Citrinin Monomer, Trimer, and Tetracyclic Alkaloid Derivatives from the Hydrothermal Vent-Associated Fungus Penicillium citrinum TW132-59

Discovery and Bioactivity Evaluation of Citrinin Derivatives from the Mangrove Sediment-Derived Fungus Talaromyces sp. SCSIO 41428

A dimeric citrinin derivative with a unique spiro[chroman-2,3'-isochroman] skeleton, xerucitrinic acid C (1), and a new citrinin derivative, cladosporin E (6), along with ten known polyketides (2-5 and 7-12), were isolated from the mangrove sediment-derived fungus Talaromyces sp. SCSIO 41428. Their structures were elucidated through comprehensive spectral data analysis. The absolute configurations of 1 and 6 were determined by quantum chemical calculations. Compound 1 exhibited significant inhibitory effects on Staphylococcus aureus and Streptococcus suis, with the MIC of 25 μg/mL for both bacterial strains. Xerucitrinin C (3) exhibited significant radical scavenging activity against DPPH, with an IC50 value of 25.4 μM, and also demonstrated inhibitory activity against phosphodiesterase-4 (PDE4). Moreover, cladosporin C (7) notably inhibited prostate cancer cells PC-3 and 22Rv1, with IC50 values of 6.10 and 9.25 μM, respectively.

Herqupenoid A, an Unparalleled Sesquiterpene-Quinone Hybrid Featuring a Multicyclic Caged 2,7-Dioxatetracyclo[5.4.0.04,11.05,9]Hendecane Fragment from Penicillium herquei

Herqupenoid A (1), a sesquiterpene-quinone hybrid with an unparalleled 5/5/6/5-fused ring skeleton based on a multicyclic caged 2,7-dioxatetracyclo[5.4.0.04,11.05,9]hendecane fragment, was isolated from fungus Penicillium herquei. Its structure was assigned by extensive spectroscopic analyses, DP4+ computational method, and single-crystal X-ray diffraction. Further pharmacology research has established that compound 1 exhibited significant anti-inflammatory activity via inhibiting NF-κB-NLRP3 axis with an IC50 value of 2.63 μM, which was stronger than the positive control dexamethasone. A putative biosynthetic pathway involving the key hemiacetal and aldol condensation reactions for 1 was also discussed.

Dicitrinols A-C: Citrinin Derivatives from Hydrothermal Vent-Associated Fungus Penicillium citrinum TW132-59

Three new unusual citrinin derivatives with a unique 6/5/7/5 core, dicitrinols A-C (1-3, respectively), were isolated via the fermentation of hydrothermal vent-associated fungus Penicillium citrinum TW132-59. Their structures were unambiguously determined by nuclear magnetic resonance, mass spectrometry, and electronic circular dichroism calculations. Dicitrinols A-C represent a novel cage carbon skeleton with a decahydro-5,9,4-(epipropane[1,1,3]triyl)cycloocta[b]furan ring system. Dicitrinols A-C showed moderate antifungal activity against Candida albicans, Cryptococcus neoformans, and Fusarium oxysporum and antibacterial activity against Staphylococcus aureus, Pseudomonas aeruginosa, and Acinetobacter baumannii with minimum inhibitory concentrations ranging from 4 to 16 μg/mL.

Discovery of 23,24-diols containing ergosterols with anti-neuroinflammatory activity from Penicillium citrinum TJ507

Citristerones A-E (1-5), five new 23,24-diols containing ergosterols, along with three known analogues, were isolated from the endophytic fungus Penicillium citrinum TJ507 obtained from Hypericum wilsonii N. Robson. Their structures and absolute configurations were determined by NMR, HRESIMS, Snatzke's method, X-ray diffraction analyses and ECD calculation. Subsequently, the anti-neuroinflammatory effects of these isolates were screened using lipopolysaccharide (LPS)-induced BV-2 microglial cells, and citristerone B (2) showed outstanding anti-neuroinflammatory activity, with IC50 value of 0.60 ± 0.04 μM. Moreover, immunofluorescence and western blot analysis suggested that citristerone B not only reduced the release of nitric oxide (NO) and proinflammatory cytokines in LPS-induced BV-2 microglial cells, but also significantly inhibited the expression of TNF-α, iNOS and NF-κB, along with the production of cellular ROS.

