“…Over the years, numerous penicillin derivatives have been prepared and examined for antibacterial activity. Additionally, a variety of new β-lactam-containing ring systems isolated from natural sources or from synthetic laboratories have been reported, including the penems, carbapenems, cephalosporins, clavulanic acids, oxapenams, oxacephams, and monocyclic, spirocyclic, and multicyclic 18 analogues. The most common classes of β-lactam antibiotics are illustrated below.…”