2-(Arylcarbonylmethyl)thio-6alpha-naphthylmethyl derivatives of dihydro-alkoxy-benzyl-oxopyrimidines (DABO) were newly found to exhibit activity against both HIV-1 and HIV-2. To further explore their structure-activity relationship, the modified S-DABO analogues (5a-g and 6e-f) with a 1-naphthylthio or phenylthio group at the C-6 position were synthesized. S-Alkylation of 5-ethyl-2-thiouracil with substituted 2-bromo-acetophenones provided crude 2-[(arylcarbonylmethyl)thio]-5-ethyl-(3H)-uracil 2a-e, which was directly subjected to toluenesulfonylation with TsCl to afford disulfonate 4a-e. Substitution of 4a-e with arylthiol afforded the desired S-DABO analogues 5a-g and 6e-f. The compounds were evaluated for their in vitro anti-HIV activity in MT-4 cells. The IC(50) values for anti-HIV-1 activity fall into the range 0.37-29.50 microM, and the IC(50) values for anti-HIV-2 activity fall into the range 23.11-181.07 microM. The results indicated that these compounds are moderately active against HIV-1 and HIV-2.