Abstract
Nocardicin A analogues 30, 34, and 38 as well as the highly strained quinone methide 43 were synthesized. β-Lactam 34 was found biologically active against several Gram-negative microorganisms in vitro; pyridinium N-oxide derivative 38 possessed activity against Gram-positive S. aureus bacterium. Masked p-quinone methide β-lactam 43 exhibited significant antimicrobial activity in vitro. A mechanism involving an oxidation in vivo is proposed for the unprecedented biological properties of nocardicins.