A new quinolinone from freshwater lake-derived fungus Myrothecium verrucaria

Three new nonenes from culture broth of marine-derived fungus Albifimbria verrucaria and their cytotoxic and anti-viral activities

Three new nonenes, verrucanonenes A‒C (1‒3), were isolated from culture broth of marine-derived fungus Albifimbria verrucaria. These compounds were isolated using silica gel column chromatography, reversed-phase medium pressure liquid chromatography, Sephadex LH-20 column chromatography, and preparative HPLC. Their structures were determined using a spectroscopic method. Cytotoxicities of these isolated compounds to A549, DU145, HCT116, and HT1080 cancer cell lines were assessed. Compounds 1‒3 exhibited cytotoxicities to DU145 cancer cell line, with IC50 values of 23.4, 28.6, and 20.1 µM, respectively. Compound 2 decreased H1N1-induced cytopathic effects on MDCK cells in a dose-dependent manner.

A New Quinazolinone Alkaloid along with Known Compounds with Seed-Germination-Promoting Activity from Rhodiola tibetica Endophytic Fungus Penicillium sp. HJT-A-6

A new quinazolinone alkaloid named peniquinazolinone A (1), as well as eleven known compounds, 2-(2-hydroxy-3-phenylpropionamido)-N-methylbenzamide (2), viridicatin (3), viridicatol (4), (±)-cyclopeptin (5a/5b), dehydrocyclopeptin (6), cyclopenin (7), cyclopenol (8), methyl-indole-3-carboxylate (9), 2,5-dihydroxyphenyl acetate (10), methyl m-hydroxyphenylacetate (11), and conidiogenone B (12), were isolated from the endophytic Penicillium sp. HJT-A-6. The chemical structures of all the compounds were elucidated by comprehensive spectroscopic analysis, including 1D and 2D NMR and HRESIMS. The absolute configuration at C-13 of peniquinazolinone A (1) was established by applying the modified Mosher's method. Compounds 2, 3, and 7 exhibited an optimal promoting effect on the seed germination of Rhodiola tibetica at a concentration of 0.01 mg/mL, while the optimal concentration for compounds 4 and 9 to promote Rhodiola tibetica seed germination was 0.001 mg/mL. Compound 12 showed optimal seed-germination-promoting activity at a concentration of 0.1 mg/mL. Compared with the positive drug 6-benzyladenine (6-BA), compounds 2, 3, 4, 7, 9, and 12 could extend the seed germination period of Rhodiola tibetica up to the 11th day.

Secondary metabolites isolated from Penicillium christenseniae SD.84 and their antimicrobial resistance effects

A pair of new quinolone alkaloid enantiomers, (Ra)-(-)-viridicatol (1) and (Sa)-(+)-viridicatol (4), and seven known compounds, namely, 2, 3 and 5-9, were isolated from Penicillium christenseniae SD.84. The structures of 1 and 4 were determined using NMR and HRESIMS data. Theoretical calculations through CD and ECD confirmed 1 and 4 as a pair of enantiomers. The MIC values of 4 against Staphylococcus aureus and methicillin-resistant S. aureus were 12.4 and 24.7 μM, respectively, compound 1 had no inhibitory activity. Antimicrobial assays of 2, 3, and 5-7 showed a moderate activity against S. aureus and methicillin-resistant S. aureus. This study demonstrated the remarkable potential of Penicillium sp. to produce new drug-resistant leading compounds, thereby advancing the mining for new sources of antimicrobial agents.

