The antifungal activity of some sulphonyl derivatives of isoxazole,pyrazole, thiazole and thiophene

Fifty-three heterocyclic sulphonyl derivatives including eight sulphonamides, three sulphonyl azides, nine sulphonohydrazides and twenty sulphonohydrazones of substituted thiophenes, and a smaller range of analogous isoxazoles pryazoles and thiazoles, were tested as potential fungicides in a simple screening procedure against Mucor mucedo, Septoria nodorum, Trichoderma viride, Chaetomium globosum and Aspergillus niger. Several thiophene-2-sulphonyl based compounds exhibited a high level of antifungal activity at 100 mg litre^?1 against the five test species, especially the mono-halogen-substituted sulphonamides and sulphonohydrazines, in which a single chlorine or bromine atom was substituted in the para position of an attached phenyl ring. The most active compound, against all five species of fungus was N-(4-chlorophenyl)-N-(trichloromethylthio) thiophene-2-sulphonamide which had average MIC₅₀ and MIC₁₀₀ values of 86 and 180 μmol respectively. (MIC₅₀ and MIC₁₀₀ values are, respectively, the concentrations required to inhibit fungal growth by 50% and to inhibit it totally.) In general, the isoxazole analogues of the thiophene-2-sulphonyl compounds exhibited a much lower fungitoxic activity, whilst the pyrazole and thiazole based compounds had little or no activity. Compared with the other results, the considerable activity shown by 4-[2′-(3,4-dichlorobenzylidene)hydrazinosulphonyl]thiophene-2-carboxylic acid was unexpected.