Increasing drug resistance towards the front line influenza neUraminidase inhibitor Oseltamivir (Tamiflu®, Roche) has recently been reported, emphasising the need to perform further studies to gain insight into receptor ligand interactions. Recently, influenza neuraminidase activity has been tackled using a novel class of mechanism-based inactivator, which incorporates fluorine atoms at positions C-2 and C-3 of sialic acid. These inactivators are anticipated to be less susceptible to drug induced resistance as they target essential catalytic amino acids. However, individual hydrogen-bonding interactions formed between these inactivators and the neuraminidase in both the Michaelis complex and at the transition-state remain unclear. The syntheses of the four novel monodeoxygenated 2,3-difluorosialic acid inactivators at position C-4,C-7, C-8 and C-9 deploying a Barton-McCombie protocol were accomplished. The time-dependant inactivation of wild type influenza neuraminidase N9 G70C by these monodeoxygenated 2,3-difluorosialic acid inactivators was tested in a fluorescent kinetic assay. Further biochemical evaluation (performed by our collaborators) in ICso measurements against a panel of influenza viruses including wild types (wt.) and Oseltamivir resistant mutants showed potent inhibition of influenza Band H1 N1 strains. We also wished to develop a further understanding of the effects of the monodeoxygenated 2,3-difluorosialic acid inactivators upon inactivation on a physical basis. Hence, we will discuss X-ray crystallographic structures, (obtained by our collaborators) of influenza neuraminidase N9 in complex with the monodeoxygenated 2,3-difluoro-sialic acid inactivators. 11