Antipathogenic effects of structurally-related Schiff base derivatives: Structure-Activity relationship

Eighteen structurally-related Schiff base derivatives, which belong to salicylidenebenzylamine and 2-hydroxy-1-naphthylidenebenzylamine families were prepared and characterized by spectroscopic techniques. All the synthesized compounds were screened in vitro for their antibacterial and antifungal activities. Human pathogenic gram-negative (Escherichia coli, Proteus mirabilis, Pseudomonas aeruginosa and Serratia marcescens), gram-positive bacteria (Staphylococcus epidermidis, Staphylococcus aureus and Bacillus subtilis), and fungi (Alternaria alternata, Aspergillus niger, Penicillium roqueforti, and Saccharomyces cerevisiae) were evaluated based on their toxicity to different concentrations of Schiff base compounds. For assessment of toxicity to pathogens, a disc diffusion assay was used to test the antimicrobial properties. The results revealed some antimicrobial activities of some of the synthesized compounds. Among the tested pathogens, the synthesized salicylidinaniline derivatives show highly potent action towards Alternaria alternata. Interestingly, a compound which contains the -Cl group is only effective against gram negative bacteria, but not gram positive bacteria. No remarkable antibacterial or antifungal activities were observed in the presence of -CH₃ or -Br group. Furthermore, most of the naphthalene-containing compounds show no growth retardation towards bacterial or fungal pathogens. On the other hand, the presence of -OH or -SH group at para or ortho position, respectively, on the aniline site is correlated with an increased inhibitory drug effect on all pathogens. The importance of our findings to the drug research and developments is discussed in the context of finding a correlation between the structural properties of the new drugs and their biological activities.