Synthesis and characterization of 5-cyclopentylsulfanyl-3H-[1,3,4]thiadiazole-2-thione and study of its single-crystal structure, FTIR spectra, thermal behavior, and antibacterial activity

A new derivative of mono-cyclopentyl-substituted 1,3,4-thiadiazole-2,5-dithiol (DMTD) was prepared by a telescopic synthesis procedure via the formation of the potassium 1,3,4-thiadiazole-2,5-dithiolate followed by a nucleophile attack on chlorocyclopentane. The pure product obtained in needle-like colorless crystals by recrystallization. The product was characterized by melting point, and FTIR, NMR, and mass spectra, and single-crystal X-ray diffraction. A comparative FTIR study on DMTD, mono- and bis-cyclopentyl-substituted DMTD showed the characteristic vibrational mode to differentiate thiol and thione structures. The crystallography analysis demonstrated the existence of thione tautomer, having C=S and C–N–H in [1,3,4]thiadiazole ring, with a possible hyper-conjugation between the S–H and double bond of C=N. Moreover, the TGA/DTA and DSC of DMTD, bis-cyclopentyl-substituted, and mono-cyclopentyl-substituted DMTD were studied to find a relationship between their thermal behavior and chemical structure. Then, DMTD, bis- and mono-cyclopentyl-substituted DMTD pharmaceutical activities were screened by the SwissADME tool. Moreover, they were evaluated in vitro for their antibacterial activity against the gram-negative (Escherichia coli ATCC 25922) and gram-positive (Staphylococcus aureus ATCC 25923) bacterial species by the disk diffusion method.