Oseltamivir is an important antiviral drug, which possess three chirality centers in its structure. From eight possible stereoisomers, only two have been synthesized and evaluated so far. We describe herein the stereoselective synthesis, computational activity prediction and biological testing of another three diastereoisomers of oseltamivir. These isomers have been synthesized using stereoselective organocatalytic Michael addition, cyclization and reduction. Their binding to viral neuraminidase N1 of influenza A virus was evaluated by quantum-chemical calculations and their anti-influenza activities were tested by an in vitro virus-inhibition assay. All three isomers displayed antiviral activity lower than that of oseltamivir, however, one of the stereoisomers, (3S,4R,5S)-isomer, of oseltamivir showed in vitro potency towards the Tamiflu-sensitive influenza viral strain A/Perth/265/2009(H5N1) comparable to Tamiflu.