New 3-hydroxy-2-naphthoic hydrazide derivatives: thiosemicarbazides and 1,2,4-triazole-3-thiones, their synthesis and in vitro antimicrobial evaluation

In this paper, we describe twelve 3-hydroxy-2-naphthoic hydrazide derivatives (six thiosemicarbazides and six 1,2,4-triazole-3-thiones) which we have synthesized. Thiosemicarbazide derivatives were prepared by condensation reaction of 3-hydroxy-2-naphthoic hydrazide with appropriate isothiocyanates. The 1,2,4-triazole-3-thiones were synthesized by the cyclization reaction of corresponding thiosemicarbazide derivatives in alkaline media. All obtained compounds have been analyzed by 1H NMR and 13C NMR spectra and evaluated for in vitro antimicrobial activity against a panel of reference strains of microorganisms, including Gram-positive bacteria, Gram-negative bacteria and fungi belonging to yeasts Candida spp. Our antimicrobial screening results indicated that some of the newly obtained compounds showed high antibacterial activity, especially against Gram-positive bacteria. Among them, the activity of compounds 1, 2 and 4 was moderate to strong against staphylococci. In addition to this, compounds 1 and 2 showed two times higher activity than cefuroxime and four times higher activity than ampicillin against Bacillus cereus ATCC 10876.