Erubescensoic Acid, a New Polyketide and a Xanthonopyrone SPF-3059-26 from the Culture of the Marine Sponge-Associated Fungus Penicillium erubescens KUFA 0220 and Antibacterial Activity Evaluation of Some of Its Constituents

Naturally Occurring Xanthones and Their Biological Implications

Xanthones are chemical substances in higher plants, marine organisms, and lower microorganisms. The most prevalent naturally occurring sources of xanthones are those belonging to the families Caryophyllaceae, Guttiferae, and Gentianaceae. Structurally, xanthones (9H xanthan-9-one) are heterocyclic compounds with oxygen and a γ-pyrone component. They are densely packed with a two-benzene ring structure. The carbons in xanthones are numbered from their nucleus and biosynthetic construct. They have mixed shikimate-acetate (higher plants) and acetate-malonate (lower organisms) biosynthetic origins, which influence their classification. Based on the level of oxidation of the C-ring, they are classified into monomers, dimers, and heterodimers. While based on the level of oxygenation or the type of ring residue, they can be categorized into mono-, di-, tri-, tetra-, penta- and hexa-oxygenated xanthones, bis-xanthones, prenylated and related xanthones, xanthonolignoids, and other miscellaneous xanthones. This structural diversity has made xanthones exhibit considerable biological properties as promising antioxidant, antifungal, antimicrobial, and anticancer agents. Structure-activity relationship studies suggest C-1, C-3, C-6, and C-8 as the key positions that influence the biological activity of xanthones. Furthermore, the presence of functional groups, such as prenyl, hydroxyl, glycosyl, furan, and pyran, at the key positions of xanthones, may contribute to their spectrum of biological activity. The unique chemical scaffolds of xanthones, their notable biological activities, and the structure-activity relationships of some lead molecules were discussed to identify lead molecules as possible drug candidates.

Antibiofilm activity of marine microbial natural products: potential peptide- and polyketide-derived molecules from marine microbes toward targeting biofilm-forming pathogens

Controlling and treating biofilm-related infections is challenging because of the widespread presence of multidrug-resistant microbes. Biofilm, a naturally occurring matrix of microbial aggregates, has developed intricate and diverse resistance mechanisms against many currently used antibiotics. This poses a significant problem, especially for human health, including clinically chronic infectious diseases. Thus, there is an urgent need to search for and develop new and more effective antibiotics. As the marine environment is recognized as a promising reservoir of new biologically active molecules with potential pharmacological properties, marine natural products, particularly those of microbial origin, have emerged as a promising source of antibiofilm agents. Marine microbes represent an untapped source of secondary metabolites with antimicrobial activity. Furthermore, marine natural products, owing to their self-defense mechanisms and adaptation to harsh conditions, encompass a wide range of chemical compounds, including peptides and polyketides, which are primarily found in microbes. These molecules can be exploited to provide novel and unique structures for developing alternative antibiotics as effective antibiofilm agents. This review focuses on the possible antibiofilm mechanism of these marine microbial molecules against biofilm-forming pathogens. It provides an overview of biofilm development, its recalcitrant mode of action, strategies for the development of antibiofilm agents, and their assessments. The review also revisits some selected peptides and polyketides from marine microbes reported between 2016 and 2023, highlighting their moderate and considerable antibiofilm activities. Moreover, their antibiofilm mechanisms, such as adhesion modulation/inhibition targeting biofilm-forming pathogens, quorum sensing intervention and inhibition, and extracellular polymeric substance disruption, are highlighted herein.

Insights into the antimicrobial properties of a cationic steroid and antibiofilm performance in PDMS-based coatings to potentially treat urinary infections

