Molecules (Jun 2012)
B-norsteroids from <em>Hymenoscyphus pseudoalbidus</em>
Abstract
Two viridin-related B-norsteroids, B-norviridiol lactone (<strong>1</strong>) and B-norviridin enol (<strong>2</strong>), both possessing distinct unprecedented carbon skeletons, were isolated from a liquid culture of the ash dieback-causing fungus <em>Hymenoscyphus pseudoalbidus</em>. Compound <strong>2</strong> was found to degrade to a third B-norsteroidal compound, 1β-hydroxy-2α-hydro-asterogynin A (<strong>3</strong>), which was later detected in the original culture. The proposed structure of <strong>1</strong> is, regarding connectivity, identical to the original erroneous structure for TAEMC161, which was later reassigned as viridiol. Compound <strong>2</strong> showed an unprecedented <sup>1</sup>H-<sup>13</sup>C HMBC correlation through an intramolecular hydrogen bond. The five-membered B-ring of compounds <strong>1–3</strong> was proposed to be formed by a benzilic acid rearrangement. The known compound asterogynin A was found to be formed from <strong>3</strong> by a β-elimination of water. All compounds were characterized by NMR spectroscopy, LC-HRMS and polarimetry.
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