Abstract: Substituted monocyclic &bgr;-lactam compounds that are N-1-thiolated monolactams, and which exhibit wide-ranging antibacterial activities, having a single 4-membered azetidinone ring in which: the N-1 nitrogen atom of the azetidinone ring is bonded to sulfur but is not sulfonated, of the formula: wherein R1-5 are independently hydrogen, alkyl, heteroalkyl, aryl, heteroaryl, alkenyl, or alkynyl; X is H, C, or O; and n=0-3. Chemical synthesis of these compounds by a [2+2]-imine-acid chloride cycloaddition, and methods for subsequent derivatization, are also disclosed. The compounds and compositions disclosed herein are useful as antibacterial and antibiotic agents.