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

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.

Stereoselective degradation of fungicide triadimenol in cucumber plants

“…1). The fungicidal activities of these against some fungi have been reported 6,7 to differ significantly, the SR form being the most fungitoxic (up to 1000-fold more active than the other three). In view of the differences in antifungal activity of the stereoisomers, it was considered important to investigate their fate individually under field conditions.…”

Effect of some triazole fungicides on intracellular pH and on cell membrane permeability in leaves of Elodea densa (Planch.) Casp.*

“…In higher the composition of the sterol pool not only in fungi plants some inhibiting effects of triazoles have also but also in various species of algae (Frasinel, been interpreted as due to the inhibition of an Patterson & Dutky, 1978) and higher plants (Schmitt enzyme involved in the synthesis of gibberellic acid & Benveniste, 1979; Schmitt, Rahier & Benveniste, (Burden et al, 1987(Burden et al, ). 1982.…”

Comparative enantioseparation of seven triazole fungicides on (S,S)‐Whelk O1 and four different cellulose derivative columns

“…For example, the R-enantiomer of diniconazole and uniconazole shows stronger fungicidal activity than the S-enantiomer, whereas the latter has higher plant growth regulating activity [2,3]. The ( -)-threo-1S,2R enantiomer of triadimenol shows the highest fungitoxicity against Rhizoctonia solani among the four enantiomers [4] and the activities of four optical isomers of paclobutrazol also differ greatly [5]. The US Food and Drug Administration requires the pharmaceutical and agrochemical industries to specify the enantiomeric purity of all optically active compounds prior to their marketing [6].…”