Synthesis and antifungal activities of N-1,3,4-thiadiazol-2-yl-4-oxo-thiochroman-2-yl-formamide derivatives

Thiochromanones and 1,3,4-thiadazoles as heterocyclic compounds have broad biological activities. In order to find novel compounds with antifungal bioactivity, substituted thiophenol and maleic anhydride were used to synthesize the intermediate 4-oxothiochromane-2-carboxylic acid. It was reacted with 2-amino-1,3,4-thiadiazol to get fourteen target compounds containing 1,3,4-thiadazole moiety. The structures of the obtained compounds were confirmed by ¹H NMR, ¹³C NMR and HR-MS. All compounds were investigated for antifungal activity via microdilution broth method. The results showed that the target compounds 3a and 3c to Epidermophyton floccosum and Mucor racemosus exhibited better antifungal activity than the positive control fluconazole, in which the minimum inhibition concentration can reach 8 μg·mL^-1 and 16 μg·mL^-1. Compound 3e showed significant inhibitory activity to Helminthosporium maydis, Sclerotinia sclerotiorum and Botrytis cinerea compared with that of the positive control carbendazim. Compound 3b exhibited inhibitory activity to Helminthosporium maydis better than the positive control carbendazim.