A series of N1-heterocyclic pyrimidinediones were extensively evaluated as HIV-1 non-nucleoside reverse transcriptase inhibitors (NNRTIs). Inhibitor 1 is active against NNRTI-resistant viruses including RT mutant K103N. The co-crystal structure of inhibitor 1 with HIV-1 RT revealed that H-bonds are formed with K101 and K103. Efforts to improve the suboptimal pharmacokinetic profile of 1 resulted in the discovery of compound 13, which represents the lead compound in this series with improved pharmacokinetics and similar potency as inhibitor 1.