Inhibition of Narcissus pseudonarcissus Phytoene Desaturase by Herbicidal 3Trifluoromethyl-1,1-biphenyl Derivatives

A synthesis program directed to the discovery of novel bleaching herbicides led to the preparation of substituted 3-trifluoromethyl-1,1ʹ-benzoxazoles and 3-trifluoromethyl-1,1ʹ-biphenyls with thiazole-, thiadiazole-, and benzthiazole substituents. Herein, we show that these compounds interfere with the biosynthesis of colored carotenoids by inhibiting the enzyme phytoene desaturase. IC;i5;i0 values for inhibition of phytoene desaturase have been determined for 62 derivatives. Several new compounds were found that inhibited phytoene desaturase up to 400-fold more potently than the commercial bleaching herbicide norflurazon. The derived relationships between chemical structure and enzyme inhibition were used to generate a model of the proposed herbicide binding site. The implication that phytoene desaturase is the target site for the substituted 3-trifluoromethyl-1,1ʹbenzoxazole and biphenyl classes of herbicides is supported by a significant correlation of the IC50values for inhibition of phytoene desaturase with the biological activity in preemergence upland tests in the greenhouse.