Cephalosporin degradations

The acidic aqueous degradation of the 7alpha-aminophenylglycinamido-containing cephalosporin cephalexin (1a) has been examined. Two major degradation products have been isolated and characterized: 3-formyl-3,6-dihydro-6-phenyl-2.5(1H,4H)-pyrazinedione (5) and 3-hydroxy-4-methyl-2(5H)-thiophenone (6). By carrying out the reaction in 18O-enriched H2O, the intramolecular nature of the cephalexin degradation has been demonstrated.