Monte R. Weimer

The discovery of Arylex™ active and Rinskor™ active: Two novel auxin herbicides.

Multiple classes of commercially important auxin herbicides have been discovered since the 1940s including the aryloxyacetates (2,4-D, MCPA, dichlorprop, mecoprop, triclopyr, and fluroxypyr), the benzoates (dicamba), the quinoline-2-carboxylates (quinclorac and quinmerac), the pyrimidine-4-carboxylates (aminocyclopyrachlor), and the pyridine-2-carboxylates (picloram, clopyralid, and aminopyralid). In the last 10 years, two novel pyridine-2-carboxylate (or picolinate) herbicides were discovered at Dow AgroSciences. This paper will describe the structure activity relationship study that led to the discovery of the 6-aryl-picolinate herbicides Arylex™ active (2005) and Rinskor™ active (2010). While Arylex was developed primarily for use in cereal crops and Rinskor is still in development primarily for use in rice crops, both herbicides will also be utilized in additional crops.

The synthesis and biological activity of 1-alkyl-4-(3-azacyclobenzoyl)-5-hydroxypyrazole herbicides

The benzoylpyrazoles belong to a class of herbicides that inhibit the enzyme 4-hydroxyphenylpyruvate dioxygenase (HPPD). This mode of action is characterized by bleaching due to the disruption of plastoquinone and α-tocopherol biosynthesis. Early studies indicated that the C(3) position of benzoylpyrazoles can accommodate a wide range of functionality. This paper describes synthetic efforts to improve cool season grass weed activity and wheat selectivity by incorporating cyclic moieties attached through nitrogen at this position. The aza substituents were generally installed by nucleophilic aromatic substitution, however, an efficient four-step method was developed for constructing substituted morpholino moieties directly on pre-formed benzoylpyrazoles. The structure-activity relationships revealed that certain piperidino moieties provided good activity on wild oat, while exhibiting selectivity toward wheat. They also showed that excellent levels of activity on wild oat and blackgrass can be achieved with morpholino substituents.