Hitoshi Kohno

Low resistance against novel 2-benzylamino-1,3,5-triazine herbicides in atrazine-resistant Chenopodium album plants

The effects of nine novel 2-benzylamino-1,3,5-triazines on photosynthetic reactions were measured in thylakoids isolated from wild-type and atrazine-resistant plants of Chenopodium album. The resistant plants have a mutation of serine for glycine at position 264 of the D1 protein. The measurement of oxygen evolution and chlorophyll a fluorescence induction indicated a 2–4-fold stronger inhibition by the 6-trifluoromethyl analogues of Photosystem II-dependent electron flow than atrazine. Analogues having a 6-methyl-, 6-monofluoromethyl or 6-difluoromethyl substitution were weak inhibitors, indicating that the 6-trifluoro group is very important for strong inhibition. All the nine novel 2-benzylamino-1,3,5-triazines were almost as active in wild-type as in atrazine-resistant thylakoids, indicating that the benzylamino substitution may be important for the lack of resistance in the atrazine-resistant plants.

Peroxidizing Phytotoxic Activity of 1, 3, 4-Thiadiazolidine-2-thiones and 1, 2, 4-Triazolidine-3, 5-dithiones

Using autotrophic Scenedesmus acutus cells incubated in the light and Echinochloa utilis culture, a series of isomeric compounds, namely 5-arylimino-3, 4-tetramethylene-1, 3, 4-thiadiazolidine-2-thiones (thiadiazolidine-thiones) and 4-aryl-l, 2-tetramethylene-1, 2, 4-triazolidine3, 5-dithiones (triazolidine-dithiones), were assayed with respect to growth inhibition, decrease of chlorophyll contents, protoporphyrin-IX accumulation and light-induced ethane formation level. The both types of phytotoxic compounds decreased chlorophyll contents, caused protoporphyrin-IX accumulation and ethane evolution, and inhibited growth of . Scenedesmus cells. They inhibited also protoporphyrinogen-IX oxidase, which led to rapid accumulation of protoporphyrin-IX, an intermediate of chlorophyll biosynthesis, just like peroxidizing herbicides such as p-nitrodiphenyl ethers and cyclic imides. Our comparative data on different sets of the aforementioned parameters suggest that both the thiadiazolidinethiones and triazolidine-dithiones are grouped as peroxidizing herbicides, affecting a crucial enzyme in the chlorophyll biosynthesis and inducing ethane formation by cell membrane destruction.

Novel 1,3,5-triazine derivatives with herbicidal activity†

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-bromo-benzylamino)-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 (PI 50 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.

Binding site of novel 2-benzylamino-4-methyl-6-trifluoromethyl-1,3,5-triazine herbicides in the D1 protein of Photosystem II

A series of replacement experiments of [14C]-triazines, [14C]-atrazine and [7-14C]-2-benzylamino-4-methyl-6-trifluoromethyl-1,3,5-triazine, bound to thylakoids isolated from wild-type and atrazine-resistant Chenopodium album (lambsquarters) were conducted. Replacement experiments of [14C]-triazines bound to wild-type Chenopodium thylakoids with non-labeled atrazine and 2-benzylamino-4-methyl-6-trifluoromethyl-1,3,5-triazine were carried out, to elucidate whether benzylamino-1,3,5-triazines use the same binding niche as atrazine. [14C]-Atrazine and [7-14C]-2-benzylamino-4-methyl-6-trifluoromethyl-1,3,5-triazine bound to wild-type thylakoids were replaced by non-labeled 2-benzylamino-4-methyl-6-trifluoromethyl-1,3,5-triazine and non-labeled atrazine, respectively. The above two replacements showed mutual competition. To clarify further whether benzylamino-1,3,5-triazines bind at the D1-protein to amino acid residue(s) different from atrazine or not, experiments to replace [7-14C]-2-benzylamino-4-methyl-6-trifluoromethyl-1,3,5-triazines bound to atrazine-resistant Chenopodium thylakoids by non-labeled atrazine, 2-(4-bromobenzylamino)-4-methyl-6-trifluoromethyl-1,3,5-triazine, DCMU and DNOC were carried out. Although the bound [7-14C]-2-benzylamino-4-methyl-6-trifluoromethyl-1,3,5-triazine was difficult to be replaced even with high concentrations of atrazine, [14C]-labeled 1,3,5-triazine was competitively replaced by non-labeled 2-(4-bromobenzylamino)-4-methyl-6-trifluoromethyl-1,3,5-triazine, DCMU or DNOC. Thus, 2-benzylamino-4-methyl-6-trifluoromethyl-1,3,5-triazine herbicides are considered to bind to the same niche at the D1 protein as atrazine, but use amino acid residue(s) different from those involved with atrazine binding.

