Hydrolysis of 3-chloro-3-cephems. Intramolecular nucleophilic attack in cefaclor.

The chemical reactivity of 3-chloro-3-cephems was found to be similar to that of the correspondingly substituted 7-aminocephalosporanic acids and 12-13 times greater than that of the correspondingly substituted 7-aminode-acetoxycephalosporanic acids. Cefaclor, 7-(D-2-amino-2-phenylacetamido)-3-chloro-3-cephem-4-carboxylic acid, was found to undergo intramolecular nucleophilic attack at the beta-lactam. Loss of chlorine from 3-chloro-3-cephem may be a general reaction subsequent to beta-lactam opening.