Advances in the chemistry of β-lactam and its medicinal applications.

b-Lactam or azetidin-2-one is an important structural motif of the penicillin, cephalosporin, carbapenem, and carbecephem classes of antibiotics.1 Naturally occurring as well as synthetic monobactams, such as nocardicins and tabtoxin, are also known for their unique antibacterial activities.2e4 Besides their importance as the key structural component of b-lactam antibiotics, b-lactams have been attracting considerable interest in organic synthesis as versatile synthetic intermediates and chiral synthons.5e13 In addition, the b-lactam scaffold has found new pharmaceutical applications other than its use as antibiotics, such as LHRH antagonists,14 cholesterol absorption inhibitors,15 and anticancer agents.16e19 The ring strain of the b-lactam skeleton facilitates ring-opening reactions,8,20,21,22 and this unique property has been exploited for the synthesis of a variety of medicinally active compounds. For the last couple of decades, a large number of b-lactam-based synthetic methods, collectively termed as ‘b-lactam synthon method’, has been developed. This method has provided highly efficient routes to a variety of non-protein amino acids, oligopeptides, peptidomimetics, and nitrogen-heterocycles, as well as biologically active natural and unnatural products of medicinal