Photosynthetic Electron Transport Inhibition by 2-Substituted 4-Alkyl-6-benzylamino-1,3,5-triazines with Thylakoids from Wild-Type and Atrazine-Resistant Chenopodium album

The effect of 2-benzylamino-1,3,5-triazines on photosynthetic electron transport (PET) was measured with thylakoids isolated from atrazine-resistant, wild-type Chenopodium album, and spinach to find novel 1,3,5-triazine herbicides bearing a strong PET inhibition. The PET inhibition assay with Chenopodium (wild-type and resistant), yielded a resistance ratio (R/ W = I50 (resistant)/I50 (wild-type)) of 324 for atrazine while for benzylamino-1,3,5-triazine derivatives of diamino-1,3,5-triazines a R/W of 11 to 160 was found. The compounds having a benzylamino group at one of the amino groups in the diamino-1,3,5-triazines have a resistant ratio down to one half to 1/30 of the atrazine value. The average resistance ratio of 21 benzylamino derivatives of monoamino-1,3,5-triazines was found to be about 4.0. The inhibition of 21 benzylamino-1,3,5-triazines assayed with atrazine-resistant Chenopodium thylakoids, indicated by pI50 (R) -values, correlated well with the PET inhibition pI50 (W) of wildtype thylakoids from Chenopodium.

New peroxidizing herbicides : activity compared with X-ray structure

The crystal structure of 3-(4-chloro-5-cyclopentyloxy-2-fluorophenyl)-5-isopropylideneoxazolidine- 2,4-dione (BW -4), chlorophthalim and oxyfluorfen were determined by X -ray analysis. The molecular size of these compounds was almost the same, but the angle between the oxazolidine and the phenyl ring (BW -4), the imide and phenyl ring (chlorophthalim ) and between the two phenyl rings (oxyfluorfen) differed. The phytotoxic activities, determined by growth inhibition of Scenedesmus cells, loss of chlorophyll, and peroxidative destruction of photosynthetic pigments, were different among these compounds. The angle and length of BW-3, BW-4 and oxyfluorfen showing best phytotoxic activity were found approximately 65 -95 ° and 11 - 13 Å, respectively. These preliminary findings indicate that both angle and length of the molecule have some bearing on peroxidative activity.

Photosynthetic Electron Transport Inhibition by Pyrimidines and Pyridines Substituted with Benzylamino, Methyl and Trifluoromethyl Groups

Abstract The decrease of the number of ring nitrogen atoms of 2-benzylamino-4-methyl-6-trifluoro-methyl-1,3,5-triazines on herbicidal activity and inhibition of photosynthetic electron trans port (PET) was assayed using thylakoids from Spinacia oleracea or atrazine-resistant Chenopodium album. Three 2-benzylamino-4-methyl-6-trifluoromethyl-1,3,5-triazines, nine pyrimidines with a benzylamino-, methyl-and trifluoromethyl-group, 2-benzylamino-6-methyl-4-trifluoromethyl-pyridine and N-benzyl-3-methyl-5-trifluoromethylaniline were synthesized and assayed. 2-(4-Bromobenzylamino)-4-methyl-6-trifluoromethylpyrimidine exhibited the highest PET inhibitory activity against Spinacia oleracea thylakoids of all compounds tested. The 2-benzylaminopyrimidines and 2-methylpyrimidines having a 4-halobenzylamino group exhibited higher PET inhibition than atrazine and 2-trifluoromethylpyrimidines against Spinacia oleracea thylakoids. These PET inhibitory active compounds also exhibited a strong and similar inhibition both against atrazine-resistant Chenopodium album thylakoids as well as against thylakoids from wild-type Chenopodium. The herbicidal activity of 4-(4-bromoben-zylamino)-2-methyl-6-trifluoromethylpyrimidine was equivalent to that of known herbicides like simetryne, simazine or atrazine.

Antagonistic effect of photosynthetic electron transport inhibitors on peroxidizing phytotoxic activity

It is shown that a number of new 2-benzylamino-1,3,5-triazines have a similar antagonistic effect to diuron on the phytotoxic activity of peroxidizing herbicides.