Phytotoxic Neocassane Diterpenes from<i>Eragrostis plana</i>

Abstract

Five new neocassane-like diterpenes (<b>1</b>-<b>5</b>) were isolated from the roots of <i>Eragrostis plana</i>. Their structures were elucidated by spectroscopic data, and the absolute configurations of the representative compounds neocassa-12(17),15-dien-3-one (<b>2</b>) and neocassa-12(13),15-diene-3,14-dione (<b>5</b>) were assigned by vibrational circular dichroism. The phytotoxic activity of compounds <b>3</b>, <b>4</b>, and <b>5</b> was evaluated against the germination and growth of <i>Ipomoea grandifolia</i> and <i>Euphorbia heterophylla</i>. Compound <b>4</b> exhibited the most potent activity for growth variables, resulting in the smallest radicle length of <i>I. grandifolia</i> and in the smallest aerial part length of <i>E. heterophylla</i>. Compound <b>5</b> reduced the germination speed index more effectively than the herbicide glyphosate (Roundup).