Design and synthesis of 7-membered lactam fused hydroxypyridinones as potent metal binding pharmacophores (MBPs) for inhibiting influenza virus PAN endonuclease

Since influenza virus RNA polymerase subunit PA_N is a dinuclear Mn²⁺ dependent endonuclease, metal-binding pharmacophores (MBPs) with Mn²⁺ coordination has been elucidated as a promising strategy to develop PA_N inhibitors for influenza treatment. However, few attentions have been paid to the relationship between the optimal arrangement of the donor atoms in MBPs and anti-influenza A virus (IAV) efficacy. Given that, the privileged hydroxypyridinones fusing a seven-membered lactam ring with diverse side chains, chiral centers or cyclic systems were designed and synthesized. A structure-activity relationship study resulted in a hit compound 16l (IC₅₀ = 2.868 ± 0.063 μM against IAV polymerase), the seven-membered lactam ring of which was fused a pyrrolidine ring. Further optimization of the hydrophobic binding groups on 16l afforded a lead compound (R, S)-16s, which exhibited a 64-fold more potent inhibitory activity (IC₅₀ = 0.045 ± 0.002 μM) toward IAV polymerase. Moreover, (R, S)-16s demonstrated a potent anti-IAV efficacy (EC₅₀ = 0.134 ± 0.093 μM) and weak cytotoxicity (CC₅₀ = 15.35 μM), indicating the high selectivity of (R, S)-16s. Although the lead compound (R, S)-16s exhibited a little weaker activity than baloxavir, these findings illustrated the utility of a metal coordination-based strategy in generating novel MBPs with potent anti-influenza activity.