Currently, multidrug-resistant (MDR) infections are one of the most important threats, driving the search for new antimicrobial compounds. Cationic peptide antibiotics (CPAs) and ceragenins (CSAs) contain in their structures cationic groups and adopt a facially amphiphilic conformation, conferring the ability to permeate the membranes of bacteria and fungi. Keeping these features in mind, an amine steroid, DOCA-NH2, was found to be active against reference strains and MDR isolates of Gram-positive Enterococcus faecalis and Staphylococcus aureus and Gram-negative Escherichia coli and Pseudomonas aeruginosa. The compound was active against all the tested microorganisms, having bactericidal and fungicidal activity, displaying minimal inhibitory concentrations (MICs) between 16 and 128 μg mL-1. No synergy with clinically relevant antibacterial drugs was found. However, the compound was able to completely inhibit the biofilm formation of bacteria exposed to the MIC of the compound. For E. coli and E. faecalis, inhibition of biofilm formation occurred at half the MIC. Besides, DOCA-NH2 inhibited the dimorphic transition of Candida albicans at concentrations 4 times lower than the MIC, and can reduce the microorganism virulence and biofilm formation was significantly reduced at both MIC and half the MIC. Polydimethylsiloxane-based coatings containing DOCA-NH2 (0.5, 1.0, and 1.5 wt%) were prepared and tested against the E. coli biofilm formation under hydrodynamic conditions similar to those prevailing in ureteral stents. A biofilm reduction of approximately 80% was achieved when compared to the control.

New Hybrid Phenalenone Dimer, Highly Conjugated Dihydroxylated C28 Steroid and Azaphilone from the Culture Extract of a Marine Sponge-Associated Fungus, Talaromyces pinophilus KUFA 1767

An undescribed hybrid phenalenone dimer, talaropinophilone (3), an unreported azaphilone, 7-epi-pinazaphilone B (4), an unreported phthalide dimer, talaropinophilide (6), and an undescribed 9R,15S-dihydroxy-ergosta-4,6,8 (14)-tetraen-3-one (7) were isolated together with the previously reported bacillisporins A (1) and B (2), an azaphilone derivative, Sch 1385568 (5), 1-deoxyrubralactone (8), acetylquestinol (9), piniterpenoid D (10) and 3,5-dihydroxy-4-methylphthalaldehydic acid (11) from the ethyl acetate extract of the culture of a marine sponge-derived fungus, Talaromyces pinophilus KUFA 1767. The structures of the undescribed compounds were elucidated by 1D and 2D NMR as well as high-resolution mass spectral analyses. The absolute configuration of C-9' of 1 and 2 was revised to be 9'S using the coupling constant value between C-8' and C-9' and was confirmed by ROESY correlations in the case of 2. The absolute configurations of the stereogenic carbons in 7 and 8 were established by X-ray crystallographic analysis. Compounds 1,2, 4-8, 10 and 11 were tested for antibacterial activity against four reference strains, viz. two Gram-positive (Staphylococcus aureus ATCC 29213, Enterococcus faecalis ATCC 29212) and two Gram-negative (Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853), as well as three multidrug-resistant strains, viz. an extended-spectrum β-lactamase (ESBL)-producing E. coli, a methicillin-resistant S. aureus (MRSA) and a vancomycin-resistant E. faecalis (VRE). However, only 1 and 2 exhibited significant antibacterial activity against both S. aureus ATCC 29213 and MRSA. Moreover, 1 and 2 also significantly inhibited biofilm formation in S. aureus ATCC 29213 at both MIC and 2xMIC concentrations.

Antibacterial and Antibiofilm Properties of Self-Assembled Dipeptide Nanotubes

Over recent decades, multidrug-resistant pathogens have become a global concern, with WHO even considering it one of the biggest threats to global health, food security, and development today, which led to the search for alternative antibacterial agents. A special class is formed by peptides composed by the diphenylalanine motif whose antibacterial properties result from their supramolecular arrangement into nanotubes. However, several other dipeptides that also form nanotubes have been largely overlooked. Here, we present the antibacterial activity of four dipeptide nanotubes. The results point to diverse mechanisms through which dipeptide nanotubes exert their effect against bacteria. Antibacterial activity was similar for dipeptide nanotubes sufficiently wide to allow water flux while dipeptides displaying smaller channels were inactive. This suggests that two of the tested dipeptides, L-Phe-L-Phe (FF, diphenylalanine) and L-Leu-L-Ser (LS), are pore forming structures able to induce membrane permeation and affect cellular hydration and integrity. Of these two dipeptides, only FF demonstrated potential to inhibit biofilm formation. The amyloid-like nature and hydrophobicity of diphenylalanine assemblies are probably responsible for their adhesion to cell surfaces preventing biofilm formation and bacteria attachment.

