Sulfonylureas chemistry

Sales of agricultural products were 600 million in 1984. Du Pont expects to double this amount by 1990. There are many new products in the pipeline. Several of these new products are weed killers based on sulfonylurea chemistry. This family of weed killers is characterized by very low toxicity to mammals and high herbicidal activity at very low application rates in the field—often less than an ounce per acre of cropland. 

Extensive use of two more recendy developed classes of herbicides will further dramatically reduce the amount of appHed to control weeds. The sulfonylurea herbicides are extremely active compounds first discovered in the mid-1970s at DuPont they have been discussed extensively (78). Sulfonjiurea herbicides have experienced a rapid and widespread success since thek commercial introduction in 1982 with chlorsulfuron (Table 5). The sulfonylureas are appHed at rates of 2—75 g/ha. The chemistry of the sulfonylurea molecule permits the synthesis of a very large number of useful analogues, consequentiy many new herbicides are anticipated for crop production. As of this writing (1996), over 350 patents have been issued to about 27 agricultural companies covering tens of millions of stmctures known or expected to be herbicidaHy active. 

A multiresidue analytical method based on sohd-phase extraction enrichment combined with ce has been reported to isolate, recover, and quantitate three sulfonylurea herbicides (chlorsulfuron, chlorimuron, and metasulfuron) from soil samples (105). Optimi2ation for ce separation was achieved using an overlapping resolution map scheme. The recovery of each herbicide was >80% and the limit of detection was 10 ppb (see Soil chemistry of pesticides). 

Thiophene sulfonamide DoM chemistry is by far the most highly explored in view of the agrochemical significance of the sulfonylurea herbicides [23]. Potential for regioselective deprotonation as a function of kinetic or thermodynamic control 38 may lead to 3- or 5-... 

Thermospray LC/MS has been extensively used for the study of sulfonylurea herbicides (1-2). These compounds are thermally labile and can not be successfully analyzed by conventional GC/MS. Early applications of thermospray LC/MS included metabolite identification and product chemistry studies. We have recently evaluated the use of thermospray LC/MS for multi-sulfonylurea residue analysis in crops and have found the technique to meet the criteria for multiresidue methods. LC/MS offers both chromatographic separation and universal mass selectivity. Our study included optimization of the thermospray ionization and LC conditions to eliminate interferences and maximize sensitivity for trace level analysis. The target detection levels were SO ppb in crops. Selectivity of the LC/MS technique simplified sample extraction and minimized sample clean up, which saved time and optimized recovery. Average recovery for these compounds in crop was above 85%. 

Univ., China) presented his recent research results entitled Structure-activity relationship of novel sulfonylurea inhibitors on AHAS . H. Matsumoto (Univ. of Tsukuba, Japan) then introduced his study Mode of action of several classes of herbicides causing photooxi dative injury in plants . The second one dealt with insecticides, where X.-H. Qian (East China Univ. of Science and Technology, China) and K. Matsuda (Kinki Univ., Japan) presented their recent findings on chemistry and biochemistry of neonicotinoids. Interchange between Pesticide Science Societies of Korea and Japan was also maintained at a seminar entitled Current and future R D activities in agrochemical area in Korea and Japan . 

Levitt, G. Discovery of the Sulfonylurea Herbicides in Syndresis and Chemistry of Agrochemicals II,... 

Recent advances in sulfonylurea herbicides, in W. Ebing (editor-in-chief) Chemistry of Plant Protection,... 

S. K. Gee, J. V. Hay, Recent developments in the chemistry of sulfonylurea herbicides, in W. Ebing (editor-in-chief) Chemistry of Plant Protection, J. Stetter (volume editor) Herbicides inhibiting branched-chain amino acid biosynthesis. Springer, Berlin Heidelberg, Volume 10, 15—46, (1994). 

Table II summarizes the metabolic transformations now known to account for sulfonylurea plant selectivities. The sulfonylureas have allowed a broad survey of plant metabolic capabilities while using a single class of chemistry.

Levitt, G. "The Discovery of the Sulfonylurea Herbicides", this volume. Levitt, G. In Pesticide Chemistry Human Welfare and the Environment Miyamato, J. Kearney, P. C., Eds.Pergamon Press, New York, Vol. 1, 1983, 243. 

The above examples of the thiophene, and pyrazole sulfonamide syntheses are representative of the breath of the synthetic programs in both areas. This is by no means a complete review of all the syntheses we have developed, but rather an indication of some of the synthetic challenges, and solutions fiiat we have encountered in the sulfonylurea program at Du Pont. Much of the chemistry... 

The herbicidal activity of sulfonylureas derived from phenylacetic esters is enhanced when the carboxylate moiety is tied up to form a butyrolactone ring. Extension of this structural modification to weakly herbicidal sulfonylureas derived from cinnamate esters gives vinylogous butyrolactones which display significantly improved efficacy. Structure-activity relationships in these two classes of compounds are discussed along with their synthesis involving a novel benzothiazinone dianion and rf/h9-metallation chemistry. 

Immunoaffinity extraction is a technique often adopted in clinical chemistry. Immu-noaffinity supports contained polyclonal antibodies covalently immobilized on sephar-ose, agarose, or silica supports. Two different kinds of supports, crushed sol-gel monoliths and sol-gel-coated highly porous silica particles, were applied to the extraction of 16 sulfonylureas in food and natural water followed by high-performance liquid chromatography-ultraviolet/diode-array detection (LC-UV/DAD) [32]. 

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