Structures and Bioactive Properties of Myrtucommulones and Related Acylphloroglucinols from Myrtaceae

Asymmetric total synthesis of polycyclic xanthenes and discovery of a WalK activator active against MRSA

The development of new antibiotics continues to pose challenges, particularly considering the growing threat of multidrug-resistant Staphylococcus aureus. Structurally diverse natural products provide a promising source of antibiotics. Herein, we outline a concise approach for the collective asymmetric total synthesis of polycyclic xanthene myrtucommulone D and five related congeners. The strategy involves rapid assembly of the challenging benzopyrano[2,3-a]xanthene core, highly diastereoselective establishment of three contiguous stereocenters through a retro-hemiketalization/double Michael cascade reaction, and a Mitsunobu-mediated chiral resolution approach with high optical purity and broad substrate scope. Quantum mechanical calculations provide insight into stereoselective construction mechanism of the three contiguous stereocenters. Additionally, this work leads to the discovery of an antibacterial agent against both drug-sensitive and drug-resistant S. aureus. This compound operates through a unique mechanism that promotes bacterial autolysis by activating the two-component sensory histidine kinase WalK. Our research holds potential for future antibacterial drug development.

Myrtucommulones and Related Acylphloroglucinols from Myrtaceae as a Promising Source of Multitarget SARS-CoV-2 Cycle Inhibitors

The LABEXTRACT plant extract bank, featuring diverse members of the Myrtaceae family from Brazilian hot spot regions, provides a promising avenue for bioprospection. Given the pivotal roles of the Spike protein and 3CLpro and PLpro proteases in SARS-CoV-2 infection, this study delves into the correlations between the Myrtaceae species from the Atlantic Forest and these targets, as well as an antiviral activity through both in vitro and in silico analyses. The results uncovered notable inhibitory effects, with Eugenia prasina and E. mosenii standing out, while E. mosenii proved to be multitarget, presenting inhibition values above 72% in the three targets analyzed. All extracts inhibited viral replication in Calu-3 cells (EC50 was lower than 8.3 µg·mL-1). Chemometric analyses, through LC-MS/MS, encompassing prediction models and molecular networking, identified potential active compounds, such as myrtucommulones, described in the literature for their antiviral activity. Docking analyses showed that one undescribed myrtucommulone (m/z 841 [M - H]-) had a higher fitness score when interacting with the targets of this study, including ACE2, Spike, PLpro and 3CLpro of SARS-CoV-2. Also, the study concludes that Myrtaceae extracts, particularly from E. mosenii and E. prasina, exhibit promising inhibitory effects against crucial stages in SARS-CoV-2 infection. Compounds like myrtucommulones emerge as potential anti-SARS-CoV-2 agents, warranting further exploration.

α-Synuclein Aggregation Inhibitory and Antiplasmodial Activity of Constituents from the Australian Tree Eucalyptus cloeziana

Amyloid protein aggregates are linked to the progression of neurodegenerative conditions and may play a role in life stages of Plasmodium falciparum, the parasite responsible for malaria. We hypothesize that amyloid protein aggregation inhibitors may show antiplasmodial activity and vice versa. To test this hypothesis, we screened antiplasmodial active extracts from 25 Australian eucalypt flowers using a binding affinity mass spectrometry assay to identify molecules that bind to the Parkinson's disease-implicated protein α-syn. Myrtucommulone P (1) from a flower extract of Eucalyptus cloeziana was shown to have α-syn affinity and antiplasmodial activity and to inhibit α-syn aggregation. 1 exists as a mixture of four interconverting rotamers. Assignment of the NMR resonances of all four rotamers allowed us to define the relative configuration, conformations, and ratios of rotamers in solution. Four additional new compounds, cloeziones A-C (2-4) and cloeperoxide (5), along with three known compounds were also isolated from E. cloeziana. The structures of all compounds were elucidated using HRMS and NMR analysis, and the absolute configurations for 2-4 were determined by comparison of TDDFT-calculated and experimental ECD data. Compounds 1-3 displayed antiplasmodial activities between IC50 6.6 and 16 μM. The α-syn inhibitory and antiplasmodial activity of myrtucommulone P (1) supports the hypothesized link between antiamyloidogenic and antiplasmodial activity.