New Alkylpyridinium Anthraquinone, Isocoumarin, C-Glucosyl Resorcinol Derivative and Prenylated Pyranoxanthones from the Culture of a Marine Sponge-Associated Fungus, Aspergillus stellatus KUFA 2017

An unreported isocoumarin, (3S,4R)-4-hydroxy-6-methoxymellein (2), an undescribed propylpyridinium anthraquinone (4), and an unreported C-glucosyl resorcinol derivative, acetyl carnemycin E (5c), were isolated, together with eight previously reported metabolites including p-hydroxybenzaldehyde (1), 1,3-dimethoxy-8-hydroxy-6-methylanthraquinone (3a), 1,3-dimethoxy-2,8-dihydroxy-6-methylanthraquinone (3b), emodin (3c), 5[(3E,5E)-nona-3,5-dien-1-yl]benzene (5a), carnemycin E (5b), tajixanthone hydrate (6a) and 15-acetyl tajixanthone hydrate (6b), from the ethyl acetate extract of the culture of a marine sponge-derived fungus, Aspergillus stellatus KUFA 2017. The structures of the undescribed compounds were elucidated by 1D and 2D NMR and high resolution mass spectral analyses. In the case of 2, the absolute configurations of the stereogenic carbons were determined by comparison of their calculated and experimental electronic circular dichroism (ECD) spectra. The absolute configurations of the stereogenic carbons in 6a and 6b were also determined, for the first time, by X-ray crystallographic analysis. Compounds 2, 3a, 3b, 4, 5a, 5b, 5c, 6a, and 6b were assayed for antibacterial activity against four reference strains, viz. two Gram-positive (Staphylococcus aureus ATCC 29213, Enterococcus faecalis ATCC 29212) and two Gram-negative (Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853), as well as three multidrug-resistant strains. However, only 5a exhibited significant antibacterial activity against both reference and multidrug-resistant strains. Compound 5a also showed antibiofilm activity against both reference strains of Gram-positive bacteria.

An Update on the Anticancer Activity of Xanthone Derivatives: A Review

The annual number of cancer deaths continues increasing every day; thus, it is urgent to search for and find active, selective, and efficient anticancer drugs as soon as possible. Among the available anticancer drugs, almost all of them contain heterocyclic moiety in their chemical structure. Xanthone is a heterocyclic compound with a dibenzo-γ-pyrone framework and well-known to have "privileged structures" for anticancer activities against several cancer cell lines. The wide anticancer activity of xanthones is produced by caspase activation, RNA binding, DNA cross-linking, as well as P-gp, kinase, aromatase, and topoisomerase inhibition. This anticancer activity depends on the type, number, and position of the attached functional groups in the xanthone skeleton. This review discusses the recent advances in the anticancer activity of xanthone derivatives, both from natural products isolation and synthesis methods, as the anticancer agent through in vitro, in vivo, and clinical assays.

Anthraquinones, Diphenyl Ethers, and Their Derivatives from the Culture of the Marine Sponge-Associated Fungus Neosartorya spinosa KUFA 1047

Previously unreported anthraquinone, acetylpenipurdin A (4), biphenyl ether, neospinosic acid (6), dibenzodioxepinone, and spinolactone (7) were isolated, together with (R)-6-hydroxymellein (1), penipurdin A (2), acetylquestinol (3), tenellic acid C (5), and vermixocin A (8) from the culture of a marine sponge-associated fungus Neosartorya spinosa KUFA1047. The structures of the previously unreported compounds were established based on an extensive analysis of 1D and 2D NMR spectra as well as HRMS data. The absolute configurations of the stereogenic centers of 5 and 7 were established unambiguously by comparing their calculated and experimental electronic circular dichroism (ECD) spectra. Compounds 2 and 5–8 were tested for their in vitro acetylcholinesterase and tyrosinase inhibitory activities as well as their antibacterial activity against Gram-positive and Gram-negative reference, and multidrug-resistant strains isolated from the environment. The tested compounds were also evaluated for their capacity to inhibit biofilm formation in the reference strains.

