N-Alkylaryltriazine Herbicides: A Possible Link Between Triazines and Phenylureas

• Published in: Weed science 1987-11, Vol.35 (6), p.763-769
• Main Authors: Gardner, Gary, Sanborn, James R., Goss, John R.
• Format: Article
• Language: English
• Subjects: AMARANTHUS; AMARANTHUS HYBRIDUS; AMARANTHUS RETROFLEXUS; ATRAZINE; Binding sites; Chlorine; Chloroplasts; DIURON; Electrons; HERBICIDAS; HERBICIDE; HERBICIDES; Phenyls; Photosystem II; Physiology, Chemistry, and Biochemistry; Phytotoxicity; Plants; Triazines
• ISSN: 0043-1745; 1550-2759
• DOI: 10.1017/S0043174500079303

A comparison of the structure of the α-methylbenzyl analogue (MBAT) of atrazine with the Photosystem II herbicides atrazine [6-chloro-N-ethyl-N′-(1-methylethyl)-1,3,5-triazine-2,4-diamine] and diuron [N′-(3,4-dichlorophenyl)-N,N-dimethylurea] suggested that N-alkylbenzyltriazines may be a structural bridge between the triazines and the phenylureas. In the phenylureas, the addition of chlorines at the meta and/or para positions produces a marked increase in activity. Chloro-substituted derivatives of MBAT were synthesized to determine whether this structure-activity relationship also applies to the alkylaryltriazines. Addition of a chlorine to MBAT at the 4-position (CMBAT) caused a substantial increase in intrinsic activity, and a second chlorine at the 3-position (DCMBAT) caused a further increase. In direct comparisons, DCMBAT was more active in vitro than terbuthylazine [6-chloro-N-ethyl-N′-(1,1-dimethylethyl)-1,3,5-triazine-2,4-diamine], the most active chlorotriazine, and was also more active than diruon. The effects of DCMBAT were also measured on triazine-resistant pigweed (Amaranthus hybridus L. # AMACH) both in vivo and in vitro. The activity of this compound in triazine-resistant chloroplasts was intermediate between that of atrazine and diruon both in inhibition of photosynthetic electron transport and in competition for diuron binding sites, with half-maximal values falling in the micromolar range. Whole plant phytotoxicity of DCMBAT on triazine-resistant pigweed was also intermediate between that of diuron and atrazine. Since DCMBAT is a triazine with biological properties similar to that of a urea, we conclude that in a functional as well as structural sense, DCMBAT is a herbicide that is a hybrid between a triazine and a urea.