Regioselective alkylation of the exocyclic nitrogen of adenine and adenosine by the Mitsunobu reaction

A novel synthetic route to N6-substitution of adenine is presented, employing the Mitsunobu reaction as the key step. A range of primary and secondary alcohols all coupled in very good to excellent yields within 30 min at 45 °C, offering a milder alternative to the traditional nucleophilic aromatic substitution of 6-chloropurine. The utility of this protocol is further demonstrated by its application to the syntheses of N6,N9-di-substituted adenines, including the potent and selective A1 adenosine receptor agonist N6-cyclopentyladenosine.