title: Two novel phytotoxic substances from Leucas aspera.
abstract: Leucas aspera (Lamiaceae), an aromatic herbaceous plant, is well known for many medicinal properties and a number of bioactive compounds against animal cells have been isolated. However, phytotoxic substances from L. aspera have not yet been documented in the literature. Therefore, current research was conducted to explore the phytotoxic properties and substances in L. aspera. Aqueous methanol extracts of L. aspera inhibited the germination and growth of garden cress (Lepidum sativum) and barnyard grass (Echinochloa crus-galli), and the inhibitory activities were concentration dependent. These results suggest that the plant may have phytotoxic substances. The extracts were then purified by several chromatographic runs. The final purification was achieved by reversed-phase HPLC to give an equilibrium (or inseparable) 3:2 mixture of two labdane type diterpenes (compounds 1 and 2). These compounds were characterized as (rel 5S,6R,8R,9R,10S,13S,15S,16R)-6-acetoxy-9,13;15,16-diepoxy-15-hydroxy-16-methoxylabdane (1) and (rel 5S,6R,8R,9R,10S,13S,15R,16R)-6-acetoxy-9,13;15,16-diepoxy-15-hydroxy-16-methoxylabdane (2) by spectroscopic analyses. A mixture of the two compounds inhibits the germination and seedling growth of garden cress and barnyard grass at concentrations greater than 30 and 3 μM, respectively. The concentration required for 50% growth inhibition (I50) of the test species ranges from 31 to 80 μM, which suggests that the mixture of these compounds, are responsible for the phytotoxic activity of L. aspera plant extract.
authors.affiliation: Department of Applied Biological Science, Faculty of Agriculture, Kagawa University, 2393 Ikenobe, Miki, Kagawa 761-0795, Japan. Electronic address: akmmominulislam@bau.edu.bd.
authors.forename: A K M Mominul
authors.initials: AK
authors.lastname: Islam
authors.affiliation: Department of Chemistry, Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku, Yokohama 223-8522, Japan.
authors.forename: Osamu
authors.initials: O
authors.lastname: Ohno
authors.affiliation: Department of Chemistry, Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku, Yokohama 223-8522, Japan.
authors.forename: Kiyotake
authors.initials: K
authors.lastname: Suenaga
authors.affiliation: Department of Applied Biological Science, Faculty of Agriculture, Kagawa University, 2393 Ikenobe, Miki, Kagawa 761-0795, Japan.
authors.forename: Hisashi
authors.initials: H
authors.lastname: Kato-Noguchi
mesh_terms: D004224:Diterpenes / Q000737:chemistry / Q000494:pharmacology; D031747:Echinochloa / Q000187:drug effects; D018525:Germination / Q000187:drug effects; D019686:Lamiaceae / Q000737:chemistry*; D031220:Lepidium sativum / Q000187:drug effects; D010936:Plant Extracts / Q000737:chemistry* / Q000494:pharmacology*
chemical_list: D004224:Diterpenes; D010936:Plant Extracts
keywords: Bioactive compounds; Diterpene; Lamiaceae; Medicinal plant; Plant growth inhibitor