Syntheses of New Isocephems and Isodethiaoxacephems as Antimicrobial Agents

The cis-configurated isocephem 26 as well as isodethiaoxacephems 21 and 33 were synthesized (Schemes 4 and 5). The key step involves chlorination of the corresponding carbanions of 23, 18 , and 31 with CF₃SO₂Cl followed by internal alkylation. β-Lactams 3, 21, 26 , and 33 were found to possess biological activity against several pathogenic microorganisms in vitro. Electronic activation of the lactam moiety in isodethiaoxacephem 33 remarkably enhanced its biological activity.