Synthesis of entecavir and its novel class of analogs.

Due to the slow kinetics of viral clearance and the spontaneous genetic variability of hepatitis B virus (HBV), antiviral therapy of chronic hepatitis B remains a clinical challenge. Entecavir (S.10; a 2'-deoxy carbocyclic guanosine analog with an exo-cyclic double bond on the 5'-position; Fig. 14.7.1) has been approved in the U.S. for the therapy of chronic hepatitis B. Entecavir is synthesized from D-ribose via a key allylic alcohol (S.3) intermediate. This intermediate is also utilized to synthesize entecavir-modified carbocyclic nucleosides S.13, S.15, S.19, and S.22.