The structure-activity relationships of the triketone class of HPPD herbicides†

Abstract

The 2-benzoylcyclohexane-1,3-diones, the triketones, are a novel class of bleaching herbicides whose mode of action is the inhibition of the enzyme p-hydroxyphenylpyruvate dioxygenase. The structure–activity relationships of this chemical class are elucidated. An ortho-substituent on the aryl ring is an absolute requirement for herbicidal activity. Beyond that, the herbicidal activity of these compounds is best correlated with the overall electron deficiency of the benzoyl group induced by 2,4-disubstitution of the aryl ring, with the most electron-deficient analogs being the most active. Moreover, the degree of electron deficiency of the benzoyl group is outwardly manifested in the acidity of the molecule. The activity of these compounds is further enhanced through additional aromatic substitution in the 3-position of the aryl ring. The greater activity of these 2,3,4-trisubstituted aryl analogs over the 2,4-disubstituted aryl analogs is due to increased intrinsic activity. © 1998 Society of Chemical Industry