In our efforts to develop novel small-molecule inhibitors for the treatment of influenza, we utilized molecular modeling and the X-ray crystal structure of the PB2 subunit of the influenza polymerase to optimize a series of acyclic β-amino acid inhibitors, highlighted by compound <b>4</b>. Compound <b>4</b> showed good oral exposure in both rat and mouse. More importantly, it showed strong potency versus multiple influenza-A strains, including pandemic 2009 H1N1 and avian H5N1 strains and showed a strong efficacy profile in a mouse influenza model even when treatment was initiated 48 h after infection. Compound <b>4</b> offers good oral bioavailability with great potential for the treatment of both pandemic and seasonal influenza.