Indole-3-carbaldehyde Semicarbazone Derivatives: Synthesis, Characterization, and Antibacterial Activities
Fernando Carrasco, Wilfredo Hernández, Oscar Chupayo, Celedonio M. Álvarez, Sandra Oramas-Royo, Evgenia Spodine, Carmen Tamariz-Angeles, Percy Olivera-Gonzales, Juan Z. Dávalos
Abstract
Four indole-3-carbaldehyde semicarbazone derivatives, 2-((5-bromo-1H-indol-3-yl)methylene)hydrazinecarboxamide ( 1 ), 2-((5-chloro-1H-indol-3-yl)methylene)hydrazinecarboxamide ( 2 ), 2-((5-methoxy-1H-indol-3-yl)methylene)hydrazinecarboxamide ( 3 ), and 2-((4-nitro-1H-indol-3-yl)methylene)hydrazinecarboxamide ( 4 ) were synthesized and characterized by ESI-MS and spectroscopic (FT-IR, 1 H NMR, and 13 C NMR) techniques. The two-dimensional NMR (in acetone-d 6 ) spectral data revealed that the molecules 1 and 2 in solution are in the cisE isomeric form. This evidence is supported by DFT calculations at the B3LYP/6-311++G(d,p) level of theory where it was shown that the corresponding most stable conformers of the synthesized compounds have a cisE geometrical configuration, in both the gas and liquid (acetone and DMSO) phases. The in vitro antibacterial activity of compounds 1 – 4 was determined against Gram-positive ( Staphylococcus aureus and Bacillus subtilis ) and Gram-negative ( Pseudomonas aeruginosa and Escherichia coli ) bacteria. Among all the tested semicarbazones, 1 and 2 exhibited similar inhibitory activities against Staphylococcus aureus (MIC = 100 and 150 μ g/mL, respectively) and Bacillus subtilis (MIC = 100 and 150 μ g/mL, respectively). On the other hand, 3 and 4 were relatively less active against the tested bacterial strains compared with 1 , 2 , and tetracycline.