We describe structure–activity relationship and optimization studies of RN-18, an HIV-1 Vif- APOBEC3G axis inhibitor. Targeted modifications of RN-18 ring C, ring B, ring A, bridge A– B, and bridge B–C were performed to identify the crucial structural features, which generated new inhibitors with similar (4g and 4i) and improved (5, 8b, and 11) activities. Two potent water-soluble RN-18 analogues, 17 and 19, are also disclosed, and we describe the ...