Prenylated phenylbutyrolactones from cultures of a marine sponge-associated fungus Aspergillus flavipes KUFA1152

Four undescribed prenylated phenylbutyrolactones, aspulvinones R, S, T and U, were isolated together with the previously reported aspulvinones A, B', H and 4-hydroxy-3,5-bis(3-methylbut-2-en-1-yl)benzaldehyde, from cultures of the marine sponge-derived fungus Aspergillus flavipes KUFA1152. The structures of the undescribed compounds were established on the basis of extensive analysis of 1D and 2D NMR and HRMS spectra. In the case of aspulvinone T, the absolute configuration of its stereogenic carbon was established by comparison of the experimental and calculated electronic circular dichroism (ECD) spectra. The structure of the previously reported compounds were elucidated by 1D and 2D NMR analysis as well as comparison of their ¹H or/and ¹³C NMR data with those reported in the literature. Aspulvinones B', H, R, S, T and a mixture of aspulvinones A and U exhibited antibacterial activity against reference strains and multidrug-resistant isolates from the environment as well as capacity to inhibit biofilm formation in the reference strains. However, none of the tested compounds showed potential synergy with clinically relevant antibiotics on multidrug-resistant isolates.

From Natural Products to New Synthetic Small Molecules: A Journey through the World of Xanthones

This work reviews the contributions of the corresponding author (M.M.M.P.) and her research group to Medicinal Chemistry concerning the isolation from plant and marine sources of xanthone derivatives as well as their synthesis, biological/pharmacological activities, formulation and analytical applications. Although her group activity has been spread over several chemical families with relevance in Medicinal Chemistry, the main focus of the investigation and research has been in the xanthone family. Xanthone derivatives have a variety of activities with great potential for therapeutic applications due to their versatile framework. The group has contributed with several libraries of xanthones derivatives, with a variety of activities such as antitumor, anticoagulant, antiplatelet, anti-inflammatory, antimalarial, antimicrobial, hepatoprotective, antioxidant, and multidrug resistance reversal effects. Besides therapeutic applications, our group has also developed xanthone derivatives with analytical applications as chiral selectors for liquid chromatography and for maritime application as antifouling agents for marine paints. Chemically, it has been challenging to afford green chemistry methods and achieve enantiomeric purity of chiral derivatives. In this review, the structures of the most significant compounds will be presented.

1,3-Dioxepine and spiropyran derivatives of viomellein and other dimeric naphthopyranones from cultures of Aspergillus elegans KUFA0015 and their antibacterial activity

Two undescribed viomellein derivatives, xanthoelegansin and spiroxanthoelegansin, were isolated together with clavatol, sitosteanone, vioxanthin, xanthomegnin, viomellein, rubrosulphin, rubrosulphin diacetate, viopurpurin , ochratoxin A, ochratoxin A methyl ester, ochratoxin B and ochratoxin β, from cultures of the marine sponge-associated fungus Aspergillus elegans KUFA0015. The structures of the undescribed compounds were established based on an extensive analysis of 1D and 2D NMR spectra as well as HRMS data. The structure of xanthoelegansin and the absolute configuration of its stereogenic carbons were confirmed by X-ray analysis. The change in conformation of xanthoelegansin was interpreted using quantum mechanical theoretical calculation data in combination with the observation of the change of the proton signals of the 1,3-dioxepine ring in 1HNMR spectra at varying temperatures. The mechanisms of the formation of xanthoelegansin and spiroxanthoelegansin from viomellein were proposed. Clavatol, sitosteanone, vioxanthin, xanthomegnin, viomellein, xanthoelegansin, rubrosulphin, rubrosulphin diacetate, ochratoxin A, ochratoxin A methyl ester, ochratoxin B and ochratoxin β were assayed for their antibacterial activity against reference strains and multidrug-resistant isolates from the environment. The tested compounds were also evaluated for their capacity to inhibit biofilm formation in the reference strains.

Marine natural products

This review covers the literature published in 2019 for marine natural products (MNPs), with 719 citations (701 for the period January to December 2019) referring to compounds isolated from marine microorganisms and phytoplankton, green, brown and red algae, sponges, cnidarians, bryozoans, molluscs, tunicates, echinoderms, mangroves and other intertidal plants and microorganisms. The emphasis is on new compounds (1490 in 440 papers for 2019), together with the relevant biological activities, source organisms and country of origin. Pertinent reviews, biosynthetic studies, first syntheses, and syntheses that led to the revision of structures or stereochemistries, have been included. Methods used to study marine fungi and their chemical diversity have also been discussed.

