Herbicidal Activity of IG

and IC-22 were further compared at 300 g ai/ha. The results of herbicidal activity against leaf mustard, common amaranth, goosefoot, barnyard grass, crab grass, and giant foxtail are listed in Tables 2.48 and 2.49. 

As shown in Tables 2.48 and 2.49, IG-21 exhibited notable post-emergence herbicidal activity comparable to IC-22. Its herbicidal activity seems better than that of IH-13 and U-13. Both IC-22 and IG-21 would be promising for finther development as post-emergence herbicides, and IG-21 also displayed modest preemergence herbicidal activity against dicotyledons. 

The herbicidal activity and corp selectivity of IG-21 (code number for development HWS) were further examined at 1,200-50 g ai/ha. IG-21 was tested for postemergence activity against a range of plant species including purslane (Portulaca oleracea), slender amaranth (Amaranthus ascendens), goosefoot (Chenopodium album), spiny amaranth Amaranthus spinosus), sugarbeet Beta vulgaris), maize Zea mays) and rice Oryza sativa). Results are shown in Table 2.50. 

Ama common amaranth Che goosefoot Bra leaf mustard Ipo morning glory 

19 Effect against leaf mustard for post-emergence application at 75 g ai/ha (after 20 days) 

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Twenty-three of IG were prepared to test their herbicidal activity. The data of herbicidal activity of IG are listed in Tables 2.39, 2.40 and 2.41. 

C) Compounds with 2,3-Cl2 or 2,6-Cl2 as Y completely lost post-emergence herbicidal activity, irrespective of the fur-2-yl, thien-2-yl or pyrid-2-yl group as R. Pre-emergence and post-emergence herbicidal activity of IG-21, IH-13,... 

On the other hand, herbicide activity of IG-21, IID-10 and some analogs were also observed on tested plants with symptoms of smnting, necrosis, and morphological effects. Some symptoms are similar to 2,4-D. Maybe IG-21, IID-10 also has auxin-type herbicidal action as they are also the derivatives of 2,4-D acid. 

During the course of screening for herbicidal antibiotics from metabolites of microorganisms, we found several compounds which exhibited herbicidal activity. Among those found were herbicidins which had been previously reported to be nucleoside antibiotics ). Also, we isolated two previously unreported compounds, hydantocidin(l) and cornexistin(2), which are produced by Streptomyces hygroscopicus SANK 63584 and Paecilomyces variotii SANK 21086, respectively ig. 1). In this paper, we first describe the isolation and determination of stmcture for hydantocidin and cornexistin and then report the herbicidal activities of these compounds... 

In this chapter, we describe the synthesis, herbicidal activity and structure-activity relationship (SAR) of alkylphosphonates lA-IK. Herbicidal activity of IC-22 and IG-21 will be discussed in detail. 

Herbicidal Activity of 0,0-Dimethyl l-(Substituted Pbenoxyacetoxy)-l-(Fur-2-yl)Metbylpbospbonates IG... 

On the basis of the preliminary bioassay, post-emergence herbicidal activity of most IG was further examined at 150 g ai/ha in the greenhouse. The results of postemergence herbicidal activity against rape, chingma abutilon, common amaranth, and white echpta are hsted in Table 2.41. 

Table 7.7 Inhibitory potency against PDHc and herbicidal activity of IC-22, IG-21, IIB-2, and...

As shown in Scheme 2.2, the introduction of heterocyclic groups in R of IC-IF led to the phosphonates IG (R =fur-2-yl), IH (R =pyrid-2-yl) and IJ (R =thien-2-yl), respectively. The replacement of the substituted phenoxy moiety by the triazole ring in IB gave l-(l-phenyl-l,2,4-triazol-3-yloxyacetoxy) alkylphosphonates IK. Several compounds in IC and IG series were found to be herbicidally active compounds against broadleaf weeds by systematic study of alkylphosphonates lA-IK. 

