N-benzyl 4,4-disubstituted piperidines as a potent class of influenza H1N1 virus inhibitors showing a novel mechanism of hemagglutinin fusion peptide interaction

The influenza virus hemagglutinin (HA) is an attractive target for antiviral therapy due to its essential role in mediating virus entry into the host cell. We here report the identification of a class of N-benzyl-4,4,-disubstituted piperidines as influenza A virus fusion inhibitors with specific activity against the H1N1 subtype. Using the highly efficient one-step Ugi four-component reaction, diverse library of piperidine-based analogues was synthesized and evaluated to explore the structure-activity relationships (SAR). Mechanistic studies, including resistance selection with the most active compound (2) demonstrated that it acts as an inhibitor of the low pH-induced HA-mediated membrane fusion process. Computational studies identified an as yet unrecognized fusion inhibitor binding site, which is located at the bottom of the HA₂ stem in close proximity to the fusion peptide. A direct π-stacking interaction between the N-benzylpiperidine moiety of 2 and F9_HA2 of the fusion peptide, reinforced with an additional π-stacking interaction with Y119_HA2, and a salt bridge of the protonated piperidine nitrogen with E120_HA2, were identified as important interactions to mediate ligand binding. This site rationalized the observed SAR and provided a structural explanation for the H1N1-specific activity of our inhibitors. Furthermore, the HA₁-S326V mutation resulting in resistance to 2 is close to the proposed new binding pocket. Our findings point to the N-benzyl-4,4,-disubstituted piperidines as an interesting class of influenza virus inhibitors, representing the first example of fusion peptide binders with great potential for anti-influenza drug development.