Bioactive Alkaloids from the Marine-Derived Fungus Metarhizium sp. P2100

The Metarhizium fungal species are considered the prolific producers of bioactive secondary metabolites with a variety of chemical structures. In this study, the biosynthetic potential of marine-derived fungus Metarhizium sp. P2100 to produce bioactive alkaloids was explored by using the one strain many compounds (OSMAC) strategy. From the rice solid medium (mixed with glucose peptone and yeast broth (GPY)), wheat solid medium (mixed with Czapek) and GPY liquid medium, one rare N-butenone spiroquinazoline alkaloid, N-butenonelapatin A (1), together with nine known compounds (2-10), were isolated and identified. Their structures were elucidated by analysis of the comprehensive spectroscopic data, including 1D and 2D NMR and HRESIMS, and the absolute configuration of 1 was determined by a single-crystal X-ray crystallographic experiment. N-butenonelapatin A (1) represents the first example of N-butenone spiroquinazoline with a rare α, β-unsaturated ketone side chain in the family of spiroquinazoline alkaloids. Compound 4 displayed antibacterial activity against Vibrio vulnificus MCCC E1758 with a minimum inhibitory concentration (MIC) value of 6.25 µg/mL. Compound 7 exhibited antibacterial activities against three aquatic pathogenic bacteria, including V. vulnificus MCCC E1758, V. rotiferianus MCCC E385 and V. campbellii MCCC E333 with the MIC values of 12.5, 12.5 and 6.25 μg/mL, respectively. Compounds 3 and 6 demonstrated anti-inflammatory activity against NO production induced by lipopolysaccharide (LPS) with the IC50 values of 37.08 and 37.48 μM, respectively. In addition, compound 1 showed weak inhibitory activity against the proliferation of tumor cell lines A-375 and HCT 116. These findings further demonstrated that fungi of the Metarhizium species harbor great potentials in the synthesis of a variety of bioactive alkaloids.

Fungal key players of cellulose utilization: Microbial networks in aggregates of long-term fertilized soils disentangled using 13C-DNA-stable isotope probing

Long-term compost application accelerates organic carbon (C) accumulation and macroaggregate formation in soil. Stable aggregates and high soil organic C (SOC) content are supposed to increase microbiota activity and promote transformation of litter compounds (i.e., cellulose) into SOC. Here, we used ¹³C-DNA-stable isotope probing with subsequent high-throughput sequencing to characterize fungal succession and co-occurrence trends during ¹³C-cellulose decomposition in aggregate size classes in soils subjected to no fertilizer (control), nitrogen-phosphorus‑potassium (NPK) fertilizers, and compost (Compost) application for 27 years. Ascomycota (mostly saprotrophic fungi) were always highly competitive for cellulose in all aggregate size classes at the early stages of cellulose decomposition (20 days). Compost-treated soil was enriched with Ascomycota compared to the control soil, wherein Sordariomycetes, the majority, strongly dominated the cellulose utilization (¹³C incorporation in DNA). ¹³C-labeled fungal communities converged in the Compost soil, with lower abundance and diversity compared with the NPK and control soils. Such convergence led to greater cellulose decomposition, indicating that compost amendment increased the capacity of a few dominant fungal taxa to decompose litter. Compost soil had more ¹³C-labeled fungal decomposers in microaggregates and lower fungal decomposers in macroaggregates when compared with the levels in the NPK and control soils. This implies that compost application facilitates fungal colonization towards smaller aggregates. Fungal interactions were reinforced in microaggregates (<250 μm), with more positive associations than those in macroaggregates (>250 μm), indicating greater fungal synergism for recalcitrant resource utilization in microaggregates. The keystone taxa in the co-occurrence networks were not related to cellulose decomposition in microaggregates, but did in macroaggregates. The findings advance a process-based understanding of cellulose utilization by fungal key players based on C and energy availability and the regulation of microbial activity at the aggregate level.

Chemical Diversity and Antimicrobial Potential of Cultivable Fungi from Deep-Sea Sediments of the Gulf of Mexico

A collection of 29 cultivable fungal strains isolated from deep-sea sediments of the Gulf of Mexico were cultivated under the “one strain, many compounds” approach to explore their chemical diversity and antimicrobial potential. From the 87 extracts tested, over 50% showed antimicrobial activity, and the most active ones were those from cultures grown at 4 °C in darkness for 60 days (resembling deep-sea temperature). PCA analysis of the LC-MS data of all the extracts confirmed that culture temperature is the primary factor in the variation of the 4462 metabolite features, accounting for 21.3% of the variation. The bioactivity-guided and conventional chemical studies of selected fungal strains allowed the identification of several active and specialized metabolites. Finally, metabolomics analysis by GNPS molecular networking and manual dereplication revealed the biosynthetic potential of these species to produce interesting chemistry. This work uncovers the chemical and biological study of marine-derived fungal strains from deep-sea sediments of the Gulf of Mexico.

