Lactams, Azetidines, Penicillins, and Cephalosporins: An Overview on the Synthesis and Their Antibacterial Activity

Since the beginning of the twentieth century, studying natural lactams and the synthetic development of new lactam derivatives have been extensively exploited in medicinal chemistry. The main reason for the high interest in this class of compounds is that the lactam moiety is present in various natural and synthetic compounds that possess a broad spectrum of biological properties, especially those of three to seven members. The construction of the β-lactam ring (2-azetidinone) is the most studied synthesis of lactams carried out by synthetic organic chemists and medicinal chemists due to its medicinal value. Azetidines have been prepared by cyclization, nucleophilic substitution, cycloaddition, ring expansion and rearrangement, ring-contraction, and reduction of β-lactams. Penicillins and cephalosporins belong to the class of drugs known as β-lactams. Naturally produced penicillins by Penicillium chrysogenum are classified as 1st generation. The 2nd, 3rd, and 4th generations are all semi-synthetic obtained from chemical synthesis starting from 6-APA. The cephalosporins in clinical use are semi-synthetic derivatives of 7-ACA, obtained from cephalosporin C, produced by Acremonium chrysogenum. Semi-synthetic penicillins and cephalosporins continue to interest many research groups to discover new antibiotics that may tackle super bacteria. 6-APA and 7-ACA are essential starting materials used in studies on the synthesis of the β-lactams drugs.