Fungicidal activity of substituted quinoxalines

Abstract

Abstract 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 ED 50 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.