The present invention relates to compounds of formula (I) and salts and metabolically labile esters thereof; wherein R is a 5 or 6 membered nitrogen containing heteroaryl group, which heteroaryl group optionally contains 1 or 2 additional heteroatoms selected from nitrogen, oxygen or sulphur and said heteroaryl group is linked to the alkylene chain (CH2)n via a nitrogen atom in the heteroaryl group; n is an integer from 2 to 4, to processes for their preparation and to their use as antibacterial agents.