Application of phosphoramidate ProTide technology significantly improves antiviral potency of carbocyclic adenosine derivatives.

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 changes affect antiviral activity and metabolic stability. Separate and distinct SARs were noted for HIV and HBV. Additionally, ProTides were prepared from the D-nucleoside D-Cd4A and the dideoxy analogues L-CddA and D-CddA. These compounds showed more modest potency improvements over the parent drug. In conclusion, the ProTide approach is highly successful when applied to L-Cd4A with potency improvements in vitro as high as 9000-fold against HIV. With a view to preclinical candidate selection we carried out metabolic stability studies using cynomolgus monkey liver and intestinal S9 fractions.

Application of phosphoramidate pronucleotide technology to abacavir leads to a significant enhancement of antiviral potency.

We report the first application of pronucleotide (ProTide) technology to the antiviral agent abacavir (Ziagen), used for the treatment of HIV infection. The phenylmethoxyalaninyl phosphoramidate of abacavir was prepared in good yield in one step. Also prepared was the corresponding phosphoramidate of the guanine nucleoside analogue "carbovir". The antiviral profile of each of the parent nucleosides was compared to that of the phosphoramidate ProTides. A significant (28- to 60-fold) increase in anti-HIV potency was noted for the ProTide of abacavir but not for that of carbovir. These findings were in agreement with the markedly higher (ca. 37-fold) levels of carbovir triphosphate that are formed in CEM cells upon response to the abacavir ProTide compared with the parent abacavir compound. In contrast the anti-HBV potency of both abacavir and carbovir were improved (10- and 20-fold, respectively) by ProTide formation. As in CEM cells, the abacavir ProTide provided significantly enhanced carbovir triphosphate levels in HepG2 2.2.15 cells over that of the parent nucleoside. On the basis of these data, a series of phosphoramidate analogues with structural variation in the ester and amino acid regions were prepared and their antiviral profiles described. In addition, the pharmacokinetic disposition of the abacavir phenylethoxyalaninyl phosphoramidate was evaluated in Cynomolgus monkeys.