1‑Hydroxy-1,8-napthyridinone (DHN) Analogs Potently Inhibit Monkeypox Virus Resolvase (Mpr)

The virally encoded Holliday junction resolvase is required for poxvirus genome replication and viral maturation. Previously, a 1-hydroxy-1,8-napthyridinone (DHN) analog (3) was discovered as an inhibitor hit of mpox resolvase (Mpr). Herein, we have conducted Mpr-based comprehensive structure–activity relationship (SAR) studies of compound 3 via the synthesis of 70 analogs of four distinct subtypes. The SAR identified a phenyl ring and a biphenyl moiety as the optimal substituent for C-3 and C-6/C-5, respectively, and that C-5 analogs are generally better than their C-6 regio-isomers. Against vaccinia virus (VACV), the tested new analogs demonstrated antiviral activity in the low μM to nM range. In the end, the best compound 5-1 conferred drastically improved inhibitory profiles against Mpr (IC50 = 36 nM, 10-fold improvement) and VACV (EC50 = 3.2 nM, 400-fold improvement) over compound 3, with significantly lower binding free energy as predicted from free energy perturbation, and highly favorable ADME properties.