Aplaviroc (AK602) is identified as the most potent agent among newly designed and synthesized SDP derivatives. Aplaviroc exerts potent activity against three wild-type R5 HIV-1 strains (HIV-1 _Ba-L , HIV-1 _JRFL and HIV-1 _MOKW ) with IC ₅₀ values of 0.1 to 0.4 nM. It is of note that Aplaviroc is substantially more potent than two previously published CCR5 inhibitors, E921/TAK-779 and AK671/SCH-C. The activity of Aplaviroc’s anti-HIV-1 is limited and similar to that seen for zidovudine. Moreover, Aplaviroc suppresses the infectivity and replication of two HIV-1 _MDR variants, HIV-1 _MM and HIV-1 _JSL , at extremely low concentrations (IC ₅₀ values of 0.4 to 0.6 nM), while these two R5 HIV-1 variants are less susceptible to zidovudine, nelfinavir, and saquinavir. Aplaviroc binds to CCR5 with high affinity. The K _d values thus determined for Aplaviroc, E913, E921/TAK-779, and AK671/SCH-C are 2.9±1.0, 111.7±3.5, 32.2±9.6, and 16.0±1.5 nM, respectively. Aplaviroc potently blocks rgp120/sCD4 binding to CCR5 with an IC ₅₀ value of 2.7 nM. These results suggest that the potent activity of Aplaviroc against R5 HIV-1 stems from its binding to ECL2B and/or its vicinity with high affinity, resulting in inhibition of gp120/CD4 binding to CCR5.