Importance of the alanine methyl ester side chain for the biological activity profile of dual-function phenyl phosphate derivatives of bromo-methoxy-zidovudine

In a systematic search for developing a virucidal spermicide with potent anti-human immunodeficiency virus (HIV) and spermicidal activities, we synthesized and evaluated 14 phosphoramidate derivatives of 5-bromo-6-methoxy-zidovudine (PP-BMZ) with differing amino acid ester side chains and para substitutions on the phenyl moiety. Anti-HIV activity was tested by measuring viral p24 antigen production as a marker of viral replication in HIV-1-infected human peripheral blood mononuclear cells. The effect of various PP-BMZ compounds on human sperm motion kinematics was analysed by computer-assisted sperm analysis. Varying the Ala side chain of the phosphoramidate group to other non-polar amino acids, including the cyclic amino acids proline and tryptophan, led to significant alterations in both anti-HIV and spermicidal activities. Our findings highlight the necessity of the Ala side chain and the presence of an electron-withdrawing para-bromo substituent on the phenyl moiety in addition to the bromo-methoxy functional groups on the thymine ring for the PP-BMZ compounds to be effective virucidal spermicides. These membrane permeable dual-function nucleoside analogues may provide the basis for a new strategy aimed at prevention of the sexual transmission of HIV while providing fertility control for women.