• antimycobacterial;
  • indole;
  • structure–activity relationship;
  • thiadiazolylhydrazone;
  • thiosemicarbazones

A series of novel thiocarbohydrazones of substituted indoles and their corresponding thiadiazole derivatives were prepared, and their structures were confirmed by different analytical and spectroscopic methods. The derivatives were prepared by a sequential synthetic strategy including substitution at N-1 position of indole ring by various aliphatic and benzylic substituents, followed by condensation with thiocarbohydrazide, and finally cyclization by triethyl orthoformate. The derivatives were tested for their antimycobacterial activity against Mycobacterium bovis BCG, and the results revealed that among the synthesized compounds, thiadiazole derivatives 4e, 4f, 4n, 4p, 4q, and 4t exhibited the highest activity with IC50 value of 3.91 μg/mL. The results indicate that the thiadiazole moiety plays a vital role in exerting antimycobacterial activity.