Synthesis of guanine a-carboxy nucleoside phosphonate (G-a-CNP), a direct inhibitor of multiple viral DNA polymerases

The synthesis of guanine α-carboxy nucleoside phosphonate (G-α-CNP) is described. Two routes provide access to racemic G-α-CNP 9, one via base construction and the other utilizing Tsuji–Trost allylic substitution. The latter methodology was also applied to the enantiopure synthesis of both antipodes of G-α-CNP, each of which shows interesting antiviral DNA polymerase activity. Additionally, we report an improved multi-gram scale preparation of the cyclopentene building block 10, starting material for the preferred Tsuji–Trost route to 9