O-[1-Ethyl-2-(3-trifluoromethylphenoxy)]ethyl-N-benzylcarbamate exhibits a marked inhibition of carotenoid biosynthesis. Forty-one analogues were synthesized and assayed for plant-type phytoene desaturase (PDS) and zeta-carotene desaturase (ZDS) inhibition in a cell-free system using recombinant enzymes obtained from Escherichia coli transformants. The target enzyme of all carbamates synthesized in this study is PDS and not ZDS; no inhibition of ZDS was observed using a 10(-4) M inhibitor concentration. Four compounds, O-[1-ethyl-2-(3-trifluoromethylphenoxy)]ethyl-N-(2-phenylethyl)carbamate (23), O-[1-ethyl-2-(3-trifluoromethylphenoxy)]ethyl-N-(2-chlorobenzyl)carbamate (25), O-[1-ethyl-2-(3-trifluoromethylphenoxy)]ethyl-N-(2-chlorobenzyl)carbamate (26), and O-[1-methyl-2-(3-trifluoromethylphenoxy)]ethyl-N-benzylcarbamate (30), were the most potent PDS inhibitors. Their pI(50) values, the negative logarithms of the molar concentration that produces a 50% inhibition, were 7.5, representing the same inhibitory activity as norflurazon. With respect to a structure-activity relationship the oxygen atom of the phenoxy group and a carbamate structure in O-(1-ethyl-2-phenoxy)ethyl-N-aralkylcarbamates studied were found to be essential for strong PDS inhibitors. Also, introduction of an ethyl group at the alpha-position of the ethylene bridge between the phenoxy group and the carbamate was important for a strong PDS inhibitor. Substituents at the 2- and/or 3-position of the phenoxybenzene ring were found to be favorable to a strong PDS inhibition of the analogues.

Enzyme activity of protoporphyrinogen-IX oxidase (Protox) prepared from 34 kinds of plant sources, containing 18 monocotyledons and 16 dicotyledons was evaluated. Protox(es) originated in monocotyledonous plants such as Zea mays cv. Anjou and DK212, Lolium perenne and Poa annua exhibited high enzyme activity, and Protox(es) in dicotyledonous plants such as Agrostemma githago and Arabidopsis thaliana showed a little higher enzyme activity than that of the above monocotyledonous plants. Highly active Protox(es) obtained from Zea mays cv. Anjou, Lolium perenne, Agrostemma githago and Arabidopsis thaliana were selected for the Protox inhibitory assay of peroxidizing herbicides. Echinochloa utilis was also selected for control. Protox inhibition by six peroxidizing herbicides such as oxyfluorfen, chlorophthalim, BW-91, pyraflufen-ethyl, DLH-1777 and LS-82556 was investigated using highly active Protox from the above monocotyledons and dicotyledons. As a result, six peroxidizing herbicides exhibited high inhibitory activity to Protox. Pyraflufen-ethyl showed the highest inhibition. The order of Protox inhibitory activity was pyraflufen-ethyl>oxyfluorfen>BW-91>chlorophthalim> DLH-1777>LS-82556, in experiment using four Protox(es) such as Zea mays cv. Anjou, Echinochloa utilis, Agrostemma githago and Arabidopsis thaliana except Lolium perenne. Oxyfluorfen exhibited the highest inhibitory activity to Protox of Lolium perenne. On the other hand, DLH-1777 showed a little less activity to Protox of Zea mays than that of other four weeds. DLH-1777 may become a model compound to find out new selective herbicides. Protox from four weeds will be used for peroxidizing herbicides assay, since the Protox showed high sensitivity to structually different peroxidizers.