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-‰uoro-phenyl)-3-(4-tri‰uoromethylbenzylthio)-4H-1,2,4-triazole (39) exhibited the highest bleaching activity, causing complete bleaching symptoms at 10 mM. In the dark condition, compound 39 inhibited the formation of such carotenoids as b-carotene, violaxanthin, neoxanthin and lutein, resulting in the formation of z-carotene, phytoene, phyto‰uene and b-zeacarotene, which were not detected in the untreated control. Treatment by compound 39 at 50 mM resulted in the amount of accumulated z-carotene being seven-fold higher than that of phytoene, phyto‰uene and b-zeacarotene. These results suggest that compound 39 might have interfered with desaturation, especially z-carotene desaturation, during carotenoid biosynthesis.

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