New phytotoxic Cassane-like diterpenoids from Eragrostis plana (Nees)

Authors: FAVARETTO, ADRIANA - Universidad De Passo Fundo; Cantrell, Charles; FRONCZEK, FRANK - Louisiana State University; Duke, Stephen; Wedge, David; ABBAS, ALI - University Of Mississippi; SCHEFFER-BASSO, SIMONE - Universidad De Passo Fundo

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/28/2019
Publication Date: 1/28/2019
Citation: Favaretto, A., Cantrell, C.L., Fronczek, F.R., Duke, S.O., Wedge, D.E., Abbas, A., Scheffer-Basso, S.M. 2019. New phytotoxic Cassane-like diterpenoids from Eragrostis plana (Nees). Journal of Agricultural and Food Chemistry. https://doi.org/10.1021/acs.jafc.8b06832.
DOI: https://doi.org/10.1021/acs.jafc.8b06832

Interpretive Summary: Natural products are a source of compounds that might be used directly as bioherbicides or as the template for new synthetic herbicides. Eragrostis plana (Nees), also known as tough lovegrass, is a problematic invasive plant in South America pastures, with reported allelopathic potential. To isolate and identify phytotoxic compounds from leaves and roots of E. plana, a systematic investigation was performed. This is the first report on a new carbon skeleton, the neocassanes and this is also the first report of three new neocassane diterpenes. The compounds identified here could be key allelochemicals and explain the allelopathic activity of E. plana. Moreover, the description of the unpublished compounds besides contributing to the chemical characterization of the species, may be the first step in the development of new bioherbicides.

Technical Abstract: Eragrostis plana (Nees), also known as tough lovegrass, is a problematic invasive plant in South America pastures, with reported allelopathic potential. To isolate and identify phytotoxic compounds from leaves and roots of E. plana, a bioassay-directed isolation of the bioactive constituents was performed. This is the first report on a new diterpene carbon skeleton, the neocassanes. This is also the first report of three new neocassane diterpenes, neocassa-1,12(13),15-triene-3,14-dione (1), 19-norneocassa-1,12(13),15-triene-3,14-dione (2), and 14-hydroxyneocassa-1,12(17),15-triene-3-one (3), identified from the roots and the known compound a-linolenic acid identified from the leaves. Compounds 1, 2, and 3 inhibited the growth of duckweed, with IC50 values of 109 ± 28; 200 ± 37 and 59 ± 15 µM, respectively. These three diterpenes increased the percentage of necrotic tissues at 333 µM, while a-linolenic acid increased this percentage at 10 µM. Compound 2 was fungicidal to Colletotrichum acutatum, C. fragariae and C. gloeosporioides. A cellular leakage assay demonstrated that the isolated compounds do not directly affect plant plasma membranes. The same compounds do not have larvicidal activity against Aedes aegypti. The compounds identified here could be key allelochemicals that explain the allelopathy of E. plana. Moreover, the description of these new compounds, besides contributing to the chemical characterization of the species, may be the first step in the development of new bioherbicides.