Discovery of N-Hydroxypyridinedione-Based Inhibitors of HBV RNase H: Design, Synthesis, and Extended SAR Studies

Hepatitis B Virus (HBV) continues to pose a significant global health challenge, with over 254 million chronic infections and current therapies being non-curative, necessitating lifelong treatment. The HBV ribonuclease H (RNase H) is essential during HBV reverse transcription by cleaving the viral pregenomic RNA after it has been copied into the (-) polarity DNA strand, enabling the viral polymerase to synthesize the (+) DNA strand. Although RNase H inhibition terminates viral replication and thus viral infectiveness, its targeting as an HBV treatment is unexploited. Its catalytic site contains four carboxylates that bind to two Mg²⁺ ions essential for RNA hydrolysis. As part of our ongoing research on RNase H inhibitors, we developed 23 novel <i>N</i>-hydroxypyridinedione (HPD) analogues. Specifically, 17 HPD imines, 4 HPD oximes, 1 2,6-diamino-4-((substituted)oxy)pyrimidine 1-oxide derivative, and 1 barbituric acid analogue were designed, synthesized, and tested for their anti-HBV activity. The HPD derivatives could be docked in the RNase H active site to coordinate the two Mg²⁺ ions and effectively inhibited viral replication in cellular assays. The 50% effective concentration (EC₅₀) values of these HPD compounds ranged from 0.5 to 73 μM, while the 50% cytotoxic concentration (CC₅₀) values ranged from 15 to 100 μM, resulting in selectivity indexes (SIs) up to 112. Furthermore, the novel HPD derivatives exhibited favourable pharmacokinetic-relevant characteristics, including high cellular permeability, good aqueous solubility, and overall drug-like properties. These findings indicate that HPD imines and oximes possess substantial antiviral potency and selectivity against HBV, underscoring the potential of the HPD scaffold as a promising framework for the development of next-generation anti-HBV agents.