Paraverrucsins A-F, Antifeedant, and Antiphytopathogenic Polyketides from Rhizospheric Paraphaeosphaeria verruculosa and Induced Bioactivity Enhancement by Coculturing with Host Plant Dendrobium officinale

Isolation of Paraphaeoketones: A Plausible Biosynthetic Explanation for Paraphaeolactones via a Benzilic Acid Rearrangement Rather than a Favorskii Rearrangement

Paraphaeoketones A-C (1-3) were isolated from the culture broth of Paraphaeosphaeria sp. KT4192. Their structures and relative configurations were determined using spectroscopic analysis and verified through density functional theory (DFT)-based chemical shift calculations. The absolute configurations of these compounds were determined by comparing the experimental electronic circular dichroism (ECD) spectra with those based on DFT calculations. We also propose a plausible biosynthetic route to 1-3. While our prior studies on the isolation and structural elucidation of paraphaeolactones (e.g., 4) led us to suggest a Favorskii rearrangement for their biosynthesis, the isolation of 2 prompted the proposal of an alternative biosynthesis for 4, featuring a benzilic acid rearrangement of 2. Moreover, an in vitro conversion of 2 into 4 was achieved successfully, suggesting that a biosynthetic pathway for paraphaeolactones involving a benzilic acid rearrangement is more plausible than the previously presumed Favorskii rearrangement pathway. Arguments based on DFT calculations for these pathways are also described.

Pseudo-Enantiomeric Paraphaeolactones and Their Biosynthetic Derivatives from Paraphaeosphaeria sp. KT4192: A Proposition of a Favorskii Rearrangement for Their Biosynthesis

Paraphaeolactones A1, A2, B1, and B2 (1-4, respectively), known arthropsadiol D (5), massariphenone (6) and its positional isomer 7, and massarilactones E (8) and G (9) were isolated from the culture broth of Paraphaeosphaeria sp. KT4192. Although the structural resemblance between 1 and 2 implies that these comprised a diastereomeric pair at the C-2 stereogenic center, electronic circular dichroism (ECD) spectral analyses revealed that they were pseudo-enantiomers possessing the common (2R)-configuration. Paraphaeolactones B1 and B2 (3 and 4) were the derivatives of 2, which equipped the 3-(1-hydroxy-2-oxopropyl)-4-methylcatechol moiety via an acetal bond at C-10. The relative configurations of their acetal carbons were elucidated by NOE experiments, and those of C-8' were deduced independently by ECD spectral analysis. The present study disclosed that 1-5, 8, and 9 contain a methylcyclohexene substructure with the same absolute configuration. This prompted us to reinvestigate the absolute configurations of known structurally related fungal metabolites, allowing us to conclude that the methylcyclohexene moieties of these natural products have the same absolute configuration despite the variety of configurations of other stereogenic centers. The plausible biosynthetic routes for 1-9 are discussed on the basis of the above conclusion. We propose a Favorskii rearrangement as the key transformation for biosyntheses of 1-4.

The Potential Use of Fungal Co-Culture Strategy for Discovery of New Secondary Metabolites

Fungi are an important and prolific source of secondary metabolites (SMs) with diverse chemical structures and a wide array of biological properties. In the past two decades, however, the number of new fungal SMs by traditional monoculture method had been greatly decreasing. Fortunately, a growing number of studies have shown that co-culture strategy is an effective approach to awakening silent SM biosynthetic gene clusters (BGCs) in fungal strains to produce cryptic SMs. To enrich our knowledge of this approach and better exploit fungal biosynthetic potential for new drug discovery, this review comprehensively summarizes all fungal co-culture methods and their derived new SMs as well as bioactivities on the basis of an extensive literature search and data analysis. Future perspective on fungal co-culture study, as well as its interaction mechanism, is supplied.

The chemical diversity, the attractant, anti-acetylcholinesterase, and antifungal activities of metabolites from biocontrol Trichoderma harzianum uncovered by OSMAC strategy

Eight new compounds (1-8) were discovered from Trichoderma harzianum associated with edible mushroom by the one strain many compounds (OSMAC) strategy. Triharzianin A (1) is the first naturally scaffold characterized by a C₁₃-prostaglandin skeleton. The configurations of 1-3, and 5 were determined by the Mosher's method, experimental and calculated ECD spectra, and plausible biosynthesis of stereospecific epoxidation. Most compounds indicated obvious feeding attractant activities to silkworm with attraction rates at 30-90%. Compound 7 showed anti-acetylcholinesterase (anti-AChE) activity with a ratio of 29% at a concentration of 50 μM for insecticidal potential. So 2,​3-​dialkylchromone (7) had potential of chemical entrapment and killing of insects. Compounds 2, 3 and 7-11 showed antifungal activities against Aspergillus fumigates, and Trichoderma sp. from mushroom with MICs ≤ 300 μM. The four fermentation extracts also indicated obvious feeding attractant activities to silkworm for the activities brought by active metabolites from T. harzianum. The material base of biocontrol induced by the interaction of host-fungal symbiont can be investigated by the antifungal metabolites against pathogen fungi.