Over 60 kinds of 1, 2, 4-thiadiazole derivatives were synthesized and their biological activities were examined. It was found that 3-methyl-5-(p-chlorophenylsulfonyl)-1, 2, 4-thiadiazole and 3-methyl-5-(p-tolylsulfonyl)-1, 2, 4-thiadiazole had the most powerful antimicrobial activity. Among the biological activities of these ring derivatives, the antimicrobial activity of the 5-phenylsulfonyl substituent seemed to depend on the-SO2-group and its conversion to the -NH-, -O-, or -S- type markedly reduced the effect. Introduction of a substituent in the para position of the benzenesulfonyl group had little effect on the antimicrobial activity but substitution of Cl with CH3 increased nematocidal effect while conversion to -SCN further increased this activity. In contrast, acaricidal activity was decreased in the -SO2- form and became effective in -S- form. Antifungal activity was tested by animal experiment. The compounds were effective against Trichophyton but ineffective against Candida. Toxicity and pharmacological tests revealed that these compounds had comparatively low toxicity.
