The rapid increase in the antibiotic resistance of microorganisms, capable of causing diseases in humans as destroying cultural heritage sites, is a great challenge for modern science. In this regard, it is necessary to develop fundamentally novel and highly active compounds. In this study, a series of N⁴-alkylcytidines, including 5- and 6-methylcytidine derivatives, with extended alkyl substituents, were obtained in order to develop a new generation of antibacterial and antifungal biocides based on nucleoside derivatives. It has been shown that N⁴-alkyl 5- or 6-methylcytidines effectively inhibit the growth of molds, isolated from the paintings in the halls of the Ancient Russian Paintings of the State Tretyakov Gallery, Russia, Moscow. The novel compounds showed activity similar to antiseptics commonly used to protect works of art, such as benzalkonium chloride, to which a number of microorganisms have acquired resistance. It was also shown that the activity of N⁴-alkylcytidines is comparable to that of some antibiotics used in medicine to fight Gram-positive bacteria, including resistant strains of Staphylococcus aureus and Mycobacterium smegmatis. N⁴-dodecyl-5- and 6-methylcytidines turned out to be the best. This compound seems promising for expanding the palette of antiseptics used in painting, since quite often the destruction of painting materials is caused by joint fungi and bacteria infection.

The effect of the reaction medium pH value on the rate and yield of enzymatic transglycosylation catalyzed by Escherichia coli purine nucleoside phosphorylase (EcPNP) and Lactobacillus leichmanii type II nucleoside deoxyribosyltransferase (LlNDTII) was investigated. In the presence of EcPNP at pH 5.5, a significant reduction in the inosine formation rate was observed, compared with that of adenosine. A substituent at the purine O⁶ position neutralizes the negative effect of the 6-oxo group on the reaction rate. A substituent at the purine N⁶ position has virtually no effect on the transglycosylation rate. In reactions catalyzed by LlNDTII, the rate of nucleoside formation from 4-oxopyrimidines was higher at pH 5.5, but the yield decreased by approximately 10% compared with that at pH 7.0; an unusual dependence of the yield of the target nucleoside on the enzyme concentration used was also revealed.