Abstract

The naturally occurring nucleoside and nucleotide antibiotics exist as either the C- or N-glycosides. They include ezomycin A₁ (C₂₆H₃₈N₈O₁₅S), ezomycin B₁ (C₂₆H₃₉N₇O₁₇S), ezomycin C₁ (C₂₆H₃₇N₇O₁₆S), ezomycin A₂ (C₁₉H₂₆N₆O₁₂), ezomycin B₂ (C₁₉H₂₅N₅O₁₃), ezomycin C₂ (C₁₉H₂₅N₅O₁₃), showdomycin (C₉H₁₁NO₆), isoshowdomycin (C₉H₁₁NO₆), maleimycin (C₇H₇NO₃), oxazinomycin (C₉H₁₁NO₇), pyrazomycin (pyrazofurin) (C₉H₁₃N₃O₆), formycin (C₁₀H₁₃N₅O₄), formycin B (C₁₀H₁₂N₄O₅), oxoformycin B (C₁₀H₁₂N₄O₆). These antibiotics contain a variety of purine and pyrimidine rings. The naturally occurring nucleoside/nucleotide antibiotics, which have been isolated from bacteria, fungi, blue-green algae, and marine sponges, have proven to be useful biochemical probes in eucaryotic, procaryotic, viral, fungal, and plant systems. The purine nucleosides inhibit protein synthesis, RNA and DNA synthesis, and methyltransferases; they have antimycoplasmal, antiviral, hypotensive, antifungal, antimycobacterial, and antitumor activities and induce sporulation. The pyrimidine nucleosides inhibit protein synthesis, virus replication, RNA and DNA synthesis, and cAMP phosphodiesterase. The imidazole nucleosides inhibit nucleic acid synthesis. The diazepin nucleosides inhibit adenosine deaminase (ADA). The indole nucleosides inhibit bacteria, yeast, fungi, and viruses. The N-nucleotide antibiotics include agrocin 84 (C₂₁H₃₄N₆O₁₆P₂), thuringiensin (C₂₂H₃₀N₅O₁₉P), phosmidosine (C₁₆H₂₄N₇O₈P), fosfadecin (C₁₃H₁₉N₅O₁₀P₂), and fosfocytocin (C₁₂H₂₀N₄O₁₃P₂). Thuringiensin, produced by B. thuringiensis, is a -exotoxin that exerts its toxic action on insects and mammals through the inhibition of RNA polymerases. Phosmidosine inhibits pore formation of Botrytis cinerea and Aspergillus niger. Fosfadecin and fosfocytocin inhibit gram-positive and gram-negative bacteria.