Interaction of benzenediazocyanides with fungal spores and its relation to their stability in light

Abstract

AbstractBenzenediazocyanides, a class of highly fungicidal compounds, were investigated with special reference to their interaction with fungal cell thiols.Spores of Fusarium culmorum took up readily diazocyanides with fungicidal properties. The 4‐hydroxy derivative was not taken up in neutral medium. Both uptake and in vitro activity of this compound were strongly enhanced by lowering of the pH, indicating that mainly the non‐ionised form (OH) was taken up. Rate of uptake of uncharged fungicidal diazocyanides was found roughly to parallel their rate of reaction with cysteine. Furthermore, a close similarity of the spectra of conversion products released by spores and of cysteine reaction products was observed. Benzenediazocyanides with electron‐donating substituents are supposed to undergo mainly addition of thiols to the nitrile group, whereas compounds with electron‐withdrawing substituents seem to undergo both addition to the nitrile group and reduction of the azo group. Consequently, it is concluded that benzenediazocyanides, like many other classes of fungicidal compounds, react with sulfhydryl groups within the fungal cell in a non‐specific way.In solution benzenediazocyanides, like other classes of azo compounds, are known to be decomposed by light. The photodecomposition products, identified as the corresponding benzenediazonium ions and phenols, turned out to be considerably less fungitoxic in vitro than the parent compounds. Benzenediazocyanides with strongly electron‐donating phenyl substituents were found to be relatively stable to light.