Camaldulensals A-C, the First Meroterpenoids Possessing Two Spatially Separated Formyl Phloroglucinols Conjugated to a Terpene Core from the Leaves of Eucalyptus camaldulensis Dehnh

Three new bis-formyl phloroglucinol-meroterpenoids (1-3), three new euglobal type formyl phloroglucinol-meroterpenoids (4-6), and one new dimeric formyl phloroglucinol (7) were isolated from the leaves of Eucalyptus camaldulensis. Camaldulensal A (1) is the first bis-isovaleryl-formyl-phloroglucinol-sesquiterpenoid. It features a novel 6/6/10/3/6/6 fused ring system and contains six stereogenic centers. Camaldulensals B (2) and C (3) are the first bis-isovaleryl-formyl-phloroglucinols, each conjugated to a monoterpene. Formyl phloroglucinol compounds (FPCs) containing two spatially separated formyl phloroglucinols conjugated to a terpene core such as 1-3 have not been reported previously. The structures of these compounds were elucidated by spectroscopic methods and computational analysis. Camaldulensals B (2) and C (3) exhibited significant antibacterial activity against methicillin-susceptible and methicillin-resistant Staphylococcus aureus. Structure activity relationships are discussed in relation to previously reported antibacterial activities of other molecules from the FPC structure class.

Phloroglucinols with hAChE and α-glucosidase inhibitory activities from the leaves of tropic Rhodomyrtus tomentosa

Four undescribed phloroglucinol meroterpenoids, rhodotomentodiones A-D, and one undescribed phloroglucinol dimer, rhodotomentodimer A, were obtained and structurally established from tropic Rhodomyrtus tomentosa leaves. Their structures were unambiguously elucidated based on the comprehensive analyses of the NMR and MS spectroscopic data, electronic circular dichroism (ECD) calculation, and single-crystal X-ray diffraction. In particular, rhodotomentodiones A and B represent the first examples of phloroglucinol meroterpenoids featuring a unique γ-pyranoid moiety. More importantly, rhodotomentodimer A exhibited the most potential human acetylcholinesterase (hAChE) and α-glucosidase inhibitory effects with IC₅₀ values of 7.5 μM and 5.6 μM, respectively. The possible interaction sites of the above potential hAChE and α-glucosidase inhibitor were achieved by molecular docking studies. These findings greatly enrich the diversity of natural products from Myrtaceae species, and provide potential candidates for the further development of anti-Alzheimer and antidiabetic diseases.

Gallomyrtucommulones G and H, New Phloroglucinol Glycosides, from Bioactive Fractions of Myrtus communis against Staphylococcus Species

Myrtaceae family is a continuous source of antimicrobial agents. In the search for novel antimicrobial agents against Staphylococcus species, bioactive fractions of Myrtus communis L., growing in the Sardinia island (Italy) have been investigated. Their phytochemical analysis led us to isolate and characterize four alkylphloroglucinol glycosides (1–4), three of them gallomyrtucommulones G–H (1,2), and myrtucommulonoside (4) isolated and characterized for the first time. The structures of the new and known compounds, endopreroxide G3 (5), myricetin-3-O-glycosides (6,7) were determined based on the spectroscopic evidence including 1D-/2D-NMR and HR-MS spectrometry. Enriched fractions as well as pure compounds were tested for their antimicrobial activity by broth micro-dilution assay against Staphylococcus epidermidis and S. aureus. Results reported herein demonstrated that gallomyrtucommulone G (1) showed a selective antimicrobial activity against both S. aureus strains (ATCC 29213 and 43300) until 16 μg/mL while gallomyrtucommulone D (3) showed the best growth inhibition value at 64 μg/mL.

Aspergillus-bees: A dynamic symbiotic association

Besides representing one of the most relevant threats of fungal origin to human and animal health, the genus Aspergillus includes opportunistic pathogens which may infect bees (Hymenoptera, Apoidea) in all developmental stages. At least 30 different species of Aspergillus have been isolated from managed and wild bees. Some efficient behavioral responses (e.g., diseased brood removal) exerted by bees negatively affect the chance to diagnose the pathology, and may contribute to the underestimation of aspergillosis importance in beekeeping. On the other hand, bee immune responses may be affected by biotic and abiotic stresses and suffer from the loose co-evolutionary relationships with Aspergillus pathogenic strains. However, if not pathogenic, these hive mycobiota components can prove to be beneficial to bees, by affecting the interaction with other pathogens and parasites and by detoxifying xenobiotics. The pathogenic aptitude of Aspergillus spp. likely derives from the combined action of toxins and hydrolytic enzymes, whose effects on bees have been largely overlooked until recently. Variation in the production of these virulence factors has been observed among strains, even belonging to the same species. Toxigenic and non-toxigenic strains/species may co-exist in a homeostatic equilibrium which is susceptible to be perturbed by several external factors, leading to mutualistic/antagonistic switch in the relationships between Aspergillus and bees.

