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

The 2-benzoylcyclohexane-1,3-diones, the triketones, are a novel class of b leaching 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 i s an absolute requirement for herbicidal activity. Beyond that, the herbici dal activity of these compounds is best correlated with the overall electro n deficiency of the benzoyl group induced by 2,4-disubstitution of the aryl ring, with the most electron-deficient analogs being the most active. More over, the degree of electron deficiency of the benzoyl group is outwardly m anifested in the acidity of the molecule. The activity of these compounds i s further enhanced through additional aromatic substitution in the 3-positi on of the aryl ring. The greater activity of these 2,3,4-trisubstituted ary l analogs over the 2,4-disubstituted aryl analogs is due to increased intri nsic activity. (C) 1998 Society of Chemical Industry.