Design, synthesis and structure-activity relationship of novel inhibitors against H5N1 hemagglutinin-mediated membrane fusion.

We reported previously that a small molecule named CL-385319 could inhibit H5N1 influenza virus infection by targeting hemagglutinin, the envelope protein mediating virus entry. In the present study, a novel series of derivatives focused on the structural variation of CL-385319 were synthesized as specific inhibitors against the H5 subtype of influenza A viruses. These small molecules inhibited the low pH-induced conformational change of hemagglutinin, thereby blocking viral entry into host cells. Compound 1l was the most active inhibitor in this series with an IC(50) of 0.22 μM. The structure-activity relationships analysis of these compounds showed that the 3-fluoro-5-(trifluoromethyl)benzamide moiety was very important for activity, and the -F group was a better substituent group than -CF(3) group in the phenyl ring. The inhibitory activity was sensitive to the benzamide because the oxygen and hydrogen of the amide served as H-bond acceptor and donor, respectively.