Fungistatic Activity of Pyrazole Derivatives Towards Aspergillus niger

Abstract

The relationship between chemical structures of 21 kinds of pyrazole derivatives and their fungistatic activity towards Aspergillus niger was investigated by the agar plate filter paper disc method. The influence of pH upon the fungistatic activity of the compounds was tested at pH 3.7, 5.2 and 7.0. The inhibition of fungal growth was estimated in terms of initial strength of activity (IS) and its durability. The IS value of 4-chloro-m-cresol (1) obtained on incubation at pH 5.2 for 3 days was defined as 100. The durability was estimated as the period required for the initial inhibition zone to disappear under continuous incubation. Pyrazole (2) itself showed no fungistatic activity and the compounds substituted with a methyl-, carboxy-, ethyloxycarbonyl-, hydrazinocarbonyl-, hydroxymethyl-, hydroxy-, nitroso-, amino-, acetamino- or diazo-group were in effective at any pH. On the other hand, the compounds bearing a phenyl or sulfur group such as 3-methyl-5-phenylpyrazole (11), 3.5-dimethyl-4-phenylpyrazole (21), 3-amidinothiomethyl-5-methylpyrazole dihydrochloride (13), 3-methyl-5-pyrazoylmethy1-N,N-dimethyldithiocarbamate (14) and 3,5-dimethyl-4-α- thiophenylpyrazole (22) showed fungistatic activity. Their IS values were inferior to that of 1, but the durabilities, except 13, were the same as or somewhat superior to that of 1. However, 3.5-diphenylpyrazole (12), in which the 3-methyl group of 11 was replaced by a phenyl group, and bis (3-methyl-5-pyrazoylmethyl) disulfide (15), which was obtained by hydrolysis or hydrogenation followed by oxidation of 13 or 14, showed complete loss of activity. © 1993, Japanese Society for Food Hygiene and Safety. All rights reserved.