Hymenosetin, a 3-decalinoyltetramic acid antibiotic from cultures of the ash dieback pathogen, Hymenoscyphus pseudoalbidus

Abstract

A 3-decalinoyltetramic acid, for which the trivial name hymenosetin is proposed, was isolated from crude extracts of a virulent strain of the ash dieback pathogen, Hymenoscyphus pseudoalbidus (= "Chalara fraxinea"). This compound was produced only under certain culture conditions in submerged cultures of the fungus. Its planar structure was determined by NMR spectroscopy and by mass spectrometry. The absolute stereochemistry was assigned by CD spectroscopy and HETLOC data. Hymenosetin exhibited broad spectrum antibacterial and antifungal activities (including strong inhibition of MRSA, as well as moderate cytotoxic effects.So far, the metabolite proved inactive in assays for evaluation of phytotoxicity, whereas viridiol, another secondary metabolite known from H. pseudoalbidus, was regarded as phytotoxic principle of the pathogen against its host, Fraxinus excelsior. Further studies will show whether hymenosetin constitutes a defence metabolite that is produced by the pathogenic fungus to combat other microbes and fungi in the natural environment.

Rickenyls A–E, antioxidative terphenyls from the fungus Hypoxylon rickii (Xylariaceae, Ascomycota)

“…NMR spectra were recorded with Bruker Avance III 700 spectrometer with a 5 mm TCI cryoprobe ( 1 H 700 MHz, 13 C 175 MHz) and Avance III 500 ( 1 H 500 MHz, 13 C 125 MHz) spectrometers. HR-ESI-MS mass spectra were obtained as described by Halecker et al (2014). The melting point of 1 was determined with a Büchi M565 instrument; compounds 2-5 were also analyzed as amorphous material and decomposed at ca.…”

Diversity and host preference of fungi co-inhabiting Cenococcum mycorrhizae

“…Some Helotiaceae, such as Ascocoryne and Hymenoscyphus spp. produce antifungal compounds (Hosoya, 1998;Morath et al, 2012;Halecker et al, 2014), and preliminary co-culture experiments indicate that Helotiaceae sp. VI is inhibitory to the growth of other fungal root endophytes (Kernaghan, unpublished).…”

Botryane, noreudesmane and abietane terpenoids from the ascomycete Hypoxylon rickii

“…NMR spectra were recorded with Bruker Avance III 700 spectrometer with a 5 mm TCI cryoprobe ( 1 H 700 MHz, 13 C 175 MHz), Bruker DMX-600 ( 1 H 600 MHz, 13 C 150 MHz) and Avance III 500 ( 1 H 500 MHz, 13 C 125 MHz) spectrometers. HRESI-MS spectra were obtained as described by Halecker et al (2014). Isolation of pure compounds was achieved if not indicated otherwise with a preparative HPLC (Gilson, Middleton, USA) equipped with a GX-271 Liquid Handler, a 172 DAD, a 305 and 306 pump (with 50SC Piston Pump Head).…”

“…Minimum inhibitory concentrations (MIC) were determined in a serial dilution assay carried out in a similar manner as previously described (Halecker et al, 2014) using various test organisms for antibacterial and antifungal activities. The in vitro cytotoxicity assay with the mouse fibroblast cell line L929 and the cervix carcinoma cell line KB3.1 (DSMZ No.…”