Phytotoxic Neocassane Diterpenes from Eragrostis plana .

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