Comparative activity of the enantiomers of triadimenol and paclobutrazol as inhibitors of fungal growth and plant sterol and gibberellin biosynthesis

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Abstract
The nature and degree of the biological activity shown by triadimenol and paclobutrazol are influenced considerably by the absolute configuration of the two asymmetric carbon atoms present in the molecules. The order of the activity of triadimenol enantiomers was found to be: fungitoxicity—1S, 2R > 1R, 2R > 1R, 2S > 1S, 2S; inhibition of gibberellin biosynthesis—1R, 2S > 1S, 2S > 1R, 2R > 1S, 2R; and inhibition of plant sterol biosynthesis—1R, 2S≈1S, 2R > 1R, 2R > 1S, 25.The relative activity of paclobutrazol enantiomers was: fungitoxicity— 2R, 3R > 2S, 3R > 2R, 3S≈2S, 3S; inhibition of gibberellin biosynthesis—2S, 3S > 2R, 3S > 2R, 3R > 2S, 3R; and inhibition of plant sterol biosynthesis—2R, 3S > 2R, 3R > 2S, 3S > 2S, 3R. These data indicate that the R configuration at the chiral carbon bearing the hydroxyl group is the prime determinant for fungitoxicity whereas enantiomers having the S configuration at this carbon are effective inhibitors of gibberellin biosynthesis. This agrees well with published data for the structurally related vinylazoles.Plant sterol C‐14a demethylation was not always inhibited by enantiomers having high fungicidal activity thus indicating that the structural features necessary for binding to the plant C‐14a demethylase may differ from those needed for the analogous fungal enzyme.

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