Disclosed herein are 1,6-diazabicyclo[3,2,1]octan-7-one compounds of Formula (I) where the substituents are as defined herein and their preparation. Also disclosed are compositions comprising the compounds, and optionally containing a further antibacterial agent and the use of the compositions in the manufacture of medicaments for preventing or treating bacterial infections. Specific examples of the compounds of formula I include trans-sulfuric acid mono-[2-(5-aminomethyl-[1,3,4]-oxadiazol-2-yl)-7-oxo-1,6- diazabicyclo[3.2.1]-octan-6-yl] ester and trans-sulfuric acid mono-[2-(5-((R)-piperidin-3-yl)-[1,3,4]-oxadiazol-2-yl)-7-oxo-1,6-diazabicyclo[3.2.1]-octane
