The synthesis of potential "combined prodrugs" where phosphonoformic acid (PFA) or phosphonoacetic acid (PAA) was attached to the 5'-0 or N4 position of 2',3'-dideoxy-3,-thiacytidine (BCH-189) is described. The anti-HIV-1 activity of 11 analogues which included carboxylic ester or phosphoric ester linkages of PFA or PAA to BCH-189 was determined in MT-4 cells. Of these compounds, the IC50 of analogues 3,4,6, and 7 ranged from 0.2 to 100 µ , while IC50 for BCH-189 in this system was 0.1 µ . In vitro hydrolysis of the various esters or amides in human plasma indicated that these agents were relatively stable in the presence of plasma esterases with Í1/2 values of up to 120 min. Moreover, lipophilicity of these compounds (partition coefficient) was determined in order to establish correlation between lipophilicity and diffusion of BCH-189 analogues into the cells. The active compounds may exert their effects by extracellular or intracellular hydrolysis to the corresponding antiviral agent BCH-189, but intrinsic anti-HIV-1 activity of some of PAA and PFA adducts, themselves, may also be involved.

A series of anti-HIV prodrugs possessing various polyaminated side arms have been developed. The incorporation of a N-Boc protected monoamine or diamine side arm into the backbone of the 2',3'-dideoxy-3'-thiacytidine 1 (BCH-189) provided an increase in antiviral potency, which could be several orders magnitude greater than the parent drug (1) depending on the cell culture systems used (MT-4 or MDMs). Twenty six 2',3'-dideoxy-3'-thiacytidine prodrugs which differ from each other by the length, the nature of the 5'-O function and the 5'-O or/and N-4 position on the nucleoside moiety were synthesized. Among this new series of prodrugs, several congeners (12c and 12a) were found to inhibit HIV-1 replication in cell culture with 50% effective concentrations EC50 of 10 and 50 nM respectively, in MT-4 cells. Compound 12c was found more active on infected MDMs cells with 50% effective concentration of 0.01 nM. The synthesis and the antiviral properties of these compounds are discussed.

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