Synthesis of novel 6-alpha and 6-beta-alkylcarbonylmethyl substituted penems

6-alpha and 6-beta Alkylcarbonylmethyl penems were synthesized from 6-alpha-bromo and 6-oxo penicillanates respectively and their in vitro antibacterial activity was studied. The compounds were generally active against Gram-positive but not against Gram-negative strains, the compounds of the 6-beta series being more active. Relatively to imipenem, taken as reference compound, the penems resulted more stable towards chemical hydrolysis in Tris-HCl buffered medium (pH 7.4) but more sensitive towards dehydropeptidase-I (DHP-I).