Studies on Nucleosides and Nucleotides. X. Nucleophilic Substitution of Secondary Sulfonyloxy Groups of Pyrimidine Nucleosides. III. Reaction of 2', 3'-Di-O-tosyluridine with Methanolic Ammonia

Abstract

1-(2', 3'-Epoxy-β-D-lyxofuranosyl) isocytosine (IV) was obtained in the reaction of 2', 3'-di-O-tosyluridine (I) with methanolic ammonia through 2', 2'-anhydro-1-(3'-O-tosyl-β-D-arabinofuranosyl) uracil (II) and 2-O-methyl-1-(2', 3'-epoxy-β-D-lyxofuranosyl)-uracil (III). Ultraviolet absorption spectra of 2-substituted-uracils and their nucleosides were comparatively examined and their pK_a values were determined. From the nuclear magnetic resonance spectra it was found that amino group of isocytosine derivatives was existed as amino form and that H₁' of 2', 3'-epoxylyxosyl nucleosides did not couple with H₂' and its signal appeared as a sharp singlet.