascorbic acid.

Polyketide glycosides from Bionectria ochroleuca inhibit Candida albicans biofilm formation

One of the challenges presented by Candida infections is that many of the isolates encountered in the clinic produce biofilms, which can decrease these pathogens' susceptibilities to standard-of-care antibiotic therapies. Inhibitors of fungal biofilm formation offer a potential solution to counteracting some of the problems associated with Candida infections. A screening campaign utilizing samples from our fungal extract library revealed that a Bionectria ochroleuca isolate cultured on Cheerios breakfast cereal produced metabolites that blocked the in vitro formation of Candida albicans biofilms. A scale-up culture of the fungus was undertaken using mycobags (also known as mushroom bags or spawn bags), which afforded four known [TMC-151s C-F (1-4)] and three new [bionectriols B-D (5-7)] polyketide glycosides. All seven metabolites exhibited potent biofilm inhibition against C. albicans SC5314, as well as exerted synergistic antifungal activities in combination with amphotericin B. In this report, we describe the structure determination of the new metabolites, as well as compare the secondary metabolome profiles of fungi grown in flasks and mycobags. These studies demonstrate that mycobags offer a useful alternative to flask-based cultures for the preparative production of fungal secondary metabolites.

Bioactive sulfur-containing sulochrin dimers and other metabolites from an Alternaria sp. isolate from a Hawaiian soil sample

Polluxochrin (1) and dioschrin (2), two new dimers of sulochrin linked by thioether bonds, were purified from an Alternaria sp. isolate obtained from a Hawaiian soil sample. The structures of the two metabolites were established by NMR, mass spectrometry data, and X-ray analysis. Metabolite 1 was determined to be susceptible to intramolecular cyclization under aqueous conditions, resulting in the generation of 2 as well as another dimeric compound, castochrin (3). An additional nine new metabolites were also obtained, including four new pyrenochaetic acid derivatives (8-11), one new asterric acid analogue (13), and four new secalonic acid analogues (14-17). Bioassay analysis of these compounds revealed 1-3 displayed antimicrobial and weak cytotoxic activities.

Traversing the fungal terpenome

Fungi (Ascomycota and Basidiomycota) are prolific producers of structurally diverse terpenoid compounds. Classes of terpenoids identified in fungi include the sesqui-, di- and triterpenoids. Biosynthetic pathways and enzymes to terpenoids from each of these classes have been described. These typically involve the scaffold generating terpene synthases and cyclases, and scaffold tailoring enzymes such as e.g. cytochrome P450 monoxygenases, NAD(P)+ and flavin dependent oxidoreductases, and various group transferases that generate the final bioactive structures. The biosynthesis of several sesquiterpenoid mycotoxins and bioactive diterpenoids has been well-studied in Ascomycota (e.g. filamentous fungi). Little is known about the terpenoid biosynthetic pathways in Basidiomycota (e.g. mushroom forming fungi), although they produce a huge diversity of terpenoid natural products. Specifically, many trans-humulyl cation derived sesquiterpenoid natural products with potent bioactivities have been isolated. Biosynthetic gene clusters responsible for the production of trans-humulyl cation derived protoilludanes, and other sesquiterpenoids, can be rapidly identified by genome sequencing and bioinformatic methods. Genome mining combined with heterologous biosynthetic pathway refactoring has the potential to facilitate discovery and production of pharmaceutically relevant fungal terpenoids.

Recent advances in natural product discovery

Natural products have been and continue to be the source and inspiration for a substantial fraction of human therapeutics. Although the pharmaceutical industry has largely turned its back on natural product discovery efforts, such efforts continue to flourish in academia with promising results. Natural products have traditionally been identified from a top-down perspective, but more recently genomics- and bioinformatics-guided bottom-up approaches have provided powerful alternative strategies. Here we review recent advances in natural product discovery from both angles, including diverse sampling and innovative culturing and screening approaches, as well as genomics-driven discovery and genetic manipulation techniques for both native and heterologous expression.

Cytotoxic dimeric epipolythiodiketopiperazines from the ascomycetous fungus Preussia typharum

Two new dimeric epipolythiodiketopiperazines, preussiadins A (1) and B (2), together with two known diastereomers, leptosins C (6) and A (7), were obtained from the mycelia of a Preussia typharum isolate. The structures of the new compounds were established by spectroscopic methods, and the absolute configurations of 1 and 2 were assigned by chemical transformations and comparisons of quantum chemical ECD and VCD calculations to experimental data. Compound 1 exhibited potent cytotoxic activity in the NCI-60 cell line panel with an average LC50 value of 251 nM. Further studies demonstrated that 1 circumvents P-glycoprotein-mediated drug resistance, yet had no significant antitumor activity in a xenograft UACC-62 melanoma model.

Diterpenes from the endangered goldenrod Solidago shortii

Species extinction is tantamount to loss of chemical diversity, and so it is important to seize all opportunities to study species on the brink of extinction. Such studies are often hampered by the limited material available, but that obstacle is surmountable through collaboration with botanical gardens and advances in instrumentation. The goldenrod Solidago shortii is one example of an endangered species native to the United States. From S. shortii, one known diterpene (1), two new diterpenes (2 and 3), and three new hydrolysis products (4-6) are described. This work was made possible through collaboration with the Missouri Botanical Garden and with the use of highly sensitive microcryoprobe NMR technology for structure elucidation and VCD spectroscopy for the determination of absolute configuration.

Crowdsourcing natural products discovery to access uncharted dimensions of fungal metabolite diversity

A fundamental component for success in drug discovery is the ability to assemble and screen compounds that encompass a broad swath of biologically relevant chemical-diversity space. Achieving this goal in a natural-products-based setting requires access to a wide range of biologically diverse specimens. For this reason, we introduced a crowdsourcing program in which citizen scientists furnish soil samples from which new microbial isolates are procured. Illustrating the strength of this approach, we obtained a unique fungal metabolite, maximiscin, from a crowdsourced Alaskan soil sample. Maximiscin, which exhibits a putative combination of polyketide synthase (PKS), non-ribosomal peptide synthetase (NRPS), and shikimate pathway components, was identified as an inhibitor of UACC-62 melanoma cells (LC50=0.93 μM). The metabolite also exhibited efficacy in a xenograft mouse model. These results underscore the value of building cooperative relationships between research teams and citizen scientists to enrich drug discovery efforts.

Spiro fused diterpene-indole alkaloids from a creek-bottom-derived Aspergillus terreus

Four metabolites, teraspiridoles A-D (2-5), formed from the merger of a diterpene and modified indole scaffold were obtained from an Aspergillus terreus isolate. The structures and absolute configurations of these natural products were established using NMR, mass spectrometry, Marfey's method, VCD, and ECD data. Teraspiridole B (3) exhibited weak inhibition of planaria regeneration/survival.