Abstract
Endophytic fungi are one of prolific sources of bioactive natural products with potential application in biomedicine and agriculture. In our continuous search for antimicrobial secondary metabolites from Fusarium oxysporum R1 associated with traditional Chinese medicinal plant Rumex madaio Makino using one strain many compounds (OSMAC) strategy, two diastereomeric polyketides neovasifuranones A (3) and B (4) were obtained from its solid rice medium together with N-(2-phenylethyl)acetamide (1), 1-(3-hydroxy-2-methoxyphenyl)-ethanone (2) and 1,2-seco-trypacidin (5). Their planar structures were unambiguously determined using 1D NMR and MS spectroscopy techniques as well as comparison with the literature data. By a combination of the modified Mosher’s reactions and chiroptical methods using time-dependent density functional theory-electronic circular dichroism (TDDFT-ECD) and optical rotatory dispersion (ORD), the absolute configurations of compounds 3 and 4 are firstly confirmed and, respectively, characterized as (4S,7S,8R), (4S,7S,8S). Bioassay results indicate that these metabolites 1–5 exhibit weak inhibitory effect on Helicobacter pylori 159 with MIC values of ≥16 μg/mL. An in-depth discussion for enhancement of fungal metabolite diversity is also proposed in this work.
Highlights
The assignment of absolute configuration (AC) is one of the most challenging tasks in the structure elucidation of chiral natural products
To determine the absolute configurations of C-4 and C-8 in 3, time-dependent density functional theory (TDDFT) method as a useful tool was applied for theoretical calculations of electronic circular dichroism (ECD) spectra [19,20]
Antimicrobial activity was investigated according to the agar dilution method described by Unemo and coworkers [23], ampicillin was used as a positive standard
Summary
The assignment of absolute configuration (AC) is one of the most challenging tasks in the structure elucidation of chiral natural products. J. Fungi 2022, 8, 40 strain many compounds (OSMAC) strategy [10,11], chemical study of the ethyl acetate extract of its rice medium resulted in the isolation of five known compounds including N(2-phenylethyl)acetamide. 1-(3-hydroxy-2-methoxyphenyl)-ethanone (2), including neovasiextract of its rice medium (1), resulted in the isolation of five known compounds furanones. N-(2-phenylethyl)acetamide (1), 1-(3-hydroxy-2-methoxyphenyl)-ethanone (2), neovasidiastereomeric polyketides originally isolated from the phytopathogenic strain. CAM231 present work highlights on assignment of ACs in and by a combined application of from Garcinia preussii [15]. Work highlights on assignment of ACs in 3 and 4 by a combined application of Mosher’s properties.
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