Rhytidenones A–F, Spirobisnaphthalenes from <i>Rhytidhysteron</i> sp. AS21B, an Endophytic Fungus
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Abstract
Rhytidenone A (<b>1</b>), a unique spirobisnaphthalene with
a 1,7-dioxaspiro[4,4]nonan-2-one motif, and five new spirobisnaphthalenes,
rhytidenones B–F (<b>2</b>–<b>6</b>), were
isolated from the extract of a cultured fungal endophyte, <i>Rhytidhysteron</i> sp. AS21B. Their structures were elucidated
mainly by analysis of NMR spectroscopic data. The structure and configuration
of <b>1</b> were further confirmed by single-crystal X-ray diffraction
analysis. Compounds <b>3</b> and <b>4</b> exhibited significant
inhibitory activity against nitric oxide production from activated
macrophages with IC<sub>50</sub> values of 0.31 and 3.60 μM,
respectively