Bleaching activity of 4-Phenyl-3-(substituted benzylthio)-4H-1,2,4-triazoles

A variety of 4-aryl- and 4-alkyl-3-(substituted benzylthio)-4H-1,2,4-triazoles were prepared and evaluated for their bleaching activity by the lettuce seedling test. Among the series of tested compounds, 4-(3-fluorophenyl)-3-(4-trifluoromethylbenzylthio)-4H-1,2,4-triazole (39) exhibited the highest bleaching activity, causing complete bleaching symptoms at 10 μM. In the dark condition, compound 39 inhibited the formation of such carotenoids as β-carotene, violaxanthin, neoxanthin and lutein, resulting in the formation of ζ-carotene, phytoene, phytofluene and β-zeacarotene, which were not detected in the untreated control. Treatment by compound 39 at 50 μM resulted in the amount of accumulated ζ-carotene being seven-fold higher than that of phytoene, phytofluene and β-zeacarotene. These results suggest that compound 39 might have interfered with desaturation, especially ζ-carotene desaturation, during carotenoid biosynthesis.