Two C23-Steroids and a New Isocoumarin Metabolite from Mangrove Sediment-Derived Fungus Penicillium sp. SCSIO 41429

Two new C23-steroids derivatives, cyclocitrinoic acid A (1) and cyclocitrinoic acid B (2), and a new isocoumarin metabolite, (3R,4S)-6,8-dihydroxy-3,4,5-trimethyl-7-carboxamidelisocoumarin (10), together with 12 known compounds (3-9, 11-15) were isolated from the mangrove-sediment fungus Penicillium sp. SCSIO 41429. The structures of the new compounds were comprehensively characterized by 1D and 2D NMR, HRESIMS and ECD calculation. All isolates were evaluated for pancreatic lipase (PL) inhibitory and antioxidant activities. The biological evaluation results revealed that compounds 2, 14 and 15 displayed weak or moderate inhibition against PL, with IC50 values of 32.77, 5.15 and 2.42 µM, respectively. In addition, compounds 7, 12 and 13 showed radical scavenging activities against DPPH, with IC50 values of 64.70, 48.13, and 75.54 µM, respectively. In addition, molecular docking results indicated that these compounds had potential for PL inhibitory and antioxidant activities, which provided screening candidates for antioxidants and a reduction in obesity.

Interaction of Norsecurinine-Type Oligomeric Alkaloids with α-Tubulin: A Molecular Docking Study

The medicinal plant Securinega virosa (Roxb ex. Willd) Baill., also known as Flueggea virosa (Roxb. ex Willd.) Royle, is commonly used in traditional medicine in Africa and Asia for the management of diverse pathologies, such as parasite infections, diabetes, and gastrointestinal diseases. Numerous alkaloids have been isolated from the twigs and leaves of the plant, notably a variety of oligomeric indolizidine alkaloids derived from the monomers securinine and norsecurinine which both display anticancer properties. The recent discovery that securinine can bind to tubulin and inhibit microtubule assembly prompted us to investigate the potential binding of two series of alkaloids, fluevirosines A-H and fluevirosinine A-J, with the tubulin dimer by means of molecular modeling. These natural products are rare high-order alkaloids with tri-, tetra-, and pentameric norsecurinine motifs. Despite their large size (up to 2500 Å3), these alkaloids can bind easily to the large drug-binding cavity (about 4800 Å3) on α-tubulin facing the β-tubulin unit. The molecular docking analysis suggests that these hydrophobic macro-alkaloids can form stable complexes with α/β-tubulin. The tubulin-binding capacity varies depending on the alkaloid size and structure. Structure-binding relationships are discussed. The docking analysis identifies the trimer fluevirosine D, tetramer fluevirosinine D, and pentamer fluevirosinine H as the most interesting tubulin ligands in the series. This study is the first to propose a molecular target for these atypical oligomeric Securinega alkaloids.

Penicilloneines A and B, Quinolone-Citrinin Hybrids from a Starfish-Derived Penicillium sp

