A new type of penem derivative (3-6) having a cyclic amidine moiety or a quaternary heterocycle moiety at the C-2 position was prepared. The susceptibility to renal dehydropeptidase-1 (DHP-1) and the antimicrobial activity of these compounds were determined. Some of these compounds (5,6) showed a broad spectrum of antibacterial activity, including activity against Pseudomonas aeruginosa.