We report the application of phosphoramidate pronucleotide (ProTide) technology to the antiviral agent carbocyclic l-d4A (l-Cd4A). The phenyl methyl alaninyl parent ProTide of l- Cd4A was prepared by Grignard-mediated phosphorochloridate reaction and resulted in a compound with significantly improved anti-HIV (2600-fold) and HBV activity. We describe modifications of the aryl, ester, and amino acid regions of the ProTide and how these ...