Nucleoside antibiotics: Structure, biological activity, and biosynthesis.

Nucleoside antibiotics are found as diverse groups of secondary metabolites of microbial origin. They include a variety of structural modifications of nucleosides and nucleotides, often leading to intricate molecules. Their biological activities are also wide ranging, including antibacterial, antifungal, antitrypanosomal, antitumor, antiviral, herbicidal, insecticidal, immunostimulating, and often immunosuppressive properties. It is not surprising that nucleoside antibiotics exhibit such diverse biological activities, because nucleosides and nucleotides play pleiotropic roles in most fundamental cellular metabolic pathways such as metabolite carriers, energy donors, secondary messengers, and co factors for various enzymes. Thus, not only nucleic acid synthesis but also protein synthesis, glycan synthesis, and glycoprotein synthesis are targets of nucleoside antibiotics. The protein kinases, key enzymes for cell proliferation and differentiation, also require nucleotides as phosphate donors.