Chiral grass herbicides

A novel series of chiral grass herbicides based on the benzyloxy substituted tetrahydrofuran ring system has been prepared. These compounds are readily accessible synthetically from diacetone-D-glucose which serves as a chiral template possessing the appropriate stereochemistry for elaboration to the active herbicides. The degree of herbicidal activity is related to the molecular shape of these compounds and especially to the orientation of the substituents around the tetrahydrofuran ring. The chemistry and empirical structure-activity relationships of these compounds will be discussed. 

Sugar herbicide RE 39571, 5,6-dideoxy-l,2-0-(l-methylethylidene)-3-0-(2-methylphenylmethyl)-a-D-xylo-hexofuranose (Figure 1), a representative of a novel series of chiral grass herbicides, has been demonstrated in our laboratories to possess a high level of preemergence herbicidal activity against grassy weeds with safety on soybeans, cotton, peanuts, and several other broadleaf crops. This herbicide has also been demonstrated to possess some broadleaf weed activity. 

In summary, these compounds represent a novel series of chiral grass herbicides that provide yet another example where chirality is very important for herbicidal activity. Additionally, the use of the sugar D-glucose as a chiral and enantiomerically pure starting material also offers the advantage of having the correct stereochemistry established inherently in the molecule. 

Metolachlor is the active ingredient of Dual , one of the most important grass herbicides for use in maize and a number of other crops. In 1997, after years of intensive research. Dual Magnum, with a content of approximately 90% (I S)-diastereomers and with the same biological effect at about 65% of the use rate, was introduced into the market. This chiral switch was made possible by the new technical process that is briefly described below. The key step of this new synthesis is the enantioselective hydrogenation of the isolated MEA imine, as depicted in Figure 1.3. 

Chiral 3-Benzyloxytetrahydrofuran Grass Herbicides Derived from D-Glucose... 

Chirality can be important in pharmaceuticals and also in other compounds that have biological activity. It can be a factor in herbicides. Dimethenamid (Frontier , BASF) is an herbicide in group 15, inhibitors of synthesis of very long-chain fatty acids. It can control a variety of annual grasses and several broadleaf weeds and is used for com crops. 

Chiral amines are important intermediates for biologically active eompounds, and enantioseleetive hydrogenation of C=N is an attractive route for their synthesis. Metolachlor is an A-chloroacetylated, alkoxyalkylated ortho-disubstituted aniline, which is the active ingredient of Dual , a herbieide used for maize and other grass crops. The original synthetic route gave a racemic mixture, but 95% of the herbicidal activity arises from the stereoisomer with (S) stereochemistry at the chiral carbon. An enantioselective route to (A)-metolaehlor has now been commereia-... 

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