Discovery of novel carbazole derivatives containing a 1,3,4-thiadiazole moiety as antifungal candidates

Fifteen novel carbazole derivatives of 2-(9H-carbazol-9-yl)-N-(5-phenyl-1,3,4-thiadiazol-2-yl)acetamide were designed, synthesized and evaluated for their antifungal activities against Pellicularia sasakii (P. sasakii), Fusarium oxysporum (F. oxysporum), Gibberella zeae (G. zeae), Phytophthora infestans (P. infestans), Cytospora mandshurica (C. mandshurica) and Capsicum wilt (C. wilt). The results of antifungal activity tests indicated that the inhibitory rates of compounds 2-(2-chloro-9H-carbazol-9-yl)-N-(5-(4-fluorophenyl)-1,3,4-thiadiazol-2-yl)acetamide (3h) and 2-(2-chloro-9H-carbazol-9-yl)-N-(5-(thiophen-2-yl)-1,3,4-thiadiazol-2-yl)acetamide (3o) against P. sasakii were 72.89% and 74.29%, respectively, which displayed better bioactivity compared with commercial fungicides hymexazol (53.09%) and carbendazim (69.65%). Meanwhile, compounds 2-(9H-carbazol-9-yl)-N-(5-(thiophen-2-yl)-1,3,4-thiadiazol-2-yl)acetamide (3f) and 2-(3-iodo-9H-carbazol-9-yl)-N-(5-(p-tolyl)-1,3,4-thiadiazol-2-yl)acetamide (3 l) exhibited the inhibition rates of 72.40% and 67.65% against C. wilt, respectively, which were better than the commercial fungicides hymexazol (50.21%) and carbendazim (65.33%).