Abstract
Marine-derived fungi have been reported to have great potential to produce structurally unique metabolites. Our investigation on secondary metabolites from marine-derived fungi resulted in the isolation of seven new polyketides (phomopsiketones D–G (1–4) and letendronols A–C (5–7)) as well as one known xylarinol (8) in the cultural broth of Letendraea sp. Their structures and absolute configurations were elucidated using a set of spectroscopic and chemical methods, including HRESIMS, NMR, single-crystal X-ray diffraction, ECD calculation, and a modified version of Mosher’s method. Compound 2 showed weak inhibition against nitric oxide production in lipopolysaccaride-activated macrophages with an IC50 value of 86 μM.
Highlights
Metabolites from marine-derived microorganisms have become important pharmacological resources [1,2]
Carbon NMR (Table 2) showed 12 signals, including one α, β-unsaturated ketone, two olefinic carbons, nine aliphatic carbons that were grouped into one methyl, five methylenes (δC 20.0, 34.5, 35.6, 37.1, and 73.8), and three oxygenated methines, by an Heteronuclear singular Quantum Coherence (HSQC) spectrum
The culture broth (20 L) was filtered and extracted with equivoluminal EtOAc three times to obtain 2.79 g of metabolite extract, which was fractionated by column chromatography (CC) over silica gel (200−300 mesh, 60 g) and eluted in a gradient of petroleum ether (P)-EtOAc(E) (20:1–1:1)
Summary
Metabolites from marine-derived microorganisms have become important pharmacological resources [1,2]. The metabolic pathways of marine-derived fungi, which can be attributed to unique marine habitats, especially those that contain sea salts, may be significantly different from terrestrial ones [6]. Marine-derived fungi have great potential to produce structurally unique metabolites and have attracted a considerable amount of attention. In our ongoing research on bioactive secondary metabolites from marine-derived fungi, we isolated an endophytic fungus Letendraea sp. We obtained two novel spiroketals (letenketals A and B) from this fungus [7]. In order to obtain more structurally novel compounds, the systematic discovery of secondary metabolites for this strain was carried out. We report the isolation, structure elucidation, and bioactivities of these compounds.
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