Classification of Aspergillus, Penicillium, Talaromyces and related genera (Eurotiales): An overview of families, genera, subgenera, sections, series and species

The Eurotiales is a relatively large order of Ascomycetes with members frequently having positive and negative impact on human activities. Species within this order gain attention from various research fields such as food, indoor and medical mycology and biotechnology. In this article we give an overview of families and genera present in the Eurotiales and introduce an updated subgeneric, sectional and series classification for Aspergillus and Penicillium. Finally, a comprehensive list of accepted species in the Eurotiales is given. The classification of the Eurotiales at family and genus level is traditionally based on phenotypic characters, and this classification has since been challenged using sequence-based approaches. Here, we re-evaluated the relationships between families and genera of the Eurotiales using a nine-gene sequence dataset. Based on this analysis, the new family Penicillaginaceae is introduced and four known families are accepted: Aspergillaceae, Elaphomycetaceae, Thermoascaceae and Trichocomaceae. The Eurotiales includes 28 genera: 15 genera are accommodated in the Aspergillaceae (Aspergillago, Aspergillus, Evansstolkia, Hamigera, Leiothecium, Monascus, Penicilliopsis, Penicillium, Phialomyces, Pseudohamigera, Pseudopenicillium, Sclerocleista, Warcupiella, Xerochrysium and Xeromyces), eight in the Trichocomaceae (Acidotalaromyces, Ascospirella, Dendrosphaera, Rasamsonia, Sagenomella, Talaromyces, Thermomyces, Trichocoma), two in the Thermoascaceae (Paecilomyces, Thermoascus) and one in the Penicillaginaceae (Penicillago). The classification of the Elaphomycetaceae was not part of this study, but according to literature two genera are present in this family (Elaphomyces and Pseudotulostoma). The use of an infrageneric classification system has a long tradition in Aspergillus and Penicillium. Most recent taxonomic studies focused on the sectional level, resulting in a well-established sectional classification in these genera. In contrast, a series classification in Aspergillus and Penicillium is often outdated or lacking, but is still relevant, e.g., the allocation of a species to a series can be highly predictive in what functional characters the species might have and might be useful when using a phenotype-based identification. The majority of the series in Aspergillus and Penicillium are invalidly described and here we introduce a new series classification. Using a phylogenetic approach, often supported by phenotypic, physiologic and/or extrolite data, Aspergillus is subdivided in six subgenera, 27 sections (five new) and 75 series (73 new, one new combination), and Penicillium in two subgenera, 32 sections (seven new) and 89 series (57 new, six new combinations). Correct identification of species belonging to the Eurotiales is difficult, but crucial, as the species name is the linking pin to information. Lists of accepted species are a helpful aid for researchers to obtain a correct identification using the current taxonomic schemes. In the most recent list from 2014, 339 Aspergillus, 354 Penicillium and 88 Talaromyces species were accepted. These numbers increased significantly, and the current list includes 446 Aspergillus (32 % increase), 483 Penicillium (36 % increase) and 171 Talaromyces (94 % increase) species, showing the large diversity and high interest in these genera. We expanded this list with all genera and species belonging to the Eurotiales (except those belonging to Elaphomycetaceae). The list includes 1 187 species, distributed over 27 genera, and contains MycoBank numbers, collection numbers of type and ex-type cultures, subgenus, section and series classification data, information on the mode of reproduction, and GenBank accession numbers of ITS, beta-tubulin (BenA), calmodulin (CaM) and RNA polymerase II second largest subunit (RPB2) gene sequences.

Two new aromatic polyketides from a sponge-derived Fusarium

In our natural product screening program from marine fungi, two new aromatic polyketides karimunones A (1) and B (2) and five known compounds (3–7) were isolated from sponge-associated Fusarium sp. KJMT.FP.4.3 which was collected from an Indonesian sponge Xestospongia sp. The structures of these compounds were determined by the analysis of NMR and MS spectroscopic data. The NMR assignment of 1 was assisted by DFT-based theoretical chemical shift calculation. Compound 2 showed antibacterial activity against multidrug resistant Salmonella enterica ser. Typhi with a MIC of 125 µg/mL while 1 was not active.