Abstract
The degradation of cephalexin (CEX) was inhibited by the addition of furfural or benzaldehyde at pH 6.00-8.50. This was due to the formation of adducts of CEX and the aldehydes at this pH region. In the acidic region (pH < 5.00) no such effects of the additives were observed because the adducts were not formed. At the pH region where the inhibitory effects are observed, CEX exhibits rate enhancement of the β-lactam cleavage due to intramolecular catalysis by the side-chain α-amino group. Since the formation constant of the adducts increased with increase of pH, the α-amino group seemed to be involved in the formation of the adducts, and this is presumably no longer available for intramolecular catalysis. The degradation rates of the adducts were smaller (about 1/10-1/1000) than those of CEX. The adducts were considered to be Schiff bases from the infrared (IR) spectra and the kinetic properties of products prepared by freeze-drying of alkaline solutions containing CEX and an aldehyde (furfural or benealdehyde).
