The rapid development of bacterial resistance to conventional antibiotics due to overuse and misuse is a major burden on the global healthcare system. In this thesis, we searched for antimicrobial agents against three organisms included in the acronym ESKAPE (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and the genus Enterobacter), which are listed by the World Health Organisation as the most critical pathogens causing difficult-to-treat infections due to emerging resistance mechanisms. Therefore, the discovery of new antibiotics is urgently needed. Two hydroxynaphthoic acid derivatives, 3-hydroxy-2-naphthoic acid with antimicrobial activity against S. aureus and Escherichia coli and 2-[(4-chloro-1-hydroxynaphthalene-2-carbonyl)amino]-2-methylpropanoic acid, which inhibits the growth of S. aureus, were previously identified by screening tests. The aims of this diploma thesis were to screen the antimicrobial properties of a series of hydroxynaphthoic acid derivatives structurally related to the initial hits, identify the most potent compound, and use it as a starting point for the synthesis of compounds with improved antimicrobial activity. We also aimed to identify protein targets of 1-hydroxy-2-naphthoic acid in the soluble fraction of S. aureus lysate by affinity chromatography on an immobilised derivative of this compound. Our results showed that the series of small molecules selectively inhibited the growth of the Gram-positive bacteria S. aureus and Bacillus thuringiensis, but not the growth of the Gram-negative bacteria E. coli and P. aeruginosa. We found that [(1-hydroxynaphthalene-2-carbonyl)amino]-2-methylpropanoic acid has a broader spectrum of activity than its chlorinated derivative, inhibiting the growth of both Gram-positive species. Among the commercially available derivatives, two compounds were further characterised, and a minimum inhibitory concentration of 125 μg/mL for 7-bromo-3-hydroxy-2-naphthoic acid against B. thuringiensis was determined. In the synthesis of the affinity ligand, it was found that the introduction of an alkyl group via an amide bond, while improving the antimicrobial activity, significantly reduced the solubility of the compound. Using affinity chromatography, we found that a 25 kDa protein specifically binds to the ligand. We were not able to identify this protein within the framework of the diploma thesis, so that its identification remains as the goal of further research.
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