New Vanadium Complexes with Natural Ligands and Potent Antimicrobial Activity

One strategy to increase the biological activity of natural compounds is based on obtaining complexes with bioactive natural ligands that produce an additive or synergistic effect when coordinated with a metal ion. In this work, four new vanadium complexes with the natural bioactive ligands piperine ( 1 ), piperic acid ( 2 ), 3-geranyl-geranyl-4-hydroxybenzoate acid ( 4 ) and glutamic acid ( 6 ) were synthesized and tested against eight microorganisms. Most complexes showed strong antimicrobial activity with minimum inhibitory concentration (MIC) ranging from 19.5 to 1250 μg/mL. Complex 9 presented MIC of 19.5 μg/mL for the fungus Epidermophyton floccosum and MIC of 39.5 μg/mL against the bacterium Escherichia coli . In general, complex 10 was the most active with MIC of 39.5 μg/mL for Gram-positive bacteria ( Staphylococcus aureus, Bacillus subtilis and Enterococcus faecalis ) and MIC of 78.1 μg/mL for Gram-negative bacteria ( E. coli, Klebsiella pneumoniae and Pseudomonas aeruginosa ) as well as for the E. floccosum fungus. The results showed that, for the most part, the formation of metal complexes potentiated antimicrobial activity as compared to their respective ligands.