Synthesis of Purinyl<i>homo</i>-Carbonucleoside Derivatives of 2-Benzylcyclopenta[<i>c</i>]pyrazol

The first members of a new class of carbocyclic nucleoside analogs were synthesized via key intermediate (±)-(cis)-2-bencylcyclopenta[c]pyrazole-4,6-dimethanol, which was obtained from the easily prepared starting compound (±)-(exo,exo)-5,6-isopropylidenedioxy-4,5,6,7-tetrahydro-4,7-methano-2H-indazole by a reaction sequence in which the key step was a one-pot oxidative cleavage of glycol 9 and reduction of the resulting dialdehyde with NaBH4. Purine moieties were coupled by nucleophilic displacement following mesylation of the latter. The new compounds 15 and 17 are active against cytomagalovirus and varicella-zoster virus at subcytotoxical concentrations.