Nucleos(t)ide analogues play pivotal roles as antiviral, cytotoxic or immunosuppressive agents. Here, we review recent reports of nucleoside analogues that exhibit broad-spectrum activity towards multiple life-threatening RNA and DNA viruses. We also present a discussion about nucleoside antimetabolites-approved antineoplastic agents-that have recently been shown to have antiviral and/or antibacterial activity. The approved drugs and drug combinations, as well as recently identified candidates for investigation and/or experimentation, are discussed. Several examples of repurposed drugs that have already been approved for use are presented. This strategy can be crucial for the first-line treatment of acute infections or coinfections and for the management of drug-resistant strains.

The number of cancer-related diseases is still growing. Despite the availability of a large number of anticancer drugs, the ideal drug is still being sought that would be effective, selective, and overcome the effect of multidrug resistance. Therefore, researchers are still looking for ways to improve the properties of already-used chemotherapeutics. One of the possibilities is the development of targeted therapies. The use of prodrugs that release the bioactive substance only under the influence of factors characteristic of the tumor microenvironment makes it possible to deliver the drug precisely to the cancer cells. Obtaining such compounds is possible by coupling a therapeutic agent with a ligand targeting receptors, to which the attached ligand shows affinity and is overexpressed in cancer cells. Another way is to encapsulate the drug in a carrier that is stable in physiological conditions and sensitive to conditions of the tumor microenvironment. Such a carrier can be directed by attaching to it a ligand recognized by receptors typical of tumor cells. Sugars seem to be ideal ligands for obtaining prodrugs targeted at receptors overexpressed in cancer cells. They can also be ligands modifying polymers’ drug carriers. Furthermore, polysaccharides can act as selective nanocarriers for numerous chemotherapeutics. The proof of this thesis is the huge number of papers devoted to their use for modification or targeted transport of anticancer compounds. In this work, selected examples of broad-defined sugars application for improving the properties of both already-used drugs and substances exhibiting anticancer activity are presented.

Pentacyclic lupane-type triterpenoids, such as betulin and its synthetic derivatives, display a broad spectrum of biological activity. However, one of the major drawbacks of these compounds as potential therapeutic agents is their high hydrophobicity and low bioavailability. On the other hand, the presence of easily transformable functional groups in the parent structure makes betulin have a high synthetic potential and the ability to form different derivatives. In this context, research on the synthesis of new betulin derivatives as conjugates of naturally occurring triterpenoid with a monosaccharide via a linker containing a heteroaromatic 1,2,3-triazole ring was presented. It has been shown that copper-catalyzed 1,3-dipolar azide-alkyne cycloaddition reaction (CuAAC) provides an easy and effective way to synthesize new molecular hybrids based on natural products. The chemical structures of the obtained betulin glycoconjugates were confirmed by spectroscopic analysis. Cytotoxicity of the obtained compounds was evaluated on a human breast adenocarcinoma cell line (MCF-7) and colorectal carcinoma cell line (HCT 116). The obtained results show that despite the fact that the obtained betulin glycoconjugates do not show interesting antitumor activity, the idea of adding a sugar unit to the betulin backbone may, after some modifications, turn out to be correct and allow for the targeted transport of betulin glycoconjugates into the tumor cells.