Discovery of alkaloids from the leaves of Isatis indigotica Fortune with neuroprotective activity

Seven alkaloids including five undescribed ones (1a/1b, 2, 3 and 5) were obtained from the leaves of Isatis indigotica Fortune. Their structures were established by extensive spectroscopic analyses. The absolute configurations of compounds 1a, 1b, 3 and 5 were determined by comparison of the experimental and calculated electronic circular dichroism (ECD) spectra. Subsequently, the neuroprotective effects of all the isolates against H₂O₂-induced injury in SH-SY5Y cells were evaluated in vitro by MTT assay. Moreover, Annexin V-FITC/PI double staining was performed, while the activities of antioxidant enzymes (SOD, CAT and GSH-Px) for compounds 1a and 1b were measured.

Freshwater Fungi as a Source of Chemical Diversity: A Review

As their name indicates, freshwater fungi occur on submerged substrates in fresh water habitats. This review brings together the chemical diversity and biological activity of 199 of the 280 known freshwater fungal metabolites published from 1992 to 2020, representing at least seven structural classes, including polyketides, phenylpropanoids, terpenoids, meroterpenoids, alkaloids, polypeptides, and monosaccharides. In addition to describing what they are, where they are found, and what they do, we also discuss strategies for the collection, isolation, and identification of fungi from freshwater habitats, with the goal of enhancing chemists' knowledge of several mycological principles. We anticipate that this review will provide a springboard for future natural products studies from this fascinating but underexplored group of Ascomycota.

Structurally diverse alkaloids produced by Aspergillus creber EN-602, an endophytic fungus obtained from the marine red alga Rhodomela confervoides

Thirteen alkaloids, which include three new diketopiperazines, namely, 3-hydroxyprotuboxepin K (4), 3,15-dehydroprotuboxepin K (5), and versiamide A (6), together with ten known alkaloid derivatives (1-3 and 7-13), were isolated from the marine red algal-derived fungus Aspergillus creber EN-602. Versiamide A (6) represents the first example of a naturally occurring quinazolinone alkaloid with a diketopiperazine ring that is derived from phenylalanine (Phe) and leucine (Leu). The structures of these compounds were elucidated by detailed interpretation of their 1D/2D NMR spectroscopic and mass spectrometric data, while the absolute configurations of compounds 1-6 were established on the basis of X-ray crystallographic analysis and time-dependent density functional (TDDFT) calculations of the ECD spectra. Compounds 1, 2, and 4 exhibited inhibitory activity against the angiotensin converting enzyme (ACE) with IC₅₀ values of 11.2, 16.0, and 22.4 μM, respectively, and compounds 5 and 6 inhibited various aquatic bacteria with MIC values that ranged from 8 to 64 μg/mL. The intermolecular interactions and potential binding sites between compounds 1-6 and ACE were investigated via molecular docking simulations.

Diverse polyketides and alkaloids from Penicillium sp. KHMM: structural elucidation, biological and molecular docking studies

As a continuation of our earlier research concerning the investigation of microbial bioactive secondary metabolites from the terrestrial Penicillium sp.KH Link 1809 isolate KHMM, the fungus was re-cultivated on a large scale to explore its bioactive compounds intensively. Fifteen compounds, including seven alkaloids (1-7), one sesquiterpene (8), an acetylenic system (9), two sterols, and sphengolipid, were identified. Their structures were established on the bases of extensive one- and two-dimensional nuclear magnetic resonance and mass measurements, and by comparison with literature data. The antimicrobial activity of the fungal extract and the corresponding compounds were studied using a panel of pathogenic microorganisms, and their in vitro cytotoxicity against the human cervix carcinoma cell line (KB-3-1) was reported as well. The molecular docking of the isolated compounds showed promising affinities for the alkaloidal compounds 4-6 towards α, β tubulins.

Three new tetralol analogs from soil-derived fungus Myrothecium verrucaria with anti-inflammatory activity

Three new tetralol analogs, myrochromanols A-C (1-3), together with 11 known trichothecenes (4-14), were isolated from a soil fungus Myrothecium verrucaria HL-P-1. The structures of the three new compounds were elucidated by extensive spectroscopic analysis including HRESIMS, NMR, and ECD calculation. All of the new compounds were tested for their anti-inflammatory activity and cytotoxicity. Compounds 1 and 3 inhibited lipopolysaccharide (LPS)-induced NO production in BV2 cells with IC₅₀ values of 26.04 and 25.80 μM, respectively.