In this section we describe the synthesis, herbicidal activity, and SAR analyses of heterocyclylmethylphosphonates IG-IJ. It has been found that IG-21 and some of its analogs have shown potential utility as an herbicide against broadleaf weeds. 

The results of SAR analysis for IG were similar to those for IC-IF, i.e., substituents Yn on the phenoxy-benzene ring greatly affected the herbicidal activity, and 2- and 4-positions in the phenoxy-benzene ring were the most essential. It showed that the fur-2-yl group was beneficial to herbicidal activity when the compound had Y as 2,4-Cl2 in structure IG. 

Like the results of SAR analyses for IG, substituents Y on the benzene ring of the phenoxy moiety greatly affected the activity as well. IH-18 (Y = 2,4-Cl2) exhibited the best herbicidal activity against dicotyledons for post-emergence at 150 g ai/ha foUowed by IH-16 (Y = 2,4,5-013) and IH-20 (Y = 2-Cl,4-F). Compounds IH with 3-CF3 4-CF3 2-Cl,4-CN 2,3-Me2 3-Me,4-Cl and 2,3-012 as Y had only 0-50 % inhibition against tested dicotyledons at 150 g ai/ha. It showed that 2,4-012 as Yn was most beneficial to post-emergence herbicidal activity, and the thienyl group was also beneficial to herbicidal activity when the compounds had Y as 2,4-012 in the structure IH. 

Structure-herbicidal activity relationships of IG, IH, and U can be summarized as follows Similarly to the SAR analyses for lA-IF, herbicidal activity was highly dependent upon the structure and position of substituents Y in the phenoxyacetyl substructure and R. ... 

A detailed study of acylphosphinates and acylphosphonates showed that they were mechanism-based inhibitors of pyruvate dehydrogenase complex (PDHc) as analogues of pyruvate. However, these phosphinates and phosphonates were not active enough to be considered as herbicides [1-3]. As stated in Chap. 2, some 1-substituted alkylphosphonates IC and IG showed notable herbicidal activity. Furthermore, the substitution of R R, R, R" and Y in phosphonate lo could be directly relevant to their herbicidal activity. Among the 1-substituted alkylphosphonates lA-IC, IC-22 (clacyfos) was found to be most eflFective against broadleaf weeds as a competitive inhibitor of PDHc (Scheme 3.1) [4]. This result prompted us to study continually on the design of novel PDHc inhibitors as potential herbicides. 

SAR analyses indicated that R R, and Y in the alkylphosphonates lo were the most essential sites for both enzyme inhibition and herbicidal activity. Me or Na as R and R, and 2,4-Cl2 as were most beneficial to activity. When 2,4-Cl2 were kept constant as Y , enzyme inhibition could be greatly enhanced by the chemical modification of R and R. Sodium salts IIB-2 and IID-10 exhibited more powerful enzyme inhibition than the corresponding alkyl phosphonates IC-22 and IG-21. However, good enzyme inhibition and herbicidal activity required an optimal combination of R, R, R, R", and Y in... 

An individual s absorbed dose is assumed to be proportional to the amount of a.i. applied. In this paper that proportion (mg a.i. absorbed/lb a.i. applied) is derived from the exposure information in USEPA s Pesticide Handlers Database (PHED, 1992) and herbicide-specific absorption data. PHED provides exposure information on 12 parts of the body (as opposed to the body as a whole). For each body part, PHED provides data on the amount of active ingredient that comes into contact with that body part per pound of active ingredient applied (amount inhaled or amount of dermal contact per pound applied). The PHED data used here assume that the individual is wearing normal clothing and gloves but not additional protective devices such as aprons or respirators. Based on atrazine- and simazine-specific studies conducted by Syngenta, the fraction of atrazine and simazine absorbed as a result of dermal contact is 0.056 when the exposure is less than or equal to 8. ig/cm2, 0.012 for exposures greater than or equal to 80 i,g/cm2, and a linear interpolated value for intermediate exposures. The fraction of the inhaled atrazine or simazine that is assumed to be absorbed is 1.0. 

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