phosphoramidate d4Tderivatives have been synthesized and evaluated as substrates for HIV-1 RT, and also tested for their in vitro anti-HIV activity. Compounds 2 and 4 are able to inhibit HIV-1 replication to the same extent as d4T and d4TMP in MT-4 cells as well as in CEM/0 cells and CEM/TK−cells. The data suggests that these phosphoramidates are hydrolysed to d4T before exerting their antiviral activity