Penicilloneines A (1) and B (2) are the first reported quinolone-citrinin hybrids. They were isolated from the starfish-derived fungus Penicillium sp. GGF16-1-2, and their structures were elucidated using spectroscopic, chemical, computational, and single-crystal X-ray diffraction methods. Penicilloneines A (1) and B (2) share a common 4-hydroxy-1-methyl-2(1H)-quinolone unit; however, they differ in terms of citrinin moieties, and these two units are linked via a methylene bridge. Penicilloneines A (1) and B (2) exhibited antifungal activities against Colletotrichum gloeosporioides, with lethal concentration 50 values of 0.02 and 1.51 μg/mL, respectively. A mechanistic study revealed that 1 could inhibit cell growth and promote cell vacuolization and consequent disruption of the fungal cell walls via upregulating nutrient-related hydrolase genes, including putative hydrolase, acetylcholinesterase, glycosyl hydrolase, leucine aminopeptidase, lipase, and beta-galactosidase, and downregulating their synthase genes 3-carboxymuconate cyclase, pyruvate decarboxylase, phosphoketolase, and oxalate decarboxylase.

Five previously undescribed citrinin derivatives from the endophytic fungus Penicillium citrinum GZWMJZ-836

Penicillium citrinum GZWMJZ-836 is an endophytic fungus from Drynaria roosii Nakaike. Five previously undescribed citrinin derivatives (1-5) and six intermediates related to their biosynthesis (6-11) were obtained from the extract of this strain's solid fermentation using multiple column chromatography separations, including high-performance liquid chromatography. The structures of these compounds were determined through comprehensive spectroscopic analyses, primarily using NMR and HRESIMS data. The stereochemistry was mainly confirmed by ECD calculations, and the configurations of C-7' in compounds 4 and 5 were determined using 13C NMR calculations. Compounds 4-5 and 8 showed antibacterial activity against five strains, with minimum inhibitory concentration values ranging from 7.8 to 125 μM. Compounds 4 and 7 exhibited inhibitions against three plant pathogenic fungi, with IC50 values ranging from 66.6 to 152.1 μM. Additionally, a putative biosynthetic pathway for compounds 1-5 derived from citrinin was proposed.

Chemical Constituents of the Deep-sea Gammarid Shrimp-Derived Fungus Penicillium citrinum XIA-16

One new alkaloid, (S)-2-acetamido-4-(2-(methylamino)phenyl)-4-oxobutanoic acid (1), was isolated from the deep-sea-derived Penicillium citrinum XIA-16, together with 25 known compounds including ten polyketones (2-11), eight alkaloids (12-19), six steroids (20-25), and a fatty acid (26). Their planar and relative structures were determined by an analysis of 1D and 2D nuclear magnetic resonance (NMR) as well as high resolution electrospray ionization mass spectroscopy (HR-ESI-MS) data. The absolute configuration of 1 was determined by comparison of the experimental and calculated electronic circular dichroism (ECD) spectra. Penicitrinol B (6) significantly inhibited RSL3-induced ferroptosis (EC50 =2.0 μM) by reducing lipid peroxidation and heme oxygenase 1 (HMOX1) expression. Under the concentration of 10 μM, penicitrinol A (7) was able to inhibit cuproptosis with the cell viabilities of 68.2 % compared to the negative control (copper and elesclomol) with the cell viabilities of 14.8 %.

Novel citrinin derivatives from fungus Penicillium sp. TW131-64 and their antimicrobial activities

Six new citrinin derivatives (1, 2, 4, 10, 11, and 16), along with fourteen known analogues, were acquired from Penicillium sp. TW131-64, a marine-derived fungus strain. The chemical structures of new compounds were identified through adopting various spectroscopic methods in combination with X-ray diffraction technology and comparison of the experimental electronic circular dichroism (ECD) with calculated ones. Among them, compounds 1-4 were nitrogen-containing citrinin derivatives existing in enantiomers which were resolved by chiral chromatography. A putative biosynthetic pathway for compounds 1-4 was proposed. Additionally, the antimicrobial activities of these compounds were detected by the broth microdilution assays. Citrinin derivatives 1, 2, 4 and their corresponding enantiomers (1a, 2a, 4a, 1b, 2b, and 4b) exhibited potent antimicrobial activities towards Helicobacter pylori standard strains and multidrug-resistant strains (MIC values ranging from 0.25 to 8 μg/mL), which were comparable or even better than metronidazole. Moreover, compounds 1a and 1b also showed remarkable broad antimicrobial effects towards Staphylococcus aureus, Enterococcus faecalis, methicillin-resistant Staphylococcus aureus (MRSA), Bacillus subtilis, vancomycin-resistant Enterococcus faecium (VRE), and Candida albicans. In summary, our studies demonstrated that citrinin enantiomers 1a-4a and 1b-4b, especially 1a and 1b, can be lead compounds in the research and development (R & D) of novel antimicrobial drugs. KEY POINTS: • 3 novel nitrogen-containing citrinin derivatives (1, 2, 4) were isolated. • citrinin derivatives 1-4 in enantiomers were resolved by chiral chromatography. • citrinin derivatives 1a and 1b showed broad and significant antimicrobial effects.

