Synthesis and antimicrobial properties of new cepham and penam derivatives with the carboxylic group in the "wrong" ß-configuration

The cepham I and the penam II with their carboxy group in the β-configuration were synthesized and assayed in vitro for antimicrobial properties. I and II, tested on Gram-pos. and Gram-neg. bacteria, both sensitive and resistant to β-lactamase inactivation, exhibited very poor activity, directed only against non-β-lactamase-producing Gram-pos. bacteria. A possible explanation for these results may be found in unfavorable steric and electronic effects deriving from the methoxy group adjacent to the pharmacophoric carboxyl function. The hydrolysis rates of I and II are similar to those of other penicillins.