Abstract:A new series of the 0-pyrimidinylsalicylates was synthesized and their herbicidal activity was examined. Some of these compounds showed very strong herbicidal activity under pre-and post-emergent treatment conditions against various kinds of grass and broadleaf weeds. Among these compounds, 0-(4, 6-dimethoxypyrimidin-2-yl) salicylic acid and its methyl ester were found to exhibit the highest activity. The herbicidal symptoms observed after the treatments included early cessation of plant growth followed by chlorosis, necrosis and plant death. The symptoms were similar to those caused by sulfonylureas and imidazolinones, which inhibit branched-chain amino acid biosynthesis.Key words: pyrimidinyl salicylates, methyl 0-(4-chloro-6-methoxypyrimidin-2-yl) salicylate, 2-alkanesulfonylpyrimidines, methyl 0-(4, 6-dimethoxypyrimidin-2-yl) salicylate, methyl 0-(4, 6-dimethoxy-s-triazin-2-yl) salicylate, acetolactate synthase, sulfonylureas.
A series of the O-pyrimidinylsalicylic acids were synthesized and their herbicidal activity was evaluated. Investigation of substituents on the benzene ring revealed that the 6-halogeno derivatives exhibited high herbicidal activity, but with severe phytotoxicity to some crops. The replacement of a bridge atom between two rings with other atoms or groups was performed. The Spyrimidinylthiosalicylic acids replaced by sulfur improved the safety to cotton plants dramatically reducing herbicidal activity against broadleaf weeds to some extent. Out of the S-pyrimidinylthiosalicylic acids, 6-chloro-2-(4,6-dimethoxypyrimidin-2-yl)thiosalicylic acid was selected as a quite promising compound for the development of a possible cotton field herbicide. * Dimethoxypyrimidines as Novel Herbicides (Part 3). For Parts 1 and 2, see Refs. 1), 2).
:The activity of a number of O-(4,6-dimethoxypyrimidin-2-yl)salicylic acids and their thio analogs inhibiting acetolactate synthase (ALS) preparation was measured. The e †ects of substituents on the salicylic-benzene ring on the inhibitory activity were analyzed quantitatively with physicochemical substituent parameters. For 6-substituted (thio)salicylic acids, the activity was shown to vary parabolically with the "intramolecularÏ steric parameterIn addition, the (E s ). higher steric dimension of substituents in terms of the STERIMOL width or length parameter lowered the activity. The Ðeld-inductive electron-withdrawing property of the 6-substituents in terms of the SwainÈLuptonÈHansch F was favorable for the activity of salicylic acid series. In 5-substituted salicylic acids, the activity was increased by electron-donating substituents with smaller size. The relationships between ALS inhibitory and herbicidal activities were also analyzed with some weed species. Both pre-and post-emergence activities against barnyard grass, Echinochloa crus-galli, were linearly related to the ALS inhibitory activity after allowing for the hydrophobic factor that may contribute to the transport processes. Those against two broad-leaved weed species, Polygonum convolvulus and Abutilon theophrasti were linearly related to the in-vitro activity with no signiÐcant participation of the hydrophobic factor.1998 SCI ( Pestic. Sci., 52, 343È353 (1998)
Absorption, distribution and metabolism of Bispyribac-sodium [sodium 2, 6-bis(4, 6dimethoxypyrimidin-2-yloxy)benzoate] or [KIH-2023] in rats orally dosed with 14C-KIH-2023 were investigated. More than 90% of the dosed radioactivity was detected in the excreta within 96 hr after dosing. Level of the radioactivity in the blood of male and female rats reached maxima at 2 and 1 hr after dosing, respectively, and then decreased rapidly to about a half level of maxima (C112). The radioactivity of tissues was lower at 96 hr after dosing than that at C112-time. Most of the radioactivity in the urine, feces, liver and plasma was detected as unchanged KIH-2023. The major radioactive compounds excreted into the bile were KIH-2023 and its glucuronide. Repeated oral administration of KIH-2023 for 15 days gave similar results from the single oral one in the excretion, tissue distribution and metabolism of 14C-KIH-2023.
The inhibition of acetolactate synthase (ALS) from etiolated pea seedlings by 2-(4, 6dimethoxypyrimidine-2-yloxy)benzoic acid (compound 2), one of the pyrimidinylsalicylic acid (PS) compounds, was desensitized by SR inhibitors but not at the alkaline pH. PS compounds including pyrithiobac (2-chloro-6-(4, 6-dimethoxypyrimidine-2-ylthio)benzoic acid) tested in this study inhibited ALS activity in the mixed-type manner with respect to pyruvate and in the non-competitive with respect to thiamine pyrophosphate (TPP). These compounds inhibited both of the two molecular species of ALS which were partially purified from pea seedlings and exhibited slow-binding properties to the crude preparation of ALS from pea seedlings in the extended-time-course experiments.The inhibition constants of the initial inhibition by PS compounds were 13-to 26-fold larger than those of the final steady state and the maximal first order rate constant (0. 69 min-1) for transition from the initial to the final steady state of the inhibition of pyrithiobac was nearly identical to those reported on other widely acknowledged ALS inhibitors.From these results, we conclude: PS compounds are slow-binding inhibitors to ALS activity, categorized in the sulfonylurea type.The binding site of PS compounds on the enzyme is considered to be located on the similar site to sulfonylureas. This binding site is judged not to be located on the regulatory center(s) but on the allosteric site in a wide sense near the catalytic center, which overlaps partially with the binding site of pyruvate and does not overlap with the binding site of TPP.Km= [E]
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