Neotricitrinols A-C, unprecedented citrinin trimers with anti-osteoporosis activity from the deep-sea-derived Penicillium citrinum W23

Marine fungi are prolific source for the discovery of structurally diverse and bioactive molecules. In our search for new anti-osteoporosis compounds from deep-sea-derived fungi, we prioritized a fungus whose extract exhibited moderate activity and rich chemical diversity. The investigation of this strain afforded a class of citrinins, including three new citrinin trimers, neotricitrinols A-C (1-3), and three known dimeric/monomeric precursors (4-6). Neotricitrinols A-C (1-3) feature a unique octacyclic carbon scaffold among the few reported citrinin trimers with their absolute configurations established by spectroscopic analysis, theoretical-statistical approaches (GIAO-NMR, TDDFT-ECD/ORD calculations), DP4+ probability analysis as well as biogenetic consideration. A plausible biosynthetic pathway linking 1-3 from the common intermediate metabolite penicitrinol A (4) was proposed. Biologically, neotricitrinol B (2) showed potential anti-osteoporosis activity by promoting osteoblastogenesis and inhibiting adipogenic differentiation on primary bone mesenchymal stem cells, while displaying no cytotoxicity.

Citriquinolinones A and B: Rare Isoquinolinone-Embedded Citrinin Analogues and Related Metabolites from the Deep-Sea-Derived Aspergillus versicolor 170217

A systematic chemical investigation of the deep-sea-derived fungus Aspergillus versicolor 170217 resulted in the isolation of six new (1-6) and 45 known (7-51) compounds. The structures of the new compounds were established on the basis of exhaustive analysis of their spectroscopic data and theoretical-statistical approaches including GIAO-NMR, TDDFT-ECD/ORD calculations, DP4+ probability analysis, and biogenetic consideration. Citriquinolinones A (1) and B (2) feature a unique isoquinolinone-embedded citrinin scaffold, representing the first exemplars of a citrinin-isoquinolinone hybrid. Dicitrinones K-L (3-4) are two new dimeric citrinin analogues with a rare CH-CH3 bridge. Biologically, frangula-emodin (32) and diorcinol (17) displayed remarkable anti-food allergic activity with IC50 values of 7.9 ± 3.0 μM and 13.4 ± 1.2 μM, respectively, while diorcinol (17) and penicitrinol A (20) exhibited weak inhibitory activity against Vibrio parahemolyticus, with MIC values ranging from 128 to 256 μM.

Spirocitrinols A and B, citrinin derivatives with a spiro[chromane-2,3'-isochromane] skeleton from Penicillium citrinum

Spirocitrinols A (1) and B (2), two new citrinin-derived metabolites possessing a spiro[chromane-2,3'-isochromane] skeleton, were isolated from cultures of Penicillium citrinum. Their structures were elucidated primarily by NMR experiments. The absolute configurations of 1 and 2 were assigned by electronic circular dichroism calculations. Compound 2 is the first naturally occurring trimeric citrinin derivative with a spiro[chromane-2,3'-isochromane] core. Compound 1 showed modest cytotoxicity against A549 human tumor cells.

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