|De Los Angeles, Maria|
Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/28/2005
Publication Date: 10/2/2005
Citation: Hernandez-Romero, Y., Acevedo, L., De Los Angeles, M., Shier, W.T., Abbas, H.K., Mata, R. 2005. Phytotoxic activity of bibenzyl derivatives from the orchid epidendrum rigidum. Journal of Agricultural and Food Chemistry. Vol. 53: 6276-6280. Interpretive Summary: Exotic plant materials may provide a novel source for biologically active compounds, e.g., pesticides. Extracts of an orchid (Epidendrum rigidum) native to Mexico was found to contain compounds that have herbicidal activity to seedlings of the weed Amarathus hypochondriacus and the aquatic plant duckweed (Lemna pausicosta). These extracts were found to contain several compounds in the chemical class of bibenzyls that were responsible for this herbicidal activity. These compounds have low toxicity to mammalian cells and may provide useful leads in developing a new family of herbicidal compounds.
Technical Abstract: A whole plant chloroform-methanol extract of the orchid Epidendrum rigidum inhibited radicle growth of Amaranthus hypochondriacus seedlings [Inhibition concentration (IC50) = 300 µg/mL]. Bioassay-guided fractionation furnished four phytotoxins, namely gigantol (1), batatasin III (2), 2,3-dimethoxy-9,10-dihydrophenathrene-4,7-diol (9) and 3,4,9-trimethoxyphenanthrene-2,5-diol (11), along with the known flavonoids apigenin, vitexin, isovetin, and the triterterpenoids 24,24-dimethyl-9,19-cyclolanostane-25-en-3Beta-ol (14) and 24-methyl-9,19-cyclolanostane-25-en-3Beta-ol (15). Stilbenoids 1, 2, 9 and 11 inhibited radicle growth of A. hypochondriacus with IC50 values of 0.65 µM, 0.1 µM, 0.12 µM and 5.9 µM, respectively. Foliar application of gigantol (1) at 1 µM to four week old seedlings of A. hypochondriacus reduced shoot elongation by 69% and fresh weight accumulation by 54%. Bibenzyls 1 and 2, as well as synthetic analogs 4’-hydroxy-3,3',5-trimethoxybibenzyl (3), 3,3',4',5-tetramethoxybibenzyl (4), 3,4'-dihydroxy-5-methoxybibenzyl (5), 3'-O-methylbatatasin III (6), 3,3',5-trihydroxybibenzyl (7) and 3,4',5-trihydroxybibenzyl (8), were tested for phytotoxicity in axenic cultures of the small aquatic plant Lemna pausicostata. All bibenzyls derivatives except 7 and 8 inhibited growth and increased cellular leakage with IC50 values of 89.9-180 µM and 89.9-166 µM, respectively. The natural and synthetic bibenzyls showed marginal cytotoxicity on animal cells. The results suggest that orchid bibenzyls may be good lead compounds for the development of novel herbicidal agents.