Abstract
The plant enzyme, 4-hydroxyphenyloyruvate dioxygenase (4-HPPD), plays an important role in the plastoquinone biosynthesis. We synthesized 4-benzoyl-5-hydroxypyrazole derivatives including practical 4-HPPD inhibitors such as sulcotrione and active form of pyrazolate, and examined their 4-HPPD inhibitory activity. Some compounds exhibited moderate to high level of activity. By the way, it is known that 4-HPPD inhibitors cause the inhibition of enzyme activity by forming a chelate combination with Fe^<2+> in the active site. Iron (II) complexation ability of benzoylpyrazoles was demonstrated by means of UV-spectrophotometric analysis under different concentration of iron (II) sulfate aqueous solution. Sulcotrion and the active form of pyrazolate showed large spectral changes in the presence of Fe^<2+>, by contrast, no apparent change were observed under Fe^<2+>-free condition. Benzoylpyrazoles, exhibiting moderate 4-HPPD inhibitory activity and bearing a substituent such as a chlorine atom or a nitro group on the benzene ring at the 2-position made change in absorbance in the presence of Fe^<2+>, respectively. On the other hand, benzoylpyrazoles, which exhibiting no activity such as Ib and Ic, didn't give any changes. These findings indicated that UV-spectrophotometric analysis using iron (II) sulfate aqueous solution presented in this session was a useful method in finding the novel candidates to be 4-HPPD inhibitors.
