Isolation of Picrotoxanes from <i>Austrobuxus carunculatus</i> Using Taxonomy-Based Molecular Networking

Abstract

A unique collection of 292 extracts from 107 New Caledonian Euphorbiaceae species <i>sensu lato</i> was profiled by LC-MS² and the metabolite content organized by molecular networking. Based on the assumption that taxon-specific molecules are more likely to be structurally novel, taxonomic data were mapped on spectral networks to detect genus-specific clusters. Using this approach, a group of compounds unique to the genus <i>Austrobuxus</i> was highlighted. The subsequent MS-guided purification of the fruit EtOAc extract of <i>Austrobuxus carunculatus</i> led to the isolation of 13 new monolactone and "norditerpene" picrotoxanes (<b>2</b>-<b>14</b>), along with the known tutin (<b>1</b>). The structures of the new compounds were elucidated by HRESIMS and NMR spectroscopic data analysis, and the absolute configurations of compounds <b>1</b>, <b>3</b>, <b>7</b>, <b>11</b>, <b>12</b>, and <b>14</b> were determined by single-crystal X-ray diffraction analysis. The relative and absolute configurations of compounds <b>4</b> and <b>5</b> were ascertained by chemical transformation of compound <b>3</b>. The absolute configurations of other members of the series have been proposed on the basis of biogenetic considerations and specific rotation values of similar sign and magnitude. Compounds <b>1</b>-<b>14</b> were evaluated for their antiproliferative activities against HCT116 colon, U87-MG glioblastoma, and A549 lung human cancer cell lines. Compounds bearing an acyl chain at C-2 (i.e., <b>2</b>, <b>4</b>, and <b>13</b>) showed IC₅₀ values in the micromolar range for the three cell lines used.