Identification of meroterpenoids from Bipolaris victoriae S27 and their potential activity against tumor metastasis and inhibition of the NF-κB signaling pathway

Three undescribed meroterpenoids, named bipolacochlioquinones A-C, together with seven known compounds, were isolated from the plant endophytic fungus Bipolaris victoriae S27 derived from the fresh stems of Rubia podantha Diels. Their structures were mainly determined by extensive spectroscopic analysis. The relative configurations of bipolacochlioquinones A-C were assigned using the ROESY spectrum, comparison of their spectral data with that reported in the literatures, and NMR calculations. Moreover, their complete absolute configurations were further established by electronic circular dichroism calculations using density functional theory. Among them, bipolacochlioquinone A is found to represent the first example of previously undescribed 6/6/6/6/6 pentacyclic dioxane-containing cochlioquinones, and bipolacochlioquinone B possesses a rare 6/6/6/6/5 pentacyclic system bearing a tetrahydrofuran ring fused to a polyketide and a sesquiterpenoid subunit. All compounds were evaluated for their inhibitory effects on tumor growth, metastasis, and the NF-κB signaling pathway. Among them, bipolacochlioquinone C and cochlioquinone A show the most potent cytotoxicities and NF-κB inhibitory activities. The effects of bipolacochlioquinone C and cochlioquinone A on the expression of NF-κB-associated proteins were also evaluated using western blotting. These results indicate that bipolacochlioquinone C and cochlioquinone A can inhibit the growth and metastasis of HCT116 and MDA-MB-231 cells by suppressing the NF-κB signaling pathway.

Enantioselective Total Syntheses of Manginoids A and C and Guignardones A and C

An enantioselective synthetic approach for preparing manginoids and guignardones, two types of biogenetically related meroterpenoids, is reported. This bioinspired and divergent synthesis employs an oxidative 1,3-dicarbonyl radical-initiated cyclization and cyclodehydration of the common precursor to forge the central ring of the manginoids and guignardones, respectively, at a late stage. Key synthetic steps include silica-gel-promoted semipinacol rearrangement to form the 6-oxabicyclo[3.2.1]octane skeleton and the Suzuki-Miyaura reaction of vinyl bromide to achieve fragment coupling. This synthesis protocol enables the asymmetric syntheses of four fungal meroterpenoids from commercially available materials.

Secondary metabolite biosynthetic diversity in the fungal family Hypoxylaceae and Xylaria hypoxylon

To date little is known about the genetic background that drives the production and diversification of secondary metabolites in the Hypoxylaceae. With the recent availability of high-quality genome sequences for 13 representative species and one relative (Xylaria hypoxylon) we attempted to survey the diversity of biosynthetic pathways in these organisms to investigate their true potential as secondary metabolite producers. Manual search strategies based on the accumulated knowledge on biosynthesis in fungi enabled us to identify 783 biosynthetic pathways across 14 studied species, the majority of which were arranged in biosynthetic gene clusters (BGC). The similarity of BGCs was analysed with the BiG-SCAPE engine which organised the BGCs into 375 gene cluster families (GCF). Only ten GCFs were conserved across all of these fungi indicating that speciation is accompanied by changes in secondary metabolism. From the known compounds produced by the family members some can be directly correlated with identified BGCs which is highlighted herein by the azaphilone, dihydroxynaphthalene, tropolone, cytochalasan, terrequinone, terphenyl and brasilane pathways giving insights into the evolution and diversification of those compound classes. Vice versa, products of various BGCs can be predicted through homology analysis with known pathways from other fungi as shown for the identified ergot alkaloid, trigazaphilone, curvupallide, viridicatumtoxin and swainsonine BGCs. However, the majority of BGCs had no obvious links to known products from the Hypoxylaceae or other well-studied biosynthetic pathways from fungi. These findings highlight that the number of known compounds strongly underrepresents the biosynthetic potential in these fungi and that a tremendous number of unidentified secondary metabolites is still hidden. Moreover, with increasing numbers of genomes for further Hypoxylaceae species becoming available, the likelihood of revealing new biosynthetic pathways that encode new, potentially useful compounds will significantly improve. Reaching a better understanding of the biology of these producers, and further development of genetic methods for their manipulation, will be crucial to access their treasures.

Peculiarities of meroterpenoids and their bioproduction

Meroterpenoids are a class of terpenoid-containing hybrid natural products with impressive structural architectures and remarkable pharmacological activities. Remarkable advances in enzymology and synthetic biology have greatly contributed to the elucidation of the molecular basis for their biosynthesis. Here, we review structurally unique meroterpenoids catalyzed by novel enzymes and unusual enzymatic reactions over the period of last 5 years. We also discuss recent progress on the biomimetic synthesis of chrome meroterpenoids and synthetic biology-driven biomanufacturing of tropolone sesquiterpenoids, merochlorins, and plant-derived meroterpenoid cannabinoids. In particular, we focus on the novel enzymes involved in the biosynthesis of polyketide-terpenoids, nonribosomal peptide-terpenoids, terpenoid alkaloids, and meroterpenoid with unique structures. The biological activities of these meroterpenoids are also discussed. The information reviewed here might provide useful clues and lay the foundation for developing new meroterpenoid-derived drugs. KEY POINTS: • Meroterpenoids possess intriguing structural features and relevant biological activities. • Novel enzymes are involved in the biosynthesis of meroterpenoids with unique structures. • Biomimetic synthesis and synthetic biology enable the construction and manufacturing of complex meroterpenoids.

Absolute Configuration of Bioactive Azaphilones from the Marine-Derived Fungus Pleosporales sp. CF09-1

Investigation of the marine-derived fungus Pleosporales sp. CF09-1 cultured in modified PDB medium led to the isolation of six new azaphilone derivatives, pleosporalones B and C (1 and 2) and pleosporalones E-H (4-7), and one known analogue (3). The absolute configurations of C-2' and C-3' in 3 were assigned by a vibrational circular dichroism method. The C-11 relative configurations for the pair of C-11 epimers (4 and 5) were established by comparing the magnitude of the computed ¹³C NMR chemical shifts (Δδ_calcd) with the experimental ¹³C NMR values (Δδ_exp) for the epimers. Antiphytopathogenic and anti- Vibrio activities were evaluated for 1-7. Pleosporalone B (1) exhibited potent antifungal activities against the fungi Alternaria brassicicola and Fusarium oxysporum with the same MIC value of 1.6 μg/mL, which were stronger than the positive control ketoconazole among these compounds. Additionally, pleosporalone C (2) displayed significant activity against the fungus Botryosphaeria dothidea (MIC, 3.1 μg/mL). Compounds 6 and 7 displayed moderate anti- Vibrio activities against Vibrio anguillarum and Vibrio parahemolyticus, with MIC values of 13 and 6.3 μg/mL for 6 and 6.3 and 25 μg/mL for 7, respectively.