Structure Elucidation of the <i>spiro</i>-Polyketide Svalbardine B from the Arctic Fungal Endophyte <i>Poaceicola</i> sp. E1PB with Support from Extensive ESI-MS^<i>n</i> Interpretation

Abstract

Svalbardines A and B (<b>1</b> and <b>2</b>) and annularin K (<b>3</b>) were isolated from cultures of <i>Poaceicola</i> sp. E1PB, an endophyte isolated from the petals of <i>Papaver dahlianum</i> from Svalbard, Norway. Svalbardine A (<b>1</b>) is a pyrano[3,2-<i>c</i>]chromen-4-one, a new analogue of citromycetin. Svalbardine B (<b>2</b>) displays an unprecedented carbon skeleton based on a 5'-benzyl-<i>spiro</i>[chroman-3,7'-isochromene]-4,8'-dione core. Annularin K (<b>3</b>) is a hydroxylated derivative of annularin D. The structure of these new polyketides, along with those of known compounds <b>4</b>-<b>6</b>, was established by spectrometric analysis, including extensive ESI-CID-MS^<i>n</i> processing in the case of svalbardine B (<b>2</b>).