Discovery and mode of action of cyclopyrimorate: A new paddy rice herbicide

Cyclopyrimorate invented by Mitsui Chemicals Agro, Inc. is a novel bleaching herbicide effective against a broad range of rice weeds, including biotypes resistant to acetolactate synthase inhibitors. It was discovered through structural modifications of a lead compound, which was designed from partial substructures of pyridazine herbicides, such as credazine and pyridafol. The target site of cyclopyrimorate was demonstrated to be homogentisate solanesyltransferase, a novel target site for commercial herbicides. Cyclopyrimorate will be on the market, thus offering a new strategy for the management of herbicide resistance. In this chapter the discovery, optimization, and mode of action of cyclopyrimorate are reviewed.