title: Herbicidal action of 2-hydroxy-3-alkyl-1,4-naphthoquinones.
abstract: The main mode of herbicidal activity of 2-hydroxy-3-alkyl-1,4-naphthoquinones is shown to be inhibition of photosystem II (PSII). The herbicidal and in vitro activities have been measured and correlated with their (Log)octanol/water partition coefficients (Log Ko/w). The length of the 3-n-alkyl substituent for optimal activity differed between herbicidal and in vitro activity. The maximum in vitro activity was given by the nonyl to dodecyl homologues (Log Ko/w between 6.54 and 8.12), whereas herbicidal activity peaked with the n-hexyl compound (Log Ko/w = 4.95). The effect of chain branching was also investigated using isomeric pentyl analogues substituted at position 3. All exhibited similar levels of in vitro activities but herbicidal activities differed, albeit moderately, with the exception of one analogue that was much less phytotoxic. Other modes of action were also investigated using two representative compounds. They did not show any activity on photosystem I or mitochondrial complex I, or generate toxic oxygen radicals by redox cycling reactions. Only moderate activity was found against mitochondrial complex III from plants, in contrast to much higher corresponding activity using an insect enzyme.
authors.affiliation: Department of Biological and Ecological Chemistry, IACR-Rothamsted, Harpenden, Hertfordshire AL5 2JQ, UK. philip.jewess@bbsrc.ac.uk
authors.forename: Philip J
authors.initials: PJ
authors.lastname: Jewess
authors.forename: James
authors.initials: J
authors.lastname: Higgins
authors.forename: Kate J
authors.initials: KJ
authors.lastname: Berry
authors.forename: Stephen R
authors.initials: SR
authors.lastname: Moss
authors.forename: Adrian B
authors.initials: AB
authors.lastname: Boogaard
authors.forename: Bhupinder P S
authors.initials: BP
authors.lastname: Khambay
mesh_terms: D000465:Algorithms; D019607:Brassicaceae / Q000187:drug effects; D019069:Cell Respiration / Q000187:drug effects; D027462:Chenopodium / Q000187:drug effects / Q000378:metabolism; D003486:Cyanides / Q000494:pharmacology; D004351:Drug Resistance; D006540:Herbicides / Q000737:chemistry / Q000633:toxicity*; D008928:Mitochondria / Q000187:drug effects; D015394:Molecular Structure; D009285:Naphthoquinones / Q000737:chemistry / Q000633:toxicity*; D010100:Oxygen / Q000378:metabolism; D018532:Pisum sativum / Q000187:drug effects; D045322:Photosynthetic Reaction Center Complex Proteins / Q000187:drug effects*; D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D010944:Plants / Q000187:drug effects*; D021281:Quantitative Structure-Activity Relationship; D020524:Thylakoids / Q000187:drug effects; D014227:Triazines
chemical_list: C467050:2-hydroxy-3-(1-methylcyclohexyl)-1,4-naphthoquinone; C467049:2-hydroxy-3-(2-methyl-3-butenyl)-1,4-naphthoquinone; D003486:Cyanides; D006540:Herbicides; D009285:Naphthoquinones; D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D014227:Triazines; D010100:Oxygen