Hyperforin and Myrtucommulone Derivatives Act as Natural Modulators of Wnt/β-Catenin Signaling in HCT116 Colon Cancer Cells

The therapeutic activities of natural plant extracts have been well known for centuries. Many of them, in addition to antiviral and antibiotic effects, turned out to have anti-tumor activities by targeting different signaling pathways. The canonical Wnt pathway represents a major tumorigenic pathway deregulated in numerous tumor entities, including colon cancer. Here, we investigated the acylphloroglucinols hyperforin (HF) from St. John's wort (Hypericum perforatum L.) and myrtucommulone A (MC A) from myrtle (Myrtus communis) and semi-synthetic derivatives thereof (HM 177, HM 297, HM298) for their effects on Wnt/β-catenin signaling. None of these substances revealed major cytotoxicity on STF293 embryonic kidney and HCT116 colon carcinoma cells at concentrations up to 10 μM. At this concentration, HF and HM 177 showed the strongest effect on cell proliferation, whereas MC A and HM 177 most prominently inhibited anchorage-independent growth of HCT116 cells. Western blot analyses of active β-catenin and β-catenin/TCF reporter gene assays in STF293 cells revealed inhibitory activities of HF, MC A and HM 177. In line with this, the expression of endogenous Wnt target genes, Axin and Sp5, in HCT116 cells was significantly reduced. Our data suggest that the acylphloroglucinols hyperforin, myrtucommulone A and its derivative HM 177 represent potential new therapeutic agents to inhibit Wnt/β-catenin signaling in colon cancer.

Antiviral Property of the Fungal Metabolite 3-O-Methylfunicone in Bovine Herpesvirus 1 Infection

Bovine herpesvirus type-1 (BoHV-1) is a widespread pathogen that provokes infectious rhinotracheitis and polymicrobial infections in cattle, resulting in serious economic losses to the farm animal industry and trade restrictions. To date, non-toxic active drugs against BoHV-1 are not available. The exploitation of bioactive properties of microbial products is of great pharmaceutical interest. In fact, fungi are a promising source of novel drugs with a broad spectrum of activities and functions, including antiviral properties. Hence, the potential antiviral properties of 3-O-methylfunicone (OMF), a secondary metabolite produced by Talaromyces pinophilus, were evaluated on BoHV-1. In this study, during BoHV-1 infection in bovine cells (MDBK), the non-toxic concentration of 5 µM OMF considerably reduced signs of cell death and increased cell proliferation. Furthermore, OMF significantly decreased the virus titer as well as the cytopathic effect and strongly inhibited the expression of bICP0, the major regulatory protein in the BoHV-1 lytic cycle. These findings were accompanied by a considerable up-regulation in the expression of the aryl hydrocarbon receptor (AhR), a multifunctional transcription factor also linked to the host’s response to a herpesvirus infection. Overall, our results suggest that by involving AhR, OMF shows potential against a BoHV-1 infection.

Total syntheses of ericifolione and its analogues via a biomimetic inverse-electron-demand Diels-Alder reaction

Driven by bioinspiration and appreciation of the structure of ericifolione, a biomimetic tautomerization/intermolecular inverse-electron-demand hetero Diels-Alder reaction cascade sequence promoted by sodium acetate to rapidly construct sterically hindered dihydropyran scaffolds was established, which allowed the first straightforward biomimetic total syntheses of ericifolione and its analogues with high simplicity. Moreover, this methodology set the stage for the preparation of relevant natural products or derivatives.

The Biomimetic Total Syntheses of the Antiplasmodial Tomentosones A and B

The first biomimetic total syntheses of natural phloroglucinols tomentosones A and B and their analogues have been accomplished. The synthetic strategy primarily referred to the potential biosynthetic precursors and their possible sequence of segments assembly by chemological evolution of the structural entities and enabled rapid access of the titled compounds in a practical fashion.