Synthesis and antibacterial activity of fused Mannich ketones

Abstract

New Mannich ketones of fused bicyclic ketones as 1-indanones and 1-tetralones were prepared using the classical acid-catalysed Mannich reaction. Known members of this family were used in comparative biological tests. Antibacterial activity of these new water-soluble compounds was reported against Pseudomonas aeruginosa, Escherichia coli, E. coli ReD31m4, Salmonella minnesota Re595, Shigella sonnei Re4350, Staphylococcus aureus, Staphylococcus saprophyticus, Micrococcus luteus and Bacillus subtilis standard strains. Human cytotoxicity of our new compounds was evaluated against HeLa cell line. Some compounds showed low cytotoxicity (56.738 nM mL −1 for 24, 47.497 nM mL −1 for 31 and 48.379 nM mL −1 for 26) and proved to be efficient antibacterial agents against the Gram-positive and partly against E. coli strains. Minimum inhibitory concentrations (MIC) changed in the range of 1.56–>200 μg mL −1. The deep rough mutants showed (generally eight times) higher sensitivity toward the compounds than the smooth E. coli. Hence, the permeability of Gram-negative outer membrane can influence the MIC values of our compounds. A preliminary quantitative structure–activity relationship (QSAR) study indicated the maximum positive charge (MaxQ +) as the parameter that most significantly affected antibacterial activity against E. coli. In B. subtilis, the influence of a topological descriptor (first-order valence-connectivity index, XV1) was also revealed; however, other strains did not yield meaningful QSAR with the set of descriptors employed.