Depicting the Chemical Diversity of Bioactive Meroterpenoids Produced by the Largest Organism on Earth

In this investigation, we explored the diversity of melleolide-type meroterpenoids produced by Armillaria ostoyae, one of the largest and oldest organisms on Earth, using extracts from liquid and solid fermentation media. The study unveiled three unprecedented dimeric bismelleolides and three novel fatty-acid-substituted congeners, along with 11 new and 21 known derivatives. The structures were elucidated by 1D and 2D NMR spectroscopy and HRESI-MS, and ROESY spectral analysis for relative configurations. Absolute configurations were determined from crystal structures and through ECD spectra comparison. A compound library of melleolide-type meroterpenoids facilitated metabolomics-wide associations, revealing production patterns under different culture conditions. The library enabled assessments of antimicrobial and cytotoxic activities, revealing that the Δ2,4 double bond is not crucial for antifungal activity. Cytotoxicity was linked to the presence of an aldehyde at C1, but lost with hydroxylation at C13. Chemoinformatic analyses demonstrated the intricate interplay of chemical modifications on biological properties. This study marks the first systematic exploration of Armillaria spp. meroterpenoid diversity by MS-based untargeted metabolomics, offering insight into structure-activity relationships through innovative chemoinformatics.

Lachnuoic Acids A-F: Ambuic Acid Congeners from a Saprotrophic Lachnum Species

Chemical prospection of an extract derived from a saprotrophic fungus Lachnum sp. IW157 resulted in the isolation and characterization of six unprecedentedly reported ambuic acid analogues named lachnuoic acids A-F (1-6). Chemical structures of 1-6 were determined based on comprehensive 1D and 2D NMR spectroscopic analyses together with HR-ESI-MS spectrometry. The relative configurations of 1-3 were defined by ROESY spectroscopic analyses while their absolute configurations were unambiguously determined by Mosher's esters method. All isolated compounds were subjected to cytotoxic, antimicrobial, antibiofilm and nematicidal activity assays where only lachnuoic acid A (1) revealed potent antimicrobial activity against Staphylococcus aureus and Bacillus subtilis at MIC values of 16.6 and 8.3 μg/mL, respectively.

Bioprospection of Tenellins Produced by the Entomopathogenic Fungus Beauveria neobassiana

Fungi are known as prolific producers of bioactive secondary metabolites with applications across various fields, including infectious diseases, as well as in biological control. However, some of the well-known species are still underexplored. Our current study evaluated the production of secondary metabolites by the entomopathogenic fungus Beauveria neobassiana from Thailand. The fermentation of this fungus in a liquid medium, followed by preparative high-performance liquid chromatography (HPLC) purification, resulted in the isolation of a new tenellin congener, namely pretenellin C (1), together with five known derivatives (2-6). Their chemical structures were elucidated by 1D and 2D nuclear magnetic resonance (NMR) spectroscopy in combination with high-resolution electrospray ionization mass spectrometry (HR-ESI-MS). We evaluated the antimicrobial and cytotoxic activities from all isolated compounds, as well as their inhibitory properties on biofilm formation by Staphylococcus aureus. Generally, tenellins displayed varying antibiofilm and cytotoxic effects, allowing us to propose preliminary structure-activity relationships (SARs). Among the tested compounds, prototenellin D (2) exhibited the most prominent antibiofilm activity, while its 2-pyridone congener, tenellin (4), demonstrated potent cytotoxic activity against all tested cell lines. Given the fact that the biological activities of the tenellins have so far been neglected in the past, our study could provide a good starting point to establish more concise structure-activity relationships in the near future.