Synthesis and mechanisms of decomposition of some cephalosporin prodrugs

The delta-3 and delta-2 methyl esters of cefazolin were synthesized. The kinetics and mechanisms of degradation of the methyl esters and the delta-3 and delta-2 isomers of pivaloyloxymethyl prodrug esters of the new cephalosporin ceftetrame (Ro 19-5247) were investigated in buffer systems and in human plasma in vitro. The major hydrolytic products of all the delta-3 and delta-2 esters were the inactive delta-2 cephalosporin free acids. The following reaction scheme describes the in vitro hydrolysis of these compounds: [formula: see text]. In addition, there was evidence of opening of the beta-lactam ring to form cephalosporoic acid when the methyl ester of cefazolin was studied in human plasma and in the presence of penicillinase. For the methyl esters, the processes represented by k12, k21, and k20 were operative in buffers; in human plasma, the processes represented by k12, k21, and k20 were operative in addition to cephalosporoic acid formation. For the isomers of the cephalosporin prodrug ester Ro 19-5248 only k12 and k20 were operative in buffers; in human plasma all pathways were operative and there was no evidence of cephalosporoic acid formation. In all cases, the processes represented by k12, k21, and k20 were subject to general and/or specific base catalysis.