The rice herbicide cafenstrole and its analogs inhibited the incorporation of [l-1 4 C]-oleate and [2-1 4 C]-malonate into very-long-chain fatty acids (VLCFAs), using Scenedesmus cells and leek microsomes from Allium porrum. Although the precise mode of interaction of cafenstrole at the molecular level is not completely clarified by the present study, it is con cluded that cafenstrole acts as a specific inhibitor of the microsomal elongase enzyme in volved in the biosynthesis of fatty acids with alkyl chains longer than C18. For a strong VLCFA biosynthesis inhibition an -S 0 2-linkage of the 1,2,4-triazole-l-carboxamides was required. Furthermore, /V,./V-dialkyl substitution of the carbamoyl nitrogen and electron-donating groups such as methyl at the benzene ring of 1,2,4-triazole-l-carboxamides produced a strong inhibition of VLCFA formation. A correlation was found between the phytotoxic effect against barnyardgrass (Echinochloa oryzicola) and impaired VLCFA formation.

No abstract

Indanofan and its analogs inhibited the elongation of stearoyl- or arachidoyl-CoA by [2-14C]-malonyl-CoA in leek microsomes from Allium porrum. Although the precise mode of interaction of indanofan at the molecular level is not completely clarified by the present study, it is concluded that indanofan and analogs act as inhibitor of the elongase enzyme involved in de novo biosynthesis of fatty acids with an alkyl chain longer than C18, called very-long-chain fatty acids (VLCFAs). For a strong inhibition of VLCFA formation chloro substituents at the benzene ring and the oxirane group were necessary. Furthermore, the greenhouse test showed strong activity for indanofan and its analogs, and the scores coincided with cell-free elongation inhibition. The cell-free assay, however, failed to indicate any activity for an analog having a methylene instead of the oxirane group, while both Digitaria ciliaris and Echinochloa oryzicola were killed with 1 kg a.i./ha. This finding cannot be discussed because the applied use rate of 1 kg a.i./ha is too high to allow for a score differentiation. For high concentrations of this compound additional unknown inhibitory effects may be involved besides fatty acid elongation.

New fluoroalkyl‐substituted 1,3,5‐triazine derivatives were synthesized and screened for herbicidal activity using a greenhouse pot test. Surprisingly, a series of 2‐alkyl‐4‐fluoroalkyl‐6‐aralkylamino‐1,3,5‐triazines e.g. 6‐(4‐bromobenzylamino)‐2‐methyl‐4‐trifluoromethyl‐1,3,5‐triazine was found to possess strong pre‐ and post‐emergence herbicidal activities, although the conventional herbicidal 1,3,5‐triazines generally should have a 2‐substituted‐4,6‐diamino‐1,3,5‐triazine structure for herbicidal activity. Our compounds show strong Photosynthetic Electron Transport inhibitory activity (PI50 c 7). Although their herbicidal effect is considered to be caused by a process similar to that for the conventional 1,3,5‐triazine herbicide atrazine, they can control atrazine‐resistant Chenopodium album effectively, and will thus form promising trial compounds for new triazine herbicide design.

A series of 2-aralkylamino-1, 3, 5-triazine derivatives was synthesized and their photosynthetic electron transport (PET) inhibitory activity was evaluated. Investigation on the relationship between PET inhibitory activity and substituents on the triazine ring revealed that 2-benzylamino-4-methyl-6-trifluoromethyl-1, 3, 5-triazine exhibited a highly PET inhibitory activity. Furthermore, introduction of a halogen or a trifluoromethyl group at 3-or 4-position of the benzene ring enhanced PET inhibitory activity, exhibiting pI50 = 6. 91-7. 29. Their PET inhibition was about 10 times stronger than that of simazine. On the absolute configuration of chiral center in 2-methyl-4-(a-methylbenzylamino) 6-trifluoromethyl-1, 3, 5-triazine, (-)-enantiomer was around 100 times stronger than (+)-enantiomer. However, the PET inhibitory activity was decreased by N-alkylation of the benzylamino group in 2-benzylamino-4-methyl-6-trifluoromethyl-1, 3, 5-triazine.