RESUMEN
Resistance developed to the majority of drugs used to treat infectious diseases warrants the design of new compounds effective against drug-resistant strains of pathogens. Recently, several groups of modified nucleosides have been synthesized and showed significant antibacterial activity in vitro, but their further studies were difficult to undertake because of their low solubility in aqueous solutions. Nevertheless, new compounds, well soluble in water-organic solutions, were synthesized and found to be more effective in inhibiting the growth of Gram-positive bacteria and mycobacteria. The water-soluble forms of modified nucleosides under study were assumed to be their depot forms. To check the assumption, the compounds were tested for hydrolysis in various media and their molecular docking was performed into the active center of the putative target, Mycobacterium tuberculosis flavin-dependent thymidylate synthase ThyX. Computer modelling showed that the water-soluble analogs do not act as ThyX inhibitors, supporting the assumption of their depot nature. The compounds were resistant to chemical hydrolysis but were hydrolyzed when incubated with porcine liver carboxylesterase, human serum, or Staphylococcus aureus 209P. The results demonstrate that the compounds are most likely depot forms of modified nucleosides.