The present invention relates to compounds according to Formula (II): or a stereoisomer, tautomer or pharmaceutically acceptable salt or ester thereof, wherein A, R1 and R2 are defined herein. Also described are pharmaceutically acceptable compositions of Formula (II) compounds as well as methods for utilizing the compounds of Formula (II) and the pharmaceutically acceptable compositions of Formula (II) compounds as antibacterial agents and β-lactamase inhibitors, useful in the treatment of infectious diseases.