Synthesis and antibacterial activity of two spiro [indole] thiadiazole derivatives

Abstract

Isatin reacts with thiosemicarbazide in 50% aqueous alcohol under reflux to give isatin-3-thiosemicarbazone (1′). Compound 1′ cyclizes on treatment with acetic anhydride and pyridine to yield 1,3′-diacetyl-5′-acetamido-3(1H)-spiro[indole-3,2′-[1,3,4]-thiadiazol]-2(1H)-one, 2′. Subsequent reaction of the diacetyl spiro compound, 2′, with hydrazine hydrate at room temperature furnished a white product, which was characterized by spectroscopic means to be 1,3′-diacetyl-5′-amino-3(1H)-spiro[indole-3,2′-[1,3,4]-thiadiazol]-2(1H)-one, 3′. All three compounds (1′, 2′, 3′) were tested for antibacterial activity against six Gram-positive and four Gram-negative bacteria. 1′ showed activity against five Gram-positive and one Gram-negative bacterial strains, while 2′ showed activity against three Gram-positive and two Gram-negative bacterial strains. Compound 3′ showed activity against four Gram-positive and three Gram-negative bacterial strains (better activity than streptomycin, the reference standard).

Keywords:

• synthesis
• isatin-3-thiosemicarbazone
• cyclization
• spiro [indole] thiadiazolone
• antibacterial activity