Design, Synthesis, Biochemical, and Antiviral Evaluations of C6 Benzyl and C6 Biarylmethyl Substituted 2‑Hydroxylisoquinoline-1,3-diones: Dual Inhibition against HIV Reverse Transcriptase-Associated RNase H and Polymerase with Antiviral Activities

Reverse transcriptase (RT) associated ribonuclease H (RNase H) remains the only virally encoded enzymatic function not targeted by current chemotherapy against human immunodeficiency virus (HIV). Although numerous chemotypes have been reported to inhibit HIV RNase H biochemically, few show significant antiviral activity against HIV. We report herein the design, synthesis, and biological evaluations of a novel variant of 2-hydroxyisoquinoline-1,3-dione (HID) scaffold featuring a crucial C-6 benzyl or biarylmethyl moiety. The synthesis involved a recently reported metal-free direct benzylation between tosylhydrazone and boronic acid, which allowed the generation of structural diversity for the hydrophobic aromatic region. Biochemical studies showed that the C-6 benzyl and biarylmethyl HID analogues, previously unknown chemotypes, consistently inhibited HIV RT-associated RNase H and polymerase with IC₅₀s in low to submicromolar range. The observed dual inhibitory activity remained uncompromised against RT mutants resistant to non-nucleoside RT inhibitors (NNRTIs), suggesting the involvement of binding site(s) other than the NNRTI binding pocket. Intriguingly, these same compounds inhibited the polymerase, but not the RNase H function of Moloney Murine Leukemia Virus (MoMLV) RT and also inhibited Escherichia coli RNase H. Additional biochemical testing revealed a substantially reduced level of inhibition against HIV integrase. Molecular docking corroborates favorable binding of these analogues to the active site of HIV RNase H. Finally, a number of these analogues also demonstrated antiviral activity at low micromolar concentrations