A virulent culture of Hymenoscyphus fraxineus, the causal agent of ash dieback, was investigated for its production of secondary metabolites in a 70 L batch fermentation. Chemical analysis of the mycelial extract by means of flash chromatography and preparative HPLC led to the isolation of a new ergostane-type steroid (1) and a new related lanostane triterpenoid (2), both revealing the same glycosylation pattern. While their planar structures were elucidated by HR-ESIMS and NMR data, relative stereochemistry was assigned by ROESY correlations in conjunction with H,H and C,H coupling constants. Absolute configuration was determined based on ROESY correlations between the aglycons and the sugar moieties, which were identified in both cases as d-mannose by GC/MS analysis of the trimethylsilylated derivatives. The isolated compounds, for which we propose the trivial names hyfraxins A (1) and B (2), were found to be cytotoxic against the mouse fibroblast cell line L929 and exhibited moderate to weak activity against Gram-positive bacteria.
Keywords: Ash dieback; Cytotoxic activity; Hymenoscyphus fraxineus; Secondary metabolites; Steroid glycoside; Triterpenoid glycoside.
Copyright © 2018 Elsevier Inc. All rights reserved.