Abstract
Discovery of novel, natural herbicides has become important to manage increasing weed resistance to synthetic herbicides and environmental issues. The systematic bioassay-guided fractionation and purification of the methylene chloride/methanol extract of the shoots of Semenovia transiliensis led to the isolation of several phytotoxic compounds. Lactuca sati va L. (lettuce, a dicot) and Agrostis stolonifera L. (bentgrass, a monocot) bioassays were used to identify and isolate the phytotoxic fractions. A number of furanocoumarin compounds isolated from S. transiliensis shoots were phytotoxic to both test species. These included psoralen, isopsoralen, heratomin, isopentenyloxyisobergapten, imperatorin, bergapten, xanthotoxin, heraclenin, and heraclenol. All the active secondary metabolites isolated from the shoots of S. transiliensis were furanocoumarins. Identification of these was accomplished using mass spectrometry and 1- and 2-dimensional NMR techniques. Phytotoxic activity of isolated compounds was evaluated in a dose–response manner from 0.3 to 1000 μM. In general, all of the compounds were more active on A. stolonifera than L. sativa. Bergaptin and xanthotoxin were the most active of the compounds, with moderate activity at 100 μM. Imperatorin and xanthotoxin inhibited growth of Lemna paucicostata Hegelm. by 50% at 29 and 60 μM, respectively. Our results show that S. transiliensis is rich in furanocoumarins, which are probably involved in various aspects of the chemical ecology of the species. Unfortunately, the general cytotoxicity of furanocoumarins makes them an unlikely candidate for pesticide discovery.