Phosphoramidate derivatives of d4T with improved anti-HIV efficacy retain full activity in thymidine kinase-deficient cells

New phosphate derivatives of the anti-HIV nucleoside analogue d4T were prepared as potential membrane-soluble pro-drugs of the bio-active free nucleotide. Some of the derivatives appear to have enhanced antiviral efficacy relative to the parent nucleoside analogue. Moreover, the derivatives appear to by-pass the dependence of the nucleoside on thymidine kinase-mediated activation, retaining full activity in thymidine kinase-deficient cells. The new analogues show particular promise for further pre-clinical development.