Cyrhetrenyl and ferrocenyl 1,3,4-thiadiazole derivatives: Synthesis, characterization, crystal structures and in vitro antitubercular activity

Abstract

A new series of cyrhetrenyl and ferrocenyl 1,3,4-thiadiazoles (TDZs) were designed, synthesized and characterized. The condensation–cyclization reaction of organometallic-cyanide with the corresponding thiosemicarbazide produces the ferrocenyl-TDZs (3a–c) and cyrhetrenyl analogues (4ac). The structures of all products were inferred from their elemental analysis, 1H and 13C NMR spectra and MS. The molecular structures of 3b and 4b were confirmed using X-ray crystallography. The electronic effects of cyrhetrenyl (4a–c) and ferrocenyl (3a–c) bound directly to the thiadiazole ring have been correlated with the chemical shift of the exocyclic amine proton and 13C shift of the carbon at the 5-position. The X-ray crystal structure of 3b and 4b indicates that the rhenium compound 4b possesses a more extensive conjugated π-system. The activity of the new organometallic-TDZs was evaluated in vitro against Mycobacterium tuberculosis. The incorporation of any organometallic fragment into the thiadiazole skeleton showed a comparable but lower antitubercular activity than isoniazid.