Synthesis and Biological Evaluation of Carbocyclic Nucleosides with 2′,3′-Dihomo-<i>xylo</i>-carbocyclic or Carbocyclic Fused to a Tetrahydrofuran Ring

New purinyl 2′,3′-dihomo-xylo-carbocyclic pentafuranosides and carbocyclic nucleosides fused with tetrahydrofuran ring were synthesized from (±)-c-4-amino-r-1,c-2,t-3-cyclopentanetrimethanol (8). The strongly acid medium in which the purine system was completed on pyrimidine derivative 9 caused condensation of the cis-hydroxymethyl groups, giving rise to a 3-oxabicyclo[3.3.0]octane structure. None of the new compounds exhibited more than very modest antiviral or antitumor activity.