Bioassay-guided isolation and structure elucidation of fungicidal and herbicidal compounds from Ambrosia salsola (Asteraceae)

Authors: PERERA, WILMER - Oak Ridge Institute For Science And Education (ORISE); Meepagala, Kumudini; FRONCZEK, FRANK - Louisiana State University; Cook, Daniel; Wedge, David; Duke, Stephen

Submitted to: Molecules
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/19/2019
Publication Date: 2/26/2019
Citation: Perera, W.H., Meepagala, K.M., Fronczek, F.R., Cook, D., Wedge, D.E., Duke, S.O. 2019. Bioassay-guided isolation and structure elucidation of fungicidal and herbicidal compounds from Ambrosia salsola (Asteraceae). Molecules. 24:1-12. https://doi.org/10.3390/molecules24050835.
DOI: https://doi.org/10.3390/molecules24050835

Interpretive Summary: Finding novel highly effective natural and ecofriendly pest control agents is one of the focuses of the agrochemical industry and plants are a source of such active compounds. We describe the isolation of active compounds against weeds and fungi from the ethyl acetate extract of Ambrosia salsola twigs and leaves. With this methodology we identified and purified twelve compounds. Three of these compounds are new. We named these three new compounds as salsolol A salsolol B and salsolol C. The structure of an herbicidal compound was determined by X-ray crystallography.

Technical Abstract: Bioassay-guided isolation and structure elucidation of fungicidal and herbicidal compounds from Ambrosia salsola (Asteraceae). The discovery of potent natural and ecofriendly pesticides is one of the focuses of the agrochemical industry and plant species are a source of many potentially active compounds. We describe the bioassay-guided isolation of antifungal and phytotoxic compounds from the ethyl acetate extract of Ambrosia salsola twigs and leaves. With this methodology we identified and purified twelve compounds (four chalcones, six flavonols and two pseudoguaianolide sesquiterpene lactones). Three new chalcones were elucidated as (S)-ß-Hydroxy-2',3,4',6' tetrahydroxy, 5 methoxydihydrochalcone (salsolol A) , (S)-ß-Hydroxy-2',4,4',6' tetrahydroxy, 3 methoxydihydrochalcone (salsolol B) and (R)-a, (R)-ß-Dihydroxy-2',3,4,4',6' pentahydroxydihydrochalcone (salsolol C) together with nine known compounds: balanochalcone, six quercetin derivatives, confertin and neoambrosin. Chemical structures were determined based on comprehensive HR-DART-MS, as well as 1D and 2D NMR experiments (DQFCOSY, HMQC and HMBC) and the absolute configurations of the chalcones were confirmed by CD spectra analysis. Crystal structure of compound confertin was determined by X-ray diffraction. The phytotoxicity of purified compounds was evaluated and neoambrosim was active against Agrostis stolonifera at 1000 µM, while confertin was active against both, Lactuca sativa and A. stolonifera at 1000 µM and 100 µM, respectively. Confertin and salsolol A and B had IC50 values of 261, 275 and 251 µM, respectively against duckweed (Lemna pausicotata). The antifungal activity was also tested against Colletotrichum fragariae A.N. Crook using a thin layer chromatography bioautography assay. Both, confertin and neoambrosin showed antifungal activity at 100 µM, however, confertin showed higher activity than neoambrosin at 100 µM.