Abstract
1-(2', 3'-Epoxy-β-D-lyxofuranosyl) isocytosines (I) and (II) were easily deaminated by heating with aqueous hydrogen chloride, yielding 2, 2'-anhydro-1-(3'-chloro-3'-deoxy-β-D-arabinofuranosyl) uracil (III), and 1-(3'-chloro-3'-deoxy-β-D-arabinofuranosyl) uracil (IV). And other isocytosine derivatives (VIII), (X), (XI), and (XVI) were also deaminated by heating at 80° for several minutes in acetic acid to corresponding anhydronucleosides, i.e. VII, IX, and XV, while 2', 3'-O-isopropylideneisocytidine (XVII) and isocytidine (XVIII) were not deaminated. Furthermore, demethoxylation of 2-O-methylpyrimidine nucleosides was studied. In the reaction of 2, 5'-anhydro-1-(2, 3'-di-O-acetyl-β-D-arabinofuranosyl) uracil (XXI) with triethylamine in methanol, 2-O-methyl-1-β-D-arabinofuranosyluracil (XXII) was not obtained, but IX as a sole product. This phenomenon showed that XXII was the intermediate. However, 2-O-methyl-1-(2', 3'-epoxy-β-D-lyxofuranosyl) uracil (XXIII), 2-O-methyl-1-(2', 3'-O-isopropylidene-β-D-ribofuranosyl) uracil (XXIV) and 2-O-methyluridine (XXV) were not demethoxylated by heating at 80° in acetic acid. Therefore, deamination in isocytosine derivatives and demethoxylation in 2-O-methylpyrimidine derivatives required one hydroxy group of up form in 2'-position or 2', 3'-epoxide ring of lyxo-form.
