Synthesis of a novel 2'-deoxy-guanine carbocyclic nucleoside 4 constructed with spiro[2.4]heptane core structure in the aglycon moiety was carried out. Radical-mediated 5-exo-dig mode cyclization and following cyclopropanation proceeded efficiently to furnish the spiro alcohol 10. Subsequent Mitsunobu-type glycosylation between 13 and 14, deoxygenation of the 2'-hydroxyl group of 16 and deprotection of 17 gave the title compound 4. Compound 4 demonstrated moderate anti-HBV activity (EC50 value of 0.12 ± 0.02 µM) and no cytotoxicity against HepG2 cells was observed up to 100 µM.
Keywords: Anti-HBV; carbocyclic nucleoside; entecavir; radical-mediated cyclization; spiro[2.4]heptane.