Sesquiterpene Lactones with Potential Use as Natural Herbicide Models (I):  trans,trans-Germacranolides

A structure−activity study to evaluate the effect of the trans,trans-germacranolide sesquiterpene lactones costunolide, parthenolide, and their 1,10-epoxy and 11,13-dihydro derivatives (in a range of 100−0.001 μM) on the growth and germination of several mono and dicotyledon target species is accomplished. Results are compared with those obtained in the same bioassay with an internal standard, the commercial herbicide Logran, to validate the results with a known active formulation and to compare the results with a commercial product to test their potential use as natural herbicide models. These compounds appear to have a more selective effects on the radicle growth of monocotyledons. Certain factors such as the presence of nucleophile-acceptor groups and their accessibility enhance the inhibitory activity. The levels of radicle inhibition obtained with some compounds on wheat are totally comparable to those of Logran and allow to propose them as lead compounds. Keywords: trans,trans-Germacranolide; costunolide; parthenolide; Logran; phytoxicity; allelopathy; herbicide; Lactuca sativa L.; Lycopersicum esculentum L.; Lepidium sativum L.; Allium cepa L.; Triticum aestivum L.