Giovanni Meazza

The inhibitory activity of natural products on plant p-hydroxyphenylpyruvate dioxygenase.

The inhibitory activity of 34 natural products of various structural classes on hydroxyphenylpyruvate dioxygenase (HPPD), the target site for triketone herbicides, and the mode of interaction of selected natural products were investigated. Recombinant HPPD from arabidopsis is sensitive to several classes of natural compounds including, in decreasing order of sensitivity, triketones, benzoquinones, naphthoquinones and anthraquinones. The triketone natural products acted as competitive tight-binding inhibitors, whereas the benzoquinones and naphthoquinones did not appear to bind tightly to HPPD. While these natural products may not have optimal structural features required for in vivo herbicidal activity, the differences in their kinetic behavior suggest that novel classes of HPPD inhibitors may be developed based on their structural backbones.

The phytotoxic lichen metabolite, usnic acid, is a potent inhibitor of plant p-hydroxyphenylpyruvate dioxygenase

The lichen secondary metabolite usnic acid exists as a (−) and a (+) enantiomer, indicating a α or β projection of the methyl group at position 9b, respectively. (−)‐Usnic caused a dose‐dependent bleaching of the cotyledonary tissues associated with a decrease of both chlorophylls and carotenoids in treated plants whereas no bleaching was observed with the (+) enantiomer. (−)‐Usnic acid inhibited protophorphyrinogen oxidase activity (I 50=3 μM), but did not lead to protoporphyrin IX accumulation. Bleaching appears to be caused by irreversible inhibition of the enzyme 4‐hydroxyphenylpyruvate dioxygenase by (−)‐usnic acid (apparent IC50=50 nM).

Synthesis of 2,3,5-triaryl-4-trifluoromethyl thiophenes

Abstract Triaryl- β -trifluoromethyl thiophenes are synthesized from 1,3-dithiolium-4-olates and various substituted 1-aryl-3,3,3-trifluoro-1-propynes. The spectroscopic characteristics of the products and the regioselectivity of the reaction are discussed.