Three new kavalactone dimers from <i>Piper methysticum</i> (kava)

<p>Three new dimeric kavalactones, designated as diyangonins A–C (<b>1–3</b>), along with two known analogs were isolated from the roots of <i>Piper methysticum</i>. Their structures were elucidated by means of extensive analysis of their 1D, 2D NMR, and mass spectroscopic data. All these dimers possess a skeleton featuring a cyclobutane ring connecting two kavalactone units in head-to-tail or head-to-head mode. Compounds <b>1</b>–<b>5</b> were evaluated for their cytotoxic activities against human tumor cell lines.</p>