Compounds of the formula (II) ##STR1## wherein R.sub.1 is CH.sub.3, CH.sub.2 OH, CHO or CH.sub.2 OCOR.sub.4 wherein R.sub.4 is a hydrocarbon of 1-7 carbon atoms and R.sub.2 is a group of the formula R.sub.3 or COR.sub.3 wherein R.sub.3 is a hydrocarbon of 1-7 carbon atoms optionally inertly substituted by halogen are useful as antibacterial agents and .beta.-lactamase inhibitory agents.