The structures of nocardicins A and B, novel monocyclic β-lactam antibiotics produced by a strain of Nocardia, have been established as 1 and 2, respectively, on the basis of spectroscopic and chemical evidence. They are the first examples of monocyclic β-lactam antibiotics possessing relatively high antimicrobial activity, and are stereochemically and biologically related to penicillins and cephalosporins.
