Metal-Chelating 2‑Hydroxyphenyl Amide Pharmacophore for Inhibition of Influenza Virus Endonuclease

The influenza virus PA endonuclease is an attractive target for development of novel anti-influenza virus therapeutics. Reported PA inhibitors chelate the divalent metal ion(s) in the enzyme’s catalytic site, which is located in the Nterminal part of PA (PA-Nter). In this work, a series of 2- hydroxybenzamide-based compounds have been synthesized and biologically evaluated in order to identify the essential pharmacophoric motif, which could be involved in functional sequestration of the metal ions (probably Mg2+) in the catalytic site of PA. By using HL1, H2L2, and HL3 as model ligands with Mg2+ ions, we isolated and fully characterized a series of complexes and tested them for inhibitory activity toward PA-Nter endonuclease. H2L2 and the corresponding Mg2+ complex showed an interesting inhibition of the endonuclease activity. The crystal structures of the uncomplexed HL1 and H2L2 and of the isolated magnesium complex [Mg(L3)2(MeOH)2]·2MeOH were solved by X-ray diffraction analysis. Furthermore, the speciation models for HL1, H2L2, and HL3 with Mg2+ were obtained, and the formation constants of the complexes were measured. Preliminary docking calculations were conducted to investigate the interactions of the title compounds with essential amino acids in the PANter active site. These findings supported the “two-metal” coordination of divalent ions by a donor triad atoms chemotype as a powerful strategy to develop more potent PA endonuclease inhibitors.