Polyoxins A-L were found to be a new class of peptide nucleosides having the structures shown in Scheme I. Hydrolytic degradation of polyoxins afforded three groups of unusual a-L-amino acids, Le., 1-(5' amino-5'-deoxy-~-~-allofuranuronosyl)-5-hydroxymethyluracil (polyoxin C) or its three nucleobase analogs, 5-O-carbamoyl-2-amino-2-deoxy-~-xylonic acid or its 3-deoxy analog, and 3-ethylidene-L-azetidine-2-carboxylic acid. These structures were established on chemical and spectroscopic evidence. 5 '-Aminofuranuronoside common to all polyoxins constitutes a nucleoside with a-amino acid nature. Sequence analysis showed polyoxins are di- or tripeptide of these moieties. The structures so elucidated embody all the interesting chemical features of polyoxins. The hypothetical biochemical significance of the structure was also discussed.