The resistance among microbes has brought an urgent need for new drugs. Thus, we synthesized a series of Schiff bases derived from the sulfa drug sulfadiazine and various salicylaldehydes. The resulting 4-[(2-hydroxybenzylidene)amino]-N-(pyrimidin-2-yl)benzene-sulfonamides were characterized and evaluated against Gram-positive and Gram-negative bacteria, yeasts, moulds, Mycobacterium tuberculosis, nontuberculous mycobacteria (M. kansasii, M. avium) and their cytotoxicity was determined. Among bacteria, the genus Staphylococcus, including methicillin-resistant S. aureus, showed the highest susceptibility, with minimum inhibitory concentration values from 7.81 µM. The growth of Candida sp. and Trichophyton interdigitale was inhibited at concentrations starting from 1.95 µM. 4-[(2,5-Dihydroxybenzylidene)amino]-N-(pyrimidin-2-yl)-benzenesulfonamide was identified as the most selective Schiff base for these strains with no apparent cytotoxicity and a selectivity index higher than 16. With respect to M. tuberculosis and M. kansasii that were inhibited within the range of 8 to 250 µM, unsubstituted 4-[(2-hydroxy-benzylidene)amino]-N-(pyrimidin-2-yl)benzenesulfonamide meets the selectivity requirement. In general, dihalogenation of the salicylic moiety improved the antibacterial and antifungal activity but also increased the cytotoxicity, especially with an increasing atomic mass. Some derivatives offer more advantageous properties than the parent sulfadiazine, thus constituting promising hits for further antimicrobial drug development.

Department of Biological and Medical Sciences Faculty of Pharmacy Charles University Akademika Heyrovského 1203 500 05 Hradec Králové Czech Republic

Department of Chemistry Faculty of Science J E Purkinje University České mládeže 8 400 96 Ústí nad Labem Czech Republic

Department of Organic and Bioorganic Chemistry Faculty of Pharmacy in Hradec Králové Charles University Akademika Heyrovského 1203 500 05 Hradec Králové Czech Republic

Department of Pharmacology and Toxicology Faculty of Pharmacy Charles University Akademika Heyrovského 1203 500 05 Hradec Králové Czech Republic

Laboratory for Mycobacterial Diagnostics and Tuberculosis Regional Institute of Public Health in Ostrava Partyzánské námĕstí 7 702 00 Ostrava Czech Republic

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