Rhytidenones A–F, Spirobisnaphthalenes from <i>Rhytidhysteron</i> sp. AS21B, an Endophytic Fungus

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 IC₅₀ values of 0.31 and 3.60 μM, respectively