No 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.

The anti-fungal and anti-bacterial activities and phytotoxicity of pyrrole-and 5-nitropyrrole-2-sulphonamides are compared with furan and thiophen analogues. Certain compounds of the group have appreciable anti-bacterial activity consistent with structure-activity investigations of other anti-bacterials derived from these heterocycles.2.1.1.1. Sodium pyrrole-2-sulphonate Pyrrole (30.0 g), pyridine-sulphur trioxide' (75 g) and 1,2-dichloroethane (250 ml) were refluxed 16 h. The solvent was decanted from the solid which was treated with water and the boiling solution neutralised with sodium carbonate. After evaporation, the residue was extracted with boiling ethanol-water (9 : 1 ; 500 ml) for 1 h; the filtered solution yielded sodium pyrrole-2-sulphonate (17.3 g) on cooling. 43

Botrytis cinerea, grown in shake culture in a liquid nutrient medium containing different amounts of triadimefon (4–40 mg litre−1), produced triadimenol as the sole major metabolite. Analysis by gas‐liquid chromatography (g.l.c.) showed the presence of (1R,2S) and (1S,2S)‐triadimenol, but no (1S,2R) or (1R,2R)‐enantiomer. The proportion of (1R,2S) to (1S,2S)‐triadimenol decreased over the period 6 to 168 h and with increased amounts of applied triadimefon. The implications of these patterns of metabolism are discussed in terms of overall fungitoxicity, the stereospecificity of the reduction process and the shortcomings of conventional, non‐chiral analysis of diastereoisomers by g.l.c. for assessing the sensitivity of fungi to such fungicides as triadimefon.

Twenty substituted quinoxalines based on the structure of 6 (or 7)‐methyl‐3‐phenyl‐1, 2‐dihydroquinoxalin‐2‐one, a fungicidally active photodegradation product of quinomethionate, were synthesised. Eleven of these compounds had ED50 values, as protectant sprays against Podosphaera leucotricha, of 0.1 mmol or less; these compounds had an aromatic substituent at the 3‐position of the quinoxaline ring. They were less active as protectant leaf dips against Erysiphe graminis f. sp. hordei than against Podosphaera leucotricha; none showed any systemic activity as a soil‐applied treatment against Podosphaera leucotricha. One compound was more active than quinomethionate as an eradicant spray. In spore germination tests on fungi from different taxonomic groups, the quinoxaline derivatives were active against only one basidiomycete (Uromyces fabae), whereas quinomethionate showed a broad spectrum of activity. The possible significance of this difference in spectrum of activity with respect to the mode of action is discussed.